Synthesis of High-Quality Biodiesel Using Feedstock and Catalyst

Feb 23, 2017 - To replace petroleum fuel, liquid biofuel will be vital in the near future. ..... 869 (biodiesel), flash point was reduced from 270 (wa...
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Synthesis of High-Quality Biodiesel Using Feedstock and Catalyst Derived from Fish Wastes Devarapaga Madhu,† Rajan Arora,‡ Shalini Sahani,† Veena Singh,† and Yogesh Chandra Sharma*,† †

Department of Chemistry, Indian Institute of Technology (BHU) Varanasi, Varanasi 221005, India Department of Chemical Engineering and Technology, Indian Institute of Technology (BHU) Varanasi, Varanasi 221005, India

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‡

ABSTRACT: A low-cost and high-purity calcium oxide (CaO) was prepared from waste crab shells, which were extracted from the dead crabs, was used as an efficient solid base catalyst in the synthesis of biodiesel. Raw fish oil was extracted from waste parts of fish through mechanical expeller followed by solvent extraction. Physical as well as chemical properties of raw fish oil were studied, and its free fatty acid composition was analyzed with GC-MS. Stable and high-purity CaO was obtained when the material was calcined at 800 °C for 4 h. Prepared catalyst was characterized by XRD, FT-IR, and TGA/DTA. The surface structure of the catalyst was analyzed with SEM, and elemental composition was determined by EDX spectra. Esterification followed by transesterification reactions were conducted for the synthesis of biodiesel. The effect of cosolvent on biodiesel yield was studied in each experiment using different solvents such as toluene, diethyl ether, hexane, tetrahydrofuran, and acetone. High-quality and pure biodiesel was synthesized and characterized by 1H NMR and FT-IR. Biodiesel yield was affected by parameters such as reaction temperature, reaction time, molar ratio (methanol:oil), and catalyst loading. Properties of synthesized biodiesel such as density, kinematic viscosity, and cloud point were determined according to ASTM standards. Reusability of prepared CaO catalyst was checked, and the catalyst was found to be stable up to five runs without significant loss of catalytic activity. KEYWORDS: fatty acid methyl esters (FAMEs), free fatty acid, tetrahydrofuran, waste crab shells, waste fish oil

1. INTRODUCTION Energy has a pivotal role in the determination of socioeconomic conditions of any country. Energy consumption of any country determines the country’s standard of living.1 Excess of energy in the surroundings can be converted, accumulated, and amplified for our daily use in a number of ways. The production of energy has always been a concern for researchers and policymakers worldwide. Energy sources are categorized into two main groups, namely, fossil and renewable energy. Fossil energy can be separated into nonrenewable and renewable energy. Nonrenewable energy sources comprise petroleum, coal, gas hydrate, gas, and fissile material, and renewable energy sources include solar, hydro, geothermal, biomass, and wind energy. Recently, the renewable energy sources are contributing more toward the total global energy requirement.2 Supporting development, indispensable characteristics of renewable energy sources depend on environmental protection. World energy is currently conflicted with the turning point of fossil fuel depletion and environmental deterioration. To prevail over this problem, renewable energy has currently been achieving more attention because of its environmental allowance. The need for energy, oil depletion, and its price, which are continually increasing, all have inclined the country to search for alternative new renewable fuels. Green energy is another term for renewable energy, which is auspicious for alternative, and it is neat and environmentally friendly. As compared with fossil energy, green energy produces lower or negligible levels of greenhouse gases and other pollutants. Emissions such as SO2, CO2, and NO2 are lower3,4 in comparison to nonrenewable energy sources and the production as well as application of green energy plays an © 2017 American Chemical Society

