Environ Sci Pollut Res DOI 10.1007/s11356-015-4824-9
POLLUTION CONTROL TECHNOLOGIES AND ALTERNATE ENERGY OPTIONS
A study on production of biodiesel using a novel solid oxide catalyst derived from waste Samrat Majhi 1 & Srimanta Ray 1
Received: 24 March 2015 / Accepted: 1 June 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract The issues of energy security, dwindling supply and inflating price of fossil fuel have shifted the global focus towards fuel of renewable origin. Biodiesel, having renewable origin, has exhibited great potential as substitute for fossil fuels. The most common route of biodiesel production is through transesterification of vegetable oil in presence of homogeneous acid or base or solid oxide catalyst. But, the economics of biodiesel is not competitive with respect to fossil fuel due to high cost of production. The vegetable oil waste is a potential alternative for biodiesel production, particularly when disposal of used vegetable oil has been restricted in several countries. The present study evaluates the efficacy of a low-cost solid oxide catalyst derived from eggshell (a food waste) in transesterification of vegetable oil and simulated waste vegetable oil (SWVO). The impact of thermal treatment of vegetable oil (to simulate frying operation) on transesterification using eggshell-derived solid oxide catalyst (ESSO catalyst) was also evaluated along with the effect of varying reaction parameters. The study reported that around 90 % biodiesel yield was obtained with vegetable oil at methanol/oil molar ratio of 18:1 in 3 h reaction time using 10 % ESSO catalyst. The biodiesel produced with ESSO catalyst from SWVO, thermally treated at 150 °C for 24 h, was found to conform with the biodiesel standard, but the yield was 5 % lower compared to that of the untreated oil. The utilization of waste vegetable oil along with waste eggshell as catalyst is significant for improving the overall economics Responsible editor: Bingcai Pan * Srimanta Ray [email protected]; [email protected] 1
Department of Chemical Engineering, National Institute of Technology Agartala, Jirania, Tripura 799055, India
of the biodiesel in the current market. The utilization of waste for societal benefit with the essence of sustainable development is the novelty of this work. Keywords Waste vegetable oil . Waste eggshell . Solid oxide catalyst . Transesterification . Biodiesel
Introduction The recent energy crisis across the globe, the massive escalation of the world energy demands, the forecasted depletion of the fossil energy sources, and the rising environmental concerns to limit the exhaust emissions have motivated the search for cleaner and efficient economic and sustainable alternative fuels for over a decade (Hoekman and Robbins 2012; Yahyaee et al. 2013). One of the alternative fuels which have gained significant attention is derived from vegetable oil through transesterification, also known as biodiesel. The biodiesel has renewable nature, produces lower emission, but possesses high flash point and high cetane number compared to the petroleum-based diesel (Kouzu et al. 2008). The vegetable oil or triglycerides (TGs) of fatty acids, on transesterification with short chain alcohol (C1–C3), produces fatty acid alkyl esters which are otherwise known as biodiesel (Khayoon et al. 2012; Zhang et al. 2010). Biodiesels produced through transesterification of vegetable oils with methanol (C1) are referred to as fatty acid methyl esters (FAME) (Zakaria and Harvey 2012; Qian et al. 2013). The triglycerides, the key raw material for FAME, having vegetable or plant origin are a sequestered carbon form. The transesterification of the triglycerides to FAME and the subsequent combustion of FAME for carbon release is therefore a sustainable way of carbon recycling (Khayoon and Hameed 2013). In spite of the favorable causes, the commercial large-
Environ Sci Pollut Res
scale production of FAME is still not considered viable, because of various socioeconomic issues. The escalating prices of raw materials and the increased cost of production are the vital ones. The cost of vegetable oil and the catalyst determines the cost of the produced biodiesel (Behçet 2011; Lin et al. 2011). In addition, utilization of edible vegetable in the biodiesel industry influences the global oil market and the price. As a result, in some of the developing countries with limited agricultural landmass per capita, the utilization of edible vegetable oil for the production of biodiesel is not profitable and even prohibited (Lin et al. 2011). To address the scarcity of feedstock for biodiesel or FAME production and to diminish the food versus fuel dispute, recent research interest have been directed towards the exploration of worthy alternatives, apart from edible vegetable oil (Pienaar and Brent 2012; Lotero et al. 2005). In this regard, waste vegetable oil from cooking or frying holds great possibilities. Waste cooking oils are generated in substantial quantities every year from industrial and commercial establishments during preparation of food products (Charpe and Rathod 2011). Used waste cooking oil is often not properly disposed, resulting in environmental pollution and economic losses. Improvement in process technologies in recent years resulted in transesterification of waste vegetable oil and production of FAME from cheaper alternative feedstock (Canakci 2007). However, the elevated cost of FAME production due to the cost of catalyst is still an economic impediment in the biodiesel production. The homogeneous acid or base catalysts are commonly employed in transesterification of vegetable oil to FAME. The base catalysts are preferred due to lower transesterification temperature. But separation of the homogenous base catalyst from the final reaction mixture is difficult and requires neutralization. The commercially used base catalyst are also hazardous and corrosive in nature, therefore require large amount of solvent and energy for effluent treatment (Georgogianni et al. 2009). Therefore, a need for the replacement of the homogenous base catalyst was felt and the heterogeneous solid oxide catalysts became relevant. Lower consumption of the catalyst, easy separation from the final reaction mixture, catalyst re-usability, less environmental issues, and low cost of production are some of the major advantages of heterogeneous solid oxide catalyst. Accordingly, heterogeneous solid oxide catalysts have gained great research interest. The heterogeneous solid oxide that catalyzed transesterification of vegetable oil have been reported with different alkali earth metal oxides and hydroxides (Granados et al. 2007; Liu et al 2008; Veljković et al. 2009), alumina supported salts (MacLeod et al. 2008; Xie and Li 2006; Xie et al. 2006a, b) and zeolites (Xie et al. 2006a, b) under variable reaction conditions. Among the different solid oxide catalysts investigated, calcium oxide (CaO) has shown great promise in
transesterification. Also, CaO being widely available in nature in the form of lime has enhanced economic advantages. Other than lime, the eggshell is a promising source of CaO. Large quantities of eggshell waste are generated routinely from food industry, which add up to the solid waste and are associated with disposal issues. The utilization of waste eggshell as CaO source in heterogeneous transesterification is linked with environmental and economic benefits, and also promotes improve sustainability of the process through value addition of waste (Suryaputra et al. 2013). Hence, the objective of the present study is to evaluate the efficacy of the waste eggshell-derived solid oxide catalyst (ESSO catalyst) in heterogeneous transesterification of waste vegetable oil produced by simulating the prolong thermal treatment like frying. The thermal treatment duration on vegetable oil was varied and the impact on transesterification efficacy, FAME quality with ESSO catalyst was assessed. The effect of varying reaction parameters on the FAME quality and yield was also evaluated. The systematic evaluation of waste eggshell-based ESSO catalyst together with different qualities of waste vegetable oil on transesterification efficacy and FAME or biodiesel quality is the novelty of this study. In addition from the waste management perspective, producing FAME from waste frying oil and using waste eggshell-based catalyst is expected to raise the economic viability and sustainability quotient of the biodiesel as alternative fuel.
