International Advanced of Technology Congress (ATCi), PWTC, Malaysia. 3-5 November 2009
Production of Biodiesel from Sludge Palm Oil by Esterification Using P-toluenesulfonic Acid Adeeb Hayyan1*, Md. Zahangir Alam1, Mohamed E.S. Mirghani1, Nassereldeen A. Kabbashi1, Yosri Mohd Siran2 and Noor Irma Nazashida Mohd Hakimi2 1
Bioenvironmental Engineering Research Unit (BERU), Department of Biotechnology Engineering , Faculty of Engineering , International Islamic University Malaysia, P.O. BOX 10, Kuala Lumpur, 50728, Malaysia. Email:
[email protected] 2 Processing & Engineering , R&D Center - Downstream , Sime Darby Research Sdn Bhd. Lot 2664 Jalan Pulau Carey,42960 Pulau Carey , Kuala Langat , Selangor , Malaysia
Abstract – Sludge palm oil (SPO) is an attractive feedstock and a significant raw material for biodiesel production. The use of SPO as feedstock for biodiesel production requires additional pretreatment step to transesterification process, which is an esterification process. The most commonly preferred catalysts used in this process are sulfuric, sulphonic, hydrochloric and P-toluenesulfonic acid (PTSA). In this study biodiesel fuel was produced from SPO using PTSA as acid catalyst in different dosages in presence of alcohol to convert free fatty acid (FFA) to fatty acid methyl ester (FAME). Batch esterification process of SPO was carried out to study the influence of PTSA dosage (0.25-10% wt/wt), molar o ratio of methanol to SPO (6:1-20:1), temperature (40-80 C), reaction time (30-120 min). The effects of those parameters on FFA content, yield of treated SPO and conversion of FFA to FAME were monitored. The study showed that the FFA content of SPO reduced from 22% to less than 0.15% using ratio of 0.5, 0.75, 1, 1.5, and 2% wt/wt PTSA to SPO. After esterification process dosage of PTSA at 0.75% wt/wt shows the highest conversion of FFA to FAME as well o as yield of treated SPO. The optimum condition for batch esterification process was 10:1 molar ratio, temperature 60 C and 60 minutes reaction time. The highest yield of biodiesel after transesterification process was 76.62% with 0.06% FFA and 93% ester content. Keywords: Biodiesel, Esterification, Free fatty acid, P-toluenesulfonic acid, Transesterification.
I.
Introduction
Biodiesel, a fuel that can be made from renewable biological sources, such as vegetable oils, animal fats and waste cooking oil, may have the potential to reduce the reliance on petroleum fuel and reduce air pollutant emissions from diesel engines. In recent years, due to diminishing petroleum reserves, increasing fuel prices and environmental problems considerable concern have been raised over diesel-powered vehicles using biodiesel as fuel in many countries[1-2]. However, in spite of the favorable impact, the economic aspect of biodiesel production is still a barrier for its development, mainly due to the lower price of petroleum fuel [3]. Currently, edible vegetable oils, such as palm oil, soybean, rapeseed and sunflower are the prevalent feedstocks for biodiesel production [4]. Obviously, production of biodiesel from edible vegetable oil results in the high price of biodiesel. Therefore, exploring ways to reduce the cost of raw material is the main interest in resent biodiesel research. There are large amounts of low grade oils from palm oil industry that can be converted to
biodiesel such as sludge palm oil (SPO), a by-product of palm oil milling process. In Malaysia SPO generated from palm oil mills reaches 200 ton/year. The use of SPO can lower the cost of biodiesel production significantly, which makes SPO a highly potential alternative feedstock for biodiesel production. SPO usually contains high amounts of free fatty acid (FFA) that cannot be converted to biodiesel using an alkaline catalyst [5]. The oil should not contain more than 2% FFA for alkaline catalyzed transesterification reaction [6]. Esterification process is used in order to pretreat the SPO by converting the FFA to fatty acid methyl ester (FAME) using acid catalyst. The most commonly preferred acid catalysts are sulfuric, hydrochloric, sulphonic acid and P-toluenesulfonic acid (PTSA) [7]. PTSA showed highest catalytic activity compared to other acid catalysts [8]. The objective of this research was to investigate the potential of SPO as low-cost raw material in biodiesel production, study the influence of PTSA dosage and the effects of reaction variables such as molar ratio, reaction time and temperature on esterification reaction as well as evaluation of biodiesel produced after Transesterification process.
