Renewable Energy 36 (2011) 2502e2507
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Enhanced in situ ethanolysis of Jatropha curcas L. in the presence of cetyltrimethylammonium bromide as a phase transfer catalyst Sintayehu Mekuria Hailegiorgis, Shuhaimi Mahadzir, Duvvuri Subbarao* Chemical Engineering Department, Universiti Teknologi PETRONAS, Bander Seri Iskandar 31750 Tronoh, Perak, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 November 2010 Accepted 2 March 2011
Limited solubility of alcohols in vegetable oils hinders transesterification reaction process. Phase transfer catalysis can be of great advantage to enhance the reaction rates. Addition of cetyltrimethylammonium bromide as a phase transfer catalyst on in situ transesterification of Jatropha curcas L. with alkaline ethanol was investigated. Use of cetyltrimethylammonium bromide increased the yield of fatty acid ethyl esters. Optimum operating conditions were experimentally established. Yield of fatty acid ethyl esters increased from 89.2 wt% to 99.5 wt% with reduced requirement of ethanol by 16.7 v%, sodium hydroxide catalyst by 33.3 wt%, at a lower temperature of 30 C and reduced mixing speed in shorter reaction time. The quality of fatty acid ethyl esters fuel conforms to the standards of ASTM D6751 and EN-14214. Ó 2011 Elsevier Ltd. All rights reserved.
Keywords: In situ transesterification Jatropha curcas L. Fatty acid ethyl esters Phase transfer catalysis Cetyltrimethylammonium bromide
1. Introduction Majority of the world energy demand is met by non-renewable fossil fuels. They are limited in nature and are getting depleted faster while contributing to the increase in greenhouse gases. Alternative renewable fuels and chemical feedstocks with zero net carbon dioxide emissions are necessary for sustainable development. One such option is biodiesel. Biodiesel can be produced by transesterification of oils and fats from agricultural or animal sources with alcohols in the presence of catalysts [1e4]. Most of the feedstocks used for biodiesel production come from edible oil sources [1] such as soybeans, palm, sunflower, rapeseed, coconut, canola, etc. Diversion of edible oils to biodiesel production can adversely affect food as well as biodiesel industry [1] and [5]. In recent times, use of non-edible oils to produce biodiesel is receiving greater emphasis as they will be cheaper compared to edible oils. Also, it is necessary to minimize the processing steps in the production of oils (such as extraction and purification) to make biodiesel cost competitive enough to make it attractive. Harrinton and D’Arcy Evans [6] demonstrated that direct transesterification of oil in the seeds is possible and it can eliminate the costs associated with oil extraction and purification steps. This process, known as in situ transesterification, was further investigated by Hass et al. [7] and [8], Georgogianni et al. [9], Qian et al. [10] and Zeng et al.
* Corresponding author. Tel.: þ60 134545514; fax: þ60 53656176. E-mail addresses:
[email protected],
[email protected] (S.M. Hailegiorgis),
[email protected] (D. Subbarao). 0960-1481/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2011.03.001
[11] using seeds of edible oils. They observed that in situ transesterification is more efficient than the conventional transesterification. Recently Giniting [12] investigated in situ transesterification of Jatropha seeds with methanol and ethanol and observed that reaction rates and yields are better with ethanol compared with methanol. Shuit et al. [5] and Kaul et al. [13] investigated in situ transesterification of Jatropha with methanol. Methanol with alkali catalyst is widely used for the transesterification of oils. The reaction is quite slow as vegetable oils and methanols are sparingly soluble in each other [14]. They form an emulsion in the presence of alkali catalyst. To enhance the reaction rate, techniques such as use of excess alcohol, mechanical agitation, ultrasonication, a co-solvent addition, higher temperature, pressure, supercritical reactive extraction etc, were investigated [15e19]. Zhang et al. [14] has investigated conventional transesterification of soybean oil assisted by phase transfer catalysis (PTC). They reported high yields (>96.5 wt %) of soybean methyl esters was achieved in a relatively shorter reaction time. PTC is a powerful technique to enhance reaction rate between two or more reactants in two or more sparingly miscible phases. Phase transfer catalyst is a chemical compound that can form a complex with reactant in phase A and diffuse into the phase B to react with the reactant in that phase; formation of the product releases the PTC which diffuses back to Phase A to facilitate the process further. Doraiswamy [20] and Starks et al. [21] described the technique of phase transfer catalysis and listed various catalysts that have been used. Quaternary onium (ammonium and phosphonium) salts are commonly used as PTC as they are much cheaper than other candidates such as crown ethers and crepitates [20]. Zhong et al.
