ARTICLE pubs.acs.org/IECR
Biodiesel from Zophobas morio Larva Oil: Process Optimization and FAME Characterization Dong Leung,† Depo Yang,*,†,§ Zhuoxue Li,† Zhimin Zhao,† Jianping Chen,‡ and Longping Zhu†,§ †
School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, People’s Republic of China School of Chinese Medicine, University of Hong Kong, HongKong, People’s Republic of China § Guangdong Technology Research Center for Advanced Chinese Medicine, Guangzhou 510006, People’s Republic of China ‡
ABSTRACT: The advancement of biodiesel production emphasizes the finding of new, low-cost, and plentiful raw materials. Insects, as one of the most plentiful biological resources worldwide, could be potential candidates for biodiesel production. In this study, Zophobas morio (Coleoptera: Tenebrionidae) was evaluated as an insect feedstock, attempting to prove the feasibility of producing qualified biodiesel. The oil content in dried Z. morio larvae was found to be 33.80 wt %. Biodiesel from Z. morio larva oil was prepared by acid esterification followed by alkaline transesterification. The parameters of the reaction were optimized at 1.25 wt % potassium hydroxide catalyst, a 5:1 methanol to oil ratio, a reaction temperature of 50 °C, and a reaction time of 45 min. Under these conditions, the maximum fatty acid methyl ester yield was 92.35 wt %. The biodiesel obtained was verified to be in compliance with the ASTM D6751 standard. This study supports the use of Z. morio larva oil as a viable and valuable raw feedstock for biodiesel production and indicates the potential use of insects as feedstock for applications in energy production.
1. INTRODUCTION As a renewable substitute for petroleum-based diesel, the production of biodiesel has become a global concern because of an increase in energy demands and the limited supply of conventional fossil diesel.1 As an environmentally friendly energy resource, biodiesel is a mixture of fatty acid methyl esters or ethanol esters that are commonly derived from renewable feedstocks such as animal fat, plant oil, and waste grease. Biodiesel can decrease the emission of carbon dioxide, hydrocarbons, and other harmful materials that cause damage to the environment.2 Since edible oils from animals and plants have competing uses, research has focused on the relatively low-cost and otherwise useless nonedible oils such as Croton megalocarpus oil and Jatropha curcas oil.3 5 However, the production of these oils demands large habitant areas and a long growth duration, which prevents substantial oil production. With the advantages of low price and the ability to recycle waste material,6 cooking oil has been proposed as a potential source. The drawback to the use of cooking oil for biodiesel production is the need for long-term, sustainable collection and refining systems. In addition, microalgae, currently considered to be one of the potential raw resources as it demonstrates a higher photosynthetic efficiency, greater biomass production, and a higher growth rate than other sources,7,8 also been restricted from practical application because of the high cost of cultivation. Therefore, it is desirable to find new raw materials for use as biodiesel resources that are not only easy to mass-produce, but also have a low cost of production. Because insects are one of the most plentiful biological resources worldwide, a great number of which have comparably shorter life cycles than plants and animals, we have proposed the use of insects as potential resources for biodiesel production. In this study, we aim to evaluate the potential use of Zophobas morio larva oil (ZMLO) as a viable and valuable raw feedstock for biodiesel production. Z. morio (Coleoptera: Tenebrionidae), r 2011 American Chemical Society
a species of beetle that undergoes complete metamorphosis and whose larvae are known by the general name superworm or zophobas, is commonly used as food for domesticated reptiles and in the protein powder industry. Z. morio has a total life cycle that lasts nearly 6 months and includes four stages: egg, larva, pupa, and adult. Generally, the Z. morio larva is 40 60 mm in length, and 5 6 mm in width at its maximum size. Fed on wheat bran and even plastic (as lately reported), its larvae prefer a dark place with an appropriate humidity ranging from 60 to 75%. Superworms can be raised throughout the year and will grow to full size within 2 months. The oil content in Z. morio larva was previously reported to be approximately 1/3 of its dry body weight, which is relatively higher than that of some other common insect species such as Bombyx mori (silkworms) and Lumbricus terrestris (earthworms).9 In this study, we evaluated the potential of ZMLO as a resource for the production of biodiesel, investigated factors affecting the production of biodiesel, and determined the optimal process conditions for the conversion of fatty acid methyl esters. Finally, the properties of biodiesel produced from ZMLO were determined as per the ASTM D6751 specifications.