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II.
RAW MATERIALS AND CHEMICALS
SPO was obtained from West Oil Mill, Carey Island, o Selangor. SPO was stored in cool room at 4 C. Methyl alcohol anhydrous 99.8% commercial grade was purchased from Mallinckrodt Chemicals USA, Ptoluenesulfonic acid 99% laboratory grade was purchased from Merck Sdn Bhd, Malaysia and Potassium hydroxide 85% were purchased from HmbG chemicals.
III.
METHODS
Firstly preheating step was performed because at room temperature SPO usually in semisolid phase. The SPO was melted in the oven at high temperature around o 80 C and the preheated SPO then was transferred into the reactor. Pretreatment of SPO using acid esterification, followed by alkaline transesterification were done. It was followed by separation and purification of biodiesel formed from the two reactions. 1) Acid esterification reaction PTSA was added into the preheated SPO at different dosages in presence of methanol to reduce FFA of SPO by converting the FFA to FAME. The mechanism for the acid esterification reaction is shown in Figure 1 [9]. Several batch esterification process were carried out to study the influence of PTSA dosages (0.25-10% wt/wt), molar ratio of methanol to SPO (6:1-20:1), reaction o temperature (40-80 C), and reaction time (30-120 min). The effects of those parameters on FFA content, yield of treated SPO and FFA to FAME conversion were measured.
Figure 1: Mechanism of acid esterification reaction
2) Alkaline transesterification reaction The objective of this chemical process is to produce a fuel with lower viscosity by reacting triglyceride with alcohol in presence of alkaline catalyst such as potassium or sodium hydroxide [8]. The mechanism for the transesterification reaction is shown in Figure 2 [10]. The process condition for transesterification reaction was: molar ratio methanol to SPO 10:1, o reaction temperature 60 C, reaction time 60 min, stirrer speed 400 rpm and 1% wt/wt KOH.
Figure 2: Mechanism of alkaline transesterification reaction
All experiments were performed in 1.5 of batch reactor with reflux condenser and all parameters were controlled by digital controller. 3) Separation and purification of biodiesel After the completion of the reaction, the excess o methanol was recovered under vacuum at 70 C with a rotary evaporator for an hour. The product was allowed to cool and equilibrate which resulted into separation of two layers in separating funnel. After one day separation time, the upper phase consisted of biodiesel with small amounts of impurities such as residual alcohol, glycerol, moisture and trace of glycerides. While the lower layer contained the glycerol with other materials (excess methanol, catalyst, soaps formed during the reaction and some entrained biodiesel and traces of glycerides). In order to remove methanol in the biodiesel, the wet crude biodiesel was dried under vacuum with a rotary evaporator. 4) Analysis Fatty acid composition of SPO was determined using GC/MS (Agilent Technologies 7890A), the capillary column was DB- wax 122-7032, with length of 30m, film thickness of 0.25µm and an internal diameter of 0.25mm. Helium was used as carrier gas with a flow o rate of 36 cm/sec, measured at 50 C, the run time was 35 min. 1 µm of neat sample was diluted in hexane prior injection into GC. Ester content was analyzed using GC/FID (Perkin Elmer Clarus 500), split-splitless mode of injector, capillary column- Polyethylene glycol o wax phase, isotherm oven at 250 C. Monoacylglycerines, Diacylglycerines, Triacylglycerines, free and total glycerol content were determined using GC/FID (Perkin Elmer Clarus 500). On-column injector, high temperature column with polysiloxy divynil benzene phase (DB-HT type), mega bore type column, o and temperature program of oven up to 350 C setting was used to detect traces compounds. Quality characteristics of SPO and FFA were tested according to MPOB methods. Yield of biodiesel produced and treated SPO were calculated using Equation 1. Product yield is defined as the weight percentage of the final
International Advanced of Technology Congress (ATCi), PWTC, Malaysia. November 3-5, 2009
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product relative to SPO weight at the beginning of experiment. Conversion is the number of converted FFA to FAME per number of initial FFA, and calculated using Equation 2. wt of product Yield (1) wt of oil
Conv.
