PNNL

Abstract

Valorization options for the aqueous fraction produced by the hydrothermal liquefaction of terrestrial feedstocks were developed. The processes focused on carboxylic acids, which are abundant in the aqueous fraction. A clean up process for the aqueous phase based on activated carbon absorption followed by liquid-liquid extraction was demonstrated that significantly reduces color bodies and inorganic contaminants while simultaneously concentrating desirable organic constituents. Conversion of the cleaned aqueous phase was then demonstrated for both a ketonization reaction and steam reforming. Condensed phase ketonization over LaxZryOz catalyst was found to exhibit both excellent hydrothermal stability and ketonization activity. Necessity for feedstock cleanup was established and stable condensed phase ketonization operation was demonstrated for ~100 hours with HTL-process derived material. Steam reforming was also demonstrated by employing a dual-bed catalyst configuration whereby carboxylic acids first undergo ketonization over CeO2 in the vapor phase followed by steam reforming of the ketone intermediates over Co/CeO2. The dual-bed approach reduced coke deposition and thus catalyst stability improved. Techno-economic analysis was used to assess economic viability for producing fuel from the bio-oil fraction and either propene (formed via hydrogenation and dehydration of acetone, the primary ketonization product) or hydrogen from the aqueous stream. The ketonization and steam reforming cases were separately modeled and benchmarked to a process utilizing anaerobic digestion. Resulting minimum fuel selling prices of $3.7, $4.2, and $4.3/GGE were obtained for the production of olefins via ketonization, reduction and dehydration; steam reforming; and anaerobic digestion processes, respectively. Both the steam reforming and anaerobic digestion processes benefited by avoiding the need for natural gas by producing the hydrogen on-site required for biocrude hydrotreatment. However, the condensed ketonization process had the lowest minimum fuel selling price because of the co-product olefins generated for sale.