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[22] and Cai et al. [23] produced biodiesel from Litsea cubeba kernel oil in the presence of hexadecyl-trimethylammonium bromide as a PTC in conventional transesterification reaction. They reported an ester exchange rate of 97.6 wt%. On the other hand, Liu et al. [24] recently investigated hydrogenation of biodiesel using thermo regulated PTC for the production of fatty alcohols. Though the catalytic effect of PTC using conventional transesterification method of biodiesel production were reported [14] [22], and [23], the present study investigates the catalytic effects of CTMAB as PTC on in situ transestrification (reactive extraction) method of biodiesel production. The catalytic effects of CTMAB on process variables such as sodium hydroxide concentration, consumption of ethanol, reaction temperature, mixing rate and reaction time were experimentally investigated. There for, the effect of cetyltrimethylammonium bromide (CTMAB) as a phase transfer catalyst (PTC) on base catalyzed in situ transesterification of Jatropha curcas L. seeds with ethanol is explored and results are compared with the same reaction condition in the absence of PTC. 2. Materials and methods Three moles of ethanol are required to react with 1 mol of triglyceride (TG) to yield 3 mol of fatty acid ethyl ester (FAEE) and 1 mol of glycerol in the presence of alkaline catalyst as shown in Eq. (1). O CH2 – O – C – R1 O CH – O – C – R2 O CH2 – O – C – R3 Triglyceride
+
alkali 3C2H5OH catalyst
Ethanol
O R1 - C – O O C R 2–C–O O C R3 – C – O
CH 2
H5
2
- OH
+ CH – OH
2
(1)
H5
C2H5 Fatty acid ethyl esters
CH
2
– OH
Glycerol
Eq. (1): Ethanolysis of triglycerides. 2.1. Materials and chemicals J. curcas L. seeds were purchased from Agro Innaz, Malaysia. Ethanol (C2H5OH, purity 99.7%), n-hexane (CH3(CH2)4CH3, purity 99%), NaOH (purity 99%), KOH (purity 85%), isopropanol (CH3CH2OHCH3, purity 99.8%), cetyltrimethylammonium bromide (C19H42BrN) are procured from Merck in Malaysia. Reagent grade acetic acid and diethyl ether (C4H18O) were purchased from R & M chemicals, Malaysia. Gas chromatographic analytical grade chemical kits were purchased from Sigma Aldrich, Malaysia. 2.2. J. curcas L. preparation and treatment J. curcas L. seed was manually dehulled and milled using Panasonic MX-799S blender and dry mill. It is necessary to reduce water content of seed particles to avoid hydrolysis of TG to form free fatty acids which can consume the alkali catalyst to form unwanted soap [1]. The moisture content of the seed was reduced in conventional oven at 75 C for 2 h. The relatively low temperature was chosen to avoid the damage to seeds and oils in them. Moisture content was determined using RH73 Mettler Toledo moisture analyzer. Particles in the size range of 0.3e0.5 mm are prepared by sieving for the in situ transesterification reaction. The oil content was determined by extracting the oil using soxhlet extractor. 20 g of seed was transferred to soxhlet thimble and extracted using 150 ml of hexane as a solvent. The extracted oil was recovered by evaporating the hexane using a vacuum evaporator at temperatures slightly higher than the boiling point of hexane. The free fatty acid value and percentage were
2503
determined by titration using potassium hydroxide solution and phenolphthalein indicator according to AOCS official method Cd 3d63 [25]. Its acid number was estimated from the free fatty acid value. 2.3. In situ transesterification experiment Twenty grams of conditioned J. curcas L. particles were gently mixed with the desired amount of CTMAB with 10 ml of ethanol in a two neck round bottom flask reactor. Required amount of ethanol with NaOH was preheated to the reaction temperature and added to the reactor to start the reaction. The round bottom flask reactor was equipped with reflux condenser (to prevent loss of alcohol), magnetic stirrer and a thermometer. The flask was immersed in a silicon oil bath thermostat. After the reaction was completed, the reaction mixtures were cooled to room temperature. Vacuum Buchner funnel filter was used to separate the