Bioresource Technology 101 (2010) 7169–7172
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Supercritical ﬂuid reactive extraction of Jatropha curcas L. seeds with methanol: A novel biodiesel production method Steven Lim, Shuit Siew Hoong, Lee Keat Teong *, Subhash Bhatia School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malaysia
a r t i c l e
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Article history: Received 20 January 2010 Received in revised form 25 March 2010 Accepted 29 March 2010 Available online 14 April 2010 Keywords: In situ esteriﬁcation/transesteriﬁcation Jatropha Biodiesel Supercritical ﬂuid Methanol
a b s t r a c t The novel biodiesel production technology using supercritical reactive extraction from Jatropha curcas L. oil seeds in this study has a promising role to ﬁll as a more cost-effective processing technology. Compared to traditional biodiesel production method, supercritical reactive extraction can successfully carry out the extraction of oil and subsequent esteriﬁcation/transesteriﬁcation process to fatty acid methyl esters (FAME) simultaneously in a relatively short total operating time (45–80 min). Particle size of the seeds (0.5–2.0 mm) and reaction temperature/pressure (200–300 °C) are two primary factors being investigated. With 300 °C reaction temperature, 240 MPa operating pressure, 10.0 ml/g methanol to solid ratio and 2.5 ml/g of n-hexane to seed ratio, optimum oil extraction efﬁciency and FAME yield can reach up to 105.3% v/v and 103.5% w/w, respectively which exceeded theoretical yield calculated based on n-hexane Soxhlet extraction of Jatropha oil seeds. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction When the price of crude oil dropped substantially to around USD 40 per barrel due to global economic crisis in early 2009, most of biodiesel production plants had to either shut down completely or cut down their production volume severely to avoid large monetary losses (Lim and Lee, 2010). The cheaper cost of mineral diesel has rendered biodiesel production no longer economically feasible. This incident has exposed the ﬁnancial fragility of biodiesel in relation to fossil fuels’ pricing mechanism. Thus, recent academic researchers have been focussing on investigating cost effective biodiesel production methods either via raw material or processing technology in order to become more competitive (Demirbas, 2008; Nielsen et al., 2008). Conventional biodiesel commercial production is based on the usage of edible energy crops such as rapeseed, soybean, oil palm and coconut. The high supply cost from these feedstocks which accounted more than 70% of the overall biodiesel production cost coupled with their competition as food sources have turned the attention to exploit other non-edible feedstocks such as Jatropha. Jatropha, which is suitable to be grown in non-arable land, has recently being hailed as a promising raw material for biodiesel production. However, its higher moisture and free fatty acid contents (15% FFA) have resulted in current commercial alkaline-based catalyst transesteriﬁcation not being suitable to be employed (Berchmans and Hirata, 2008). The complicity of multi-stage processing involved (extraction, drying, * Corresponding author. Tel.: +60 4 5996467; fax: +60 4 5941013. E-mail address: [email protected]
(L.K. Teong). 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.03.134
degumming and deacidiﬁcation) will add to the production cost and thus contribute negatively to the biodiesel cost effectiveness. Recent publication indicated that reactive extraction of Jatropha curcas L. seeds using acidic catalyst (sulphuric acid) to produce biodiesel has the potential to reduce the high processing cost (Shuit et al., 2010). This method differs from conventional biodiesel production in which the oil-bearing solid energy crops will be in contact directly with alcohol instead of pre-extracted liquid oil. In this case, the alcohol will also act as an extraction solvent while esteriﬁcation and transesteriﬁcation proceed simultaneously in a single step. This process can reduce both the processing time and cost as the energy-intensive extraction phase (chemical solvent or physical pressing) is avoided. Meanwhile, biodiesel production from Jatropha oil via non-catalytic supercritical methanol had also been proven to be more superior in terms of reaction time, product separation, FAME yield and process complicity compare to conventional biodiesel processing (Hawash et al., 2009). Fluid in a supercritical phase can be considered as an intermediate between liquid and gas. This special state has attributed to several distinctive characteristics such as low viscosity, high diffusion coefﬁcients, variation of density and dielectric constant as a function of pressure. Consequently, supercritical ﬂuids (SCF) are excellent extraction solvents as well as chemical reaction reagents. Therefore, it will be interesting to investigate the potential of SCFs in direct contact with the oil-bearing solid materials for biodiesel production. The main objective of this research is to determine the feasibility of non-catalytic supercritical reactive extraction using methanol to produce biodiesel from J. curcas L. seeds in a high-pressure
