Bioresource Technology 156 (2014) 283–290
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Ultrasound-enhanced rapid in situ transesterification of marine macroalgae Enteromorpha compressa for biodiesel production Tamilarasan Suganya, Ramachandran Kasirajan, Sahadevan Renganathan ⇑ Department of Chemical Engineering, Alagappa College of Technology, Anna University, Chennai 600025, India
h i g h l i g h t s Enteromorpha compressa is a proven to be potential source for biodiesel production. Co-solvent was introduced to enhance the efficiency of reactive in situ method. Maximum yield of ME 98.89% was achieved using ultrasonication technique. The reaction parameters were optimized to increase the yield of ME. In situ transesterification was found to be a suitable method for macroalgae biomass.
a r t i c l e
i n f o
Article history: Received 31 October 2013 Received in revised form 11 January 2014 Accepted 14 January 2014 Available online 24 January 2014 Keywords: Enteromorpha compressa Biodiesel In situ transesterification NMR Ultrasonication
a b s t r a c t In situ transesterification of Enteromorpha compressa algal biomass was carried out for the production of biodiesel. The maximum methyl esters (ME) yield of 98.89% was obtained using ultrasonic irradiation. Tetra hydro furan (THF) and acid catalyst (H2SO4) was found to be an appropriate co-solvent and catalyst for high free fatty acids (FFA) content E. compressa biomass to increase the efficiency of the reactive in situ process. The optimization study was conducted to obtain the maximum yield and it was determined as 30 vol% of THF as a co-solvent, 10 wt% of H2SO4, 5.5:1 ratio of methanol to algal biomass and 600 rpm of mixing intensity at 65 °C for 90 min of ultrasonic irradiation time. The produced biodiesel was characterized by 1H nuclear magnetic resonance spectroscopy (1H NMR) analysis. Kinetic studies revealed that the reaction followed the first-order reaction mechanism. Rapid in situ transesterification was found to be suitable technique to produce biodiesel from marine macroalgae feedstock. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction The current crisis of pollution caused by the burning of fossil fuels as well as their declining reserves is driving research into the development of renewable bio-fuels (Razif Harun et al., 2011). Biodiesel fuel, which consists of the simple alkyl esters of fatty acids (preferentially methyl esters (ME)), has acquired a growing interest as an alternative to diesel fuels made from renewable sources. Biodiesel has two main advantages, the mitigation of carbon dioxide and as a substitute for petroleum (Chisti, 2008). In addition to meeting an engine performance and the environmental criteria, biodiesel has to compete economically with diesel fuels in order to survive in the market. One way of reducing the biodiesel production costs is to use the less expensive feedstocks. Marine macroalgae has been shown to be an appropriate substitute for a diesel fuel (Suganya et al., 2013). Macroalgae also have certain ⇑ Corresponding author. Tel.: +91 9941613532; fax: +91 4422352642. E-mail address: [email protected] (S. Renganathan). 0960-8524/$ - see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2014.01.050
advantages compared to other energy crops, including a high growth rate, short growth time and high biomass production. Conventional method for the production of biodiesel from algae and other types of oil feedstocks involves various stages; oil extraction, purification (degumming, deacidification, dewaxing, dephosphorization, dehydration, etc.) and esterification/transesterification. The requirement of these multiple processing stages constitutes over 70% of the total production cost of biodiesel (Zeng et al., 2009). Therefore, development of in situ extraction, direct transesterification or simply as reactive extraction has the potential to cut down the processing cost with any kind of feedstocks. Reactive extraction differs from the conventional biodiesel production process in which the oil bearing material contacts with the alcohol directly instead of reacting with extracted oil. In other words, extraction and transesterification proceed in one single step, with alcohol acting as an extraction solvent and a transesterification reagent (Georgogianni et al., 2008b). Several authors (Pena et al., 2009; Boocock et al., 1998) have discussed the problem of the mass transfer limitations in
