Oxidation of methyl mercaptan over an activated carbon in a fixed-bed reactor

A gas containing approximately 1000 ppm of methyl mercaptan (CH3SH) was used to test an oxidative reaction system for the purification of gas. Experiments were performed for 3.0 h periods in a fixed-bed reactor containing 0.25-5.0 g of Hydrodarco activated carbon in the temperature and pressure ranges 323-448 K and 122-364 kPa, respectively. The gas hourly space velocity was varied from 938 to 4000 h(-1), with the O-2/CH3SH ratio varying from 1.1 to 1.33 times the stoichiometric ratio. Dimethyl disulfide was the main product, while CO2 was produced in small amounts. At temperatures above 373 K, 99.99% conversion of the mercaptan was achieved. It was established that higher conversion of CH3SH could be achieved while keeping CO2 production to a minimum by using an O-2/CH3SH ratio in the feed gas close to 1.10 times the stoichiometric ratio, Catalyst deactivation occurred due to deposition of dimethyl disulfide on the catalyst. A kinetic study of this process was performed, and a rate equation for the conversion of CH3SH to (CH3)(2)S-2 and H2O was obtained. Since catalyst deactivation occurred by fouling due to deposition of(CH3)(2)S-2 on the catalyst, the initial rates were considered to be global rates without deactivation effects. According to the Langmuir-Hinshelwood model, the overall rate equation was derived on the basis of the mechanism where the rate-determining step is a surface reaction. The rate data obtained using granular activated carbon were collected well with the rate equation.