The significance of structural components of lignocellulosic biomass on volatile organic compounds presence on biochar - a review

The product of thermochemical processing of lignocellulosic biomass is biochar. It has a range of properties that make it suitable for a variety of economic applications. However, during pyrolysis and torrefaction, volatile organic compounds (VOCs) are released and may redeposit on the surface of the biochar. Some of these compounds may be harmful to the environment and humans. Bibliometric study shows that, to date, studies on the release of VOCs from biochar have been of an inventory nature and concerned with specific case studies of the specific types of biomass. To date, there has been no comprehensive and systematic analysis of the influence of lignocellulosic biomass properties and pyrolysis/torrefaction process parameters on VOC formation and redeposition on biochar. In this paper, the analysis is presented of the potential harmfulness of VOCs released during the thermochemical processing of lignocellulosic biomass components, based on cellulose, hemicellulose, and lignin pyrolysis/torrefaction chemistry data. 10 volatile organic compounds from cellulose, hemicellulose, and lignin pyrolysis were identified as potentially harmful due to the following properties: carcinogenicity, toxicity, flammability, skin corrosion/irritation, eye irritation, and mutagenicity, with different degrees of harmfulness. Additionally, the VOCs identified on biochar samples show a potential hazard. Among 140 identified compounds, 33 of them had harmful properties. Therefore, the redeposition on biochar of ketones, aldehydes, cyclic and aromatic hydrocarbons including polyaromatic hydrocarbons, and their derivatives, esters, and furans may lead to environmental contamination due to their release from biochar. A new niche for systematic research on the development of new knowledge regarding the biochars produced from biomass as a source of pollutant emission has been identified.