Comparative evaluation of corrosion behavior of Aegle Marmelos Correa diesel, biodiesel, and their blends on aluminum and mild steel metals

C H A P T E R

17 Comparative evaluation of corrosion behavior of Aegle Marmelos Correa diesel, biodiesel, and their blends on aluminum and mild steel metals Vinoth Thangarasu, R. Anand Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu, India

O U T L I N E 17.1 Introduction

444

17.2 Sources to produce biodiesel

445

17.3 Biodiesel production techniques 17.3.1 Preheating and blending 17.3.2 Microemulsification 17.3.3 Thermal cracking 17.3.4 Transesterification

446 447 447 447 447

17.4 Composition of biodiesel

450

17.5 CI engine components and their material selection

450

17.6 Metal corrosion in biodiesel

451

17.7 Corrosion of nonferrous metal in biodiesel 17.7.1 Biodiesel corrosion on copper 17.7.2 Biodiesel corrosion on copper and its alloys 17.7.3 Comparison of biodiesel corrosion on different metals

454 454

17.10.1.1 Fruit collection and seed extraction 17.10.1.2 Maceration oil extraction

17.10.2 Biodiesel production and characterization 17.10.2.1 Heterogeneous acid catalyst preparation from crude glycerol 17.10.2.2 Esterification process 17.10.2.3 Base-catalyzed transesterification 17.10.3 Characterization of AMC biodiesel 17.10.4 Physicochemical properties of biodiesel 17.10.4.1 Acid value 17.10.4.2 Saponification value 17.10.4.3 Iodine value 17.10.4.4 Density 17.10.4.5 Viscosity and calorific value 17.10.4.6 Cloud and pour point 17.10.4.7 Flash and fire point 17.10.4.8 Conradson carbon residue 17.10.5 Metal sample and biodiesel blend preparation 17.10.6 Corrosion study

454 455

17.8 Effect of water and microbes on the fuel tank 456 17.9 Techniques to monitor corrosion 17.9.1 Mass loss 17.9.2 Electrochemical techniques 17.9.3 Noncontact profilometry 17.10 Materials and methodology 17.10.1 Oil extraction

Advanced Biofuels https://doi.org/10.1016/B978-0-08-102791-2.00017-9

457 457 457 458 458 458

17.11 Results and discussion 17.11.1 Heterogeneous acid catalyst characterization 17.11.2 Physicochemical properties 17.11.3 Corrosion characteristics

443

459 459

460

460 460 460 460 461 461 461 462 462 462 462 462 463

463 463 464 464 464 466

Copyright © 2019 Elsevier Ltd. All rights reserved.

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17. COMPARATIVE EVALUATION OF CORROSION BEHAVIOR OF AEGLE MARMELOS CORREA DIESEL, BIODIESEL

17.12 The economic impact of metal corrosion on use biodiesel for the transport sector 467 17.13 Conclusions

468

Nomenclature

468

17.1 INTRODUCTION Since the commencement of civilization and industrialization, energy has become an indispensable part of the society to preserve growth and sustain life. Fossil fuels meet significant energy demand in the world [1]. Every day we encounter copious technological advancements that make people’s lives much more comfortable than ever. The current generation is driven toward electrical alternatives due to the threat posed by the fast depleting rate of fossil fuels. The most common example is the field of automobiles where there are countless proposals for electrical alternatives made every day. Even then, the need for research on unconventional modifications in the existing engines and fuels always stands high. According to the Indian oil ministry, fuel consumption during the year of 2017 touched 200 million tons, which is the highest consumption in the last 16 years. Compared to India, fuel consumed in China was 575 million while U.S.A. consumed 1 billion tons in 2017. Although at any rate, fossil fuels are not sufficient to fulfill the rapidly growing energy demand. Globally, daily consumption of oil has reached up to 85 million barrels which will be rising to 113 million barrels in the next 15 years according to a conservative study. There is a requirement for alternate and renewable sources to tackle the energy demand as well as keeping the environment safe [2]. Bioenergy productions from biofuels have emerged as one of the most popular sources. The biofuels are a promising, renewable, and ecofriendly source of energy that can substitute petrodiesel fuels [3]. Biofuels are the promising energy source to avoid the effects of growing energy demand on the environment; they are safe for humans and the environment and in the near future will satisfy present energy demand with almost fewer emissions of both air pollutants and greenhouse gases than fossil fuels [4]. The overdependence on fossil fuel, increasing oil demand and monetary value cause environmental problems. Thus, it stimulated the search for new alternatives to fossil fuels [2]. The emission of CO, unburned hydrocarbons, and particulate matter is decidedly less from biodiesel produced from edible oil, inedible oil, animal

Acknowledgments 468 References 468

fats, algae, etc., compared to fossil fuels [5,6]. Biodiesels are the universal proven solution for this depletion crisis. Biodiesel is an ecofriendly and renewable source of energy that can be utilized as an alternative fuel for petroleum diesel due to high similarities in the properties and high calorific value [7]. Presently the primary sources of biodiesel production are from plant oils, animal fat, and algae [8]. However, due to food crises the edible feedstock like soybean (glycine max), groundnut (Arachis hypogaea), sunflower (Helianthus annuus), barley (Hordeum vulgare), etc., are not considered for biodiesel production. In India, various inedible seeds like karanja (Pongamia Pinnata), neem (Azadirachta Indica), drumstick (Moringa oleifera), cotton seeds (Gossypium hirsutum), wild mustard (Cleome viscose), soapnut (Sapindus Mukorossi Gaertn), etc., are available abundantly [9,10]. Biodiesel is described as long-chain mono alkyl esters derived from vegetable or tallow by transesterification process. Straight vegetable oil is having high viscosity and density due to which it cannot be directly used in an unmodified diesel engine. They lead to deposition of gums, clogging in the fuel filter, and poor atomization when fuel gets injected in the combustion chamber in engines [11]. Transesterification is the process to reduce the viscosity and density of vegetable oil by converting the triglycerides into three monoalkyl esters. The first step for biodiesel production is oil extraction from seeds. There are many methods to extract oil from seeds; among them solvent extraction (microwave or ultrasound assisted) is a beneficial way to extract oil even when using materials having less content of oil compared to conventional pressing. Hexane is the most widely used solvent in oil extraction from seeds, but its impact on human health is dangerous [12]. By considering the impact, researchers are focusing on developing alternative solvent in oil extraction like ethanol, isopropanol, butanol, a-pinene, p-cymene, and D-limonene. Microwave-assisted and ultrasoundassisted extraction methods take less time, less heat input which allows extraction of oil at a lower temperature with less amount of solvent [13]. It is seen that only a few advancements have been done in the field of oil extraction from inedible seeds with green solvents,

IV. APPLICATIONS

17.2 SOURCES TO PRODUCE BIODIESEL

even though by employing the same advanced methods, oil extraction yield is less as stated by Yogesh C. Sharma et al. [14]. The vegetable oils and animal fats are the primary sources for biodiesel production by using transesterification process. Transesterification is the reaction between triglycerides and alcohol which produces ester and glycerol with the aid of base or acid catalyst [15]. The widely used alcohols in biodiesel synthesis are methanol and ethanol [16]. In transesterification, commonly methanol is used due to its high reactivity, lower boiling point, and low cost compared to other alcohols. Biodiesel is commonly synthesized with the help of homogeneous alkali hydroxide or heterogeneous alkaline oxide [17]. Each form of catalyst has its own merits and demerits, but nowadays most of the researchers are focusing on heterogeneous alkaline oxides as they are easily separable, recyclable, and prevent soap formation. It is because the heterogeneous catalyst can be easily separated after biodiesel production. Moreover, the heterogeneous catalyst has high reusability with only a small decrease in yield [18]. In nature various types of corrosion take place; in a diesel engine the corrosion behavior is magnified and is more dangerous. In a standard diesel engine the period of corrosion varies: typically it is not more than 500 h before the cylinder lining of the gasket is penetrated by the water jacket. High quality of biodiesel is required to meet the diesel engine compatibility. So, the partial conversion of triglycerides into methyl esters or incomplete purification of biodiesel may contain unconverted triglycerides such as di and monotriglycerides, free fatty acids, catalyst, and alcohol. These impurities may deposits gums in the engine components which cause corrosion during storing, transportation, and utilizing in a diesel engine [19]. Compared to commercial diesel, biodiesel has a superior lubricity property to dissolve the metallic parts in the fuel. Corrosion will happen even more quickly on engine running with biodiesel due to quicker degradation through oxidation [20,21], moisture adsorption [22], and other contamination [23]. Therefore, the study of corrosion characteristics of biodiesel with engine components and inhibitors for biodiesel corrosion becomes a significant part to meet the diesel engine compatibility and commercialize the biodiesel. Compression ignition engine components are made up of a variety of metals and nonmetals. Fuel tank, pump system, fuel line system, fuel filters, cylinder liner, piston and fuel injector are the major engine components in contact with fuel. In the recent days, automotive industries are focusing on lightweight materials to reduce the fuel consumption and overall vehicle weight. Energy consumption and performance of engine can be reduced by using lightweight metals [24]. Aluminum and magnesium are

445

lightweight nonferrous metals which are getting attention in automotive industries [25]. Piston, piston ring, cylinder, transmission, etc., are made up of aluminum metal. Wohlecker et al. and Pagerit et al. reported that adoption of lightweight metals would reduce 1.9% e8.2% of fuel consumption with every 10% reduction in vehicle weight [26,27]. Very few studies have been conducted on corrosion studies of aluminum and mild steel in biodiesel. Haseeb et al. have been done an extensive review on biodiesel corrosion on diesel engine components [28]. Biodiesel is more corrosive than diesel on copper and bronze materials [29]. Copper and ferrous alloys easily get corroded when they come in contact with biodiesel which is produced from fat-based feedstocks [30]. Kaul et al. studied the corrosion characteristics of Jatropha curcas, karanja, mahua, and Salvadora biodiesels on aluminum piston. They reported that aluminum metals were more vulnerable to corrosion in J. Curcas and Salvadora biodiesels compared to other two biodiesels [31]. Electrochemical corrosion study of aluminum metal in different biodiesels was carried out by Dı´az-Ballote et al. They found that corrosion behaviors of aluminum in biodiesel with alkali and aqueous solutions were similar to each other [32]. A literature survey on the corrosion characteristics study of aluminum and mild steel metals in biodiesel has shown a lack of publication in this area. Moreover, no research work was carried out for corrosion study of aluminum and mild steel metals in Aegle Marmelos Correa (AMC) biodiesel. Here comes the need of corrosion characteristics study of aluminum and mild steel in AMC biodiesel and to attain the comparative assessments of corrosion of these two metals, aluminum and mild steel.

17.2 SOURCES TO PRODUCE BIODIESEL Oils extracted from inedible feedstocks are not suitable for cooking purpose due to their toxic composition [33,34]. Literature survey on the existing work is much more critical before selecting the inedible vegetable oil source to produce biodiesel. Recently, much research has been done to utilize the various edible and inedible oils for the biodiesel production. In this, they concluded that biodiesel produced from inedible oils has advantages over edible oils. The biodiesel produced from inedible oil feedstocks can overwhelm the issues related to edible oil feedstocks such as food versus fuel, economic and environment [33,35]. Besides, inedible oil seeds grow in the wasteland, forests, well-drained land with proper aeration and can be cultivated in unused lands of rural area. It can also be planted in public areas such as national highways, irrigation canals, and along rail roads. Production of biodiesel from inedible oil

IV. APPLICATIONS

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17. COMPARATIVE EVALUATION OF CORROSION BEHAVIOR OF AEGLE MARMELOS CORREA DIESEL, BIODIESEL

feedstocks can provide energy to the rural areas and also develop the business, employment opportunities to the rural people and also help the nation to become energy secure in the future. All these issues influence the sustainability of biodiesel production. Numerous researches have been done in biodiesel production from inedible oils feedstocks, and it was concluded that these feedstocks could be a renewable and alternative fuel to fossil fuels [36]. Inedible feedstock trees are well adjusted to wilderness or semiwilderness region conditions, and it requires low moisture content and fertility to grow. Also, they are usually spread through seed or cuttings. The waste seed cake after oil extraction might be utilized as manure for soil advancement [37]. A few potential treeborne oilseeds and inedible feedstocks sources have been known as suitable sources to produce biodiesel [38]. Table 17.1 demonstrates the potential inedible oilseeds for biodiesel generation. In the accompanying area, a concise description of different sorts of inedible plant oils will be exhibited.

