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J Europaisches Paten tarn tEuropean Patent OfficeOffice europ6en des brevets (11) Publication number: 0 224 721 B1

EUROPEAN PATENT SPECIFICATION

int. ci.5: C07G 1/00, D21C 3/20Date of publication of patent specification :05.06.91 Bulletin 91/23

(fQ Application number: 86115034.0

(22) Date of filing : 29.10.86

Recovery of lignin.

@ Priority: 05.11.85 US 795069 @ Proprietor: Repap Technologies Inc.2650 Eisenhower AvenueValley Forge, PA 19482 (US)@ Date of publication of application10.06.87 Bulletin 87/24 (72) Inventor : Lora, Jairo H.450 Forrest AvenueNorristown PA 19401 (US)Inventor: Katzen, Raphael2868 Alpine TerraceCincinnati OH 45208 (US)Inventor: Cronlund, Malcolm434 S. Saddlebrook CircleChester-Springs PA 19425 (US)Inventor : Wu, Chih FaeApt. C 291 Murray DriveKing of Prussia PA 19406 (US)

Publication of the grant of the patent :05.06.91 Bulletin 91/23

Designated Contracting States :AT BE CH DE ES FR GB IT LI NL SE

References cited :US-A- 2 331 154US-A- 3 223 697US-A- 3 585 104TAPPI JOURNAL, vol. 68, no. 8, August 1985,pages 94-97, Norcross, Georgia, US; J.H. LO-RA et al.: "Organosolv pulping: a versatileapproach to wood refining "@ Representative : Patentanwalte Griinecker,Kinkeldey, Stockmair & Partner

Maximilianstrasse 58W-8000 Munchen 22 (DE)

CQCMSiCM Note : Within nine months from the publication of the mention of the grant of the European patent, anyperson may give notice to the European Patent Office of opposition to the European patent granted.Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been

filed until the opposition fee has been paid (Art. 99(1) European patent convention).Q.LU

Jouve, 18, rue Saint-Denis, 75001 PARIS

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EP 0 224 721 B1formed which has been difficult to filter or centrifuge.Tappi Journal, Vol. 68, No. 8, pages 94-97 des-cribes the fractionation of hardwoods into pulp, lignin,and hemicellulose in a multi-stage alcohol extractions pilot plant by Organasolv Pulping. Lignin is obtainedas a dry powder having a number average molecularweight of about 1000 and a polydispersity of about 3.

DescriptionBACKGROUND OF THE INVENTION

This invention relates to a process for precipitat-ing lignin from a solution of lignin in a water miscibleorganic solvent, and to an apparatus for carrying outthe process.Processes far treating wood with organic sol-vents, such as alcohols, to separate the wood's lignin,hemicellulose, sugar and cellulose fractions are nowwell known, see, for example, U.S. patent 1,856,567and U.S. Patent 3,585,104. Such solvent pulping pro-cesses have appeared to be attractive alternatives toconventional chemical pulping processes, such askraft and sulfite pulping processes which suffer fromrelatively high equipment costs and pollution prob-lems.One solvent pulping process, disclosed in U.S.Patent 4,100,016, has appeared to be particularlyattractive in providing highly efficient recovery of itsalcohol solvent, separation of the cellulose and ligninfractions of wood, and recovery of cellulose pulp withno appreciable air or water pollution or solid wasteproducts. This patented process has also providedhardwood pulps with yields, strengths, Kappa num-bers, viscosities, fiber strengths and bleachabilitycharacteristics that are equal to or better than kraftand sulfite hardwood pulps.However, the recovery of lignin from thealcohol/water extract or "black liquor", produced as aby-product of the solvent pulping process of U.S.Patent 4,100,016, has been relatively inefficient anddifficult to control. Lignin has been recovered from theblack liquor in this patent by first stripping (preferablyvacuum stripping) alcohol from the black liquor andthen separating the lignin which precipitates from thestripper bottoms or tails (preferably by thickening andthen centrifuging the settled solids from the stripperbottoms). However, a portion of the lignin has tendedto precipitate as a sticky tar or gum on the internal sur-faces of the stripper, thereby fouling the stripper andreducing its efficiency in recovering alcohol from theblack liquor. The lignin also has tended to precipitatefrom the stripper bottoms as a sticky amorphous masswhich has been difficult to handle and has requiredsubstantial crushing to convert the lignin mass into apowder.As a result, more efficient ways have been soughtfor removing lignin from the black liquor produced bya solvent pulping process such as is disclosed in U.S.Patent 4,100,016. One method has involved precipi-tating lignin from the alcohol/water black liquor bydiluting it with water, see Rydholm, "Pulping Proces-ses", pp. 672-673. Interscience Publishers, New York(1971). However, this method has resulted in veryslow settling rates of the lignin, and in some cases, avery stable collodial suspension of the lignin has been

