Current efficiencies and regeneration of poisoned raney nickel in the electrohydrogenation of glucose to sorbitol

Poisoning of the Raney nickel cathode during the paired syntheses of sorbitol and gluconic acid has been studied. Sorbitol poisons the Raney nickel powder cathode and sorbitol current efficiencies decrease from 100% to <50%. Current losses of the poisoned Raney nickel were due to hydrogen evolution. Electrocatalytic activity was restored by washing the Raney nickel in a 17 wt% NaOH solution at 60°. This procedure, when performedin situ for the undivided packed bed flow reactor, increased sorbitol current efficiencies from 35–45% to 70–100%. The effects of glucose concentration and applied current on sorbitol and gluconic acid current efficiencies havealso been examined. High sorbitol current efficiencies were obtained with fresh Raney nickel when glucose concentrations were high and the current low. The high gluconic acid current efficiencies were independent of current and glucose concentration. To maintain high sorbitol current efficiencies as glucose was consumed, a systematic procedure for lowering the applied current was developed in which the current was decreased from 500 mA per 10 g of Raney nickel at 1.6M glucose to <100 mA per 10 g at 0.2M glucose.