Catalytic applications of calcium rich waste materials for biodiesel: Current state and perspectives

Energy Conversion and Management 127 (2016) 273–283

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Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman

Review

Catalytic applications of calcium rich waste materials for biodiesel: Current state and perspectives Rui Shan a,b,d,1, Che Zhao a,b,1, Pengmei Lv a,b,c, Haoran Yuan a,b,⇑, Jingang Yao d a

Guangzhou Institute of Energy Conversion, Key Laboratory of Renewable Energy, Chinese Academy of Sciences, Guangzhou 510640, China Key Laboratory of New and Renewable Energy Research and Development, Guangzhou 510640, China c Key Laboratory of Natural Gas Hydrate, Chinese Academy of Sciences, Guangzhou 510640, China d School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China b

a r t i c l e

i n f o

Article history: Received 24 June 2016 Received in revised form 19 August 2016 Accepted 6 September 2016

Keywords: Biodiesel Ca-based waste materials Solid catalyst Transesterification

a b s t r a c t The synthesis of heterogeneous catalysts from waste materials has become increasingly popular over the past two decades. Among them, Ca-based catalysts have widely been tested in the transesterification reaction because of their relatively high catalytic activity and the large amount of feedstock (calcium rich waste materials) available. Those Ca-based catalysts can be simply prepared via the high temperature calcination and using these waste materials to generate the catalyst in addition to the target product makes the system more cost effective and environmentally friendly. This review presents general information related to the recent progress in the development of various Ca-based catalysts derived from waste materials for biodiesel production. The materials described include eggshells, mollusk shells, bones, large-scale industrial wastes and so on. Meanwhile, based on this collection of data and information, the catalytic activity mechanism, future challenges and prospects of renewable resources derived catalysts are also discussed. Ó 2016 Elsevier Ltd. All rights reserved.

Contents 1. 2.

3. 4. 5. 6.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biological sources derived Ca-catalysts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Shells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.1. Mollusk shells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.2. Eggshells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.3. The comparison of catalytic activity of CaO from different precursors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Bones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1. The direct use of calcined bones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2. The use of modified bones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Large-scale industrial wastes derived Ca-based catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The reaction mechanism of calcium rich waste materials derived catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Challenge and future trends of calcium rich waste material derived catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

⇑ Corresponding author at: Guangzhou Institute of Energy Conversion, Key Laboratory of Renewable Energy, Chinese Academy of Sciences, Guangzhou 510640, China. E-mail address: [email protected] (H. Yuan). 1 Both authors contributed equally to this work. http://dx.doi.org/10.1016/j.enconman.2016.09.018 0196-8904/Ó 2016 Elsevier Ltd. All rights reserved.

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1. Introduction Recently, due to the excessive consumption of fossil fuel and the increasing urgent concern about greenhouse gas emissions, exploiting alternative energy sources has drawn much attention [1]. Biodiesel, as a renewable, sustainable and non-toxic biofuel, is regarded as a main alternative for fossil fuel in many countries [2,3]. Commonly, biodiesel can be produced via the transesterification of vegetable oils, animal fats, waste greases or algal oil with C1-C2 alcohols in the presence of homogeneous basic or acidic catalysts [4,5]. Homogeneous base catalysts (e.g. KOH and NaOH) have been frequently used for the transesterification reaction due to their rather high catalytic activity under mild conditions compared to homogeneous acid catalysts (e.g. H2SO4 and HCl) [6]. Unfortunately, these homogeneous basic or acidic catalysts are corrosive for the reactors, and their separation is very tedious. Furthermore, in order to meet the stipulated quality, a large amount of water is used in the wash and purification steps which results in the rather high production cost [7]. As a result of these issues, heterogeneous catalysts are exploited and adopted to catalytically produce biodiesel, which commonly possess the following outstanding advantages e.g., ease of separation, lack of corrosion, and less environmental damage [8]. In general, the heterogeneous catalysts can be categorized into two types: acids and bases. Since the acid catalyzed transesterification processes usually required long reaction time and achieved at high reaction temperature, base catalyzed transesterification process can be considered as the most attractive process to date [9]. Consequently, diverse types of solid base catalysts have been explored, such as alkali or alkaline earth oxides, supported alkali metals, calcined hydrotalcite, and anion exchange resins [3,10–12]. Among all these heterogeneous bases, calcium oxide (CaO) catalysts have drawn great interest because of the benefits associated with mild reaction condition, non-toxicity, high basicity, relatively economical, less impact on environment, excellent yield of biodiesel produced and its lower solubility in biodiesel [13]. Also, many researchers proved that the CaO catalyst was more active in transesterification reaction than anion-exchange resin and the MgAAl mixed oxide, and although, potassium-loaded catalysts resulted in the faster reaction rate, its reusability was very inferior to the CaO catalyst [14,15]. In order to reduce the catalyst synthesis cost and metal losses during reaction, many researchers have drawn a great intention in the design and development of catalytic materials derived from earth abundant and low cost renewable resources to improve the overall sustainability of catalytic processes [16,17]. Calcium rich waste materials as a kind of low cost renewable resources are widely available in the world [16,18]. The use of such wastes for catalyst preparation has a significant potential for biodiesel synthesis: (1) the Ca-based catalysts have moderate catalytic activity in the transesterification reaction; (2) the use of those catalysts can partly prevent the environmental impact and disposal problem; (3) the catalysts can be prepared at low cost, which can reduce the high synthesis cost of biodiesel and make it an increased competitiveness; (4) the utilization of those catalysts would produce a higher value applications for the recycled wastes. Particularly, in recent years, the use of Ca-based heterogeneous catalyst from a variety of calcium rich waste materials for biodiesel synthesis has been the subject of enormous investigations [15]. These calcium rich waste materials included eggshells, mollusk shells, animal bones, industry wastes and so on based on their origin. In the light of these comments, the purpose of the present review is aimed to provide a series of Ca-based catalysts being classified according to their applications for biodiesel production

including the direct use of those waste materials and the use via a variety modified methods. Finally, the catalytic activity mechanism, the future challenges and prospects of calcium rich waste materials derived catalysts are also discussed. 2. Biological sources derived Ca-catalysts 2.1. Shells Waste shells (such as chicken eggshell, crab, mussel, and clamshell) are one of the most common calcium rich waste materials abundant in nature. Every year, especially in over populated countries, a large amount of waste shells would generate a waste disposal problem [15,43]. Since the major component of those shells is CaCO3, CaO-based catalysts were easily obtained for biodiesel synthesis under the high temperature (typically 600–1000 °C) [44]. 2.1.1. Mollusk shells CaO-based catalysts derived from calcined mollusk (such as snail, crab, mussel, clamshell, abalone, and shrimp) shells have been proven to be successfully used for biodiesel synthesis. The synthesis of CaO-based catalysts from mollusk shells was listed in Table 1. 2.1.1.1. The direct use of calcined mollusk shells. The snail shell can be proposed as a low-cost material to acquired CaO catalyst for biodiesel production. Birla et al. [19] have investigated calcined snail shell as CaO catalyst for the biodiesel production. After calcined snail shell at 900 °C, the CaO obtained has exhibited good catalytic activity in the transesterification of waste frying oil. The biodiesel yield obtained under optimal conditions 87.28%. The sea snail Cerithidea obtusa is a kind of marine gastropod mollusk in the family Potamididae and commonly lived in the muddy coastal areas. Lee et al. [34] utilized the CaO catalysts derived from this sea snail shell for biodiesel synthesis. In their study, XRD and XRF results revealed that after calcined at 800 °C, the content of CaO in the obtuse horn shells was more than 98%. The one variable at a time method was used to investigate the catalytic activities of obtained in the transesterification process. The biodiesel conversion was 86.75% at 6 h, catalyst loading of 5 wt.% and methanolto-oil molar ratio of 12:1. Oyster shell is a waste material from shellfish farms. The large consumption of oyster every year resulted in the large amount of oyster shell waste. Nakatani et al. [22] have utilized waste oyster shell as raw material to synthesize catalyst. After calcined powdered oyster shell above 700 °C, the CaCO3 of oyster shell transformed to CaO. Under the optimum conditions, the biodiesel yield was 73.8% with high biodiesel purity of 98.4 wt.%. The Turbonilla striatula is widely lived in swamp areas, rivers and agricultural fields. Due to its large consumption in food industry, the generation of this kind of waste shell is abundant. The use of this waste shell as CaO catalyst for biodiesel production was reported by Boro et al. [26]. After calcined at 800 °C, the shell was indeed all converted into CaO. Biodiesel yield of 93.3% was obtained at 65 °C, with catalyst amount of 3.0 wt.% and methanol-to-oil molar ratio of 9:1. The result also illustrated that 700–900 °C was the suitable calcination temperature for catalyst synthesis. Crab shell is another source of CaCO3 in the nature. Boey et al. [24] confirmed that the calcined crab shells could be successfully utilized for biodiesel synthesis. In their other study [25], a CaO catalyst derived from the cockle (Anadara granosa) shell (another large-produced food waste in the South East Asian region) was explored. The maximum biodiesel yield of 97.48 ± 0.24 was obtained using this calcined shell. Sirisomboonchai et al. [35] used calcined scallop shell in transesterification of the inedible oil. The authors found that although only 86% biodiesel yield was achieved,

Table 1 Summary of various types of mollusk shells derived catalysts for biodiesel production. Mollusk shell

Oil

Catalyst

Preparation condition of catalyst

Reaction condition

Ya (or C) (%)

Ref.

