Techno-economic and environmental assessment of CO2 conversion to methanol: Direct versus indirect conversion routes

Methanol as a clean energy source is one of the most important industrial petrochemical products that it is used as a fuel, solvent, and intermediate substance for other component production. Methanol is directly synthesized from CO2 in the direct process, while in the indirect one, CO2 is converted to CO in a water gas shift reactor as an intermediate. In this research, both direct and indirect processes are designed and simulated via Aspen Plus simulator at steady state condition for comparing not only their efficiencies, but also their economic and environmental analysis for the first time. The optimum operating conditions of processes are obtained to achieve the maximum methanol production at a fixed feed rate of 228,417 tons/year CO2 waste gas supply. Furthermore, the best process is selected by TOPSIS decision making method by comparing the capital cost and environment issues of the direct and indirect processes. The results show that direct methanol synthesis has a superior environmental and financial efficiency compared to the indirect process as the fixed capital investment is 506 million USD for the direct process and 578 million USD for the indirect method. This is while the net profit amount is opposite, 132 million USD for direct and 135 million USD for indirect processes with the payback periods of about 7 and 8 years for the direct and indirect processes, respectively.