important role in diminishing the greenhouse impact. Carbon dioxide released from the chemical energy obtained from biofuels (via photosynthesis using solar energy) is maintaining CO2 levels because green plants are taking the released CO2 from the environment. To replace petroleum fuel, liquid biofuel will be vital in the near future.5 Biofuels comprise biodiesel, biomethanol, bioethanol, biobutanol, vegetable oil, biogas, and biohydrogen. The most important liquid biofuels are biodiesel and bioethanol. Biodiesel is a diesel alternative, whereas bioethanol is a gasoline substitute. For transportation purposes, liquid biofuel has currently drawn attention in a number of countries because of its sustainability, renewability, biodegradability, and availability, as well as its imminent role in regional advancement, inception of rural job creation, and diminishing greenhouse gas emissions. Oxygen content is the biggest difference between petroleum and biofuel feedstocks. Biofuels are reliable and are obtained from renewable sources, accessible, sustainable, and locally available, and are nonpolluting. On the basis of their production technology, biofuels can be categorized into first-generation biofuels (FGBs), second-generation biofuels (SGBs), third-generation biofuels (TGBs)6 and fourth-generation biofuels.7 Different catalysts are used for the synthesis of biodiesel. Most widely used catalysts are enzymatic and acid/base homogeneous and heterogeneous catalysts. Enzymatic catalysts have attracted attention as they can withstand free fatty acid Received: Revised: Accepted: Published: 2100

December 15, 2016 February 11, 2017 February 23, 2017 February 23, 2017 DOI: 10.1021/acs.jafc.6b05608 J. Agric. Food Chem. 2017, 65, 2100−2109

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Journal of Agricultural and Food Chemistry

2. EXPERIMENTAL PROCEDURES

(FFA) and water contents, thus assisting in the purification of biodiesel and glycerol. On the other hand, the enzymatic catalysts cannot be used commercially as they are costly and show unstable activities with reaction rates much lower than those of homogeneous catalysts.8 Common catalysts used for biodiesel synthesis are homogeneous acid/base catalysts, such as sodium or potassium hydroxide, sodium methoxide, sodium ethoxide, sulfuric acid, and hydrochloric acid. They have relatively higher kinetic rates with high conversion with insignificant side reactions. However, there are numerous drawbacks of using them such as their corrosive nature and increase in pH of the final product.9 Removal of homogeneous catalysts after transesterification also poses technical problems, and a large amount of wastewater is produced during biodiesel cleaning and separation.10 In the homogeneous catalytic transesterification, low-quality glycerol is produced and thus involves a meticulous process for purification; catalyst recovery is not possible, requiring its neutralization at the end of the reaction, and producing undesired salts that need to be separated. Also, it requires the FFA content in feedstock to be 3% necessitates removal of FFAs and moisture. Culminating all of these reasons increases the processing cost of biodiesel and its byproducts. To settle all these issues, heterogeneous catalysts such as zeolites, clays, sulfonic ionexchange resins, pure or mixed oxides, and heterogeneous guanidines are being developed. Heterogeneous catalysts can be separated easily and reused; an insignificant amount of wastewater is produced, and separation of biodiesel from glycerol is simplified.11,12 Reusability of heterogeneous catalysts makes the process more economically feasible, and also the nontoxic, noncorrosive nature makes the process environmentally friendly. Previous studies have shown that the fish oil extracted from fish waste13 gave good results for the synthesis of biodiesel.14 India’s total fish production in the year 2012−2013 was 9,019,148 tons, which includes marine fish production of 3,275,091 tons and inland fish production was 5,744,057 tons. During fish industry processing, approximately 20−80% of fish waste is generated as waste from the total fish weight.15 Waste generated from fish is used as raw material for the synthesis of biodiesel. In the present work, fish oil has been used as raw material for the synthesis of biodiesel because the fish market generates huge amounts of fish waste from which fish oil can be generated.16,17 Fish oil extracted from waste not only reduces the amount of waste but also reduces the amount of total cost of biodiesel synthesis. From an Indian perspective, it is strenuous to produce biodiesel from the waste sources (fish oil extracted from discarded parts of fish and CaO from waste crab shells) because of the scarcity of ample feedstock as well as raw material for the catalyst preparation. It provides less expensive and more potential option to curtail the overall price of biodiesel production. From a literature survey, it was clear that very few studies are available on the transesterification of high acid value feedstocks such as fish oil or Millettia pinnata using CaO as base heterogeneous catalyst. Present work explores the preparation of waste CaO derived from waste crab shells and the efficacy of the catalyst in the transesterification of fish oil extracted from waste parts of fish of Indian origin. The properties of prepared biodiesel were considered per ASTM standards.

