Oxidation and hydrolysis of lactic acid in near-critical water

Hydrothermal reactions (oxidation and hydrolysis) involving lactic acid (LA ) were studied at temperatures ranging from 300 to 400 degrees C and a nomi nal pressure of 27.6 MPa. Kinetic models were developed with respect to con centrations of LA and total organic carbon (TOC), respectively. The best-fi t model for LA oxidation with 95% confidence limits is -d[LA]/dt = 10(18.7/-4.2) X exp(-226 +/- 46.6 kJ/mol/RT)[LA](0.88+/-0.11)[O-2](0.16+/-0.19). S imilarly, the best-fit TOC model for lactic acid oxidation is -d[TOC]/dt = 10(4.3+/-2.5) exp(-68.4 +/- 27.2 kJ/mol/RT)[TOC] (0.62+/-0.33)[O-2](0.36+/- 0.26) The best-fit TOC model for lactic acid hydrolysis is -d[TOC]/dt = 10( 8.4+/-2.1) exp(-125 +/- 26.7 kJ/mol/RT)[TOC]. On the basis of identified li quid and gaseous products, pathways for hydrothermal reactions involving la ctic acid were proposed. Acetic acid and acetaldehyde were confirmed as the major liquid intermediates for oxidation and hydrolysis reactions, respect ively. Carbon monoxide and methane were identified as the major gaseous byp roducts from these reactions. These results demonstrated the potential of c ompletely oxidizing, as well as converting, lactic acid into other organic products, in high-temperature water.