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batch reactor with n-hexane as co-solvent. Methanol was chosen since it has a milder supercritical condition (513.15 K, 8.1 MPa) and lower boiling point (338.15 K) for easier separation from the products. The effects of solid particle size of Jatropha seeds and reaction temperatures on the FAME yield and oil extraction efﬁciency were studied extensively to obtain a clearer picture of its suitability and future prospects. 2. Methods 2.1. Materials J. curcas L. oil seeds used in this study were purchased from Misi Bumi Alam Sdn. Bhd., Malaysia. Methanol of 99.8% purity was purchased from HmbG Chemicals, Germany. Analytical grade n-hexane of 99% purity (Merck, Germany) was used as co-solvent. Methyl heptadecanoate (99.5% purity) as internal standard and standard references for methyl esters which include methyl palmitate, methyl stearate, methyl oleate and methyl linoleate were all obtained from Fluka Chemie, Germany.
Then, the reaction mixture was ﬁltered and the solid residue was washed thrice with 30 ml of recycled n-hexane. In order to separate the FAME from glycerol and any n-hexane insoluble by-product from the SCF reactive extraction, the ﬁltrate was stirred with 100 ml recycled n-hexane for 30 min before being transferred to separating funnel (Tizvar et al., 2009). The upper dark yellow colour layer was decanted after 1 h and excess n-hexane was evaporated to recover the FAME. The separation procedure was repeated twice for the lower dark brown colour layer to ensure complete separation of FAME from glycerol. The volume of the collected pure FAME sample was then measured and recorded for extraction efﬁciency calculation as shown below. Density of un-reacted oil and its methyl esters was considered to be equal since the difference was less than 5% at room temperature (Veny et al., 2009). This was validated by subjecting the post-reaction dried Jatropha seeds to Soxhlet extraction to determine the amount of leftover oil.
Extraction efficiency ð%Þ ¼
Final volume of collected FAME sample 100% Total volume of oil in the original sample
2.2. Preparation of J. curcas L. seeds 2.4. Product analysis Laboratory Analytical Procedure (LAP) as provided by NREL (National Renewable Energy Laboratory, USA) (Hames et al., 2008), was utilized to ensure uniformity of the Jatropha solid content at ambient conditions. Jatropha samples were thoroughly mixed and placed in dry pan to a maximum depth of 1 cm. The samples were subsequently placed into a drying oven (Memmert UNB800, Germany) at 45 °C for 3 days. The oven-dried samples were cooled to room temperature before grounded using a chopper (Moulinex, France). Moisture content of grounded samples based on a 105 °C dry weight basis which was calculated by placing in the same oven at 105 °C repeatedly until constant weight was achieved. After drying, the Jatropha samples were then screened using a vibrator sieve shaker (Retsch, Germany). The sieving period was 15 min and three solid particle size fractions (60.5, 61.0 and 62.0 mm) were collected. For the oil content measurement, Soxhlet extractor with solvent n-hexane in excess was utilized. Jatropha seeds (20 g) from each solid fraction studied were extracted for 24 h before being evaporated in the rotary evaporator (Buchi, Switzerland) and the remaining oil was measured.
The FAME samples were analyzed by using gas chromatography (GC) (Perkin–Elmer, Clarus 500) equipped with Nukol™ capillary column (15 m 0.53 mm; 0.5 lm ﬁlm thickness) and ﬂame ionization detector (FID). Helium gas was used as the carrier gas with the initial oven temperature set at 110 °C (held for 0.5 min) and then increased to 220 °C (held for 8 min) at a rate of 10 °C/min. The temperatures of the detector and injector were ﬁxed at 220 and 250 °C, respectively. Each sample of 1 ll, diluted with n-hexane and methyl heptadecanoate (internal standard), was injected into the column. Peaks of different methyl esters were identiﬁed by comparison with the peaks of pure methyl ester standard compound. The yield of FAME in the samples was calculated as shown in equation below.