2.1. Materials. The crab shells used for synthesis of the catalyst were collected from Jas Dry Fish Merchant-India MART Toothukudi, Tamil Nadu, India. Fish oil was extracted from the discarded parts of fish. Methyl alcohol, sulfuric acid, deuterated chloroform, sodium sulfate, hexane, toluene, tetrahydrofuran (THF), acetone, and diethyl ether were of analytical reagent (AR) grade and were purchased from Merck Ltd., Mumbai, India. 2.2. Fish Oil Extraction. Waste parts of fish such as tails, maw, eyes, and viscera were collected from the local fish market (Varanasi), India. The collected discarded parts of fish were washed with hot distilled water to eliminate impurities such as blood and solid particles. The water content of waste parts of fish was removed with a hot air oven maintained at 102 °C for 2 h. Dried waste parts of fish were cut into small pieces. Fish oil was extracted from these small pieces through a mechanical expeller at room temperature. Some amount of oil remained in the dried matter after extraction of fish oil through the mechanical expeller. This remaining oil was extracted through solvent extraction using petroleum ether as solvent. Physical properties of waste fish oil such as acid value, density, kinematic victory, boiling point, and unsaponifiable matter were determined as shown in Table 1.

Table 1. Physical and Chemical Properties of Waste Fish Oil property color acid value unsaponifiable matter density at 15.5 °C boiling point cloud point saponification value pour point kinematic viscosity, at 40 °C flash point water content iodine value copper strip corrosion

units

ASTM standard

mg KOH/g % w/w g/cm3 °C °C mg KOH/g °C mm2/s

ASTM D 664 ASTM D1065 ASTM D 1298

°C %

ASTM D 1510 ASTM D 97 ASTM D 445 ASTM ASTM ASTM ASTM

D D D D

93 2709 2500 130

value yellowish red 11.89 0.78 0.899 >356 13 187 −1 25.51 270 0.009 110 no corrosion observed

2.3. Catalyst Preparation. Waste crab shells were dried in a hot air oven at 102 °C for 2 h to remove water content present in the waste crab shells. The dried waste crab shells were ground into powder using a ball mill. Then the powder was calcined in a muffle furnace at 800 °C for 4 h. The calcined material was ground into fine powder with the help of an agate mortar. Catalytic poisoning will occur when the catalyst is placed in contact with air because of the presence of moisture and carbon dioxide.12 Although the catalytic poisoning was less because of water and carbon dioxide, the poisoning was found to be consequential. Therefore, the catalyst was placed in a plastic bottle container and then in a desiccator to avoid poisoning. The catalyst was characterized with various analytical techniques (XRD, FT-IR, TGA/ DTA, and SEM/EDX) and used in the transesterification reactions. 2.4. Characterization of Biodiesel by Proton NMR Analysis. The conversion of triglycerides (oil) to fatty acid methyl ester (biodiesel) was analyzed using proton NMR spectroscopy. The 1H NMR spectrum of biodiesel product is shown in Figure 1. A singlet signal at 3.69 ppm represents the methoxy protons of FAME, whereas the triplet at 2.30 ppm represents α-methylene protons of fatty acid derivatives.18−20 The percentage conversion of fish oil to biodiesel was calculated by the ratio of integrated signals (area under the signal obtained by integration) at 3.69 ppm (AME) and 2.30 ppm (ACH2) in the following equation: C = 100(2XA CH3)/(3A CH2 ) = 100(2 × 3)/(3 × 2.07) = 96.61%

(1) 2101

DOI: 10.1021/acs.jafc.6b05608 J. Agric. Food Chem. 2017, 65, 2100−2109

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Journal of Agricultural and Food Chemistry

Figure 1. NMR spectrum of biodiesel synthesized from waste fish oil.