2. EXPERIMENTAL SECTION 2.1. Materials. Z. morio larvae were bought from the FangCun aquarium market in Guangzhou, People’s Republic of China. After drying in a 55 °C oven for 48 h, the insects were smashed and immersed in an amount of n-hexane for fat extraction for 12 h. The acid value (AV) of the final ZMLO was 2.18 mg of KOH g 1. Received: July 3, 2011 Accepted: December 14, 2011 Revised: December 11, 2011 Published: December 14, 2011 1036
dx.doi.org/10.1021/ie201403r | Ind. Eng. Chem. Res. 2012, 51, 1036–1040
Industrial & Engineering Chemistry Research
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Table 1. ZMLO Fatty Acid Profile and Comparison with Other Oils ZMLO (wt %)
chicken fat12 (wt %)
mutton fat12 (wt %)
soybean oil13 (wt %)
palmitic acid (C16:0)
32.74
24.65
28.10
11.90
3.50
palmitoleic acid (C16:1)
2.16
6.92
0.42
0.30
0.10
heptadecanoic acid (C17:0)
0.58
0.14
0.14
a
a
stearic acid (C18:0)
9.36
6.25
27.20
4.10
0.90
fatty acid composition
oleic acid (C18:1)
29.43
45.18
31.28
23.26
54.10
linoleic acid (C18:2)
22.53
12.58
1.59
54.20
22.30
linolenic acid (C18:3)
0.85
0.38
0.88
6.31
a
water content (μg g 1) iodine number
454 73.33
saponification value
199.88
peroxide value molecular weight a
rapeseed oil13 (wt %)
a 851.29
Not detected.
Figure 1. Effect of methanol to oil ratio on methyl ester conversion: 1.0 wt % catalyst, 50 °C reaction temperature, and reaction time of 45 min at an agitation speed of 3000 rpm.
All analytical grade reagents (potassium hydroxide, methanol, n-hexane, sodium sulfate anhydrous) were purchased from Tianjin Baishi Chemical Industry Co. Ltd. 2.2. Experimental Procedure. 2.2.1. Acid Pretreatment. With a detected initial AV of 2.18 mg of KOH g 1 oil, ZMLO required pretreatment by acid catalyst esterification to lower the AV. Initially, ZMLO (120 g, 0.14 mol) and methanol (45 mL, 1.11 mol) were added to a flask in a ratio of 1:8 with an amount of sulfuric acid (0.12 g, 1 wt % ZMLO).10 The contents were heated at 70 °C for 2 h. Then the mixture was allowed to settle for 2 h, and the methanol water fraction in the top layer was removed. The oil phase was washed with distilled water until a neutral pH was achieved. This procedure was followed by the removal of the residual methanol by rotary evaporation. 2.2.2. Base-Catalyzed Transesterification. A flask containing ZMLO (10 g) was heated to the desired temperature in an oil bath. The flask was constantly agitated at a speed of 3000 rpm throughout the experiment. A calculated amount of potassium hydroxide, used as the catalyst in this study, was dissolved in a corresponding amount of methanol in a volumetric flask. Once the oil reached the desired temperature, the prepared potassium hydroxide methanol solution was added to the oil, and that moment was considered the starting time for the reaction. When the reaction had proceeded for the desired duration, the reaction flask was transferred to a beaker containing water at 15 °C to cool the reaction mixture. After settling for 24 h, two distinct liquid phases formed, with a crude ZMLO methyl ester phase at the top and a glycerol phase remaining at the bottom of the flask. To ensure a high rate of transesterification, the timing of the removal
of the glycerol phase during the transesterification process is critical.11 The ZMLO methyl ester layer was washed several times with warm deionized water (70 °C) until it reached neutrality. In the final step, the removal of methanol and water was carried out by heating the solution at 100 °C in a decompression rotary evaporator. The purified ZMLO methyl esters were tested to confirm that they possessed the properties of biodiesel. 2.3. Analytical Methods. 2.3.1. Acid Value. The acid values of the reaction mixture in the acid pretreatment stage and the basecatalyzed transesterification were determined by the acid base titration technique. 2.3.2. FAME Properties Evaluation. The fatty acid methyl ester (FAME) yield was determined as per the method specified in EN 14103. The properties of biodiesel produced from ZMLO were determined as per the ASTM D6751 specification.