FAME yield ð%Þ Total weight of methyl esters in collected FAME sample Total weight of oil in the original sample 100% ð2Þ ¼
2.3. Experimental procedures 3. Results and discussion All the experimental runs for SCF reactive extraction to convert extracted oil from J. curcas L. seeds into biodiesel were carried out in a high-pressure reactor. The detail description of reactor is described elsewhere (Mazaheri et al., 2010). In a typical run, 20 g of blended and sieved Jatropha seeds were loaded into the 450 ml reactor together with 200 ml of methanol (solvent to seed ratio was ﬁxed at 10.0 ml/g) and 50 ml of n-hexane (2.5 ml/g of co-solvent to seed ratio). Methanol would act both as an extraction agent and transesteriﬁcation reagent while the addition of n-hexane was required to increase the oil solubility in the reaction mixture as well as separating the FAME from the glycerol in the later process (Georgogiannia et al., 2008; Shuit et al., 2010). The reaction mixture was ﬁrst subjected to mechanical agitation at 400 rpm for 30 min at room conditions before being heated to the desired reaction temperature. The operating pressure and reaction time, which were not being studied independently were not controlled but correlated by the reaction temperature. The heating rate was adjusted so that the ﬁnal temperature was always reached in the shortest possible time (45–80 min) after which the mixture would be quench immediately with cooling water to room temperature.
Moisture content of the J. curcas L. seeds subjected to drying at 105 °C was calculated to be at an average of 8.34 wt%. Total oil content in Jatropha seeds was discovered to vary according to different solid fractions (un-sieved: 37.8 wt%, <2.0 mm: 54.4, <1.0 mm: 62.4 wt% and <0.5 mm: 60.9). The distribution of oil inside the seeds was in agreement with those reported in the literature (Kumar and Sharma, 2008; Sayyar et al., 2009). Fig. 1 shows the effect of different temperatures and their corresponding pressures towards oil extraction efﬁciency with different range of solid particle sizes. In general, the oil extraction efﬁciency of J. curcas L. seeds increased with increasing temperature and pressure as higher temperature and pressure typically favoured the expulsion of oil from the shell (Berchmans and Hirata, 2008). The minimum oil extraction efﬁciency at lower temperatures (200–240 °C) was higher than 65% v/v for all solid fractions due to the contribution of n-hexane in the pre-stirring stage. Higher increment rate for oil extraction efﬁciency was discovered at temperature above 240 °C since supercritical ﬂuid extraction began to take effect. Thus, it can be concluded that the effect of co-solvent is rather sig-
S. Lim et al. / Bioresource Technology 101 (2010) 7169–7172
110.0 Extraction efficiency (% v/v)
2.0 mm 1.0 mm 0.5 mm
80.0 70.0 60.0 50.0 200ºC/40 Mpa
240ºC/90 Mpa 260ºC/140 Mpa 280ºC/180 Mpa 300ºC/240 Mpa Temperature/Pressure (ºC/MPa)
Fig. 1. Effect of varying temperatures and pressures to oil extraction efﬁciency with different particle size.
FAME yield (% w/w)
1.0 mm 0.5 mm
60.0 40.0 20.0 0.0 200ºC/40 Mpa
240ºC/90 Mpa 260ºC/140 Mpa 280ºC/180 Mpa 300ºC/240 Mpa
Temperature/Pressure (ºC/MPa) Fig. 2. Effect of varying temperatures and pressures to biodiesel (FAME) yield with different particle size.