liquid from the solid residue. The solid residue was further washed with 20 ml ethanol to recover the remaining liquid in the solid residue. The liquid mixtures were diluted with distilled water to minimize further reactions. The resulting liquid was in the form of an emulsion. Nhexane (50 ml) was added to the liquid mixtures to faster the clarification of the mixture in to two phases. The top layer contains mixture of FAEE and n-hexane while the bottom layer contains glycerol, ethanol, sodium hydroxide, CTMAB, water and unspent oil. The top layer is recovered and then washed with warm (50e60 C) water several times to remove contaminants. N-hexane and remaining traces of water were removed from the FAEE using vacuum evaporator. The same procedure was repeated without CTMAB. Each experiment was done in duplicate. The actual quantity of FAEE was measured and stored in a screw capped bottle for analysis. Maximum expected quantity of FAEE was estimated based on stoichiometery. FAEE yield was determined using the relation;
Yield of FAEE ¼
Actual measured weight of FAEE 100 Maximum expected weight of FAEE
(2)
2.4. Process variables The process of transesterification is affected by CTMAB concentration, NaOH concentration, ethanol to seed ratio, reaction temperature, agitation speed and reaction time. Experiments were performed with; CTMAB/NaOH (molar ratio): 0, 0.5, 1, 1.5, 2, and 2.5; NaOH/J. curcas L. seeds (w%): 0.068, 0.338, 0.675, 1.013, 1.35 and 1.68; Ethanol/J. curcas L. seeds (v/w): 3, 4.5, 6, 7.5, 9, 10.5, 12; Reaction temperature ( C): 30, 40, 50, 60 and 70; Agitation speed (rpm): 100, 200, 300, 400, 500, 600, 700 and 800; and Reaction time (minutes): 30, 60, 90, 120, 150, 180, 210, 240. The optimum value, based on the FAEE yield, for a parameter was determined by keeping all other parameters constant. Using the determined optimum value for that parameter, the optimum value for the next parameter was investigated. Thus, optimum process conditions were established and corresponding FAEE yield was measured. 2.5. Analytical methods The physicochemical properties of FAEE were evaluated to determine its fuel quality. A calibrated pycnometer (Jayteck, UK) was utilized for density measurement. Brookfield (model cap 2000þ, USA) viscometer was employed to determine its viscosity. The flash point was measured using PenskeMartens automatic
S.M. Hailegiorgis et al. / Renewable Energy 36 (2011) 2502e2507
3. Results and discussion 3.1. J. curcas L. seeds and oil properties The moisture content of dried seed was found to be 1.3%w/w of seed. The oil content of the seed was found to be 52.8%(w/w of seed). The oil content was in the range of the values reported in literature elsewhere [5] ranging from 35 to 60%. The acid percentage of the oil was found to be 0.67%. It was well below 1% and hence the transesterification reaction can be catalyzed by base catalyst [9]. Table 1 presents the physicochemical properties of J. curcas L. oil used in the present investigation. 3.2. In situ transesterification 3.2.1. Effect of CTMAB to base catalyst ratio Fig. 1 illustrates the effect of PTC (CTMAB) on the yield of FAEE (operating conditions: 7.5v/w of ethanol/J. curcas L. seed, 0.675 wt% of NaOH/J. curcas L. seed, 30 C reaction temperature, 300rpm agitation speed and 150 min reaction time). In the absence of CTMAB, the maximum yield of FAEE was 88.2 wt% and an optimum FAEE yield (99.2 wt %) was achieved at 1 M ratio of CTMAB to NaOH. Increase in the yield of FAEE is due to the effect of CTMAB acting as a phase transfer catalyst. The cation of CTMAB (C19H42Nþ, abbreviated as Qþ) may be helping as an intermediate carrier agent to facilitate anion of ethoxide reactant (C2H5O) transfer from polar ethanol/glycerol phase in to the non-polar oil phase in the seed where intrinsic reactive extraction takes place between transferred reactant anions (C2H5O) and TG followed by transfer of di-glyceride anions (CH2COOR3CHCOOR2CH2O, abbreviated as DG) to the bulk alcohol/glycerol phase with the carrier agent. However, increasing the concentration of CTMAB beyond the optimum value reduced the yield of FAEE.
