廃活性白土に残留する植物油のバイオディーゼル燃料への変換(<シンポジウム特集>生活空間・身の回りの粘土 : 粘土圏環境における粘土の利用)

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Activated bleaching earth (ABE) is a commonly used adsorbent in decolorization process of fat and oil refining. The ABE is manufactured by treating montmorillonite clay with mineral acids such as sulfuric acid. During acid treatment, structure of the clay becomes porous by eluting basic metallic components such as aluminum, iron and magnesium. The activated clay has a large specific surface area and a large adsorption capacity enough to adsorb colored materials in oil refining process. Waste ABE, filtered cake of used ABE in the decolorization process, contains 35-40% processing oil by weight. Discharged amount of the waste ABE in Japan is estimated approximately 80,000 tons a year. Although it is reutilized in part as subsidiary sources for Portland cement, compost etc., additional applications are required for stable waste material recycling. Recently, special attention is given to fatty acid methyl esters (FAME) as potential substitutes of fossil fuels. The FAME, which is also known as biodiesel fuel (BDF), is converted from vegetable oil by transesterification and shows suitable properties as a diesel fuel. The BDF is considered a carbon neutral and eco-friendly fuel due to its regenerative potential and biodegradability. Its mutagenic effects, furthermore, are significantly lower than those of fossil fuels. Although the vegetable oils embeded in waste ABE are expected to be converted into BDF, it is difficult to apply a conventional conversion method. Because the vegetable oils react with methanol in the pore of ABE, it is hard to separate BDF from ABE. Potassium hydroxide, generally used as a transesterification catalyst, faces another problem because of neutralization by ABE. Park reported the lipase-catalyzed production of FAME from waste ABE. Lipase worked actively in the presence of waste ABE and organic solvent such as n-hexane. Oils adsorbed inside the pore of waste ABE were extracted by the solvent, which made it possible to separate the liquid phase from the solid phase. The waste ABE worked not only as a medium for dispersion of reaction mixture but also as an adsorbent for by-produced glycerol. The organic solvent was evaporated from the FAME solution and was possibly reutilized. However, because the organic solvent is harmful to health and the environment, it is better to use a safe and harmless solvent or a solvent-free process. To improve the lipase-catalyzed BDF production process from waste ABE, a diesel fuel was used as the organic solvent as a substitute of harmful n-hexane. The esterification rate in diesel fuel was higher than that in n-hexane. Furthermore, the separating process of the solvent was not required, because the final product was a mixture of FAME and diesel fuel. The results of fuel analysis demonstrated that the BDF consisting of FAME and diesel fuel was fit to those in the diesel fuel specifications based on Japanese Industrial Standards (JIS). Thus, the BDF production process was simplified by using diesel fuel as a solvent instead of using n-hexane.
日本粘土学会の論文
2005-04-05

廃活性白土に残留する植物油のバイオディーゼル燃料への変換(<シンポジウム特集>生活空間・身の回りの粘土 : 粘土圏環境における粘土の利用)

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