Energy Fuels 2010, 24, 3634–3638 Published on Web 05/20/2010
: DOI:10.1021/ef100109u
Simple Continuous Production Process of Biodiesel Fuel from Oil with High Content of Free Fatty Acid Using Ion-Exchange Resin Catalysts Naomi Shibasaki-Kitakawa, Takahiro Tsuji, Kouhei Chida, Masaki Kubo, and Toshikuni Yonemoto* Department of Chemical Engineering, Tohoku University, Aoba-yama 6-6-07, Aoba-ku, Sendai 980-8579, Japan. Received January 28, 2010. Revised Manuscript Received April 28, 2010
A simple continuous production process of biodiesel fuel, fatty acid esters from oils with high content of free fatty acid (FFA), was constructed using the heterogeneous ion-exchange resin catalysts. In the system, the expanded-bed reactor packed with the cation-exchange resin catalyst for esterification of the FFA and that with the anion-exchange resin catalyst for transesterification of the triglyceride were connected in series. When the mixed solution of the crude rice bran oil with a 14 wt % FFA and alcohol was supplied to the proposed system, the fatty acid esters with a high conversion of more than 98.6% could be continuously produced without any extra operation such as dewaxing/degumming of the raw oil, removal of the byproduct, and addition of alcohol.
Recently, oils with high content of FFA, such as crude rice bran oil (RBO)5-8 and jatropha oil,9,10 have received much attention as an inexpensive source of biodiesel fuel. The esterification of FFA with alcohol using the homogeneous acid catalyst, such as H2SO4 or HCl,
1. Introduction Biodiesel fuel has received much attention as a nontoxic, biodegradable, and renewable energy alternative to petroleum fuels. The fuel, fatty acid ester (RCOOR0 ), is mainly produced by the transesterification of triglyceride (G(COOR)3), which is one of the constituents of vegetable or animal oils with the alcohol (R0 OH) catalyzed by a homogeneous alkali catalyst, such as NaOH or KOH:1-4 OH-
GðCOORÞ3 þ 3R0 OH s f 3RCOOR0 þ GðOHÞ3
Hþ
RCOOH þ R0 OH s f RCOOR0 þ H2 O
has been proposed as an alternative pretreatment for the main transesterification process.11-14 The alkali catalyst was consumed by the neutralization reaction with the acid catalyst for the pretreatment so that an excess amount of the catalyst must be supplied to the main reaction stream. To overcome this problem, Kasim et al.15 proposed a production method of biodiesel fuel from RBO and methanol under supercritical conditions using carbon dioxide as a cosolvent. The high yield of the fatty acid methyl ester (FAME) of 94.8% was obtained at 30 MPa and 300 °C using the dewaxed/degummed RBO with a 3 wt % FFA content. However, about 16% of the formed FAME was converted to the unstable trans-isomer because of high temperature and high pressure. Lai et al.16 developed a two-step reaction using the enzyme lipase, having catalytic activities for both of esterification and transesterification. More than a 98% conversion was attained using Novozyme 435 at 50 °C for the dewaxed/degummed RBO with a high FFA content (20-60 wt %). However, many extra
ð1Þ
Here, G(OH)3 is the byproduct glycerine. The raw oils often contain free fatty acid (FFA, RCOOH) formed by the triglyceride hydrolysis: GðCOORÞ3 þ 3H2 O f 3RCOOH þ GðOHÞ3
ð2Þ
The FFA reacts with the alkali catalyst to form an alkali soap RCOONa: RCOOH þ NaOH f RCOONa þ H2 O
ð3Þ
The soap contaminates the fuel by dispersing the micelles of the byproduct glycerine and lowers the fuel yield by interfering with the phase separation of the fuel and glycerine. Thus, the refining process to remove the FFA in the raw oils to less than 0.5 wt % is normally required for the biodiesel fuel production.