100
98
Et hy l es t ers y ield (w t %)
flash point analyzer (FP93 5G2, ISL, France). The acid value was analyzed by conventional titration method based on AOCS official method Cd 3d-63 [25]. Mono-glyceride (MG), di-glyceride (DG) and TG compositions of FAEE were determined by gas chromatography (GC) based on ASTM D 6584-08 [26]. The GC used was equipped with an on column ejection and flame ionization detector. HT 5 column with 0.32 mm, 0.1 mm and 30 m of diameter, flame thickness and length were used, respectively. The biodiesel sample was silyated with N-methyl-Ntrimethylsilyltrifluoracetamide (MSTFA) before analyzed with GC. Two internal standards and four reference materials were used to create the calibration curves. MG, DG and TG were determined by comparing with monooleine, dioleine and trioleine, respectively. The operating temperature of the column was set at initial temperature of 50 C for 1 min, and then increased to 150 C at a rate of 15 C per minute and the rate decreased to 7 C/min until it reached to 230 C and increased again to 30 C/min while it was reached to 380 C and maintained at this temperature for 10 min. Helium was used as a carrier gas with a flow rate of 3 ml/min in which the FID was set at a temperature of 380 C. FAEE compositions were investigated using gas chromatography spectrometry, GCeMS (QP 5000 series, Shimadzu Japan).
96
94
92
90
88 0
0.5
1 1.5 Molar ratio of CTMAB/NaOH
2
2.5
Fig. 1. Effect of CTMAB/NAOH on FAEE yield (operating conditions: 7.5v/w of ethanol/ Jatropha curcas L.seeds, 0.675 wt% of NaOH/JCL seeds, 30 C, 300 rpm agitation speed and 150 min reaction time). The error bars are obtained from the standard deviation of duplicate experimental values.
3.2.2. Effect of ratio of NaOH to J. curcas L. seed in the presence of CTMAB The effect of ratio of NaOH to J. curcas L. seed (in wt%) in the presence of CTMAB is shown in Fig. 2. For comparison, the effect of ratio of NaOH to J. curcas L. seed (in wt%) in the absence of CTMAB is also shown in Fig. 2. Other operating conditions used are 7.5v/w of ethanol/J. curcas L. seed, 30 C reaction temperature, 300 rpm agitation speed, 150 min reaction time at CTMAB to NaOH molar ratio of 1. In the absence of CTMAB, highest yield of FAEE was 89.1 wt% at a NaOH concentration of 1.013 wt%. In presence of CTMAB, highest yield of FAEE was 98.8 wt% at a NaOH concentration of 0.675 wt%. Hence, reactions assisted by CTMAB gave advantage of 9.7 wt% increment in yield and at the same time use of CTMAB reduced the consumption of NaOH by 33.3 wt%. 3.2.3. Effect of ratio of ethanol/J. curcas L. seed The effect of ratio of volume of ethanol to weight of J. curcas L. seed on the yield of FAEE in the presence of CTMAB is shown in Fig. 3. For comparison, the effect of ratio of volume of ethanol to weight of J. curcas L. seed on the yield of FAEE in the absence of 100
90
80 Et hy l es t ers y ield (w t %)
2504
70
60
50
40
30
Table 1 Physicochemical properties of Jatropha curcas L. oil.
