Researchers from three US national labs (Berkeley, Pacific Northwest and Sandia) has demonstrated a separation-free, ionic-liquid (IL)-based process to convert biomass to an advanced biofuel (the sesquiterpene bisabolene).

The process, described in an open access paper in the RSC journal Green Chemistry, is also the first to demonstrate full consumption of glucose, xylose, acetate, and lactic acid in the presence of the IL cholinium lysinate ([Ch][Lys]).

Bisabolene is a chemical precursor to bisabolane—a potential renewable diesel and jet fuel that phase separates readily when released to the fermentation broth, enabling efficient recovery via two-phase extractive fermentation with an organic overlay.

Lower cost and higher efficiency biomass deconstruction remains a critical hurdle towards large-scale deployment of affordable lignocellulosic biofuels. Certain ionic liquids (ILs) have unique solvent properties that enable more efficient and uniform deconstruction of a wide array of lignocellulosic biomass types, including disruption of lignin and decrystallization of cellulose. These advantages are counterbalanced by process development challenges created by the toxicity of many ILs towards hydrolytic enzyme mixtures and biofuel production strains.

This toxicity can be mitigated by extensive water washing to remove residual ILs prior to saccharification or fermentation, by use of a new class of lower toxicity ILs, by development of IL-tolerant enzyme mixtures and biofuel production strains, or by a combination of these techniques.

… To achieve high fermentation performance in the presence of ionic liquids, we employ the robust and metabolically flexible host Rhodosporidium toruloides.

—Sundstrom et al.

In the study, the team demonstrated bisabolene production from sorghum hydrolysate in a scalable one-pot process comprising IL pretreatment, saccharification, and fermentation.

They achieved high titers of bisabolene relative to those previously obtained using a multi-step process. Conversion efficiency improved with scale, demonstrating the feasibility of integrating all biomass conversion unit operations within the biorefinery.

This study is the first demonstration of a fully consolidated process combining IL pretreatment, enzymatic saccharification, and biocatalysis for production of the advanced biofuel precursor bisabolene using an engineered host. This is also the first such demonstration with R. toruloides, or with any host capable of co-consuming alternative substrates including xylose, lactic acid, and aromatic lignin decomposition products.

The process proved to be robust under high-intensity conditions at bench and larger scales, with both the deconstruction and bioconversion platforms improving performance at scale despite the presence of organic acids produced during biomass deconstruction. No separations were required prior to saccharification or fermentation, and minimal media additions are required to facilitate bioconversion, resulting in an efficient and streamlined process.

… With further intensification and optimization, this process is a promising new approach towards commercial production of low-cost and low-impact lignocellulosic biofuels.

—Sundstrom et al.

Resources

• Eric Sundstrom, Junko Yaegashi, Jipeng Yan, Fabrice Masson, Gabriella Papa, Alberto Rodriguez, Mona Mirsiaghi, Ling Liang, Qian He, Deepti Tanjore, Todd R. Pray, Seema Singh, Blake Simmons, Ning Sun, Jon Magnuson and John Gladden (2018) “Demonstrating a separation-free process coupling ionic liquid pretreatment, saccharification, and fermentation with Rhodosporidium toruloides to produce advanced biofuels” Green Chemistry doi: 10.1039/C8GC00518D