Materials and methods Materials Soybean oil was chosen as the vegetable oil feedstock for the study. Soybean oil used in the study was procured locally from available commercial brands of edible soybean oil (Agartala, Tripura, India) and the brand was not varied throughout the study. The approximate composition of fatty acid in the soybean oil is summarized in Table 1. Analytical grade methanol (99.5 % purity, Qualigens Fine Chemicals, Mumbai, India) was used for the transesterification reaction. Eggshell-derived solid oxide catalyst (ESSO catalyst) used in the study was
Table 1 Fatty acid composition of soybean oil (Canakci 2007; Liu et al. 2008; Samart et al. 2009)
Name of the fatty acid
Fatty acid
Percent weight
Palmitic Stearic Oleic Linoleic Linolenic
16:1 18:0 18:1 18:2 18:3
11.75 3.15 23.26 55.53 6.31
Environ Sci Pollut Res
prepared from the eggshells (chicken) collected from the waste of the food canteen of the institute (Agartala, Tripura, India).
fatty acid methyl ester (FAME) and glycerol (Eq. 1). The rate of conversion of triglycerides to FAME can be accelerated by using suitable catalyst.
Simulated waste vegetable oil
Triglyceride ðSWVOÞ þ methanol þ ESSO
In order to understand the impact of thermal treatment of soybean oil, on the FAME quality and FAME yield, simulated waste vegetable oil (SWVO) is produced by thermally treating the soybean oil, simulating the cooking (frying) operation. The SWVO is later used for transesterification reaction. To prepare SWVO, thermally untreated soybean oil samples are subjected to thermal treatment in glass reactors with temperature kept invariant at 150 °C. The duration of the thermal treatment was varied from 24–72 h. The thermally untreated soybean oil sample is considered as SWVO with 0 h of treatment exposure. All the SWVO samples are characterized in terms of oil properties and assessed for FAME yield in transesterification reaction. Catalyst preparation The collected eggshells were washed in cold tap water; the membrane was separated and discarded. The washed eggshells were subsequently dried for 48–50 h in the direct sun before subsequent treatment. The dried egg shells were crushed and sieved. The sieved particle has particle size between 0.074 mm (200 meshes) to 0.174 mm (100 meshes). The eggshell particles were thereafter thermally stabilized and calcined in a muffle furnace (Simeco, Kolkata, India) in static air condition at a designated temperature for specific time duration and thereafter aircooled to ambient temperature to prepare the eggshellderived solid oxide (ESSO) catalyst. The calcination temperature was varied from 750–950 °C, based on the findings reported in the literature (Viriya-Empikul et al. 2012). The calcination duration was maintained invariant at 2 h. The thermally synthesized catalyst was used as-is for transesterification. The ESSO catalyst was stored in hermetically sealed container for subsequent use and characterization.
¼ fatty acid methyl ester ðFAMEÞ þ glycerol þ ESSO
ð1Þ
FAME was synthesized in a batch-type transesterification reaction with ESSO catalyst. Transesterification experiments were carried in a distillation flask fitted with a counter current water cooled condenser and a methanol reflux arrangement. The distillation flask was kept in a water bath equipped with a thermometer to maintain the reaction temperature. The reaction liquid was continuously stirred at 200±50 rpm with a magnetic stirrer and magnetic stirred bar. The schematic of the experimental setup is shown in Fig. 1. According to the results of Liu et al. (2008), 65 °C was reported to be the optimum temperature for the transesterification of oil. Thus, the reaction temperature was kept invariant at 65±2 °C for all reactions. Transesterification is a reversible reaction. Accordingly, increased methanol/oil ratio is expected to favor FAME formation in transesterification reaction. Therefore, the methanol/oil ratio is considered as an experimental parameter and is varied to study the effect on the yield of FAME from transesterification of different SWVO. The other experimental parameters that varied include amount of catalyst (catalyst loading), type of catalyst (catalyst calcination temperature), and reaction time. SWVO subjected to different extent of thermal treatment (duration of treatment) were also assessed. The levels at which various experimental parameters are varied in one factor at a time approach is summarized in Table 2. After the completion of the reaction, the product was allowed to settle overnight to produce two distinctive liquid phases, i.e. methyl ester phase at the top and glycerol phase at the bottom. The FAME is then separated from the glycerol phase by using a separating funnel, and then stored for the subsequent analytical tests. Experiments were conducted in triplicates to estimate the error (uncertainty).
Transesterification procedure Transesterification reaction of fat and oil (triglycerides) is such a reaction which implicates replacement of glycerol molecule from triglycerides (an ester of glycerol) by another alcohol molecule with glycerol produced as a byproduct. Stoichiometry of transesterification shows that 3 mol of alcohol reacts with 1 mol of triglyceride to give 3 mol of fatty acid esters and 1 mol of glycerol. Transesterification of triglyceride with methanol produces
Catalyst characterization The characterization of eggshell catalyst was performed by infrared spectroscopy using Fourier transformation analysis (FT-IR). The measurement of absorbance in FTIR was performed using scans in the range of 400 to 3900 cm −1 . The formation and transformation of the ESSO catalyst with calcination temperature was
Environ Sci Pollut Res Fig. 1 Schematic representation of the experimental setup for transesterification
determined by the peak-matching technique, using corresponding values of the peak from the standard IR spectral list.
Result and discussion Effect of thermal treatment on SWVO Effect on viscosity
Analytical methods The specific gravity of SWVO and FAME sample were determined using specific gravity bottle following standard specific gravity determination protocol. The viscosity of FAME and SWVO samples were determined by Redwood viscometer (Simeco, Kolkata, India) in a modified protocol. The flash point and fire point of the FAME was determined using Penske-Martin closed cup apparatus. The pour point of FAME was determined using standard pour point apparatus. The FAME and SWVO samples were scanned in UV-visible spectrophotometer (Lambda 35, Perkin Elmer, Mumbai, India) between 200 to 700 nm to monitor the change in absorbance with respect to change in functional moieties. The FAME and SWVO samples were also analyzed in IR spectrophotometer using Fourier transformation between 400– 4000 cm−1 to confirm the transesterification and impact of reaction variables (oil type) on FAME. The formation of FAME group was monitored in 1300 to 1060 cm−1 wavenumber region. Table 2
The thermal treatment has been observed to have a profound effect on the properties of SWVO. The viscosity of SWVO increased significantly with increase in the duration of the thermal treatment (Fig. 2a). The increase in viscosity of thermally treated oil with treatment time may be attributed to the formation of polymerized or branched or oxidized products. The viscosity of FAME obtained from different SWVO (SWVO 0, 24, 48, and 72) that are subjected different thermal treatment duration is presented in Fig. 2b. The viscosity of FAME obtained from different SWVO also increased with the increase in the thermal treatment duration. Also, prolonging the thermal treatment of the oil was observed to reduce the transesterification yield (Fig. 2b). Increased polymerized product formation makes the SWVO difficult to transesterify and reduces the conversion of triglycerides into FAME. Thus, the duration of thermal treatment and the viscosity of SWVO were observed to have major impact on the yield of FAME.