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transesterification reactions due to low oil solubility in alcohol phase; this problem slows down the reaction resulting in low ester yield. An alternative to solve this problem is the use of a cosolvent that accelerates the reaction. To perform the reaction in a single phase and increase the miscibility of oil in alcohol, co-solvents such as benzene, hexane, THF, chloroform, petroleum ether and dichloromethane have been tested in this present investigation. Several investigations have been conducted on in situ transesterification with conventional feedstocks (Mondala et al., 2009; Harrington and D’Arcy-Evans, 1985; Haas and Scott, 2007; Qian et al., 2008; Shuit et al., 2010). In situ transesterification of marine macroalgae biomass was reported as a first time for biodiesel production in this present study. In the last two decades, ultrasonication, the chemical reaction during ultrasound irradiation, has developed into an expanding research area. Ultrasound energy is known to produce chemical and physical effects that arise from the collapse of cavitation bubbles. The collapse of cavitation bubbles disrupts the phase boundary in a two-phase liquid system and causes emulsification by ultrasonic jets that impinge one liquid into the other (Mason and Lorimer, 2002). This effect can be employed for biodiesel production (Stavarache et al., 2005; Colucci et al., 2005). Therefore, ultrasonic irradiation was employed in this present investigation. The main objective of this study is to produce biodiesel from Enteromorpha compressa by in situ transesterification process under ultrasonic irradiation. The suitable co-solvent was selected for the in situ transesterification of E. compressa biomass which has high FFA. The reaction parameters were optimized to increase the yield of biodiesel. The produced biodiesel was characterized by 1H NMR spectroscopy analysis. Kinetic studies were implemented to find out the order of the in situ transesterification reaction, reaction rate constants and activation energy required for the reaction.
2. Methods 2.1. Materials Sulphuric acid (H2SO4) and hydrochloric acid (HCl) used as acid catalysts, sodium hydroxide (NaOH), potassium hydroxide (KOH) used as alkali catalysts were purchased from Sisco Research Laboratory (SRL), Mumbai, India. Organic solvents of the analytical grade (Extra pure 99%) were purchased from Merck Ltd., Mumbai, India. They were reused after preliminary distillation. 2.2. Collection of algal sample E. compressa Macroalgae species was collected from Rameswaram, Mandapam, South coast (Gulf of Mannar), India. The macroalgae were collected by hand picking from the intertidal and sub tidal regions. The sample collection was carried out during the low tide period.
2.4. Pre-treatment of algal biomass by ultrasonication Dry algal biomass along with water (water to biomass ratio as 3:1 v/w) was taken in a conical flask. Ultrasonication was carried out using an ultrasonic probe (Hielscher UP 400S, Germany) at 24 kHz with constant temperature (50 ± 1 °C) for 6 min. After the destruction of the algal cell wall, the biomass was dried in shade conditions and in an oven at 60 ± 5 °C (Suganya et al., 2013). The pretreated algal biomass was loaded for effective in situ transesterification.