SUMMARY OF THE INVENTION10 An aim of the invention is to provide a relativelysimple way of recovering lignin from an alcohol/waterblack liqour in high yields and high rates in an easy tohandle and useful form.15 This is achieved, in accordance with the inven-tion, by a process for precipitating lignin from a solu-tion of lignin in a water miscible organic solvent,characterized by diluting the lignin-containing solutionwith water and an acid to form a diluted aqueous sol-20 ution with : a pH of less than 3, an organic solvent con-tent of less than 30% (by volume), and a temperatureof less than 75C.The lignin, which precipitates from the diluted

aqueous solution, can be dried to a powder which25 requires little or no crushing to convert it into a fineuniform size suitable for use without further significantprocessing.The lignin product of the above process, prefer-ably has a number average molecular weight of 80030 to 1500 g/mol and a polydispersity of less than 4.Further provided, in accordance with anotheraspect of the invention, is an apparatus for carryingout the process by precipitating lignin from, a blackliquor, that is, an apparatus for pulping wood or other35 fibrous plant material with a water miscible organicsolvent to produce a black liquor as a by-product andfor subsequently recovering the solvent from theblack liquor, characterized by :a) means for diluting the black liquor with an40 aqueous acid to precipitate lignin from the result-ing diluted black liquor and leave a lignin-dep-leted supernatant ;b) means for thereafter separating the precipi-tated lignin from the lignin-depleted supernatant;

45 c) means for thereafter removing the organic sol-vent from the lignin-depleted supernatant to forma solvent- and lignin-depleted supernatant ; andd) means for thereafter recycling a portion of thesolvent- and lignin-depleted supernatant to the50 diluting means for use as the aqueous acid.BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a flow chart of a process for producing55 cellulose pulp from wood by treating the woodwith an aqueous alcohol solvent and for recover-ing lignin from the alcohol/water black liquor thatis a by-product of the process.