Different experimental variables and their levels
Type of soybean oil
Treatment time of oil (hours)
Methanol/oil ratio (mole/mole)
Reaction time (hours)
Catalyst calcination temperature (°C)
Catalyst loading (% (w/w))
Thermally untreated oil SWVO-24 SWVO-48 SWVO-72
0 24 48 72
9:1 15:1 18:1
1 2 3 4
750 850 950
5 10 15
Environ Sci Pollut Res Fig. 2 Effect of thermal cycling on a viscosity of SWVO and b viscosity of FAME, and percent yield of FAME
Effect on specific gravity
UV-visible spectroscopic analysis
The specific gravity is an important parameter for biodiesel or FAME. Accordingly the standard viscosity values have been established for FAME in ASTM D6751, which is 0.86–0.90. FAME having density lower than the standard increase emission and damages the engine (Hoekman and Robbins 2012; Srivastava and Prasad 2000). High density FAME is also not desirable for fuel purpose. The duration of thermal treatment on SWVO was observed to increase the specific gravity of the oil (Fig. 3a). Transesterification of different SWVO from different thermal treatment showed a similar trend (Fig. 3b). The FAME produced from SWVO-0 and SWVO-24 has specific gravity within the acceptable range (ASTM standard), the specific gravity of FAME produced from SWVO-48 is at the upper limit of the standard, whereas, the specific gravity of FAME produced from SWVO-72 were beyond the acceptable range. Increased specific gravity of FAME from SWVO subjected to longer thermal treatm e n t i s l in k e d w i t h h i g h e r v i s c o si t y a n d l ow e r transesterification yield (Fig. 2b). Prolonged thermal treatment of vegetable oil polymerize, isomerize, and oxidize the fatty acid molecules and produce larger or branched or oxidized molecules resulting in increase in specific gravity, loss of functional groups, and reduced transesterification yield (Charpe and Rathod 2011).
The UV-visible spectroscopic analysis was performed to understand the transformation of the SWVO on thermal treatment. Monitoring SWVO samples in the UV spectrum furnished a good indication of the oxidation of oil with increase in thermal treatment duration. The increase in treatment duration exhibits a shift in the UV absorbance peak (Fig. 4a, b). The UV absorbance shift towards higher wavelength. The change in UV absorbance pattern is primarily due to the formation of products of oxidation which include trines, unsaturated ketones, aldehydes, and other secondary products of oxidation. The increase in absorbance is also noted with increase in thermal treatment time perhaps due to formation of conjugated dienes. The formation of oxidized and conjugated products explains the changes in the properties of the SWVO with increasing thermal treatment duration.
Fig. 3 a Effect of thermal cycling at 150 °C in the specific gravity of soybean oil. b Effect of thermal cycling at 150 °C in the specific gravity of FAME
FT-IR spectra analysis The transesterification product, i.e. FAME, is analyzed by infrared spectroscopy to confirm the FAME formation through functional group analysis. In transesterification, the methoxy-carbonyl group was formed in FAME substituting the carbonyl group in the SWVO. Figure 5a presents the FTIR spectral profile of the raw material, SWVO, and the product of transesterification, FAME. The absorption peak at
Environ Sci Pollut Res Fig. 4 a Effect of thermal cycling at 150 °C on soybean oil. b Effect of thermal cycling at 150 °C on soya-FAME
1103 cm-1 in the raw material, SWVO, due to the occurrence of C-CH2-O group in the SWVO disappears in FAME. Meanwhile, new absorption peaks at 1436 and 1197 cm−1 confirm the presence of –CH3 and O-CH3 groups in the FAME. The formation of the methoxy functional group confirmed the formation of FAME. Comparison among the various transesterification product (FAME) produced from different SWVO that are subjected different extent of thermal treatment showed diminishing fingerprint peak at 1197 cm−1, conforming lower yield of FAME from transesterification of SWVO subjected to longer thermal treatment (Fig. 5b). Effect of methanol/oil ratio According to the literature, the methanol/oil molar ratio for alkali-catalyzed process is near about 6:1, whereas for acid catalyzed reaction, the methanol/oil ratio rises up to 30:1 to ensure high conversion (Zhang et al. 2003). The methanol/oil ratio is varied at three levels, 9:1, 15:1, and 18:1, based on the literature data and preliminary results. The effect of varying methanol/oil ratio on the yield of FAME for SWVO-0 and SWVO-24 is shown in Fig. 6a, b. Increasing methanol/oil ratio increased the FAME yield. However, the FAME yield from SWVO-24 was lower than SWVO-0 for all levels of methanol/oil ratio. It is being observed that increasing the methanol/oil molar ratio from 9:1 to 18:1 increases the FAME yield from 87 to 92 % for SWVO-0 and from 84 to 86 % for SWVO-24, respectively. Methoxy groups are assumed to be formed on the Fig. 5 Comparison of FT-IR spectral profiles of a SWVO and SWVO-FAME b among various SWVO-FAME
surface of the catalyst when excess amount of methanol is used, forcing the reaction to shift towards product side. Hence, high methanol/oil ratio enhances the rate of conversion. However, increased unreacted methanol due to reduced functional groups solubilizes the glycerol, and thereby restricts the reaction (Eevera et al. 2009). Accordingly, lower degree of enhancement with increasing methanol/oil ratio was observed for thermally treated SWVO. Effect of the reaction time on the yield of fame T h e y i e l d o f FA M E w a s m o n i t o r e d v a r y i n g t h e transesterification reaction time from 0–4 h. Increased yield of FAME was noted on increasing transesterification reaction time from 1 to 3 h. A maximum transesterification yield of 91 % was recorded after 3 h of transesterification with a catalyst concentration of 10 % (w/w), methanol/oil ratio 9:1, at 65 °C (Fig. 7). Further increase in the reaction time up to 4 h and longer slightly decreases the yield of FAME approximately by 2 %. This is because longer reaction duration causes hydrolysis of esters, forming fatty acids (Eevera et al. 2009; Samart et al. 2009) and reversibility of the transesterification reaction cause the decrease in the yield of FAME on longer reaction duration. Effect of catalyst loading (mass ratio) The effect of ESSO loading on transesterification was investigated for varied catalyst loading percent. The ESSO catalyst
Environ Sci Pollut Res Fig. 6 Effect of methanol ratio on yield of FAME a SWVO-0 and b SWVO-24 (reaction condition: time 3 h, catalyst 10 %, catalyst calcination temperature 950 °C)
loading was varied from 5 to 15 % (w/w). The results are shown in Fig. 8. At the initial phase of the reaction, low catalyst concentration (5 %) results in the lower yield of FAME, because the catalyst concentration was insufficient to catalyze the reaction for completion. This indicates that the amount of catalyst basic site is a strong determining factor for the transesterification of vegetable oil (Ngamcharussrivichai et al. 2008). As a result, increase in the concentration of the catalyst (10 %) resulted in the increased yield of FAME. By increasing the concentration of the catalyst further, no enhancement in the FAME yield was observed. The reason for this decreasing trend was due to the formation of soap in presence of high amount of catalysts, which increased the viscosity of the reactants and lowered the yield (Eevera et al. 2009). The lower yield of FAME at higher catalyst loading can also be attributed to the diffusion problems that arise inside the batch reactor due to accumulation of the excess catalyst on the reactor bottom and walls which lower the activity of the catalyst (Buasri et al. 2012). Effect of calcination temperature on the catalyst The FT-IR profile of ESSO catalyst with respect to calcination temperature at 850 and 950 °C are presented in Fig. 9a. A
