A Review on Methanol as a Clean Energy Carrier: Roles of Zeolite in Improving Production Efficiency

Abstract

Clean methanol can play an important role in achieving net zero emission targets by decarbonizing the energy and chemical sectors. Conventionally, methanol is produced by using fossil fuel as raw material, which releases a significant amount of greenhouse gases (GHGs) into the environment. Clean methanol, which is produced by hydrogen (H2) from renewable sources (green H2) and captured carbon dioxide (CO2), is totally free from the influence of fossil fuel. Due to its vast applications, clean methanol has potential to substitute for fossil fuels while preventing further GHGs emissions. This review addresses the feasibility of producing clean methanol from renewable resources, i.e., green H2 and captured CO2. Availability of these raw materials is the main factor involved in establishing the circular economy of methanol, therefore, their potential sources and the possible pathways to access these sources are also summarized. Renewable energy sources such as solar, wind and biomass should be utilized for producing green H2, while CO2 captured from air, and more likely from point emission sources, can be recycled to produce clean methanol. After producing methanol from CO2 and H2, the removal of by-product water by distillation is a big challenge due its high energy consumption. An alternative approach for this methanol-water separation is membrane technology, which is an energy saving option. Water-selective zeolite membranes can separate water post-synthesis, as well as during the synthesis. Production efficiency of methanol can be enhanced by utilizing zeolite membranes inside the methanol synthesis reactor. Furthermore, CO2 conversion as well as methanol selectivity, purity and yield can also be increased significantly by selectively removing by-product water using a zeolite membrane reactor.