2.5. Experimental set up for in situ transesterification under ultrasonic irradiation A thermostatic ultrasonic cleaner (WS 1200–40) with 40 kHz operating frequency and maximum power of 1200 W (working power being set at 100%) was employed to implement the ultrasonic irradiation. The in situ transesterification process was carried out, using the pre-treated biomass. Algal biomass with optimized particle size and moisture content was taken in a three-necked round bottom flask, which is placed in a thermostatic ultrasonic cleaner with a mechanical stirrer used as a reactor for the in situ transesterification process. Initially, a suitable catalyst to biomass (wt%) was mixed with various investigated volumes of the alcohol (methanol to biomass ratio (v/w)). An appropriate volume of the selected co-solvent (vol%) was mixed with the reacting alcohol mixture (methanol along with catalyst) and it was heated separately. Then methanol, co-solvent and catalyst mixture was added to the reaction flask. A three-necked flask filled with sample mixtures (algal biomass, co-solvent, methanol and catalyst) was submerged in the ultrasonic reactor and heated from 45 to 70 °C. The mechanical stirrer was fixed in the middle neck for stirring. A water cooled reflux condenser was attached in one side neck of the flask and sampling was done in another neck. Three trial runs were carried out for each combination of reactants and process conditions. The major in situ transesterification reaction and product purification steps used, are shown in Fig. 1. After the transesterification step the reaction mixture was allowed to stand for 1 h to enable its contents to settle. The reaction mixture was filtered to separate the solid biomass from the liquid layer. The solid biomass residues were washed twice by re-suspension in methanol for 10 min, to recover traces of the ME product left in the residues. Water was added to the filtrate to facilitate the separation of the hydrophilic components of the extract and then transferred to a separating funnel. The upper layer is a hydrophobic one consisting of the co-solvent with ME and the lower phase consists of glycerol and impurities. The pooled hydrophobic layer was separated, washed with water (to remove left-over traces of the catalyst and methanol) and then dried over anhydrous sodium sulphate. The ME product was then filtered and evaporated to obtain the pure ME.
2.6. Selection of catalyst 2.3. Preparation of algal biomass The collected algae were brought to the laboratory and washed with fresh water followed by distilled water to separate the potential contaminants such as adhering impurities, sand particles, epiphytes and animal castings. The algal biomass were dried in shade and in an oven at 60–70 °C and then pulverized. The particle size distribution was determined using a sieve analyzer as per the American Society for Testing and Materials (ASTM) standards (Suganya and Renganathan, 2012).
Acid catalysts such as H2SO4 and HCl and base catalysts such as NaOH and KOH were used to study and select a suitable catalyst for the in situ transesterification.
2.7. Selection of co-solvent The appropriate co-solvent was selected from among six different solvents, such as benzene, hexane, tetrahydrofuran, chloroform, petroleum ether and dichloromethane.
T. Suganya et al. / Bioresource Technology 156 (2014) 283–290
285
Fig. 1. Experimental set up for in situ transesterification under ultrasonic-irradiation.
2.8. Optimization of in situ parameters The reaction parameters, such as, catalyst concentration (wt% to biomass), co-solvent concentration (vol% to methanol), methanol to biomass ratio (v/w), mixing intensity (rpm), temperature (°C) and reaction time(min) which influence the yield of ME, were optimized.
The yield of ME was calculated using the following formula (Eq. (1)) (Rashid et al., 2010)
ð1Þ
2.10. Characterization of biodiesel produced by in situ transesterification ME produced from macroalgae biomass by the in situ method, was characterized by 1H NMR. 1H NMR spectra were obtained using a BRUKER 500 MHz AVANCE III instrument with CDCl3 as solvent and TMS as an internal standard. 1H spectra were recorded with pulse duration of 45 °C and 16 scans. A simple formula (Eq. (2)) for conversion (%) is
C ¼ 100
2AME 3ACH2
dXA ¼ kð1 XA Þ dt
ð2Þ
where C – percentage conversion of algal oil to ME, AME – integration value of the methoxy protons of the ME (the strong singlet). ACH2 Integration value of the methylene protons. Factors 2 and 3 were derived from the fact, that the methylene carbon possesses two protons, while the alcohol (methanol derived) carbon has three attached protons. 2.11. Kinetic studies for in situ transesterification reaction In the present investigation, the kinetic studies were carried out with first-order and second-order kinetic mechanism.