Fig. 7 Effect of reaction time on yield of FAME (reaction condition: methanol/oil ratio 18:1, catalyst 10 %, catalyst calcination temperature 950 °C, oil type SWVO-0)
study of FT-IR spectra of ESSO catalyst shows major absorption bands at 1415, 875, and 700 cm−1, which are attributed to asymmetric stretch, out of plane bend and in-plane bend vibration modes, respectively, for CO3−2 molecules. Upon calcination, eggshell starts to lose carbonate and absorption bands of CO3−2 and absorbance band of the molecules shift to higher energy (i.e., 400, 1450, 3400 cm−1). This has been attributed to the decrease of the reduced mass of the functional group attached to the CO3−2 ion spectroscopy. ESSO catalyst sample calcined at 950 °C was the most active catalyst. In presence of the ESSO catalyst calcined at 950 °C, a yield of 91 % was obtained (Fig. 9b). Higher temperature calcination led to desorption of carbon dioxide from the eggshell catalyst, producing more basic sites that catalyzed the reaction. Comparison of the FAME quality and cost analysis The characterization results of FAME obtained from transesterification of SWVO in terms of specific gravity, flash point/fire point, and pour point are compared with the ASTM standards of biodiesel (ASTM D 6751). The specific gravity of FAME produced from SWVO-0 and SWVO-24 are 0.875±
Fig. 8 Effect of catalyst loading on yield of FAME (reaction condition: methanol/oil ratio 18:1, reaction time 3 h, catalyst calcination temperature 950 °C, oil type SWVO-0)
Environ Sci Pollut Res Fig. 9 a FT-IR spectra of eggshell catalyst calcined at different calcination temperature. b Effect of catalyst calcination temperature on the yield of FAME. (reaction condition: methanol/oil ratio 18:1, catalyst 10 %, catalyst reaction time 3 h, oil type SWVO-0)
0.015 and 0.884±0.016, respectively. The values are within the acceptable range (0.86–0.90). The flash point of the FAME from SWVO-0 and SWVO-24 are 115±7 °C and 121±8 °C, respectively. The observed fire point of SWVO-0 is 156±5 °C and SWVO-24 is 162±6 °C, respectively. Both the values are within the acceptable limits established in the standard (100–170 °C). The pour point of the FAME from SWVO-0 and SWVO-24 were observed to be lower than 3 °C (flow did not cease until 1±1 °C), better than that defined in the standard. The stability of the FAME samples are more than 3 h, limits specified in the standard. The comparison concludes that the FAME produced from SWVO thermally treated up to 24 h is comparable with biodiesel standard and can be acceptable commercially. The cost analysis of the FAME was performed to justify the economic viability of the product, SWVO-FAME. The eggshells are well-known waste materials, which are generated everyday on a large scale from household, restaurants, food industries, bakeries, etc. The eggshell used in the study is obtained free of cost from local restaurants and hostel, which would otherwise be disposed as municipal solid waste. The cost of calcination of eggshell is the only cost involved in the production of solid oxide eggshell catalyst for transesterification. The computed price of solid oxide eggshell catalyst is much lower than the price of commercially available calcium oxide (purity 0.90). Commercial fryers currently available utilize an average of 20–25 L of oil under optimum cooking conditions. With restaurants changing oil every week, a minimum of 20 L of oil waste will be generated from a single restaurant every week. The waste oil disposal system is available in several cities in developed countries. Considering the transesterification yield obtained in the study the cost of transesterified methyl ester from waste oil (SWVO-FAME) is computed to be lower than the price of biodiesel produced available commercially. Thus the utilization of thermally treated SWVO, reported in this study, presents a cost effective and environmental friendly energy solution.
Conclusion The impact of various experimental variables on the transesterification of simulated waste vegetable oil (SWVO) was evaluated. The duration of thermal treatment that oil was subjected varied over 0–72 h. The transesterification product (FAME) yield was observed to diminish with increasing thermal treatment time. FAME produced from SWVO subjected to 24 h thermal treatment was found to be acceptable as per ASTM D 6751 standard. Increased thermal treatment duration of SWVO increased the viscosity and specific gravity of the oil and the resultant FAME. The results show that the yields of FAME arrived at the maximum value at the reaction time around 3 h, and then slightly decrease at the reaction time of 4 h and longer. Initially, the yield of FAME increases with the catalyst loading from 5–10 %, but with further increase in catalyst concentration, a negligible increase in the yield of FAME is observed. Excess methanol is desirable for the reaction to achieve the maximum yield, and the methanol concentration of 18:1 is found to be ideal. The reaction temperature is kept at 65 °C, because at a higher temperature, the methanol gets vaporized inhibiting reaction to progress as it reaches to its boiling point. An efficient heterogeneous solid oxide-based (ESSO) catalyst is used for the synthesis of FAME by transesterification. The optimum condition for transesterification of SWVO for FAME was reported to be 65 °C for 3 h with 18:1 methanol/oil ratio and 10 % (w/w) ESSO catalyst calcined at 950 °C. The study reported that around 90 %, FAME yield was obtained with methanol/oil molar ratio of 18:1 in 3 h reaction time using 10 % ESSO catalyst with SWVO-0. The FAME yield of SWVO-24 is 85 %, which is 5 % lower than SWVO-0 under identical condition. The infrared spectroscopic (FT-IR) analysis was used to confirm the production of FAME. The computed production cost of FAME, otherwise known as biodiesel by the process reported in the present study, is found to be lower than commercially available biodiesel in the current market. The
Environ Sci Pollut Res
utilization of waste for societal benefit with the essence of sustainable development is the novelty of this work and the conversion of thermally treated SWVO, similar to waste frying (cooking) oil, using ESSO catalyst (produced from waste), reported in this study, presents a cost effective environmental friendly energy solution with great social implication. Acknowledgment The authors would like to acknowledge the National Institute of Technology, Agartala, specially the Department of Chemical Engineering, for providing access to the departmental laboratory to execute the project. The authors would also like to express their gratitude to the TEQIP-II for the financial support to present the work. Student author would also like to acknowledge SC Welfare Department, Government of Tripura, for the financial assistance provided in the form of scholarship.