MeOH:Oil (mol:mol)

Catalyst loading (wt.%)

Time (min)

Temperature (°C)

Others

Y = 87.28 Y = 98.5

[19] [20]

Y = 98.5

[21]

WFO Palm oil

CaO CaO

Calcined at 900 °C for 3.5 h Calcined at 800 °C for 3 h

6.03 12

2.0 5

420 90

60 65

Snail shell

Soybean oil

KBr/CaO and kaolin

6

2

120

65

Oyster shell Oyster shell

Soybean oil Soybean oil

CaO KI/CaO

/ 10

25 1 (mol/g)

300 240

65 50

/ Stirring speed: 400 rpm

Y = 73.8 C = 79.5

[22] [23]

Mud crab (Scylla serrata) Cockle (Anadara granosa)

Palm olein Palm olein

CaO CaO

Snail shell and kaolin (mass ratio of 4:1) calcined at 800 °C for 3.5 h, 40 wt.% KBr loaded, and activation at 500 °C for 3 h Calcined at 1000 °C for 3 h Shell calcined at 1000 °C for 4 h, impregnated with KI of 40 wt.%, and calcined at 500 °C for 3 h Calcined at 900 °C for 2 h Calcined at 900 °C for 2 h

/ 10% (v/v) of THF in methanol /

5 4.9

150 180

65 65

/ /

C = 98.8 C = 99.4

[24] [25]

Turbonilla striatula shell Turbonilla striatula shell

Mustard oil WCO

CaO H2SO4, Ba/ CaO

0.5:1 (wt/wt) 0.54:1 (wt/ wt) 9 6

3 1

360 180

65 65

/ Pre-esterification, Stirring speed: 900 rpm

Y = 93.3 C > 98

[26] [27]

Mussel shell Freshwater mussel shell

Soybean oil Chinese tallow oil

CaO CaO

24 12

12 1.5

480 90

60 70

/ /

Y = 94.1 Y = 99.8

[28] [29]

Clamshell (Mereterix mereterix) Clamshell (Meretrix meretrix)

WFO

CaO

6.03

/

360

60

/

Y > 89

[30]

Palm olein

CaO

9

1

120

65

Stirring speed: 900 rpm

Y = 98.0

[31]

White bivalve clamshell Capiz shell Obtuse horn shell Scallop shell Scallop shell

WFO Palm oil Palm oil WCO Rapeseed oil

CaO CaO CaO CaO

18 8 12 6 12

8 3 5 5 9

180 360 360 120 120

65 60 / 65 65

/ Stirring speed: 700 rpm / / /

Y = 95.84 Y = 93 C = 86.75 Y > 86 Y = 93.2

[32] [33] [34] [35] [36]

Angel wing shell (Cyrtopleura costata)

CaO

150

9

60

65

Stirring speed: 300 rpm

Y = 84.11

[37]

Shrimp shell

Microalgae Nannochloropsis oculata oil Rapeseed oil

9

2.5

180

65

/

C = 89.1

[38]

Turtle shell

Rapeseed oil

KF/CaO

9

3

180

70

/

Y = 97.5

[39]

Cyrtopleura costata seashell

Palm oil

Ca(OH)2

5

5

50

/

Microwave irradiation

Y = 96.0

[40]

Albalone shell

Palm oil

CaO

9

7

150

65

/

Y = 96.2

[41]

Mixed seashells

Palm oil

30

10

180

60

/

Y = 98.0

[42]

CaO

Calcined at 900 °C for 3 h Shell calcined at 900 °C for 3 h, Ba loading of 1 wt.%, and calcined at 900 °C Calcined at 1050 °C for 2 h Calcined at 900 °C for 4 h, impregnated in deionized water, and activated at 600 °C for 3 h Calcined at 900 °C for 3.5 h Shell calcined at 900 °C for 4 h, refluxed with water for 12 h, and calcined at 600 °C for 3 h Calcined at 900 °C for 4 h Calcined at 900 °C for 2 h Calcined at 800 °C for 3 h Calcined at 1000 °C for 2 h Immersing in a NaCl aqueous solution, adding SiO2 and Al2O3 fine particles, and calcined at 900 °C Calcined at 900 °C for 2 h

Shell carbonization at 450 °C, loading KF of 25 wt.%, and activated at 250 °C Shell carbonization at 500 °C, loading KF of 25 wt.%, and activated at 300 °C Calcined at 900 °C for 2 h, and exposed in atmospheric moisture for 7 days Shell calcined at 800 °C for 4 h, ethanol-treatment temperature of 100 °C Calcined at 600 °C for 2 h, added Zn (NO3)2
6H2O and Al2O3, and calcined at 500 °C for 2 h

R. Shan et al. / Energy Conversion and Management 127 (2016) 273–283

Sea snail River snail shell

MeOH = Methanol, Y = Yield, C = Conversion. a The maximum biodiesel yield (or conversion), / = Not studied. WCO = Waste cooking oil, WFO = Waste frying oil. 275

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R. Shan et al. / Energy Conversion and Management 127 (2016) 273–283

the resulting catalyst still showed higher catalytic activity than commercial CaO. The waste mussel shell also could be converted to CaO under calcination temperature more than 950 °C. Rezaei et al. [28] explored waste mussel shell derived CaO catalysts and used response surface methodology (RSM) method to study the effects of different parameters. Another freshwater mussel, an aquatic bivalve mollusk was used and prepared by a calcination impregnation activation method [29]. The shell was first calcined at 900 °C, and then was impregnated in deionized water and finally activated at 600 °C. The as-synthesized CaO catalyst exhibited a rather large surface area of 23.2 m2/g. By using Chinese tallow oil as foodstocks, the biodiesel yield could reach 90%. The repetitive study showed that the prepared catalyst could be reused at least 7 cycles. Nair et al. [30] used clamshell (Mereterix mereterix) derived CaO catalyst to produce biodiesel. The shell calcined at 900 °C for 3.5 h resulted in the highest activity. The maximum yield (>89%) and conversion (>97%) were obtained. Girish et al. [32] explored the white bivalve clam shells derived CaO catalyst and used in the transesterification reaction. After calcined at 900 °C, the shells were all transformed into active CaO phase. A high biodiesel yield of 95.84% could be achieved. Currently, the production of Capiz (A. cristatum) in archipelago countries, especially in several parts of Indonesia, was quite large also produced significant amounts of shell waste. The Capiz shell was utilized by Suryaputra et al. [33] for synthesizing the CaO catalyst for biodiesel preparation. Under the optimal conditions, the biodiesel yield was up to 93%. The shell of Cyrtopleura costata (Angel Wing Shell) usually widely distributed in swamp areas, rivers and agricultural fields. Syazwani et al. [37] reported that calcined Cyrtopleura costata could be utilized in the biodiesel synthesis from microalgae Nannochloropsis oculata. After calcined at 900 °C, the as-prepared CaO catalyst exhibited the highest basicity and surface area and the fatty acid methyl esters (FAME) yield of 84.11% could be achieved using the inedible oil and the prepared CaO catalyst. 2.1.1.2. The use of modified mollusk shells. It is known to us that the waste material-derived CaO catalysts, like most solid base catalysts, had a rather lower reaction rate compared to the soluble catalysts (e.g. NaOH and KOH) in the transesterification reaction due to their limited active sites on the surface. Consequently, the longer reaction time and higher amount of catalysts would be required and finally raised the synthesis cost. In order to accelerate the transesterification rate catalyzed by waste material-derived CaO catalysts, various modified techniques have been explored for the synthesis of high efficiency shell-derived CaO catalysts, e.g. loading of active compounds onto shells, co-solvent method, organic solvent modification method, hydration method and so on. Potassium salts (such as KBr, KI and KF) have been proved to be a kind of high catalytic activity phase which could be impregnated on the shell-derived CaO to enhance its catalytic performance in the transesterification reaction. Yang et al. [38] impregnated KF on the incomplete carbonization of shrimp shell to explore a cost-effective catalyst for biodiesel production. Shrimp shell widely available in the world because the abundant consumption of shrimp food every year. Shrimp shell was also rich in chitin which can be converted to saccharides under suitable conditions. In this study, the shrimp shell was first carbonated at 450 °C, and then impregnated KF with the amount of 25 wt. %, and finally calcined at 250 °C. The as-synthesis catalyst showed rather high activity in the transesterification of inedible oil. A biodiesel conversion of 89.1% could be reached after 3 h at 65 °C and 2.5 wt.% catalyst with methanol-to-oil molar ratio of 9:1. The study also indicated that the incomplete carbonization step could possess a porous framework structure, which could make the active phase KF easily impregnated on the shrimp shell surface. And the

