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 O2/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 O2/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)2S2 and H2O was obtained. Since catalyst deactivation occurred by fouling due to deposition of (CH3)2S2 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.