Microwave enhanced catalytic conversion of canola-based methyl ester

C H A P T E R

6 Microwave enhanced catalytic conversion of canola-based methyl ester: optimization and parametric study Awais Bokhari1,2, Lai Fatt Chuah3, Leow Zi Yan Michelle1, Saira Asif 4, Muhammad Shahbaz1, Majid Majeed Akbar5, Abrar Inayat6, Farrukh Jamil2, Salman Raza Naqvi7, Suzana Yusup1 1

Biomass Processing Lab, Centre for Biofuel and Biochemical Research (CBBR), Chemical Engineering Department, Institute of Self-Sustainable Living, Universiti Teknologi PETRONAS, Seri Iskandar, Perak, Malaysia; 2Chemical Engineering Department, COMSATS University Islamabad, Lahore Campus, Pakistan; 3Malaysia Marine Department Northern Region, Gelugor, Penang, Malaysia; 4Department of Botany, PMAS Arid Agriculture University, Rawalpindi, Pakistan; 5Institute of Chemical Engineering and Technology, University of the Punjab, Lahore, Pakistan; 6Department of Sustainable and Renewable Energy Engineering, University of Sharjah, United Arab Emirates; 7School of Chemical and Material Engineering, National University of Science and Technology (NUST), Islamabad, Pakistan

O U T L I N E 6.1 Introduction

154

6.2 Methodology 6.2.1 Preparation of catalyst 6.2.2 Characterization of catalyst 6.2.3 Experimental setup for microwave assisted transesterification

156 156 156 156

6.3 Results and discussions 157 6.3.1 Characterization of conventional CaO catalyst 157 6.3.1.1 FTIR analysis 157 6.3.1.2 Scanning electron microscope (SEM) analysis 158 6.3.2 Optimization study of biodiesel yield via microwave assisted method 158 6.3.2.1 Analysis of Variance (ANOVA) analysis of biodiesel yield via microwave assisted method 158

Advanced Biofuels https://doi.org/10.1016/B978-0-08-102791-2.00006-4

153

6.3.2.2 Predicted versus actual plot for canola oil transesterification 160

6.3.3 Perturbation plot for biodiesel yield via microwave assisted method

161

6.3.4 Three-dimensional (3-D) surface plots

161

6.3.4.1 Effect of alcohol-to-oil ratio and reaction time on biodiesel yield

161

6.3.4.2 Effect of alcohol-to-oil ratio and catalyst amount on biodiesel yield

161

6.3.4.3 Effect of alcohol-to-oil ratio and microwave frequency on biodiesel yield

161

6.3.4.4 Effect of reaction time and catalyst amount on biodiesel yield

162 6.3.4.5 Effect of reaction time and frequency of microwave on biodiesel yield 163

Copyright © 2019 Elsevier Ltd. All rights reserved.

154

6. MICROWAVE ENHANCED CATALYTIC CONVERSION OF CANOLA-BASED METHYL ESTER

6.3.4.6 Effect of catalyst amount and frequency of microwave on biodiesel yield 163

6.4 Conclusions

164

6.1 INTRODUCTION In the 21st century, the utilization and production of biodiesel as an alternative fuel is widely accepted by many [1]. In order to fulfill our energy requirements, biodiesel is produced [2]. However, the production of biodiesel is not a new concept [3]. It is dated back to1800s when the French government demonstrated the use of peanut oil as a fuel to replace diesel at the Paris Exhibition. In 1853, Duffy and Patrick made great strides when they improved the transesterification of vegetable oil, as they believed that farmers could benefit from producing their own fuel [4]. From the early 1970s till now, South Asia and South East Asia also developed the biodiesel production technologies to reduce agriculture and environmental issues. With the high credibility on the production of biodiesel, Malaysia then started research and development by utilizing their huge palm oil plantations. The current crude oil consumption of about 700,000 barrels per day and the limited oil reserves have positioned biodiesel as a future fuel for diesel engines in Malaysia [5]. One of the best substitutions for the conventional petro-based diesel fuel is the biodiesel, a renewable biofuel, consisting of esters of fatty acid produced by the catalytic reaction between triglyceride (TG) and alcohol. The byproduct of the catalytic reaction is glycerol. This renewable biofuel is said to have the ability to replace the fuels in diesel engine due to the great molecular similarities between them. Since vegetable oils and animal fats are found abundantly in Malaysia, this makes the biodiesel fuel to be readily obtainable. From the environmental viewpoint, biodiesel is proven to have distinct advantages over petrodiesel in the following ways [6]: • Clean burning fuel with a low emission. • Higher cetane number hence gives excellent lubricity. • The higher flash point makes it safer to handle, transport and store. • Nontoxic and high biodegradability. Generally, transesterification is a catalyzed chemical reaction. Conventionally, sodium hydroxide (NaOH) and potassium hydroxide (KOH) are used as a homogeneous catalyst in the transesterification reaction. Unfortunately, over the past few years, the homogeneous catalyst faced many drawbacks. One of the major drawbacks faced is the need to remove both the catalyst and

