Preliminary investigation of low pressure membrane distillation of methyl bisulphate from its solutions in fuming sulphuric acid combined with hydrolysis to methanol

A new method of conversion of methane to methanol consists of two steps: methane esterification and hydrolysis of the ester to methanol. Up to now the hydrolysis was performed in the reaction mixture obtained in the first stage. The disadvantages were that much sulphuric acid was produced and a very large amount of water had to be added. Authors as the first propose the extraction of the ester before the hydrolysis. This is the first attempt on the utilization of membrane distillation as the second step of conversion of methane to methanol. In this study the possibility of application of a LPMD (low pressure membrane distillation) for the separation of ester–oleum mixture was investigated. It was found that in the first stage only the sulphur trioxide passed through the membrane due to its high vapour pressure over oleum. Then, because of depletion in SO3, methyl bisulphate was separated from the mixture. Owing to this phenomenon the production of sulfuric acid and the amount of added water can be reduced. The efficiency of ester separation was close to 100%. After LPMD ester was adsorbed in water where hydrolysis took place.