Abstract: The invention relates to a process for treating bleaching liquors from pulping processes based on organic acids. The process is characterized in that inorganic acid, such as nitric acid, phosphoric acid and/or sulphuric acid, is added into a bleaching liquor obtained from the bleaching or a stage closely associated with bleaching, whereby organic acids contained in the bleaching liquor are released into the bleaching liquor. The organic acids are then separated from the bleaching liquor and recycled to the cooking stage to be used as cooking chemicals. The nitrogen-, phosphor- and/or sulphur-containing product thereby produced, from which organic acids have been separated, is recovered to be used as a fertilizer or as raw material for a fertilizer.

Abstract: The invention provides for methods for producing pulp (comprising cellulose) and lignin from lignocellulosic material, such as wood chips. The methods involve acid catalyzed hydrolysis. Lignocellulosic material having a relatively high moisture concentration can be used as the starting material. The lignocellulosic material is impregnated with an acid (preferably nitric acid) and heated. During the heating lignin is depolymerized at relatively low temperatures, and the acid catalyst is distilled off. The acid catalyst can be collected and recycled after impregnation and heating. The lignocellulosic material is then digested in an alkaline solution under heat, dissolving the lignin and allowing the pulp to be removed. Acid is added to the black liquor to precipitate the lignin which is then removed. The resultant amber liquor can be further processed into other ancillary products such as alcohols and/or unicellular proteins.

Abstract: A process for refining lignocellulose raw materials, especially wood chips, saw dust, annual plants or wood waste, includes dewatering the lignocellulose raw materials discharged from a digester, extracting condensate produced during dewatering, and refining the dewatered lignocellulose raw materials in a refiner.

Abstract: The invention relates to a process for producing pulp from a fibre-based raw material using, as the cooking reagent, a solvent mixture which is based on organic acids and also contains furfural. The method is applicable to herbaceous plants, in particular.

Abstract: A method and apparatus for cleaning condensate, produced during the production of cellulose pulp, including evaporation of spent liquor, utilizing a cleaning plant having several condensers, coupled in series. Process steam from the last evaporation stage and unclean condensate are introduced into a combined stripper/condenser, the process steam and the condensate being brought to flow in opposite directions so that direct heat exchange occurs, resulting in volatile compounds of the condensate being separated and taken up by the steam with simultaneous indirect cooling, resulting in condensation of the main part of the process steam, and the remaining process steam gradually flowing further on, the process steam being successively cooled first resulting in water and turpentine being condensed and collected and subsequently methanol being condensed.

Abstract: Separation of dissolved and colloidal high molecular weight organic by-products from liquors or filtrates in a cellulosic pulping process through a filtration media to improve the overall efficiency of the process.

Abstract: This invention relates to a process of treating a lignocellulosic material to produce bio-ethanol. The process includes the steps of: (a) exposing the ligno-cellulosic material to conditions including a pH not less than about 8, and steam at a first pressure, to produce a step (a) product; (b) explosively discharging the step (a) product to a second pressure less than the first pressure-to produce a step (b) product; and (c) further processing the step (b) product to produce bio-ethanol and other co-products. In another embodiment, the invention relates to a conical auger fractionation column. The fractionation column includes a column body having an input and an output. A conical filter is positioned inside the column body, the filter having a larger diameter end directed toward the input and a smaller diameter end directed toward the output.

Abstract: Depolymerized lignins contained within black liquor are transferred to an organic solvent, soluble in organic matter and insoluble of aqueous sodium compounds contained within the black liquor. Upon separation of the aqueous sodium compounds from the organic solvent, saturated with contained depolymerized lignins, depolymerized lignins are removed from the organic solvent to result in depolymerized lignins and a separated organic solvent suitable for recycling. Resulting aqueous sodium compounds are concentrated by a multiple effect evaporator to provide liquor to digest wood chips. Whereby depolymerized lignins, substantially free from sodium compounds, are separated from a black liquor. Accordingly this invention modifies black liquor without employing a lime kiln and a recovery boiler, producing a molten smelt.

Abstract: A water soluble, surface active, polymeric agent is mixed with digestion liquor, preferably with an additional surface active defoamer coagulant agent prior to or during acidification of the alkaline digestive liquor. This results in an easily separable, non-gelatinous, non-gummy, coagulated lignin as a solids, particulate fraction that tends to float on a clarified liquid fraction containing recoverable salts. The solids fraction and the liquid frictions are easily separated, one from the other, by a gravity separation step.