TABLE 17.1

17.3 BIODIESEL PRODUCTION TECHNIQUES The oil extracted from edible and inedible seeds and animal fats have a higher viscosity than diesel fuel. The higher viscosity of the straight vegetable oil is the main reason to prevent the utilization of oils in unmodified diesel engine [39]. Hence, the viscosity of oil must be reduced before utilizing in a diesel engine. Recently, there are numerous techniques, methods, and processes that are widely used to convert the vegetable oils into biodiesel [40]. In this, preheating, the direct blending of vegetable oil into diesel, and microemulsion with solvents are conventional methods to reduce the viscosity of vegetable oil without chemical converting [41,42]. Transesterification and thermal cracking are the recent methods to convert vegetable oil into biodiesel [3]. Transesterification is the widely used chemical conversion technique to reduce the viscosity of vegetable or animal fat oils. Thermal cracking or pyrolysis is the method to produce a diesellike fuel from vegetable oil or oil.

Potential inedible feedstocks and their oil content [36]. Oil content

Inedible vegetable source

Plant part

Seed (wt.%)

Kernel (wt.%)

Azadirachta indica (neem)

Seed, kernel

20e30

25e45

Aphanamixis polystachya (wall.) Parker

Kernel

e

35

Annona muricata

Seed

e

20e30

Annona squamosa

Seed

15e20

e

Aleurites trisperma

Kernel

e

e

Asclepias syriaca (milkweed)

Seeds

20e25

0.019

Barringtonia racemosa Roxb. (L.) Spreng.

Seed

e

e

Brassica carinata (Ethiopian mustard)

Seed, kernel

42

2.2e10.8

Balanites aegyptiaca (desert date)

Kernel

Bombax malabaricum

Seed

18e26

e

Calophyllum inophyllum L.

Seed, kernel

65

22

Crambe abyssinica

Seed

30e38

e

Ceiba pentandra

Seed

24e40

e

Cerbera odollam (sea mango)

Seed, kernel

54

6.4

Croton tiglium

Seed, kernel

30e45

50e60

Cuphea

Seed

20e38

e

Crotalaria retusa L. (fabaceae)

Seed

15

e

Eruca sativa gars

Seed

35

e

Garcinia indica

Seed

45.5

e

IV. APPLICATIONS

36e47

447

17.3 BIODIESEL PRODUCTION TECHNIQUES

17.3.1 Preheating and blending The primary issue with vegetable oils not suitable for an unmodified diesel engine is higher viscosity and poor volatility. These problems can be rectified by preheating and direct blending with diesel fuel. There are few investigations that have been done on the indirect use of vegetable oil in a diesel engine with some modification. Senthilkumar et al. [43] have investigated the effect of different preheating temperature of vegetable oil in unmodified single cylinder diesel engine with a rated power of 2.8 kW at 1500 rpm. The vegetable oil is preheated to 60, 80, and 100
C and there is a significant reduction in the viscosity and surface tension of the vegetable oil that facilitates better atomization and hence reduces the CO and CO2 emissions. Moreover, it diminishes the ignition delay and combustion duration. The NOx emission is increasing with respect to increasing the preheat temperature of vegetable oil [44]. Blending of biodiesel with conventional diesel is a way of reducing the viscosity of biodiesel and improving the performance and combustion characteristics [45,46]. The main advantage of direct blending with diesel or alcohol is no need of engine modification and simple way in implementation over other methods [47e49]. A blend of 10% and 20% of the conventional diesel can be directly utilized in the compressionignition engine without engine modification [39,50]. The physical properties of vegetable oils can be significantly improved by blending with alcohol. Direct utilization of vegetable oils and the utilization of high percentage of the blend are generally not satisfactory for indirect or direct injection diesel engines [51].

17.3.2 Microemulsification The process of solubilization of vegetable oils and alcohols mixture with the addition of surfactants is called microemulsification. Methanol and ethanol are poorly miscible with nonpolar vegetable or animal fat-based oils, so surfactants are required to increase miscibility. The higher viscosity of vegetable oils can also be reduced in microemulsions with solvents like 1-butanol, ethanol, methanol, and diesel [52]. A colloidal dispersion of vegetable oil microstructure with solvents in the range of 1e150 nm is known as a microemulsion. The emulsified fuel mixture can be directly used in the engine which is thermodynamically stable [53,54]. Microemulsification has been considered as an easy and best way to reduce the higher viscosity of vegetable oils [55e57].

17.3.3 Thermal cracking Thermal cracking is the thermal degradation of organic materials into diesellike fuel with the addition of a

catalyst in the presence of nitrogen atmosphere [58]. Vegetable oils or seeds, waste biomass, animal fats, and alkyl esters can be pyrolyzed. The primary constituents obtained from the pyrolysis of vegetable oil are alkanes, alkenes, alkadienes, aromatics, and carboxylic acids in different ratios. The chain length of liquid fuel extracted by thermal cracking of vegetable oil is probably closer to the chain length of diesel fuel. Moreover, the physical properties of pyrolyzed fuel such as flash point, fire point, density, viscosity, and pour point are lower than the diesel fuel. The pyrolyzed fuel has the similar calorific fuel of diesel fuel, though the cetane number of pyrolyzate is lower than diesel fuel. The sulfur, water, and sediment contents are present in the pyrolyzed vegetable oil which are within the ASTM D6751 limits. However, the carbon residue, ash, and pour point values have exceeded the standards [59e61]. Thermal cracking can be classified by depending on the heating rate into three types which are slow pyrolysis, flash pyrolysis, and fast pyrolysis. Table 17.2 shows the operating parameters range of three different pyrolysis processes [62]. Numerous research works have been done in the pyrolysis of inedible vegetable oils and their seed cakes, for example, Madhuca indica, castor oil, Pongamia pinnata, tung, and Jatropha curcas, to get alternative ecofriendly substitutes to fossil fuels in diesel engine applications. Diesel and less quantity of petroleum and kerosene were extracted by pyrolysis of tung oil after saponification with lime [56,61,63].

17.3.4 Transesterification Transesterification is defined as the chemical conversion process of triglycerides with alcohol into alkyl esters with the help of a catalyst [64]. In this process, commonly used alcohols are methanol and ethanol due to their low cost and easy availability. Transesterification is an ecofriendly process carried out under mild conditions. This process can be used to produce biodiesel from a variety of feedstocks. Vegetable or animal oilsebased triglycerides consist of three fatty acids linked to one glycerol moiety. In this reaction, triglycerides are reacted with an alcohol and produce esters and

TABLE 17.2

Pyrolysis process types and their operating ranges.

Parameter

Slow pyrolysis

Fast pyrolysis

Flash pyrolysis

Pyrolysis temperature (K)

550e950

850e1250

1050e1300

Heating rate (K/s)

0.1e1

10e200

41,000

Particle size (mm)

5e50

0.1

0.2

Heating time (s)

450e550

0.5e10

0.5

IV. APPLICATIONS

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17. COMPARATIVE EVALUATION OF CORROSION BEHAVIOR OF AEGLE MARMELOS CORREA DIESEL, BIODIESEL

C

CH2O

CH2OH

R

O

Catalyst HOC

C

HOC

CH3OH Methanol

R

Fatty acid methyl ester

O

O CH2O

RCOOCH3

R

C

C

CH2O

R

C

R

O

O

Di-glycerides

Triglycerides

CH2OH

CH2OH

Catalyst HOC

RCOOCH3

CHOH

CH3OH

R

C

Methanol

Fatty acid methyl ester

O CH2O

C

CH2O

R

C

R

O

O

Mono-glycerides

Di-glycerides

CH2OH

CH2OH

Catalyst

Methanol

CH2O

C

RCOOCH3

CHOH

CH3OH

CHOH

Fatty acid methyl ester CH2OH

R

Glycerol O

Mono-glycerides

FIGURE 17.1

Transesterification reaction mechanism.

glycerol through three stepwise reactions. The stepwise transesterification is given in Fig. 17.1. Transesterification can be classified as catalytic and noncatalytic processes [65]. The catalyzed transesterification process can be classified into acid and base catalyzed processes. Depending on the nature of the catalyst phase, further the acid or base catalyst can be divided into three subclasses such as homogeneous, heterogeneous, and enzymatic catalyst [66,67]. The conversion efficiency of homogeneous catalyzed transesterification is better when the FFA is less than 1 mg of KOH/g of oil. Two-step transesterification process is needed when the free fatty acid (FFA) value is greater than 1 mg of KOH/g of oil [68]. The main limitations of homogeneous catalyst are soap formation during the transesterification process and expensive separation

of catalyst after the process. As a result of such problems, feedstocks which are having high FFA can be easily converted by the heterogeneous catalyst. Numerous studies have reported that heterogeneous and enzymatic catalysts are the best catalysts for the conversion of triglycerides into methyl esters [69,70]. The heterogeneous catalyst has many advantages over homogeneous catalyst which are: easy removal of catalyst, reusability, easy purification, and fewer hazards. Table 17.3 presents the various catalyst transesterification process of different inedible oils. Though the transesterification process has many advantages, there are few drawbacks associated with this process. The processing time of transesterification of vegetable oil is quite high, and it requires few posttreatment processes such as separation, water washing,

IV. APPLICATIONS

TABLE 17.3

Production of biodiesel from some inedible feedstocks by catalyzed transesterification. Catalysts

Catalyst concentration

Alcohol

Molar ratio

Temperature (o C)

Reaction time (hour)

Biodiesel yield (%)

Jatropha curcas L.

H2SO4

0.8%

Methanol

9:1

45

2

90e91

KOH

0.55%e0.7% (w/w)

Methanol

5:1

60

0.24

98e99

Rhizopus oryzae (RL)

4% (w/w)

Methanol

3:1

30

60

80

Pseudomonas cepacia lipase immobilized

e

Ethanol

e

50

8

98

NaOH

0.7%e1% (w/w)

Methanol

3:10 (v/v)

50

2

90.1e98

Calophyllum inophyllum L.

KOH

1.5%

Methanol

6:1

65

4

85

Rice bran

NaOH

0.75% (w/w)

Methanol

9:1

55

1

90.2

Pongamia pinnata

NaOH

1e1.5 (w/w)%

Methanol

6:1

65

0.6e3

90.4

KOH

1%

Methanol

6:1

65

3

97e98

Azadirachta indica

NaOH

0.6% (w/w)

Methanol

6:1

65

1

83

Hevea brasiliensis

NaOH

1% (w/w)

Methanol

6:1

60

1

84.46

KOH

1.2% (w/w)

Methanol

6:1

25

1

97

NaOH

1.5% (w/w)

Methanol

6:1

25

1

97.4

KOH

1.5% (w/w)

Methanol

6:1

e

1

98

Terminalia catappa

CH3CH2ONa

0.2:1

Methanol

6:1

e

e

93

Cerbera odollam

NaOH

1% (w/w)

Methanol

6:1

64.7

1

8.3

Montmorillonite KSF

4% (w/w)

-

10:1

150

2

48.32

Melia azedarach

NaOH

1% (w/w)

Methanol

9:1

36

0.6

63.8

Jojoba

KOH

1.35% (w/w)

Methanol

6:1

25

1

83.5

Raphanus sativus

NaOH

0.6% (w/w)

Ethanol

11.7:1

38

1

99.1

Stillingia oil

Novozym435, lipozyme TLIM, and lipozyme RMIM

15% (w/w)

Methanol

1:5

40

10

89.5

Croton megalocarpus

KOH

1% (w/w)

Methanol

30% (w/w)

60

1

88

Moringa oleifera

NaOCH3

1% (w/w)

Methanol

6:1

60

1

Camelina sativa

17.3 BIODIESEL PRODUCTION TECHNIQUES

IV. APPLICATIONS

Inedible oil

449

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17. COMPARATIVE EVALUATION OF CORROSION BEHAVIOR OF AEGLE MARMELOS CORREA DIESEL, BIODIESEL

and heating. More amount of water is required to purify the biodiesel [71,72]. Supercritical methanol, a noncatalytic transesterification process, is a way to solve the problems with catalytic transesterification. In this, the dielectric value of methanol is lowered by heating to supercritical temperature state to make a single phase of reactants. As a result, the overall reaction is to be completed in a short duration of time [61]. Furthermore, the noncatalytic process requires no catalyst and purification is easier than the catalytic process. In this, there is no soap formation during the process. There is a limitation associated with supercritical methanol transesterification which is the expensive cost of equipment to attain the high temperature and pressure [48]. Recently, much research is being done in supercritical methanol transesterification of inedible feedstocks under various operating conditions.