20 0
Property
Unit
Quantity
Acid value Free fatty acid content Saponification Value Kinematic viscosity at 40 C Specific gravity at 25 C
mg KOH/g % mg KOH/g mm2/s
1.67 0.67 201.82 29.13 0.91
0.2
0.4 0.6 0.8 1 1.2 1.4 Ratio of NaOH to Jatropha curcas l. seed (wt%)
1.6
1.8
Fig. 2. Effect of ratio of NaOH to Jatropha curcas L. seed (wt%) on FAEE yield (operating conditions: 7.5v/w of ethanol/Jatropha curcas L. seeds, 1 M ratio of CTMAB/NaOH, 30 C, 300rpm agitation speed, 150 min reaction time, (;) with CTMAB and (C) without CTMAB). The error bars are obtained from the standard deviation of duplicate experimental values.
S.M. Hailegiorgis et al. / Renewable Energy 36 (2011) 2502e2507 100
2505
100 95
90
Et hy l es t ers y ield (w t %)
Et hy l es t ers y ield (w t %)
90 80
70
60
50
2
3
4
5
6
7
8
9
10
80 75 70 65 60
40 1
85
11
Volume of ethanol to Jatropha curcas l. seed ratio (v/wt)
55 Fig. 3. Effect of ratio of ethanol/Jatropha curcas L. seed (v/w) on FAEE yield. (operating conditions: 1 M ratio of CTMAB/NaOH, 0.675 wt% of NaOH/Jatropha curcas L. seeds, 30 C, 300rpm agitation speed, 150 min reaction time, (;) with CTMAB and (C) without CTMAB). The error bars are obtained from the standard deviation of duplicate experimental values.
CTMAB is also shown in Fig. 3. Other operating conditions used are 30 C reaction temperature, 300 rpm agitation speed, 150 min reaction time at CTMAB to NaOH molar ratio of 1 and NaOH to seed weight ratio of 0.675. In the absence of CTMAB, highest yield of FAEE was 88.5 wt% at a volume of ethanol to weight of seed of 9. In the presence of CTMAB, highest yield of FAEE was 99.3 wt% at a volume of ethanol to weight of seed of 7.5. Hence, reactions assisted by CTMAB gave10.8wt% additional yield of FAEE and reduced the consumption of ethanol by 16.7%(v/w). 3.2.4. Effect of reaction temperature The effect of reaction temperature on the yield of FAEE in the presence of CTMAB is shown in Fig. 4. For comparison, the effect of reaction temperature on the yield of FAEE in the absence of CTMAB is also shown in Fig. 4. Other operating conditions used are 300rpm agitation speed, 150 min reaction time at CTMAB to NaOH molar ratio of 1 and NaOH to seed weight ratio of 0.675, ratio of volume of ethanol to weight of J. curcas L. seeds of 7.5. In the absence of
50 100
200
300
400 500 600 Mixing speed (rpm)
700
800
900
Fig. 5. Effect of the mixing speed (rpm) on FAEE yield (operating conditions: 7.5v/w of ethanol/Jatropha curcas L. seeds, 1 M ratio of CTMAB/NaOH, 0.675 wt% of NaOH/ Jatropha curcas L. seeds, 30 C, 150 min reaction time, (;) with CTMAB and (C) without CTMAB). The error bars are obtained from the standard deviation of duplicate experimental values.
