(245a) Production of Bio-Butanol from Wheat Straw: A Proposal for Sustainable Design

Production of bio-butanol from wheat straw: a proposal for sustainable design

Dorothee Luise Kurz, Randi Neerup, Anders Lodberg, Anjan Kumar Tula*

Department of Chemical and Biochemical Engineering,

Technical University of Denmark, DK-2800 Lyngby, Denmark

*antu@kt.dtu.dk

The usage of second-generation biomass is gaining more interest because it provides the opportunity to sustainably produce an important fuel using a bioprocess [1]. Butanol is an important fuel because of its similar properties to gasoline and its higher energy density than ethanol [1]. The step towards bio-based processes and bio-based fuels is both important and advantageous due to the reduction in CO₂ emissions and other greenhouse gasses that are emitted primarily from the combustion of fossil fuel.

Using a systematic, hierarchal, 12 task approach for performing (sustainable) process design, a production process for bio-butanol utilizing wheat straw as the raw material was designed and evaluated for producing 4,300 metric tons of bio-butanol per year with a yield of 0.11 kg product per kilo of raw material and a bio-butanol purity of 99.5 wt%. The reaction path considered for the production of bio-butanol is the ABE fermentation with Clostridium beijerinckii [2]. Two commercially by-products, acetone and ethanol, are produced during the reaction (carried out in a fermenter). These two by-products are of importance because acetone can be sold as a chemical solvent and ethanol can be used as biofuel [3]. The fermenter outlet consists of a multi-component mixture of butanol, acetone, ethanol and water and a minor amount of acids. First, acetone and ethanol are separated from the mixture using distillation; acetone is then further purified. Second, butanol is separated from the broth using liquid-liquid extraction. Butanol is further purified by distillation. This design is used as the base case design that is evaluated for further improvement.

Using an economic analysis, improvement targets are identified for process improvement related to heat integration and process optimization in order to reduce the process operating costs. The improvements up to this point are economic-based.

To achieve a more sustainable design, a sustainability [4] and LCA analysis [5] is performed in order to identify further improvement targets related to sustainability. These targets are met through the elimination and/or minimization of limitations in the process, identified from the sustainability analysis. The final design is a more sustainable, economic viable design. 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.

References:

[1] A. Ranjan and V. S. Moholkar, "Biobutanol: science, engineering, and economics," Int. J. Energy Res., vol. 36, no. 3, pp. 277-323, Mar. 2012.

[2] T. Ezeji, N. Qureshi, and H. P. Blaschek, "Butanol production from agricultural residues: Impact of degradation products on Clostridium beijerinckii growth and butanol fermentation," Biotechnol. Bioeng., vol. 97, no. 6, pp. 1460-1469, 2007.

[3] E. Sklavounos, "Conditioning of SO 2 - ethanol-water ( SEW ) spent liquor from lignocellulosics for ABE fermentation to biofuels and chemicals," Aalto University, 2014.

[4] A. Carvalho, H. A. Matos, and R. Gani, "SustainPro-A tool for systematic process analysis, generation and evaluation of sustainable design alternatives," Comput. Chem. Eng., vol. 50, pp. 8-27, Mar. 2013.

[5] S. Kalakul, P. Malakul, K. Siemanond, and R. Gani, "Integration of life cycle assessment software with tools for economic and sustainability analyses and process simulation for sustainable process design," J. Clean. Prod., vol. 71, pp. 98-109, May 2014.