Catalyzed sulfonation of methane to methanesulfonic acid

Direct sulfonation of methane with SO3 to methanesulfonic acid (MSA) and methylbisulfate was investigated in sulfuric acid using Hg(I), Hg(II), and Rh(III)-salts as catalysts. O2 was found to be an important component for the regeneration of the catalyst. The effects of O2 pressure, temperature, SO3 concentration, methane pressure, and catalyst concentration were examined on the rates of SO3 conversion to MSA and methylbisulfate. The results of this investigation show that after 5 h at 148 ◦C using fuming sulfuric acid as the solvent, 360 psig CH4 reacts with 21 mmol of SO3 to give a 44% conversion of SO3 to MSA in the presence of 40 psig O2 and 0.075 mmol of Hg(CF3SO3)2 as the catalyst. The corresponding MSA selectivity is 87%. Conducting the reaction at higher temperature, higher O2 pressure and higher initial concentration of SO3, leads to a reduction of the selectivity to MSA and an increase in the selectivity to CH3OSO3H. A mechanism for the formation of MSA and CH3OSO3H is proposed in the light of the experimental results. © 2003 Elsevier B.V. All rights reserved.