Synthesis of lactic acid from dihydroxyacetone: use of alkaline-earth metal hydroxides

By-products from bio-based processes show great potential as renewable feedstock sources. In this context, upgrading the biodiesel by-product glycerol is highly promising. This paper focuses on the production of lactic acid from dihydroxyacetone, which is a primary oxidation product of glycerol, under mild reaction conditions (ambient pressure and temperatures below 90 °C) with alkaline-earth metal hydroxides. Whereas both Ca(OH)2 and Ba(OH)2 effectively catalysed the formation of lactic acid in the liquid phase, lactic acid was not formed with Mg(OH)2 at 25 °C. The final yield was higher with Ca(OH)2 (59%) than with Ba(OH)2 (50%). With Ca(OH)2, increasing reaction temperatures resulted in higher reaction rates. At 85 °C, however, competing side and degradation reactions were dominating, limiting the yield of lactic acid to 36%. We demonstrated that the method can be directly applied to dihydroxyacetone in fermentation broths. This research opens up a new synthesis route for lactic acid from dihydroxyacetone and glycerol, respectively.