New Approaches to Biodiesel Production by Ethanolysis with Calcium Hydroxide Catalyst Using Thermal Pretreatment with Glycerol

562 J. Jpn. Inst. Energy, Vol.Journal 89, No. of 6, the 2010 Japan Institute of Energy, 89, 562-566 (2010)

Original Paper

Hendrex KAZEMBE-PHIRI ＊ 1, Yukihiko MATSUMURA ＊ 1, and Tomoaki MINOWA ＊ 2

(Received February 10, 2010)

This was a study to pursue new sustainable sources of power in Malawi and other developing countries of Sub-Saharan Africa by investigating a novel approach for biodiesel production via ethanolysis of pretreated oil feedstock with calcium hydroxide using thermal pretreatment with glycerol. 0.5 g of Groundnut

(Arachis hypogaea) oil feedstock premixed with glycerol and Ca(OH)2 was thermally pretreated at 100℃ and stirred at 1000 rpm for 1-3 h. The triglycerides (TG) decomposed into diglycerides (DG) and monoglycerides (MG), which are reactive intermediates of the ethanolysis. This effect of pretreatment was investigated in comparison with the effect of other catalyst. Then, the pretreated oil was reacted under the following conditions: 100℃, 12-to-1 ethanol (EtOH)-to-oil molar ratio, stirring at 1000 rpm, catalyst load of 2 wt%, time from 0.5-2 h. Thermal pretreatment with glycerol achieved a significant fatty acid ethyl ester (FAEE) yield of 76 wt% (comparable to the yields obtained with calcium oxide (h-CaO) and surface-modified calcium oxide (s-CaO)).

In tests on the reuse of the Ca(OH)2 catalyst in repeated reactions, the yield did not decrease sharply with repetitive use. Given that all of the materials tested in our experiments are available renewably in Sub- Saharan Africa, we believe that biodiesel production via ethanolysis has the potential to provide a sustainable source of power in that region.

Key Words Developing countries, Thermal pretreatment, Glycerol, Calcium hydroxide, Biodiesel, Ethanolysis

1. Introduction Africa have local access to bio-ethanol (EtOH), bio-oils, and

The developing countries of Sub-Saharan African region hydrated lime, or calcium hydroxide (Ca(OH)2), and these require the accelerated introduction of renewable energy cheap local resources1）～3） make biodiesel production via in order to satisfy rising energy demands in a world where ethanolysis economically feasible. oil resources are running low and the crisis of global warm- While these prospects are encouraging, there have been ing looms. Biodiesel is trusted as a viable energy solution, no earlier studies to measure heterogeneously catalyzed but the prospects for conventional biodiesel production are ethanolysis reactions with catalysts such as Ca(OH)2, in held back by a lack of local capacity for manufacturing comparison with reactions via methanolysis. One factor methanol and homogeneous catalysts. One promising so- holding back the research has been the low reactivity so lution would be a biodiesel fuel produced from locally avail- far shown by the resources4）5） mentioned above. Thus, able vegetable oils, alcohol and catalysts. Our group has improved reaction kinetics of ethanolysis will be key to the proposed the use of sunflower oil and ethanol with a cal- introduction of this technology. In a previous report we de- cium oxide catalyst. Most of the countries of Sub-Saharan scribed our success in improving the reactivity of CaO cata- ＊ 1 Department of Mechanical System Engineering, lyst by surface modification. The performance of surface- Hiroshima University, Graduate School of Engineering modified calcium oxide (s-CaO) 6） shows the great potential 1-4-1, Kagamiyama, Higashi-Hiroshima-shi, Hiroshima 739-8527, Japan of Ca(OH)2 as a solid base catalyst for biodiesel production. ＊ 2 Biomass Technology Research Center, Surface modification, however, takes considerable time and National Institute of Advanced Industrial Science and requires high-temperature treatment. During our last study Technology, Chugoku Center 2-2-2, Hiro-Suehiro, Kure-shi, Hiroshima 737-0197, Japan we happened to notice improvements in the reactivity of J. Jpn. Inst. Energy, Vol. 89, No. 6, 2010 563

Ca(OH)2 samples processed only by thermal treatment with 2.3 Ethanolysis reaction glycerol instead of surface modification. If this catalyst can Four treatments were conducted: Ti to Tiv as described be used without the extra step of surface modification, its in Table 2. Treatment Ti employed a mixture of Ca(OH)2 feasibility for application in biodiesel production will be and oil without thermal pretreatment before the reaction. greatly enhanced. The purposes of this study were to de- Treatment Tii employed a mixture of Ca(OH)2 and oil with termine the effectiveness of this“glycerol pretreatment” thermal pretreatment. Treatment Tiii employed a mixture and to elucidate the mechanism behind the glycerol pre- of Ca(OH)2, oil, and GL without thermal pretreatment. Treat- treatment effects. ment Tiv employed a mixture of Ca(OH)2, oil, and GL with