(7) Goffman, F. D.; Pinson, S.; Bergman, C. J. Am. Oil Chem. Soc. 2003, 80, 485–490. (8) Ju, Y. H.; Vali, S. R. J. Sci. Ind. Res. 2005, 64, 866–882. (9) Patil, P. D.; Gnaneswar, V.; Deng, S. Ind. Eng. Chem. Res. 2009, 48, 10580–10856. (10) Lu, H.; Liu, Y.; Zhou, H.; Yang, Y.; Chen, M.; Liang, B. Comput. Chem. Eng. 2009, 33, 1091–1096. (11) Haas, M. J.; Michalski, P. J.; Runyon, S.; Nunez, A.; Scott, K. M. J. Am. Oil Chem. Soc. 2003, 80, 97–102. (12) Canakci, M.; Van Gerpen, J. Trans. ASAE 2001, 44, 1429–1436. (13) Goff, M. J.; Bauer, N. S.; Lopes, S.; Sutterlin, W. R.; Suppes, G. J. J. Am. Oil Chem. Soc. 2004, 81, 415–420. (14) Ataya, F.; Dube, M. A.; Ternan, M. Energy Fuels 2007, 21, 2450– 2459. (15) Kasim, N. S.; Tsai, T.; Gunawan, S.; Ju, Y Bioresour. Technol. 2009, 100, 2399–2403. (16) Lai, C.; Zullaikah, S.; Vali, S. R.; Ju, Y. J. Chem. Technol. Biotechnol. 2005, 80, 331–337.
*To whom correspondence should be addressed. Telephone: þ81-22795-7255. Fax: þ81-22-795-7258. E-mail:
[email protected]. (1) Freedman, B.; Butterfield, R. O.; Pryde, E. H. J. Am. Oil Chem. Soc. 1986, 63, 1375–1380. (2) Noureddini, H.; Zhu, D. J. Am. Oil Chem. Soc. 1997, 74, 1457– 1463. (3) Ma, F.; Hanna, M. A. Bioresour. Technol. 1999, 70, 1–15. (4) Komers, K.; Skopal, F.; Stloukal, R; Machek, J. Eur. J. Lipid. Sci. Technol. 2002, 104, 728–737. (5) Sinha, S.; Agarwal, A. K.; Garg, S. Energy Convers. Manage. 2008, 49, 1248–1257. (6) Lin, L.; Ying, D.; Chaitep, S.; Vittayapadung, S. Appl. Energy 2009, 86, 681–688. r 2010 American Chemical Society
ð4Þ
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Energy Fuels 2010, 24, 3634–3638
: DOI:10.1021/ef100109u
Shibasaki-Kitakawa et al.
Table 1. Physical Properties of Ion-Exchange Resins
Table 2. Experimental Conditions for Batchwise Reaction System
Diaion
character exchange group cross-linking density [%] diameter [mm] ion-exchange capacity [mol/m3 resin]
PK208LH
PA306S
cation I 4 0.40-0.60 1.2 103
anion I 3 0.15-0.43 0.79 103
operations, such as dewaxing/degumming of the crude RBO, pretreatment of the lipase, stepwise methanol addition, and removal of the byproduct, were required. Zullaikah et al.17 also constructed a two-step production process using the homogeneous sulfuric acid catalyst, which has catalytic activities for the transesterification as well as the esterification. However, the rate of the transesterification catalyzed by the sulfuric acid was much lower than that catalyzed by the alkali catalyst,4 and the process was not efficient. The purpose of this research is to construct a simple continuous production process of biodiesel fuel from the inexpensive oils with high content of FFA. In the system, an expanded-bed reactor packed with a heterogeneous cationexchange resin catalyst for esterification of the FFA and that with an anion-exchange resin catalyst for transesterification of the triglyceride18,19 were connected in series. First, the esterification and transesterification of the crude RBO were sequentially conducted in the batchwise system to investigate each reaction behavior. The continuous production of the fatty acid ethyl ester (FAEE) was then conducted by sequentially supplying the mixed solution of the crude RBO and ethanol to the reactors.