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EP 0 224 721 B1chips can be contacted by the primary, secondary andfresh solvents from accumulators 3, 6 and 7 as des-cribed above.The lignin, hemicelluloses, othersaccharides andextractives (e.g., resins, organic acids, phenols andtannins) from the wood and the ethanol, which are allpresent in the black liquor at a temperature of 180 to210C and under a pressure of 20.2 to 35.4 bars (20to 35 atmospheres) in the recovery feed accumulator5, are then recovered by first flashing the black liquorinto a flash tank 11 to recover part of the ethanol. Theflash tank 11 can be at atmospheric pressure for sim-plicity of operation or at reduced pressure to furthercool the black liquor and enhance the alcohol reovery.The reduction in pressure in the flash tank 11 causespartial vaporization of the ethanal and leaves the resi-dual black liquor in the flash tank with an ethanol con-tent of 30 to 45%, preferably 35 to 40%. The residualblack liquor is cooled during this step to a temperatureof less than 95, preferably down to 80 to 92, but notbelow 70 to avoid premature precipitation of lignin inthe flash tank 11. The ethanol/water vapors obtainedare condensed and recycled, along with any make-upethanol, water and/or acid, to the fresh solventaccumulator 7 for use in treating subsequent batchesof wood chips.Lignin is then separated from the residual blackliquor, discharged from the flash tank 11, by the pro-cess of this invention. This step is carried out by dilut-ing and preferably cooling the residual black liquor, asit leaves the flash tank 11, with water and acid to forma diluted residual black liquor with : a) an alcohol con-tent of less than 30% (by volume), preferably 10 to25%, particularly 12 to 21%, with an alcohol contentof 8% being a practical minimum for subsequentlyrecovering the alcohol economically ; b) a tempera-ture of less than 75C, preferably less than 60C, par-ticularly 35 to 55C ; and c) a pH of less than 3,preferably less than 2.5, particularly 1.5 to 2.5. In thisstep, particular temperatures are not critical, althoughproviding higher temperatures in the diluted residualblack liquorwill generally increase settling rates of thelignin but will yield a darker colored lignin and maydecrease its yields. 75C is a maximum temperatureto avoid the formation of tarry lignin precipitates, andambient temperature (e.g., 20C) is a practical mini-mum, although lower temperatures (e.g., down to0C) can be used if low settling rates can be tolerated.Temperatures below 65C, particularly below 60C,provide a significantly lighter colored lignin precipi-tate. Also, particular pH's of the diluted residual blackliquor are not critical in this step, but lower pH'sincrease the yield of precipitated lignin from thediluted residual black liquor and permit the use ofhigher temperatures in the diluted residual blackliquor. However, lowering pH below 1 provides little orno additional improvement in yield, and for thisreason, a pH of 1 is a practical minimum although

Fig. 2 is a schematic sectional view of an exampleof an apparatus for precipitating lignin from thealcohol/water black liquorfrom the process of Fig.1. 5DETAILED DESCRIPTION OF THE PREFERREDEMBODIMENTS

The process shown in Fig. 1 initially involves pulp-ing a batch of wood chips that are loaded from a hop- 10per 1 into an extractor 2. The extractor 2 is operatedin accordance with the aforesaid U.S. Patent4,100,016 at an elevated temperature (e.g., 180 to210C) and an elevated pressure (e.g., 20 to 35atmospheres) and with a solvent comprising : 40 to 1580% (by volume) of a water miscible lower aliphaticalcohol of 1 to 4 carbon atoms (e.g., methanol,ethanol, isopropanol or tert-butanol) ; 20 to 60%water ; and if needed, a small amount of a strongwater soluble acid, such as a mineral acid (e.g., hyd- 20rochloric, sulfuric, phosphoric or nitric acid) or anorganic acid (e.g., oxalic acid).Preferably, the wood chips in the extractor 2 arepreheated with low pressure steam, and then, a twice-used 60% ethanol/40% water, primary solvent from a 25primary solvent accumulator 3 contacts the woodchips in the extractor 2. The primary solvent is rapidlyrecirculated through the extractor 2 and through apeak load (e.g., steam-heated) heat exchanger 4 toraise the temperature of the wood chips to 190 to 30200C in a few (preferably not more than 5) minutes.After this first pulping step is completed, the resultingextract or "black liquor" in the extractor 2 is displacedinto a recovery feed accumulator 5 by a once-used60% ethanol/40% water, secondary solvent (prefer- 35ably heated to 190 to 200C) from a secondary sol-vent accumulator 6. At the end of this displacement,the secondary solvent in the extractor 2 is displacedinto the primary solvent accumulator 3 by a fresh 60%ethanol/40% water solvent (preferably heated to 190 40to 200C) from a fresh solvent accumulator 7. Thefresh solvent in the extractor 2 is then drained into thesecondary solvent accumulator 6. Once the extractor2 has been drained, it is vented, alcohol-rich vaporsfrom the extractor are condensed in a water-cooled 45("C.W.") condensor8, and the resulting ethanol/watermixture from the condensor 8 is recycled to the freshsolvent accumulator 7. After venting the extractor 2,residual alcohol in the pulp in the extractor is thenstripped with low pressure steam, and the resulting 50alcohol/water vapors are condensed and recoveredas discussed below. After steam stripping, the pulp inthe extractor 2 is sluiced with water, piped to a holdingtank 9 and pumped through a pulp screen 10. Thepulp can then be suitably subjected to conventional 55pulp handling, bleaching and paper-making proced-ures. The extractor 2 can be loaded with anotherbatch of wood chips from the hopper 1, and the wood

