Mechanocatalytic CC Bond Cleavage of Cellulose: A Novel Approach for Selective Production of Lactic Acid

Production of lactic acid (LA) from cellulose is one of the most attractive processes in biorefineries, owing to its surging demand for biodegradable plastics. However, its industrial implementation has been challenging because of high toxicity and/or high production cost of the catalysts used in the process. In this work, we report a novel process for the selective production of LA from cellulose by using abundant and low-toxicity reagents only, by means of carbonate salt-assisted mechanocatalysis and subsequent subcritical water treatment. In the first mechanocatalytic step, comilling cellulose with a carbonate salt and kaolin, a solid acid, promotes not just hydrolysis of cellulose to obtain water-soluble cellulose but also cleavage of robust CC bonds in the formed water-soluble cellulose to obtain LA and formic acid. The CC bond cleavage appears to be mediated by in situ formed metal cations originating from the feed carbonate salts being decomposed during the mechanochemical step. The subsequent subcritical water treatment improved LA yield while drastically suppressing the formation of hydroxymethylfurfural (HMF). This selectivity is attributed to high pH due to the solubilized metal cations, suppressing the dehydration reaction of fructose intermediate to form HMF.