Takekazu Kasuno’s scientific contributions

In order to study solid base catalyst for biodiesel production with environmental benignity, transesterification of edible soybean oil with refluxing methanol was carried out in the presence of calcium oxide (CaO), -hydroxide (Ca(OH)2), or -carbonate (CaCO3). At 1h of reaction time, yield of FAME was 93% for CaO, 12% for Ca(OH)2, and 0% for CaCO3. Under the same reacting condition, sodium hydroxide with the homogeneous catalysis brought about the complete conversion into FAME. Also, CaO was used for the further tests transesterifying waste cooking oil (WCO) with acid value of 5.1mg-KOH/g. The yield of FAME was above 99% at 2h of reaction time, but a portion of catalyst changed into calcium soap by reacting with free fatty acids included in WCO at initial stage of the transesterification. Owing to the neutralizing reaction of the catalyst, concentration of calcium in FAME increased from 187ppm to 3065ppm. By processing WCO at reflux of methanol in the presence of cation-exchange resin, only the free fatty acids could be converted into FAME. The transesterification of the processed WCO with acid value of 0.3mg-KOH/g resulted in the production of FAME including calcium of 565ppm.

For developing a process of biodiesel production with environmental benignity, much interest has been focused on solid base catalysts such as calcium oxide for transesterification of vegetable oils with methanol. In this paper, the active phase of calcium oxide was investigated by characterizing the catalyst collected after achieving the conversion of edible soybean oil into its methyl ester at reflux of methanol in a glass batch reactor. Calcium oxide combined with the by-produced glycerol, so that calcium diglyceroxide was a major constituent of the collected catalyst. The absence of calcium methoxide was clear from the spectrum of solid-state 13C-NMR. The chemical change of calcium oxide was not observed, when the yield of FAME reached 30%. The collected catalyst was not as active as the fresh one (calcium oxide), but was reused without any deactivation. In order to identify the active phase of the collected catalyst, we prepared calcium diglyceroxide by immersion of calcium oxide with refluxing methanol in the presence of glycerol. Calcium diglyceroxide prepared as the reference sample was as active as the collected catalyst in the transesterification, and was tolerant to air-exposure.

Waste cooking oils were studied as the raw material for biodiesel production using calcium oxide as the solid base catalyst in refluxing methanol. Edible soybean oil and waste cooking oil from restaurants were converted into biodiesel completely within 2 hr. However, catalyst recovery after the reaction markedly decreased for the waste cooking oil, due to dissolution of the solid base catalyst. Most of the solid base catalyst was converted into calcium methoxide and glyceroxide, and trace of saponified calcium was collected after the reaction of the waste cooking oil. Waste cooking oil from homes increased the catalyst recovery, in comparison with waste oil from restaurants. The catalyst recovery was considerably improved by a removal of free fatty acids. Both polar fraction and moisture in the waste cooking oil were minor poisons for the solid base catalyst. Based on the results, improvement of the biodiesel production requires protection for the solid base catalyst from the poisoning species contained in the waste cooking oil.

Transesterification of soybean oil was carried out with methanol over calcium oxide at methanol refluxing temperature, in order to study the application of heterogeneous catalytic process to biodiesel production. The catalyst samples were prepared by calcination of the precipitated calcium carbonate at 900°C in the prescribed atmosphere, an ambient air or a helium gas flow. Calcium oxide prepared in an ambient air catalyzed the transesterification of soybean oil, but yield of the fatty acid methyl esters was only 10% for 4h. The calcination in a helium gas flow markedly intensified the activity of calcium oxide, as the obtained catalyst sample completed the transesterification for 2h. The obtained oil after completing the transesterification had appropriate properties for diesel fuel oil. The active catalyst prepared in a helium gas flow has a higher base strength (15.0 < H_ < 18.4) than the dull one in an ambient air (9.3 < H_ < 15.0). Additionally, the base quantity was 5times larger for the active catalyst. The dull catalyst could be activated by calcination at 300°C in a helium gas flow. The poisoning species in an ambient air was elucidated through the activity test for a series of the catalyst sample obtained by conditioning the partial pressure of CO 2 and moisture in the calcining atmosphere.