Hydrothermal decomposition experiments of glycerin with an alkali showed that glycerin could be converted into lactic acid with a high yield of about 90 mol % based on glycerin used. Discussion on the pathway for the conversion of glycerin to lactic acid suggests that glycerin is first decomposed to pyruvaldehyde with elimination of hydrogen by a H− shift to the adjacent hydrogen. Pyruvaldehyde formed is then converted into lactic acid ion by the benzilic acid rearrangement.

A two-step hydrothermal process to improve the production of acetic acid was discussed. The first step was to accelerate the formation of 5-hydroxymethyl-2-furaldehyde (HMF), 2-furaldehyde (2-FA), and lactic acid (LA), and the second step was to further convert the furans (HMF, 2-FA) and LA produced in the first step to acetic acid by oxidation with newly supplied oxygen. The acetic acid obtained by the two-step process had not only a high yield but also better purity. The contribution of two pathways via furans and LA in the two-step process to convert carbohydrates into acetic acid was roughly estimated as 85-90%, and the ratio of the contributions of furans and LA to yield acetic acid was estimated as 2:1. The fact that WO of carbohydrates is not capable of producing a large amount of acetic acid, while the two-step process can enhance the acetic acid yield, can be explained because formic acid is a basic product of direct oxidation of carbohydrate, and acetic acid in WO of carbohydrates may come from the oxidation of dehydration products of aldose.

The conversion mechanism of cellulosic biomass to lactic acid in subcritical water without the addition of any alkaline catalyst is discussed. Results showed that this conversion mechanism appears to follow the same pathways elucidated in the conversion of sugar to lactic acid in an alkaline solution. Further, it is suggested that water in the subcritical region may act as an effective acid–base catalyst.

No abstract