(195c) TEA and LCA of Renewable Hydrocarbon Fuels and Co-Products from Lignocellulosic Biomass Via 2,3 Bdo Fermentation, Separation, Dehydration and Oligomerization.

Production of fuels and chemicals from renewable feedstock is a well-known concept and after decades of commercial operation, first generation biorefineries have reached a high maturity level [1]. These first generation biofuels compete with food resources and have detrimental effects associated with land use change. As a result, second generation biofuels obtained from non-edible resources, such as agricultural residues, and other lignocellulosic sources have emerged as a promising alternative [2]. One example is the biochemical conversion of lignocellulosic biomass to hydrocarbon fuels. The National Renewable Energy Laboratory (NREL) performed a detailed techno-economic analysis (TEA) in 2018 of a pathway that produces a blend of diesel and naphtha from corn stover [3]. In this process 2,3 butanediol (BDO) is the key intermediate obtained via fermentation and adipic acid produced from lignin is the main co-product.

In our work we assessed the feasibility of this integrated biorefinery through an update of NREL’s 2018 TEA and by performing a well-to-wheel (WTW) life cycle assessment (LCA). More specifically, we examined the effect of 1) adding a downstream separation system that concentrates BDO from the dilute fermentation broth and 2) varying fermentation conversion and BDO titer concentration. While NREL already assessed feasibility through a TEA, no LCA has been developed for this pathway. Furthermore, the flowsheet in place does not include any type of BDO separation step and to the best of our knowledge there isn’t an environmental sensitivity study that accounts for varying fermentation conditions.

The suggested separation scheme concentrates BDO from a dilute fermentation broth and consists of two units: 1) a zeolitic adsorption system and 2) a pervaporation membrane. Experimental runs at a lab bench scale have been conducted for adsorption and pervaporation by collaborators at the Georgia Tech and Oak Ridge National Laboratory, respectively [2]. The experimental data has been used to parametrize these separation systems and implement them in the biorefinery process flowsheet. ASPEN Plus ® and Pyomo were used as the modelling tools.

An LCA of the overall process has also been developed, with global warming as the main impact category. The proposed LCA evaluates every stage in the production of 1GGE of fuel. This LCA accounts for the harvesting, handling, preprocessing and transport of the biomass, the process conversion inside the biorefinery and the end-use of the fuel at the vehicle’s engine. In addition, we evaluated the effect of varying fermentation conditions in the overall LCA. We used NREL’s 2018 report and our internal models for the mass and energy balances and for the remaining lifecycle inventory (LCI) process, to perform the other lifecycle impact calculations we used openLCA and Argonne’s GREET model.

Our results show that the proposed separation system can concentrate BDO from 10wt% to 95wt%. This dramatically reduces the stream flowrate and causes a significant decrease in capital costs of downstream equipment and operating costs associated with heating and pressurizing. An update to the TEA indicates that the adsorption system reduces the MFSP of the fuel to $2.37/GGE. Moreover, the LCA results indicate that for a base BDO titer of 100g/L, the WTW emissions of the fuel are 7.2kg/GGE, 40% lower compared to fossil fuels. Our results also indicate that emissions linearly decrease with increasing BDO titer but increase with conversion (at higher conversion we require less biomass, thus we obtain less lignin, which is utilized for internal utility consumption). Finally, the effect of adipic acid production through co-product displacement was also evaluated in the LCA.

References

[1] McKendry, P. (2002). Energy production from biomass (part 1): overview of biomass. Bioresource Technology, 83(1), 37–46.

[2] Segovia-Hernández, J. G., & Sánchez-Ramírez, E. (2022). Current Status and Future Trends of Computer-Aided Process Design, Applied to Purification of Liquid Biofuels, Using Process Intensification: A Short Review. Chemical Engineering and Processing-Process Intensification, 108804.

[3] NREL, 2018. Ryan Davis, Nicholas Grundl, Ling Tao, Mary J. Biddy, Eric C. D. Tan, Gregg T. Beckham, David Humbird, David N. Thompson, and Mohammad S. Roni. Biochemical Deconstruction and Conversion of Biomass to Fuels and Products via Integrated Biorefinery Pathways. National Renewable Energy Lab.

[4] Church, A. L., Sun, N., Yan. J., Karp, E., Tan, E., McNamara, I., Freeman, C., Liu, J., Glezakou, V., Zhang, D., Dunn, J., Valentino, L. (2021). 2,3-Butandiol (BDO) Separations. Separations Consortium Technology Area Session: Performance-Advantaged Bioproducts, Bioprocessing, Separations, and Plastics.https://www.energy.gov/sites/default/files/2021-04/beto-18-peer-review-2...