ð3Þ
Rearrangement of the above Eq. (3)
dXA ¼ kð1 XA Þ dt
2.9. Determination of ME yield
grams of methylesters produced Yield of methylesters ð%Þ ¼ 100 grams of oil used in reaction
2.11.1. First-order kinetics In terms of conversion, the first-order rate equation for in situ transesterification reaction can be expressed as Eq. (3)
ð4Þ
Integrating of the above equation gives (Eq. (5)) (Carmo et al., 2009)
lnð1 XA Þ ¼ kt
ð5Þ
where XA is the conversion of triglycerides (TG) (%), t is the time of reaction (min) and k is the reaction rate constant (min1). A plot was drawn with ln (1 XA) as a function of reaction time (t) at various temperature ranging from 45 to 65 °C. The coefficient of determination (R2) of the straight lines were determined to calculate reaction rate constant and order of the reaction. 2.11.2. Second-order kinetics According to the second-order kinetics, the rate equation of the in situ transesterification reaction is as follows Eq. (6)
ðrA Þ ¼
dCA 2 ¼ kCA dt
ð6Þ
where k is the reaction rate constant for the second-order reaction and CA is concentration of TG. Since the TG concentration is related to the conversion XA
C A ¼ C A0 ð1 XA Þ
ð7Þ
In terms of conversion, the rate equation is as follows (Eq. (8)):
dXA ¼ kCA0 ð1 XA Þ2 dt
ð8Þ
where CA0 is the initial TG concentration of the reaction. Upon the integration of Eq. (8), the following equation is obtained (Eq. (9)) (Marjanovic et al., 2010):
XA ¼ kCA0 t 1 XA
ð9Þ
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T. Suganya et al. / Bioresource Technology 156 (2014) 283–290
where XA is the ME conversion (%), t is the time of reaction (min) and k is the reaction rate constant (ml/mol⁄min1). The reaction rate constants were determined using the slope of the dependence of XA/(1 XA) on t. The slope from the linear equation is divided with the initial concentration of TG to get the rate constant for the second-order transesterification reaction.
produced the maximum ME yield of 48.65% along with acidified methanol (Fig. 2a). Petroleum ether and dichloromethane produced 35.65% and 29.86% yield of ME, respectively. Benzene gave 21.41% of ME yield. Chloroform and hexane produced
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Ultrasound-enhanced rapid in situ transesterification of marine macroalgae Enteromorpha compressa for biodiesel production Tamilarasan Suganya, Ramachandran Kasirajan, Sahadevan Renganathan ⇑ Department of Chemical Engineering, Alagappa College of Technology, Anna University, Chennai 600025, India
h i g h l i g h t s Enteromorpha compressa is a proven to be potential source for biodiesel production. Co-solvent was introduced to enhance the efficiency of reactive in situ method. Maximum yield of ME 98.89% was achieved using ultrasonication technique. The reaction parameters were optimized to increase the yield of ME. In situ transesterification was found to be a suitable method for macroalgae biomass.
a r t i c l e
i n f o
Article history: Received 31 October 2013 Received in revised form 11 January 2014 Accepted 14 January 2014 Available online 24 January 2014 Keywords: Enteromorpha compressa Biodiesel In situ transesterification NMR Ultrasonication
a b s t r a c t In situ transesterification of Enteromorpha compressa algal biomass was carried out for the production of biodiesel. The maximum methyl esters (ME) yield of 98.89% was obtained using ultrasonic irradiation. Tetra hydro furan (THF) and acid catalyst (H2SO4) was found to be an appropriate co-solvent and catalyst for high free fatty acids (FFA) content E. compressa biomass to increase the efficiency of the reactive in situ process. The optimization study was conducted to obtain the maximum yield and it was determined as 30 vol% of THF as a co-solvent, 10 wt% of H2SO4, 5.5:1 ratio of methanol to algal biomass and 600 rpm of mixing intensity at 65 °C for 90 min of ultrasonic irradiation time. The produced biodiesel was characterized by 1H nuclear magnetic resonance spectroscopy (1H NMR) analysis. Kinetic studies revealed that the reaction followed the first-order reaction mechanism. Rapid in situ transesterification was found to be suitable technique to produce biodiesel from marine macroalgae feedstock. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction The current crisis of pollution caused by the burning of fossil fuels as well as their declining reserves is driving research into the development of renewable bio-fuels (Razif Harun et al., 2011). Biodiesel fuel, which consists of the simple alkyl esters of fatty acids (preferentially methyl esters (ME)), has acquired a growing interest as an alternative to diesel fuels made from renewable sources. Biodiesel has two main advantages, the mitigation of carbon dioxide and as a substitute for petroleum (Chisti, 2008). In addition to meeting an engine performance and the environmental criteria, biodiesel has to compete economically with diesel fuels in order to survive in the market. One way of reducing the biodiesel production costs is to use the less expensive feedstocks. Marine macroalgae has been shown to be an appropriate substitute for a diesel fuel (Suganya et al., 2013). Macroalgae also have certain ⇑ Corresponding author. Tel.: +91 9941613532; fax: +91 4422352642. E-mail address: [email protected] (S. Renganathan). 0960-8524/$ - see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2014.01.050
advantages compared to other energy crops, including a high growth rate, short growth time and high biomass production. Conventional method for the production of biodiesel from algae and other types of oil feedstocks involves various stages; oil extraction, purification (degumming, deacidification, dewaxing, dephosphorization, dehydration, etc.) and esterification/transesterification. The requirement of these multiple processing stages constitutes over 70% of the total production cost of biodiesel (Zeng et al., 2009). Therefore, development of in situ extraction, direct transesterification or simply as reactive extraction has the potential to cut down the processing cost with any kind of feedstocks. Reactive extraction differs from the conventional biodiesel production process in which the oil bearing material contacts with the alcohol directly instead of reacting with extracted oil. In other words, extraction and transesterification proceed in one single step, with alcohol acting as an extraction solvent and a transesterification reagent (Georgogianni et al., 2008b). Several authors (Pena et al., 2009; Boocock et al., 1998) have discussed the problem of the mass transfer limitations in
284
T. Suganya et al. / Bioresource Technology 156 (2014) 283–290
transesterification reactions due to low oil solubility in alcohol phase; this problem slows down the reaction resulting in low ester yield. An alternative to solve this problem is the use of a cosolvent that accelerates the reaction. To perform the reaction in a single phase and increase the miscibility of oil in alcohol, co-solvents such as benzene, hexane, THF, chloroform, petroleum ether and dichloromethane have been tested in this present investigation. Several investigations have been conducted on in situ transesterification with conventional feedstocks (Mondala et al., 2009; Harrington and D’Arcy-Evans, 1985; Haas and Scott, 2007; Qian et al., 2008; Shuit et al., 2010). In situ transesterification of marine macroalgae biomass was reported as a first time for biodiesel production in this present study. In the last two decades, ultrasonication, the chemical reaction during ultrasound irradiation, has developed into an expanding research area. Ultrasound energy is known to produce chemical and physical effects that arise from the collapse of cavitation bubbles. The collapse of cavitation bubbles disrupts the phase boundary in a two-phase liquid system and causes emulsification by ultrasonic jets that impinge one liquid into the other (Mason and Lorimer, 2002). This effect can be employed for biodiesel production (Stavarache et al., 2005; Colucci et al., 2005). Therefore, ultrasonic irradiation was employed in this present investigation. The main objective of this study is to produce biodiesel from Enteromorpha compressa by in situ transesterification process under ultrasonic irradiation. The suitable co-solvent was selected for the in situ transesterification of E. compressa biomass which has high FFA. The reaction parameters were optimized to increase the yield of biodiesel. The produced biodiesel was characterized by 1H NMR spectroscopy analysis. Kinetic studies were implemented to find out the order of the in situ transesterification reaction, reaction rate constants and activation energy required for the reaction.
