Electrochemical Hydrogenation of Soybean Oil with Hydrogen Gas

Soybean oil has been partially hydrogenated in a proton exchange membrane (PEM) electrochemical reactor, with H2 gas as the anode feed and source of hydrogen. The reactor is similar in design to that used in a H2/O2 fuel cell, with a membrane electrode assembly composed of a Pd-black powder cathode and a Pt-black powder anode fixed to the opposite surfaces of a Nafion 117 cation-exchange membrane. The PEM reactor was operated at a moderate temperature (60-90 (degree)C) and 1 atm of pressure using commercial-grade soybean oil as the cathode feed. The effects of the current density, temperature, and oil flow rate on oil hydrogenation current efficiency and product selectivity were investigated. The oil hydrogenation current efficiency (the efficiency of electrogenerated H2 addition to fatty acid double bonds) increased with temperature, decreased with current density, and ranged from 45 to 97%. Partially hydrogenated oil products were characterized by a low percentage of trans-fatty acid isomers (which are known contributors to coronary heart disease) and a moderately high concentration of saturated stearic acid (typical of nonselective, precious metal hydrogenation catalysts). An improvement in fatty acid hydrogenation selectivity was achieved by increasing the oil feed flow rate and inserting a turbulence promoter into the oil feed channel of the PEM reactor. The use of a bimetallic cathode (Pd/Co or Pd/Fe) increased the selectivity of the hydrogenation process, at the expense of a drop in current efficiency and an increase in the trans isomer content of hydro-oil products.