3. RESULTS AND DISCUSSION 3.1. Oil Extraction. The percentage of dehydrated ZML accounted for the weight of the fresh insect was 43.05 wt %, and the oil content from dry Z. morio larva bodies was tested to be 33.80 wt %. Consequently, 1 kg of fresh Z. morio larvae could yield approximately 145.5 g of ZMLO. 3.2. Acid Pretreatment. The preparation of ZMLO methyl ester was carried out by an acid pretreatment to lower the AV below 2.0 mg of KOH g 1. Having successfully achieved an AV of 0.55 mg of KOH g 1, conversion of the ZMLO could continue with the base-catalyzed transesterification. 3.3. Properties of ZMLO. After completion of the series of reactions resulting in the production of ZMLO methyl esters, the fatty acid composition of ZMLO was determined by GC MS analysis. Table 1 shows a comparison between the fatty acid composition of ZMLO and several widely used animal fats, such as chicken fat and mutton fat, together with soybean oil and rapeseed oil, the two most popular plant oils used for biodiesel production in the USA and Europe, respectively. The three primary fatty acids found in all five oils are palmitic acid, oleic acid, and linolenic acid. Palmitic acid (C16:0) was found to be the major fatty acid in ZMLO, at a composition of 32.74%, while the oleic acid (C18:1) content was found to be 29.43%, a little higher than that in soybean oil. The linoleic acid (C18:2) content was similar to that in rapeseed oil at 22.53%. The ratio of saturated 1037
dx.doi.org/10.1021/ie201403r |Ind. Eng. Chem. Res. 2012, 51, 1036–1040
Industrial & Engineering Chemistry Research
Figure 2. Effect of catalyst amount on methyl ester conversion: 5:1 methanol to oil ratio, 50 °C reaction temperature, and reaction time of 45 min at an agitation speed of 3000 rpm.
