In an effort to address the USA Congressional biofuels mandate of 36 billion gallons per year goal by 2022 and the production of advanced biofuels and biochemicals, it is imperative that we develop integrated technologies overcoming the barriers for advanced biofuels and chemicals. Butanol is not only an advanced drop in biofuels but also an important chemical and industrial solvent. It has several advantages over ethanol as a drop-in biofuel such as higher energy content, potential for higher blending percentage with gasoline, lower vapor pressure, and lower hygroscopy. Butanol can be produced by fermentation of cellulosic biomass sugars using Clostridium acetobutylicum or C. beijerinckii under anaerobic conditions. However, there are many unsolved challenges for making biobutanol technically, and economically viable. The unsolved challenges lie in severe product (butanol) inhibition during bioprocessing, which leads to low ABE (Acetone, Butanol and Ethanol) yield, low productivity, and very low product concentration (<3 wt%), causing high energy consumption and high costs in downstream product separation and purification. There are two ways for solving these problems. One is the modification of microorganisms for ABE fermentation by metabolic and genetic engineering, which could keep the microorganisms alive and active under higher concentration of products in the broth. This could significantly increase the product yield, productivity, and concentration and hence reduce the production costs. However, this is still an unrealized long term goal. Another approach is the development of efficient separation and purification processes for product recovery. And, even if the modification of microorganisms becomes a reality, product separation and purification will still remain a major critical challenge (Huang et al. 2014).
In this work, we develop integrated bioprocessing (fermentation) -in situ separation and purification (product removal) (IBSP) processes. Among the three most promising separation methods – solvent extraction, membrane pervaporation and adsorption, we studied membrane pervaporation integrated in-situ with bioprocessing by process modeling and simulation to determine the effect of integrated (IBSP) approach. The integration of biobuanol fermentation with in situ separation and purification technology can not only remove product inhibition and improve the yield and productivity but also reduce the energy consumption and hence reduce the production costs. This is also applicable to other bioproducts manufacture and can play a vital role in the success of the future bio-economy.
[Reference] Huang et al., Separation and purification of biobutanol during bioconversion of biomass. Separation and Purification Technology, 2014 (8): 132:513–540.