CTMAB, highest yield of FAEE was 87.7wt% at a reaction temperature of 50 C. In the presence of CTMAB, highest yield of FAEE was 99.0wt% at a reaction temperature of 30 C. Hence, reactions assisted by CTMAB gave 11.3 wt% additional yield of FAEE and reduced the reaction temperature to room temperature. 3.2.5. Effect of mixing speed The effect of the mixing speed on the yield of FAEE in the presence of CTMAB is shown in Fig. 5. For comparison, the effect of the mixing speed on the yield of FAEE in the absence of CTMAB is also shown in Fig. 5. Other operating conditions used are 150 min reaction time at
100 100 98
90
Et hy l es t ers y ield (w t %)
Et hy l es t ers y ield (w t %)
96 94 92 90 88
80
70
60
86 84
50
82 80 20
40 30
40 50 60 Reaction temperature (oC)
70
80
Fig. 4. Effect of reaction temperature ( C) on FAEE yield (operating conditions: 7.5v/w of ethanol/Jatropha curcas L. seeds, 1 M ratio of CTMAB/NaOH, 0.675 wt% of NaOH/ Jatropha curcas L. seeds, 300 rpm agitation speed, 150 min reaction time, (;) with CTMAB and (C)without CTMAB). The error bars are obtained from the standard deviation of duplicate experimental values.
0
50
100 150 Reaction time (minutes)
200
250
Fig. 6. Effect of the reaction time (minutes) on FAEE yield (operating conditions: 7.5v/ w of ethanol/Jatropha curcas L. seeds, 1 M ratio of CTMAB/NaOH, 0.675 wt% of NaOH/ Jatropha curcas L. seeds, 30 C, 300 rpm agitation speed, (;) with CTMAB and (C) without CTMAB). The error bars are obtained from the standard deviation of duplicate experimental values.
2506
S.M. Hailegiorgis et al. / Renewable Energy 36 (2011) 2502e2507
CTMAB to NaOH molar ratio of 1 and NaOH to seed weight ratio of 0.675, ratio of volume of ethanol to weight of seed of 7.5 and reaction temperature of 30 C. In the absence of CTMAB, highest yield of FAEE was 88.4wt% at a mixing speed of 600 rpm. In the presence of CTMAB, highest yield of FAEE was 99.5 wt% at a mixing speed of 400 rpm. Hence, reactions assisted by CTMAB gave 11.1 wt% additional yield of FAEE and reduced the mixing speed by 200 rpm. 3.2.6. Effect of reaction time The effect of reaction time on the yield of FAEE in the presence of CTMAB is shown in Fig. 6. For comparison, the effect of reaction time on the yield of FAEE in the absence of CTMAB is also shown in Fig. 6. Other operating conditions used are CTMAB to NaOH molar ratio of 1 and NaOH to seed weight ratio of 0.675, ratio of volume of ethanol to weight of seed of 7.5 and reaction temperature of 30 C, mixing speed of 400 rpm. In the absence of CTMAB, highest yield of FAEE was 89.2 wt% at a reaction time of 180 min. In the presence of CTMAB, highest yield of FAEE was 99.5wt% at a reaction time of 150 min. Hence, reactions assisted by CTMAB gave 10.3 wt% additional yield of FAEE and reduced the reaction time by 30 min.
Table 2 Optimum operating conditions of fatty acid ethyl esters production. Parameter
Value
Ratio of ethanol to Jatropha curcas L. seeds Ratio of CTMAB to NaOH Ratio of NaOH to Jatropha curcas L. seeds Reaction temperature Agitation speed Reaction time
7.5v/w 1 mol per mol 0.675 wt% 30 C 300 rpm 150 min
Table 3 Properties of fatty acid ethyl esters as compared to international standards. Property
Units
Kinetic viscosity at 40 C Density at 15 C Acid value Flash point Mono-glyceride Di-glyceride Triglyceride
mm2/s kg/m3 mgKOH/g C % mass % mass % mass
FAEE value
Required by ASTM D6751
Required by EN-14214
4.8
1.9e6
3.5e5
867 0.21 173