parameter
value
solution weight [g] molar ratio of ethanol to total fatty acid residue shaking rate [rpm] temperature [°C] cation-exchange resin [g wet] anion-exchange resin [g wet]
20 3.6:1 150 50 10 10
Figure 1. Schematic diagram of continuous production system of biodiesel fuel with cation- and anion-exchange resin catalysts.
chloride ions with the hydroxyl ions, similar to the conventional water treatment process, and then washed with reverse osmosis (RO) water, followed by ethanol. The content of the hydroxyl ion in the resin was measured by titration to be more than 95 mol %. The cation-exchange resin was supplied in an activated H-form (more than 99 mol %) and just used for the experiments after washing with the ethanol. For the batchwise experiment, 13 g of the crude RBO and 7 g of ethanol were poured into the glass bottle. By assuming triglyceride and FFA being triolein and oleic acid, respectively, the molar ratio of ethanol to the total oleic acid residue contained in the crude RBO was estimated to be 3.6:1. The bottle was shaken at 150 spm in a thermal bath (Yamato Scientific Co., Ltd., Tokyo, Japan, BW400 and BF200) at 50 °C. To start the esterification reaction, 10 g of the cationexchange resin catalyst was placed in the bottle. The catalyst concentration was 33 wt %. At specific time intervals, samples of the solutions were collected and the concentrations of the reactants and products in the solution were determined using an HPLC system equipped with a UV detector (Hitachi, Ltd., Tokyo, Japan, D-7000 series) and an Inertsil ODS column (particle size 3.0 μm, i.d. 2.1 mm, length 150 mm; GL Science, Inc., Tokyo, Japan). Acetonitrile (99.5%), 2-propanol (99.7%), and 4.57 mol/m3 phosphate buffer (pH 2.5) were used as the mobile phase, which flowed at 0.5 cm3/min through the column using a gradient technique.23-25 These reagents were purchased from Wako Pure Chemical Industries, Ltd., Osaka, Japan. The temperature of the column oven was 40 °C. The wavelengths were 205 nm. After the esterification, the cation-exchange resin was removed by filtration and 10 g of the anion-exchange resin catalyst was placed in the filtered reaction solution. The catalyst concentration was 33 wt %, similar for the esterification. The
2. Experimental Section 2.1. Batchwise Reaction System. The crude RBO was kindly donated by Sanwa Yushi Co., Ltd., Tendo, Japan, and was filtered to remove any solid contents. Its common components are 82 wt % triglyceride, 14 wt % FFA, 2 wt % sterol, and 0.14 wt % vitamin E, and the average molecular weight is about 869. The sterol and vitamin E can be provided as functional food ingredients and will be recovered in a future process. Therefore, ethanol (Wako Pure Chemical Industries, Ltd., Osaka, Japan, special grade, 99.5%) was used as the second reactant instead of toxic methanol. In addition, ethanol is readily available from fermentative processes using biomass from a varied source so that the formed fatty acid ethyl ester is considered to be an entirely renewable and environmentally preferable fuel.20-22 The cation-exchange resin, Diaion PK208LH, and the anionexchange resin, Diaion PA306S, were used as the heterogeneous solid catalysts for the esterification and transesterification, respectively. Both resins were kindly donated by Mitsubishi Chemical Co., Ltd., Tokyo, Japan. The physical properties of the resins are summarized in Table 1. The anion-exchange resin was supplied in the chloride form so that the resin was mixed with a 1 mol/dm3 sodium hydroxide solution to displace the (17) Zullaikah, S.; Lai, C.; Vali, S. R.; Ju, Y. Bioresour. Technol. 2005, 96, 1889–1896. (18) Shibasaki-Kitakawa, N.; Honda, H.; Kuribayashi, H.; Toda, T.; Fukumura, T.; Yonemoto, T Bioresour. Technol. 2007, 98, 416–421. (19) Tsuji, T.; Kubo, M.; Shibasaki-Kitakawa, N.; Yonemoto, T. Energy Fuels 2009, 23, 6163–6167. (20) Rodrigures, R. C.; Volpato, G.; Ayub, M. A. Z.; Wada, K. J. Chem. Technol. Biotechnol. 2008, 83, 849–854. (21) Vieitez, I.; Silva, C.; Alckmin, I.; Borges, G. R.; Corazza, F. C.; Oliveira, J. V.; Grompone, M. A.; Jachmanian, I. Energy Fuels 2009, 23, 558–563. (22) Valle, P. W. P. A; Rezende, T. F.; Souza, R. A.; Fortes, I. C. P.; Pasa, V. M. D. Energy Fuels 2009, 23, 5219–5227.
