(396b) Electrochemical Oxidation of Glycerol Combined with Product Adsorption

Electrochemical oxidation of glycerol was investigated. Target product of oxidation is dihydroxyacetone. The main challenge of the process is limitation of cleavage products with ongoing oxidation. In this project it was investigated, whether cleavage of the oxidation intermediate dihydroxyacetone can be limited by adsorbing it on ion exchange resin parallel to the oxidation of glycerol. The anion exchange resin Lewatit VP OC 1065 (a cross-linked polymer with primary amine substituent) is capable of adsorbing dihydroxyacetone (the primary oxidation product of glycerol) reversibly.

Electrochemical oxidation was carried out in batch operation in a thin layer pump cell. Anode and cathode compartment were separated by an ion exchange membrane. A diamond coated electrode was used as anode; a platinum grid was used as cathode. Na₂SO₄ (moderate acidic), K₂HPO₄ (neutral), and Na₂CO₃ (moderate alkaline) were used as electrolytes.

The kinetics of adsorption of dihydroxyacetone with anion exchange resin was investigated in a fixed bed reactor. The resin was located as fixed bed in the anolyte loop.

Results

During electrochemical oxidation the desired products (glyceraldehyde and dihydroxyacetone) are formed with good selectivity and current yield at the beginning of the electrolysis process. But with ongoing process the fraction of cleavage products (glycolaldehyde and formic acid) increases. From adsorptive removal of dihydroxyacetone improved selectivity and yield was expected. Reaction of dihydroxyacetone with anion exchange resins is slow and reversible. The adsorbed form of dihydroxyacetone dominates the solid/liquid-equilibrium. The dissolution rate of dihydroxyacetone (with water, with aqueous hydrochloric acid as well as with aqueous sodium carbonate solution) is very slow.

Because of the slow adsorption rate of dihydroxyacetone the inline combination of electrochemical oxidation and adsorption with anion exchange resins does not show the expected significant influence on selectivity of electrochemical glycerol oxidation.