relative high catalytic activity of prepared catalyst was owing to the special structure of the modified shrimp shell. A similar work was conducted by Xie et al. [39]. KF was impregnated on the incomplete carbonization turtle shell to synthesize anther novel high performance solid biodiesel catalyst. The authors utilized a similar route to prepare incomplete carbonization shell and subsequently impregnated KF on the modified shell. The biodiesel yield could be reached up to 97.5% after 3 h with 3 wt.% catalyst loading. The mechanism of the synthesized catalyst was the same with the former study. KI was another active phase that can be impregnated on the CaO catalyst to improve its catalytic performance. Jairam et al. [23] impregnated KI on the calcined oyster shell to explore a high efficacy catalyst. The authors revealed that the portlandite and potassium iodide on the catalyst surface contributed to its subsequent high surface area. In another work, potassium salts KBr was utilized to be impregnated on the calcined mixed snail shell and kaolin [21]. First, the calcined snail shell and kaolin were mixed and ground, and then were impregnated with 40 wt.% amount of KBr, and finally activated at 500 °C for 3 h. A high biodiesel yield of 98.5% could be achieved using the as-synthesized catalyst. Barium (Ba) salt is another kind of active ingredient which can be doped on CaO to improve its catalytic activity in biodiesel synthesis. Ba doped CaO catalysts derived from waste shells of Turbonilla striatula were prepared by Boro et al. [27] and used in the transesterification of waste cooking oil (WCO). After peresterification, the biodiesel conversion could be above 98% under the optimum reaction conditions. The authors found that the catalytic activity was highly influenced by the catalyst basicity and the presence CaO and BaO might have acted like active species during the reaction. A co-solvent (such as tetrahydrofuran, acetone, and diethyl ether) method is recently gaining the interest of researchers in their efforts towards accelerating the reactions rate, reducing the need of reaction conditions and also improving the quality of the synthesized biodiesel [45]. Roschat et al. [20] explored a highly efficient CaO-based catalyst using tetrahydrofuran as a co-solvent and river snail shell as a precursor for biodiesel production. A desired FAME yield of 98.5% was obtained using this kind of solvent. A hydration method using ethanol as a modification agent to prepare a highly efficient abalone shell derived catalyst was developed by Chen et al. [41]. After abalone shell derived CaO treated with ethanol, the organic solvent made significant increase in the surface area and basicity and a decrease in crystalline size of the catalyst at 100 °C, which attributed to the increased catalytic activity of catalyst. The maximum yield of FAME for the ethanol modified could reach 96.2%. Thermal hydration-dehydration is another technique to improve the morphology of catalyst. By using this method, Asikin-Mijan et al. [31] explored a natural waste clamshell (Meretrix meretrix) derived CaO for biodiesel synthesis. After hydrationdehydration process, the surface area and basicity of the prepared catalyst could increase significantly. If prolonged this process, more Ca(OH)2 was formed which could promote basicity of catalyst. After calcined at 900 °C and then refluxed with water for 12 h in the temperature of 60 °C, and finally calcined at 600 °C for 3 h, the synthesized catalyst exhibited the highest activity. The triglyceride conversion could be up to 98%. The Cyrtopleura costata seashell derived catalysts were successfully synthesized by a hydration method and used for biodiesel synthesis [40]. The seashells were first calcined at 900 °C for 2 h and then hydrated by atmospheric moisture. Under microwave assisted, the maximum biodiesel yield (96.0%) could be achieved. Jindapon et al. [42] used dissolution-precipitation method to synthesize waste mixed seashells derived heterogeneous base

[55] Y = 98

Y = 92.7

/

Ultrasonic power: 120 W 60

2.1.2. Eggshells Bird (such as chicken, duck, quail and ostrich) eggshell is also a kind reliable raw material to acquire CaO [57]. Table 2 shows a series of eggshell-derived catalysts obtained through different kinds of methods and their utilizations in biodiesel synthesis.

60 8 9 Ostrich eggshell

CaO Palm oil

Quail eggshell

MeOH = Methanol, Y = Yield, C = Conversion. a The maximum biodiesel yield (or conversion), / = Not studied, WCO = Waste cooking oil.

/ 1.5

Soybean oil deodorizer distillate Palm oil Duck eggshell

12

Acid-treated for 2 h and calcined at 800 °C for 2 h Calcined at 800 °C for 4 h CaO

10 H2SO4, CaO

Palm oil Chicken eggshell

10

9 CaOASiO2

Jatropha/Karanja oils Chicken eggshell

15

ZnOACaO

Palm oil Soybean oil/WCO Nahor oil Chicken eggshell Eggshell Chicken eggshell

277

catalysts for the transesterification of palm oil with methanol. The authors mixed Zn and Al compounds with waste shells to improve the catalytic performance of catalysts. The results indicated that after calcined at 500 °C, the synthesized catalyst exhibited the highest basicity and surface area due to the enhanced dispersion of CaO, generated from thermal decomposition of Ca(OH)2, CaZn2(OH)6
2H2O and Ca(NO3)2 on the Al2O3. The maximum FAME yield could be above 98.0% under the suitable conditions. Furthermore, the catalytic stability of synthesized catalyst was significantly improved due to a strong interaction of the mixed oxide nanocrystallites with the Al2O3 surface.

[56]

[54] Y = 94.6 Pre-esterification 80

65

[53] Y = 80.2 / 480

60

[52] Y = 98.2/95.8 65 5 12

1 h/1.5 h

65

[49] [50] [51] Y = 96.7 Y = 98/97 Y = 94 / RT 65 15 5.8 5 18 6 10

Calcined at 800 °C for 4 h Calcined for 3 h at 900 °C Calcined at 800 °C for 2 h and 2 wt.% Li loaded Eggshell was calcined at 900 °C for 4 h and chemically activated by ZnO using 3 wt.% of Zn(NO3)2 as ZnO precursor; modified catalyst was calcined at 900 °C for 4 h 0.4 M Na2SiO3 added and calcined at 800 °C for 4 h Calcined at 900 °C CaO CaO H2SO4, Li/CaO

4 9 240

/

[46] [47] [48] Y = 95 Y = 95 Y = 90

/ Pre-esterification Pre-esterification; Stirring speed: 700 rpm Microwave power: 900 W / Pre-esterification 65 65 65 180 150 150 CaO H2SO4, CaO H2SO4, CaO Soybean oil Karanja oil Jatropha curcas oil

3 2.5 2 9 8 8 Calcined at 1000 °C for 2 h Calcined at 900 °C for 2 h Calcined at 900 °C for 2.5 h

Catalyst loading (wt.%) MeOH:Oil (mol:mol)

Chicken eggshell Chicken eggshell Chicken eggshell

Preparation condition of catalyst Catalyst Oil Eggshell

Table 2 Summary of various types of eggshells derived catalysts for biodiesel production.

Reaction condition

Time (min)

Temperature (°C)

Others

Ya (or C) (%)

Ref.

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2.1.2.1. The direct use of eggshells. The chicken eggshell was found to be the most common bird eggshell and nearly 4 million tons per year of eggshell wastes were produced in China alone [18]. Wei et al. [46] first synthesized derived CaO catalyst from chicken eggshell for biodiesel production. In their study, the CaO catalyst was easily obtained by calcining eggshell at 1000 °C. The prepared catalyst exhibited high activity and over 95% biodiesel yield was obtained under the suitable conditions. Chicken eggshells could also be used as a catalyst source for biodiesel production from non-edible feedstocks (such as karanja oil and Jatropha curcas oil) with high free fatty acid (FFA) value. Since the eggshell derived CaO is a kind of alkali catalyst, a pre-esterification step should be used to remove any FFA before the base transesterification reaction. Similarly, Sharma et al. [47] utilized calcined chicken eggshell (900 °C) as a CaO catalyst for biodiesel synthesis from karanja oil (acid number 19.88 mg KOH/g). Following initial esterification with methanol catalyzed by H2SO4, a high biodiesel yield of 95.0% and conversion of 97.4% was obtained at an 8:1 methanolto-oil molar ratio, 2.5 wt.% catalyst loading, and 2.5 h reaction time at 65 ± 0.5 °C. Chavan et al. [48] focused on biodiesel production from jatropha curcas oil (acid number 17.88 mg KOH/g) in presence of chicken eggshells derived catalyst. After acid esterification, the biodiesel yield was up to 90% under the optimum reaction conditions. Waste duck eggshell is another bird eggshell which has high content of CaCO3. Yin et al. [54] explored duck eggshell derived CaO catalyst for biodiesel production. In their study, the maximum biodiesel yield of 94.6% was obtained after the peresterification of inedible oil. Eggshells could also be used as catalyst for biodiesel production from both commercial fresh soybean oil and WCO at room temperature [50]. After 11 h of regular stirring, high yield of FAME was obtained from soybean oil (98%) and WCO (97%), and WCO was used without any esterification pretreatment. The reusability of the eggshell-derived catalyst was demonstrated for five cycles for WCO and ten cycles for fresh soybean oil. The catalyst can be stored for at least three months without any decrease in its catalytic activity and for a year with only 10% decrease in FAME yield. 2.1.2.2. The use of eggshells with various modified method. In order to enhance reaction rates of the transesterification reaction catalyzed by eggshell derived catalysts, a series of techniques (such as acidtreatment, assisted transesterification techniques (ATT), and loading of active compounds onto shells) were also used to accelerate the transesterification reaction rate [44]. Acid-treated can be a method to remove the dense cuticle layer of eggshell to developed large pores of eggshell surface. Utilizing this method, Cho and Seo [55] have explored an acid-treated quail eggshell derived catalysts for biodiesel synthesis. Quail egg is the