17.4 COMPOSITION OF BIODIESEL Triglyceride is the predominant component of oils which is derived from vegetable seeds or animal fats. The structure of triglycerides is indicated schematically in Fig. 17.2. In triglyceride, long-chain hydrocarbons of fatty acids are denoted as R. Glycerol is a sticky and highly viscous molecule which is attached to the three fatty acids. Hence, the glycerol component must be removed from triglycerides to reduce the viscosity of the vegetable oil. Transesterification is the process to separate the three fatty acids from glycerol as shown in Fig. 17.2. In this, resulted product alkyl esters are known as biodiesel and glycerol is removed as a byproduct. These esters have a few acronyms to depict the biodiesel but commonly biodiesel is called fatty acid methyl esters (FAME). The biodiesel yield of transesterification process can be calculated by measuring the percentage of CH2O

C

17.5 CI ENGINE COMPONENTS AND THEIR MATERIAL SELECTION Fuel feed system, combustion system, and exhaust system are the three crucial systems fuel go through

R

C

H2O

O CHO

ester conversion [23]. The composition of biodiesel relies upon the types of feedstocks which are used to produce the biodiesel. The physicochemical properties of biodiesel such as cetane number, pour point, viscosity, and oxidation stability mainly depend on the percentage of different saturated and unsaturated esters present in the biodiesel. Furthermore, there is a chance of impurities being present in the biodiesel after transesterification process, which affect the properties of the fuel. Thus, types of feedstocks and posttreatment process also influence the physicochemical properties of biodiesel. Higher cetane number, lower pour point, and less viscosity are the desirable properties to utilize the biodiesel as an alternative fuel in a diesel engine. The chemical composition of biodiesel is the same as that of its parent vegetable oil or animal fat [73]. The percentages of unsaturation and saturation may vary with types of feedstocks used. The oxidation stability of biodiesel decreases with increasing the percentage of unsaturation. Table 17.4 shows the percentage of saturated, unsaturated, and polyunsaturated fatty acids of different biodiesels. It is evident that biodiesels derived from edible oils such as coconut and palm oil are composed of higher percentages of saturated fatty acids. But the biodiesel produced from rapeseed, canola, and sunflower feedstocks are having higher percentages of unsaturated fatty acids. So, palm and coconut oilbased biodiesel are less susceptible to oxidation than soybean, sunflower, and rapeseed biodiesels. Table 17.5 shows the oxidation stability of biodiesel derived from different feedstocks. It can be seen that palm oil methyl ester has good oxidation stability than other methyl esters.

R

+

3 H3C

Methanol O

HC

OH

H2O

OH + OH

Glycerol CH2O

C

R

O Triglyceride

FIGURE 17.2 Overall transesterification reaction.

IV. APPLICATIONS

O

OH R

C Ester

OCH3

451

17.6 METAL CORROSION IN BIODIESEL

TABLE 17.4

Saturated and unsaturated fatty acid methyl ester content of various biodiesels [60,74]. Peanut

Rapeseed

Canola

Coconut

Palm

Soybean

Sunflower

Tallow

51.2

15.3

12.77

47.9

39

22.3

20.43

48.9

62.4

66.8

3.2

Saturated (%)

19.3

5.6

7.1

87.4

Mono unsaturated (%)

47.1

21.9

60.2

9.9

Poly unsaturated (%)

33.6

72.5

32.7

2.7

TABLE 17.5

9.8

Oxidation properties of different fatty acid methyl esters [74].

Property

Palm oil methyl ester

Rapeseed methyl ester

Soybean methyl ester

Oxidization stability (hour)

6.65

4.5

1.28

Iodine number (mg I2/g of oil)

52

110

128

Methyl linolenate

0.3

7.7

7.2

during internal combustion [75]. The fuel is pumped by fuel feed system, which delivers the fuel to highpressure pump through fuel filters. The high-pressure pump transfers the fuel to various injectors. The fuel lubricates the various sliding components like plunger and barrel [74]. A variety of materials come in contact with fuel when it flows in an internal combustion engine. This material can be classified as metallic and nonmetallic materials. The most widely used ferrous materials in the internal combustion engine are carbon steel, stainless steel, and cast iron, likewise nonferrous material, for example, aluminum, copper, and copper alloys. Also, the plastics and elastomers are categorized as nonmetallic materials. Table 17.6 demonstrates the general materials chosen for the respective parts and components in a CI engine. There is a chance of causing corrosion on these materials when fuel interacts with them at various stages, different loads, temperature, and velocity [76]. Hence, it is imperative to realize the impacts of biodiesel toward individual material groups in the CI engine. The friction, wear, and corrosion characteristics of IC engine parts may vary with materials when they interact with biodiesel. Apart from that, it is very essential to decide the perfect percentage of biodiesel which performs better in tribocorrosion study.

17.6 METAL CORROSION IN BIODIESEL Corrosion is defined as the electrochemical attack on metals by the surrounding medium. The surrounding medium can be atmosphere, fuel, etc. As a general fact, biodiesels are said to produce more corrosion than commercially available diesel because of various factors. Diesel’s inability to produce more corrosion than biodiesel is attributed to its unavailability of corrosion inducing sulfur atoms. Sulfur atoms in the presence

of metals can trigger complex reactions which can corrode the metal surfaces. However, this corrosion is considered to be trivial when compared to the level of corrosion caused by biodiesel. Biodiesel causes corrosion on many metallic and nonmetallic parts of a diesel engine due to its chemical composition and properties. The corrosiveness of biodiesel is mainly attributed to its free fatty acid content and the impurities that remain after the transesterification process [77]. In addition to this, biodiesel is hygroscopic in nature and it absorbs moisture from the atmosphere. Due to high water content present in biodiesel, it promotes microbial growth which ultimately leads to corrosion of various parts in fuel delivery system. The corrosion rate on aluminum by canola-based biodiesel was heavily dependent on the level of impurities present [32]. Washing the biodiesel with hot water after the transesterification process reduced the level of corrosion induced by biodiesel to a large extent. Also, the corrosive nature of biodiesel was reduced to a greater extent by adding certain additives [31,78]. Moreover, biodiesel exhibits very good lubricity characteristics. On immersing metal strips into biodiesel, biodiesel tends to dissolve more amount of metal owing to its very high lubricity. These dissolved metals will then accelerate the biodiesel degradation and ultimately the corrosion rate. The nature of the metal that is being exposed to biodiesel also influences the corrosion rate. Metals like aluminum, brass, copper and cast iron act as catalysts for oxidation of biodiesel. Hence it results in the formation of primary oxidation products and ultimately secondary oxidation products which are depicted by an increase in the corrosion rate of these metals. In fact, some metals like copper, tin, brass, bronze, zinc, and lead tend to corrode rapidly in the presence of biodiesel [79]. Hence it is not advisable to use these metals for manufacturing any part in fuel

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TABLE 17.6

Types of materials used in engine components and its parts [74].

Main parts

Components

Materials

Fuel tank

Housing Gasket

Steel, plastic, paint, coating Elastomer, paper, cork, copper

Fuel feed pump

Aluminum alloy, iron-based alloy, copper-based alloy

Fuel lines

High pressure Low pressure

Steel Plastics, rubber

Fuel filter

Filter cartridge

Paper

Housing

Aluminum, plastic

Fuel pump

Aluminum alloy, iron-based alloy, copper-based alloy

Fuel injector

Stainless steel

Cylinder

Piston assembly

Exhaust system

Cylinder head

Gray cast iron, cast aluminum, forged aluminum

Cylinder barrels

Gray cast iron, steel, cast aluminum

Cylinder liner

Gray cast iron, aluminum

Valves

Steel casting

Piston

Sand-cast aluminum, die-cast aluminum, forged aluminum, gray cast iron

Piston pin

Steel

Piston ring

Special cast iron, steel

Bearing

Copper alloy

Connecting rod

Steel, aluminum alloy

Exhaust manifold

Cast iron

Exhaust pipe

Steel

Catalytic converter

Stainless steel, ceramic fiber, aluminum fiber

Muffler

Steel

delivery system. On the other hand, some metals like carbon steel, EN24, EN31 are resilient to corrosion by biodiesels [74]. As a general rule, the corrosive nature of biodieseldiesel blend increases with an increase in biodiesel concentration. But this is not always true because the corrosive nature majorly depends on the parent oil that is used for producing the biodiesel. The corrosive nature of biodiesel is also determined by a parameter known as Total Acid Number (TAN) which is found out using titration methods. TAN is a direct reflection of the FFA content present in biodiesel. FFA are those acids which are not present as fats (triglycerides) in biodiesel. Saponification value is another parameter which is often confused with TAN. In saponification reaction, the triglycerides present in the biodiesel are hydrolyzed to yield free fatty acids which then react with a base to form soap. On the other hand, the titration experiments which are done to find the TAN involves a reaction between the free fatty acids which are not linked to any triglycerides and the base. Saponification value gives an estimate of the number of fats present in the

biodiesel whereas TAN gives an estimate of the amount of FFA content present. Both these parameters are inversely related to each other. A very high saponification value implies high FFA content in the form of triglycerides and hence a very low FFA content in the biodiesel. Free fatty acids in the form of triglycerides (fats) do not influence the corrosion characteristics as long as the water content in the biodiesel is very low. So the immediate threat to corrosion is the FFA content (measured using TAN) present freely in the biodiesel. Also, TAN is an indirect measure of the rate of the transesterification reaction. Incomplete or slow transesterification reaction implies a high value of FFA content and TAN because the triglycerides are not effectively getting converted into esters thus leaving a very high content of FFA in the transesterified biodiesel. TAN also depends on the chemical composition of the parent oil used for producing the biodiesel. On exposing biodiesel to an oxidizing environment, the saturated components remain stable and nonreactive whereas the unsaturated components are particularly unstable and deteriorate rapidly. Though oxidation of biodiesel

