The techno-economic feasibility and carbon footprint of recycling and electrolysing CO2 emissions into ethanol and syngas in an isobutene biorefinery

Abstract

With the prevalent need for more circular and carbon-neutral chemicals and fuels such as bio-isobutene (bio-IBN), bioethanol, and syngas, the integration of waste and emission valorisation technologies with biorefinery production is critical for greater resource efficiency and Europe's green transition. To determine the technical feasibility, economic value, and carbon footprint of recycling and electrolysing CO2 available during 2nd generation bio-IBN production into by-products, the material and energy process flows of bio-IBN production (scenario 1), bio-IBN integrated low temperature (LT) CO2 electrolysis for ethanol production (scenario 2), and bio-IBN integrated high temperature (HT) CO2 electrolysis for syngas production (scenario 3), were each simulated and tested in the biochemical process engineering software SuperPro Designer, MS Excel biorefinery template, and the LCA software GaBi_ts, respectively. The results suggest that biorefinery biowaste and CO2 conversion enable higher CO2 savings for scenario 1's bio-IBN product (0.587 kg CO2eq./kgIBN) and scenario 3's syngas product (0.359 kg CO2eq./kgSyngas) compared to other products on the market. However, only scenario 3 was able to generate a net profit at the base scale ($67.92 million) and required financial support (i.e. capital grant payments) to render a positive NPV2021. While scaling production to >102,955.96 tIBN/year improved production costs per product, with scenario 3 being the exception, economic returns are not possible or feasible due to resource and technological constraints. Given the state of development of bio-IBN production, more technically mature biorefineries (e.g., bioethanol) could serve as a safer source of CO2 for HT CO2 electrolysis product manufacture in the future. Considering their carbon savings, selling bio-IBN and syngas at premium prices of $3.42/kgIBN and $1.60/kgsyngas, rather than their market prices, could be justified to obtain profitability and a positive NPV2021.