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smallest among the bird eggshells and the size of quail eggs is only a half of one chicken egg [57]. In this study, after acid-treated with HCl solution, the quail eggshell was calcined above 800 °C. The resulting catalyst steadily maintained high conversions of over 98% during repeated fivefold usage at 65 °C with 1.5 wt.% catalyst and methanol-to-oil molar ratio of 12:1. The high catalytic activity of quail eggshell catalyst was owing to the closely developed large pores which could provide a large amount of strong basic sites and the efficient channels for the rapid diffusion of oil molecules. The use of ATT can reduce the requirement of reactor operation conditions while achieving the highest yield. Two types of ATTs (included microwave-assisted and ultrasonic-assisted methods) are commonly used in biodiesel synthesis from vegetable oils or animal fats [58]. Microwave is basically electromagnetic radiation, which can transfer energy directly to the reactants and thereby give rise to intense localized heating. Consequently, the preheating step is eliminated and the reaction can be completed in a shorter time [59]. Khemthong et al. [49] tested the catalytic activity of calcined chicken eggshell for biodiesel synthesis with microwave assisted. With 900 W microwave power, the maximum yield of FAME was up to 96.7%. Ultrasound, another assisted transesterification technique, is the process of propagating an oscillating sound pressure wave with a frequency greater than the upper limit of the human hearing range [58]. When ultrasonic waves pass through a mixture of vegetable oil and methanol, rather fine emulsions can be generated. These emulsions have large interfacial areas, which provide more reaction sites, which increased the rate of the transesterification reaction [60,61]. Chen et al. [56] explored waste ostrich eggshell derived CaO for biodiesel synthesis with the ultrasonic-assisted. (An ostrich egg is the largest bird egg in the world. Each ostrich eggshell is over 20 times the weight of each chicken egg [56,62].) The biodiesel yield could reach 92.7% under the optimal conditions. Boro et al. [51] have tried to load an active ingredient lithium salt onto CaO to improve the catalytic activity of eggshell derived CaO catalyst. Li doped chicken eggshell derived CaO catalysts were prepared for biodiesel production from inedible feedstock (such as Nahor oil). With loading of 2 wt.% Li, the resulting catalyst exhibited the highest activity. Under the optimum reaction conditions, the maximum biodiesel conversion of 94% was obtained. The formation of mixed LiACa phase along with the presence of Li2O and CaO contributed to the good performance of catalyst. In another work, chicken eggshell mixed with transition metal oxides (ZnO, MnO2, Fe2O3 and Al2O3) to prepare high efficiency solid catalysts for biodiesel production was reported by Joshi et al. [52]. It was reported that the basicity of transition metal impregnated CaO was much higher than that of neat CaO because of the synergistic relation between multi-metal ions [63]. In their study, the resulting ZnOACaO mixed catalyst was found to be the most efficient catalyst in comparison to others due to the greatest surface area and most basic strength of the ZnOACaO mixed oxide. The maximum conversion for the transesterification of Jatropha and Karanja oils was achieved by using 5 wt.% catalyst at 65 °C with 12:1 methanol-to-oil molar ratio. The authors noted that the suitable calcination temperature contributed to the effectiveness of the catalysts. Besides, the stable CaOASiO2 catalysts were successfully synthesized through a biomimetic silicification approach by using eggshell and Na2SiO3 as raw materials [53]. It was known to us that lysozyme that was widely existed within the eggshell matrix, showed desirable silicification-inducing capability [64,65]. In this work, the eggshell was directly utilized to acquire eggshell-SiO2 composites, which could offer a promising precursor for synthesizing CaOASiO2 catalysts. The resulting CaOASiO2 catalysts exhibited a good stability due to the better distribution of Si compounds on the CaO surface and the formation of CaAOASi bond.

2.1.3. The comparison of catalytic activity of CaO from different precursors A comparison of the behavior of waste ostrich eggshell and chicken eggshell which used as precursors to catalysts for the transesterification of used cooking oil has been recently made [62]. The maximum biodiesel yield is 96% and 94% for the calcined ostrich eggshell and chicken eggshell under its optimum reaction conditions, respectively. The ostrich eggshell derived CaO catalyst was found to be more active due to its higher surface area, higher basicity and smaller particle size compared to the calcined chicken eggshell. Another comparison of the behavior of two different kinds of shells: mollusk and egg as precursors to catalysts for biodiesel production has been recently made by Viriya-empikul et al. [66]. The authors compared the activities of waste shells of egg, golden apple snail, and Meretrix venus derived CaO catalysts through the transesterification reaction. The results indicated that eggshell shell derived catalyst exhibited the highest catalytic activity while the Meretrix venus shell derived catalyst had the worst catalytic performance. The catalytic activity of catalyst was mainly owing to the Ca content in the catalyst and the surface area of catalyst. A similar result was concluded by Correia et al. [67]. In their study, the catalytic activities of CaO obtained from crab shell and eggshell were investigated in the transesterification of vegetable oil. The calcined eggshell was found to be more active compared to calcined crab shell because of the higher surface content of Ca for eggshell compared with that of crab shell. Soybean transesterification was performed using CaO from different sources (commercial, synthesized from chicken eggshell and produced by a carbothermal route) to develop a comparative study [68]. The authors found that all CaO catalysts studied yielded FAME above 93% with 4 h and 3 wt.% catalyst loading, in relation to the soybean oil, reflux and 600 rpm stirring. The results also indicated that the leached calcium does not cause important homogeneous catalysis. An activity comparison between the calcined natural dolomitic rock and waste mixed seashells for biodiesel synthesis was made by Jaiyen et al. [69]. After calcined at 800 °C, the dolomite derived catalyst (mixed CaOAMgO) exhibited a higher thermal stability and higher basicity than that of mixed seashells derived CaO catalyst. Although, both kinds of catalysts could achieve a high biodiesel yield of 98%, the calcined dolomite derived catalyst could exhibit faster reaction rate than the other one. The presence of MgO dispersed in the CaO matrix was important for the superior physicochemical and catalytic properties of the natural dolomite calcined at 800 °C. Kouzu et al. [36] compared the catalytic activity of the calcined limestone with calcined scallop shell for rapeseed oil transesterification to produce biodiesel. The resulted indicated that the shellbased catalyst was much less active than the limestone-based catalyst due to the NaCl impurity existed in the scallop shell. The authors also found that the addition of NaCl would cause a fairy increase in the crystalline size which could decrease the basicity of catalyst. From these comparisons mentioned above, the catalytic ability of shells derived catalyst depends mainly on the surface area of the prepared CaO. The larger catalyst surface area consists of more catalytic basic centers which are accessible for the initiation of reaction, leading to higher transesterification rates. Since the component of shells is similar, it could be concluded that, basically, if the CaO solids are carefully obtained by calcining theses precursors at sufficiently severe conditions and handled adequately, the source for obtaining CaO is irrelevant. Besides, the impurities play an important role in the calcium based wastes, and the properly added impurity will significantly improve the catalytic of shell derived CaO catalyst.

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279

2.2. Bones

3. Large-scale industrial wastes derived Ca-based catalysts

Waste animal (such as fish, bird and domestic animals) bone is another kind of the Ca-based waste material which is widely available in the nature. After the bone was calcined at high temperature, the b-Ca3(PO4)2 and CaO phases could be formed and used as the active component the transesterification reaction. Besides, the nature hydroxyapatite (HAP) contained in bones was also proved to be a good support for catalyst synthesis. The utilization of waste animal bones as catalysts for biodiesel production was shown in Table 3.