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17.6 METAL CORROSION IN BIODIESEL

has few positive outcomes, it is generally undesirable because it is the major source of corrosion. On storing biodiesel for a very long time, fuel aging occurs which results in the formation of hydroperoxides initially which is then followed by the formation of secondary oxidation products like ketones, aldehydes, and carboxylic acids which increase the FFA content and TAN tremendously. This increased acidity as a result of all the oxidation products formed leads to electrochemical processes like rusting and corrosion [80]. Moreover, it leads to the formation of insoluble gums which tend to block the fuel filters and injection nozzle. It also increases the viscosity of the fuel due to thickening of oils present in biodiesel. Antioxidants are now widely used to increase the induction period of oxidation and thus reduce the amount of oxidation products that are produced. However, the effectiveness of the antioxidant depends majorly on the chemical composition of the biodiesel and also the type of antioxidant being used. Hence antioxidants are not known to be a successful solution for tackling biodiesel’s oxidation and corrosion effects. The corrosiveness of biodiesel can also stem out of the impurities present like free glycerol and methanol, remains of alkali catalysts. These impurities arise due to incomplete transesterification process. Sometimes the operating conditions of the engine can trigger the reverse transesterification reaction where esters in the presence of water yields methanol and free fatty acids. These free fatty acids on reacting with the metal parts cause corrosion. Different metals endure different corrosion rates on being exposed to biodiesel. Copper was found to be more vulnerable toward corrosion when compared to leaded bronze [75]. In the same literature study, biodiesel under long-term oxidation effects was found to produce severe corrosion compared to fresh biodiesel. Terne sheet steel which is majorly used in manufacturing fuel tanks was exposed to diesel blended with 5% biodiesel. It was found that corrosion occurred on terne sheet metal, and it was much higher than the corrosion that happened on exposing it to 2% blend and pure diesel. They concluded that with an increase in the concentration of biodiesel in the biodiesel-diesel blends, the corrosion rates also increased [74]. In another literature study, the corrosion effects on piston metal and piston liner metal by biodiesel-diesel blends were studied. They concluded that piston (made of aluminum) was found to be more resistant to corrosion than piston liner (made of cast iron) when exposed to various biodiesel-diesel blends [31]. However, both the corrosion rates were found to fall under the permissible limits. In a similar literature study, static immersion tests were done on various metals like cast iron, copper, carbon steel, and 316 stainless steel. They concluded that copper exhibited maximum corrosion

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rate among all the metals taken into consideration. Carbon steel and 316 stainless steel were resistant toward corrosion as they showed negligible weight losses after static immersion tests [30]. Copper, on the other hand, showed negligible weight loss at room temperature, but it was found to corrode at elevated temperatures. Corrosion characteristics of biodiesel are standardized using ASTM D130 copper strip tarnish test in which copper strips were immersed in pure biodiesel for certain period of time and the tarnish effects on the copper strips were evaluated from the scale of light tarnish 1A to severe tarnish 4A-C based on comparison with standardized copper strips. Biodiesels tend to corrode different metals on different scales of magnitude depending on the metal taken into consideration [81]. This type of corrosion study is quite significant as the fuel comes in contact with various metallic and nonmetallic parts during its flow from the fuel tank to fuel injector. Fuel flows from the fuel tank through a fuel filter to fuel feed pump. The fuel feed pump feeds the fuel to the injection pump and ultimately to the fuel injectors. All these subsystems are made up of ferrous materials (cast iron, mild steel) and nonferrous materials (aluminum and copper alloys). As the fuel comes in contact with these parts at different operating temperatures, loads, and velocities, the amount of wear and corrosion induced by the fuel keeps varying. Hence a simple copper corrosion test and evaluating the total acid number does not quantify the corrosion characteristics of any biodiesel completely [30]. Corrosion effects on various metallic and nonmetallic parts have to be evaluated to a very high precision to ensure that biodiesel can be safely used in diesel engines. Copper corrosion tests are now widely replaced by static immersion tests where metal strips are immersed in pure biodiesel or biodiesel blends with diesel or fatty acids or alcohols for a certain period of time (varies from hours to years). After that particular time period has elapsed, the strips are removed and examined carefully to measure the weight losses in each strip and thus calculating the corrosion rates. However, this method is also known to be ineffective as the weight losses cannot be measured to a very high accuracy. For any two metals strips which are having similar weight losses, it is not logical enough to conclude that both of them have same corrosion rates. In-depth analysis of the chemistry and mechanism of corrosion is required in order to evaluate the corrosion characteristics to a very high level of precision. This is achieved by certain electrochemical methods which yield results in a computerized form having a very high degree of precision. One such method which is commonly being used nowadays is Electrochemical Impedance Spectroscopy (EIS) where the corroded metal strip is itself made to act as an electrode and the

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17. COMPARATIVE EVALUATION OF CORROSION BEHAVIOR OF AEGLE MARMELOS CORREA DIESEL, BIODIESEL

rate at which electrochemical reactions occur at the electrode-electrolyte interface is measured using highlevel complex instruments [82]. At present, the corrosion data available on various engine parts which come under direct contact of the fuel is obscure, and there are a limited number of works focusing on this aspect. Hence, for using biodiesels confidently in diesel engines, its corrosive nature has to be evaluated under a wide range of operating variables, environmental conditions, and chemical compositions.

17.7 CORROSION OF NONFERROUS METAL IN BIODIESEL 17.7.1 Biodiesel corrosion on copper Copper is one of the highly applied materials in automotive components, especially for the fuel pump components. However, published research shows that biodiesel causes enhanced corrosion activity and rapid degradation in copper base components within the CI engine [76,83]. Fazal et al. [84] have conducted much research, investigating the behavior of copper in palm biodiesel. An experiment was carried out by immersing copper (99.9%, commercially pure) in palm biodiesel (B100) for 200, 300, 600, 1200, and 2880 h of immersion period. The experiment results for an immersion period of 200e2880 h shows that there is an increase in the corrosion rate up to a maximum rate at 600e1200 h immersion time and decreases gradually [84]. This decrease is due to the increasing thickness of corrosion products on the copper surface tends to decrease the area of contact for corrosion activity, thus reducing the corrosion rate of the sample. An interesting finding in this research also shows that there is a difference in the appearance of test coupons before and after exposure to biodiesel for different periods. They found the bluish-green color is firstly seen around the edges of the sample. It is found to increase upon an increase in the immersion time of the sample, which finally covers the entire surface of the sample in a strong greenish color. This is due to the conversion of the copper compound on the surface of the sample, whereby the increase in the immersion time increases the thickness of the corrosion product. There is a chance of formations of small pits randomly on the surface of the sample exposed in the biodiesel environment for 200 h. The pits are also found to increase in size with the increase in immersion time. Elemental analysis through EDS also shows that there is an increase in the oxygen and carbon content with the increase in immersion time of copper in biodiesel due to oxidation reactions [84]. Geller et al. [30] supported this finding by stating that copper and copper alloys are highly reactive and more

prone to degradation in the biodiesel environment. Copper and copper alloys are susceptible to pitting and also discoloration due to the formation of oxide species.

17.7.2 Biodiesel corrosion on copper and its alloys Brass coupons show a lesser extent of corrosion rate in comparison to copper yet with similar corrosion patterns. Copper coupons in contact with 20% biodiesel solution show a higher percentage of weight loss, that is, 0.71%, while increasing biodiesel content to 80% gives a slight increment in the weight loss, that is, 0.74% [30]. Brass coupons are less reactive in a lower concentration of biodiesels where weight loss of the samples exposed to 20% biodiesel was an average of 0.46% while those exposed to 80% biodiesel lost approximately 0.74% weight. Geller et al. [30] concluded that copper and/or brass components should be replaced with steel-based materials as it may affect the storage, transport, quality, and utilization of the biodiesel. The performance of leaded bronze in comparison to copper in palm oil solution was investigated by Haseeb et al. [29]. The experiment involves the immersion of copper (99.99% commercially pure) and leaded bronze (87% Cu, 6% Sn, 6% Pb) in three solutions, B0, B50, and B100 at two different immersion temperatures that is room temperature and 60
C. Based on the above results, it is seen that the corrosion rate of copper and leaded bronze in biodiesel is higher when compared with diesel in all solutions [29]. It is also seen that leaded bronze is less reactive and more compatible in diesel and biodiesel environment as compared to copper. Further analysis also shows that copper tends to form oxide on its surface in B100 at room temperature, while it turns black at 60
C. For leaded bronze, test coupons at 60
C is cleaner and more shining compared with those tested at room temperature. The TAN assessment also shows that there is an increase in the TAN value of biodiesel upon exposure, whereby the increment is found to be similar in both copper and leaded bronze immersed solution. It was also found that the oxidation product increases with increasing biodiesel percentage in the solution [84]. Sgroi et al. [85] supported these findings by stating that the use of copper alloys not only causes corrosion problems but also the possibility of fuel pollution by copper ions which may eventually affect the reagent used in the chemical reactors of the fuel processors within the CI system. Pitting corrosion was also seen in bronze filter of oil nozzles after several hours of exposure to biodiesel at 70
C. Based on these findings, it was recommended that the use of copper-free components

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17.7 CORROSION OF NONFERROUS METAL IN BIODIESEL

should be emphasized especially in oil pumps and filters in contact with biodiesel environment. Edible oils face the problem of high feedstock cost and affect the food storage, supply, and demand trend when it is increased in utilization as biodiesel production feedstock. Therefore, inedible oils such as P. pinnata, Calophyllum inophyllum, M. indica, and J. curcas are widely investigated as a replacement for biodiesel feedstock [68,86,87].

17.7.3 Comparison of biodiesel corrosion on different metals Parameswaran et al. [88] compared the corrosion rate of copper and brass in contact with P. pinnata oil (B100). It is seen that the corrosion rate of copper is much higher when compared to brass in contact with biodiesel for an immersion period of 100 h. It was explained that brass is mainly the alloy of copper and zinc, making it more resistant to corrosion activity. The conductivity measurement of solution upon complete immersion also shows that brass exhibits lower conductance value as compared to copper. This indicates that there is a higher increase in the ionic content in copper biodiesel solution as a result of the increased corrosion activity [88]. Aquino et al. [89] studied the effects of natural light intensity and temperature on the corrosion activity of brass and copper samples. The experiment to evaluate the influence of light was conducted by immersing the samples for duration of 5 days in commercial biodiesel (B100) at room temperature, in the presence and absence of light. The immersion was also carried out in an oven set to 55
C, in order to simulate the condition of no light. The results show that the condition with presence or absence of light incidence at room temperature gives similar corrosion rate to both copper and brass, with a slightly higher indication of corrosion under the presence of light [89]. However, it was seen that the condition in the absence of light and higher temperature (55
C) shows a drastic decrease in the corrosion rate measured for both copper and brass samples. It was explained that the limitation to oxygen absorption and replenishment at higher temperature limits the corrosion rate activity in the immersed sample. The optimum condition with least corrosion rate however contradicts with the optimum condition for storage stability of biodiesel. It is seen that based on the induction period and viscosity measurement, the absence of light and at room temperature are the most suitable conditions for the storage of biodiesel [89]. Induction period measures the duration leading to oxidative degradation of biodiesel. Further study on the relationship between immersion time and fuel stability was conducted by Fazal et al. [90]

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by comparing the fuel properties and palm oil composition after immersion of mild steel and copper sample for a period of 20, 40, and 60 days. The gas chromatography analysis of the fuel upon immersion shows that methyl oleate is the major constituent of palm oil biodiesel. However, it is seen that there is a drastic and continuous reduction of methyl oleate in copper exposed solution, within the 20e60 days duration, giving a final amount of 24.62% methyl oleate in the solution when compared to the initial 46.16% methyl oleate before immersion. Mild steel however shows a much lesser reduction with a final amount of 42% methyl oleate after 60 days of immersion. Methyl oleate is an unsaturated component providing oxidation sites such as double bonds that offer more reaction sites for a metal ion leading to oxidation degradation of biodiesel. It is seen that copper has a higher tendency to react with these sites when compared to mild steel, thus leading to reduction of methyl oleate in the solution. It was also seen that copper affects the instability of the biodiesel solution giving it a lower induction period when compared to mild steel biodiesel solution. Fazal et al. [90] stated that the induction period decreases with the decrease in the methyl oleate content, thus affecting the fuel properties of copper in biodiesel. Copper immersed biodiesel also shows higher kinematic viscosity, water content, and TAN of the solution when compared to mild steel immersed biodiesel. This is associated with the higher corrosion rate exhibited by copper in comparison to mild steel. The EDS analysis also shows that there is a higher content of oxygen detected on the copper sample surface than that of mild steel. This implies that there are more oxides in the copper surface, and also inside the corrosion pits. The increase in immersion time also tends to increase the oxygen content detected on the sample surface. Enzhu Hu et al. [91] studied the corrosion behavior of biodiesel fuel produced from rapeseed oil and methanol on common automotive materials, that is, aluminum, copper, mild carbon steel, and stainless steel. The findings are in line with other researches in the field, stating that corrosion rate of rapeseed biodiesel on stainless steel and aluminum was less than those of copper and mild carbon steel. This is attributed to the reactivity and oxidation of both copper and mild steel. Minor corrosion effects were seen in aluminum and stainless steel, similar to those of diesel. This may be due to the formation of films of metal oxide, which prevents metal oxidation, thus giving lower corrosion rates. However, the corrosion rates of all four metals are still lower in diesel when compared to biodiesel environment. This is attributed to the higher amount of saturated fatty acids in diesel, giving it a better stability when compared to biodiesel. It was also seen that there is a higher percentage of oxygen and carbon elements on

