Abstract
The functionalization of methane by halogens and subsequent condensation to higher hydrocarbons has received much attention for valorization of the vast conventional and unconventional natural gas reserves. Despite its potential advantages over the analogous methanol-mediated route, there are some challenges and technical problems such as selectivity of monohalomethanes, catalyst deactivation during methyl halide to hydrocarbons (MeXTH) transformation step, and halogen handling and recycling. Only chlorine and bromine give satisfactory results based upon thermodynamic analysis. Oxyhalogenation using HX (X=Cl or Br) as a halogen source is preferred for the first step as the HX by-product from methyl halide condensation step can be directly recycled. The commonly used shape selective SAPO-34 and HZSM-5 catalysts suffer from rapid deactivation due to coke deposition and dealumination by the resulting HX in MeXTH. Various measures have been developed to overcome this problem such as using nano-sized or hierarchically structured zeolites. Nevertheless, the MeXTH is far less studied than the methanol to hydrocarbons (MTH) reaction. This chapter presents a review on the chemistry, thermodynamics, and mechanism of the reactions involved in the two-step upgrading of methane via methyl halides. The catalyst types and recent technical developments are also presented.
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