Industrial wastes (such as lime mud, carbide slag, and blast furnace slag) are abundant worldwide. Therefore, those wastes can also be used in terms of catalyst, which can not only partly alleviate disposal problems but also reduce the synthesis cost of catalyst. Lime mud is the by-product from paper making industry and the CaCO3, unslaked CaO and Ca(OH)2 are the main compositions (as shown in Table 4) [81,82]. About 10 million tons lime mud was generated in 2011 from paper industry [83], which was increasing with the expanded demand for papers. Up to now, lime mud was primarily abandoned outside, which resulted in a serious environmental crisis and the land occupation. Therefore, conversion of the lime mud to a beneficial and economical viable product could partly solve this problem. Li et al. [83] used lime mud derived CaO for biodiesel production. The results revealed that the catalytic activity of catalyst was mainly attributed to its basic strength. After impregnated with 20 wt.% KF and calcined at 600 °C, the lime mud derived catalyst exhibited the high catalytic activity. Oil conversion of 99.09% could be obtained under the suitable conditions. In an extension to this study [84], the effect of water and CO2 on catalytic performance of lime mud derived catalyst was evaluated. After calcination at 700 °C and followed hydrated by deionized water, the as-prepared catalyst possessed a higher ability in resisting water and CO2 than commercial CaO. And glycerol yield of 88.53% could be achieved for the transesterification reaction under the optimal conditions. Carbide slag is a solid waste from the hydrolysis reaction of calcium carbide in the industrial production of ethyne gas [80]. Every year, about millions of tons of carbide slag are generated which resulted in the disposal problem and environmental pollution [80]. The composition of a typical carbide slag is listed in Table 4. Li et al. [85] successfully explored carbide slag derived CaO catalyst for biodiesel synthesis. After calcined the carbide slag waste at 650 °C, the FAME yield of 91.3% was obtained after 30 min at 65 °C with 1.0 wt.% catalyst and 9 methanol-to-oil molar ratio. The authors also revealed that the strong basicity of synthesized catalyst contributed to its high catalytic activity. Blast furnace slags is another kind of industrial wastes originated from iron manufacture and processing. The composition of a typical raw blast furnace slag is listed in Table 4. Blast furnace slag could be used as a precursor for preparing a hydrocalumite, and this hydrocalumite and its derivatives could be applied for the transesterifications of triglycerides [86]. In the transesterification of n-ethyl butyrate, slag-made hydrocalumite samples provided higher catalytic activities than those of the common hydrocalumite due to the interfusion of slag-derived impurity elements, such as Fe and Mn, which could act as catalyst promoters. After calcined at 800 °C, above 97% FAME yield was achieved using this slag-made hydrocalumite. Bottom ash waste was generated from woody biomass gasification, and CaCO3 was found to be the main component in the ash. Maneerung et al. [87] found that after calcined at 800 °C, the obtained CaO catalysts exhibited high biodiesel production activity, and over 90% yield of ME could be achieved at the optimum reaction conditions. Experimental kinetic data fitted well the pseudo-first order kinetic model. The activation energy (Ea) of the transesterification reaction was calculated to be 83.9 kJ/mol. High CaCO3 contained palm kernel shell biochar (PKSB) was found to be a promising source material for the CaO-based catalyst. Kostic´ et al. [88] successfully used the low-cost basic catalyst derived from PKSB for biodiesel synthesis. The results showed that the effect of reaction temperature and methanol-to-oil molar ratio on the FAME synthesis was significant, while the effect of catalyst loading was statistically negligible. The optimum reaction conditions were found to be catalyst loading of 3 wt.%, temperature of

2.2.1. The direct use of calcined bones Chakraborty et al. [70] first used utilized calcined fish bone as solid catalyst for biodiesel production. RSM method was also used to optimize the parametric conditions. The result indicated the maximum FAME yield of 97.73% could be obtained by using this novel catalyst in another work, Madhu et al. [71] have utilized the discarded parts of fish as feedstock oils and catalysts in biodiesel synthesis. The esterification reaction was followed by the transesterification of waste fish oil (with acid value of 11.89 mg KOH/g). The biodiesel conversion was above 96% under moderate experimental conditions. The domestic animals bones which mainly contained HAP and CaCO3 could also use as feedstocks for the catalyst of the transesterification reaction. Obadiah et al. [74] utilized calcined waste sheep bone in the transesterification reaction. Under the optimal reaction conditions, the methyl ester (ME) conversion was 96.78%. A high calcination temperature contributed to the catalytic activity of catalyst. Calcined waste bovine bone was directly used for biodiesel synthesis [75]. After calcined at 750 °C, the optimum yield of ME (97%) was obtained under the optimal conditions. The authors also concluded that the major components of calcined bone were CaO and crystalline HAP after calcined above 650 °C. The CaO existed in the catalyst contributed to the catalytic activity of catalyst. Waste chicken bone has the similar components with the domestic animals bones [76]. After calcined at 900 °C, the waste chicken bone exhibited good performance in the transesterification of low FFA WCO (1.86 mg KOH/g). A high biodiesel yield of 89.33% was obtained owing to the dense active basic site on its surface.

2.2.2. The use of modified bones Since the major component of bones was natural HAP, many researchers have used calcined waste animal bones as the catalyst support for biodiesel synthesis [78]. More recently, natural HAP derived from waste fish (Lates calcarifer) bone has been effectively utilized as a support heterogeneous copper acid catalyst [72]. The Taguchi robust design method was used to optimize the reaction. The maximum oleic acid conversion was found to be 91.86% under the optimum parametric values. In another work [72], a novel Ni/ Ca/HAP solid acid catalyst was synthesized using wet impregnation method and calcined waste fish scale as the support. RSM method was used to determine the optimal parametric values for the esterification reaction. Under the conditions of 0.80 mL/min methanol flow rate, 30 wt.% Ni(NO3)2
6H2O dosage and 300 °C calcination temperature, the corresponding maximum conversion of FFAs to FAME was 59.90%. In the second transesterification step, 98.40% yield of biodiesel was achieved using calcined fish scale base catalyst. Chen et al. [77] investigated calcined waste pig bone derived HAP as a support for K2CO3 to prepare a cost-effective solid base catalyst for biodiesel production. In this study, the highest biodiesel yield of 96.4% was obtained under the optimum prepared conditions. The high total basicity of resulting catalyst contributed to its high catalytic activity.

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Table 3 Summary of various types of bones derived catalysts for biodiesel production. Bone

Oil

Catalyst

Preparation condition of catalyst

Reaction condition Catalyst loading (wt.%)

Time (min)

Temperature (°C)

Others

Y = 97.73

[70]

Y > 96

[71]

C = 91.86

[72]

C = 59.90 (FFA conversion)

[73]

Y = 96.78

[74]

Y = 97

[75]

Y = 89.33

[76]

Y = 96.4

[77]

b-Ca3(PO4)2

Calcined at 997.42 °C for 2 h

6.27

1.01

300

70

H2SO4, b-Ca3(PO4)2

Calcined at 900 °C for 2 h

6.5

1.5

120

55

Fish bone

Oleic acid

Cu/HAP

50 wt.% Cu(NO3)2
5H2O impregnated, 90 °C freezedrying temperature, and calcined at 500 °C for 4 h

/

/

60

70

Waste fish scale

Frying soybean oil

Ni/Ca/HAP

30 wt.% Ni(NO3)2
6H2O impregnated, and calcined at 300 °C for 4 h

/

2.0

120

60

Sheep bone

Palm oil

HAP

Calcined at 800 °C

18

20

240

65

Bovine bone

Soybean oil Low FFA WCO Palm oil

CaO

Calcined at 750 °C for 6 h

6

8

180

65

b-Ca3(PO4)2

Calcined at 900 °C for 4 h

15

5g

240

65

K/HAP

Pig bone calcined at 900 °C for 4 h, 30 wt.% K2CO3 loaded, and calcined at 600 °C

9

8

90

65

/

Fish bone

Chicken bone Pig bone

Soybean oil WFO

Ref.

MeOH:Oil (mol:mol)

Stirrer speed: 500 rpm Preesterification, Stirrer speed: 900 rpm 0.8 mL/min ethanol flow rate and 1000 rpm stirrer speed 0.8 mL/min ethanol flow rate and 700 rpm stirrer speed Stirrer speed: 900 rpm Stirrer speed: 150 rpm /

Fish bone

Ya (or C) (%)

MeOH = Methanol, Y = Yield, C = Conversion. a The maximum biodiesel yield (or conversion), / = Not studied, WFO = Waste frying oil, WCO = Waste cooking oil, HAP = Hydroxyapatite.

Table 4 The chemical composition of selected waste materials. Waste material

Lime mud Carbide slag Blast furnace slag

Composition (wt.%)

Ref.

SiO2

CaO

Al2O3

MgO

K2O

Fe2O3

TiO2

Na2O

BL

5.98 2.51 34.58

49.44 71.09 40.09

0.37 1.96 14.78

0.16 0.09 5.29

/ 0.02 /

0.06 / 1.53

/ 0.04 0.78

1.90 / /

41.99 22.85 /

[79] [80] [18]

BL = the burning loss, / = not studied or trace amount.

65 °C and methanol-to-oil molar ratio of 9:1 and the corresponding maximum biodiesel FAME content was 99%. The synthesized catalyst could be reused without any treatment in three consecutive cycles with no significant drop in activity. 4. The reaction mechanism of calcium rich waste materials derived catalysts As discussed in previous sections, the waste materials are mainly composed of CaCO3 and the formation of CaO during different catalyst preparation methods for biodiesel synthesis. Concerning mechanism on the vegetable oil transesterification catalyzed by CaO, Gryglewicz pointed out that the catalytically active phase was calcium methoxide (Ca-Met) produced by a reaction of CaO with methanol during the transesterification reaction [89], and detailed study on the mechanism of manufactured CaO was also carried out by Kawashima et al. [90]. On the other hand, Kouzu et al. [91] found that the conversion of CaO into Ca-Met was not appreciable. Although no data to characterize the surface of CaO was collected, there was a possibility that the vegetable oil transesterification was catalyzed by the original surface of CaO. By the way, they also found that another calcium compound acted as the catalytically active phase after the appreciable amount of glycerol was by-produced: CaO reacted with glycerol under the

transesterifying condition. The resultant Ca species was identified as calcium glyceroxide (Ca-Gly), and Ca-Gly was slightly less active in the vegetable oil transesterification than CaO. Besides, it should be noted that the vegetable oil transesterification is catalyzed by not only the basic sites generated on surface of CaO catalyst but also the soluble substance leached away from CaO catalyst [92]. Although, the leaching behavior and the following homogeneous contribution toward the vegetable oil transesterification appear independent of type of the active phase, Granados et al. and Sousa et al. found that the contribution of this homogeneous catalysis could be considered negligible [14,68,93]. In conclusion, due to a combination of the variable active phase and the homogeneous contribution during reaction, the CaOcatalyzed transesterification is too complicated to be understood sufficiently without the further study.

