Prospects of <i>n</i>-Butanol Production from Carbon Dioxide via Ethanol Dimerization

Higher alcohols, such as n-butanol, are promising products of CO2 utilization due to their potential uses as energy carriers or chemicals. However, their direct formation from CO2 or via syngas is hindered by low yields. Here, we designed a novel 3-step process to produce n-butanol from CO2 via syngas and ethanol. Design strategies for an ethanol–butanol–water mixture over a wide composition range have also been discussed in detail. Process performance investigation revealed that the conversion of syngas to ethanol had little effect on the total annualized cost (TAC) of n-butanol and CO2 utilization efficiency (CUE), but TAC decreased and CUE increased steadily with the increasing conversion of ethanol to n-butanol to $1739/t and 47%, respectively. Conversion to n-butanol should be at least 20% for a positive CUE and a bypass strategy around the n-butanol reactor was proposed to benefit from >40% conversion. At modest conversions in both reactors (30–40%), the H2 cost should fall to about $600–700/t for the proposed n-butanol process from CO2 utilization to be viable. Moreover, once 30–40% Guerbet conversion is achieved, further catalysis development should focus on improving selectivity.