(23) Komers, K.; Stloukal, R.; Machek, J.; Skopal, F.; Komersova, A. Fett/Lipid 1998, 100, 507–512. (24) Holcapek, M.; Jandera, P.; Fischer, J.; Prokes, B. J. Chromatogr., A 1999, 858, 13–31. (25) Komers, K.; Stloukal, R.; Machek, J.; Skopal, F. Eur. J. Lipid. Sci. Technol. 2001, 103, 363–371.
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: DOI:10.1021/ef100109u
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Figure 3. Time courses of concentrations of FFA (a) and FAEE (b) during batchwise esterification with cation-exchange resin catalyst.
on the FFA conversion, the amount of the cation-exchange resin packed in the first column was regulated in the range of 21.5-55.5 g (wet) by changing the column length between 30 and 75 cm. The amount of the anion-exchange resin packed in the second column was fixed at 33.1 g (wet) according to the previous work.18 The effluent solutions from the top of the columns were collected, and the concentrations of the reactants and products in the solution were determined using the HPLC system mentioned in section 2.1.
3. Results and Discussion 3.1. Batchwise Esterification and Transesterification Behavior. Figure 2 shows the HPLC chromatograms of the crude RBO (a), the samples obtained after the batchwise esterification (b), and transesterification (c). Three peaks of the FFA (O), five peaks of the triglyceride (), five peaks of the diglyceride (4), and one peak of the sterol (2) were observed in Figure 2a. No peak of the monoglyceride was detected. This meant that the monoglyceride was not contained in the crude RBO. The FFA peaks were identified as linolenic acid, linoleic acid, and oleic acid in turn of elution, and the respective concentrations were calculated on the basis of calibration curves. However, the peaks of the triglyceride could not be identified because there were many combinations of linolenic acid, linoleic acid, and oleic acid residues. The peaks of the diglyceride could also not be identified. The peaks of the FFA (O) became smaller, and three peaks of the product, the fatty acid ethyl ester (FAEE, b), appeared in Figure 2b. These peaks were identified as ethyl linolenate, ethyl linoleate, and ethyl oleate in turn of elution, and the respective concentrations were also calculated. The peaks, except for the FAEE (b) and sterol (2), completely disappeared in Figure 2c. Figure 3 shows the time courses of the concentrations of FFA and FAEE during the batchwise esterification. The concentrations of three FFAs, oleic acid, linoleic acid, and linolenic acid, gradually decreased, while those of the corresponding three FAEEs increased. About 20% of the FFA still remained in the reaction solution at 12 h. The FFA conversion would be higher with a longer reaction time, but prolonging the esterification time is undesirable for the construction of an efficient production process. The esterification
Figure 2. HPLC chromatograms of crude RBO (a) and samples obtained after batchwise esterification (b) and transesterification (c).
