(144e) Techno-Economic Analysis of Biomass to Fuel Via the MixAlco Process

Because of dwindling fossil fuel resources, there is growing interest in developing cost-effective processes that convert biomass to fuels. MixAlco is a robust process that converts lignocellulose into secondary alcohols (isopropanol and higher), which can be used directly as transportation fuel or converted to hydrocarbons (e.g., gasoline). The process has five main steps: (1) pretreatment with lime, (2) fermentation with a mixed culture of acid-forming microorganism to obtain carboxylate salts, (3) dewatering with a high-efficiency vapor-compression evaporator, (4) thermal conversion of salts to ketones, and (5) hydrogenation of the ketones to mixed alcohols. Optionally, the alcohols can be oligomerized to hydrocarbons using zeolite catalysts. This work focuses on process synthesis, simulation, integration, and cost estimation of several process configurations of the MixAlco process. For every step, design alternatives were investigated and compared to determine the most profitable and sustainable process design. The configuration in which pretreatment and fermentation are performed in piles is significantly more cost-effective than in conventional tanks. A novel heat exchanger has very high heat transfer coefficients (28,000 Btu/(h?ft²?^oF)), which allows the vapor-compression evaporator to operate with very small approach temperatures (0.35^oF). This evaporator saves both capital and energy, which significantly benefits process economics. Sensitivity analyses were performed to determine process economics under various conditions, such as multiple feedstocks (type and cost), hydrogen (source and price), and plant capacity.