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17. COMPARATIVE EVALUATION OF CORROSION BEHAVIOR OF AEGLE MARMELOS CORREA DIESEL, BIODIESEL

the corrosion oxide layer of biodiesel. Hu et al. [91] explained that the reaction between metal oxides and fatty acids of biodiesel leads to the production and adherence of reaction salts on the surface of the exposed metals. This leads to the increase in oxygen and carbon content detected on the biodiesel immersed samples. Much research comparing the overall performance of various materials in contact with biodiesel has been conducted across the globe. This is an essential comparison as the components within a CI engine consist of both ferrous and nonferrous metals, with different corrosion reaction and stability toward biodiesel. A study by Fazal et al. [90] comprises of comparison of corrosion deterioration and oxidation stability of common automotive component materials such as aluminum, copper and stainless steel, brass and cast iron in both petroleum diesel and palm biodiesel. They found that aluminum is the most compatible material among the nonferrous materials showing the least difference in corrosion rates between diesel (B0) and biodiesel (B100) environment. The decomposition of biodiesel produces copper and iron ions that tend to further activate various other chemical reactions. Cursaru et al. [92] experimented on the corrosion behaviors of aluminum, copper, and mild carbon steel exposed to sunflower biodiesel (B100), biodiesel blend (B20), and conventional petroleum diesel (B0) after static immersion tests in B0, B20, and B100 at room temperature and 60
C for 3000 h. It is noted that the increase in temperature increases the corrosion rate. This can be attributed to the TAN factor. High TAN factor in biodiesel is due to the formation of free fatty acid in the solution. The experimental research indicates that increase in the immersion temperature causes the TAN factor to increase in the biodiesel, and consequently the oxidation of metal in the biodiesel environment increases. The increase in temperature leads to higher oxygen content and moisture adsorption which eventually gives a higher corrosion rate. The corrosion rate of all metals show similar observation in regards of lower corrosion rate in diesel when compared to biodiesel. As seen in various research, copper tends to exhibit higher corrosion rate when compared to other materials under the same condition [28,29]. The present research studies the behaviors of aluminum and mild steel in the presence of AMC biodiesel and its blends. However, significant and published research on this scope is not available yet.

17.8 EFFECT OF WATER AND MICROBES ON THE FUEL TANK Microbial growth in presence of water in diesel tank results in corrosion which was directly proportional to

water quantity [93]. Anaerobic sulfate-reducing bacteria were found in the diesel tank when the fuel was stored for more than 400 days in the tank. In the second day itself, aerobic bacteria were detected in the storage tank whereas on the ninth day yeast and fungi were seen and bacterial colony deterioration due to pH change was observed after 145 days. If the development of biomass is avoided at the interface of oil-water, it reduces the development of colonies of anaerobic sulfate-reducing bacteria. It was reported that corrosion was more in grounded diesel storage tank than aerial tank with facilitated water drainage by making system inclined 30 degrees to the horizontal which results in corrosion reduction. In comparison to mineral diesel biodiesel holds 20 times more water. Water saturation level was more in biodiesel (1395 ppm) than diesel (62 ppm). In the aerobic rich (initial 84% aeration) fuel mixtures, biodiesel blends (B5, B10, B20, B50, and B100) and water incubation reported existence of methanogens, nitrate, and sulfate-reducing bacteria, thereby rendering the biodiesel to microbial degradation. Corrosion can happen in the storage tank by two mechanisms: microbiologically influenced and chemical corrosion [94]. Carbon steel beam electrode (WBE) is used for studying the corrosion mechanism of carbon steel in soybean biodiesel in the existence of tap water [95]. In the storage tank WBE was placed horizontally as well as vertically. The corroded electrode by contact of tap water is inserted into the biodiesel. At biodiesel-water interface cathodic currents were generated on several wires after 20 mins of water addition. Anodic and cathodic currents were detected after 2 h. As time passes up to 72 h complete electrode came in contact with water and corroded the entire part which was in contact with water. Rusting happened up to 120 h. In biodiesel, water is soluble in less quantity (0.2%), thus water separates by condensation from biodiesel and forms a layer between biodiesel and the metal surface. As water has high density and is insoluble in biodiesel, it comes to the bottom of the tank with impurities such as chloride during stagnant conditions which lead to cathodic and anodic reaction at the metal surface. On the periphery of the water drop, the oxygen concentration was higher than in the bulk water which leads to a cathodic reaction on the periphery of the water drop and anodic reaction took place in the central part of the bulk of water due to high ion-promoted corrosion. Water presence in the tank was the cause of fuel degradation because water promotes microbial growth which leads to microbiologically influenced corrosion. Microbiologically influenced corrosion is a prime factor and it is due to the high rate of biofouling [96]. The carbon steel was exposed in fresh and salt water for 60 days to analyze anaerobic microbial decomposition by imaging techniques. The pitting corrosion strips

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17.9 TECHNIQUES TO MONITOR CORROSION

were observed on the surface [97]. Three different groups of strips exposed in following three different circumstances seawater dipping, interface seawater and biodiesel, and biodiesel dipping. The carbon strip polarization resistance (RP) was inspected at the biodiesel layer which came top of the seawater due to low density. After inspection it was reported that instantaneous corrosion rate was inversely proportional to polarization resistance (RP). In 10 days period of exposure of carbon steel to biodiesel shows that corrosion rate decreases from 5  104 to 106 cm2, which was an indication of oxygen removal from biodiesel. From the 12th day of exposure, corrosion rate was increasing and on 18th-day exposure it was increased up to 1  103 cm2, after that corrosion rate remained constant. The corrosion rate value was slightly lower for seawater than biodiesel/seawater interface. Hydrolysis results into the production of an intermediate which leads to an accelerated rate of corrosion of metals. This acidic intermediate was responsible for the oxidation process. The stability of the biodiesel has been reported to be lower than 4 days of half-life period maintaining at 17
C [98].

17.9 TECHNIQUES TO MONITOR CORROSION The mass loss and electrochemical impedance spectroscopy are methods for exploring the corrosivity of biodiesel.

17.9.1 Mass loss Mass loss is one of the cheap, easy, and most widely recognized strategies to explore the corrosion rate. Many researchers have used immersion test followed by weight loss method to calculate the corrosion rate. The mass loss experiment procedure is given in ASTM G31 standard. ASTM G1 standard method gives the general procedure to clean the material samples [99]. A technique to examine the corrosion of biodiesel by mass loss strategy is as per the following: • The samples have to be polished with emery paper and then cleaned with acetone solvent. The polished samples should be weighted before being immersed in biodiesel fuel for a specific period. • After a certain period of immersion, the materials have to be removed from biodiesel. Then the excess amount of biodiesel is removed by sodium hydroxide followed by water washing. • Finally, the water-washed material is dried to evaporate the water weight. The following equation

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(17.2) is used to calculate the material loss and rate of corrosion. Corrosion rateðmpyÞ 534  mass lossðgÞ ¼ Densityðg=cm2 Þ  Areaðin2 Þ  TimeðhÞ

(17.1)

Fazal et al. [100] investigated the degradation of automotive components such as copper, brass, aluminum, and cast iron on palm biodiesel by mass loss method over 2880 at room temperature. They found that copper showed less corrosion inhibition in palm biodiesel compared to other materials. The corrosion rate of palm biodiesel on copper is found to be 0.39,278 miles per year. Palm biodiesel is found to form more corrosion on the metal surface compared to diesel. Corrosion characteristics of palm biodiesel on magnesium and aluminum were carried out by K.V. Chewa et al. [101]. Kaul et al. [31] investigated the corrosiveness of biodiesel derived from jatropha oil, karanja oil, mahua oil, and salvadora oil on the metallic piston by immersion test. In this study, they found that biodiesel of jatropha and salvadora formed more corrosion on the metallic and nonmetallic surface.

17.9.2 Electrochemical techniques Electrochemical impedance spectroscopy is a modern instrument in corrosion research that is gradually advancing into becoming portable. Time-dependent data of ongoing processes can be extracted from electrochemical impedance spectroscopy experiments because it is a nondestructive method [102]. Electrochemical technique is used when the corrosion mechanism is occurring in the liquid phase. Biodiesel corrosion on metals can be evaluated by electrochemical impedance methods because a small quantity of water is present in biodiesel. There are numerous electrochemical techniques available to measure the corrosion rate. The potentiostatic technique is the most commonly used one [99]. Principles to quantify corrosion rate utilizing these methods are available. The primary advantage of electrochemical impedance method over conventional mass loss method is a short time and capability to measure meager corrosion rates [103]. ASTM G59 standard gives a detailed procedure to carry out this method. The electrochemical test is carried out in a glass beaker which contains electrolyte with three electrodes. In this, platinum, calomel, and metal sample are connected to counter, reference, and working electrode as reference, respectively. Most of the real-life applications, for instance, corrosion of metals, contain many complex reactions with complex behaviors. In those cases, impedance replaces resistance as a more generic parameter.

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The capability of the circuit to oppose the flow of electric current is measured as impedance. The term impedance refers to the frequency dependent current flow in any circuit element. Corrosion study of biodiesel on aluminum metal was carried out by Da´az-Ballot et al. [32]. In this, the effect of KOH and NaOH on biodiesel was studied using EIS and open circuit potential techniques. They found that initially open circuit potential of biodiesel is negative and further it is changed to positive with an increase in time. In a short period biodiesel species were reacted with the aluminum surface and produced corrosion on its surface which acts as a passive layer due to which negative values were observed. After several washing cycles, the negative values of open circuit potential changed to positive values due to a decrease in electrochemical reaction on the aluminum metal surface. As a result, this study reveals that corrosivity of biodiesel on aluminum metal can be quantitatively evaluated using electrochemical impedance spectroscopy technique.

