Catalytic Conversion of Dihydroxyacetone to Lactic Acid with Brønsted Acids and Multivalent Metal Ions

S. Lux and M. Siebenhofer

Abstract
The exploitation of by-products from chemical processes shows high potential for the development of new synthesis routes for valuable chemicals. Glycerol, provided as a by-product from the biodiesel manufacturing process, is a potential feedstock chemical. From dihydroxyacetone, a primary oxidation product of glycerol, lactic acid may be obtained. The catalytic effect of Brønsted acids and multivalent metal ions on the conversion of dihydroxyacetone to lactic acid in aqueous solutions was investigated. Lactic acid yields of 83 % were achieved when carrying out the reaction under reflux boiling conditions with the catalyst HCl in excess. High acidity of the reaction solution is essential for the dehydration of dihydroxyacetone to pyruvic aldehyde. Consecutive conversion of pyruvic aldehyde to lactic acid was accelerated by multivalent metal ions (e.g. Al3+). The Lewis acid Al2(SO4)3 provides both acidic reaction conditions for dehydration of dihydroxyacetone to pyruvic aldehyde and acceleration of lactic acid formation from pyruvic aldehyde. Lactic acid yields of up to 78 % were obtained with Al2(SO4)3.

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Keywords
lactic acid, Brønsted acid, Lewis acid, dihydroxyacetone, glycerol