fatty acids (C16:0, C17:0, C18:0) to unsaturated fatty acids (C16:1, C18:1, C18:2, C18:3) in ZMLO was found to be 32.68:54.97. Heptadecanoic acid (C17:0), which can be found in ZMLO, does not commonly exist in plant oils. Properties such as the water content, iodine number, saponification value, peroxide value, and molecular weight of ZMLO are also given in Table 1. 3.4. Effect of the Methanol to Oil Ratio. The transesterification reaction was studied at five different mole ratios varying from 3:1 to 11:1 with the other factors kept constant: 1.0 wt % catalyst, temperature of 50 °C, and reaction time of 45 min. Figure 1 depicts the effect of the methanol mole ratio on the conversion of methyl esters. Although the stoichiometric methanol to oil mole ratio is 3:1, excess methanol can drive the reaction toward products yielding more methyl esters, as transesterification is a reversible reaction.14 A tiny phase separation was observed at a ratio of 3:1; a small amount of glycerol was generated, and the quantity of ester conversion was found to be the lowest, 79.6%. The yield of methyl esters reached a maximum of 89.28% at a methanol to oil ratio of 5:1 and then decreased at ratios above 5:1. During the process, it became obvious that the residual methanol made the ester phase more obscure when the methanol to oil ratio was 9:1 and above. This observation could be explained by the fact that the excess methanol worked as an emulsifier to increase the solubility of glycerol, which makes the separation of glycerol from the ester layer more complicated together with an apparent loss of ester products.15 A methanol to oil ratio of 5:1 was concluded to be the optimal condition from both an efficiency and an economic point of view. 3.5. Effect of Catalyst Concentration. The catalyst concentration is one of the vital factors influencing the conversion efficiency of the transesterification of fatty acids. The concentration of potassium hydroxide was varied at 0.5, 0.75, 1.0, 1.25, and 1.5 wt %. The other reaction conditions were as follows: temperature of 50 °C, reaction time of 45 min, and optimal methanol to oil ratio of 5:1, as described in section 3.4. The effect of the catalyst concentration on the conversion of methyl esters is depicted in Figure 2. A low concentration (0.5 wt %) led to a yield of 79.24% due to insufficient active catalyst centers. The yield was increased and reached a maximum at 1.25 wt % but then decreased at higher catalyst concentrations because of the occurrence of saponification. These results agree with research using jatropha, karanja, and polanga oils, which found that an excess amount of catalyst favors the formation of soap and increases the viscosity of the product.15,16
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Figure 3. Effect of temperature on methyl ester conversion: 5:1 methanol to oil ratio, 1.25 wt % catalyst amount, and reaction time of 45 min at an agitation speed of 3000 rpm.
Figure 4. Effect of reaction time on methyl ester conversion: 5:1 methanol to oil ratio, 1.25 wt % catalyst, and 50 °C reaction temperature at an agitation speed of 3000 rpm.
3.6. Effect of Reaction Temperature. A higher reaction temperature can decrease the viscosity of oil and result in an increased reaction rate. In this study, the experiments were conducted using the methanol to oil ratio and the catalyst amount that were determined to be optimal, while the 45 min reaction time remained constant. The effect of the reaction temperature on the methyl ester yield is shown in Figure 3. Increasing the temperatures from 20 to 50 °C, the yield increased 4.67%. It was 91.9, 89.27, and 87.23% at the temperatures of 50, 35, and 20 °C, respectively. However, if the temperature increased to 65 °C, there was a slight reduction in the conversion as a result of an increase of saponification and methanol evaporation. This observation is in agreement with previous studies indicating that a low temperature requires a greater reaction time to obtain a higher ester yield.17 High temperatures were found to lead to the generation of bubbles that could be observed during the research; less methanol remained in the liquid phase to take part in the reaction. Therefore, 50 °C was chosen as the optimum temperature. 3.7. Effect of Reaction Time. The effect of reaction time on the yield of methyl esters was studied at 15 min intervals ranging from 15 to 60 min with the previously mentioned optimal reaction conditions. The results are presented in Figure 4. The findings revealed that the methyl ester yield increased up to a reaction time of 45 min. The reaction could not properly take place in the 15 and 30 min intervals, showing low yields of 85.58 and 89.52%, respectively. The 45 min reaction time was considered optimal, at which a 92.35% yield of fatty acid methyl esters was identified. The yield decreased at reaction times in excess of 45 min because, at the longer time intervals, the catalyst would react with the fatty acids, causing additional saponification. 3.8. Properties of the Produced Biodiesel from ZMLO. All physical and chemical properties were experimentally evaluated 1038
dx.doi.org/10.1021/ie201403r |Ind. Eng. Chem. Res. 2012, 51, 1036–1040
Industrial & Engineering Chemistry Research
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Table 2. Fuel Properties of Biodiesel Produced from Z. morio Larva Oil properties
test method
ZMLO biodiesel
soybean biodiesel19
flash point (°C)
130 min
ASTM D93
159
178
water and sediments (vol %)
0.05 max
ASTM D2709
