Impact of low-chemical storage pretreatment of loblolly pine bark on biochar from microwave pyrolysis

Bowlby, Kymberly; Wendt, Lynn M.; Wahlen, Bradley D.; Cheng, Ming-Hsun; Zhao, Haiyan

doi:10.1016/j.eti.2025.104592

Impact of low-chemical storage pretreatment of loblolly pine bark on biochar from microwave pyrolysis

Journal Article · Wed Oct 29 00:00:00 EDT 2025 · Environmental Technology & Innovation

DOI:https://doi.org/10.1016/j.eti.2025.104592· OSTI ID:3013936

Bowlby, Kymberly ^[1]; Wendt, Lynn M. ^[2]; ^[3]; ^[1]; ^[1]

Univ. of Idaho, Idaho Falls, ID (United States)
Univ. of Idaho, Idaho Falls, ID (United States); Idaho National Laboratory (INL), Idaho Falls, ID (United States)
Idaho National Laboratory (INL), Idaho Falls, ID (United States)

Forest product residues such as bark represent a low-cost, abundant feedstock for bioenergy, but their high ash and alkali and alkaline earth metal (AAEM) content limit thermochemical conversion efficiency. This study evaluates the use of low-severity chemical pretreatments during anaerobic storage to improve the performance of microwave pyrolysis for loblolly pine bark. Bark was treated with dilute sulfuric acid (0.1% and 1%, w/w) or sodium hydroxide (4%, w/w) and incubated anaerobically for one or two weeks to simulate in-pile biorefinery storage. The most effective treatment—1% H2SO4 for two weeks—reduced AAEM content by 35.7% and increased bio-oil yield by 11% compared to untreated controls, while also reducing pyrolysis gas production. In contrast, alkali treatment did not reduce AAEM levels and led to decreased bio-oil yields with increased gas formation. Although biochar yields were relatively stable across treatments, their physicochemical characteristics varied significantly. Acid-treated bark yielded biochars with higher carbon content, lower O/C and H/C ratios, greater surface area, and enhanced heating values. These improvements suggest that chemical pretreatment during storage can tailor biochar quality for specific end uses. Biochars produced under optimized conditions exhibited properties suitable for soil amendment, carbon sequestration, and solid fuel applications. This integrated approach—combining storage, mild chemical conditioning, and microwave pyrolysis—provides a viable pathway to enhance the value and sustainability of bark-derived bioenergy products.

View Accepted Manuscript (DOE)

Research Organization:: Idaho National Laboratory (INL), Idaho Falls, ID (United States)

Sponsoring Organization:: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Office of Sustainable Transportation. Bioenergy Technologies Office (BETO); USDOE Office of Nuclear Energy (NE)

Grant/Contract Number:: AC07-05ID14517

OSTI ID:: 3013936

Journal Information:: Environmental Technology & Innovation, Journal Name: Environmental Technology & Innovation Vol. 40; ISSN 2352-1864

Publisher:: ElsevierCopyright Statement

Country of Publication:: United States

Language:: English

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Impact of low-chemical storage pretreatment of loblolly pine bark on biochar from microwave pyrolysis

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