Figure 2. GC-MS analysis and identification of fatty acid methyl ester composition in waste fish oil.

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Journal of Agricultural and Food Chemistry Table 2. Free Fatty Acids and Their Composition (%) of Waste Fish Oil sr

retention time

compound name

composition (%)

corresponding fatty acid

corresponding fatty acid strucure

1 2 3 4 5 6 7 8 9 10

17.37 19.32 19.55 21.06 21.25 21.29 21.46 22.77 24.33 24.66

myristic acid methyl ester palmitoleic acid methyl ester palmitic acid methyl ester arachidonic acid methyl ester oleic acid methyl ester linoleic acid methyl ester stearic acid methyl ester eicosapentaenoic acid methyl ester (EPA) docosahexaenoic acid methyl ester (DHA) erucic acid methyl ester

5.51 9.70 14.09 3.21 11.03 3.45 4.05 19.96 13.93 1.08

myristic acid palmitoleic acid palmitic acid arachidonic acid oleic acid linoleic acid stearic acid eicosapentaenoic acid docosahexaenoic acid erucic acid

CH3(CH2)12COOH CH3(CH2)5CHCH(CH2)7COOH CH3(CH2)12COOH CH3(CH2)10(CHCH)4COOH CH3(CH2)14CHCHCOOH CH3(CH2)10(CHCH)3COOH CH3(CH2)16COOH CH3(CH2)8(CHCH)5COOH CH3(CH2)8(CHCH)6COOH CH3(CH2)18(CHCH)COOH

C denotes the conversion (%) of triglycerides to fatty acid methyl esters; the factors 2 and 3 in the numerator and denominator are ascribed to the number of protons on methylene and the number of protons on methyl ester. 2.5. Gas Chromatography−Mass Spectrometry (GC-MS) Analysis. Fish oil methyl esters were analyzed with the GC-MS (GC-Mass Spectrometer PerkinElmer; mass range, 20−620 Da (amu)). Samples were prepared to analyze when 0.03 mL of fish oil methyl esters was mixed with 2.1 mL of hexane. Figure 2 represents the GC-MS chromatogram in which the X-axis corresponds to retention time and the Y-axis corresponds to % of relative abundant. Using the known compound spectrum from the NIST 2011 library, unknown compound spectrum was predicted with the help of Turbo Mass software. The major fish oil methyl esters were myristic acid methyl ester (5.51%), palmitoleic acid methyl ester (9.70%), palmitic acid methyl ester (14.09%), arachidonic acid methyl ester (3.21%), oleic acid methyl ester (11.03%), linolenic acid methyl ester (3.45%), stearic acid methyl ester (4.05%), eicosapentaenoic acid methyl ester (EPA) (19.96%), docosahexaenoic acid methyl ester (DHA) (13.93%), and erucic acid methyl ester (1.08%) as shown in Table 2. 2.6. FT-IR Analysis of Biodiesel. Purified biodiesel was characterized with FT-IR spectroscopy as shown in Figure 3. A

with the acid of the base catalyst. In the present case, the acid value of the feedstock was found to be 11.89, which is quite high, and acid esterification was performed to convert FFAs into corresponding FAMEs. In acid esterification, a fish oil:methanol (1:8) molar ratio was poured in an indigenously fabricated three-necked round-bottom flask, and 1% (v/v) of sulfuric acid was added to it; the content was mechanically agitated on a water bath at 60 °C. The esterification reaction was completed in 120 min. After completion of the reaction, the reaction mixture was poured in a separating funnel followed by rotavapor separation. After esterification, the acid value was reduced to 200 °C was due to the removal of water content present in the uncalcined waste crab shells, and further weight loss (7.2%) observed at 200 < T > 500 °C was due to the loss of some amount of organic compounds present in the uncalcined waste crab shells. Sharp weight loss (41.08%) 2104