Abstract: A method for the preparation of pulp by means of alkaline cooking, in which method spent liquor is transferred to pressurized tanks, and at least one liquor is expanded corresponding to a temperature difference of 1 to 5° C. The generated steam is led to turpentine recovery. Thus, the removal of turpentine and gases dissolved in said liquor is effective, the amount of recovered turpentine increases, and pulp of better washability and higher quality is obtained.

Abstract: The invention relates to a process for treating bleaching liquors from pulping processes based on organic acids. The process is characterized in that inorganic acid such as nitric acid, phosphoric acid and/or sulphuric acid, is added into a bleaching liquor obtained from the bleaching or a stage closely associated with bleaching, whereby organic acids contained in the bleaching liquor are released into the bleaching liquor. The organic acids are then separated from the bleaching liquor and recycled to the cooking stage to be used as cooking chemicals. The nitrogen-, phosphor- and/or sulphur-containing product thereby produced, from which organic acids have been separated, is recovered to be used as a fertilizer or as raw material for a fertilizer.

Abstract: An apparatus and method are provided to reduce the size of solid clumps of material and thereby permit reuse of the material. In particular, the apparatus and method allow for reuse of sediment accumulated in a storage area for paper pulping byproducts. The sediment is conveyed from the storage area to an tank. In the tank, the sediment is agitated to produce reduced-size clumps of the sediment. The reduced-size clumps are in a slurry that is capable of being burned at least one of a facility that produces paper pulp and a facility that produces paper products.

Abstract: A method for removal of pollutants from a pulping process byproduct liquor, the method comprising injecting an oxygen-containing gas into said liquor and condensing the water vapor from the stripping gas so as to produce a condensate comprising pollutants. Also a method of controlling the flow rate and/or temperature of a pulping process byproduct liquor, the process comprising injecting an oxygen-containing gas into the liquor in a reactor, processing the liquor in a flash tank so as to create a cooled liquor and combining at a least a portion of the cooled liquor with new liquor as the new liquor enters, or while the new liquor is in, the reactor.

Abstract: Separation of dissolved and colloidal high molecular weight organic by-products from liquors or filtrates in a cellulosic pulping process to improve the overall efficiency of the process.

Abstract: The method described herein will produce depolymerized lignins substantially free from sodium compounds. Black liquor supplied from a pulping process is utilized for providing a mixture of depolymerized lignins dispersed and dissolved in a solution containing sodium hydroxide. The mixture is then separated to form depolymerized lignins and a solution containing sodium hydroxide. Following separation, the depolymerized lignins are then extracted with water to produce an extractate containing sodium compounds. The extracted depolymerized lignins, containing sodium compounds, are then reacted with an acid to form sodium salts to form a slurry. The slurry containing sodium salts is, by means of a salt splitting method, separated from the extracted depolymerized lignins to produce substantially sodium free depolymerized lignins.

Abstract: Compositions for enhancing the strength and humidity resistance of lignocellulosic fibrous materials such as paper. The compositions are comprised of at least one lignin derivative and a solvent system whereby the solvent system is comprised of water and at least one organic solvent. Suitable lignin derivatives include but are not limited to lignosulfonate, lignosulfonate/kraft lignin, lignosulfonate/organosolv, and mixtures thereof.

Abstract: In a tall oil refining operating plant, a warm water loop is disclosed for cooling the tall oil heads fraction extracted from the crude tall oil, rather than the conventional use of cold water. This avoids condensation and the subsequent solidification of athraquinone pulping aid remaining in the crude tall oil; thus, avoiding fouling of the cooling towers. The temperature of the warm-water is controlled automatically by tempering the cold water entering the warm water “cooling” loop, while removing excessively warm water from said loop to the cooling tower system, as needed.

Abstract: The process of the present invention purposefully precipitates a portion of the dissolved lignin onto pulp fibers to improve pulp yield of unbleached pulp. The resulting retention of lignin on the pulp creates an increase in pulp yield. Washing the pulp in a series of washer stages sequentially removes entrained lignin. Between each of the washer stages, adding dilution water repulps a pulp mat that exits from a prior washer stage and creates a pulp stream for a next washer stage. After at least one of the washer stages, adding an acidifying agent to the pulp stream forms a pulp product by precipitating the entrained lignin onto cellulosic fibers contained in the pulp stream. Finally, the process removes the pulp product from the series of washer stages with the pulp product having at least about a 1 unit increase in Kappa number.