experimental condition for the batchwise reaction system is summarized in Table 2. At specific time intervals, samples of the solutions were collected and the concentrations of the reactants and products in the solution were determined using the HPLC system mentioned above. 2.2. Continuous Reaction System. Figure 1 is a schematic diagram of the continuous production system. Two waterjacketed columns (Kiriyama Glass Work Co., Tokyo, Japan, ILC-FW11) with an inner diameter of 11 mm were individually packed with the cation-exchange resin, PK208LH, and the anion-exchange resin, PA306S, respectively, and then connected in series. The temperature of each column was kept constant at 50 °C using a hot-water recirculating system. The reaction solution at a molar ratio of ethanol to the total fatty acid residue in the crude RBO of 3.6:1 was supplied to the bottom of the first column at a constant flow rate of 0.10 cm3/min using a plunger pump (Hitachi, Ltd., Tokyo, Japan, Intelligent pump L-6210). The effluent from the top of the first column was directly supplied to the bottom of the second column without any extra operation such as removing the byproduct and/or adding alcohol. In order to investigate the effect of the residence time 3636
Energy Fuels 2010, 24, 3634–3638
: DOI:10.1021/ef100109u
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triglyceride as well as a strong activity for the esterification of the FFA. The conversions of the triglyceride and diglyceride were greater than 97.5% after the transesterification. Therefore, the batchwise operation that combined the esterification with the cation-exchange resin catalyst and the transesterification with the anion-exchange resin catalyst enabled the production of the FAEE with a high purity from the crude RBO without dewaxing and degumming. 3.2. Continuous Esterification and Transesterification Behavior. Figure 5 shows the time courses of the concentrations of FFA and FAEE in the effluent from the first column packed with 35.4 g (wet) of the cation-exchange resin. The concentrations of FFA and FAEE started to increase at 3 h and became constant after 5 h, when the steady state was attained. The residence time of the first column was calculated to be 3.4 h by considering the bed void fraction and the resin porosity. The value was roughly consistent with the time when the concentrations of FFA and FAEE started to increase. Figure 6 shows the effect of the residence time of the first column on the FFA conversions at the steady state. The FFA conversions increased with the residence time, and the oleic acid and linoleic acid conversions reached about 90% at 5.1 h. The remaining FFA can be removed by adsorption on the anion-exchange resin in the second column. Therefore, the residence time of the first column was set at 5.1 h, which corresponded to the amount of the cation-exchange resin of 55.5 g (wet). Figure 7 shows the time courses of the residual ratio of the triglyceride and the concentration of FAEE in the effluent from the second column. The starting time to supply the reaction solution to the first column was set to zero. The residence time of the second column was 3.0 h. The residual ratio of the triglyceride was almost zero up to 36 h. The concentration of FAEE increased after 10 h and became constant from 20 to 36 h, when the steady state was attained. After 36 h, the residual ratio of the triglyceride increased and the concentration of FAEE decreased because of the reduction of the catalytic activity of the anion-exchange resin. The catalytic activity of the resin can be completely recovered by a regeneration treatment and repeated use.18 In order to discuss the progress of the reaction in detail, the conversions of each reactant and total concentration of the product in the effluents from the first and second columns are listed in Table 3. About 91% of the FFA was converted to FAEE by esterification in the first column, and the unreacted FFA was completely removed by adsorption on the resin in the second column. The triglyceride and diglyceride were mainly converted to FAEE by the transesterification in the second column, and the final conversions were greater than 98.6%. In addition, the byproduct glycerol was also adsorbed on the anion-exchange resin and the adsorbed glycerol was eluted during the regeneration treatment (data is not shown). Thus, by supply of the mixed solution of the crude RBO and ethanol to two-column reactors packed with the cation- and anion-exchange resins, respectively, in series, the biodiesel fuel with a high conversion and purity could be continuously produced without any extra operation such as dewaxing/ degumming of the raw oil, removal of the byproduct, and addition of alcohol.
