Overcoming Challenges of Integrating Pretreatment with Enzymatic Saccharification and Microbial Fermentation Using Ionic Liquids (ILs) or Bionic Liquids (BILs)

Ionic liquids (ILs), solvents composed entirely of paired ions, have been used in a wide variety of process chemistry and renewable energy applications. Imidazolium-based ILs show remarkable abilities to dissolve biomass, and are thus an ideal media for biomass pretreatment and depolymerization. Although very efficient, imidazolium cations are currently expensive and therefore their large scale use and industrial deployment, e.g. in biorefineries, is limited. In an attempt to replace imidazolium-based ILs with ILs derived from renewable sources that retain their efficiency for biomass pretreatment, we have developed a class of biocompatible ILs derived from choline and amino acids. The lower microbial and enzyme toxicity of these recently-developed renewable ionic liquids (ILs), or bionic liquids (BILs), helps overcome the challenges associated with the integration of pretreatment with enzymatic saccharification and microbial fermentation. We increased biomass digestibility at >30 wt% loading by understanding the relationship between ionic liquid and biomass loading, yielding 41.1 g/L of ethanol (equivalent to an overall yield of 74.8% on glucose basis) using an integrated one-pot fed-batch system. Our technoeconomic analysis indicates that the optimized one-pot configuration provides significant economic and environmental benefits for cellulosic biorefineries by reducing the amount of ionic liquid required by ~90% and pretreatment related water inputs and wastewater generation by ~85%. In turn, these improvements can reduce net electricity use, greenhouse gas-intensive chemical inputs for wastewater treatment, and waste generation. The result is an overall 40% reduction in the cost of cellulosic ethanol produced and a reduction in local burdens on water resources and waste management infrastructure.