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Journal of Agricultural and Food Chemistry that occurred under 500 < T > 789 °C is due to the complete conversion of calcium carbonate into calcium oxide by releasing carbon dioxide; furthermore, there was no significant weight loss because stable calcium oxide formation had taken place. 3.5. FT-IR Analysis. Figure 8 shows the FT-IR spectra of calcined crab shells 800 °C. FT-IR spectra of calcined crab

major advantages that proved calcium oxide to be a good catalyst in the transesterification. The pore volume and average pore width of catalyst were 0.03013 cm3/g and 73.6034 Å, respectively. 3.7. Effect of Reaction Parameters on Biodiesel Yield. To optimize biodiesel production, the effects on biodiesel yield due to various parameters, namely, catalyst loading, oil-tomethanol molar ratio, reaction time, reaction temperature, and stirrer speed, were studied. The effect of cosolvent 22 (tetrahydrofuran) on the yield was also investigated. In the heterogeneous transesterification process, the reaction mixture constitutes a three-phase system due to the presence of solid catalyst, methanol, and oil phases, which cause mixing problems. The cosolvent increases the mutual solubility of oil23 and methanol, resulting in better mass transfer. Consequently, we get higher initial reaction rates, shorter reaction time, and better yield. The catalyst loading was studied in the range of 1−3%. The oil-to-methanol molar ratio was varied from 1:4 to 1:14. Cosolvent was kept proportionate to methanol (1:1). Reaction time was varied from 30 to 130 min; the reaction temperature was varied from 35 to 85 °C; and stirrer speed was varied from 350 to 850 rpm. 3.8. Effect of Catalyst Loading on Biodiesel Yield. A series of experiments was carried out at different catalyst loadings and at different oil to methanol ratios, keeping other parameters constant. The loading of catalyst was varied from 1 to 3 wt % and the oil to methanol molar ratio from 1:4 and 1:14. Figure 10 represents the combined effect of catalyst

Figure 8. FT-IR spectrum of calcium oxide derived from crab shells.

shells show a major absorption band at 506 cm−1 characteristic of a Ca−O bond.9 The absorption band at 1083 cm−1 and symmetric stretching vibration band at 1483 cm−1 correspond to an insignificant amount of carbonate (CO3−2) present in the catalyst derived from the waste crab shells. The FT-IR absorption band at 3646 cm−1 indicates the existence of −OH stretching vibration because of a water molecule present on the surface of the CaO catalyst. 3.6. Brunauer−Emmett−Teller (BET) Surface Area of CaO. Figure 9 represents the BET surface area of CaO derived

Figure 10. Effect of catalyst loading on biodiesel yield.

loading and oil to methanol molar ratio on biodiesel yield with and without the addition of cosolvent. As the results illustrate, there was a significant and sharp improvement in biodiesel yield by increasing loading of catalyst to 2.5 wt %. Maximum biodiesel yield (96%) was obtained at 2.5 wt % with the addition of cosolvent. Oil mixed with methanol forms a welldispersed emulsion, and a sufficient amount of catalyst provides proper contact, which leads to reactions resulting in a high yield of biodiesel;24 beyond 2.5 wt % of catalyst, there was no significant increase in biodiesel yield. This could be attributed to the fact that catalyst makes the reaction mixture more viscous, causing difficulty in mass transfer.25 Transesterification of triglycerides is a reversible process, and excess quantities of methanol facilitate biodiesel conversion26 because methanol molecules will contact easily with triglycerides. High yield (96%) of pure biodiesel occurred at an oil to methanol ratio of

Figure 9. BET of calcium oxide (CaO) derived from waste crab shells.

