Inhibition and deactivation effects in catalytic wet oxidation of high-strength alcohol-distillery liquors

The removal efficiency of total organic carbon (TOC) from raw high-strength alcohol-distillery waste liquors was evaluated using three different treatments: thermolysis (T), noncatalytic wet oxidation (WO), and solid-catalyzed wet oxidation (CWO); The distillery liquors (TOC = 22500 mg/L, sugars = 18000 mg/L, and proteins = 13500 mg/L) were produced by alcoholic :fermentation of enzymatic hydrolyzates from steam-exploded timothy grass. TOO-abatement studies were conducted batchwise in a stirred autoclave to evaluate the influence of the catalyst (7:3, MnO2/CeO2 mixed oxide), oxygen partial pressure (0.5-2.5 MPa), and temperature (453-523 K) on T; WO, and CWO processes. Although CWO outperformed T and WO, TOC conversions did not exceed similar to 60% at the highest temperature used. Experiments provided prima facie evidence for a gradual fouling of the catalyst and a developing inhibition in the liquors which impaired deep TOC removals. Occurrence of catalyst deactivation by carbonaceous deposits was proven experimentally through quantitative and qualitative experiments such as elemental analysis and X-ray photoelectron spectroscopy. Inhibition toward further degradation of the liquors was ascribed to the occurrence of highly stable antioxidant intermediates via the Maillard reactions between dissolved sugars and proteins. A lumping kinetic model involving both reaction inhibition by dissolved intermediates and catalyst deactivation by carbonaceous deposits was proposed to account for the distribution of carbon in the liquid, solid, and the vapor phases.