Abstract: A process for producing a pulp from cellulose-containing material, wherein the material is reacted with formic acid as the solvent, and cooked at approximately the boiling temperature of the solvent, whereby return condensation is used. Annual plants, deciduous or coniferous wood can be used as the cellulose-containing material. In one variant of the process, the cellulose-containing material is only slightly warmed, whereby backflow cooling is used, and then a precisely predetermined quantity of hydrogen peroxide is slowly added to the liquid at a constant rate. This process variant can be repeated at a lower cooking temperature. The pulp thus obtained is preferably utilized in the production of cellulose, and in particular in the production of paper or cardboard. It is proposed that the lignin, which is isolated from the cellulose-containing material, have further applications, whereby such lignin is, after the pulp has been separated from the solvent, itself precipitated out in water.

Abstract: A method for cooking chips, involving steaming the chips, impregnating the chips with impregnating liquid in an impregnation vessel, which impregnating liquid comprises fresh cooking liquid and spent liquor, extracting spent liquor from the impregnation vessel, cooking the impregnated chips in cooking zones including an introductory co-current cooking zone and a concluding counter-current cooking zone, extracting spent liquor from the digester at a position between the said co-current and counter-current cooking zones, transferring the said spent liquor from the digester to at least one position upstream of the digester, circulating the cooking liquid in a bottom circulation within the said counter-current cooking zone, heating the circulating cooking liquid by means of heat exchange, and supplying wash liquid to the bottom of the digester.

Abstract: An alkaline cellulose pulp pulping process treats soap and fiber-containing liquids to separate fibers from the liquids prior to further treatment of the liquids (e.g. by evaporation and combustion, or by cooking to produce tall oil). Black liquor containing soap, and/or washer filtrate containing soap, are fed to one or more soap separating tanks, and then the soap fraction from the top of the tanks is fed to a pressure screen where fiber separation takes place (preferably at a temperature of at least 70.degree. C.). Black liquor may be added to the soap fraction to dilute it, and preferably simultaneously raise its temperature. The pressure screen has a screen surface with holes of 0.4 mm diameter or less, or slots with a width of 0.2 mm or less.

Abstract: A method and arrangement for increasing evaporation capacity in a multi-stage evaporation plant of spent liquor of a pulp mill. The method includes increasing the pressure of vapor discharged from an evaporation stage by a separate booster, and supplying the vapor having increased pressure to the following evaporation stage. In the arrangement the booster (A-E) is provided in a conduit through which vapor is supplied from one evaporation stage onwards for increasing the pressure of the vapor conducted in the conduit.

Abstract: A method of creating a number of separate product streams from an agricultural waste material, comprising: providing a starting material consisting of an agricultural waste material; hydrolyzing the starting material with an acid solution at atmospheric pressure, and temperatures not exceeding about 100.degree. C., to create an absorbent, hydrolyzed solid residue and a xylose-containing liquor; reserving the xylose-containing liquor; and delignifying the hydrolyzed solid residue with a basic solution, to create a fiber solid residue suitable for use as an absorbent material, and a dissolved lignin-containing solution.

Abstract: Provided is a process for removing metals from a bleaching plant spent liquor and recovering a chelating agent which includes the steps of: heating a spent liquor containing a chelate comprising metals bound in a chelating agent to a temperature of at least about 140.degree. C.

Abstract: A method for adjusting the chlorine equilibrium in a sulphate cellulose process, wherein part of the chlorine contained in the cycle is separated and removed. In the method, strong odour gases from the sulphate cellulose process are introduced into a soda recovery boiler for burning so that chlorine contained in the liquor is in the form of hydrogen chloride (HCl) in the upper part of the soda recovery boiler and can subsequently be separated from the flue gases in a flue gas scrubber. The chlorine equilibrium is adjusted by removing part of the chlorine-containing washing solution.

Abstract: A method wherein a methanol-containing waste gas stream, such as a pulp mill waste stream which contains methanol and other waste products, including methyl mercaptans, is passed in contact with a catalyst comprising certain supported metal oxides in the presence of an oxidizing agent; preferably the gas stream is contacted with the catalyst, in the presence of the oxidizing agent, for a time sufficient to convert at least a portion of the methanol to formaldehyde (CH.sub.2 O).

