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Topic Review
Black Liquor Gasification
Black liquor gasification is a thermochemical conversion process in which black liquor—the aqueous, alkaline spent cooking liquor generated during chemical pulping and containing dissolved lignin-derived organic matter together with inorganic sodium- and sulfur-containing pulping chemicals—is converted under substoichiometric oxidizing conditions into a combustible product gas and an inorganic recovery stream [1][2]. Unlike conventional black-liquor recovery-boiler operation, which primarily combusts the organic fraction, gasification uses controlled partial oxidation, with oxygen, air, steam, or their combinations as gasifying agents, to form a synthesis-gas mixture principally containing carbon monoxide, hydrogen, carbon dioxide, water vapor, and, depending on process conditions, methane and sulfur-bearing gases [1]. The concept encompasses gasifier configurations that process concentrated liquor at elevated temperature, including entrained-flow, fluidized-bed, and supercritical-water systems, provided that conversion of the liquor’s organic fraction to gas is coupled with retention or recovery of its inorganic chemical constituents [2][3]. It excludes simple combustion and gasification of solid biomass not derived from pulping liquor.
  • 5
  • 08 Oct 2026
Topic Review
Oxidative Delignification
Oxidative delignification is the chemical removal or structural breakdown of lignin from lignocellulosic material through oxidation of its aromatic and side-chain functional groups. The process involves an oxidizing species—such as molecular oxygen, hydrogen peroxide, ozone, chlorine dioxide, or an oxidatively active catalyst—that modifies lignin by introducing oxygen-containing groups, cleaving interunit linkages, fragmenting the macromolecular structure, and promoting dissolution or separation from the carbohydrate matrix [1][2][3]. Its defining objective is the preferential transformation and removal of lignin while retaining cellulose and, where relevant, a substantial fraction of hemicellulose. Oxidative delignification is therefore distinct from nonoxidative delignification, which relies primarily on hydrolytic, nucleophilic, or reductive reactions, and from bleaching in the narrower sense, which may chiefly remove chromophoric groups without causing extensive lignin solubilization. The term encompasses both oxidative pretreatment of lignocellulosic biomass and oxidative stages used in pulp processing, provided that lignin oxidation is central to the process [1][2][3].
  • 4
  • 22 Oct 2026
Topic Review
Delignification Technologies
Delignification technologies comprise the physical, chemical, physicochemical, biological, or integrated process methods used to remove, redistribute, solubilize, or structurally modify lignin within lignocellulosic materials, particularly wood and other plant cell walls. Their defining objective is to reduce the covalent and physical associations between lignin and the carbohydrate fractions—cellulose and hemicellulose—while altering biomass porosity, surface accessibility, and lignin–carbohydrate interactions [1]. The term includes operations such as alkaline, acidic, organosolv, oxidative, ionic-liquid, steam-explosion, mechanical, fungal, and enzymatic treatments when these processes produce measurable lignin separation or deconstruction [2][3][4]. Delignification is therefore broader than simple extraction: a process may qualify even when lignin is only partially removed, redistributed, depolymerized, or chemically transformed. It is distinct from cellulose hydrolysis or general biomass size reduction, although these operations may be combined with delignification in multistage pretreatment systems [1][2]. The resulting lignin-rich and carbohydrate-rich fractions may differ in composition and structure from the original wood, depending on the treatment chemistry and process conditions [3][4].
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  • 23 Oct 2026
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