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EP 0 224 721 B1lower pH's can be used. At a pH of less than 3, ligninwill precipitate from the residual black liquor in highyield and at a high rate as fine solids. These lignin sol-ids can then be separated from the remaining dilutedresidual black liquor supernatant in a conventional 5manner. Preferably, the lignin solids are separatedby : allowing them to settle out as a paste of 6 to 12%(by weight) solids in a conventional clarifier or settlingtank 12 ; then concentrating this paste of lignin solidsin a conventional centrifugal separator 13 to form a 10wet cake of 30 to 40% solids ; and then drying this wetcake to form a uniform fine, free flowing powder.In diluting the residual black liquor from the flashtank 11 with the water and acid to precipitate lignin,any conventional water soluble acid can be utilized wwhich will provide the diluted residual black liquor witha pH of less than 3.0, preferably less than 2.50. Forexample, a strong mineral acid (e.g., hydrochloric, nit-ric, sulfuric or phosphoric acid) or a strong organicacid (e.g., oxalic acid) can be used. Preferably, the zowater and acid are mixed together before they areused to dilute the residual black liquor. In this regard,a particularly preferred mixture of acid and water is aresidual black liquor supernatant that is derived froma previous batch of wood chips and that has been 25recycled and used to dilute the residual black liquorfrom the flash tank 11 after : a) the supernatant hasbeen separated from the lignin solids from the previ-ous batch of wood chips in the settling tank 12 and thecentrifugal separator 13 ; and b) the alcohol content 30of the supernatant has been recovered in a conven-tional solvent recovery tower 14 provided with a con-ventional solvent condenser 15 as described below.This recycled residual black liquor supernatant orstripper bottoms, when used for diluting the residual 35black liquor from the flash tank 11, provides higheryields and faster settling of lignin solids precipitatingin the settling tank 12 and centrifugal separator 13.In precipitating lignin from the residual blackiiquorfrom the flask tank 11, the method of diluting the 40residual blackliquorwith the water and acid also is notcritical, so long as there is rapid and intimate mixingof the residual black liquor with the acid and water. Forexample, the residual black liquor can be suitablydiluted by adding it to the acid and water in a conven- 45tional static dispersion mixer. The residual blackliquor can also be diluted by adding it as a finelydivided stream to a stream comprising a solution ofthe water and acid, for example, by means of a ven-turi-type device, generally 20, as shown schemati- socally in Fig. 2. The residual black Iiquorfrom flash tank11 in Fig. 1 can be pumped through a small nozzle 21located at about the center of a pipe 22 in the venturi-type device 20 in Fig. 2, and the acid and water solu-tion can flow in the pipe 22 towards the settling tank 5512 in Fig. 1. As the residual black liquor is injected bythe nozzle 21 into the acid and water solution in the

