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New one-pot high-yield “high-gravity” process for cellulosic ethanol; potential for drop-in fuels

Researchers with the US Department of Energy (DOE)’s Joint BioEnergy Institute (JBEI) have developed a “high-gravity” one-pot process for producing ethanol from cellulosic biomass that gives unprecedented yields while minimizing water use and waste disposal. “High gravity” means high biomass loading—the higher the biomass loading, the lower the costs for converting it to fuels.

The process utilizes a combination of ionic liquid pretreatment, enzymatic saccharification, and yeast fermentation for the production of concentrated fermentable sugars that result in high-titer cellulosic ethanol. Details on this one-pot process for producing ethanol from cellulosic biomass have been reported in the RSC journal Energy and Environmental Science.

The use of dilute bio-derived ionic liquids (a.k.a. bionic liquids) enables one-pot, high-gravity bioethanol production due to their low toxicity to the hydrolytic enzyme mixtures and microbes used. We increased biomass digestibility at >30 wt% loading by understanding the relationship between ionic liquid and biomass loading, yielding 41.1 g L−1 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.

—Xu et al.

The new one-pot process for making cellulosic ethanol was enabled by the discovery and use of a renewable ionic liquid derived from amino acids that commercially available enzyme mixtures and organisms can tolerate, said Blake Simmons, JBEI’s Chief Science and Technology Officer and head of the Deconstruction Division.

This eliminates the need for separations, recoveries and other operational steps, generating significant cost savings.

Using bionic liquids in our new one-pot high-gravity process we were able to increase biomass digestibility and obtain ethanol titer yields of 41.1 grams/liter, which exceeds the production distillation required for industrial ethanol production. The reduction in water consumption combined with the improved overall process economics moves us closer to more affordable and sustainable second-generation biofuels.

—Seema Singh

In addition to Simmons and Singh, who is the corresponding author, other co-authors are Feng Xu, Jian Sun, Suryanarayana Konda, Jian Shi, Tanmoy Dutta and Corinne Scown.

Simmons and Singh believe that their one-pot process for producing cellulosic ethanol could also be applied to advanced drop-in bio-hydrocarbon fuels. They are currently working with researchers in JBEI’s Fuels Synthesis Division to develop a microbial host capable of producing these advanced biofuels.

While there is no other ionic liquid system on the planet right now that performs as effectively as ours, we still need to improve on increasing yields and developing a microbial organism that can consume all of the sugars present in the biomass. Then we need to develop a host microbe that can generate advanced drop-in biofuels in addition to ethanol.

—Blake Simmons

This research was supported by the DOE Office of Science.

Resources

  • Feng Xu, Jian Sun, N. V. S. N. Murthy Konda, Jian Shi, Tanmoy Dutta, Corinne D. Scown, Blake A. Simmons and Seema Singh (2016) “Transforming biomass conversion with ionic liquids: process intensification and the development of a high-gravity, one-pot process for the production of cellulosic ethanol” Energy Environ. Sci. doi: 10.1039/C5EE02940F

Comments

SJC

Excellent, cellulose ethanol makers can join the four in the mid west in making billions of gallons from corn stalks NOT corn grain.

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