from crab shells. BET of CaO was measured with nitrogen gas adsorption−desorption isotherms at −196 °C. The surface area of CaO derived from crab shells was 16.01 m2/g, which was calculated from the isotherm linear plot drawn between relative pressure (P/Po) and quantity of nitrogen adsorbed (cm3/g STP). According to previous work, calcium oxide (CaO) derived from pulverized limestone was found to have a surface area of 13.00 m2/g, which is slightly less than that found in the present work (calcium oxide derived from crab shells). This high surface area of CaO derived from crab shells is one of the 2105

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Journal of Agricultural and Food Chemistry 1:10, beyond which the yield begins to stagnate or ebb. The high molar ratio of methanol interferes with the separation of glycerol. The glycerol produced in the reaction diffuses in excess methanol and remains in the solution, driving back the reversible reaction and lowering the yield.27 Moreover, in each experiment, it was also observed that the addition of cosolvent contributes significantly to an increase in yield. 3.9. Effect of Reaction Temperature on Biodiesel Yield. The transesterification of fish oil using 2.5 wt % of CaO catalyst was performed at temperatures of 35−85 °C with an oil to methanol ratio of 1:10, reaction time of 90 min, and a stirrer speed of 650 rpm. Figure 11 represents the effect of

Figure 12. Effect of reaction time on biodiesel yield.

addition of cosolvent. Moreover, the presence of cosolvent was found to increase the yield for all of the tested reactions. 3.11. Effect of Stirrer Speed on Biodiesel Yield. Mixing is important in transesterification reactions because oils and fats are immiscible in solid catalysts and partially soluble in alcohol. Experiments were conducted in which stirrer speed was varied between 350 and 850 rpm while other parameters were kept constant: the catalyst loading was kept at 2.5 wt %, the oil to methanol ratio at 1:10, and the reaction temperature at 65 °C for 90 min. Figure 13 represents the effect of stirrer speed on Figure 11. Effect of reaction temperature on biodiesel yield.

temperature on the biodiesel yield with and without the addition of cosolvent. There was a gradual increase in biodiesel yield on increasing the temperature from 35 to 65 °C. The optimum temperature was found to be 65 °C with the addition of cosolvent because high biodiesel yield occurred at this temperature. Due to the high viscosity of oils, methanolysis is usually performed near the boiling point of methanol (65 °C) to decrease viscosity, enhance mass transfer, and increase reactivity of reactants.28 Temperature has a significant effect on the reaction rate, but after a threshold temperature (65 °C), the biodiesel yield starts to decrease. When the temperature was increased beyond 65 °C, no significant effect on biodiesel yield was observed; rather, the yield was decreased to some extent. This may be due to vaporization of methanol, which leads to reduced contact with the reactants. 3.10. Effect of Reaction Times on Biodiesel Yield. Reaction time required for transesterification depends on the reaction temperature as well as on the degree of mixing.29 Experiments were conducted by varying the reaction time in the range of 30−130 min at a catalyst loading of 2.5 wt %, a reaction temperature of 65 °C, an oil to methanol ratio of 1:10, and a stirrer speed of 650 rpm. Figure 12 represents the effect of reaction time on biodiesel yield with and without the addition of cosolvent. The yield showed improvement upon increasing the reaction time to 90 min. Increasing the time beyond 90 min led to a slight decrease in yield. This is because a longer reaction time favors reverse reaction of hydrolysis of esters along with soap formation from fatty acids.30 Hence, controlling the reaction time is critical for enhancing yield. The optimal reaction time for transesterification of fish oil was found to be 90 min at 65 °C and 650 rpm along with the

Figure 13. Effect of agitation speed on biodiesel yield.