pipe 22, the residual black liquor is rapidly diluted and

cooled by the acid and water in the pipe 22. Ligninrapidly precipitates as fine solids from the resultingdiluted residual black liquor in the pipe 22, which sol-ids can be easily collected and concentrated in thesettling tank 12 and centrifugal separator 13.In precipitating lignin in accordance with theabove-described embodiment of the process of thisinvention, the yield and settling rates of the lignin aregenerally a function of : a) the wood species ; b) theprocess conditions utilized in the extractor 2 ; c) thetemperature, pH and solids content of (i) the residualblack liquor from the flash tank 11 and (ii) the acid andwater used to dilute it ; and d) the ratio of residualblack liquor to the acid and water used to dilute it. Forexample, the lignin from softwoods, such as spruce,is preferably precipitated at a temperature after dilu-tion of 40 to 60C using an acid and water solutionwith a pH of 1.5 to 2.5 and with a ratio of residual blackliquor to the acid and water solution of 0.5 to 1. Forhardwoods such as aspen, it is preferred to use anacid and water solution with a pH of 1.2 to 2.2 and atemperature after dilution of less than 50C. In thisregard, it is preferred to use a ratio of residual blackliquor to the acid and water solution of : a) 0.2 to 0.8if the temperature after dilution is above 40C ; and b)0.6 to 1.0 if the temperature after dilution is less than40C (e.g., down to ambient temperature). Forhardwoods, such as sweetgum, maple and oak, it ispreferred to use a temperature after dilution of 40 to60C, an acid and water solution with a pH of 1.5 to2.5, and a ratio of residual black liquor to the acid andwater solution of 0.35 to 0.7.As shown in Fig. 1, the ethanol content of theclarified residual black liquor supernatant from thesettling tank 12 and centrifugal separator 13 is pref-erably recovered in the solvent recovery tower 14 andsolvent condenser 15. The ethanol content of thesupernatant can be stripped (e.g., down to 200 ppm)in a conventional manner in the solvent recoverytower 14 at atmospheric pressure. Preferably, thetower 14 is heated by heating and recycling a portionof the bottoms stream from the tower 14 in a heatexchanger 24, using the low pressure steam used tostrip residual ethanol from the pulp in the extractor 2.The ethanol/water vapors from the tower 14 are con-densed in a conventional manner in the water-cooledcondenser 15 (or by heat exchange with the stripperfeed) and are then recycled to the fresh solventaccumulator 7 together with the ethanol/water mixturewhich condenses from the low pressure steam in theheat exchanger 24. The ethanol content of the super-natant from the settling tank 12 and centrifugalseparator 13 can be suitably recovered in high yieldin a simple manner, without lignin precipitating withinthe solvent recovery tower 14 and forming tarry orgummy deposits on the internal surfaces of the tower.A portion of the bottoms stream removed from thesolvent recovery tower 14 is preferably concentrated

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EP 0 224 721 B1for precipitating lignin without departing from thescope of these aspects of the invention of sacrificingall of their material advantages. The process andapparatus hereinbefore described being merely pre-ferred embodiments. For example, the process of thisinvention can alternatively be carried out by sepa-rately adding an acid and water to a solution of lignindissolved in a water miscible organic solvent to forma diluted aqueous solution with a pH of less than 3, anorganic solvent content of les than 30% and a tem-perature of less than 75C, from which diluted solutionthe lignin will precipitate as uniform fine solids. In thisregard, the acid can be separately added to the resi-dual black liquor from the flash tank 11 in Fig. 1 byadding the acid to the primary solvent from the prim-ary solvent accumulator 3 before the primary solventis used in the extractor 2 for pulping wood chips to pro-duce the black liquor (which becomes, after removalof ethanol in the flash tank 11, the residual blackliquor). Also, the process of this invention can be car-ried out with a water miscible organic solvent otherthan a lower aliphatic alcohol (preferably ethanol),such as acetone, glycol orglycerol, or with a mixtureof such solvents. Also, this process can be carried outwith lignin extracted from any fibrous plant material,such as bamboo, bagasse, and cereal straws, and notjust wood.