Nso Ns
acids and the highest fatty acids were palmitic, elaidic and linoelaidic acids.
( 2)
Nso Where Conv. = conversion of FFA to FAME Nso = FFA content at the start of reaction (%) Ns = FFA content at the end of reaction (%)
IV.
RESULTS AND DISCUSSIONS
1. Characteristics of SPO SPO is a by-product of palm oil milling process. It refers to the oil losses at various stages of milling process, mainly sterilizer condensate and sludge separator that is recovered as low quality oil [18, 19]. It consists of oil, water and particulate matter from various processes in palm oil mill. Usually SPO is collected in a sludge pit after milling process. The oil floated on the top layer, whereas the sludge settled at the bottom of the sludge pit [19]. At present SPO is normally used as a feedstock in soap industry to produce low quality soap. In order to increase the value of SPO, it is proposed as an alternative feedstock for biodiesel production, which in return can reduce the production cost of biodiesel. Table1 illustrates quality characteristics of SPO which was used in this study. Based on saponification value the calculated average molecular weight was 823.9 and FFA content of SPO in this study was 22.33%. There are several studies related to characterization of SPO have been done. SPO is characterized by its moisture content (below 2%), FFA (5-45% as palmitic acid), peroxide value (PV) (1.36-21.81meq/kg), Iodine value (IV) (40-55.9), Saponification value (173.8-197.9 mg KOH/g) and unsaponification matter (0.082-0.910%) [20]. It was found that the characteristics of SPO used in this study are within these ranges. According to the “Company Profile Environmental Systems” these are the main characteristics of SPO: extremely stabilized water oilemulsion, high viscosity, only small particles in SPO, high amount of asphaltenes and aromatic compounds and different behavior of sludge oil among each other [21]. Study of fatty acid composition of SPO is very important to identify the carbon chains and its properties. Table 2 shows fatty acid composition of SPO and it was found that the majority fatty acids in SPO were saturated fatty
Table 1: Characteristics of SPO
Parameters Free fatty acid, FFA (%) Peroxide value (meq/kg) Moisture content (%) Iodine value, IV DOBI (Index) Dirt (%) Saponification value (mg KOH/g oil) Unsaponification matter (%) Average molecular weight Mwt Acid value (mg KOH/mg) Density (kg/l) @ 40oC Ester value (EV) Surface tension mN/m @40oC Refractive index Heat of combustion cal/g Pour point oC Cloud point oC
Values 22.33 3.2 1.243 52.9 0.97 0.216 190 2.37 823.935 44.2134 0.8598 113.46 29.69 1.4638 9587.08 32.4 31.7
The saturated fatty acids and FFA content of SPO were very high, which make SPO exists in semisolid phase or solid phase at room temperature. Hence it has higher pour and cloud point as compared to normal crude palm oil. The high percentage of trans-fatty acids, elaidic and linoelaidic, in SPO makes it low quality oil and non edible oil, which is the main reason for cheap SPO price. Higher saturated fatty acids in SPO give higher cetane number and the oil is less prone to oxidation, which is an advantage to SPO if it is converted to biodiesel fuel. Table 2: Fatty acid composition of SPO
Fatty acids
Structure
Lauric acid
C12
International Advanced of Technology Congress (ATCi), PWTC, Malaysia. November 3-5, 2009
wt% 0.08