2. Methods 2.1. Materials Sulphuric acid (H2SO4) and hydrochloric acid (HCl) used as acid catalysts, sodium hydroxide (NaOH), potassium hydroxide (KOH) used as alkali catalysts were purchased from Sisco Research Laboratory (SRL), Mumbai, India. Organic solvents of the analytical grade (Extra pure 99%) were purchased from Merck Ltd., Mumbai, India. They were reused after preliminary distillation. 2.2. Collection of algal sample E. compressa Macroalgae species was collected from Rameswaram, Mandapam, South coast (Gulf of Mannar), India. The macroalgae were collected by hand picking from the intertidal and sub tidal regions. The sample collection was carried out during the low tide period.
2.4. Pre-treatment of algal biomass by ultrasonication Dry algal biomass along with water (water to biomass ratio as 3:1 v/w) was taken in a conical flask. Ultrasonication was carried out using an ultrasonic probe (Hielscher UP 400S, Germany) at 24 kHz with constant temperature (50 ± 1 °C) for 6 min. After the destruction of the algal cell wall, the biomass was dried in shade conditions and in an oven at 60 ± 5 °C (Suganya et al., 2013). The pretreated algal biomass was loaded for effective in situ transesterification.
2.5. Experimental set up for in situ transesterification under ultrasonic irradiation A thermostatic ultrasonic cleaner (WS 1200–40) with 40 kHz operating frequency and maximum power of 1200 W (working power being set at 100%) was employed to implement the ultrasonic irradiation. The in situ transesterification process was carried out, using the pre-treated biomass. Algal biomass with optimized particle size and moisture content was taken in a three-necked round bottom flask, which is placed in a thermostatic ultrasonic cleaner with a mechanical stirrer used as a reactor for the in situ transesterification process. Initially, a suitable catalyst to biomass (wt%) was mixed with various investigated volumes of the alcohol (methanol to biomass ratio (v/w)). An appropriate volume of the selected co-solvent (vol%) was mixed with the reacting alcohol mixture (methanol along with catalyst) and it was heated separately. Then methanol, co-solvent and catalyst mixture was added to the reaction flask. A three-necked flask filled with sample mixtures (algal biomass, co-solvent, methanol and catalyst) was submerged in the ultrasonic reactor and heated from 45 to 70 °C. The mechanical stirrer was fixed in the middle neck for stirring. A water cooled reflux condenser was attached in one side neck of the flask and sampling was done in another neck. Three trial runs were carried out for each combination of reactants and process conditions. The major in situ transesterification reaction and product purification steps used, are shown in Fig. 1. After the transesterification step the reaction mixture was allowed to stand for 1 h to enable its contents to settle. The reaction mixture was filtered to separate the solid biomass from the liquid layer. The solid biomass residues were washed twice by re-suspension in methanol for 10 min, to recover traces of the ME product left in the residues. Water was added to the filtrate to facilitate the separation of the hydrophilic components of the extract and then transferred to a separating funnel. The upper layer is a hydrophobic one consisting of the co-solvent with ME and the lower phase consists of glycerol and impurities. The pooled hydrophobic layer was separated, washed with water (to remove left-over traces of the catalyst and methanol) and then dried over anhydrous sodium sulphate. The ME product was then filtered and evaporated to obtain the pure ME.
2.6. Selection of catalyst 2.3. Preparation of algal biomass The collected algae were brought to the laboratory and washed with fresh water followed by distilled water to separate the potential contaminants such as adhering impurities, sand particles, epiphytes and animal castings. The algal biomass were dried in shade and in an oven at 60–70 °C and then pulverized. The particle size distribution was determined using a sieve analyzer as per the American Society for Testing and Materials (ASTM) standards (Suganya and Renganathan, 2012).
Acid catalysts such as H2SO4 and HCl and base catalysts such as NaOH and KOH were used to study and select a suitable catalyst for the in situ transesterification.
2.7. Selection of co-solvent The appropriate co-solvent was selected from among six different solvents, such as benzene, hexane, tetrahydrofuran, chloroform, petroleum ether and dichloromethane.