in a conventional manner, for example, in multipleeffect evaporators 26. In this step, scaling or foulingof the evaporation equipment is not a significant prob-lem because there are no substantial amounts of highmolecular weight lignin in the bottoms stream from the 5solvent recovery tower 14. The resulting syrup, con-taining hemicelluloses together with small amounts ofother saccharides, extractives and very low molecularweight lignin (i.e., lignin with a molecular weight ofless than 400 g/mol), can be burned to recover its fuel 10value, used as animal feed, or converted to otherchemical products.A second portion of the bottoms stream removedfrom the tower 14 is preferably used as the acid andwater solution for diluting the residual black liquor 15from the flash tank 11 in order to precipitate lignintherefrom. In this regard, the second portion of thebottoms stream from the tower 14 is preferably cooledto a temperature of less than 50C, preferably 25 to40C (about 0C being a practical minimum), and its 20pH is adjusted, if necessary, to 1.0 to 3.0 by adding astrong water soluble acid to it. Then, the cooled andacidified second portion of the bottoms stream(hereinbefore called the "recycled residual blackliquor supernatant") is intimately and rapidly mixed 25(e.g., in the venturi-type device 20 of Fig. 2) with theresidual black liquor to dilute and cool the residualblack liquor and precipitate lignin.The very pure lignin, which precipitates as finesolids from the diluted residual black liquor in the settl- 30ing tank 12, can be subsequently removed from thecentrifugal separator 13, water-washed and dried in aconventional manner (e.g., by spin flash drying) toform a fine (e.g., -80 mesh) uniform, free flowing,water insoluble powder. This lignin can be charac- 35terized as having : a relatively low number averagemolecular weight of 800 to 1500 g/mol, preferably 900to 1300g/mol ;a narrow moiecularweight distribution,i.e., a polydispersity of less than 4, preferably no morethan 3, particularly only 1.5 to 2.7 ; and a methoxyl 40content approximately equal to the methoxyl contentof native lignin (i.e., 20% for hardwoods and 14% forsoftwoods). This lignin also has a glass transition tem-perature which is preferably 100 to 170, particulaly130 to 150. These characteristics show, inter alia, the 45purity and low degree of chemical modification of thelignin as obtained by the process of this invention.This lignin can be used, for example, as a phenol for-maldehyde resin extender in the manufacture of par-ticle board and plywood. This lignin can also be used 50in the manufacture of molding compounds, urethaneand epoxy resins, antioxidants, controlled-releaseagents and flow control agents.The process, product and apparatus aspects ofthis invention and many of their attendant advantages 55will be understood from, the foregoing description,and it will be apparent that various modifications andchanges can be made in the process and apparatus

Claims1. Aprocess for precipitating lignin from a solution

of lignin in a water miscible organic solvent, charac-terised by diluting the lignin-containing solution withwater and an acid to form a diluted aqueous solutionwith a pH of less than 3, an organic solvent content ofless than 30% by volume and a temperature of lessthan 75C.2. The process according to claim 1, character-ised by providing the organic solvent content of thediluted aqueous solution in the form of a lower alipha-tic alcohol of 1 to 4 carbon atoms.3. The process according to claim 2, character-ised by forming the diluted aqueous solution with a pHof less than 2.5.4. The process according to claim 3, character-ised by forming the diluted aqueous solution with atemperature of less than 60C.5. The process according to claim 4, character-ised by forming the diluted aqueous solution with atemperature of 35 to 55C.6. The process according to claim 2, character-ised by forming the diluted aqueous solution with analcohol content of 10 to 25% by volume.7. The process according to claim 6, character-ised by forming the diluted aqueous solution with analcohol content of 12 to 21% by volume and with atemperature of less than 65C.