6.5 Future recommendations

165

Acknowledgments

165

References

165

the saponified product from the free fatty acid (FFA) after the transesterification reaction [7]. Besides, homogeneous catalyst shows intolerance to moisture and low FFA in the feedstock. Since homogeneous catalysts could not be reused, researchers came up with the conception of a heterogeneous catalyst. Calcium oxide (CaO), a heterogeneous catalyst, shows great potential in the transesterification reaction [8]. The catalyst can be reused, is noncorrosive and environmentally friendly. Since CaO has a tolerance for moisture and FFA, the use of lower quality waste or used oil is highly acceptable [9]. Furthermore, CaO is said to be one of the inexpensive catalysts as it can be easily obtained from waste shells such as chicken eggshells, seashells and crab shells. Recently, enzymatic catalyst has caught the attention of many researchers and it is found to have recorded success. Vegetable oil serves as shortening, for flavor, and can be used to heat or cook other foods besides serving nutritional purposes. Some people also utilized vegetable oil to meet their daily energy requirements by using them in lamps and to ignite a fire. Not only that, vegetable oil was extensively used during the first and second world wars to run army trucks and cars. Among the most commonly used oils are fish oil, corn oil and nut oil [10]. Vegetable oils and fats are most commonly known as TG [11]. The chemical structure of TG consists of a three-carbon backbone with a long hydrocarbon chain attached to each of the carbon. Along with this chain, oxygen atom and carbonyl carbon are attached to it. Oils derived from vegetables or fats mostly contain 18carbon long chain with 0 to 3 double bonds on chain [12]. The chain length and the double bond will be influencing the biodiesel methyl esters. The usage of the vegetable oils and fats as an alternative way of energy production exhibits many advantages. Most of the vegetable oils are produced domestically, thus reducing the fossil diesel import. Vegetable oil is biodegradable in nature, nontoxic and less hazardous to health than fossil diesel. Since vegetable oil has reasonable cetane number, this results in less knocking tendency in engines [13]. Furthermore, it is considered environmentally friendly as it has low sulfur content. In the recent years, due to some problems associated with different feedstock, such as durability of engine and contamination, most researchers have developed different paths to produce biodiesel such as via direct use or blending with fossil diesel, microemulsification and thermal cracking and ends with

II. PRODUCTION

6.1 INTRODUCTION

the most common technique used, namely transesterification [14]. Transesterification process is needed to lower the oil’s viscosity. Transesterification is a stepwise process and excess alcohol is used to drive the reaction forward. This reaction proceeds in the presence or absence of catalyst [15]. The transesterification reaction utilizes different types of alcohols in the presence or absence of a catalyst. Most researchers used short chain alcohols such as methanol, ethanol, propanol and butanol to carry out the transesterification reaction [15]. Among all the alcohols mentioned, ethanol is widely used, as it is renewable and more sustainable [16]. However, methanol is cheaper and readily available [17]. Transesterification process takes place in three steps. Some unwanted compounds such as monoglyceride (MG) and diglyceride (DG) will be produced from the reaction. Commonly, biodiesel is produced using alkaline catalysts such as NaOH, KOH and sodium methoxide (NaOCH3). Alkaline catalysts generally are very sensitive to the presence of water and FFA. Thus, the water content should be maintained below 0.05 wt% for a high ester yield [18]. Water is also known to hydrolyze TG to produce fatty acids and glycerol, thus inactivating the base catalyst and inhibiting any further reaction [19]. In order to convert fat and oil into biodiesel, methanol is most commonly used as an alcohol. Since homogeneous base catalyst process gives high reaction rate and low reaction times, this process is preferred industrially. Not only that base catalyst process has been shown to require a low alcohol to oil ratio and a low reaction temperature [20]. TG molecule reacts with three short chain alcohol molecules, releasing an ester molecule each time, whereby it converts to DG, then MG, and finally to glycerol. However, at room temperature, the TG and alcohol are considered immiscible. The reactants are considered essential if they are mixed [21]. The first reaction for conversion of TG to DG will be the rate-determining step, since the activation energy for the reaction is highest for TG following by MG [13]. Reaction time and temperature are known to affect reaction conversion. According to Noureddini and Zhu (1997), a high temperature is favorable as the reaction kinetics are constant, thus reducing the reaction time. They found out that in order for a complete conversion to take place, the temperature is being elevated from 40 to 60
C [22]. Furthermore, most researchers maintain a molar ratio of alcohol to oil of 6 to allow greater conversion and ester yield [23]. As mentioned in the previous process, alkaline catalysts are highly sensitive to FFA. Thus, many researchers have proposed the replacement of alkali with acid catalyst. Commonly, the most used catalysts include sulfuric acid (H2SO4), hydrochloric acid (HCl) and phosphoric acid (H3PO4). One of the major benefits of using acid catalyst is that they are capable of alkyl esterification of free fatty acids and

