Current efficiency for soybean oil hydrogenation in a solid polymer electrolyte reactor

Soybean oil has been hydrogenated electrocatalytically in a solid polymer e lectrolyte (SPE) reactor, similar to that in H-2/O-2 fuel cells, with water as the anode feed and source of hydrogen. The key component of the reactor was a membrane electrode assembly (MEA), composed of a precious metal-blac k cathode, a RuO2 powder anode, and a Nafion(R) 117 cation-exchange membran e. The SPE reactor was operated in a batch recycle mode at 60 degrees C and one atmosphere pressure using a commercial-grade soybean oil as the cathod e feed. Various factors that might affect the oil hydrogenation current eff iciency were investigated, including the type of cathode catalyst, catalyst loading, the cathode catalyst binder loading, current density, and reactan t flow rate. The current efficiency ordering of different cathode catalysts was found to be Pd > Pt > Ph > Ru > Ir. Oil hydrogenation current efficien cies with a Pd-black cathode decreased with increasing current density and ranged from about 70% at 0.050 A cm(-2) to 25% at 0.490 A cm(-2). Current p ulsing for frequencies in the range of 0.25-60 Hz had no effect on current efficiencies. The optimum cathode catalyst loading for both Pd and Pt was 2 .0 mg cm(-2). Soybean oil hydrogenation current efficiencies were unaffecte d by Nafion(R) and PTFE cathode catalyst binders, as long as the total bind er content was less than or equal to 30 wt % (based on the dry catalyst wei ght). When the oil feed flow rate was increased from 80 to 300 ml min(-1), the oil hydrogenation current efficiency at 0.100 A cm(-2) increased from 6 0% to 70%. A high (70%) current efficiency was achieved at 80 ml min(-1) by inserting a nickel screen turbulence promoter into the oil stream.