Tar-rich coal in-situ pyrolysis provides a promising pathway for oil and gas production in coal-rich and oil-deficient countries. However, the retention behavior of tar during underground coal pyrolysis remains poorly understood. In this study, based on tar-rich coal in-situ pyrolysis simulated experiments, pyrolysis char generated under different stress conditions was progressively crushed using a step-by-step crushing approach, and trapped oil was recovered from different particle-size fractions through ultrasonic extraction. Combined with low-field nuclear magnetic resonance (LF-NMR) and gas chromatography-mass spectrometry (GC-MS), the occurrence characteristics and retention mechanisms of tar during in-situ pyrolysis were systematically investigated. The results indicate that stress confinement governs the occurrence behavior of trapped oil by regulating the evolution of pore-fracture structure. With increasing stress, trapped oil gradually shifts from a dispersed distribution within multi-scale pores toward enrichment in closed or weakly connected pores. Meanwhile, the tar retention mechanism evolves from selective retention of specific components to overall migration inhibition, with a critical transition occurring at 12.5MPa. Below 12.5MPa, stress-induced pore and fracture development improves pore connectivity and promotes tar expulsion, resulting in the selective enrichment of nitrogen-containing and polar compounds in the retained fraction. Above 12.5MPa, pore-fracture compaction and closure hinder the overall migration and expulsion of tar, leading to significant retention of originally mobile components, including aliphatics and phenols. Results from the step-by-step crushing-extraction experiments further demonstrate pronounced scale-dependent occurrence characteristics of trapped oil within closed pores of different sizes. Specifically, extracts from coarse fractions (10-20 mesh) are dominated by nitrogen-containing and polar compounds; intermediate fractions (20-80 mesh) are enriched in aliphatics; and fine fractions (80-200 mesh) are characterized by enrichment in phenols and partial aromatics.
Biocoke production, sustainable agricultural waste management, and the value addition of biochar are increasingly important for the steel, coal, and agricultural industries. Although biochar has been explored as a blending material in coal for cokemaking, limited research has examined the combined influence of biomass type, preparation methods, and pyrolysis conditions on char properties as it relates to coking behaviour when blended with coal. This study investigates the effects of biomass structure, preparation method, and pyrolysis temperature on biochar properties derived from banagrass and wheat straw (grass-type) and acacia (hardwood). Five preparation methods were evaluated at pyrolysis temperatures between 400°C and 800°C. Raw and pelletised acacia chars showed high densities (665-950.8kg /m³ at 800°C) and high surface areas (up to 338m²/g at 800°C), reflecting the preservation of their lignified cellular structure during pyrolysis. In contrast, pelletised banagrass chars showed lower surface areas (as low as 2.38m²/g) while maintaining high densities (up to 630kg/m³ at 800°C). Pelletisation increased banagrass char density (~228 to ~596kg/m³) and yield (~28 to ~32 daf wt%), while washing reduced banagrass ash content from 14-11wt% to 5-11wt%. The results demonstrate that low surface area, high density chars can be produced from herbaceous biomass through crushing and pelletisation, whereas the woody biomass tends to preserve its structural cohesion and pore network during pyrolysis, leading to chars with high surface areas even after pelletisation.
With the growing demand for sustainable solutions and carbon credits, pyrolysis has emerged as a key biorefinery technology for converting biomass waste into biofuels. This study investigates the effects of pyrolysis residence time (0.5-3h) on the properties, composition, and environmental risks of multiphase products derived from anaerobic digestion residues of pig manure. The results demonstrate that residence time governs product distribution and reaction pathways. The early stage of pyrolysis (0-1h) is dominated by volatile release and aromatization, which significantly enriches the carbon content of biochar. Prolonging pyrolysis time beyond 1h triggers carbon gasification and secondary reactions, which reduce solid yield while promoting the development of porous structure, and enhance the generation of CO and H2 through the cracking of nitrogen-containing compounds and CH4-CO2 dry reforming. An optimal residence time of 1h is identified, achieving a balance between product quality and environmental benefits. At this condition, biochar exhibits the highest carbon content, well-developed porosity, and efficient heavy metal stabilization. Meanwhile, the process intensifies syngas (CO, H2) production and reduces emissions of CO2, CH4, and HCN. This work clarifies the regulatory role of residence time in pyrolysis from a reaction mechanism perspective, providing support for the safe, efficient, and resourceful utilization of organic waste.
Currently, lignin still remains as a largely underutilized chemical precursor; hence, its electrochemical depolymerization over iron oxide or carbonaceous catalysts presents a promising route to produce value-added aromatics. Herein, this study proposes a novel, cost-effective, and highly efficient electrocatalyst: magnetic biochar (MBC) synthesized via the co-pyrolysis of biomass and red mud (RM). To maximize catalytic performance of the MBC, synthesis parameters were systematically optimized. Linear Sweep Voltammetry (LSV) analysis revealed that the optimal catalytic activity was achieved using maple wood (MW) as the precursor, pyrolyzed at 900 °C, with a MW-to-RM mass ratio of 5: 1 (M-MBC–5/1–900). This optimal composite exhibited a highly graphitized mesoporous skeleton with a specific surface area of 126.95 m2/g. M-MBC–5/1–900 demonstrated robust stability throughout a 6-hour continuous electrolysis at a constant current density of 50mA/cm2, alongside highly practical magnetic separability (an average recovery efficiency of ~80.2%). Moreover, its electrocatalytic performance notably outperformed conventional transition metal-based catalysts (Fe2O3, Fe3O4, and commercial metallic iron powder) and raw RM. Subsequent characterizations via gel permeation chromatography (GPC) confirmed the successful depolymerization of lignin, evidenced by a drastic 80.8% reduction in the weight-average molecular weight (Mw plummeted from 2759 to 530g/mol). Fourier Transform infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR) further verified the cleavage of macromolecular networks into value-added short-chain organic acids and aromatic monomers. This study demonstrates the feasibility of utilizing RM-derived MBC as an electrocatalyst, presenting a sustainable strategy for lignin valorization.
Ficus natalensis barkcloth was upgraded by torrefaction, water-only hydrothermal carbonization (HTC), and HCl-assisted HTC to examine the trade-off between carbon enrichment and retention of a handleable fibrous product. TOR-200 retained 84.02% of the initial mass and 83.6% of the feedstock energy while retaining Grade 2 handleability in a preliminary qualitative bending screen. TOR-250 increased the higher heating value to 20.51 MJ kg⁻¹ but reduced the mass and energy yields to 39.33% and 48.2%, respectively. HTC-2.5HCl-200-1 produced the highest fixed-carbon content (45.31wt.%), calculated higher heating value (21.50 MJ kg⁻¹), and BET specific surface area (58.422m² g⁻¹), but retained only 20.36% of the initial mass and 26.1% of the feedstock energy. Log R₀ was used to represent temperature–time exposure for all treatments, whereas CSF was used only within the acid-assisted series; the two descriptors were not treated as numerically equivalent. ICP-MS identified treatment-dependent changes in elemental concentrations, but complete solid–liquid mineral recoveries could not be calculated. No single treatment optimized all measured properties. The results therefore provide a property-based screening framework: mild torrefaction favored solid and structural retention, whereas stronger torrefaction and acid-assisted HTC favored carbon and surface development at the expense of product recovery. Application-specific mechanical, combustion, activation, and adsorption tests remain necessary.
