THE ELECTROCATALYTIC HYDROGENATION OF GLUCOSE .2. RANEY-NICKEL POWDER FLOW-THROUGH REACTOR MODEL

A computer model which simulates the operation of a flow-through Raney nickel powder electrocatalytic hydrogenation reactor for the synthesis of sorbitol from glucose with simultaneous H-2 evolution has been developed. The model utilizes porous electrode theory, considers both mass-transfer and surface kinetics effects, and contains no adjustable parameters. Hydrogen evolution on Raney nickel is described by a Volmer-Heyrovsky rate expression. The rate equation for glucose hydrogenation is identical to that for the chemical catalytic synthesis of sorbitol with pressurized H-2 gas. For constant-current reactor operation, computed sorbitol current efficiencies match well with experimental data for a range of current densities (0.0053 to 0.021 A/cm2) and glucose feed concentrations (0.4 to 1.6M), with an average error of 8.8%. Calculations show that a large fraction of adsorbed hydrogen on the nickel cathode surface is produced by the oxidation of electrogenerated H-2 via the backward Heyrovsky reaction. According to the model, significantly higher sorbitol current efficiencies can be achieved by pulsing the current to the reactor.