Advanced purification of isopropanol and acetone from syngas fermentation

Abstract

BACKGROUND: Isopropanol and acetone production by syngas fermentation is a promising alternative to conventional fossil carbon-dependent production. However, this alternative technology has not yet been scaled up to an industrial level owing to the relatively low product concentrations (about 5 wt% in total). This original research aims to develop cost-effective and energy-efficient processes for the recovery of isopropanol and acetone from highly dilute fermentation broth (>94 wt% water) for large-scale production (about 100 kt_IPA+AC y⁻¹). RESULTS: Vacuum distillation and pass-through distillation enhanced with heat pumps or multi-effect distillation were efficiently coupled with regular atmospheric distillation and extractive distillation in several innovative intensified downstream processes. Over 99.2% of isopropanol and 100% of acetone were recovered as high-purity end-products (>99.8 wt%). Advanced heat pumping (mechanical vapor recompression) and heat integration techniques were implemented to decrease total annual costs (0.109–0.137 USD kg_IPA+AC⁻¹), reduce energy requirements (1.348–2.043 kW_th h kg_IPA+AC⁻¹) and lower CO₂ emissions (0.067–0.191 kg_CO2 kg_IPA+AC⁻¹), resulting in highly competitive recovery processes. CONCLUSION: The proposed three novel isopropanol and acetone recovery processes from dilute broth significantly contribute to the expansion of sustainable industrial fermentation. Furthermore, this original research is the first one to develop novel pass-through distillation technology for the complex isopropanol–acetone–water system. All the designed processes are highly economically competitive and environmentally viable. In addition to recovering efficiently both isopropanol and acetone, the designed downstream processes offer the possibility to enhance the fermentation process by recycling all the present microorganisms and reducing fresh-water requirements.