155

simultaneously transesterification of the TG. However, it was found that the acid catalyst process is much slower than the alkaline catalyst process [24]. For a process to complete, the acid catalyst requires up to 24 h. In order to achieve high alkyl ester yield, Freedmann et al. (1986) have recommended the use of a higher alcohol:oil molar ratio. Unfortunately, the high molar ratio increases the costs of alcohol recovery and product separation costs. Overall, homogeneous acid catalyst process is less favorable in the industry as it provides slower reaction rate, high molar ratios, and the corrosive nature of the acid catalyst. Since acid catalysts have the ability to handle oils high in FFA, a two-step process is used by combining acid and base catalysts [25]. However, this process still requires complicated and long product separation [26]. Not only that, pretreatment for water is also necessary in the two-step process. Besides, the corrosive nature of the acid catalyst also makes it industrially less favorable [27]. The large amount of acid catalyst content may burn TG which lead toward poor biodiesel yield. The process to improve biodiesel production has been ongoing for decades. Since homogeneous catalyst is costly as it requires for product purification, thus, heterogeneous catalyst for both acid and alkali have been investigated by many researchers [28]. Among the type of heterogeneous catalysts investigated by Georgogianni et al. (2009) are MgeAl hydrotalcite and potassium ions impregnated zirconium dioxide (ZrO2). They concluded that the yield of fatty acid methyl ester (FAME) was directly proportional to the concentration used. Researchers also studied the sulfonation of amorphous organic carbon in pursuit of inexpensive and renewable catalysts. Comparing the method using homogeneous catalyst, heterogeneous catalyst can easily be regenerated and reused. Hence, they are more economically viable [29]. However, the reaction time would be double and longer since they have rather low reaction rates. Up to now, many studies have been conducted on biodiesel production using heterogeneous catalyst specifically on alkaline earth metal oxides and zeolites [30]. As mentioned earlier, CaO in particular has been proven to possess good performance. The transesterification reaction of oil and methanol which is catalyzed by CaO shows a biodiesel yield higher than 90 wt% as reported by [31]. Malaysia is well known for its edible seafood sector and is also surrounded by many islands such as the Pangkor Island and Penang where seashells are available widely. This vast amount of shells available could be a promising resource of catalysts for biodiesel production. Biodiesel yield as high as 90wt% was being reported from the transesterification of palm olein oil with methanol catalyzed by CaO which was obtained from bone and eggshell [32]. Unfortunately, the reaction requires a longer reaction time in order to achieve satisfactory conversion of oil to biodiesel. Microwave radiation can

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6. MICROWAVE ENHANCED CATALYTIC CONVERSION OF CANOLA-BASED METHYL ESTER

speed up the reaction [33], lower the reaction time and increase the fatty acid alkyl ester yield [34]. Besides, canola oil is easily obtained in Malaysia. Unfortunately, the biodiesel production using canola oil and CaO catalyst using microwave radiation has not been studied well. Response Surface Methodology (RSM) is a powerful tool to be applied in microwave assisted study to find the effect and optimization of experimental parameters such as temperature, pressure, and particle size of feedstock on response variable such as biodiesel yield [35]. In this study, the effect of conventional CaO in the biodiesel production of canola oil and its operating conditions are investigated. The objectives of this research are outlined as follows: i. To conduct an optimization study on biodiesel production from canola oil and CaO catalyst assisted by microwaves at several parameter conditions such as temperature, amount of catalyst, microwave frequency and alcohol-to-oil ratio with RSM. ii. To compare between biodiesel production from canola oil and CaO catalyst via microwave assisted and supercritical condition methods. The microwave assisted biodiesel production from canola oil and CaO catalyst is carried out under several parameter conditions for optimization study. The parameters such as temperature, amount of catalyst, microwave frequency and alcohol-to-oil ratio are carried out with RSM. The production of biodiesel is characterized with Gas Chromatography-Flame Ionized Detector (GC-FID). The biodiesel obtained using microwave-assisted and supercritical condition methods are compared in order to find the quantity of biodiesel produced.