Abstract: This invention provides for the recovery of lignin and other by-products from the pulping of fibrous plant material. In accordance with this invention, solvents and filtrates are recovered and recycled for reuse. This results in significant solvent and energy savings. Filtrates from the bleaching and delignification of the pulp are recycled for reuse in pulping, separation, and recovery of lignin and other by-products which results in significant energy savings and mitigation if not the elimination of pollution typically associated with bleaching. This invention also relates to products derived from the process and apparatus for carrying out the process. Lignins of various molecular weights and by-products of the pulping process are also recovered. The lignins are precipitated in high yields and at a high rate from a black liquor produced by pulping wood at high temperature and pressures. As a by-product of this process a purified furfural product is recovered.

Abstract: The invention relates to a method for fractionating a solution by a chromatographic simulated moving bed method in which the liquid flow is effected in a system comprising at least two sectional beds in different ionic forms. The fractions enriched with different components are recovered during a multi-step sequence including the following operations, i.e., phases: feeding phase, eluting phase, and recycling phase. The liquid present in the sectional packing material beds with its dry solids concentration profile is recycled during the recycling phase in a loop comprising one, two, or more sectional packing material beds. The method can be employed for the following examples, fractionating sulphite cooking liquor, molasses, and vinasse.

Abstract: A method for separating lignocellulosic material into (a) lignin, (b) cellulose, and (c) hemicellulose and dissolved sugars. Wood or herbaceous biomass is digested at elevated temperature in a single-phase mixture of alcohol, water and a water-immiscible organic solvent (e.g., a ketone). After digestion, the amount of water or organic solvent is adjusted so that there is phase separation. The lignin is present in the organic solvent, the cellulose is present in a solid pulp phase, and the aqueous phase includes hemicellulose and any dissolved sugars.

Abstract: A process is disclosed for extracting pure, coarse-grain silicic acid crystals from silicic acid-containing spent lye in cellulose production, comprising adding coarse-grain silicic acid to alkalized spent lye, lowering the pH of the alkalized spent lye to about 9 such that a sediment is formed, separating the sediment formed into coarse grain and fine grain silicic acid with little lignin and lignin-containing spent lye free from silicic acid, and separating the coarse grain and fine grain silicic acid with little lignin into course grain silicic acid and lignin. At least part of the course grain silicic acid separated is fed back to the alkalinized spent lye to be desilicified.

Abstract: A method of recovering energy from waste liquors from cellulose pulp processes produces high quality superheated steam, a savings in material costs is achieved, and the utilization factor of the pulp mill is improved (that is the number of shutdowns for service is reduced). A main stream of waste liquor from cellulose pulp processing is divided into first and second streams. The first stream is combusted in the recovery boiler to produce steam and the steam is fed to a superheating boiler. The second stream of waste liquor is gasified outside the recovery boiler to produce a combustible gas and an inorganic fraction. The inorganic fraction is not fed to the recovery boiler, but is separately recovered. The combustible gas is burned in the superheating boiler to superheat steam produced from combusting the first stream of waste liquor, the combustible gas providing substantially the only source of fuel for superheating the steam in the superheating boiler.

Abstract: The invention relates to a method of adjusting the sulphur balance of a sulphate cellulose plant, in which method black liquor is concentrated and heat treated by keeping it at a temperature higher than the cooking temperature for a certain time period to separate the sulphur compounds contained in the black liquor as gaseous sulphur compounds therefrom in the last evaporation stage of a series of evaporation stages.

Abstract: A method of preparing a digesting liquor having high sulphidity from a spent liquor obtained from digesting cellulosic fiber material, optionally without a conventional causticizing step is provided. Thermal decomposition of the spent liquor is conducted under reducing conditions in a reactor at a pressure of from atmospheric pressure up to about 150 bar and at a temperature of about 500.degree. to 1600.degree. C. so that a combustible gas phase containing hydrogen sulphide is formed in the reactor and extracted therefrom, and a phase of solid or molten material of substantially sodium sulphide or potassium sulphide, or mixtures thereof. The solid or molten material is dissolved in an aqueous liquid to produce said digesting liquor. The invention hydrogen sulphide is recovered from the gas phase and returned to the reactor to be present during the thermal decomposition of the spent liquor.

