Low temperature electrochemical hydrogenation of soybean oil

A novel low temperature (25°C--75°C) electrochemical process for the hydrogenation of vegetable oils has been developed. This is accomplished by the reduction of unsaturated fatty acids via a chemical pathway using formate ion as a mediator. The reduced form of the oxidized mediator is regenerated electrochemically at the cathode. The low temperature of operation results in formation of lowered amount of trans isomers and other unwanted side products for the same extent of hydrogenation as is observed for commercial high temperature and high pressure processes. Recent health studies have implicated trans fatty acids as potential coronary heart disease causing components of vegetable oils. Approximately 80% reduction in trans isomer content was obtained using the electrochemical process as compared to the commercial gaseous hydrogenation processes. Since the hydrogenation of the fatty acid double bonds take place by transfer hydrogenation, the use of large amount of catalyst is eliminated in this process. Regeneration of the mediator (i.e. hydrogen donor) reduces the amount of electrocatalyst required to maintain a high rate of hydrogenation reaction. In addition to circumventing the need to produce, compress, store and transport hydrogen gas for the molecular hydrogenation process, the electrochemical process leads to improved product selectivity and lowers the risk of explosion.; Experiments were conducted under constant potential and constant current conditions using nickel as a hydrogenation catalyst. The constant potential studies at -0.5 V vs SCE yielded up to 23% reduction of iodine value (a measure of the extent of hydrogenation) while the constant current studies at 10 mA/cm2 resulted in over 54 reduction in iodine value. The rise in trans isomer content was only 4% and 7% for the two sets of experiments. Nearly 100% Faradaic efficiencies were achieved by this process. Additional studies were conducted using palladium on silica and novel amorphous Ni-P catalysts as hydrogenation catalysts. Experiments were also conducted to recycle the electrocatalyst solution in subsequent hydrogenation. The results indicate that the reuse of the mediator did not adversely affect the hydrogenation performance in terms of iodine value reduction and trans isomer formation. In addition, hydrogenation of two other sources of long chain fatty acid triglycerides (namely, lecithin and canola oil) was also carried out. As a part of this research, the process variables were studied in depth to evaluate their effects on the hydrogenation process and to identify the optimal range of operation. A mathematical model was developed to describe the kinetics of the process and to predict the fatty acid profile obtained.