Wet oxidation of thermochemical aqueous effluent utilizing char catalysts in microreactors

Authors: TEWS, IVA - Washington State University; Terrell, Evan; MOOD, SOHRAB - Washington State University; GARCIA-PEREZ, MANUEL - Washington State University

Submitted to: Journal of Cleaner Production
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2022
Publication Date: 6/1/2022
Citation: Tews, I.J., Terrell, E., Mood, S.H., Garcia-Perez, M. 2022. Wet oxidation of thermochemical aqueous effluent utilizing char catalysts in microreactors. Journal of Cleaner Production. 351. Article 131222. https://doi.org/10.1016/j.jclepro.2022.131222.
DOI: https://doi.org/10.1016/j.jclepro.2022.131222

Interpretive Summary: The production of fuels and chemicals from biomass (wood, grass, agriculture residues) creates wastewater products for which treatment can be challenging. This is largely due to the complicated nature of the molecular products that are generated during biomass processing. This study analyzes wastewater treatment in this context with a technology known as "wet oxidation," which seeks to convert potential organic pollutants to more benign end-products like carbon dioxide and acetic acid. This is achieved through reactions with hydrogen peroxide and catalysts based on engineered carbonaceous chars. In particular, this study employs a range of analytical techniques to advance the understanding of how these complex organic mixtures in wastewater are ultimately treated. This work advances knowledge toward improving the environmental friendliness of renewable energy technologies using biomass.

Technical Abstract: Production of bio-oil or biocrude from thermochemical processes such as pyrolysis and hydrothermal liquefaction respectively, is considered a promising path for the production of alternative fuels and chemicals. However, these technologies create an aqueous phase byproduct contaminated with high concentrations of organic compounds. Traditional wastewater technologies rely on biological processing which is not resistant to the toxic levels of organic compounds present. Wet oxidation of aqueous phase byproducts is a promising processing alternative for such a dilute stream and a potential production pathway for value-added products such as acetic acid. Wet oxidation was carried out at near ambient temperature (75 – 90 °C) and atmospheric pressure in the presence of a hydrogen peroxide oxidant and a char catalyst activator on three individual aqueous phases (BTG WS, HTL WD 55, and HTL WD 57). The three aqueous phases were thoroughly analyzed by TOC, COD, Total Phenol, Total Acid Number, and individual constituents via GCMS. The two wood HTL aqueous phases (WD 55 and WD 57) were quite similar in every regard as can be seen by the COD of 44.8 and 41.5 g O2/L respectively. The BTG WS aqueous phase was much more complex in nature with a 10X higher COD of 364.5 g O2/L. This was validated by ICRMS analysis which revealed the more complex molecules not visible by regular mass spectrometry. Oxidation was carried out in a novel microreactor due to its superior transport capabilities. All the tests were conducted with a cellulose-based char catalyst doped with Nitrogen or Iron Oxide. Oxidation to small molecular weight compounds such as acetic acid was achieved in the oxidation of both HTL aqueous phase. The bio-oil aqueous phase was not as easily oxidized however, significant reduction in total organic carbon and chemical oxygen demand was achieved. Final products of the oxidation process contained 5.04 (BTG), 0.555 (WD 55), 1.643 (WD 57) mg acetic acid/g liquid effluents. Our results confirm that wet oxidation is a promising process for the processing of aqueous effluents from biomass thermochemical conversion processes.