This research, published as a journal pre-proof in the Journal of Analytical and Applied PyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More, was conducted by Muhammad Rizwan, Asma Leghari, Akash Kumar, Azhar Laghari, Adil Mansoor, Muhammad Asif Nawaz, and Xiaolong Zhou. It explores how hydrothermal carbonization (HTC) can be used as a pretreatment method to improve the pyrolytic performance of wood-derived biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More, specifically targeting lignin-rich lignocellulose. The study compares untreated biomass (NLB) with HTC-treated biomass (HLB) to analyze the resulting biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More, syngasSyngas, or synthesis gas, is a fuel gas mixture consisting primarily of hydrogen and carbon monoxide. It is produced during gasification and can be used as a fuel source or as a feedstock for producing other chemicals and fuels.   More, and tar, aiming to create a sustainable process for producing high-value bioenergy products. The authors note that the complex structure and high oxygen content of lignin make its conversion challenging, and pretreatment is often necessary to improve product quality and selectivity. The findings suggest that this integrated process offers a way to enhance syngas generation, lower emissions, and optimize biorefinery product selection.

The study found that HTC pretreatment fundamentally changes the structure and chemical properties of the biomass. Spectroscopic analysis revealed that the HTC-treated biochar (HLB) had a defective carbon structure with enhanced crystallinity and maintained its integrity even at higher temperatures. This is in contrast to the untreated biochar (NLB), which showed a non-monotonic evolution in its textural properties, with a significant drop in surface area at 1000∘C due to pore collapse. The treated biochar, on the other hand, showed a steady rise in surface area from 3.33 to 67.53 m2/g between 400∘C and 1000∘C. At 1000∘C, the treated biochar (HLB-T10) retained active oxygen functionalities, while the untreated biochar (NLB-T10) had minimal oxygen content, showing the remarkable thermal stability of the treated material.

One of the most significant findings of the research is the impact of HTC pretreatment on syngas composition. Compared to the untreated biomass, the pyrolysis of the treated biomass yielded substantially more valuable gases and fewer undesirable emissions. The study found that the yield of hydrogen (H2​) increased from 22.45% to 40.4% and carbon monoxide (CO) increased from 32.3% to 33.4%. This is because the HTC process “pre-removes” oxygen, primarily as CO2​ and H2​O, reducing the oxygen-to-carbon ratio and creating a more aromatic, carbon-rich matrix. Consequently, carbon dioxide (CO2​) emissions drastically lowered from 39.95% to 11.5% in the treated biomass. This preconditioning redirects the pyrolytic chemistry toward selective deoxygenation, boosting hydrogen and carbon monoxide yields while limiting CO2​.

The study also analyzed the tar produced from both processes. The tar from the untreated biomass (NLB) was dominated by carboxylic acids, which increased to 28.08% at 1000∘C. In contrast, the HTC-treated biomass (HLB) produced tar primarily consisting of desirable aromatic compounds such as esters and phenols. The composition shifted toward monoaromatic esters and phenolics without the need for catalytic support. This highlights HTC’s ability to reshape decomposition routes and enhance product selectivity. The final char from the HTC-treated biomass was also more graphitic and contained fewer tar residues than the char from the raw biomass pyrolysis. These results underscore the potential of the HTC-pyrolysis process to efficiently convert biomass into high-quality gaseous fuels and valuable chemicals.

Source: Rizwan, M., Leghari, A., Kumar, A., Laghari, A., Mansoor, A., Nawaz, M. A., & Zhou, X. (2025). Controlled Hydrothermal Carbonization of Wood-derived Lignin-rich Lignocellulose: Redefining Pyrolytic Pathways to Tailored Biochar and Hydrogen-Enriched Syngas. Journal of Analytical and Applied Pyrolysis.