biodiesel yield with and without the addition of cosolvent. Initially, there is a significant increase in yield on increasing stirrer speed. This is because the reaction mixture exists in two phases and the agitation helps to intersperse oil and methanol, leading to relative homogenization and greater contact between reactants. High biodiesel yield, 95%, occurred at the optimum stirrer speed of 650 ppm. Increasing the stirring speed beyond the optimum value led to no significant increase in yield due to vaporization of methanol, reducing its contact with other reactants. In each experiment, it was found that the addition of cosolvent gave a higher yield. The presence of cosolvent accelerates the homogenization of the two-phase system into a single phase. Consequently, it helps obtain a higher yield of biodiesel at minimum stirrer speed. 2106

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3.13. Separation and Purification. The reaction mixture was poured into a separating funnel after completion of the transesterification reaction to separate biodiesel from its byproducts. Biodiesel was taken from the separating funnel after clear separation through gravity and was washed with hot distilled water. The water remaining after washing was removed with a rotavapor, and the biodiesel was centrifuged to remove trace amount of solid particles. Thereafter, each characterization of biodiesel was done according to ASTM standards. Physical and chemical properties of synthesized biodiesel are provided in Table 4; the density was reduced from 0. 0.899

3.12. Effect of Cosolvent on Biodiesel. The effect of cosolvent on biodiesel yield was observed by taking different cosolvents such as toluene, diethyl ether, hexane, THF, and acetone as shown in Figure 14. The cosolvent to methanol

Table 4. Physical and Chemical Properties of Waste Fish Oil Biodiesel property color acid value density at 15.5 °C boiling point cloud point pour point kinematic viscosity, at 40 °C flash point cetane number calorific value water content copper strip corrosion

Figure 14. Effect of cosolvents on biodiesel yield.

molar ratio was fixed at 1:1, whereas other factors such as the methanol:oil ratio (1:10), reaction temperature (65 °C), stirrer speed (650 rpm), and catalyst loading (2.5%) were kept constant. The reaction mixture exists as a two-phase system in which methanol exhibited a hydrophilic nature and fish oil exhibited a hydrophobic nature. This immiscibility between alcohol and oil can be reduced by using cosolvents31,32 to drive the reaction mixture toward the product side. The molar ratio (methanol:oil) of the reaction mixture is a more important factor for the production of biodiesel because the transesterification process is reversible;33 to shift the reaction to the product side, we need to use a greater amount of methanol in the reaction mixture. Instead of using a greater amount of methanol, cosolvent was added to the reaction mixture, which reduced not only the amount of methanol but also other factors such as reaction time, reaction temperature, and stirrer speed. Among all of the cosolvents, the biodiesel yield (95%) was highest in the case of THF. THF causes the reaction mixture (oil phase and alcohol phase) to be more homogeneous, and also it reduced the energy consumption. Therefore, we selected THF as cosolvent for the synthesis of biodiesel. Optimization of THF determined and was found maximum at 1:1 (cosolvent:alcohol) as shown in Figure 15.

unit mg KOH/g g/cm3 °C °C °C mm2/s °C cal/g %

ASTM standard ASTM D 664 ASTM D 1298 ASTM D 1510 ASTM D 97 ASTM D 445 ASTM ASTM ASTM ASTM ASTM

D 93 D613 D 4809 D 2709 D 130

value yellowish red 1.78 0.869 356 1.02 −1 4.99 150 9650 0.001 no corrosion observed

