Techno-economic assessment of sustainable isoprene production coupled with carbon dioxide sequestration using genetically engineered Synechococcus elongatus UTEX 2973

Abstract

Isoprene is a promising precursor for industrial products like rubber, chemicals, and fuels. Efforts to develop sustainable technologies to produce renewable isoprene from CO₂ using photosynthetic microorganisms are gaining significant attention. This study employs metabolically engineered Synechococcus elongatus UTEX 2973 expressing the isoprene synthase (IspS) gene from Pueraria montana and the isopentenyl diphosphate isomerase (IDI) gene from Escherichia coli, along with a chemical inhibitor (alendronate) to inhibit geranyl diphosphate synthase (CrtE) and redirect flux toward enhanced isoprene production. This work presents a conceptual design of a sustainable isoprene production plant utilizing industrial flue gas as the sole CO₂ source, together with a preliminary techno-economic evaluation to estimate its potential viability. For a 1000 tonne isoprene production plant, a total capital project investment of 21.16 million $ is estimated which includes equipment and associated costs. The total operating cost including variable and fixed costs is estimated to be 2.234 million $ per year. The minimum isoprene selling price (MISP) estimated over a range of isoprene productivity levels suggests that MISP is negatively correlated with isoprene productivity. An MISP of 16.17 $ per kg is achieved at the base-case scenario considering the isoprene productivity of 22.32 g per m³ per day. Sensitivity analysis identifies key variables including isoprene productivity, project length, cost of land and total capital investment that can enhance the overall economics of the process, offering insights for future investigations. Cost reduction could be further achieved by genetically improving microbial strains, optimizing capital investments, and refining process strategies.