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Acid esterification process is a typical method of producing biodiesel from high FFA oil [11]. Esterification process is used in order to pretreat the SPO by converting the FFA to FAME using acid catalyst. The most commonly preferred acid catalysts are sulfuric, hydrochloric, sulphonic acid and PTSA [7]. PTSA showed highest catalytic activity compared to other acid catalysts [8]. FFA of SPO in this study was 22.33%. The yield of biodiesel decreases considerably if the FFA content in the oil is greater than 2%. Canakci and van Gerpan [11-12] found that transesterification would not occur if FFA content in the oil is about 3%. Therefore, for this study the FFA is limit to a maximum of 2% for all esterification experiments. The major factors affecting esterification process are: dosages of acid, molar ratio methanol to SPO, temperature and reaction time. Each is discussed in the following sections. 2.1 Effect of PTSA dosage The dosage of PTSA catalyst was varied in the range of 0.25 - 10 wt%. The results showed that PTSA was very effective catalyst in esterification process. The dosage of acid catalyst used in esterification process affected the conversion of FFA to FAME and the yield of treated SPO. Figure 3 shows the effect of different dosage of PTSA on FFA content of SPO. The FFA content decreased from 22.33% to less than 2% in dosage range of 0.75 - 10 wt%. However based on the maximum yield of treated SPO, 0.75wt% of PTSA gave the highest yield with 99% of treated SPO, and FFA conversion of 90.9% after esterification process. There was no significant increase observed in the yield of treated SPO and FFA conversion using higher dosage of PTSA, 1 - 10wt%. It was reported -5 that using 6.40*10 mol of PTSA as acid catalyst can decrease the FFA content in soybean oil from 20.5% to 1.1% and the yield after reaction obtained was only o 48% the reaction condition was 12:1 molar ratio, 180 C temperature, and 60 min reaction time [13]. Guan et al. [8] also claimed that PTSA has the highest catalyst activity than other acid catalysts such as bezenesulfonic acid and sulfuric acid, where they obtained was 97.1% yield using 4 wt% of PTSA in the presence of dimethyl ether.
100 80 60 40
Yield & Conversion%
2. Esterification process of SPO
120
24 22 20 18 16 14 12 10 8 6 4 2 0
FFA% Limits of FFA% Yield% Of Treaed SPO Conv. of FFA to FAME
20 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 Dosage of PTSA wt%
Figure 3: Effect of dosages of PTSA acid on reduction of FFA content, yield of treated SPO & conversion of FFA to FAME
2.2 Effect of molar ratio Molar ratio is one of the important factors that affect the conversion of FFA to FAME, as well as the overall production cost of biodiesel. Acid catalyst process needs extra methanol than transesterification. However, in practice, the molar ratio should be higher than that of stoichiometric ratio in order to drive the reaction towards completion [14]. The molar ratio of methanol to SPO was varied between 6 to 20. Figure 4 describes the effect of molar ratio on the yield and the reduction of FFA content of SPO. The yield of treated SPO increased when molar ratio increased from 6:1 to 10:1, and no significant change observed with higher molar ratio. On the other hand, a minimum of 10:1 molar ratio is required to reduce the FFA content of SPO from 22.33% to below than 2%, which is the limits of FFA for transesterification reaction. Canakci and Van Gerpan [11-12] advocate the use of large excess quantity of methanol (15:1-35:1) while using the sulfuric acid as catalyst. Diserio [13] used 12:1 molar ratio to decrease the FFA content in soybean oil from 20.5% to 1.1% using PTSA as acid catalyst. 120
24 22 20 18 16 14 12 10 8 6 4 2 0
100 80 60 40 20 0 0
2
4
6
8
10
12
14
16
18
Molar Ratio
International Advanced of Technology Congress (ATCi), PWTC, Malaysia. November 3-5, 2009
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22
Yield% & Conversion%
1.08 46.2 4.45 37.99 9.85 0.02 0.33
Free Fatty Acid%
C14 C16 C18 C18-1 C18-2 C18-3 C20
Free Fatty Acid%
Myristic acid Palmitic acid Stearic acid Elaidic acid Linoelaidic acid Alpha-Linolenic acid Arachidic acid
FFA% Limits of FFA% Yield% of Treaed SPO Conv.% of FFA to FAME
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120