niﬁcant at the beginning of the process while supercritical ﬂuid extraction dominates at higher temperatures to bring the total oil extraction efﬁciency to 100%. For different solid particle sizes, smaller particle size generally exhibited higher oil extraction efﬁciency because of the higher surface area in contact and less hindrance from the outer hard shell covering the oil seeds (Shuit et al., 2010). However, particle size 60.5 mm showed the only exception to the fundamental theory as it was found exhibiting almost constant extraction efﬁciency (69.0–79.3% v/v) throughout the process. This is due to its smaller particle size which is below the critical weight for the supercritical ﬂuids reactive extraction process. Consequently, most of the solid particles has higher probability to agglomerate and form paste material and thus reduce the effective surface area for the oil extraction. The high oil content for Jatropha oilseeds is also responsible for its sticky nature which further enhances the agglomeration process (Sayyar et al., 2009). On the other hand, supercritical ﬂuid extraction was found to perform exceptionally better for particle size 61.0 mm as shown in Fig. 1. The higher pressure in supercritical condition was able to extract more oil trapped deep inside the core of oil seeds compared to conventional 24 h Soxhlet extraction using n-hexane, as evident from the oil extraction efﬁciency more than theoretical efﬁciency at 105.3% v/v for particle size 61.0 mm. Fig. 2 shows the variation of temperature and pressure towards FAME yield for supercritical reactive extraction with different solid particle sizes. At lower temperatures (6240 °C), FAME yield was extremely low as predicted due to the poor miscibility of methanol with the extracted oil without the addition of catalyst or supercritical condition (Hawash et al., 2009; Shuit et al., 2010). Oil conversion to FAME was found to be directly proportional to reaction temperature particularly beyond the supercritical condition where
conversion rate was intensiﬁed. Smaller particle sizes with higher extraction efﬁciency were favourable for higher FAME yields with the only exception at particle size 60.5 mm (maximum 71.4% w/ w at 300 °C) since the low oil extraction efﬁciency limits its FAME conversion. Therefore, it can be concluded that the rate of oil extraction is higher than the rate of transesteriﬁcation at low temperature range due to the signiﬁcant extraction efﬁciency of n-hexane. However, at higher temperature range, supercritical condition enabled the transesteriﬁcation to proceed at a much higher pace than the extraction of oil (Hawash et al., 2009). The 103.5% of FAME yield exceeding theoretical 100% yield for particle size 61.0 mm at 300 °C was due to the excess oil being extracted as explained earlier. Another signiﬁcant ﬁnding was that the un-sieved Jatropha oil seeds which contained different solid particle size would tend to inhibit FAME conversion in the supercritical reactive extraction process. The varying particle size was expected to render the reaction rate inconsistent while larger solid particle size which easier to settle down will reduce the oil-methanol contact area for the transesteriﬁcation process. Consequently, screening of blended J. curcas L. seeds to a smaller particle size through sieving is important in order to maximize the FAME or biodiesel output.
4. Conclusions The experimental work above for the novel supercritical reactive extraction technology of J. curcas L. seeds has proven its huge potential for commercial production of biodiesel from oil seeds. Almost 100% oil extraction efﬁciency and FAME yield can be achieved in a relatively short time by skipping the conventional oil extraction stage which might take up to 24 h. Furthermore, no catalyst
S. Lim et al. / Bioresource Technology 101 (2010) 7169–7172
is required which will greatly simplify downstream processes such as catalyst separation and washing. The solid particle size was found to be a signiﬁcant factor of which the optimum is at particle size 61.0 mm while the reaction temperature of 300 °C is required for maximizing FAME yield. Acknowledgements The authors are grateful for a Research University (RU) Grant No. 814062, Short Term Grant No. 6039015 and Postgraduate Incentive Grant No. 8021016 from Universiti Sains Malaysia, which has fully supported this research and USM Vice-Chancellors Award of a student scholarship to Steven Lim. References Berchmans, H.J., Hirata, S., 2008. Biodiesel production from crude Jatropha curcas L. seed oil with a high content of free fatty acids. Bioresour. Technol. 99, 1716– 1721. Demirbas, A., 2008. Biofuels sources, biofuel policy, biofuel economy and global biofuel projections. Energy Convers. Manage. 49, 2106–2116. Georgogiannia, K.G., Kontominasa, M.G., Pomonisa, P.J., Avlonitisb, D., Gergis, V., 2008. Conventional and in situ transesteriﬁcation of sunﬂower seed oil for the production of biodiesel. Fuel Process. Technol. 89, 503–509.
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