6.2 METHODOLOGY RSM was applied to study multiple experimental conditions with a few combinations of parameters to optimize the biodiesel yield. In this study, four independent variables, alcohol-to-oil ratio, reaction time (min), catalyst amount (wt%) and frequency of the microwave (W), were used. These variables were classified into axial, low, high level factor points and center points. Center point variable determines the accuracy of results obtained as experiment is carried out based on the standard deviation of the biodiesel yield calculated. The experimental runs were performed randomly. This is to reduce any unknown variability in the response. RSM is an efficient and effective way to study multiple experimental conditions with different parameters to optimize the process. Since a number of factors are involved in this research and they will affect one another, RSM technique is used to obtain optimal conditions. Some of the many advantages of using RSM is that it saves time for parameters test and smoothens the experimental progress [36].

6.2.1 Preparation of catalyst Before using the conventional CaO powder in transesterification, the powder was further calcined at 400
C for 4 h under static air in order to prepare a pure CaO-based activated catalyst [37]. The purpose of this heat treatment is to decompose any calcium carbonate into CaO, since CaO readily combined with air from the environment to form calcium carbonate.

6.2.2 Characterization of catalyst CaO catalyst was sent to Centralized Analytical Lab for characterization with Fourier Transform Infrared Spectroscopy (FTIR) to identify the organic compounds present, Brunauer-Emmett-Teller (BET) method to identify the surface area, volume and average pore diameter.

6.2.3 Experimental setup for microwave assisted transesterification A microwave-assisted biodiesel production setup is depicted in Fig. 6.1. All the experiments were performed by using a 250 mL three-neck round bottom flask with a condenser attached to avoid alcohol losses, which was placed in a microwave set up. A thermocouple was put inside one of the neck of the round bottom flask in order to monitor and control the reaction temperature. A separating funnel was required in order to separate the phases of reaction mixture. A rotary vacuum evaporator assembly was used for the evaporation of retained methanol and water in the product. Feedstock: canola oil was poured into the threeneck round bottom flask and heated until the desired temperature according to the experiment designed by RSM. As the feedstock oil reached the desired temperature, mixture of alcohol (methanol) and conventional CaO calcined catalyst was poured into the flask. The reaction continues for specific reaction time following the RSM. The magnetic stirrer speed was adjusted based on RSM as well. After the completion of the reaction, the mixture was separated under gravity with the help of a separating funnel. The bottom layer has desired product and top layer contained excess methanol, glycerol and also catalyst. The desired product was washed with the deionized warm water until the pH is neutral. The remaining amount of water and methanol in the desired product evaporated under vacuum in the rotary evaporator. After reaction, separation, and washing, the desired product acid value was calculated. The same experimental procedure was repeated for each run. The 30 samples were characterized qualitatively by GC-FID. The yield of biodiesel oil will be weighed and measured. Eq.

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157

6.3 RESULTS AND DISCUSSIONS

Cooling water outlet

Condenser

Cooling water inlet

Microwave oven Three neck flask Magnetic stirrer

FIGURE 6.1 Microwave experimental setup.

(6.1) shows the calculation method for production of biodiesel yield. Biodiesel Oil Yieldðwt%Þ ¼

(6.1)

Total mass of biodiesel oilðgÞ Mass of canola oilðgÞ

6.3 RESULTS AND DISCUSSIONS 6.3.1 Characterization of conventional CaO catalyst 6.3.1.1 FTIR analysis FTIR analysis was performed to analyze the type of organic matters based on their chemical bonding

characteristics and inorganic matters like oxides. Fig. 6.2 shows the FTIR bands of CaO that were calcined for 4 h at 400
C. Based on the peak 3643 cm1, the group is identified as OeH stretching and H-bonded group with a low concentration of calcium hydroxide (Ca(OH)2) in the sample. The hydroxide is the remaining component during the carbonation process. The bands at 1468.43 cm1 and 873.94 cm1 correspond to two different elongation modes of CeO bonds while the bands at 1116.06 cm1 and 574.78 cm1 are the harmonic vibration of these elongation modes (Table 6.1). This agrees well with the results. The minor bands at 3434.49 cm1 and 1637.87 cm1 correspond to OeH stretching with H bonded and C]C stretching, respectively. Comparing with other CaO catalytic samples calcined at different temperatures, the findings in this study are comparable to those previously reported. At

52.0 50 48 46 44 42 40

873.94 1116.06 1637.87 3434.49

574.78

1468.43

38 36 34 32 %T 30 28 26 24 22 20 18 16 14 12 10 8.6 4000.0

3643.15

3000

2000

1500

Wave number (cm–1)

FIGURE 6.2 Infrared spectroscopy of conventional CaO. II. PRODUCTION

1000

450.0

158

6. MICROWAVE ENHANCED CATALYTIC CONVERSION OF CANOLA-BASED METHYL ESTER

TABLE 6.1

Functional groups and compounds identified for conventional CaO.

