Genomic Science Program
U.S. Department of Energy | Office of Science | Biological and Environmental Research Program

Performance Thresholds for Co-Utilization of Lignin-Derived Aromatics and Sugars

Authors:

Nawa Baral1,2* (nrbaral@lbl.gov), Deepanwita Banerjee1,2, Aindrila Mukhopadhyay1,2, Blake Simmons1,2, Steven Singer1,2, Corinne Scown1,2,3,4, Jay Keasling1,2,4

Institutions:

1Joint BioEnergy Institute; 2Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory; 3Energy Analysis and Environmental Impacts Division, Lawrence Berkeley National Laboratory; 4University of California–Berkeley

Goals

Enhance understanding of the economic viability of noncombustion lignin utilization routes, and determine the minimum conversion threshold from lignin stream to product that must be achieved.

Abstract

Efficient lignin conversion is vital to the production of affordable, low-carbon fuels and chemicals from lignocellulosic biomass. However, lignin conversion remains challenging, and the alternative (i.e., combustion) can emit harmful air pollutants. This study explores the economic and environmental tradeoffs between lignin combustion and microbial utilization for producing bisabolene as a representative biobased fuel or chemical. Considering three different biomass feedstocks—biomass sorghum, switchgrass, and clean pine—the project primarily addressed two important questions: (1) what quantity of lignin must be utilized by the host microbe to render the strategy of co-utilizing sugars and lignin-derived bioavailable intermediates economically feasible and (2) what proportion of lignin can be utilized while still achieving the Renewable Fuel Standard life-cycle greenhouse gas (GHG) emissions reduction goal of a 60% reduction relative to petroleum equivalent.

Results for switchgrass and clean pine–based biorefineries show that using lignin to increase fuel yields rather than combusting it reduces the capital expenditures for the boiler and turbogenerator if the facilities process more than 1,100 bone-dry tons (bdt) feedstock per day and 560 bdt/day, respectively (Baral et al. 2023). No comparable advantage was observed for lower-lignin sorghum feedstock. Deconstructing lignin to bioavailable intermediates and utilizing those small molecules alongside sugars to boost product yields is economicallyattractive if the overall lignin-to-product conversion yield exceeds 11 to 20% by mass (Baral et al. 2023). Although lignin-to-fuel/chemical conversion can increase GHG emissions, most of the lignin can be diverted tofuel/chemical production while maintaining a >60% life-cycle GHG footprint reduction relative to diesel fuel(Baral et al. 2023). The results underscore that lignin utilization can be economically advantageous relative to combustion for higher-lignin feedstocks, but efficient depolymerization and high yields during conversion are both crucial to achieving viability.

References

Baral, N. R., et al. 2023. “Economic and Environmental Trade-Offs of Simultaneous Sugar and Lignin Utilization for Biobased Fuels and Chemicals,” ACS Sustainable Chemistry & Engineering 12(7), 2563–76.