5. Challenge and future trends of calcium rich waste material derived catalysts As discussed in previous sections, the use of catalysts from calcium rich waste materials not only makes the process of biodiesel production more affordable and sustainable but also can counter the environmental complications. Although these catalysts show

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acceptable reactivity towards the transesterification of vegetable oil, there are still challenges for those catalysts. Calcium rich waste material derived catalyst, as a kind of heterogeneous catalyst, has an inherent drawback of mass transfer resistance because the reaction mixture constitutes a three-phase system (catalyst, oil and alcohol) which results in a lower reaction rate and higher production cost [94,95]. In order to solve the mass transfer problems associated with calcium rich waste material derived catalyst, many researchers have utilized structure promoters or catalyst supports to provide more specific area and pore for active species which could act with large triglyceride molecules [45,95]. A serious of intensification technologies (such as microwave, ultrasonic, and co-solvent method) were explored to eliminate the mass transfer resistance of immiscible reactants [96]. Once the mass transfer resistance is reduced, it may lead to a shorter reaction time and lower energy consumptions. Hence, in the future work, the exploration of efficient intensification technologies will make the material derived catalysts more commercially for the industrial application. The main component of most calcium rich waste materials derived catalysts was CaO, and the CaO catalyst was not stable and usually suffered from tremendous leaching problem during reaction [93,97]. The degree of the leaching affected the lifetime expectancy of CaO catalyst. And what was worse, biodiesel was contaminated with the leached Ca species. For instance, the quality standard of European lays it down that calcium content of biodiesel is limited to 5 ppm [77,98]. The removal of Ca2+ ions from the biodiesel product commonly requires additional separation/purification processes, which would generate a large amount of waste water to the environment. In addition, CaO catalyst was also rapidly contaminated by water or CO2 (the formation of nonactive phase CaCO3 and Ca(OH)2 on its surface) under ambient conditions, thus resulting in a decreased catalytic activity [99]. What’s more, the CaO catalyst also can react with the by-produced glycerol under the transesterifying condition, and then is transformed into Ca-Gly and the new phase Ca-Gly had lower catalytic activity compared to CaO [14,41]. Thereby, the design of efficient and catalytically stable calcium rich waste materials derived CaO based catalysts that can improve the overall efficiency of biodiesel production dramatically is still an important challenge. In order to stabilize these waste materials derived CaO catalysts, one probable way was to mixed these oxides with other chemical compound to form stable composite catalysts against their leaching during the reaction, such as MgOACaO, CaOASiO2, CaOAZnO, and CaOACeO2 mixed oxides [53,100–103]. Those mixed oxides could prevent the Ca2+ ions leaching from the catalyst by the formation of stable phase between CaO and other oxides to a certain extent. Besides, during the transesterification reaction, these stable composite could also restrain the formation of Ca-Gly on the catalyst surface. Therefore, future work is to find more effective chemical compounds to form stable composite catalysts against the problems of waste derived CaO catalyst. The synthesis cost of biodiesel was also a big challenge for the application of calcium rich waste material derived catalysts. Although, the source of these waste derived catalysts was very cheap, before catalyst could be used in the transesterification reaction, many synthesis procedures (such as calcination, impregnation, and anneal) should be used. All these operations are expensive from the point of view energetic and economic. Besides, the feedstock of biodiesel contributed to the main cost (70–80%) of whole biodiesel synthesis [104]. As a result, the use of inedible oils could also be another effective method to reduce biodiesel price. However, most inedible oils contain high FFA and water and trace salts. Before the calcium rich waste materials derived catalysts could be used in the reaction, those oils should need be treated through multiple chemical processes [30]. Hence, till now, a

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technologically reasonable way to convert the inedible oils into biodiesel with the help of calcium rich waste materials derived catalysts was to combine the solid acid catalytic esterification with the preliminarily elimination of FFA. The rational design of novel and efficient catalysts for biodiesel production especially from inedible feedstock is also an important challenge. 6. Conclusion The utilization of solid catalysts for biodiesel production from calcium rich renewable resources is an emerging research field since recent studies have proved the technical feasibility and the environmental and economic benefits of those catalysts used in the (trans)esterification reaction. The large scale use of those wastes will offer an economic way to the utilization of Ca-waste materials and convert those wastes to value added products. However, although these solid catalysts showed acceptable reactivity towards the transesterification of refined vegetable oils, their reactivity to the transesterification of inedible feedstock is generally unsatisfactory. In addition, numerous waste materials derived CaO catalysts are not stable and suffered leaching problem during reaction. Thereby, the design of high-efficient and catalytically stable CaO catalysts which can be utilized in biodiesel synthesis is still an important challenge. And significant improvements are still necessary in the design of waste catalyst to minimize the need for commercially sourced components (such as the use of inedible feedstock), and to reduce cost of processing steps necessary to create the desired final catalyst. Notwithstanding the calcium rich waste materials derived catalyst to be explored further, the outlook of progressing intense and diverse researches is the evidence of their potential as heterogeneous catalysts in biodiesel synthesis at the industrial level. Acknowledgements This paper is financially supported by National Natural Science Funds of China (51406207), Youth Innovation Promotion Association, Chinese Academy of Sciences (CAS) (2014320), Guangdong High-level Personnel of Special Support Program (2014TQ01Z379) and Science and Technology Program of Guangzhou in China (2014Y2-00522). References [1] Wan L, Liu H, Skala D. Biodiesel production from soybean oil in subcritical methanol using MnCO3/ZnO as catalyst. Appl Catal B 2014;152–153:352–9. [2] Leung DYC, Wu X, Leung MKH. A review on biodiesel production using catalyzed transesterification. Appl Energy 2010;87:1083–95. [3] Lee AF, Bennett JA, Manayil JC, Wilson K. Heterogeneous catalysis for sustainable biodiesel production via esterification and transesterification. Chem Soc Rev 2014;43:7887–916. [4] Shan R, Chen G, Yan B, Shi J, Liu C. Porous CaO-based catalyst derived from PSS-induced mineralization for biodiesel production enhancement. Energy Convers Manage 2015;106:405–13. [5] Hums ME, Cairncross RA, Spatari S. Life-cycle assessment of biodiesel produced from grease trap waste. Environ Sci Technol 2016;50:2718–26. [6] Su F, Guo Y. Advancements in solid acid catalysts for biodiesel production. Green Chem 2014;16:2934–57. [7] Luque R, Lovett JC, Datta B, Clancy J, Campelo JM, Romero AA. Biodiesel as feasible petrol fuel replacement: a multidisciplinary overview. Energy Environ Sci 2010;3:1706–21. [8] kumar M, Sharma MP. Selection of potential oils for biodiesel production. Renew Sust Energy Rev 2016;56:1129–38. [9] Semwal S, Arora AK, Badoni RP, Tuli DK. Biodiesel production using heterogeneous catalysts. Bioresour Technol 2011;102:2151–61. [10] Lu Y, Zhang Z, Xu Y, Liu Q, Qian G. CaFeAl mixed oxide derived heterogeneous catalysts for transesterification of soybean oil to biodiesel. Bioresour Technol 2015;190:438–41. [11] Amani H, Ahmad Z, Hameed BH. Highly active alumina-supported Cs-Zr mixed oxide catalysts for low-temperature transesterification of waste cooking oil. Appl Catal A 2014;487:16–25.

