Prospects of n-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.