Oxidation of methanol and total reduced sulfur compounds with ozone over V 2O 5/TiO 2 catalyst: Effect of humidity

Abstract

The purpose of this study was to investigate the feasibility of using ozone-enhanced catalytic oxidation for the treatment of high volume, low concentration (HVLC) waste gas streams at a Kraft pulp and paper mill that contain hazardous air pollutants such as methanol (CH 3OH), reduced sulfur compounds (TRS), including dimethyl sulfide (DMS), dimethyl disulfide (DMDS), methanethiol (MT), hydrogen sulfide (H 2S), and saturated with moisture. This paper reports that ozone-enhance V 2O 5-TiO 2 catalyzed oxidation is a stable and effective process to remove methanol and TRS compounds in the presence of moisture that has composition similar to the effluent stream coming out of a pulp mill blow tank. The effect of moisture on the oxidation of CH 3OH, MT and DMS was studied using V 2O 5/TiO 2 as a catalyst at different feed compositions (C methanol: 1000 and 7500 ppm; C DMS: 250 and 1000 ppm; and C MT: 250 and 1000 ppm) and gas hourly space velocities (37,000–150,000 h −1) at 250 °C and O 3-to-substrate mole ratio of 2.1. Conversions of methanol and TRS compounds were high and the main products were CO 2, CO and SO 2 with small amounts of partial oxidation products. Increasing the relative humidity of the gas stream from zero to 18,000 ppm reduced the conversion of methanol, whereas the conversion of TRS compounds was not affected, although the selectivity for partial oxidation products of TRS compounds decreased. High moisture levels have inhibition effect on the reactions because of competitive adsorption of methanol and water on to the same sites. The increase in the complete oxidation of TRS products could be due to forming hydroxyl ion radicals in presence of ozone and water molecules. Possible reaction mechanisms have been proposed for the complete oxidation of methanol and TRS compounds with ozone based on the product distribution.