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Lin L et al (2011) Opportunities and challenges for biodiesel fuel. Appl Energ 88(4):1020–1031. doi:10.1016/j.apenergy.2010.09.029 Liu X et al (2008) Transesterification of soybean oil to biodiesel using CaO as a solid base catalyst. Fuel 87(2):216–221. doi:10.1016/j. fuel.2007.04.013 Lotero E et al (2005) Synthesis of biodiesel via acid catalysis. Ind Eng Chem Res 44(14):5353–5363. doi:10.1021/ie049157g MacLeod CS et al (2008) Evaluation of the activity and stability of alkalidoped metal oxide catalysts for application to an intensified method of biodiesel production. Chem Eng J 135(1):63–70. doi:10.1016/j. cej.2007.04.014 Ngamcharussrivichai C, Totarat P, Bunyakiat K (2008) Ca and Zn mixed oxide as a heterogeneous base catalyst for transesterification of palm kernel oil. Appl Catal A-Gen 341(1):77–85. doi:10.1016/j.apcata. 2008.02.020 Pienaar J, Brent AC (2012) A model for evaluating the economic feasibility of small-scale biodiesel production systems for an-farm fuel usage. Renew Energ 39:483–489. doi:10.1016/j.renene.2011.08. 048 Qian J et al (2013) Cogeneration of biodiesel and nontoxic rapeseed meal from rapeseed through in-situ alkaline transesterification. Bioresource Technol 128:8–13. doi:10.1016/j.biortech.2012.10.017 Samart C, Sreetongkittikul P, Sookman C (2009) Heterogeneous catalysis of transesterification of soybean oil using KI/mesoporous silica. Fuel Process Technol 90(7):922–925. doi:10.1016/j.fuproc.2009. 03.017 Srivastava A, Prasad R (2000) Triglycerides-based diesel fuels. Renew Sust Energ Rev 4(2):111-133. doi:10.1016/S1364-0321(99)00013-1 Suryaputra W et al (2013) Waste capiz (Amusium cristatum) shell as a new heterogeneous catalyst for biodiesel production. Renew Energ 50:795–799. doi:10.1016/j.renene.2012.08.060 Veljković VB et al (2009) Kinetics of sunflower oil methanolysis catalyzed by calcium oxide. Fuel 88(9):1554–1562. doi:10.1016/j.fuel. 2009.02.013 Viriya-Empikul N et al (2012) Biodiesel production over Ca-based solid catalysts derived from industrial wastes. Fuel 92(1):239–244. doi: 10.1016/j.fuel.2011.07.013 Xie W, Li H (2006) Alumina-supported potassium iodide as a heterogeneous catalyst for biodiesel production from soybean oil. J Mol Catal A-Chem 255(1):1–9. doi:10.1016/j.molcata.2006.03.061 Xie W, Peng H, Chen L (2006a) Calcined Mg–Al hydrotalcites as solid base catalysts for methanolysis of soybean oil. J Mol Catal A-Chem 246(1):24–32. doi:10.1016/j.molcata.2005.10.008 Xie W, Peng H, Chen L (2006b) Transesterification of soybean oil catalyzed by potassium loaded on alumina as a solid-base catalyst. Appl Catal A-Gen 300(1):67–74. doi:10.1016/j.apcata.2005.10.048 Yahyaee R, Ghobadian B, Najafi G (2013) Waste fish oil biodiesel as a source of renewable fuel in Iran. Renew Sust Energ Rev 17:312– 319. doi:10.1016/j.rser.2012.09.025 Zakaria R, Harvey AP (2012) Direct production of biodiesel from rapeseed by reactive extraction/in situ transesterification. Fuel Process Technol 102:53–60. doi:10.1016/j.fuproc.2012.04.026 Zhang Y et al (2003) Biodiesel production from waste cooking oil: 1. Process design and technological assessment. Bioresource Technol 89(1):1-16. doi:10.1016/S0960-8524(03)00040-3 Zhang L et al (2010) Synthesis and component confirmation of biodiesel from palm oil and dimethyl carbonate catalyzed by immobilized lipase in solvent-free system. Fuel 89(12):3960–3965. doi:10. 1016/j.fuel.2010.06.030
POLLUTION CONTROL TECHNOLOGIES AND ALTERNATE ENERGY OPTIONS
A study on production of biodiesel using a novel solid oxide catalyst derived from waste Samrat Majhi 1 & Srimanta Ray 1
Received: 24 March 2015 / Accepted: 1 June 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract The issues of energy security, dwindling supply and inflating price of fossil fuel have shifted the global focus towards fuel of renewable origin. Biodiesel, having renewable origin, has exhibited great potential as substitute for fossil fuels. The most common route of biodiesel production is through transesterification of vegetable oil in presence of homogeneous acid or base or solid oxide catalyst. But, the economics of biodiesel is not competitive with respect to fossil fuel due to high cost of production. The vegetable oil waste is a potential alternative for biodiesel production, particularly when disposal of used vegetable oil has been restricted in several countries. The present study evaluates the efficacy of a low-cost solid oxide catalyst derived from eggshell (a food waste) in transesterification of vegetable oil and simulated waste vegetable oil (SWVO). The impact of thermal treatment of vegetable oil (to simulate frying operation) on transesterification using eggshell-derived solid oxide catalyst (ESSO catalyst) was also evaluated along with the effect of varying reaction parameters. The study reported that around 90 % biodiesel yield was obtained with vegetable oil at methanol/oil molar ratio of 18:1 in 3 h reaction time using 10 % ESSO catalyst. The biodiesel produced with ESSO catalyst from SWVO, thermally treated at 150 °C for 24 h, was found to conform with the biodiesel standard, but the yield was 5 % lower compared to that of the untreated oil. The utilization of waste vegetable oil along with waste eggshell as catalyst is significant for improving the overall economics Responsible editor: Bingcai Pan * Srimanta Ray [email protected]; [email protected] 1
Department of Chemical Engineering, National Institute of Technology Agartala, Jirania, Tripura 799055, India
of the biodiesel in the current market. The utilization of waste for societal benefit with the essence of sustainable development is the novelty of this work. Keywords Waste vegetable oil . Waste eggshell . Solid oxide catalyst . Transesterification . Biodiesel
Introduction The recent energy crisis across the globe, the massive escalation of the world energy demands, the forecasted depletion of the fossil energy sources, and the rising environmental concerns to limit the exhaust emissions have motivated the search for cleaner and efficient economic and sustainable alternative fuels for over a decade (Hoekman and Robbins 2012; Yahyaee et al. 2013). One of the alternative fuels which have gained significant attention is derived from vegetable oil through transesterification, also known as biodiesel. The biodiesel has renewable nature, produces lower emission, but possesses high flash point and high cetane number compared to the petroleum-based diesel (Kouzu et al. 2008). The vegetable oil or triglycerides (TGs) of fatty acids, on transesterification with short chain alcohol (C1–C3), produces fatty acid alkyl esters which are otherwise known as biodiesel (Khayoon et al. 2012; Zhang et al. 2010). Biodiesels produced through transesterification of vegetable oils with methanol (C1) are referred to as fatty acid methyl esters (FAME) (Zakaria and Harvey 2012; Qian et al. 2013). The triglycerides, the key raw material for FAME, having vegetable or plant origin are a sequestered carbon form. The transesterification of the triglycerides to FAME and the subsequent combustion of FAME for carbon release is therefore a sustainable way of carbon recycling (Khayoon and Hameed 2013). In spite of the favorable causes, the commercial large-
Environ Sci Pollut Res
scale production of FAME is still not considered viable, because of various socioeconomic issues. The escalating prices of raw materials and the increased cost of production are the vital ones. The cost of vegetable oil and the catalyst determines the cost of the produced biodiesel (Behçet 2011; Lin et al. 2011). In addition, utilization of edible vegetable in the biodiesel industry influences the global oil market and the price. As a result, in some of the developing countries with limited agricultural landmass per capita, the utilization of edible vegetable oil for the production of biodiesel is not profitable and even prohibited (Lin et al. 2011). To address the scarcity of feedstock for biodiesel or FAME production and to diminish the food versus fuel dispute, recent research interest have been directed towards the exploration of worthy alternatives, apart from edible vegetable oil (Pienaar and Brent 2012; Lotero et al. 2005). In this regard, waste vegetable oil from cooking or frying holds great possibilities. Waste cooking oils are generated in substantial quantities every year from industrial and commercial establishments during preparation of food products (Charpe and Rathod 2011). Used waste cooking oil is often not properly disposed, resulting in environmental pollution and economic losses. Improvement in process technologies in recent years resulted in transesterification of waste vegetable oil and production of FAME from cheaper alternative feedstock (Canakci 2007). However, the elevated cost of FAME production due to the cost of catalyst is still an economic impediment in the biodiesel production. The homogeneous acid or base catalysts are commonly employed in transesterification of vegetable oil to FAME. The base catalysts are preferred due to lower transesterification temperature. But separation of the homogenous base catalyst from the final reaction mixture is difficult and requires neutralization. The commercially used base catalyst are also hazardous and corrosive in nature, therefore require large amount of solvent and energy for effluent treatment (Georgogianni et al. 2009). Therefore, a need for the replacement of the homogenous base catalyst was felt and the heterogeneous solid oxide catalysts became relevant. Lower consumption of the catalyst, easy separation from the final reaction mixture, catalyst re-usability, less environmental issues, and low cost of production are some of the major advantages of heterogeneous solid oxide catalyst. Accordingly, heterogeneous solid oxide catalysts have gained great research interest. The heterogeneous solid oxide that catalyzed transesterification of vegetable oil have been reported with different alkali earth metal oxides and hydroxides (Granados et al. 2007; Liu et al 2008; Veljković et al. 2009), alumina supported salts (MacLeod et al. 2008; Xie and Li 2006; Xie et al. 2006a, b) and zeolites (Xie et al. 2006a, b) under variable reaction conditions. Among the different solid oxide catalysts investigated, calcium oxide (CaO) has shown great promise in
transesterification. Also, CaO being widely available in nature in the form of lime has enhanced economic advantages. Other than lime, the eggshell is a promising source of CaO. Large quantities of eggshell waste are generated routinely from food industry, which add up to the solid waste and are associated with disposal issues. The utilization of waste eggshell as CaO source in heterogeneous transesterification is linked with environmental and economic benefits, and also promotes improve sustainability of the process through value addition of waste (Suryaputra et al. 2013). Hence, the objective of the present study is to evaluate the efficacy of the waste eggshell-derived solid oxide catalyst (ESSO catalyst) in heterogeneous transesterification of waste vegetable oil produced by simulating the prolong thermal treatment like frying. The thermal treatment duration on vegetable oil was varied and the impact on transesterification efficacy, FAME quality with ESSO catalyst was assessed. The effect of varying reaction parameters on the FAME quality and yield was also evaluated. The systematic evaluation of waste eggshell-based ESSO catalyst together with different qualities of waste vegetable oil on transesterification efficacy and FAME or biodiesel quality is the novelty of this study. In addition from the waste management perspective, producing FAME from waste frying oil and using waste eggshell-based catalyst is expected to raise the economic viability and sustainability quotient of the biodiesel as alternative fuel.
