Performance of zeolites and product selectivity in the gas-phase oxidationof 1,2-dichloroethane

The deep oxidation of 1,2-dichloroethane (DCE) over Ii-type zeolites (H-Y, H-ZSM-5 and H-MOR) was evaluated. Experiments were performed on conditions of lean chlorocarbon concentration (around 1000ppmv) under dry and humid co nditions, between 200 and 550 degreesC in a conventional fixed-bed reactor. The high density of Bronsted acid sites, proved by temperature-programmed desorption (TPD) of ammonia and diffuse reflectance FT-IR of adsorbed pyrid ine measurements, make H-ZSM-5 zeolite an effective catalyst for DCE decomp osition. Vinyl chloride was identified as an intermediate in 250-400 degree sC range. When vinyl chloride was destroyed at higher temperatures, all the zeolites showed a great selectivity (>90%) to HCl. CO was promoted in quan tity reflecting the difficulty of its oxidation over these zeolite catalyst s. The activity of the zeolites was reduced in the presence of water vapour (15,000 ppmv). It was noticed that the addition of water to the feed strea m did not alter the order of activity observed in the dry experiments. More over, the presence of water in the DCE decomposition changed significantly the reaction product distribution. Vinyl chloride formation was found to be significantly lowered over the three zeolites, and selectivity to CO2 form ation was largely enhanced. The X-ray powder diffraction (XRD) analysis of the deactivated samples indicated partial destruction of the zeolite crysta l structure during reaction. (C) 2000 Elsevier Science B.V. All rights rese rved.