17.9.3 Noncontact profilometry Noncontact profilometry techniques mainly focus on measuring the topography surface of corroded materials without reforming the sample surface by making physical contact with a stylus. The profilometers that operate under the principle of axial chromatism (confocal profilometers) and optical triangulation (laser profilometers) are the two primary classifications of commercial noncontact profilometers. In laser profilometers, a beam of light is concentrated on the target through focusing lens. The reflected light from the lens is made to target on the photodetector through the second lens. The resultant signal obtained from the photodetector differs from one point to another point at which it struck. Similarly, the point at which the beam signal strikes the detector also varies according to the height of the target surface. The axial resolution is in order of micrometers. Confocal profilometers inject a beam of white light with high chromatic aberration property into a lens. As a result, each signal wavelength targets in different distance from the lens. The height on the target surface is estimated by the coincidence of surface with the focal point of monochromatic light. It is identical to laser profilometer, in which the beam strikes the point in the detector varies with the wavelength and the resultant signal generated by the detector also varies with the wavelength based on the point at which the beam strikes the detector. The axial resolution is in the order of nanometers. The scanning profilometers based on confocal and laser technologies are automatic in executing the function. The instrument starts with the scan once it is

being defined by the user without applying any further inputs. The resolution can be enhanced by increasing the number of data points. The resolution can be diminished by reducing instrument demand, electronic data file size, and resolution of beam rather than by limiting the measurements needed to be handled manually. The software packages are available along with the automated scanning to improve the wide range of operations and analyses. For example, surface parameters and pit depth distributions are determined automatically. Consider an aluminum sample immersed in biodiesel extracted from P. pinnata for 100 h; pith depth distribution and surface topography are estimated for this sample by laser profilometry. The automated data manipulation and scanning are the added advantage of profilometry instruments. In addition, software associated with these instruments made them an efficient tool for corrosion analysis. But, the main limitation of this system is to balance step size and data file size for the larger area. In complex operations such as feature separation or extraction, the software package used to calculate the data results in artifacts. Moreover, in certain software packages, the surface features are extracted using an algorithm designed to remove anomalies. Therefore, narrow pits can be removed from peakpit distribution calculation. The pit depth and peak heights are realized on the corroded surface and it can be compared with the height of uncorded surface if required. For example, the point below the original surface or measured surface on the uncorded surface is considered as the highest point on the measured signal. Due to the narrow focal depth in laser profilometers, the area can be measured in a single scan even when the surface height varies randomly. Whereas, confocal profilometers are capable of measuring larger height ranges [99].

17.10 MATERIALS AND METHODOLOGY The reagents and auxiliary materials used for the transesterification are potassium hydroxide (KOH, 85% purity, SRL), methanol (CH3OH, 99% purity, CDH), and hydrochloric acid (HCl, 37% purity). The solvents used in this work include laboratory grade acetone and heptane.

17.10.1 Oil extraction Aegle Marmelos Correa (AMC) is generally called as bael in Hindi, vilvam in Tamil, golden apple, and wood apple in English. AMC is a species of tree native to India, Srilanka, and Bangladesh. However, it is broadly available in Southeast Asia countries like Pakistan, Burma,

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Vietnam, and Thailand. Its fruits are used in Ayurvedic medicine and leaves of the tree are used to worship Lord Shiva. The AMC fruit has a smooth, woody shell with a green, gray, or yellow peel. Fruit takes around 11 months to ripen on the tree and can reach the size of a bigger grapefruit, and some are considerably bigger. The outer shell of the fruit is hard and difficult to break by hand, so mallet or hammer is required to break the fruit. 17.10.1.1 Fruit collection and seed extraction The sharp, mature AMC fruits were collected from a well-grown tree from a clean and noncontaminated area between May and June, in different areas of Erode and Trichy districts, Tamilnadu. The AMC seeds were extracted by breaking the shell and then softened with water for an hour to remove the pulp. Then the extracted seeds were dried in sunlight for 48 h. Household mixer grinder (750 W) was used to crush the seeds, and the crushed particles were separated using sieves of three particle sizes (0.75 mm, 1.09 mm, and 2.18 mm). The average particle size was estimated by the average size of the sieves between which the seed particles were caught as given in Eq. (17.2). dp ¼

dp; max þ dp; min 2

(17.2)

where, dp ¼ Average particle size, mm. 17.10.1.2 Maceration oil extraction Maceration is carried out using 100 g seed in a threeneck round bottom flask using 400 mL solvent (acetone: heptane). The flask is kept in a container half-filled with

Aegle marmelos correa fruit

Seed

water to keep the solvent temperature below the atmospheric temperature to reduce the solvent evaporation at the time of stirring. A stirrer rod was introduced into the flask through the top, and the speed of stirring is adjusted to 600 rpm by using a digital rpm indicator and the knob. The experimental setup used for oil extraction is given in Fig. 17.3. The extraction was carried out by varying acetone: heptane ratio (0/100, 25/75, 50/50, and 100/0). As the solvent mixture percentage is of more or less than 50/ 50 by volume, it caused no significant impact on the amount of oil extracted. Moreover, so the experiment was held out with acetone:heptane (50/50% by mass) to get out the most favorable and the ideal duration of extraction. Then yield was calculated for various time intervals (1, 2, 3, 4, 10, and 16 h) to identify the role of time in extraction. It was found that beyond 4 h there was no significant increase in oil yield. So 1.5, 2.5, and 4 h were considered for optimizing the yield with various seed particle sizes of 1.02, 2.18, and 3.6 mm. The extracted solvent seed mixture is filtered using Whatman Grade No.44 ashless filter paper by vacuum filtration. The oil-solvent mixture was poured into a ceramic conical funnel; the filter paper was fitted in the bottom of the funnel. It took few hours to filter 1 L of solvent-oil mixture. The top of the funnel is closed at the time of filtration to prevent the evaporation of the solvent. Oil and solvents were separated by using distillation. Distillation was done by using a three-neck flask and a reflux condenser. A conventional heater was used for heating the mixture. Acetone and heptane were

Solven

Bi-section fruit Gel removal Motor

Stirrer rod Round Bottom

Seed powder

Schematic diagram of oil extraction setup

FIGURE 17.3

Seed

Schematic diagram of oil extraction process from AMC fruit.

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evaporated at 50 and 94
C, respectively, and collected in separate flasks y. Pure AMC oil was obtained after distillation. The percentage of raw oil extracted from AMC seeds was calculated using Eq. (17.3). Oil Yield ð%Þ ¼

Weight of oil extracted ðgÞ  100 (17.3) Weight of seed ðgÞ

Degumming is the process of converting nonhydratable phosphatides present in the oil into phosphatidic acids making them hydratable. Acid degumming is done on purpose to remove nonhydratable gums. AMC seed oil was heated up to 80
C and orthophosphoric acid (0.2% vol.) was added and then stirred for 15 min by a magnetic stirrer. After 15 min, the mixture was allowed to cool to room temperature. Then hot water at 55e60
C was added to the mixture, stirred for 15 min, and kept for settling down; finally, gums were removed by filtration.

17.10.2 Biodiesel production and characterization The free fatty acid (FFA) value is an essential parameter for deciding the transesterification process for vegetable oil. In this study, the acid value of oil was found by titrating 1 g of the oil mixed with 1:2 ratio of diethyl ether and ethanol against 0.1N KOH (burette solution). If the acid value of raw oil is more than 2.0 mg of KOH/g of oil, two-step transesterification process will be required for biodiesel production [104,105]. 17.10.2.1 Heterogeneous acid catalyst preparation from crude glycerol The heterogeneous acid catalyst preparation was conducted in a microwave oven at 255 W. The ratio of glycerol and sulfuric acid (36% concentration) were taken in 1:2 into the flask and gently stirred at 500 rpm. Then the mixture was irradiated to 180
C using microwave heating for 20 min, to expedite the partial carbonization and sulfonation. The product was cooled to room temperature and then repeated water wash was done until pH value reached between 6 and 7 to obtain carbon compound. The glycerol-based acid catalyst was obtained after filtering followed by drying in a hot air oven at 120
C for 12 h to remove moistures [106]. 17.10.2.2 Esterification process The esterification was done in a microwave oven with irradiation power of 255 W and stirring speed of 600 rpm for 10 min to reduce the FFA content of AMC oil. In this process, a mixture of oil to methanol molar ratio (1:6) was taken in a two-neck flat bottom flask (250 mL) fitted with a reflux condenser. The reactants were initially heated up to 60
C, followed by adding

0.5 wt% of heterogeneous acid catalyst [107]. After the accomplishment of the esterification process, the product was poured into a separating funnel (250 mL) to settle down the product for 5 h. The excess methanol and free fatty acid settled in the upper layer and esterified oil settled at the bottom of the separating funnel. The esterified oil was separated and purified by further transesterification process. 17.10.2.3 Base-catalyzed transesterification The transesterification process was conducted on a hot plate with stirring speed of 600 rpm, the ultrasonic processor (900 W) and microwave processor (850 W). A mixture of AMC seed oil to methanol ratio of 1:6 and 1 wt% of homogeneous catalyst KOH was taken in the flask (250 mL). The experiment was carried out at 60
C for 5e60 min [108,109]. After that, the product was poured into a separating funnel to settle down for 5 h. Two distinct layers of biodiesel and glycerol were formed. The excess amount of methanol, glycerol, and catalyst from biodiesel was removed by washing with hot water.

17.10.3 Characterization of AMC biodiesel 1

H nuclear magnetic resonance (NMR) spectra of “2267A-S” (7 mg each) in chloroform were obtained using a 300 MHz AVANCE II (Bruker Biospin, Switzerland) spectrometer equipped with a 5 mm BBO probe. The experiments were recorded at 25
C using standard pulse sequence library of Topspin 3.2 followed by processing of the data by using Topspin software. The total biodiesel yield was determined by the percentage of free acid methyl ester (%FAME) and volume of biodiesel obtained (Eq. 17.4). The %FAME was identified using NMR and calculated according to the formula as given in Eq. (17.5) [33e35]. Biodiesel Yield ð%Þ ¼ % FAME from NMR  Volume of Biodiesel product %FAME ¼

2ACH3  100 3ACH2

(17.4) (17.5)

where ACH3 ¼ integration value of the methoxy protons at 3.66 ppm ACH2 ¼ integration value of the methylene protons at 2.26 ppm GC-MS was used to identify the molecules present in the AMC biodiesel sample. The GC-MS analysis was carried out using the Retex-5 column (30 m  0.32 mm) with an injection temperature of 300
C, and column

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TABLE 17.7

Chemical composition of Aegle Marmelos Correa biodiesel.

Fatty acid

Molecular formula

Percentage (%)

Molecular weight (g/mol)

Palmitic acid (S)

C16H32O2

25.06

256.4

Stearic acid (S)

C18H36O2

6.75

284.48

Oleic acid (US)

C18H34O2

26.69

282.47

Linoleic acid (US)

C18H32O2

24.48

280.445

Linolenic acid (US)

C18H30O2

15.43

278.43

Archidic acid (S)

C20H40O2

0.10

312.5304

Behenic acid (S)

C22H44O2

0.16

340.58

Lingoceric acid (S)

C24H48O2

0.22

368.63

temperature of 60
C. The fatty acid profile of AMC biodiesel is given in Table 17.7.

