# US 8,771,464 B2 · Method for separating lignin from black liquor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,771,464 B2 - Document ID: US8771464B2 - Status: Granted - Kind: B2 - Application number: 13/118,666 - Filed: 2011-05-31 - Published: 2011-12-08 - Granted: 2014-07-08 - Earliest claimed: 2010-06-03 - Assignees: FPInnovations - Applicants: Lamfeddal Kouisni; Michael Paleologou - Inventors: Lamfeddal Kouisni; Michael Paleologou - Web page: https://patentgrep.com/patent/US8771464B2 ## CPC - D21C 11/0057: {Oxidation of liquors, e.g. in order to reduce the losses of sulfur compounds, followed by evaporation or combustion if the liquor in question is a black liquor (deodorisation of gases D21C11/08; combustion D21C11/12, D21C11/14)} - C07G 1/00: Low-molecular-weight derivatives of lignin (high-molecular-weight derivatives of lignin {C08H6/00}) - C08H 8/00: Macromolecular compounds derived from lignocellulosic materials {(pretreatment thereof B27N)} - D21C 11/0007: {Recovery of by-products, i.e. compounds other than those necessary for pulping, for multiple uses or not otherwise provided for (volatile compounds obtained by decomposition of spent liquors in order to regenerate them D21C11/125; compounds obtained by fractionating the liquors in order to regenerate them D21C11/0042)} - D21C: PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR - C07G: COMPOUNDS OF UNKNOWN CONSTITUTION (sulfonated fats, oils or waxes of undetermined constitution C07C309/62) - C08H: DERIVATIVES OF NATURAL MACROMOLECULAR COMPOUNDS (polysaccharides C08B; natural rubber C08C; natural resins or their derivatives C09F; bituminous materials C10) ## Abstract A method was developed for: a) improving the filterability of acid-precipitated lignin from kraft black liquors, b) increasing the dry solids content of the final lignin product, c) reducing the acid requirements and d) minimizing or eliminating TRS emissions during the acidification of black liquor to produce lignin and/or the subsequent suspension of the lignin in acid and/or the washing of the lignin with acid. No major difference in the chemical composition, MWD and main functional groups was found in the lignin of the present invention compared with lignins produced by conventional methods. ## Claims ### Claim 1 In a process for removing lignin from black liquor by acidifying the black liquor with an acidifier and filtering the acidified black liquor, the improvement wherein the black liquor is oxidized with an oxidising agent consisting essentially of oxygen prior to said acidifying to eliminate total reduced sulphur (TRS) in the black liquor with oxidation of sulphides, mercaptans and disulphides by said oxidising agent at a temperature effective for oxidation to thiosulphate- and other oxidized sulphur compounds and oxidation of said thiosulphate to sulphate, and such that hemicelluloses and other organics in the black liquor are oxidized by said oxidising agent at said temperature to form an acidifying agent selected from isosaccharinic acids, acetic acid, formic acid, lactic acid, oxalic acid, carbon dioxide and acidic lignin degradation products and mixtures thereof, with generation of heat through said oxidation, the generated heat leading to the creation of nucleation sites for the formation of lignin particles through lignin colloid agglomeration and coagulation, of a size easy to filter and wash, said acidifying agent reducing the acidifier requirement for said acidifying. ### Claim 2 (depends on 1) The process of claim 1, wherein the acidifying is to a black liquor pH of not more than 10.8. ### Claim 3 (depends on 1) The process of claim 1, wherein said acidifier requirement is reduced by at least 10% to 40% by said acidifying agent. ### Claim 4 (depends on 1) The process of claim 1, wherein said black liquor is oxidized prior to said acidifying with oxygen gas. ### Claim 5 A process for separating lignin from black liquor comprising: a) oxidizing black liquor containing lignin with an oxidising agent consisting essentially of oxygen to remove total reduced sulphur (TRS) in the black liquor with oxidation of sulphide in said black liquor by said oxidising agent at a temperature effective for oxidation to thiosulphate and oxidation of said thiosulphate to sulphate and such that hemicelluloses and other organics in the black liquor are oxidized by said oxidising agent at said temperature to form an acidifying agent with generation of heat through said oxidation, and allowing the generated heat to create a nucleation sites for the formation of lignin particles of a size easy to filter and wash, b) subsequently, acidifying the oxidized black liquor to precipitate lignin from the black liquor, and c) filtering precipitated lignin particles from the acidified liquor of step b). ### Claim 6 (depends on 5) The process of claim 5, further including: d) washing the lignin recovered from step c) with a strong acid and water to produce a purified lignin product. ### Claim 7 (depends on 6) The process of claim 6, wherein following black liquor oxidation, the acidifying is with said acidifier, said acidifier being selected from carbon dioxide and sulphuric acid and-the washing is with sulphuric acid. ### Claim 8 (depends on 7) The process of claim 7, wherein the acidifying is with an acidifier selected from carbon dioxide contained in a flue gas or the gaseous emissions from an effluent treatment system and the sulphuric acid used is that contained in the spent acid from a chlorine dioxide generator, a tall oil plant and/or a demineralizer plant. ### Claim 9 (depends on 5) The process of claim 5, wherein the acidifying is to a black liquor pH of not more than 10.8. ### Claim 10 (depends on 5) The process of claim 5, wherein the filtering is at a filtering rate greater than the filtering rate for a corresponding non-oxidized, acidified black liquor. ### Claim 11 (depends on 5) The process of claim 5, wherein the lignin particles are of a larger particle size than lignin particles filtered from a corresponding non-oxidized, acidified black liquor. ### Claim 12 (depends on 5) The process of claim 5, wherein the dry solids content of the lignin product is higher than that from a corresponding non-oxidized, acidified black liquor. ### Claim 13 (depends on 5) The process of claim 5, wherein the acidifying is with sulphur dioxide, organic acids or acid contained in the hydrolysate from the pre-hydrolysis of wood chips prior to pulping. ### Claim 14 (depends on 13) The process of claim 13, wherein the hydrolysate from the pre-hydrolysis of wood chips prior to pulping is obtained using steam, water or sulphuric acid. ### Claim 15 (depends on 5) The process of claim 5, wherein the acidifying agent is selected from the group consisting of isosaccharinic acids, acetic acid, formic acid, lactic acid, oxalic acid, carbon dioxide and acidic lignin degradation products. ### Claim 16 (depends on 15) The process of claim 15, wherein the acidifying agent participates in the acidifying whereby the acidifier is employed in an amount less than that for acidification of a corresponding non-oxidized, black liquor. ### Claim 17 (depends on 16) The process of claim 16, wherein said acidifier requirement is reduced by at least 10% to 40% by said acidifying agent. ### Claim 18 (depends on 15) The process of claim 15, wherein said lignin particles in c) have a size of 5 to 10 μm average diameter. ### Claim 19 (depends on 5) The process of claim 5, wherein said lignin particles in c) have a size of 5 to 10 μm average diameter. ### Claim 20 (depends on 5) The process of claim 5, wherein said oxidizing is with oxygen gas.