24 22 20 18 16 14 12 10 8 6 4 2 0
100 80 60 40
Yield & conversion%
FFA%
24 22 20 18 16 14 12 10 8 6 4 2 0
120 100 80 60 40
FFA% Limits of FFA% Yield% of Teated SPO conversion% of FFA to FAME
20 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
Limits of FFA%
Reaction Time min Yield% of Treated SPO Conv.% of FFA to FAME
Figure 6: Effect of reaction time on reduction of FFA content, yield of treated SPO & conversion of FFA to FAME
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3. Transesterification process 10
20
30
40
50
60
70
80
Temperature C
Figure 5: Effect of temperature on reduction of FFA content, Yield of treated SPO & conversion of FFA to FAME
2.4 Effect of reaction time In order to achieve perfect mass transfer between the reagents and SPO during esterification reaction, it must be stirred well at constant rate and sufficient reaction time. It has been observed that the yield of treated SPO slightly increases with increase in reaction time. Figure 6 shows the effect of reaction time on the reduction of FFA content, yield and conversion of FFA to FAME. The results obtained from the present study revealed that, about 60 minutes of reaction was sufficient for the completion of esterification reaction, which gave highest yield of treated SPO, as well as highest conversion. After 60 minutes the FFA content decreases
During esterification process, FFA is converted to FAME in the presence of acid catalyst. Whereas triacylglycerines is converted to FAME during transesterification process in the presence of alkaline catalyst. The SPO which was pretreated by esterification process in different PTSA dosages (0.5%, 0.75%, 1.0%, 1.5% and 2%) was further transesterified under the most often used reaction conditions: molar o ratio methanol to SPO 10:1, reaction temperature 60 C, reaction time 60 minute, stirrer speed 400 rpm and 1% wt/wt KOH. The yield of biodiesel from SPO and its FFA content is shown in Figure 7. It was observed that the highest yield of biodiesel from SPO was obtained from sample which was treated by 0.75% and 1.0% PTSA. The results of FFA content was less than 0.5 for all samples and meet the standard specification for biodiesel fuel (B100) blend stock for distillate fuels ASTM D 6751-02 and EN 14214. 90
80 International Advanced of Technology Congress (ATCi), PWTC, Malaysia. November 3-5, 2009 70 60 50 40 30
0.3 0.25 0.2 0.15 0.1
FFA%
0
0 90 100
of Biodiesel
Free Fatty Acid%
The reaction temperature maintained by most researchers during different steps ranges between 45 o 65 C. Figure 5 presents the effect of reaction temperature on the yield, FFA and conversion. In this study the optimum reaction temperature was found to o be 60 C. At this temperature the yield of treated SPO obtained was 99%, the FFA content reduced to below 2%, as well as the conversion of FFA to FAME was very high, (around 90%). The boiling point of methanol is o o 64.5 C. Hence at temperatures higher than 64.5 C, methanol evaporates and causes lower yield obtained o o at reaction temperatures of 70 C and 80 C. Study by Leung and Guo [15] showed that temperature higher o than 50 C had a negative impact on the product yield for neat oil, but had a positive effect for waste oil with higher viscosities. Guan et al. [8] found that the yield of o FAME reached 97.1% when reaction done at 80 C, using 4 wt% of PTSA in the presence of dimethyl ether for a 2hour reaction time.
Yield & Conversion%
2.3 Effect of reaction temperature
from 22.33% to 2%. It was reported elsewhere that o using 12 wt% methanol in oil at 70 C, the acid value of oil reduced from 14 mg-KOH/g-oil to below 1 mgKOH/g-oil in 2 hr [16]. Study by Veljkovic et al. [17] showed that esterification reduced the FFA level from about 35% to less than 2% in 25 and 50 min for the molar ratio of 18:1 and 13:1, respectively.