VKOH ¼ Volume of KOH, mL N ¼ Normality of KOH, mol/mL WS ¼ Weight of sample, g

17.10.4 Physicochemical properties of biodiesel Fuel characterization is most essential to know suitability of fuel in the engine. Fuel characterization gives a proper idea about its advantages and disadvantages over conventional fuel. Fuel characterization of diesel, AMC oil, and its biodiesel was done by determining physicochemical properties according to ASTM 6751 and EN 14214 standards. Those physicochemical properties are iodine value, calorific value, kinematic viscosity, density, cloud point, pour point, flash point, fire point, acid value, saponification value, carbon residue, and oxidative stability. 17.10.4.1 Acid value The acid value is defined as the weight of KOH in mg required to neutralize the organic acids present in 1 g of a sample of fat. To determine acid value standard method is EN 14104 titration method, which is used for measuring the acid value of raw oil and biodiesel. This method used 50 mL of ethanol and diethyl ether mixture to dissolve 1 g of the fat sample to produce a fat solution. In this method, phenolphthalein indicator is used for indicating endpoint of the titration. In this method, beaker solution is prepared by dissolving 1 g of sample into the solvent and adding two to three drops of indicator. This beaker solution is titrated with burette solution which is 0.1 N aqueous solution of potassium hydroxide (KOH). The acid value of the sample was calculated using the following equation: Acid value ¼

MW  N  VKOH Ws

where MW ¼ Molecular weight of KOH, g/mol

(17.6)

17.10.4.2 Saponification value Saponification number of a fuel is defined as an amount of potassium hydroxide in mg required for complete neutralization of free and combine acid present in 1 g of the fuel sample. The standard method for determination of saponification value of oil and biodiesel is ASTM D 1962 titration method, which was used to determine the saponification value of AMC oil and biodiesel. In this method, two beaker solutions are prepared as test and blank by dissolving 1 g sample of fat into 10 mL ethanol solvent into one beaker and taking only 10 mL ethanol solvent in another beaker. In the above mentioned two beakers 25 mL of 0.5 N ethanolic KOH is quantitatively added and named as test and blank. This test and blank beaker solutions are heated for 30 min at boiling temperature of water by taking care of evaporation of solution, using a reflux condenser. After that the samples are allowed to reach room temperature. Two to three drops of phenolphthalein indicator is added to both beaker solutions. Finally, test and blank solutions are titrated against burette solution 0.5N HCl. The saponification value was calculated using the following equation. Saponification value ¼

MW  N  ðVBlank  VTest Þ Ws (17.7)

where MW ¼ Molecular weight of KOH, g/mol VBlank ¼ Volume of HCl for Blank sample, mL VTest ¼ Volume of HCl for the Test sample, mL N ¼ Normality of KOH, mol/mL WS ¼ Weight of sample, g

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17.10.4.3 Iodine value The standard method for determination of iodine value of oil and biodiesel is mentioned in standard EN 14111, which was used to determine iodine value of AMC oil and its biodiesel. In this method, two beaker solutions are prepared as test and bank by dissolving 1 g of fat into 10 mL chloroform solvent in one beaker and taking only 10 mL chloroform solvent in another beaker, respectively. In the above mentioned two beakers 20 mL of iodine monochloride reagent is transferred and mixed thoroughly. Then the samples were allowed for incubation up to 30 min in a dark place. After the incubation period, 10 mL of potassium iodine solution was added to test and blank solutions by taking care of complete mixing using rinsing beaker sides with 50 mL of distilled water. The test and blank samples

Calorific value ¼

Weight of fuel at 15 C
Volume of fuel at 15 C

MW  N  ðVBlank  VTest Þ  100  103 Ws (17.8)

where MW ¼ Molecular weight of Na2S2O3, g/mol VBlank ¼ Volume of Na2S2O3 for Blank sample, mL VTest ¼ Volume of Na2S2O3 for Test sample, mL N ¼ Normality of Na2S2O3, mol/mL WS ¼ Weight of sample, g 17.10.4.4 Density The density of diesel, oil, and biodiesel was determined as per the ASTM D1298 and IS 1448: Part 32: 1992 standard at 15
C. In this method, fuel was poured up to the mark into already weighted 60 mL vessel. Then this fuel is maintained at 15
C using defreezer chamber and weighted. The weight difference between filled and empty vessel is the weight of fuel samples. The density of fuel samples can be estimated using the following equation.

(17.9)

17.10.4.5 Viscosity and calorific value According to ASTM D445 standard kinematic viscosity of fuel, samples were determined at 40
C using Brookfield viscometer (DV2TLV). Bomb calorimeter was used to measure calorific value of fuel samples and experiment was performed as per ASTM D240 standard. In a crucible, 1 g of sample was taken and burnt in the presence of pure oxygen by electrical ignition. The rise in temperature and heat released during the combustion were measured to check effective heat capacity of water; dry benzoic acid was used as a test fuel. The calorific value of the sample is found using the following equation.

Water equivalent of calorimeter ð2883 Cal=
CÞ  Rise in temperature ð
CÞ Mass of sampleðgÞ

were titrated till the color changes to pale straw, against 0.1 normality of aqueous solution of sodium thiosulfate (Na2S2O3). Then, 1 mL of the starch indicator was added to the solution, and color of the solution was changed to purple color. Then again titrate till the solution color changes to colorless. The following formula was used to determine the iodine value of the fat sample. Iodine value ¼

Density ¼

(17.10)

17.10.4.6 Cloud and pour point Subzero equipment was used to determine cloud and pour point of diesel, oil, and biodiesel samples as per ASTM D2500 standard. This equipment consists of a refrigerated chamber in which four places are there for four glass tubes having 12 cm height and 3 cm diameter with the copper vessel. The 50 mL sample-filled tube is closed by using rubber cork and placed into the refrigerated chamber and observed for every
C drop in temperature by taking out from the chamber. Cloud point temperature is the temperature at which cloud forms in fuel. After the identification of cloud point, experiment was run further to find out pour point. Pour point temperature is the temperature when the fuel sample became motionless when tilting the glass tube to a horizontal position for 5 s. 17.10.4.7 Flash and fire point According to ASTM D93 standard method, Open Cup Cleveland apparatus was used to estimate the flash point and fire point of diesel, oil, and biodiesel. Flash and fire point were determined by taking a fuel sample in test cup up to marked level and heating this cup by an electric heater and passing gas flame over fuel surface for every 1
C rise in temperature. The flash point was recorded as the temperature at which the flash appeared at fuel surface with the help of an external ignition source. The fire point was noted as the temperature at which fuel vapor catches fire when introducing the

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ignition source at fuel surface and continues the fire minimum of 5 s after removal of ignition source. 17.10.4.8 Conradson carbon residue A carbon residue apparatus was used to find out the amount of carbon residue of diesel oil and biodiesel fuels. The measurement was carried out according to the ASTM D4530 method. This method was used to find out the amount of carbon residue present after pyrolysis of the fuel sample. It is envisioned to bring a few ideas of relative coke forming properties. In this experiment, 5 g of moisture-free fuel sample was taken in the iron crucible of the apparatus. The iron crucible was then placed in the center of Skidmore crucible of the apparatus. After that, both the crucibles were closed with a lid and an exit was made for the vapors to escape, once they formed. The electric oven was used to heat the fuel samples. In this, the oven temperature was slowly increased up to 500
C with a heating rate of 10
C/min and this temperature was maintained for 15 min to pyrolysis the fuel sample. Nitrogen gas was purged during this pyrolysis process with the flow rate of 600 mL/min. After the pyrolysis of fuel, the oven power supply was shut off, but nitrogen flow continues until the sample temperature reaches 150
C. When the oven temperature reaches 150
C, the crucible was taken out from the oven and kept in a desiccator to reduce the sample temperature to 30
C. Finally, the carbon residue was weighted in a precision weighing balance, and mass percentage of carbon residue was below: % carbon residue ¼

A  100 Ws

(17.11)

where A ¼ Carbon residue, g WS ¼ Weight of sample, g

and 10 00 sides. The chemical composition of aluminum and mild steel is given in Table 17.8. The metal samples were polished with 400, 1200, and 1500 grade of emery paper to remove scratches and impurities present on the surface. Then, the metals strips were cleaned with distilled water followed by acetone solvent. The metal samples were immersed in five sets of fuel samples such as diesel (B0), biodiesel (B100), and three biodiesel-diesel blends. In this, letter B denotes the biodiesel, and the binary number represents the quantity of biodiesel blended in percentage. Pure diesel and pure biodiesel are denoted as B0 and B100, respectively. On the other hand B10, B20, and B50 are composed of 10, 20, and 50 of biodiesel solution, respectively. In this experiment, three biodiesel blends such as B10, B20, and B50 were prepared for ultrasonic mixing.

17.10.6 Corrosion study EIS measurements are carried out by applying a small sinusoidal potential (or current) of fixed frequency. The corresponding response is recorded, and the impedance is computed for the given frequency. The same experiment is repeated for a full range of frequencies. Finally, a graph is plotted and analyzed. Electrochemical cells can be modeled into a network of passive electrical circuit elements. Such a network is called as an equivalent circuit. The EIS response of an equivalent circuit can be calculated and compared to the actual EIS response of the electrochemical cell. Study of corrosion is quite complicated; thus by converting the complex reaction into a simple electrical circuit makes the study easier for researchers having little knowledge of chemistry. There are three electrodes such as platinum, calomel, and metal sample which are connected to the computer using a potentiostat and a waveform generator. The impedance of a Randles cell is given by Z ¼ Ru þ

17.10.5 Metal sample and biodiesel blend preparation Aluminum and mild steel metals with dimension of 150 mm length, 10 mm thickness, and 100 mm width were purchased from the local company. The metals were cut into 5 strips of a square with 2 mm thickness TABLE 17.8

1 1  juCdl Rp

(17.12)

where Cdl is the double layer capacitance, Rp is the polarization resistance/charge transfer resistance, and Ru is the system resistance/electrolyte resistance. Bode plot and Nyquist plot are usually plotted to determine the

Material chemical composition of aluminum and mild steel. Chemical composition (%)

Metal

C

Mn

P

S

Zn

Si

Cu

Mg

Cr

Fe

Al

Aluminum

0.5

0.05

e

0.02

0.02

0.4

1

4

0.5

0.5

Balance

Mild steel

0.15

0.66

0.02

0.02

e

e

e

e

e

Balance

e

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Counter electrode Working electrode Reference electrode

Potentiostat

Computer

FIGURE 17.4

Electrochemical cell

Schematic representation of EIS experimental setup.

circuit parameters. In Nyquist plot, -Zimag is taken in the Y-axis, and Zreal is taken in the X-axis. In bode plot, Yaxis represents log(jZj) whereas X-axis represents log(frequency). Each of these metal strips was immersed separately and entirely in five different blends of biodiesel-diesel, namely, B0, B10, B20, B50, and B100 for 100 and 600 h. The aluminum and mild steel test samples that have been labeled and then tied to thin bamboo sticks using a tie string. The tie is secured with sellotape to ensure that the test sample is always in a vertically upright position while being entirely immersed in the solution in the beaker. The beaker is then tightly closed with shrink wrap material to prevent contamination and moisture from the environment from affecting the immersion test process. After immersing each metal strip in their respective blend for 100 h, the metal strip sample is connected as the reference electrode in the EIS setup, and 0.5 N KOH solution was chosen as the electrolyte [110]. The EIS experiments were conducted for a few minutes, and the corresponding Bode plots and Nyquist plots for different samples were obtained. The experimental setup is as shown in Fig. 17.4.

17.11 RESULTS AND DISCUSSION 17.11.1 Heterogeneous acid catalyst characterization The X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) of glycerol-based acid catalyst were done to demonstrate its physical and chemical characteristics. The X-ray diffraction (XRD) method was used for identifying the structure of a heterogeneous acid solid material. X-ray diffraction image

of a crystal is the fingerprint of the crystal. XRD patterns of carbon catalyst are shown in Fig. 17.5A. The peaks between 10 to 30 and 35 to 50
indicate the amorphous nature of carbon sample. FT-IR is shown in Fig. 17.5B. The peaks at 1172 and 1630 cm1 conform to the stretching modes of C]C in catalyst matrix. The SO3H groups are active sites of glycerol-based carbon catalyst which present in peaks at 1037 and 1177 cm1. The presence of sharp peaks at 1629 and 3351 cm1 confirm the presence of stretching modes of phenolic OH and COOH functionalities, respectively.

17.11.2 Physicochemical properties To evaluate the potential of AMC biodiesel as a replacement for diesel fuel, the physical and chemical properties of the AMC biodiesel were determined. A comparison of physical and chemical properties of the diesel, extracted oil, and biodiesel are given in Table 17.9. The acid value of the AMC oil was found to be 2.3 mg of KOH/g of an oil which was higher than EN 14,214 limit. The acid value was 0.2 mg of KOH/g of oil after the esterification process. The biodiesel yield was 93% when 1 wt% of KOH was used. The density of the fuel is a crucial parameter in the fuel injection process and moreover, it is associated with the viscosity, heating value, and cetane number. The density of AMC biodiesel is 880 kg/m3, which falls within the EN 14214 standard. The cloud and pour point are the two essential properties of the low-temperature application. The cloud and pour point of AMC biodiesel are 4 and 1
C, respectively, which is nearer to diesel fuel value, so the obtained biodiesel can be used in the low-temperature environment. Flash point of AMC biodiesel is about 165
C, which is three times higher than diesel fuel.