Wavenumber (cmL1)

Functional groups

Type of compounds

3643.15

OeH stretching

Alcohol

3434.49

OeH stretching, H-bonded

Alcohol

1468.43

C]C stretching

Aromatic

1116.06

CeO stretching

Alcohol, esters and carboxylic acids

574.78e873.94

CeH out-of-plane bending in aromatic ring

Aromatic compounds

FIGURE 6.3

Different sizes of catalyst.

FIGURE 6.4

700
C, vibration bands in the region 1270e1150 cm1 are assigned to OH groups directly bonded to the phenolic aromatic ring [38]. 6.3.1.2 Scanning electron microscope (SEM) analysis The calcined CaO catalyst is observed to comprise of the irregular shape of particles as seen from the SEM image in Fig. 6.3. Various sizes and shapes of the particles can be seen. Comparing with the SEM images of the previous study [39], SEM images of the CaO catalyst shows that particle sizes decrease while pore size increases after activation. A cakelike sticky structure as shown in Fig. 6.4 was observed to reorganize themselves in aggregates after the reaction. This finding is comparable with the findings reported by other researcher works [39]. These changes led to a deactivation of the catalyst by blocking the contact between the active catalytic sites and the reactants.

6.3.2 Optimization study of biodiesel yield via microwave assisted method RSM was utilized to assess the parametric effect of four independent variables which are alcohol-to-oil

Aggregation of calcined CaO catalyst.

ratio, reaction time (min), microwave frequency (W), and amount of catalyst used (wt%). The biodiesel yield (wt%) is considered as an output response for a given set of variables. All the experiments were performed according to the designated runs set by Design Expert 8.0 software. At each designed run, biodiesel yield (wt%) was calculated as the response variable. Table 6.2 shows the detailed experimental designed run along with its output variable for canola oil. From the table, the minimum biodiesel yield was obtained at alcohol-to-oil ratio of 8:5, reaction time of 45 min, 3.5 wt% of catalyst loading, and microwave frequency of 65 W. The maximum biodiesel yield was obtained at alcohol-tooil ratio of 5, reaction time of 30 min, 2 wt% of catalyst loading and microwave frequency of 80 W. 6.3.2.1 Analysis of Variance (ANOVA) analysis of biodiesel yield via microwave assisted method ANOVA was employed statistically to analyze and confirm the significant level of each parameter toward output response which is the biodiesel yield. Table 6.3 shows the ANOVA results produced by statistical analysis of biodiesel yield as the output response variable.

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6.3 RESULTS AND DISCUSSIONS

TABLE 6.2 Detailed experimental run with output variable. RUN

Alcohol-to-oil ratio

Reaction time (min)

Catalyst amount (wt%)

Frequency of the microwave (W)

Biodiesel yield (wt%)

1

8.50

45.00

3.50

65.00

39.16

2

8.50

45.00

3.50

65.00

45.75

3

8.50

45.00

3.50

65.00

46.33

4

12.00

60.00

2.00

80.00

49.67

5

8.50

45.00

3.50

6.50

40.22

6

8.50

45.00

6.50

65.00

50.34

7

8.50

45.00

3.50

65.00

42.22

8

12.00

60.00

5.00

50.00

47.12

9

8.50

45.00

0.50

65.00

71.63

10

12.00

30.00

2.00

80.00

69.87

11

12.00

60.00

5.00

50.00

66.15

12

8.50

15.00

3.50

65.00

66.30

13

5.00

60.00

2.00

50.00

51.52

14

8.50

45.00

3.50

95.00

62.90

15

5.00

30.00

5.00

50.00

50.09

16

5.00

60.00

5.00

50.00

60.26

17

1.50

45.00

3.50

65.00

70.15

18

12.00

30.00

2.00

50.00

55.23

19

12.00

30.00

5.00

80.00

52.76

20

5.00

60.00

2.00

80.00

40.00

21

8.50

45.00

3.50

35.00

50.66

22

12.00

60.00

2.00

50.00

55.35

23

5.00

30.00

2.00

50.00

72.26

24

5.00

30.00

2.00

80.00

77.00

25

5.00

60.00

5.00

80.00

47.39

26

5.00

30.00

5.00

80.00

62.54

27

12.00

60.00

5.00

80.00

59.15

28

12.00

30.00

5.00

50.00

42.60

29

8.50

75.00

3.50

65.00

43.51

30

8.50

45.00

3.50

65.00

45.00

The percentage error in the model can be determined from the model P-value based on the percentage of error in the model along with its individual and combined effects of the input variables [40]. Table 6.3 shows the ANOVA results of the canola oil transesterification. The probability value is an important parameter as it must be less than 0.05 for the particular variable or model to be significant on the response variable. Since the model P-value obtained 0.0001 is less than 0.05, this indicated that the model is significant