thermal pretreatment. Treatments Ti and Tii were blank

2. Experimental experiments with no glycerol added. Treatment Tiii was a 2.1 Apparatus blank experiment in terms of thermal pretreatment. In the The pretreatment and ethanolysis reaction were both experiments with the thermal pretreatment, the pretreat- performed in an air-tight 15 cm3-reaction vessel made of ment time was fixed at 3 h. After the pretreatment, etha- pressure-resistant glass with a magnetic star-stirrer placed nol (EtOH) was added to commence the ethanolysis reac- inside to ensure complete mixing. The reactor was heated tion under the conditions shown in Table 3. in an oil bath temperature-controlled by a PID temperature Calcium oxide (h-CaO) and surface-modified calcium ox- controller. ide (s-CaO) were prepared by previously described meth- ods 6） in order to test comparative reactions under similar 2.2 Thermal pretreatment conditions (Table 3) without the pretreatment or added glyc- The first step of the thermal pretreatment was to mix erol. Each of the above treatments was conducted in dupli- oil with glycerol (GL) and Ca(OH)2 catalyst in a vessel and cate for each data point. After the reactions, all of the prod- heat the vessel to the desired temperature (see the condi- ucts were processed as reported previously 6） and centri- tions in Table 1). After quenching of the mixture with cold fuged at 4000 rpm for 10 min. When the phase separation water at 4℃ and shaking for 20-30 min, the concentrations was attained, the upper organic layer was analyzed for fatty of triglycerides (TG), diglycerides (DG), monoglycerides acid ethyl esters (FAEE). (MG) and glycerol (GL) were measured in a gas chromato- graph. The same analysis was repeated on a blank sample 2.4 Regeneration and reuse of Ca(OH)2 under similar conditions except the addition of Ca(OH)2, The repetitive use of the Ca(OH)2 was also tested for the glycerol and heating. The concentration was expressed as case of pretreatment with glycerol. Treatment Tiv was rep- a molar amount of a specific volume, where the volume licated several times to collect the“used Ca(OH)2”in a was calculated as sum of the volumes of the oil and glyc- sufficient quantity to conduct this experiment. The used erol. Each experimental run was conducted in duplicate. Ca(OH)2 was regenerated by the procedure shown in Fig. 1 (the regenerated product is hereinafter referred to as

“purified Ca(OH)2”). The calcination increased the BET surface area from 11.71 m2/g to 19.34 m2/g. The basic strength and basicity were determined by the procedure described by Table 1 Conditions for thermal pretreatment Heating time [h] 1-3 Temperature [℃] 100 Table 3 Conditions for ethanolysis Oil feedstock [g] 0.5 Reaction time [h] 0.5-2 GL [kg/kg-oil] 0.13 Temperature [℃] 100 Catalyst load [kg/kg-oil] 0.02 EtOH-to-oil molar ratio 12:1 Mixing speed [rpm] 1000 Mixing speed [rpm] 1000

Table 2 Summary of treatment combinations for ethanolysis reactions

Treatment Composition Thermal GL addition pretreatment

Ti a mixture of Ca(OH)2 and oil without thermal treatment prior to reaction no no

Tii a mixture of Ca(OH)2 and oil with thermal pretreatment prior to reaction yes no

Tiii a mixture of Ca(OH)2, oil, and GL without thermal pretreatment prior to reaction no yes

Tiv a mixture of Ca(OH)2, oil, and GL with thermal pretreatment prior to reaction yes yes 564 J. Jpn. Inst. Energy, Vol. 89, No. 6, 2010

2.6 Materials The crude oil in this study was produced from a feedstock of groundnut (Arachis hypogaea) seeds in a hydrau- lic oil press 6）. Its fatty acid composition, free fatty acid (FFA) content and acid value (AV) were described elsewhere 6） in which both FFA and AV achieved acceptable limits for

ethanolysis. In addition, we used commercial Ca(OH)2 as our catalytic material which was sieved to under 75 μm as is shown in the same report 6）. Prior to the ethanolysis reaction, both the crude oil that we dried in a vacuum (dryer) desiccator and anhydrous EtOH, (alcoholic reactant) were treated as described in our previous study 6）. The Fig. 1 Regeneration of used Ca(OH)2 phase separation was performed in a centrifugal separator Table 4 Conditions for ethanolysis using“used” and“purified” (Centrifuge 2420, Kubota, Japan). Ca(OH)2

Reaction time [h] 3 3. Results and Discussion Temperature [℃] 100 3.1 Thermal pretreatment of oil feedstock and elucidation EtOH-to-oil molar ratio 12:1 Fig. 2 plots the effect of the thermal pretreatment on the Oil feedstock [g] 0.5 decomposition of groundnut oil. As the plot shows, the TG Catalyst load [kg/kg-oil] 0.02 for treatment was 0.99 ± 0.01 mol/dm3. The TG break- GL (when added) [kg/kg-oil] 0.13 down was significant when heat was applied to the oil, Mixing speed [rpm] 1000 reaching 0.06 ± 0.01 mol/dm3. In turn, this decomposition led to DG and MG concentrations of 0.19 and 0.75 mol/ 7） Kouzu et al. . The basic strength of the original Ca(OH)2 dm3, respectively. These results are consistent with those － was in the range of 7.2

