Prospects of Producing Higher Alcohols from Carbon Dioxide: A Process System Engineering Perspective

Higher alcohols are promising products for large-scale CO2 utilization due to their potential large volume use as chemical energy carriers and fuel additives. Although the catalysts for these transformations are still in early stages of development, it is advantageous to examine their expected process level performance to guide further scientific progress. Here, we performed prospective techno-economic and environmental evaluations of 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol syntheses from captured CO2 and green H2 via the syngas route (i.e., CO2 to syngas to higher alcohol) for the best case (ideal) conversion and selectivity. While 1-pentanol and 1-hexanol plants show economic viability, the costs of manufacturing the other two alcohols exceed their respective revenues. In all the four processes, the cost of raw materials, utilities, and wastewater treatment accounts for about 83%, 12%, and 5% of the cost of manufacturing, respectively (neglecting CAPEX). Sensitivity analysis shows that the cost of H2 has to drop to about 2100 and 1700 $ t-1 from the current level of ca. 2500 $ t-1 for 1-propanol and 1-butanol processes to break even. In all four processes, the fraction of H2 feed lost to byproduct water ranges from 55 to 60%, which is an inherent issue with thermocatalytic hydrogenation of CO2. Although a standalone green 1-propanol plant is not presently viable, a hybrid process combining a recently studied synthesis route (using ethylene and CO2-derived syngas) and the novel route based solely on CO2 can minimize the carbon footprint without sequestration and also be profitable at the prevailing hydrogen cost.

Automated summary

Higher alcohols have the potential to be widely used in large-scale CO2 utilization, serving as chemical energy carriers and fuel additives. In this study, prospective techno-economic and environmental evaluations were conducted to examine the synthesis of 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol from captured CO2 and green H2. The results showed that 1-pentanol and 1-hexanol plants are economically viable, while the costs of manufacturing the other two alcohols exceed their revenues. Sensitivity analysis suggested that the cost of H2 needs to be reduced for the processes to break even. A hybrid process combining a recently studied synthesis route and the novel route based solely on CO2 was found to reduce carbon footprint and be profitable.