for canola oil designed variables with respect to the response. The reliability of the fitted model with the output response can be determined by the F-value. The highest F-value for reaction time indicates the highest influence on the biodiesel yield. The output response which is the biodiesel yield was fitted to the input process variables through the regression analysis (R2). The coefficient of determination R2 is a measurement of the degree of fitness for the data whereby a larger value approaching 1.00 indicated the data fitted

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6. MICROWAVE ENHANCED CATALYTIC CONVERSION OF CANOLA-BASED METHYL ESTER

TABLE 6.3

ANOVA analysis of the transesterification reaction.

Source

Sum of squares

df

Mean square

F value

Model

3204.71

14

228.91

9.93

<.0001

Significant

A

132.26

1

132.26

5.74

.0301

Significant

B

403.77

1

403.77

17.52

.0008

Significant

C

219.25

1

219.25

9.52

.0076

Significant

D

36.02

1

36.02

1.56

.2304

Insignificant

AB

329.24

1

329.24

14.29

.0018

Significant

AC

7.62

1

7.62

0.33

.5738

Insignificant

AD

23.33

1

23.33

1.01

.3303

Insignificant

BC

660.23

1

660.23

28.65

<.0001

Significant

BD

390.66

1

390.66

16.95

.0009

Significant

CD

0.02

1

0.02

0.00

.9771

Insignificant

A2

383.87

1

383.87

16.656

.0010

Significant

B2

216.35

1

216.35

9.39

.0079

Significant

C2

513.91

1

513.91

22.30

.0003

Significant

D2

294.60

1

294.60

12.79

.0028

Significant

model equation for the canola oil which represents a polynomial model is given below: Biodiesel yield ðwt%Þ

P-Value

¼ 43:11333333  2:3475A  4:10166667B  3:0225C þ 1:225D þ 4:53625AB þ 0:69AC þ 1:2075AD þ 6:42375BC  4:94125BD þ 0:035CD þ 3:741041667A2 þ 2:808541667B2 þ 4:328541667C2 þ 3:277291667D2 (6.2) where A ¼ alcohol-to-oil ratio, B ¼ reaction time, C ¼ catalyst amount, D ¼ microwave frequency

6.3.2.2 Predicted versus actual plot for canola oil transesterification

R2 ¼ 0.9026, adjusted R2 ¼ 0.8118, adequate precision ¼ 13.255

the model well [41]. The R2 value was measured at 0.9026. This shows that the regression model represents the experimental data well. Therefore, this model is adequate to represent the effect of experimental parameters on biodiesel yield in this study. Response surface equation was produced in terms of actual and coded term for the output response model. The regression

Generated models with respective coefficients were used to predict the output response theoretically by using the ANOVA. The obtained results were compared with the experimental data. Fig. 6.5 shows the graphical plot of the predicted values of biodiesel yield versus actual experimental values based on the experimental design set by RSM. From Fig. 6.5, it can be clearly seen that the experimental values are well fitted with the predicted values since all the points are close to the center linear line.

Predicted vs. actual 90.00

Predicted (wt %)

80.00 70.00 60.00 50.00 40.00 30.00 30.00

40.00

50.00

60.00

Actual (wt %)

FIGURE 6.5 Actual versus predicted plot for canola oil.

II. PRODUCTION

70.00

80.00

161

6.3 RESULTS AND DISCUSSIONS

6.3.3 Perturbation plot for biodiesel yield via microwave assisted method Perturbation provides the outline variables views on the output response. This perturbation plot takes the higher influencing variable terms for the approximation which involves both the curvature and the risk under consideration. Based on Fig. 6.6, reaction time (B) which has the largest F-value produces the highest effect on the response followed by catalyst amount (C), alcohol-to-oil ratio (A) and frequency of microwave (D). The effect is deduced based on the steepness of each slope shown in the graph in Fig. 6.6.

