Evaluation of alternative processes of methanol production from CO2: Design, optimization, control, techno-economic, and environmental analysis

Converting carbon dioxide (CO2) to methanol via direct hydrogenation has been regarded as an essential part of the pursuit of a decarbonized energy economy. This study first explored and evaluated alternative processes for converting CO2 to methanol, in which six schemes based on adiabatic and/or non-adiabatic fixed-bed reactors were focused. The research scope includes rigorous process design, optimization, techno-economic and environmental assessment, and control. The generated results indicate that the two-reactor system (Scheme 5), which employs a non-adiabatic one as the first stage and a adiabatic one follows, has the lowest production cost. This process reveals great potential for decarbonization (i.e. CO2-e = −1.314 Ton-CO2/Ton-MeOH), whereas less economic attractiveness (i.e. minimum required selling price (MRSP) of methanol = 998 USD/Ton, average market price = 378 USD/Ton). Correspondingly, the maximum allowable CO2 emission from utilizing hydrogen (MACEH2) was found to be 6.554 Ton-CO2/Ton-H2. This indicated that using hydrogen produced from steam methane reforming (SMR) with carbon capture on both syngas and flue gas (i.e. 5.7 Ton-CO2/Ton-H2) leads to net decarbonization. Furthermore, if the emission associated with the CO2 feed (specific energy = 2.8 GJ/Ton-CO2) is also considered, net decarbonation would be achieved by using hydrogen produced from biomass gasification (i.e. 3.1 Ton-CO2/Ton-H2). A more comprehensive comparison between various CO2 utilization processes, in terms of the decarbonization ability and economics, was performed. Through this, it is concluded that there has been no existing CO2-based process that is attractive in both aspects. Finally, a suitable control strategy was proposed for the selected scheme, which suitably handles the throughput and composition disturbances.