Materials and methods Materials Soybean oil was chosen as the vegetable oil feedstock for the study. Soybean oil used in the study was procured locally from available commercial brands of edible soybean oil (Agartala, Tripura, India) and the brand was not varied throughout the study. The approximate composition of fatty acid in the soybean oil is summarized in Table 1. Analytical grade methanol (99.5 % purity, Qualigens Fine Chemicals, Mumbai, India) was used for the transesterification reaction. Eggshell-derived solid oxide catalyst (ESSO catalyst) used in the study was
Table 1 Fatty acid composition of soybean oil (Canakci 2007; Liu et al. 2008; Samart et al. 2009)
Name of the fatty acid
Fatty acid
Percent weight
Palmitic Stearic Oleic Linoleic Linolenic
16:1 18:0 18:1 18:2 18:3
11.75 3.15 23.26 55.53 6.31
Environ Sci Pollut Res
prepared from the eggshells (chicken) collected from the waste of the food canteen of the institute (Agartala, Tripura, India).
fatty acid methyl ester (FAME) and glycerol (Eq. 1). The rate of conversion of triglycerides to FAME can be accelerated by using suitable catalyst.
Simulated waste vegetable oil
Triglyceride ðSWVOÞ þ methanol þ ESSO
In order to understand the impact of thermal treatment of soybean oil, on the FAME quality and FAME yield, simulated waste vegetable oil (SWVO) is produced by thermally treating the soybean oil, simulating the cooking (frying) operation. The SWVO is later used for transesterification reaction. To prepare SWVO, thermally untreated soybean oil samples are subjected to thermal treatment in glass reactors with temperature kept invariant at 150 °C. The duration of the thermal treatment was varied from 24–72 h. The thermally untreated soybean oil sample is considered as SWVO with 0 h of treatment exposure. All the SWVO samples are characterized in terms of oil properties and assessed for FAME yield in transesterification reaction. Catalyst preparation The collected eggshells were washed in cold tap water; the membrane was separated and discarded. The washed eggshells were subsequently dried for 48–50 h in the direct sun before subsequent treatment. The dried egg shells were crushed and sieved. The sieved particle has particle size between 0.074 mm (200 meshes) to 0.174 mm (100 meshes). The eggshell particles were thereafter thermally stabilized and calcined in a muffle furnace (Simeco, Kolkata, India) in static air condition at a designated temperature for specific time duration and thereafter aircooled to ambient temperature to prepare the eggshellderived solid oxide (ESSO) catalyst. The calcination temperature was varied from 750–950 °C, based on the findings reported in the literature (Viriya-Empikul et al. 2012). The calcination duration was maintained invariant at 2 h. The thermally synthesized catalyst was used as-is for transesterification. The ESSO catalyst was stored in hermetically sealed container for subsequent use and characterization.
¼ fatty acid methyl ester ðFAMEÞ þ glycerol þ ESSO
ð1Þ
FAME was synthesized in a batch-type transesterification reaction with ESSO catalyst. Transesterification experiments were carried in a distillation flask fitted with a counter current water cooled condenser and a methanol reflux arrangement. The distillation flask was kept in a water bath equipped with a thermometer to maintain the reaction temperature. The reaction liquid was continuously stirred at 200±50 rpm with a magnetic stirrer and magnetic stirred bar. The schematic of the experimental setup is shown in Fig. 1. According to the results of Liu et al. (2008), 65 °C was reported to be the optimum temperature for the transesterification of oil. Thus, the reaction temperature was kept invariant at 65±2 °C for all reactions. Transesterification is a reversible reaction. Accordingly, increased methanol/oil ratio is expected to favor FAME formation in transesterification reaction. Therefore, the methanol/oil ratio is considered as an experimental parameter and is varied to study the effect on the yield of FAME from transesterification of different SWVO. The other experimental parameters that varied include amount of catalyst (catalyst loading), type of catalyst (catalyst calcination temperature), and reaction time. SWVO subjected to different extent of thermal treatment (duration of treatment) were also assessed. The levels at which various experimental parameters are varied in one factor at a time approach is summarized in Table 2. After the completion of the reaction, the product was allowed to settle overnight to produce two distinctive liquid phases, i.e. methyl ester phase at the top and glycerol phase at the bottom. The FAME is then separated from the glycerol phase by using a separating funnel, and then stored for the subsequent analytical tests. Experiments were conducted in triplicates to estimate the error (uncertainty).
Transesterification procedure Transesterification reaction of fat and oil (triglycerides) is such a reaction which implicates replacement of glycerol molecule from triglycerides (an ester of glycerol) by another alcohol molecule with glycerol produced as a byproduct. Stoichiometry of transesterification shows that 3 mol of alcohol reacts with 1 mol of triglyceride to give 3 mol of fatty acid esters and 1 mol of glycerol. Transesterification of triglyceride with methanol produces
Catalyst characterization The characterization of eggshell catalyst was performed by infrared spectroscopy using Fourier transformation analysis (FT-IR). The measurement of absorbance in FTIR was performed using scans in the range of 400 to 3900 cm −1 . The formation and transformation of the ESSO catalyst with calcination temperature was
Environ Sci Pollut Res Fig. 1 Schematic representation of the experimental setup for transesterification
determined by the peak-matching technique, using corresponding values of the peak from the standard IR spectral list.