(waste fish oil) to 0. 869 (biodiesel), flash point was reduced from 270 (waste fish oil) to 150 (biodiesel), and pour point was reduced from 13 (waste fish oil) to 1.02 (biodiesel). Kinematic viscosity (at 40 °C) was reduced from 25.51 (waste fish oil) to 4.99 (biodiesel) because the density is directly proportional to viscosity. The calorific value of synthesized biodiesel was 9650 cal/g, and the moisture content was found to be 0.001%. This synthesized biodiesel was checked with a copper strip, and no corrosion was observed. Calcium oxide derived from waste crab shells delivered good results for the synthesis of biodiesel when compared with other catalysts derived from waste materials as shown in Table 5. 3.14. Reusability and Leaching Property of Catalyst. The leaching effect of CaO derived from waste crab shells catalyst was determined in synthesized biodiesel using waste fish oil. It was ratified by elemental analysis using SEM/EDS analysis after completion of the reaction. It was revealed that there was no change in calcium and oxygen amounts. Further examination of catalyst leaching was conducted,34 and no catalyst leaching was observed. After separation of methanol, catalyst was used in the transesterification reaction, and it was found that there was no change in its activity.35 After a washing with methanol, the catalyst was reused in two manners. In the first process, the catalyst was calcined at 750 °C and reused up to five runs, and in the second process, it was reused without calcination up to five runs as shown in Figure 16. Calcined catalyst gave more conversion than one without calcination. Consequently, it was inferred that calcination provided better activity of the sites of catalyst and hence amended the biodiesel production. 3.15. Conclusion. Biodiesel was synthesized from waste fish oil through esterification and transesterification reactions. A novel heterogeneous solid base catalyst (calcium oxide (CaO))

Figure 15. Optimization of THF (cosolvent) with methanol (solvent). 2107

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Journal of Agricultural and Food Chemistry Table 5. Summary of Different Kinds of Waste Catalysts Used in the Synthesis of Biodiesel reaction conditions catalyst CaO CaO CaO CaO CaMg(CO3)2 KAl(SO4)2 K2O β-Ca3(PO4)2 hydroxyapatite

waste material

catalyst amount (wt %)

crab shells snail mollusc shells exoskeleton (Pila globosa) mollusc shells chicken egg shells dolomite alum coal fly ash loaded KNO3 rohu fish (Labeo rohita) bone sheep bone

methanol to oil molar ratio

2.5 2 4

reaction temperature (°C)

reaction time (h)

conversion (C) or yield (Y)

65 60 60

1.5 8 5

Y = 96.6% C = 99.58% C = 97.8%

12:1 6:1 10:1

3 3 7.09 15 1.01 20

9:1 6:1 18:1 15:1 6.27:1 18:1

65 67.5 170 70 70 65

3 3 12 8 5 4

Y = 95% Y = 91.8% Y = 92.5% C = 87.5% Y = 97.7% C = 96.78%

Notes

The authors declare no competing financial interest.

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Figure 16. Reusability of catalyst with and without calcination.

was derived from waste crab shells and characterized with SEMEDX, XRD, FT-IR, and TGA/DTA. Synthesized biodiesel was characterized with proton NMR and FT-IR. Free fatty acid composition of waste fish oil was determined using GC-MS. The effects of various parameters such as stirrer speed, temperature of the reaction, reaction time, and catalyst loading on biodiesel conversion and yield were studied. The effect of cosolvent on biodiesel was further studied by using different solvents such as toluene, diethyl ether, hexane, THF, and acetone. A high yield of 96.6% pure biodiesel was obtained at 2.5 wt % of synthesized catalyst and 1:12 oil:methanol molar ratio at 65 °C for 90 min. Reusability of catalyst up to five times without loss of activity was observed. No catalyst leachability was observed in transesterification reactions. The qualities of biodiesel were ascertained per ASTM biodiesel standard and obtained near specification.

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AUTHOR INFORMATION

Corresponding Author

*(Y.C.S.) E-mail: [email protected]. Phone: +91 542 6702865. Fax: +91 542 6702876. ORCID

Yogesh Chandra Sharma: 0000-0003-1331-9523 Funding

We acknowledge the support of Central Instrument Facilities, Indian Institute of Technology (BHU), India, and also thank the Institute for financially supporting an assistantship through the Institute Fellowship. We also acknowledge financial assistance from DST as DST-IBSA project (GP/LT/Chemistry/15-16-01). 2108

DOI: 10.1021/acs.jafc.6b05608 J. Agric. Food Chem. 2017, 65, 2100−2109

Article

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DOI: 10.1021/acs.jafc.6b05608 J. Agric. Food Chem. 2017, 65, 2100−2109