282

R. Shan et al. / Energy Conversion and Management 127 (2016) 273–283

[12] Paterson G, Issariyakul T, Baroi C, Bassi A, Dalai A. Ion-exchange resins as catalysts in transesterification of triolein. Catal Today 2013;212:157–63. [13] Boro J, Deka D, Thakur AJ. A review on solid oxide derived from waste shells as catalyst for biodiesel production. Renew Sust Energy Rev 2012;16:904–10. [14] Kouzu M, Hidaka J. Transesterification of vegetable oil into biodiesel catalyzed by CaO: a review. Fuel 2012;93:1–12. [15] Marinkovic´ DM, Stankovic´ MV, Velicˇkovic´ AV, Avramovic´ JM, Miladinovic´ MR, Stamenkovic´ OO, et al. Calcium oxide as a promising heterogeneous catalyst for biodiesel production: current state and perspectives. Renew Sust Energy Rev 2016;56:1387–408. [16] Bennett JA, Wilson K, Lee AF. Catalytic applications of waste derived materials. J Mater Chem A 2016;4:3617–37. [17] Shan R, Shi J, Yan B, Chen G, Yao J, Liu C. Transesterification of palm oil to fatty acids methyl ester using K2CO3/palygorskite catalyst. Energy Convers Manage 2016;116:142–9. [18] Balakrishnan M, Batra VS, Hargreaves JSJ, Pulford ID. Waste materialscatalytic opportunities: an overview of the application of large scale waste materials as resources for catalytic applications. Green Chem 2011;13:16–24. [19] Birla A, Singh B, Upadhyay SN, Sharma YC. Kinetics studies of synthesis of biodiesel from waste frying oil using a heterogeneous catalyst derived from snail shell. Bioresour Technol 2012;106:95–100. [20] Roschat W, Siritanon T, Kaewpuang T, Yoosuk B, Promarak V. Economical and green biodiesel production process using river snail shells-derived heterogeneous catalyst and co-solvent method. Bioresour Technol 2016;209:343–50. [21] Liu H, Guo Hs, Wang Xj, Jiang Jz, Lin H, Han S, Pei Sp. Mixed and ground KBrimpregnated calcined snail shell and kaolin as solid base catalysts for biodiesel production. Renew Energy 2016;93:648–57. [22] Nakatani N, Takamori H, Takeda K, Sakugawa H. Transesterification of soybean oil using combusted oyster shell waste as a catalyst. Bioresour Technol 2009;100:1510–3. [23] Jairam S, Kolar P, Sharma-Shivappa R, Osborne JA, Davis JP. KI-impregnated oyster shell as a solid catalyst for soybean oil transesterification. Bioresour Technol 2012;104:329–35. [24] Boey PL, Maniam GP, Hamid SA. Biodiesel production via transesterification of palm olein using waste mud crab (Scylla serrata) shell as a heterogeneous catalyst. Bioresour Technol 2009;100:6362–8. [25] Boey PL, Maniam GP, Hamid SA, Ali DMH. Utilization of waste cockle shell (Anadara granosa) in biodiesel production from palm olein: optimization using response surface methodology. Fuel 2011;90:2353–8. [26] Boro J, Thakur AJ, Deka D. Solid oxide derived from waste shells of Turbonilla striatula as a renewable catalyst for biodiesel production. Fuel Process Technol 2011;92:2061–7. [27] Boro J, Konwar LJ, Thakur AJ, Deka D. Ba doped CaO derived from waste shells of T striatula (TS-CaO) as heterogeneous catalyst for biodiesel production. Fuel 2014;129:182–7. [28] Rezaei R, Mohadesi M, Moradi GR. Optimization of biodiesel production using waste mussel shell catalyst. Fuel 2013;109:534–41. [29] Hu S, Wang Y, Han H. Utilization of waste freshwater mussel shell as an economic catalyst for biodiesel production. Biomass Bioenergy 2011;35:3627–35. [30] Nair P, Singh B, Upadhyay SN, Sharma YC. Synthesis of biodiesel from low FFA waste frying oil using calcium oxide derived from Mereterix mereterix as a heterogeneous catalyst. J Clean Prod 2012;29–30:82–90. [31] Asikin-Mijan N, Lee HV, Taufiq-Yap YH. Synthesis and catalytic activity of hydration-dehydration treated clamshell derived CaO for biodiesel production. Chem Eng Res Des 2015;102:368–77. [32] Girish N, Niju SP, Begum KM Meera Sheriffa, Anantharaman N. Utilization of a cost effective solid catalyst derived from natural white bivalve clam shell for transesterification of waste frying oil. Fuel 2013;111:653–8. [33] Suryaputra W, Winata I, Indraswati N, Ismadji S. Waste capiz (Amusium cristatum) shell as a new heterogeneous catalyst for biodiesel production. Renew Energy 2013;50:795–9. [34] Lee SL, Wong YC, Tan YP, Yew SY. Transesterification of palm oil to biodiesel by using waste obtuse horn shell-derived CaO catalyst. Energy Convers Manage 2015;93:282–8. [35] Sirisomboonchai S, Abuduwayiti M, Guan G, Samart C, Abliz S, Hao X, et al. Biodiesel production from waste cooking oil using calcined scallop shell as catalyst. Energy Convers Manage 2015;95:242–7. [36] Kouzu M, Kajita A, Fujimori A. Catalytic activity of calcined scallop shell for rapeseed oil transesterification to produce biodiesel. Fuel 2016;182:220–6. [37] Syazwani O Nur, Rashid U, Yap YH Taufiq. Low-cost solid catalyst derived from waste Cyrtopleura costata (Angel Wing Shell) for biodiesel production using microalgae oil. Energy Convers Manage 2015;101:749–56. [38] Yang L, Zhang A, Zheng X. Shrimp shell catalyst for biodiesel production. Energy Fuel 2009;23:3859–65. [39] Xie J, Zheng X, Dong A, Xiao Z, Zhang J. Biont shell catalyst for biodiesel production. Green Chem 2009;11:355–64. [40] Marwan Indarti E. Hydrated calcined Cyrtopleura costata seashells as an effective solid catalyst for microwave-assisted preparation of palm oil biodiesel. Energy Convers Manage 2016;117:319–25. [41] Chen G, Shan R, Yan B, Shi J, Li S, Liu C. Remarkably enhancing the biodiesel yield from palm oil upon abalone shell-derived CaO catalysts treated by ethanol. Fuel Process Technol 2016;143:110–7. [42] Jindapon W, Jaiyen S, Ngamcharussrivichai C. Seashell-derived mixed compounds of Ca, Zn and Al as active and stable catalysts for the

[43] [44]

[45]

[46] [47]

[48]

[49]

[50]

[51]

[52]

[53]

[54]

[55]

[56]

[57]

[58]

[59]

[60]

[61]

[62]

[63]

[64]

[65]

[66]

[67]

[68]

transesterification of palm oil with methanol to biodiesel. Energy Convers Manage 2016;122:535–43. Salvi BL, Panwar NL. Biodiesel resources and production technologies – a review. Renew Sust Energy Rev 2012;16:3680–9. Boey PL, Maniam GP, Hamid SA. Performance of calcium oxide as a heterogeneous catalyst in biodiesel production: a review. Chem Eng J 2011;168:15–22. Alhassan Y, Kumar N, Bugaje IM, Pali HS, Kathkar P. Co-solvents transesterification of cotton seed oil into biodiesel: effects of reaction conditions on quality of fatty acids methyl esters. Energy Convers Manage 2014;84:640–8. Wei Z, Xu C, Li B. Application of waste eggshell as low-cost solid catalyst for biodiesel production. Bioresour Technol 2009;100:2883–5. Sharma YC, Singh B, Korstad J. Application of an efficient nonconventional heterogeneous catalyst for biodiesel synthesis from Pongamia pinnata oil. Energy Fuel 2010;24:3223–31. Chavan SB, Kumbhar RR, Madhu D, Singh B, Sharma YC. Synthesis of biodiesel from Jatropha curcas oil using waste eggshell and study of its fuel properties. RSC Adv 2015;5:63596–604. Khemthong P, Luadthong C, Nualpaeng W, Changsuwan P, Tongprem P, Viriya-empikul N, et al. Industrial eggshell wastes as the heterogeneous catalysts for microwave-assisted biodiesel production. Catal Today 2012;190:112–6. Piker A, Tabah B, Perkas N, Gedanken A. A green and low-cost room temperature biodiesel production method from waste oil using egg shells as catalyst. Fuel 2016;182:34–41. Boro J, Konwar LJ, Deka D. Transesterification of non edible feedstock with lithium incorporated egg shell derived CaO for biodiesel production. Fuel Process Technol 2014;122:72–8. Joshi G, Rawat DS, Lamba BY, Bisht KK, Kumar P, Kumar N, et al. Transesterification of Jatropha and Karanja oils by using waste egg shell derived calcium based mixed metal oxides. Energy Convers Manage 2015;96:258–67. Chen G, Shan R, Li S, Shi J. A biomimetic silicification approach to synthesize CaO-SiO2 catalyst for the transesterification of palm oil into biodiesel. Fuel 2015;153:48–55. Yin X, Duan X, You Q, Dai C, Tan Z, Zhu X. Biodiesel production from soybean oil deodorizer distillate using calcined duck eggshell as catalyst. Energy Convers Manage 2016;112:199–207. Cho YB, Seo G. High activity of acid-treated quail eggshell catalysts in the transesterification of palm oil with methanol. Bioresour Technol 2010;101:8515–9. Chen G, Shan R, Shi J, Yan B. Ultrasonic-assisted production of biodiesel from transesterification of palm oil over ostrich eggshell-derived CaO catalysts. Bioresour Technol 2014;171:428–32. Tan YH, Abdullah MO, Nolasco-Hipolito C. The potential of waste cooking oilbased biodiesel using heterogeneous catalyst derived from various calcined eggshells coupled with an emulsification technique: a review on the emission reduction and engine performance. Renew Sust Energy Rev 2015;47:589–603. Adewale P, Dumont M-J, Ngadi M. Recent trends of biodiesel production from animal fat wastes and associated production techniques. Renew Sust Energy Rev 2015;45:574–88. Kumar R, Kumar GR, Chandrashekar N. Microwave assisted alkali-catalyzed transesterification of Pongamia pinnata seed oil for biodiesel production. Bioresour Technol 2011;102:6617–20. Badday AS, Abdullah AZ, Lee K-T. Optimization of biodiesel production process from Jatropha oil using supported heteropolyacid catalyst and assisted by ultrasonic energy. Renew Energy 2013;50:427–32. Choedkiatsakul I, Ngaosuwan K, Assabumrungrat S. Application of heterogeneous catalysts for transesterification of refined palm oil in ultrasound-assisted reactor. Fuel Process Technol 2013;111:22–8. Tan YH, Abdullah MO, Nolasco-Hipolito C, Taufiq-Yap YH. Waste ostrich-and chicken-eggshells as heterogeneous base catalyst for biodiesel production from used cooking oil: catalyst characterization and biodiesel yield performance. Appl Energy 2015;160:58–70. Lee HV, Taufiq-Yap YH, Hussein MZ, Yunus R. Transesterification of jatropha oil with methanol over Mg-Zn mixed metal oxide catalysts. Energy 2013;49:12–8. Liu C, Yang D, Jiao Y, Tian Y, Wang Y, Jiang Z. Biomimetic synthesis of TiO2SiO2-Ag nanocomposites with enhanced visible-light photocatalytic activity. ACS Appl Mater Interfaces 2013;5:3824–32. Ramanathan M, Luckarift HR, Sarsenova A, Wild JR, Ramanculov EK, Olsen EV, et al. Lysozyme-mediated formation of protein-silica nano-composites for biosensing applications. Colloid Surface B 2009;73:58–64. Viriya-Empikul N, Krasae P, Puttasawat B, Yoosuk B, Chollacoop N, Faungnawakij K. Waste shells of mollusk and egg as biodiesel production catalysts. Bioresour Technol 2010;101:3765–7. Correia LM, Saboya RM, Campelo Nde S, Cecilia JA, Rodriguez-Castellon E, Cavalcante Jr CL, et al. Characterization of calcium oxide catalysts from natural sources and their application in the transesterification of sunflower oil. Bioresour Technol 2014;151:207–13. de Sousa FP, dos Reis GP, Cardoso CC, Mussel WN, Pasa VMD. Performance of CaO from different sources as a catalyst precursor in soybean oil transesterification: kinetics and leaching evaluation. J Environ Chem Eng 2016;4:1970–7.

