Low Temperature Catalytic-Transfer Hydrogenation of Candlenut Oil

Abstract

Fatty acids containing more than one double bond (polyunsaturated fatty acids) indicated by high iodine value (more than 120 g I₂/100 g oil) are prone either to oxidative degradation or thermal degradation leading to the appearance of undesirable compounds or to thermal oligo-/polymerization causing gum formation. Therefore, polyunsaturated bonds in the fatty acid chains should be hydrogenated into monounsaturated ones. The conventional method using hydrogen (direct hydrogenation) at relatively high temperature and pressure with the aid of nickel as catalyst, which prone to explosion due to the presence of free gaseous hydrogen at high temperature and pressure. Catalytic transfer-hydrogenation (CTH) therefore is proposed as a promising alternative method, enabling CTH at room condition without the presence of free hydrogen. This research is focused to explore effects of temperature and reaction time to iodine value reduction on CTH of candlenut oil, including kinetics of its methyl ester. The hydrogenation utilizes Ag-Ni/silica 150 Å as catalyst and potassium formate (6M) as hydrogen donor. Three reaction temperatures were selected (40^oC, 60^oC and 78^oC), where each reactions were performed for 4, 8, 12 and 16 hours. Hydrogenation was performed in batch reactor using isopropyl alcohol as solvent. Results showed that iodine values decreased with the increase of temperature and longer reaction time. The iodine value was still decreasing at 16 hours reaction time, indicating the possibility of longer reaction time. However, at 16 hours time, the iodine value yield has been within biodiesel standard range (Indonesian National Standard). The hydrogenation was first order reaction towards methyl ester double bonds concentration. K_o and E for candlenut methyl ester were 163.15/hour and 25.26 kJ/mol.