Free Fatty Acid%
Figure 4: Effect of molar ratio on reduction of FFA content, yield of treated SPO and conversion of FFA to FAME
Yield% of Biodiesel Limits of FFA% FFA%
6
Parameters
Ester content Monoacylglycerines Diacylglycerines Triacylglycerines Free glycerol Total glycerol Acid value
Test method EN14103 EN14105 EN14105 EN14105 EN14105 EN14105 EN14104
Unit
Specificat ions
%(molmol−1) %(molmol−1) %(molmol−1) %(molmol−1) %(molmol−1) %(molmol−1) mg KOH g−1
96.5 max 0.8 max 0.2 max 0.2 max 0.02 max 0.25 max 0.5 max
Results After Transesterification Reaction 0.5% 0.75% 1% 81 93 81 0.43 0.06 0.39 0.11 0.01 0.01 2.92 0.01 0.01 0.01 0.01 0.01 0.43 0.02 0.1 0.27 0.14 0.14
dosage of acid catalyst was insufficient. Dosages of 0.75 and 1wt% of PTSA to SPO meet European standard specification for biodiesel fuel except of ester content. Table 3: properties of biodiesel from SPO
V. CONCLUSION
Figure 7: Effect of PTSA at different dosages after transesterification reaction
In this study, the production of biodiesel from SPO having high FFA content was investigated. It was found that pretreatment step by esterification process was very important step in biodiesel production. It can be concluded that SPO is an attractive alternative feedstock for biodiesel production. The optimum conditions for esterification process was 0.75 wt% PTSA o to SPS, 10:1 molar ratio, 60 C temperature, and 60 minutes reaction time. The yield of biodiesel after transesterification was 76.62% and ester content was 93%. Others properties of biodiesel produced were favourable compared to the European standard specifications.
4. Characteristics of Biodiesel from SPO
Acknowledgements
The properties of biodiesel fuel vary with their origins. Fatty acids compositions of raw materials play very important role in the properties of biodiesel. It was found that biodiesel from SPO contain high percentage of saturated fatty acids. These saturated fatty acids give biodiesel fuel advantages in terms of higher cetane number and better oxidation stability, i.e. the fuel is less prone to oxidation. On the other hand the disadvantage is the fuel has higher cloud point and pour point.
The authors would like to thank the personnel of Processing & Engineering of Sime Darby Research Sdn Bhd and Sime Darby Biodiesel Sdn Bhd for supplying sludge palm oil and assisting in analysis work. We would like to thank the Department of Biotechnology Engineering, International Islamic University Malaysia (IIUM) for providing the facilities to undertake the research.
Some properties of biodiesel fuel from SPO is reported in Table 3 according to EN 14214 specification for biodiesel fuel. From the table it can be seen that the highest ester content achieved after transesterification was with 0.75% of PTSA, although it did not meet the specification. For 0.5% of PTSA, uncomplete transesterification was observed, indicated by high amount of Triacylglycerines. This shows that, for a given specific transesterification reaction condition, insufficient amount of acid catalyst during esterification process affects the FFA content, as well as transesterification process itself, and hence the final product. Referring back to Figure 3, the FFA content of SPO treated with 0.5% PTSA is still above 2 %. This also proves that transesterification with alkaline catalyst is not effective when the FFA of oil is more than 2% and International Advanced of Technology Congress (ATCi), PWTC, Malaysia. November 3-5, 2009
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[11] M. Canakci, J. Van Gerpen, Biodiesel production via acid catalysis. Trans Am Eng, 1999; 42(5):1203-1210. [12] M. Canakci, J. Van Gerpen, Biodiesel production from oils and fats with high free fatty acids. Trans ASAE 2001; 44:1429-36. [13] M.DI. Serio, R. Tesser, L.. Pengmei, E. Santacesaria, Heterogeneous Catalyst for Biodiesel Production. Energy & fuel, 2008, 22,207-217. [14] A. S. Ramadhas, S. Jayaraj, C. Muraleedharan, Biodiesel production from high FFA rubber seed oil. Fuel. 2005. 84: 335340. [15] DYC. Leung, Y. Guo, Transesterification of neat and used frying oil: Optimization for biodiesel production. Fuel process Technology, 2006; 87:883-90.