2.5 Analyses For the analysis of both the thermal pretreatment and ethanolysis reaction mixtures, we employed the gas chro- matograph equipped with an auto-sampler, a capillary col- umn (MET-Biodiesel, Supelco) and a flame ionization detector (FID) for the FAEE concentration. The oven temperature was changed so that after an isothermal period of 1 min at 50℃, the temperature was raised at 15℃/min to 180℃, 7℃/min to 230℃, and 30℃/min to 380℃, and then was held for 10 min. Helium was used as carrier gas, and injector and detector temperatures were set at 250 and 380 ℃, respectively. Fig. 2 Concentration for TG, DG, MG and GL J. Jpn. Inst. Energy, Vol. 89, No. 6, 2010 565

4）5）11） 3.2 Effect of thermal pretreatment with glycerol and Ca(OH)2 than the low-activity systems reported previously . on ethanolysis The findings described in the previous section explain Fig. 3 plots how the reaction time influenced the FAEE the possible mechanism behind this enhanced reactivity. yields of different treatments. Treatments Ti and Tii both The thermal pretreatment decomposes TG, which increases showed almost no catalytic effect, regardless of the reac- the concentrations of DG and MG, reactive intermediates tion time. The poor performance of Treatment Ti agrees whose solubility is higher than TG in readiness for the quite well with the findings of Suppes et al.4） and Meher et subsequent ethanolysis. The high reactivity of DG and MG al.11） who studied conventional methanolysis catalyzed by sharply accelerates the speed of the ensuing ethanolysis

Ca(OH)2 but reported low catalytic effect. The plot for treat- reaction. With the Ca(OH)2, we can therefore expect a com- ment Tii indicates that the thermal pretreatment with oil bination effect from the alkaline catalyst and enhanced TG and Ca(OH)2 without addition of GL had no significant ef- decomposition in the thermal pretreatment. This was our fect on ethanolysis. original finding, and we believe that it demonstrated an In comparison to the above two treatments, treatment innovative approach. We should add that our approach

Tiii achieved better and significant FAEE yields under the employs only renewable materials of types readily avail- same reaction conditions. This tells us that GL must be able in Sub-Saharan Africa. present to achieve improved yields, and that GL activated In comparison with previous studies, our yields were 13） the Ca(OH)2 in the reaction. We also found, however, that inferior to those of two other groups: Zhu et al. and Tateno the lack of a thermal pretreatment limited the performance and Sasaki 14） who achieved higher yields (over 90 wt%) somewhat. This finding agrees with the report from King with calcium oxide (CaO) and with Ca(OH)2, respectively. et al. 9） on the impacts of the thermal pretreatment of bio- However, they used methanol, which is much more reac- oils. tive than ethanol.

The FAEE yields from Treatment Tiv (thermal pretreatment with glycerol) were significant, and superior to the 3.3 Regeneration and reuse of used Ca(OH)2 yields of all of the other treatments. The pretreatment of Fig. 4 shows FAEE yields for the“ used” and“ purified” the TG (oil) with glycerol and Ca(OH)2 activity was expected Ca(OH)2. The“used Ca(OH)2”conferred almost no catalytic to confer a combined effect, one which is likely to be im- effect. The BET surface area (11.71 m2/g) confirmed our portant to the development of a successful ethanolysis re- suspicion that the surface-active sites of the catalyst were action for biodiesel production. Our group would like to too contaminated to react effectively. propose this treatment as an innovative approach for ef- The“ purified Ca(OH)2” showed a considerable improve- fective biodiesel production with solid catalysts. ment, with a yield of 9.60 wt%. The thermal activation or cal-

In comparison with other solid catalysts, treatment Tiv, cination regenerated the catalyst activity of this system, lead- thermal pretreatment with glycerol, performed compara- ing to an increase in the BET surface area to 19.34 m2/g. Then, bly to the activities with the catalysts s-CaO and h-CaO. by adding glycerol to prepare the“ purified Ca(OH)2 + GL,” Based on this evidence of the comparative performances, we achieved an FAEE yield of 59.11 wt%, the highest re- our ethanolysis reaction system with Ca(OH)2 as a solid corded in this study. This result suggests that thermal pre- base catalyst turns out to have a much higher reactivity treatment with glycerol is important even for the optimal regeneration of the catalyst.

Fig. 3 Effect of reaction time on FAEE yield for various treat- Fig. 4 Fatty acid ethyl ester (FAEE) yields [wt%] from ethanolysis ment catalyzed by “used” and “purified” Ca(OH)2 566 J. Jpn. Inst. Energy, Vol. 89, No. 6, 2010

Acknowledgements The authors gratefully acknowledge the financial sup- port from the Malawi Government for the scholarship of this research study. Special acknowledgements are due to Dr. Masato Kouzu for kindly providing valuable details on his experiences in heterogeneous catalysis. Over and above, we are indebted to various people from Japan, Malawi, and other parts of the world for their help with the preparation of this manuscript.

Fig. 5 FAEE yields from ethanolysis catalyzed by recycled and References “purified Ca(OH)2” 1）Hagan, E. B., Biofuels Assessment Report - ECOWAS Sub-Region, Proceedings of the AU/Brazil/UNIDO

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