R. Shan et al. / Energy Conversion and Management 127 (2016) 273–283 [69] Jaiyen S, Naree T, Ngamcharussrivichai C. Comparative study of natural dolomitic rock and waste mixed seashells as heterogeneous catalysts for the methanolysis of palm oil to biodiesel. Renew Energy 2015;74:433–40. [70] Chakraborty R, Bepari S, Banerjee A. Application of calcined waste fish (Labeo rohita) scale as low-cost heterogeneous catalyst for biodiesel synthesis. Bioresour Technol 2011;102:3610–8. [71] Madhu D, Singh B, Sharma YC. Studies on application of fish waste for synthesis of high quality biodiesel. RSC Adv 2014;4:31462–8. [72] Chakraborty R, RoyChowdhury D. Fish bone derived natural hydroxyapatitesupported copper acid catalyst: Taguchi optimization of semibatch oleic acid esterification. Chem Eng J 2013;215–216:491–9. [73] Chakraborty R, Das SK. Optimization of biodiesel synthesis from waste frying soybean oil using fish scale-supported Ni catalyst. Ind Eng Chem Res 2012;51:8404–14. [74] Obadiah A, Swaroopa GA, Kumar SV, Jeganathan KR, Ramasubbu A. Biodiesel production from palm oil using calcined waste animal bone as catalyst. Bioresour Technol 2012;116:512–6. [75] Smith SM, Oopathum C, Weeramongkhonlert V, Smith CB, Chaveanghong S, Ketwong P, et al. Transesterification of soybean oil using bovine bone waste as new catalyst. Bioresour Technol 2013;143:686–90. [76] Farooq M, Ramli A, Naeem A. Biodiesel production from low FFA waste cooking oil using heterogeneous catalyst derived from chicken bones. Renew Energy 2015;76:362–8. [77] Chen G, Shan R, Shi J, Liu C, Yan B. Biodiesel production from palm oil using active and stable K doped hydroxyapatite catalysts. Energy Convers Manage 2015;98:463–9. [78] Zhang P, Wu T, Jiang T, Wang W, Liu H, Fan H, et al. Ru-Zn supported on hydroxyapatite as an effective catalyst for partial hydrogenation of benzene. Green Chem 2013;15:152–9. [79] Cheng J, Zhou J, Liu J, Cao X, Cen K. Physicochemical characterizations and desulfurization properties in coal combustion of three calcium and sodium industrial wastes. Energy Fuel 2009;23:2506–16. [80] Sun R, Li Y, Zhao J, Liu C, Lu C. CO2 capture using carbide slag modified by propionic acid in calcium looping process for hydrogen production. Int J Hydrogen Energy 2013;38:13655–63. [81] Sun R, Li Y, Liu C, Xie X, Lu C. Utilization of lime mud from paper mill as CO2 sorbent in calcium looping process. Chem Eng J 2013;221:124–32. [82] Qin J, Cui C, Yang C, Cui X, Hu B, Huang J. Dewatering of waste lime mud and after calcining its applications in the autoclaved products. J Clean Prod 2016;113:355–64. [83] Li H, Niu S, Lu C, Liu M, Huo M. Transesterification catalyzed by industrial waste-lime mud doped with potassium fluoride and the kinetic calculation. Energy Convers Manage 2014;86:1110–7. [84] Li H, Niu S, Lu C, Cheng S. The stability evaluation of lime mud as transesterification catalyst in resisting CO2 and H2O for biodiesel production. Energy Convers Manage 2015;103:57–65. [85] Li F, Li H, Wang L, Cao Y. Waste carbide slag as a solid base catalyst for effective synthesis of biodiesel via transesterification of soybean oil with methanol. Fuel Process Technol 2015;131:421–9. [86] Kuwahara Y, Tsuji K, Ohmichi T, Kamegawa T, Mori K, Yamashita H. Transesterifications using a hydrocalumite synthesized from waste slag: an economical and ecological route for biofuel production. Catal Sci Technol 2012;2:1842–51.

283

[87] Maneerung T, Kawi S, Wang C-H. Biomass gasification bottom ash as a source of CaO catalyst for biodiesel production via transesterification of palm oil. Energy Convers Manage 2015;92:234–43. [88] Kostic´ MD, Bazargan A, Stamenkovic´ OS, Veljkovic´ VB, McKay G. Optimization and kinetics of sunflower oil methanolysis catalyzed by calcium oxide-based catalyst derived from palm kernel shell biochar. Fuel 2016;163:304–13. [89] Gryglewi S. Rapeseed oil methyl esters preparation using heterogeneous catalysts. Bioresour Technol 1999;70:249–53. [90] Kawashima A, Matsubara K, Honda K. Acceleration of catalytic activity of calcium oxide for biodiesel production. Bioresour Technol 2009;100:696–700. [91] Kouzu M, Kasuno T, Tajika M, Yamanaka S, Hidaka J. Active phase of calcium oxide used as solid base catalyst for transesterification of soybean oil with refluxing methanol. Appl Catal A 2008;334:357–65. [92] Granados ML, Poves MDZ, Alonso DM, Mariscal R, Galisteo FC, Moreno-Tost R, et al. Biodiesel from sunflower oil by using activated calcium oxide. Appl Catal B 2007;73:317–26. [93] Granados ML, Alonso DM, Sádaba I, Mariscal R, Ocón P. Leaching and homogeneous contribution in liquid phase reaction catalysed by solids: the case of triglycerides methanolysis using CaO. Appl Catal B 2009;89:265–72. [94] Liu X, He H, Wang Y, Zhu S, Piao X. Transesterification of soybean oil to biodiesel using CaO as a solid base catalyst. Fuel 2008;87:216–21. [95] Baskar G, Aiswarya R. Trends in catalytic production of biodiesel from various feedstocks. Renew Sust Energy Rev 2016;57:496–504. [96] Borges ME, Díaz L. Recent developments on heterogeneous catalysts for biodiesel production by oil esterification and transesterification reactions: a review. Renew Sust Energy Rev 2012;16:2839–49. [97] Yoosuk B, Udomsap P, Puttasawat B, Krasae P. Modification of calcite by hydration-dehydration method for heterogeneous biodiesel production process: the effects of water on properties and activity. Chem Eng J 2010;162:135–41. [98] Xie W, Zhao L. Heterogeneous CaO-MoO3-SBA-15 catalysts for biodiesel production from soybean oil. Energy Convers Manage 2014;79:34–42. [99] Witoon T, Bumrungsalee S, Vathavanichkul P, Palitsakun S, Saisriyoot M, Faungnawakij K. Biodiesel production from transesterification of palm oil with methanol over CaO supported on bimodal meso-macroporous silica catalyst. Bioresour Technol 2014;156:329–34. [100] Rubio-Caballero JM, Santamaría-González J, Mérida-Robles J, Moreno-Tost R, Jiménez-López A, Maireles-Torres P. Calcium zincate as precursor of active catalysts for biodiesel production under mild conditions. Appl Catal B 2009;91:339–46. [101] Kumar D, Ali A. Transesterification of low-quality triglycerides over a Zn/CaO heterogeneous catalyst: kinetics and reusability studies. Energy Fuel 2013;27:3758–68. [102] Thitsartarn W, Kawi S. An active and stable CaO-CeO2 catalyst for transesterification of oil to biodiesel. Green Chem 2011;13:3423–30. [103] Albuquerque MCG, Azevedo DCS, Cavalcante CL, Santamaría-González J, Mérida-Robles JM, Moreno-Tost R, et al. Transesterification of ethyl butyrate with methanol using MgO/CaO catalysts. J Mol Catal A-Chem 2009;300:19–24. [104] Yang L, Takase M, Zhang M, Zhao T, Wu X. Potential non-edible oil feedstock for biodiesel production in Africa: a survey. Renew Sust Energy Rev 2014;38:461–77.