Abstract: The invention relates to a method for the fractionation of sulphite cooking liquor by a chromatographic simulated moving bed system in which the liquid flow is effected in a system comprising at least two chromatographic sectional packing material beds. In this method, at least one fraction enriched with monosaccharides and one fraction enriched with lignosulfonates are recovered during a multi-step sequence comprising the following phases: feeding phase of sulphite cooking liquor, eluting phase and recycling phase. The liquid present in the sectional packing material beds with its dry solids profile is recycled in the recycling phase in one or more loops comprising one or more sectional packing material beds.

Abstract: Digestion liquor is used in the paper pulping process to dissolve lignins and free the cellulose fiber from raw wood chips. After pulping, spent digestion liquor is laden with lignins. Heretofore, it was known that lignins could be coagulated by acidification of the digestion liquor, but such method coagulated the lignins in a slimy gelatinous mass that was difficult to separate from the liquor. It has been discovered that the addition of water soluble, surface active, polymeric agents to the digestion liquor prior to acidification, results in an easily separable lignin coagulant after acidification.

Abstract: The process for producing hydrogen peroxide, used in the bleaching of pulp, uses the hydrogen generated wholly or partly by the gasification or partial combustion of cellulose spent liquors used in digesting cellulose material to produce the hydrogen peroxide.

Abstract: This invention relates generally to a method for extracting lignosulfonate for the manufacture of vanillin and other specialty chemicals. Specifically, the invention relates to a method for recovering lignosulfonates from newsprint comprising the steps of:a) converting newsprint to a crumb pulp comprising of from about 20% to about 50% crumb pulp fiber solids by weight on an oven dry basis and the remainder water;b) cooking the crumb pulp in a medium comprising crumb pulp and cooking acid solution selected from the group consisting of sodium bisulfite, magnesium bisulfite, ammonium bisulfite, calcium bisulfite or mixtures thereof wherein the weight ratio of cooking acid solution to the crumb pulp fiber is from about 3 to about 6 for sufficient time and sufficient temperature and pressure for lignosulfonate removal;c) separating the crumb pulp fiber from the spent sulfite liquor; andd) recovering the lignosulfonates from the spent sulfite liquor.

Abstract: A method for adjusting the sulphur/sodium ratio in a soda recovery boiler when strong sulphurous odour gases are burned therein. According to the method, sodium is introduced into the soda recovery boiler in an amount proportional to the amount of sulphur either as sodium hydroxide, sodium carbonate compounds or soap, whereby the sodium and sulphur react, forming sodium sulphate, which can be removed from the flue gases together with fly ash.

Abstract: The sulphur content and/or the sulphur compound composition of a melt in a recovery boiler of a pulp mill is adjusted by bringing a gas into contact with the melt. The gas may be a gaseous sulphur compound or a reducing gas. Bringing the gas into contact with the melt increases the sodium sulphide content of the melt while decreasing the sodium carbonate content, so that the sulphidity of the melt increases. The sulphur-containing gas may be produced by pressure heat treatment of black liquor, so that the black liquor burned in the recovery boiler has a lower sulphur content and thereby reduces the boiler sulphur emissions, and boiler corrosion problems.

Abstract: Method of recovering energy from waste liquors from pulp processes, wherein the waste liquor is burned in a waste liquor recovery boiler and energy is recovered from the flue gases by producing saturated or partially superheated steam in the recovery boiler. According to the invention, a portion of the waste liquor is gasified in a gasifying reactor in order to produce combustion gas. The combustion gas is burned in a separate superheating boiler, in which the steam produced in the recovery boiler is superheated.

Abstract: Kraft pulp of increased strength (e.g. at least about 15% greater tear strength at a specified tensile for fully refined pulp, and as much as about 27%) is produced by keeping the dissolved organic material (DOM) concentration below about 100 g/l (e.g. <50 g/l) throughout substantially the entire kraft cook. This may be done by extracting liquor containing a level of DOM substantial enough to adversely affect pulp strength, and replacing some or all of the extracted liquor with liquor containing a substantially lower effective DOM level than the extracted liquor, so as to positively affect pulp strength. The replacement liquor may be water, white liquor, pressure heat treated black liquor, washer filtrate, cold blow filtrate, or combinations, or the extracted liquor can be treated to remove or passivate the DOM (e.g. by precipitation, ultrafiltration, or absorption).