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(a)

(b)

100

–1

1037.83 cm ,

90 80 70 60

–1

1629.83 cm ,

50 –1

3351.38 cm , 40 –1

1177.84 cm , 20

10

30

40

60

50

70

80

30 4000

3500

3000

TABLE 17.9

Density at

3

(kg/m )

Acid value (mg of KOH/g) Cloud point

(o C)

Pour point temp Flash point Fire point

1000

500

Cm

(a) XRD pattern and (b) FT-IR spectrum of glycerol-based carbon acid catalyst.

Physicochemical properties of diesel, AMC oil, and AMC biodiesel.

Properties 15
C

1500

–1

2 Theta/ degree

FIGURE 17.5

2000

2500

AMC oil

AMC biodiesel

EN 14214/ASTM D6751

Test methods

824

910

880

860e900

EN ISO 12185

5.6

0.2

0.5 max.

EN 14104

4

1

0

4

54

325

62

335

0 0

(
C)

14

(
C)

(
C) 40
C

Diesel

2

ASTM D 2500

a

NS

ASTM D 97

164

130 min

ASTM D 93

175

NS

ASTM D 93

NS

2.39

27.92

3.6

3.5e5

EN ISO 3104

Calorific value (MJ/kg)

42

39.46

37.5

NS

D240

Cetane number

47

58

47 (min)

D976

Carbon residue (% m/m)

0.0109

0.025

0.3 max.

EN ISO 10370

Saponification (mg KOH/g)

NS

277

224

NS

D1962

Iodine value (mg of I2/g)

NS

85

56

120

EN 14111

Peroxide value (ppm)

NS

50

NS

NS

NS

NS

98.96

NS

NS

NS

Viscosity at

Fat content

(mm /sec)

a

g/100
g

0.03

NS, not specified. a Location & season dependent.

Therefore, AMC biodiesel is the safer fuel compared to diesel for storage and transportation, and during combustion it can also prevent the unexpected ignition. Calorific value is the influential property of fuel because the higher calorific value is suitable for combustion as it improves the engine performance. The calorific value of AMC biodiesel is 39.46 MJ/kg which is only 6% less than diesel, so the AMC biodiesel can give better

performance in engine application. The AMC biodiesel can give better flow and atomization at low temperature because its kinematic viscosity is 3.6 mm2/s, which is within the ASTM limits. The iodine value of AMC biodiesel was 56 mg of I2/g of oil, which indicates that unsaturated compounds in biodiesel are less and it improves the oxidation stability and prevents gum deposition on storage [111].

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17. COMPARATIVE EVALUATION OF CORROSION BEHAVIOR OF AEGLE MARMELOS CORREA DIESEL, BIODIESEL

17.11.3 Corrosion characteristics The corrosion tests on various metals were carried out using Electrochemical Impedance Spectroscopy which revealed that B50 blend performs auspiciously among all the other blends. Nyquist plots of aluminum and mild steel are shown in Fig. 17.6 and Fig. 17.7. In these plots the blend with a bigger curve or semicircle is said to produce less corrosion on that particular metal because the corresponding polarization resistance is higher. Initially, when EIS tests were run for samples immersed for 100 h, it was found that B100 was more resistant toward producing corrosion in all metals compared to all the other blends. At the initial stages of 100 h when oxidation effect does not prevail much, pure biodiesel produces less corrosion and in fact provides more lubrication due to the presence of lubricating moieties like esters. After B100, B50 was found to

produce less corrosion. The amount of corrosion caused by B50 will be lesser than B100 because of the corrosion inducing sulfur atoms present in commercially available diesel. However, this corrosion is considered to be mild corrosion because in the later stages when the oxidation effect of biodiesel starts dominating, the corrosion caused by commercially available diesel is somewhat negligible. Also, B0 induces more corrosion than B50 and B100. This is attributed entirely to the presence of sulfur atoms present in the commercially available diesel. However, the corrosion inducing effects of B10 and B20 are somewhat random, and it depends on the dominance of one’s effect over another. In the first set of results taken for 100 h, the one with more % of diesel might have caused more corrosion, and in the second set of results taken for 600 h, the one with more % of biodiesel might have caused more corrosion because of

25 B0 (100 hour) B10 (100 hour) B20 (100 hour) B50 (100 hour) B100 (100 hour) B0 (600 hour) B10 (600 hour) B20 (600 hour) B50 (600 hour) B100 (600 hour)

Zi (ohms)

20

15

10

5

0 20

40

30

50

60

70

Zr (ohms)

FIGURE 17.6

Nyquist impedance plots of aluminum metal at different immersion times in biodiesel and its blends

16000 B0 (100 hour) B10 (100 hour) B20 (100 hour) B50 (100 hour) B100 (100 hour) B0 (600 hour) B10 (600 hour) B20 (600 hour) B50 (600 hour) B100 (600 hour)

14000

Zi (ohms)

12000 10000 8000 6000 4000 2000 0 0

5000

10000

15000

20000

25000

30000

Zr (ohms)

FIGURE 17.7

Nyquist impedance plots of mild steel metal at different immersion times in biodiesel and its blends.

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17.12 THE ECONOMIC IMPACT OF METAL CORROSION ON USE BIODIESEL FOR THE TRANSPORT SECTOR

TABLE 17.10

Electrical parameters of different metals immersed in biodiesel and its blends extracted from the electrochemical impedance results. Rp (Ohm sq.cm)

Metals

Cdl (F/sq.cm)

Ru (Ohm sq.cm)

100 h

600 h

100 h

600 h

100 h

22.78

22.93

1.04  105

4.3  106

4

5

Impedance Log(Z/Ohm)

600 h

100 h

600 h

1.481

3.202

2.922

4.884

1.395

2.886

2.907

4.702

6.057

1.450

2.833

B0 Aluminum Mild steel

6.4  10

23.57

20.61

1.18  10

20.12

19.67

1.36  105

1.68  105

4

5

8.202

43.48 þ4

þ4

1.15  10

2.7  10

6.957

7.366

B10 Aluminum Mild steel

þ4

22.25

20.14

1.11  10

9.95  10

1.09 10

22.07

17.58

1.19  105

1.69  105

8.058

1.52  10

þ4

B20 Aluminum Mild steel

4

24.55

20.44

1.04  10

25.46

17.61

1.66  105

þ4

0.00007

1.24  10

21,500

2.962

4.864

7.29  106

1.66  105

17.13

1.463

2.962

B50 Aluminum Mild steel

5

22.86

18.86

8.79  10

30.64

18.44

2.06  105

5

5

6.0  10

8.79  10

21,110

3.0097

4.868

5.77  106

14.53

13.26

1.609

2.948

17,320

3.096

4.835

B100 Aluminum Mild steel

23.81

21.42

6.73  10

5

0.00006

oxidation. However, their order cannot be decided because of the closeness between B10 and B20 regarding concentration. Nevertheless, B100 always induced less corrosion and has a broader curve in Nyquist plot generated for 100 h corrosion test. In the case of 600 h corrosion test, the oxidative corrosion effects of biodiesel completely dominated the corrosion effects of commercially available diesel. As we have discussed earlier, long-term storage of biodiesel can lead to oxidation thus forming primary and secondary oxidation products which induce corrosion in various metal parts. The trend is completely opposed as to the previous trend where pure biodiesel was said to produce less corrosion. In this case, B0 was found to produce less corrosion compared to all the other blends. As already discussed, corrosion caused by sulfur atoms present in commercial diesel is mild compared to the corrosion caused by the secondary products of biodiesel oxidation reactions. Once the secondary products are formed, the corrosion effects of biodiesel start increasing, and the curve gets flattened as time goes on. That is the reason why B100 curve changes from a wide curve in 100 h corrosion test to a flat and small curve in 600 h corrosion test. Even in this test, B50 was found to be the second best after B0. B50 performs better than other biodiesel-diesel blends and that holds good for this observation too. As far as B10 and B20 are concerned, they will always produce more corrosion

þ4

1.58  10

compared to B0 because of the presence of biodiesel. In B10 and B20, even this small concentration of biodiesel plays a significant role in producing more corrosion compared to B0 because of the severe oxidation that occurs on long-term storage. Also, B10 and B20 cause more corrosion compared to B100 because of the additional corrosion inducing effects of the high percentage of commercial diesel. However, the trend is somewhat unpredictable and random because of the closeness of B10 and B20 regarding concentration. Also, the trend depends on the metal that is being used. Since the corrosion inducing abilities of B10 and B20 are very high compared to the other three blends, it is of less interest to study their trends. Hence B50 can be used as a proper fuel which imparts minimal corrosion to various engine components that balance perfectly between diesel’s sulfur corrosion and biodiesel’s oxidative corrosion. The electrical parameters of aluminum and mild steel metal extracted from EIS are presented in Table 17.10.

17.12 THE ECONOMIC IMPACT OF METAL CORROSION ON USE BIODIESEL FOR THE TRANSPORT SECTOR The major difficulties associated with biodiesel are poor oxidation stability, material incompatibility,

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17. COMPARATIVE EVALUATION OF CORROSION BEHAVIOR OF AEGLE MARMELOS CORREA DIESEL, BIODIESEL

corrosive nature, high viscous nature, friction, wear instability, etc. Most of the tests were discussed for biodiesel to meet EN 41214 standard only, apart from these biodiesels must meet different standards for their commercialization. Hence, it can be concluded that massive investment is needed to use biodiesel in transport sector, unless the problems above mentioned are resolved. The improvement of tribocorrosion characteristics of biodiesel will bring several benefits which include reduced specific fuel consumption, reduced engine-out emissions, improved engine performance, an improved lifetime of the engine, and easy commercial use of biodiesel. On the whole, little improvement in tribocorrosion characteristics of biodiesel can contribute a lot to world fuel economy and environmental pollution.

The electrochemical impedance techniques were used to evaluate the corrosion phenomena of AMC biodiesel and its blends on aluminum and mild steel for 100 and 600 h. In this condition, aluminum was more corroded than mild steel. Therefore, mild steel is more resistant to biodiesel corrosion than aluminum. During the immersion of metals in biodiesel and its blends, B50 exhibits less corrosion inducing capability compared to all the other blends. B0 was found to produce more corrosion in the initial stages before it was overshadowed by the corrosion induced by rapid oxidation of biodiesel in all the other blends. B100 was found to produce less corrosion at the beginning; but as time progressed, it produced way more corrosion because of the oxidation products that were being produced. B10 and B20 were always found to produce more corrosion than B50 and B100 in both the metals. Hence B50 is found to perform auspiciously under all the situations.

AMC ASTM B0 B5 B10 B100 B20 B50 CH3CH2ONa CH3OH CH3ONa CI CO CO2 EIS

Aegle Marmelos Correa American Standard for Testing Material 100% Diesel Five% Biodiesel þ95% Diesel 10% Biodiesel þ90% Diesel 100% Biodiesel 20% Biodiesel þ80% Diesel 50% Biodiesel þ50% Diesel Sodium ethoxide Methanol Sodium methoxide Combustion Ignition Carbon monoxide Carbon dioxide Electrochemical Impedance Spectroscopy

European Standard Fatty Acid Methyl Ester Free Fatty Acid Fourier TransformeInfrared Spectroscopy Gas chromatography mass spectroscopy Sulfuric acid Hydrochloric acid Iodine Value Potassium hydroxide Sodium hydroxide Nuclear Magnetic Resonance Nitrogen oxides Parts per million Total Acid Number X-ray diffraction

Acknowledgments This work was supported by the Department of Science and TechnologyeYoung Scientist Scheme, New Delhi, India. [Project No. DST-YSS/2015/000429]; and the Director, National Institute of Technology, Tiruchirappalli, India for extending the facilities to carry out the research work.

17.13 CONCLUSIONS

NOMENCLATURE

EN FAME FFA FTIR GC-MS H2SO4 HCl IV KOH NaOH NMR NOx ppm TAN XRD

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IV. APPLICATIONS

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IV. APPLICATIONS