Design and economic analysis of a macroalgae-to-butanol process via a thermochemical route

Highlights: • Novel macroalgae-to-butanol plants are designed and assessed for U.S. and S. Korea. • The lowest MBSP of 1.97 $/L was obtained for the S. Korean natural gas import plant. • S. Korean plant with no fossil utilities had lowest CO₂ avoided cost of 620 $/tCO₂e. • Macroalgae-to-butanol plants CO₂ avoided costs are competitive with other biofuels. • CO₂ avoided costs of assessed plants are most sensitive to changes in gasoline price. - Abstract: In this work, a first of its kind assessment of butanol production from macroalgae through a thermochemical route is carried out. Different process configurations were designed and simulated in Aspen Plus to quantify their mass and energy balances. Furthermore, economic and environmental metrics such as the minimum butanol selling price (MBSP), and cost of CO₂ equivalent emissions (CO₂e) avoided were used to assess the potential of the different configurations under different market scenarios, with comparisons carried out amongst the configurations as well as against standard literature references of similar processes. Finally, a sensitivity analysis was used to assess the impact that changes in key parameters have on the considered metrics. The results show that configurations which import natural gas and electricity as utility sources alongside the macroalgae feedstock offer the lowest MBSP, however they do poorly when cost of CO₂e avoided is considered. On the other hand, the configurations which utilize only macroalgae offer the best potential for cost of CO₂e avoided but have the poorest values for MBSP. In addition, the cost of CO₂e avoided obtained for the best configurations are in line with literature references. However, the MBSP values are higher than literature references for butanol derived from cellulosic feedstock primarily due to the high ash content in seaweed. The sensitivity analyses results show that changes in gasoline prices have a very significant effect on the plant configurations in the South Korean market, but not as significantly in the United States market.