Result and discussion Effect of thermal treatment on SWVO Effect on viscosity
Analytical methods The specific gravity of SWVO and FAME sample were determined using specific gravity bottle following standard specific gravity determination protocol. The viscosity of FAME and SWVO samples were determined by Redwood viscometer (Simeco, Kolkata, India) in a modified protocol. The flash point and fire point of the FAME was determined using Penske-Martin closed cup apparatus. The pour point of FAME was determined using standard pour point apparatus. The FAME and SWVO samples were scanned in UV-visible spectrophotometer (Lambda 35, Perkin Elmer, Mumbai, India) between 200 to 700 nm to monitor the change in absorbance with respect to change in functional moieties. The FAME and SWVO samples were also analyzed in IR spectrophotometer using Fourier transformation between 400– 4000 cm−1 to confirm the transesterification and impact of reaction variables (oil type) on FAME. The formation of FAME group was monitored in 1300 to 1060 cm−1 wavenumber region. Table 2
The thermal treatment has been observed to have a profound effect on the properties of SWVO. The viscosity of SWVO increased significantly with increase in the duration of the thermal treatment (Fig. 2a). The increase in viscosity of thermally treated oil with treatment time may be attributed to the formation of polymerized or branched or oxidized products. The viscosity of FAME obtained from different SWVO (SWVO 0, 24, 48, and 72) that are subjected different thermal treatment duration is presented in Fig. 2b. The viscosity of FAME obtained from different SWVO also increased with the increase in the thermal treatment duration. Also, prolonging the thermal treatment of the oil was observed to reduce the transesterification yield (Fig. 2b). Increased polymerized product formation makes the SWVO difficult to transesterify and reduces the conversion of triglycerides into FAME. Thus, the duration of thermal treatment and the viscosity of SWVO were observed to have major impact on the yield of FAME.
Different experimental variables and their levels
Type of soybean oil
Treatment time of oil (hours)
Methanol/oil ratio (mole/mole)
Reaction time (hours)
Catalyst calcination temperature (°C)
Catalyst loading (% (w/w))
Thermally untreated oil SWVO-24 SWVO-48 SWVO-72
0 24 48 72
9:1 15:1 18:1
1 2 3 4
750 850 950
5 10 15
Environ Sci Pollut Res Fig. 2 Effect of thermal cycling on a viscosity of SWVO and b viscosity of FAME, and percent yield of FAME
Effect on specific gravity
UV-visible spectroscopic analysis
The specific gravity is an important parameter for biodiesel or FAME. Accordingly the standard viscosity values have been established for FAME in ASTM D6751, which is 0.86–0.90. FAME having density lower than the standard increase emission and damages the engine (Hoekman and Robbins 2012; Srivastava and Prasad 2000). High density FAME is also not desirable for fuel purpose. The duration of thermal treatment on SWVO was observed to increase the specific gravity of the oil (Fig. 3a). Transesterification of different SWVO from different thermal treatment showed a similar trend (Fig. 3b). The FAME produced from SWVO-0 and SWVO-24 has specific gravity within the acceptable range (ASTM standard), the specific gravity of FAME produced from SWVO-48 is at the upper limit of the standard, whereas, the specific gravity of FAME produced from SWVO-72 were beyond the acceptable range. Increased specific gravity of FAME from SWVO subjected to longer thermal treatm e n t i s l in k e d w i t h h i g h e r v i s c o si t y a n d l ow e r transesterification yield (Fig. 2b). Prolonged thermal treatment of vegetable oil polymerize, isomerize, and oxidize the fatty acid molecules and produce larger or branched or oxidized molecules resulting in increase in specific gravity, loss of functional groups, and reduced transesterification yield (Charpe and Rathod 2011).
The UV-visible spectroscopic analysis was performed to understand the transformation of the SWVO on thermal treatment. Monitoring SWVO samples in the UV spectrum furnished a good indication of the oxidation of oil with increase in thermal treatment duration. The increase in treatment duration exhibits a shift in the UV absorbance peak (Fig. 4a, b). The UV absorbance shift towards higher wavelength. The change in UV absorbance pattern is primarily due to the formation of products of oxidation which include trines, unsaturated ketones, aldehydes, and other secondary products of oxidation. The increase in absorbance is also noted with increase in thermal treatment time perhaps due to formation of conjugated dienes. The formation of oxidized and conjugated products explains the changes in the properties of the SWVO with increasing thermal treatment duration.
Fig. 3 a Effect of thermal cycling at 150 °C in the specific gravity of soybean oil. b Effect of thermal cycling at 150 °C in the specific gravity of FAME
FT-IR spectra analysis The transesterification product, i.e. FAME, is analyzed by infrared spectroscopy to confirm the FAME formation through functional group analysis. In transesterification, the methoxy-carbonyl group was formed in FAME substituting the carbonyl group in the SWVO. Figure 5a presents the FTIR spectral profile of the raw material, SWVO, and the product of transesterification, FAME. The absorption peak at
Environ Sci Pollut Res Fig. 4 a Effect of thermal cycling at 150 °C on soybean oil. b Effect of thermal cycling at 150 °C on soya-FAME
1103 cm-1 in the raw material, SWVO, due to the occurrence of C-CH2-O group in the SWVO disappears in FAME. Meanwhile, new absorption peaks at 1436 and 1197 cm−1 confirm the presence of –CH3 and O-CH3 groups in the FAME. The formation of the methoxy functional group confirmed the formation of FAME. Comparison among the various transesterification product (FAME) produced from different SWVO that are subjected different extent of thermal treatment showed diminishing fingerprint peak at 1197 cm−1, conforming lower yield of FAME from transesterification of SWVO subjected to longer thermal treatment (Fig. 5b). Effect of methanol/oil ratio According to the literature, the methanol/oil molar ratio for alkali-catalyzed process is near about 6:1, whereas for acid catalyzed reaction, the methanol/oil ratio rises up to 30:1 to ensure high conversion (Zhang et al. 2003). The methanol/oil ratio is varied at three levels, 9:1, 15:1, and 18:1, based on the literature data and preliminary results. The effect of varying methanol/oil ratio on the yield of FAME for SWVO-0 and SWVO-24 is shown in Fig. 6a, b. Increasing methanol/oil ratio increased the FAME yield. However, the FAME yield from SWVO-24 was lower than SWVO-0 for all levels of methanol/oil ratio. It is being observed that increasing the methanol/oil molar ratio from 9:1 to 18:1 increases the FAME yield from 87 to 92 % for SWVO-0 and from 84 to 86 % for SWVO-24, respectively. Methoxy groups are assumed to be formed on the Fig. 5 Comparison of FT-IR spectral profiles of a SWVO and SWVO-FAME b among various SWVO-FAME
surface of the catalyst when excess amount of methanol is used, forcing the reaction to shift towards product side. Hence, high methanol/oil ratio enhances the rate of conversion. However, increased unreacted methanol due to reduced functional groups solubilizes the glycerol, and thereby restricts the reaction (Eevera et al. 2009). Accordingly, lower degree of enhancement with increasing methanol/oil ratio was observed for thermally treated SWVO. Effect of the reaction time on the yield of fame T h e y i e l d o f FA M E w a s m o n i t o r e d v a r y i n g t h e transesterification reaction time from 0–4 h. Increased yield of FAME was noted on increasing transesterification reaction time from 1 to 3 h. A maximum transesterification yield of 91 % was recorded after 3 h of transesterification with a catalyst concentration of 10 % (w/w), methanol/oil ratio 9:1, at 65 °C (Fig. 7). Further increase in the reaction time up to 4 h and longer slightly decreases the yield of FAME approximately by 2 %. This is because longer reaction duration causes hydrolysis of esters, forming fatty acids (Eevera et al. 2009; Samart et al. 2009) and reversibility of the transesterification reaction cause the decrease in the yield of FAME on longer reaction duration. Effect of catalyst loading (mass ratio) The effect of ESSO loading on transesterification was investigated for varied catalyst loading percent. The ESSO catalyst