6.3.4 Three-dimensional (3-D) surface plots 3-D plots are often used to describe the independent and combine effect of the process variables on the output response. These graphs are also known as surface plots as the process variable and its combined effect are plotted as a surface response. Table 6.3 represents the combined effects of the process response from which some effects are significant and some are insignificant. The 3-D surface plots of process parameters for canola oil esterification assisted by microwave are discussed in this section. The independent and combined effects of four influencing variables on biodiesel yield are discussed. 6.3.4.1 Effect of alcohol-to-oil ratio and reaction time on biodiesel yield Fig. 6.7 shows the combined effect of alcohol-to-oil ratio and reaction time on biodiesel yield. The reaction time is shown to be the most important factor that affects the response with respect to alcohol-to-oil ratio, the

frequency of microwave and catalyst amount. In this plot, it can be seen that the biodiesel yield reduces as the alcohol-to-oil ratio increases. The biodiesel yield reduces as well with the increase of the reaction time. The increase in the reaction time results in less oil yield as the process has already reached it maximum resident time for the reaction to happen. In this plot, the lowest biodiesel yield can be obtained at the highest reaction time which is 60 min and the highest alcohol-to-oil ratio of 12:1. The similar effects have been studied by Gupta et al. [42] where calcium diglyceroxide catalyzed biodiesel production from waste cooking oil in the presence of microwaves. 6.3.4.2 Effect of alcohol-to-oil ratio and catalyst amount on biodiesel yield Fig. 6.8 shows the 3-D effect of alcohol-to-oil ratio and catalyst amount on biodiesel yield. The figure shows that biodiesel yield decreases by increasing amount of alcohol. The biodiesel yield reduces by increasing the amount of alcohol from 5 to 12 when the catalyst amount is constant. The maximum reduction on biodiesel yield was achieved at a ratio of 12:1. The biodiesel yield decreases when the number of catalyst increases. The lowest biodiesel yield was identified as the highest catalyst amount which is 5 wt%. From this plot, it can be concluded that the lowest biodiesel yield was obtained at 12:1 alcohol-to-oil ratio and 5 wt% of catalyst via the microwave assisted method. 6.3.4.3 Effect of alcohol-to-oil ratio and microwave frequency on biodiesel yield The frequency of the microwave is the least process variable that contributes to the reduction of biodiesel Perturbation

65

Biodiesel yield (wt %)

60

55

50

B C A D

45

D

CA B

45 –1.000

–0.500

0.000

0.500

Deviation from reference point (coded units)

FIGURE 6.6 Perturbation plot.

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1.000

162

6. MICROWAVE ENHANCED CATALYTIC CONVERSION OF CANOLA-BASED METHYL ESTER

Biodiesel yield (wt %)

65 60 55 50 45 40 60.00 54.00 48.00

12.00 11.00 10.00

42.00

B: reaction time (min)

9.00 8.00

36.00

7.00

A: alcohol to oil ratio

6.00 30.00 5.00

Biodiesel yield (wt %)

FIGURE 6.7 Effect of alcohol-to-oil ratio and reaction time on biodiesel yield.

65 60 55 50 45 40 5.00 4.40

12.00 11.00

3.80 10.00

9.00

3.20 8.00

C: catalyst amount (wt %) 2.60

7.00 6.00 2.00 5.00

A: alcohol to oil ratio

FIGURE 6.8 Effect of alcohol-to-oil ratio and catalyst amount on biodiesel yield.

yield. In Fig. 6.9, the biodiesel yield decreases significantly by increasing the frequency of the microwave. From the plot also, it can be seen that higher alcoholto-oil ratio also affects the reduction of the biodiesel yield. However, the reduction seen is not as significant as compared to the microwave frequency. This is due to the longitudinal vibrations of the microwave probe that are transmitted into the liquid as microwave waves consist of alternate expansions and compressions. Thus, higher microwave frequency will increase the mass transfer efficiency between alcohol and oil. The obtained results are verified by the findings of Milano

et al. [43] for the optimization of biodiesel production by microwave irradiation assisted transesterification for waste cooking oil and Calophyllum inophyllum oil via RSM. 6.3.4.4 Effect of reaction time and catalyst amount on biodiesel yield Fig. 6.10 show that biodiesel yield decreases when the amount of catalyst is increased. The decrease of biodiesel yield was significant when the amount of catalyst increased from 2 to 3.8 wt%. From 4.4 to 5 wt%, there is still decrement in the biodiesel yield. However, it is not

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163

6.3 RESULTS AND DISCUSSIONS

Biodiesel yield (wt %)

65 60 55 50 45 40 80.00 74.00 68.00 62.00 10.00

56.00 D: frequency of microwave (watt) 50.00 5.00

6.00

11.00

12.00

9.00 8.00 A: alcohol to oil ratio

7.00

Biodiesel yield (wt %)

FIGURE 6.9 Effect of alcohol-to-oil ratio and frequency of microwave on biodiesel yield.