References [1]
[2]
[3]
W.G. Wang. W.R, D.W. Lyons, N.N. Clark, M. Gautam, P.M. Norton, Emissions from Nine Heavy Trucks Fueled by Diesel and Biodiesel Blend without Engine Modification. Environ. Sci. Technol, 2000. 34: 933-939. A. Duran, M. Lapuerta, J. Rodriguez-Fernandez, Neural Networks Estimation of Diesel Particulate Matter Composition from Transesterified Waste Oils Blends. Fuel, 2005. 84: 20802085. G. Antolin, FV. Tinaut, Y. Briceno, V. Castrano, C.Perez, AI. Ramirez, J. Weertman, optimization of biodiesel production by sunflower oil transesterification. Bioresource Technol, 2002. 83:111-4.
[4]
C.J. Shieh, H.F. Liao, C.C. Lee, Optimization of lipase-catalyzed biodiesel by response surface methodology. Bioresource Technol. 2003. 88: 103-6.
[5]
A. Hayyan, Md. Z. Alam, N. A. Kabbashi, M. E. S. Mirghani, Y. M. Siran, N. I. N. M. Hakimi, Pretreatment of Sludge palm oil (SPO) for Biodiesel production by Esterification. Symposium of Malaysian Chemical Engineers (SOMchE). Proceeding book, 2008. Vol 2, 485-490.
[6]
K. Liu, Preparation of fatty acid methyl esters for gaschromatographic analysis of lipids in biological materials. JAOCS, 1994. 71 (11): 1179-1187.
[7]
F. Ma, MA. Hanna, Biodiesel production; a review. Bioresource technology, 1999; 70:1-15.
[8]
G. Guan, K. Kusakabe, N. Sakurai, K. Moriyama, Transesterification of vegetable oil to biodiesel fuel using acid catalysts in presence of dimethyl ether. Fuel. 2009, 88:81-86.
[9]
J. Lifka, B. Ondruschka, influence of mass transfer on the production of biodiesel. Chem. Eng. Technol, 2004, 27, NO.11.
[16] H. LU, Y. Liu, H. Zhou, Y. Yang, M. Chen, B. Liang, Production of biodiesel from Jatropha Curcas L. oil. Computers and chemical engineering. 2009, 33: 1091-1096. [17] V. B. Veljlkovic, S. H. Lakicevic, O.S. Stamenkovic. Z. B. Todorovic, M. L. Z.Lazic, Biodiese production from tobacco (Nicotiana tabacum L.) seed oil with high content of free fatty acid. Fuel, 2006. 85:2671-2675. [18] T.S. Tang, Composition and properties of palm oil products. In Advances in oil palm research, 2000. Volume II. (Ed. by Y. Basiron, B.S. Jalani & Chan K.W.).Kuala Lumpur: Malaysian Palm Oil Board (MPOB), pp 888-889. [19] W.L. Siew, Quality index of crude palm oil using discrimination functions. PORIM Report PO (149d) 89. [20] K. Ainie, W.L. Siew, Y.A. Tan and A.N. Ma, Characterization of a by-product of palm oil milling. Elaeis, 7 (2): 165-173. [21] Company profile environmental systems. (n.d). Retrieved on 28th April 2007 from Environmental Systems Website: http://www.essorp.com
[10] E. Lotero, Y. Liu, D. E. Lopez, K. Suwannakarm, D. A. Bruce, J. G. Goodwin, Jr. Synthessis of biodiesel via acid catalysis. Ind. Eng. Chem. 2005, 44, 5353-5363.
International Advanced of Technology Congress (ATCi), PWTC, Malaysia. November 3-5, 2009
