(245f) Sustainable Production of Butanol – Evaluation of a Bio-Based Process

Today fossil fuels take up around 80% of the global primary energy consumption, of which nearly 60 % is used by the transportation sector. Since the transportation sector is responsible for a significant fraction of the greenhouse gases emissions, substitution of oil derived fuels by biofuels, could significantly decrease environmental impacts, besides providing gains on the socio-economic levels as well. Of the renewable liquid fuel options, butanol is a promising candidate due to its higher energy density, better solubility in existing hydrocarbon fuels, lower vapor pressure and lower corrosiveness [1].

In this work, using a systematic 12 step hierarchal approach for performing (sustainable) process design, a biobutanol production process has been designed. Wheat straw has been selected as the biomass to produce 7.5 m³ of butanol/year with a yield of 0.11 Kg of butanol per Kg of raw material. The reaction mechanism considered for the process synthesis and design is the ABE fermentation route using genetically modified strain, Clostridium beijerinckii BA101 AA3 [2], which can survive higher butanol concentrations. The fermenter outlet consists of a multi-component mixture of ABE solvents with a concentration of 13g/L of butanol together with butyric and acetic acid as main impurities. In the downstream separation process, acetone and ethanol are first recovered followed by Liquid-Liquid extraction to extract butanol from the aqueous phase. In the extraction unit mesitylene is used as the solvent due to its high distribution coefficient, butanol selectivity and low aqueous solubility [3]. Due to high boiling point difference between mesitylene and butanol 99.95% of the solvent is recovered thereby reducing the fresh solvent requirement. Finally a distillation column is used to obtain pure butanol as the bottom product while the top butanol-water Azeotrope is recycled back to the Liquid-Liquid extraction.

By using LCA, economic and sustainability analyses, hot-spots were identified to improve the base case design [4, 5]. These identified hot-spots were addressed through heat integration and process optimization. The final design generated is more sustainable and economically viable solution. In this poster, the process design method will be presented and the output from each step related to the production of bio-butanol will be given.

[1] Dürre P., Biobutanol: an attractive biofuel, Biotechnology Journal Vol 2, 1525-1534, December 2007.

[2] Ezeji, T.C., Qureshi, N., Blaschek, H.P. Production of acetone, butanol and ethanol by Clostridium beijerinckii BA101 and in situ recovery by gas stripping. World Journal of Microbiology & Biotechnology, 19 595-603, 2003.

[3] Kraemer K. Separation of butanol from acetone-butanol-ethanol fermentation by a hybrid extraction distillation process, 20th European Symposium on Computer Aided Process Engineering, 2010.

[4] Kalakul, S., Malakul, P., Siemanond, K., & Gani, R. Integration of life cycle assessment software with tools for economic and sustainability analyses and process simulation for sustainable process design. Journal of Cleaner Production, 71, 98–109, 2014.

[5] Carvalho, A., Matos, H. A., & Gani, R. SustainPro—A tool for systematic process analysis, generation and evaluation of sustainable design alternatives. Computers & Chemical Engineering, 50, 8–27, 2013.