Synthesis of methanol from methane: Challenges and advances on the multi-step (syngas) and one-step routes (DMTM)

• We report a background of methane oxidation to methanol throughout multistep process (syngas route).
• Methane to methanol direct oxidation processes in gas phase were revised (DMTM routes).
• Catalyst-free processes for methane oxidation to methanol display low conversion.
• The methanol selectivity on solid-catalyzed methane partial oxidation depends on catalyst, temperature and oxidant.
• Methane oxidation to methanol over Cu or FeZSM5 catalysts has been highly promising.

To transform the methane oxidation to methanol in a selective, straight, economically attractive, and less energy-intense process is a goal pursued by the industry since its discovery. Methane is the main constituent of shale and natural gas while methanol is either a fuel as feedstock in the chemical industry. Thus, to develop a technology that combines an affordable raw material with a strategic product became pivotally important for the chemical industry. Currently, the industrial route for methanol production from methane is accomplished via a syngas process, passing by stream catalytic reform of products (i.e., CO and H2). This is a costly route due to its high-energy consumption. Alternatively, methane partial oxidation to methanol (i.e. DMTM route) in a single step can constitute a more economically viable strategy. Toward achieving this goal, different approaches were proposed; nonetheless, until now, any was industrially feasible. In this review, we paid particular attention to the methane direct oxidation processes to methanol carried out in a gas phase under homogeneous or heterogeneous conditions. In general, heterogeneous processes are solid-catalyzed in the gas phase, while homogeneous processes occur without a catalyst. We too assessed the advances achieved in the traditional route to producing methanol from syngas, as well as recent developments of syngas production from methane.

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