Figure 4. Time courses of residual ratios of triglyceride and FFA and total concentration of FAEE during batchwise sequential esterification and transesterification with anion- and cationexchange resin catalysts.
was stopped before reaching complete conversion, and during the next transesterification process, the unreacted FFA (RCOOH) in the solution would be removed by adsorption on the anionexchange resin:26,27 RCOOH þ Sþ ðOH- Þ f Sþ ðRCOO- Þ þ H2 O
ð5Þ
Here, S is the resin frame. The FFA adsorbed on the resin can be easily removed in the regeneration process without any extra operation. To construct an optimum operating process, therefore, the batchwise esterification was stopped at 12 h. In order to discuss the progress of the reaction in detail, the residual ratio of the triglyceride to that of the crude RBO was calculated on the basis of the peak area A of the HPLC chromatogram as peak5 P Ai residual ratio½% ¼ 100
i ¼ peak1
peak5 P i ¼ peak1
ð6Þ
Aiðcrude RBOÞ
The residual ratio of the diglyceride was also calculated similar to that for the triglyceride. The time courses of the residual ratios of the triglyceride and FFA and total concentrations of the FAEE during the batchwise esterification and transesterification are plotted in Figure 4. The residual ratio of the triglyceride (0) hardly decreased during the esterification, while it rapidly decreased from the start of the transesterificaion and became almost zero at 1 h. The FFA (]) remaining at the end of the esterification rapidly decreased and became almost zero immediately after the transesterification started. The concentration of FAEE (b) increased during not only the esterification but also the transesterification. In particular, the increase in the latter process was significant and about 90% of the final amount of FAEE was formed. Table 3 summarizes the conversions of each reactant and the total concentration of the product obtained at 12 h of the batchwise esterification and then at 2 h of the transesterification after the 12 h esterification. About 81% of the FFA was converted to FAEE by the esterification, and the residual FFA was completely removed by the adsorption on the resin. About 5% of the triglyceride was also converted to FAEE during the esterification process because the cation-exchange resin had a weak catalytic activity for the transesterification of the
4. Conclusions
(26) Bills, D. D.; Khatri, L. L.; Day, E. A. J. Dairy Sci. 1963, 46, 1342– 1347. (27) Eychenne, V.; Mouloungui, Z. J. Am. Oil Chem. Soc. 1998, 75, 1437–1440.
A simple continuous production process of biodiesel fuel from the inexpensive FFA rich crude RBO was constructed. 3637
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: DOI:10.1021/ef100109u
Shibasaki-Kitakawa et al.
Table 3. Conversion of Each Reactant and Total Concentration of Product Obtained at Batchwise and Continuous Esterification and Transesterification with Cation- and Anion-Exchange Resin Catalysts batchwise
continuous
operation mode
esterification (12 h)
esterification (12 h) þ transesterification (2 h)
effluent from first column
effluent from second column
FFA conversion [%] triglyceride conversion [%] diglyceride conversion [%] total FAME concn [mol/dm3]
81.4 4.7 1.6 0.15
100 97.8 97.5 1.00
91.1 4.1 3.3 0.16
100 98.6 100 1.68
Figure 5. Time courses of concentrations of FFA (a) and FAEE (b) in effluent from the first column packed with 35.4 g (wet) of cationexchange resin catalyst.
Figure 7. Time courses of residual ratio of triglyceride (a) and concentration of FAEE (b) in effluent from the second column packed with anion-exchange resin catalyst.
esterification of FFA and that with the anion-exchange resin catalyst for the transesterification of the triglyceride were connected in series. The results led to the following conclusions: (1) the various FFAs contained in the crude RBO can be converted to FAEE by esterification using the cationexchange resin catalyst PK208LH; (2) the various triglycerides and diglycerides in the crude RBO can be converted to FAEE by transesterification using the anion-exchange resin catalyst PA306S; (3) the remaining FFA in the solution can be removed by adsorption on the anion-exchange resin PA306S. By supply of a mixed solution of the crude RBO and ethanol to the proposed system, therefore, biodiesel fuel with high conversion and purity could be continuously produced without any extra operation.
Figure 6. Effect of residence time of the first column on FFA conversions at steady state.
In the system, the expanded-bed reactor packed with the heterogeneous cation-exchange resin catalyst for the
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