Environ Sci Pollut Res Fig. 6 Effect of methanol ratio on yield of FAME a SWVO-0 and b SWVO-24 (reaction condition: time 3 h, catalyst 10 %, catalyst calcination temperature 950 °C)
loading was varied from 5 to 15 % (w/w). The results are shown in Fig. 8. At the initial phase of the reaction, low catalyst concentration (5 %) results in the lower yield of FAME, because the catalyst concentration was insufficient to catalyze the reaction for completion. This indicates that the amount of catalyst basic site is a strong determining factor for the transesterification of vegetable oil (Ngamcharussrivichai et al. 2008). As a result, increase in the concentration of the catalyst (10 %) resulted in the increased yield of FAME. By increasing the concentration of the catalyst further, no enhancement in the FAME yield was observed. The reason for this decreasing trend was due to the formation of soap in presence of high amount of catalysts, which increased the viscosity of the reactants and lowered the yield (Eevera et al. 2009). The lower yield of FAME at higher catalyst loading can also be attributed to the diffusion problems that arise inside the batch reactor due to accumulation of the excess catalyst on the reactor bottom and walls which lower the activity of the catalyst (Buasri et al. 2012). Effect of calcination temperature on the catalyst The FT-IR profile of ESSO catalyst with respect to calcination temperature at 850 and 950 °C are presented in Fig. 9a. A
Fig. 7 Effect of reaction time on yield of FAME (reaction condition: methanol/oil ratio 18:1, catalyst 10 %, catalyst calcination temperature 950 °C, oil type SWVO-0)
study of FT-IR spectra of ESSO catalyst shows major absorption bands at 1415, 875, and 700 cm−1, which are attributed to asymmetric stretch, out of plane bend and in-plane bend vibration modes, respectively, for CO3−2 molecules. Upon calcination, eggshell starts to lose carbonate and absorption bands of CO3−2 and absorbance band of the molecules shift to higher energy (i.e., 400, 1450, 3400 cm−1). This has been attributed to the decrease of the reduced mass of the functional group attached to the CO3−2 ion spectroscopy. ESSO catalyst sample calcined at 950 °C was the most active catalyst. In presence of the ESSO catalyst calcined at 950 °C, a yield of 91 % was obtained (Fig. 9b). Higher temperature calcination led to desorption of carbon dioxide from the eggshell catalyst, producing more basic sites that catalyzed the reaction. Comparison of the FAME quality and cost analysis The characterization results of FAME obtained from transesterification of SWVO in terms of specific gravity, flash point/fire point, and pour point are compared with the ASTM standards of biodiesel (ASTM D 6751). The specific gravity of FAME produced from SWVO-0 and SWVO-24 are 0.875±
Fig. 8 Effect of catalyst loading on yield of FAME (reaction condition: methanol/oil ratio 18:1, reaction time 3 h, catalyst calcination temperature 950 °C, oil type SWVO-0)
Environ Sci Pollut Res Fig. 9 a FT-IR spectra of eggshell catalyst calcined at different calcination temperature. b Effect of catalyst calcination temperature on the yield of FAME. (reaction condition: methanol/oil ratio 18:1, catalyst 10 %, catalyst reaction time 3 h, oil type SWVO-0)
0.015 and 0.884±0.016, respectively. The values are within the acceptable range (0.86–0.90). The flash point of the FAME from SWVO-0 and SWVO-24 are 115±7 °C and 121±8 °C, respectively. The observed fire point of SWVO-0 is 156±5 °C and SWVO-24 is 162±6 °C, respectively. Both the values are within the acceptable limits established in the standard (100–170 °C). The pour point of the FAME from SWVO-0 and SWVO-24 were observed to be lower than 3 °C (flow did not cease until 1±1 °C), better than that defined in the standard. The stability of the FAME samples are more than 3 h, limits specified in the standard. The comparison concludes that the FAME produced from SWVO thermally treated up to 24 h is comparable with biodiesel standard and can be acceptable commercially. The cost analysis of the FAME was performed to justify the economic viability of the product, SWVO-FAME. The eggshells are well-known waste materials, which are generated everyday on a large scale from household, restaurants, food industries, bakeries, etc. The eggshell used in the study is obtained free of cost from local restaurants and hostel, which would otherwise be disposed as municipal solid waste. The cost of calcination of eggshell is the only cost involved in the production of solid oxide eggshell catalyst for transesterification. The computed price of solid oxide eggshell catalyst is much lower than the price of commercially available calcium oxide (purity 0.90). Commercial fryers currently available utilize an average of 20–25 L of oil under optimum cooking conditions. With restaurants changing oil every week, a minimum of 20 L of oil waste will be generated from a single restaurant every week. The waste oil disposal system is available in several cities in developed countries. Considering the transesterification yield obtained in the study the cost of transesterified methyl ester from waste oil (SWVO-FAME) is computed to be lower than the price of biodiesel produced available commercially. Thus the utilization of thermally treated SWVO, reported in this study, presents a cost effective and environmental friendly energy solution.
Conclusion The impact of various experimental variables on the transesterification of simulated waste vegetable oil (SWVO) was evaluated. The duration of thermal treatment that oil was subjected varied over 0–72 h. The transesterification product (FAME) yield was observed to diminish with increasing thermal treatment time. FAME produced from SWVO subjected to 24 h thermal treatment was found to be acceptable as per ASTM D 6751 standard. Increased thermal treatment duration of SWVO increased the viscosity and specific gravity of the oil and the resultant FAME. The results show that the yields of FAME arrived at the maximum value at the reaction time around 3 h, and then slightly decrease at the reaction time of 4 h and longer. Initially, the yield of FAME increases with the catalyst loading from 5–10 %, but with further increase in catalyst concentration, a negligible increase in the yield of FAME is observed. Excess methanol is desirable for the reaction to achieve the maximum yield, and the methanol concentration of 18:1 is found to be ideal. The reaction temperature is kept at 65 °C, because at a higher temperature, the methanol gets vaporized inhibiting reaction to progress as it reaches to its boiling point. An efficient heterogeneous solid oxide-based (ESSO) catalyst is used for the synthesis of FAME by transesterification. The optimum condition for transesterification of SWVO for FAME was reported to be 65 °C for 3 h with 18:1 methanol/oil ratio and 10 % (w/w) ESSO catalyst calcined at 950 °C. The study reported that around 90 %, FAME yield was obtained with methanol/oil molar ratio of 18:1 in 3 h reaction time using 10 % ESSO catalyst with SWVO-0. The FAME yield of SWVO-24 is 85 %, which is 5 % lower than SWVO-0 under identical condition. The infrared spectroscopic (FT-IR) analysis was used to confirm the production of FAME. The computed production cost of FAME, otherwise known as biodiesel by the process reported in the present study, is found to be lower than commercially available biodiesel in the current market. The
Environ Sci Pollut Res
utilization of waste for societal benefit with the essence of sustainable development is the novelty of this work and the conversion of thermally treated SWVO, similar to waste frying (cooking) oil, using ESSO catalyst (produced from waste), reported in this study, presents a cost effective environmental friendly energy solution with great social implication. Acknowledgment The authors would like to acknowledge the National Institute of Technology, Agartala, specially the Department of Chemical Engineering, for providing access to the departmental laboratory to execute the project. The authors would also like to express their gratitude to the TEQIP-II for the financial support to present the work. Student author would also like to acknowledge SC Welfare Department, Government of Tripura, for the financial assistance provided in the form of scholarship.
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