T. Suganya et al. / Bioresource Technology 156 (2014) 283–290
285
Fig. 1. Experimental set up for in situ transesterification under ultrasonic-irradiation.
2.8. Optimization of in situ parameters The reaction parameters, such as, catalyst concentration (wt% to biomass), co-solvent concentration (vol% to methanol), methanol to biomass ratio (v/w), mixing intensity (rpm), temperature (°C) and reaction time(min) which influence the yield of ME, were optimized.
The yield of ME was calculated using the following formula (Eq. (1)) (Rashid et al., 2010)
ð1Þ
2.10. Characterization of biodiesel produced by in situ transesterification ME produced from macroalgae biomass by the in situ method, was characterized by 1H NMR. 1H NMR spectra were obtained using a BRUKER 500 MHz AVANCE III instrument with CDCl3 as solvent and TMS as an internal standard. 1H spectra were recorded with pulse duration of 45 °C and 16 scans. A simple formula (Eq. (2)) for conversion (%) is
C ¼ 100
2AME 3ACH2
dXA ¼ kð1 XA Þ dt
ð2Þ
where C – percentage conversion of algal oil to ME, AME – integration value of the methoxy protons of the ME (the strong singlet). ACH2 Integration value of the methylene protons. Factors 2 and 3 were derived from the fact, that the methylene carbon possesses two protons, while the alcohol (methanol derived) carbon has three attached protons. 2.11. Kinetic studies for in situ transesterification reaction In the present investigation, the kinetic studies were carried out with first-order and second-order kinetic mechanism.
ð3Þ
Rearrangement of the above Eq. (3)
dXA ¼ kð1 XA Þ dt
2.9. Determination of ME yield
grams of methylesters produced Yield of methylesters ð%Þ ¼ 100 grams of oil used in reaction
2.11.1. First-order kinetics In terms of conversion, the first-order rate equation for in situ transesterification reaction can be expressed as Eq. (3)
ð4Þ
Integrating of the above equation gives (Eq. (5)) (Carmo et al., 2009)
lnð1 XA Þ ¼ kt
ð5Þ
where XA is the conversion of triglycerides (TG) (%), t is the time of reaction (min) and k is the reaction rate constant (min1). A plot was drawn with ln (1 XA) as a function of reaction time (t) at various temperature ranging from 45 to 65 °C. The coefficient of determination (R2) of the straight lines were determined to calculate reaction rate constant and order of the reaction. 2.11.2. Second-order kinetics According to the second-order kinetics, the rate equation of the in situ transesterification reaction is as follows Eq. (6)
ðrA Þ ¼
dCA 2 ¼ kCA dt
ð6Þ
where k is the reaction rate constant for the second-order reaction and CA is concentration of TG. Since the TG concentration is related to the conversion XA
C A ¼ C A0 ð1 XA Þ
ð7Þ
In terms of conversion, the rate equation is as follows (Eq. (8)):
dXA ¼ kCA0 ð1 XA Þ2 dt
ð8Þ
where CA0 is the initial TG concentration of the reaction. Upon the integration of Eq. (8), the following equation is obtained (Eq. (9)) (Marjanovic et al., 2010):
XA ¼ kCA0 t 1 XA
ð9Þ
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T. Suganya et al. / Bioresource Technology 156 (2014) 283–290
where XA is the ME conversion (%), t is the time of reaction (min) and k is the reaction rate constant (ml/mol⁄min1). The reaction rate constants were determined using the slope of the dependence of XA/(1 XA) on t. The slope from the linear equation is divided with the initial concentration of TG to get the rate constant for the second-order transesterification reaction.
produced the maximum ME yield of 48.65% along with acidified methanol (Fig. 2a). Petroleum ether and dichloromethane produced 35.65% and 29.86% yield of ME, respectively. Benzene gave 21.41% of ME yield. Chloroform and hexane produced