Abstract: To decrease the sulfur emissions of a sulfate pulp mill, and achieve other advantages, black liquor is heated at a temperature higher than the cooking temperature of the sulfate cook (e.g. between 190.degree. C.-350.degree. C.) and the sulfidity of white liquor produced from the black liquor is adjusted by adjusting the temperature and/or retention time of the heat treatment so that a predetermined amount of sulfur compounds are separated from the black liquor. Pressure heat treatment may occur prior to or after evaporation of the black liquor, or between evaporation stages. Preferably, the sulfur containing gas is thereafter divided into different fractions which are separately cornbusted.

Abstract: This invention relates to an alkaline scrubber for condensate stripper off-gases. In particular, this invention relates a process for selectively removing hydrogen sulfide and methyl mercaptan from a gas stream containing these compounds and methanol. Such gas streams are commonly generated during pulp and paper production.

Abstract: The invention relates to the prehydrolysis of lignocellulose by passing an acidic or alkaline solution through solid lignocellulosic particles with removal of soluble components as they are formed. The technique permits a less severe combination of pH, temperature and time than conventional prehydrolysis. Furthermore, greater extraction of both hemicellulose and lignin occurs simultaneously in the same reactor and under the same conditions.

Abstract: Apparatus for a pulp and paper mill, and methods of acting on liquid effluents produced in the mill, which minimizes the discharge of polluting gaseous and liquid effluents to the environment. Liquid effluents from the bleach plant are concentrated (e.g. evaporated), incinerated (e.g. gasified), leached, crystallized (e.g. freeze crystallized) then washed, and then fed to the plant chemical recovery loop. White liquor produced from the recovery boiler melt is fully oxidized and used in place of caustic in the bleach plant. Essentially all sulfuric acid, sulfur dioxide, caustic, and chlorine dioxide necessary for the pulp mill is produced from mill liquid effluents and gas waste streams, on site at the pulp mill. Typical bleaching sequences that can be used are DE.sub.op D.sub.n D, or AZE.sub.o PZP.

Abstract: Paper pulp (e.g. kraft pulp) is produced utilizing at least two different supplies of cooking liquor, one having low sulfide content, and the other high sulfide content. The high sulfide content supply is typically used to impregnate the pulp or otherwise treat it first, while the second supply is used in other cooking stages (e.g. a digester), whether co-current or countercurrent. The different sulfur content liquors are obtained by heat treating (under pressure) black liquor to drive off sulfur compounds, and absorbing them into white liquor to produce a high sulfide stream. The low sulfide stream is made by conventional treatment of the black liquor after heat treating and evaporation. Utilizing multiple sulfide content supplies results in an optimum viscosity/kappa ratio and/or pulp strength properties for the pulp produced.

Abstract: To decrease the sulfur emissions of a sulfate cellulose mill, black liquor is heated before the last effect of the evaporation at a temperature higher than the cooking temperature of the sulfate cook and the sulfidity of white liquor is adjusted by adjusting the temperature and/or retention time of the heat treatment so that a predetermined amount of sulfur compounds are separated from the gaseous black liquor. Preferably, the sulfur containing gas is thereafter divided into different fractions and separately combusted.

Abstract: A method of producing high quantities of ethanol and a high quality pulp to produce a variety of papers. The method comprises preparing the bamboo by chipping, shredding and washing. This bamboo fiber is then processed in two stages of prehydrolysis to separate the ethanol producing portion from the pulp producing portion. The ethanol producing portion is condensed and subject to enzymatic hydrolysis and fermentation to produce an ethanol product. The pulp producing portion is processed in two stages of digestion to produce a pulp in high yield that is suitable to produce a variety of papers.

Abstract: A method for the manufacture of products containing fibers of lignocellulosic material which involves the disintegration of a lignocellulosic material into fibers and forming and pressing of the fiber web into the product in question, which is preferably in the form of fiberboard (board products). The material that forms the fibers is impregnated with lignin in conjunction with water and at a pH which does not substantially exceed 12.5. When the lignin has been absorbed by the material it is fixed against leaching by water through the modification of said lignin into an essentially water-insoluble form.

Abstract: Combined acidification and evaporative concentration of sulfite based chemical and sulfite based semichemical spent liquors expel massive amounts of gaseous sulfur dioxide and water vapor from the spent liquor.The concentration of the expelled sulfur dioxide is sufficiently high so that the sulfur dioxide and water vapor can be recycled directly, without further separation, to produce fresh sulfite pulping liquor.