(246g) Biochemical Process Design: The Sustainable Production of Biobutanol from Wheat Straw Using Clostridium Acetobutylicum

The world’s ever-increasing human population paired with global industrial development indicates an increase in the demand for alternative energy sources such as biofuels (Hannon, 2010). Much like bioethanol, biobutanol is a promising candidate for decreasing greenhouse gas emissions. Biobutanol offers several advantages over bioethanol, such as a lower volatility, higher energy density, and better compatibility with regular gasoline (Dürre, 2007). Industrial biobutanol production faces many challenges, and has since the advent of the chemical synthesis of butanol been a less economical production method. Recent headway into feedstock alternatives, downstream separation methods, and metabolic engineering, however, has lead to the resurgence of pilot- and industrial-scale biobutanol production plants in China (Jiang, 2015).

The aim of this work is to evaluate the current state of biobutanol technology, together with an attempt to design a sustainable, economically feasible and viable production process. The design problem is broken down into 12 hierarchical tasks, that outline how a process is transitioned from an idea to a viable process.

The first considerations of the design problem involve reviewing the history and literature of biobutanol. The biological pathway and feedstock are large initial considerations for the process. This work focuses on classical ABE fermentation using Clostridium acetobutylicum, as it is currently the most well-researched pathway for commercial viability. Wheat straw is used as a cheap alternative feedstock. Biobutanol production conventionally utilized starch-based feedstock, but alternative feedstocks are becoming a necessity due to price competition and the food-versus-fuel debate (Luiz, 2014). Overcoming product cell-inhibition during fermentation is the primary technical challenge facing ABE fermentation, which subsequently also leads to downstream separation difficulties.

This work analyzes the use of wheat straw as a second-generation lignocellulosic feedstock. Enzymatic pretreatment and hydrolysis is performed using Novozymes enzymes, followed by continuous fermentation using a C. acetobutylicum strain BKM19 (Jang, 2013). ABE products are extracted via liquid-liquid extraction (LLE) in a separate extraction column, using mesitylene (1,3,5-trimethylbenzyne) as a solvent. Butanol is separated through a series of distillation columns, and a final butanol purity of >99% is obtained through membrane separation from the remaining acetic acid. The process is simulated using PRO/II and aimed at a production of 6000 tons of butanol per year. Economic analysis is performed using the costing analysis software ECON. The base case design is evaluated for optimization, heat integration, and minimal environmental impacting tools for process integration and LCA sustainability analysis. These evaluations are finally implemented in an alternative design.