Effect of dielectric barrier discharge plasma hydrogenation on oxidation stability of biodiesel derived from vegetable oils

Abstract

A parallel-plate type dielectric barrier discharge (DBD) plasma was utilized to produce partially hydrogenated fatty acids methyl ester (PH-FAME) derived from soybean and palm FAME. PH-FAME exhibits improved oxidation resistance, resulting in a longer storage time and a delay in changing fuel properties. The DBD plasma reaction occurred at atmospheric pressure and ambient temperature without a catalyst. The best condition for 35 mL of soybean FAME hydrogenation was using 25% H2 at ambient temperature for 5.5 h. An increase in saturated and monounsaturated FAMEs corresponded to a reduction of iodine value from 128 to 67.4. This condition created trans fatty acids of about 3.67%. The oxidation stability increased from 2.13 to 10 h and the cloud point increased from -1 to 11°C. As for 300 mL PH-palm FAME production, the optimal condition was 100 W input power, 1 mm gas gap size, and 80% H2 at ambient temperature for 5 h. The iodine value decreased from 50.2 to 43.5 without trans fatty acid formation. The oxidation stability was enhanced to 20 from 12.8 h, while the cloud point rose from 13.5 to 16˚C. The production costs of PH-FAME based on soybean and palm FAME were 36.96 and 8.39 baht per liter, respectively. The DBD plasma is one of the alternative methods that can be employed in the hydrogenation process, but it is necessary to be improved to obtain a reasonable production cost.