Wet oxidation of aqueous polyvinyl alcohol solution

Wet air oxidation of aqueous solutions of poly(vinyl alcohol) (PVA) has been studied in a batch autoclave reactor at temperatures ranging from 175 to 250°C in an excess of oxygen of 0-300% and at oxygen partial pressures (PO2) of 0.53-2.11 MPa. No destruction of PVA was observed below 175°C. The decomposition of PVA and the removal of total organic carbon (TOC) and chemical oxygen demand (COD) rapidly increased at reactor temperatures above 200°C. PVA decomposition was more sensitive to the reaction temperature than to PO2 or the excess oxygen ratio. About 90% destruction of PVA occurred in 90 min at 200°C, 0% excess oxygen, and 0.7 MPa oxygen partial pressure. Whereas the amount of excess oxygen had little effect on PVA destruction, it accelerated COD and TOC removal. The main intermediates analyzed were carboxylic acids, in particular formic and acetic acids. Further oxidation of these acids resulted in carbon dioxide (CO2) and carbon monoxide (CO). The conversions of PVA to CO2 and CO were 78% and 5%, respectively, after 4 h of reaction at 200°C and 100% excess oxygen. The experimental results indicate that, of the two main intermediates, formic acid was short-lived, whereas acetic acid limited the wet oxidation process. Biodegradability of the solution substantially increased upon wet oxidation.