65 60 55 50 45 40 5.00 4.40 3.80 60.00 3.20

54.00 48.00

2.60

42.00

C: catalyst amount (wt %)

36.00

B: reaction time (min)

2.00 30.00

FIGURE 6.10 Effect of reaction time and catalyst amount on biodiesel yield.

so significant. Based on this plot, it is better to use a higher amount of catalyst. The biodiesel yield also decreases as the reaction time increases. About 30 to 42 min of reaction time reduces the biodiesel yield significantly. After 48 min, the reduction of biodiesel yield is no longer significant. 6.3.4.5 Effect of reaction time and frequency of microwave on biodiesel yield The effect of reaction time and frequency of microwave on biodiesel yield is shown in Fig. 6.11. The frequency of microwave has a significant impact on the reduction of biodiesel yield. From 68 to 80 W, the

biodiesel yield shows a significant increase. For the frequency of microwave from 50 to 62 W there is almost no significant change on the biodiesel yield though it is actually increasing. When the reaction time between the canola oil and the methanol increases, the biodiesel yield increases proportionally as well. High frequency of microwave and long reaction time result in higher biodiesel yield. 6.3.4.6 Effect of catalyst amount and frequency of microwave on biodiesel yield The effect of catalyst amount and frequency of microwave on biodiesel yield is shown in Fig. 6.12. The

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6. MICROWAVE ENHANCED CATALYTIC CONVERSION OF CANOLA-BASED METHYL ESTER

Biodiesel yield (wt %)

164

65 60 55 50 45 40 80.00 74.00 68.00 60.00

62.00

54.00 48.00

56.00

42.00

D: frequency of microwave (watt)

36.00

B: reaction time (min)

50.00 30.00

Biodiesel yield (wt %)

FIGURE 6.11 Effect of reaction time and frequency of microwave on biodiesel yield.

65 60 55 50 45 40 80.00 74.00 68.00 5.00

62.00

4.40 3.80

56.00

3.20

D: frequency of microwave (watt)

2.60

C: catalyst amount (wt %)

50.00 2.00

FIGURE 6.12 Effect of catalyst amount and frequency of microwave on biodiesel yield.

frequency of microwave reduces the biodiesel yield significantly. As the frequency increases from 68 to 80 W, the biodiesel yield increases by more than 0.5 wt %. For the catalyst amount, when the catalyst used increases, the biodiesel yield decreases. However, it does not show much significant change. High frequency of microwave and low catalyst amount result in low biodiesel yield.

6.4 CONCLUSIONS In this study, Design Expert 8.0 software was used to study the parametric influence on the process through systematic experimental approach. The microwave reactor successfully converted the canola to respective methyl ester in shorter reaction time. The transesterification reaction optimized conditions have been obtained

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REFERENCES

by varying several parameters such as alcohol-to-oil ratio, reaction time (min), amount of catalyst (wt%), and microwave frequency (W). The optimized biodiesel yield using the microwave-assisted method was found to be 77 wt% at the operating parameters of alcohol-tooil ratio (5:1), reaction time of 30 min, 2% weight catalyst and 80 W of microwave frequency. From this, it can conclude that canola oil has a strong potential to become a feedstock to produce biodiesel. The regression model which is the quadratic model obtained from RSM is significant to optimize the response variable which is the biodiesel oil yield. From the results, reaction time has the most crucial effect on the biodiesel yield with Pvalue less than 0.05. The microwave is a very desirable tool for the transesterification process, as it lowers the cost of processing, speeds up the transesterification process, does not require an elevated temperature and requires very less amount of catalyst.

6.5 FUTURE RECOMMENDATIONS In canola oil transesterification, future research work is very important to investigate the effect of other intensification technologies such as ultrasonics and cavitation. This is important for optimization of biodiesel yield. Different types of alcohol may be considered to explore their effect on the acidity of the product. Also, a different type of homogeneous catalyst, acid and base, with the same operating conditions can be experimented to see the optimum catalyst to give best results in both reactions. Furthermore, the kinetics of this transesterification between canola oil and conventional calcined CaO catalyst has not been studied well. This will help expand the work and make a better prediction for any change in the system.

Acknowledgments The authors would like to thank MyRA grant (0153AB-K19), biomass processing laboratory, Universiti Teknologi PETRONAS and Malaysia Marine Department for the support.

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