Dielectric barrier discharge plasma for catalytic-free palm oil hydrogenation using glycerol as hydrogen donor for further production of hydrogenated fatty acid methyl ester (H-FAME)

Abstract

Catalytic-free parallel-plate-type dielectric barrier discharge (DBD) plasma was successfully employed to hydrogenate palm oil using glycerol as hydrogen donor in place of hydrogen gas for further production of hydrogenated fatty acid methyl ester (H-FAME) with enhanced oxidation stability. Most suitable reaction condition was 1:5 oil to glycerol molar ratio, 1 cm discharge gap size, 0.5 L/min He gas flow rate, atmospheric pressure, ambient temperature (rising to about 100 °C due to plasma heating), and 500 rpm stirring rate for 2 h at 130 W input power. Findings revealed that plasma could extract hydrogen radicals from glycerol, and they successfully reacted with CC bonds. Hydrogenated palm oil was subsequently converted into hydrogenated FAME (H-FAME) via conventional base-catalyzed transesterification. Higher saturation degree of H-FAME compared to FAME produced directly from palm oil was indicated by reduction of iodine value to 52.2 from 59.2. Oxidation stability of H-FAME was significantly enhanced from 17.7 to 23.1 h while cloud point slightly changed from 14.0 to 14.8 °C. Plasma reactive species generated during reaction and possible mechanisms of glycerol decomposition and plasma hydrogenation were presented. Developed catalytic-free plasma hydrogenation process is highly environmentally friendly and presents a way to add more value to waste glycerol and provide other potential hydrogen sources.