Influence of acid-catalyzed dehydration and pressure on woody biomass carbonization: Exploring carbon yield, heteroatom functionalities, and biochar atomistic structure

Abstract

This study investigates optimal carbonization conditions for biochar production, focusing on pressure and acid pretreatments to maximize carbon yield and enhance biochar functionality. Over thirty combinations of pressure and acid type were tested, including organic acids (CH₃COOH and HCOOH) and inorganic acids (H₃PO₄ and H₂SO₄), using hybrid poplar wood as feedstock. The results show that carbon conversion efficiencies up to 72 wt % were achieved with organic acids under pressures ≥ 20 bar. Inorganic acids produced biochar doped with phosphorus (P) and sulfur (S), demonstrating the potential for customizing biochar properties to specific applications. To understand biochar transformations at the molecular level, we employed a range of advanced characterization techniques, such as solid-state ¹³C NMR, ICP-OES, XPS, BPCA, LDI FT-ICRMS, and ESR, as well as 3D atomistic modeling of up to 13,000 atoms. These methods revealed how pressure and acid pretreatments influence the chemical composition, porosity, and atomistic structure of the resulting biochar. The study provides valuable insights into the relationship between processing conditions and biochar properties, demonstrating that optimized carbonization processes can improve production efficiency and reduce biomass requirements. This scalable approach offers significant potential for reducing carbon emissions and makes biochar a promising material for carbon storage, soil amendment, and other environmental applications.