Kinetic Model for Recovering Acetic Acid from Hydrothermal Liquefaction Aqueous Byproducts of Biomass Wastes

With increasing environmental concerns related to waste management, the exploration of sustainable processing alternatives has gained significant interest such as hydrothermal liquefaction (HTL). This study presents a kinetic model for the production of acetic acid from the aqueous phase (AP) byproduct of HTL. Wet air oxidation (WAO), a technique commonly employed in wastewater treatment to mitigate the environmental impacts of toxic aqueous waste streams, facilitates the conversion of hydrocarbons into simpler compounds such as CO2 and water. Notably, acetic acid (AA) is a stable intermediate of wet oxidation, particularly in the subcritical regime, operating below the critical point of water (374 degrees C, 221 bar). By precisely controlling the temperature and residence time of WAO, this study evaluates the potential to maximize the AA concentration while minimizing the presence of other organic compounds. A comprehensive kinetic model is developed, encompassing the decomposition and oxidation of typical compound classes found in HTL-AP. The model is applied to a sample feedstock of AP obtained from the HTL of cattle manure digestate containing 12% acid whey, processed at 320 degrees C for 30 min, based on prior research. The study investigates the trends in AA formation from these compounds across different temperatures and residence times. By utilizing this technique to extract and concentrate AA, there is potential for reducing the carbon footprint associated with its conventional production from natural gas. Moreover, the targeted production of AA from biomass waste feedstocks aligns with the principles of a circular bioeconomy and enhances the overall economics of HTL processing. Additionally, this approach contributes to the conservation of rare metals such as rhodium and iridium, traditionally employed as catalysts in AA production.