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10P 0 224 721 B18. The process according to claim 6, character-ised by forming the diluted aqueous solution with atemperature of less than 60C and a pH of 1.5 to 2.5.9. The process according to claim 8, character-ised by forming the diluted aqueous solution with a 5temperature of 35 to 55C and alcohol content of 12to 21% by volume.10. The process according to claim 1, character-ised by using, as the water for diluting the lignin-con-taining solution, water which is in addition to water walready present in the solution.11. The process according to claim 10, character-ised by intimately and rapidly mixing the lignin-con-taining solution with a mixture of the acid and theadditional water to form the diluted aqueous solution. 1512. The process according to claim 1, character-ised by utilising, as the lignin-containing solution, asolution obtained by contacting wood or other fibrousplant material with the organic solvent at an elevatedtemperature and an elevated pressure to produce a 20cellulose pulp and a black liquor containing lignin andthe organic solvent, and then separating the pulp fromthe black liquor.13. The process according to claim 12, character-ised by utilising the acid and water in a mixture which 2salso contains hemicelluloses, other saccharides, ext-ractives and lignin with a molecular weight of less than400 g/mol.14. The process according to claim 13, character-ised by utilising, as the acid and water mixture, a recy- 30cled aqueous acid obtained by diluting the black liquorwith the aqueous acid to form a diluted black liquorfrom which lignin is precipitated, leaving a black liquorsupernatant ; removing the organic solvent from theblack liquor supernatant to produce a residual black 35liquor supernatant ; and then recycling a portion of theresidual black liquor supernatant for use as theaqueous acid in diluting the black liquor.15. The process according to claim 14, character-ised byutilising,astheorganicsolvent,aloweralipha- 40tic alcohol of 1 to 4 carbon atoms.16. The process according to claim 15, character-ised by providing the diluted black liquor with a pH ofless than 2.5.

17. The process according to claim 16, character- 45ised by providing the diluted black liquor with a tem-perature of less than 60C.18. The process according to claim 15, character-ised by providing the diluted black liquor with analcohol content of 10 to 25% by volume. so19. The process according to claim 18, character-ised by providing the diluted black liquor with a pH of1.5 to 2.5 and a temperature of less than 60C.20. The process according to claim 19, character-ised by providing the diluted black liquor with a tern- 55perature of 35 to 55C and an alcohol content of 12to 21% by volume.21 .The process according to claim 14, character-

6

ised by the fact that the black liquor contains waterbefore it is diluted with the recycled aqueous acid.22. The process according to claim 21, character-ised by the fact that the black liquor is intimately andrapidly mixed with the recycled aqueous acid to formthe diluted black liquor.23. The process according to claim 15, character-ised by providing the diluted black liquor with a tem-perature of 70 to 95C and the recycled aqueous acidwith a temperature of less than 50C.24. The process according to claim 23, character-ised by providing the diluted black liquor with a tem-perature of 80 to 92C and the recycled aqueous acidwith a temperature of 25 to 40C.25. An apparatus for pulping wood or other fibr-ous plant material with a water miscible organic sol-vent to produce a black liquor as a by-product and forsubsequently recovering the solvent from the blackliquor, characterised by :a) means for diluting the black liquor with anaqueous acid to precipitate lignin from the result-ing diluted black liquor and leave a lignin-dep-leted supernatant ;b) means for thereafter separating the precipi-tated lignin from the lignin-depleted supernatant;c) means for thereafter removing the solvent fromthe lignin-depleted supernatant to form a solvent-and lignin-depleted supernatant ; andd) means for thereafter recycling a portion of thesolvent- and lignin-depleted supernatant to thediluting means for use as the aqueous acid.

26. The apparatus according to claim 25, charac-terised by the fact that the diluting means isassociated with means for removing a portion of thesolvent from the black liquor before diluting the blackliquor.27. The apparatus according to claim 26, charac-terised by the fact that the recycling means isassociated with means for adding a strong water sol-uble acid to the solvent- and lignin-depleted supernat-ant before recycling it to the diluting means.28. The apparatus according to claim 25, charac-terised by the fact that the diluting means includes anarrangement for intimately and rapidly mixing theblack liquor with the aqueous acid.

Anspriiche1. Verfahren zum Ausfallen von Lignin aus einerLosung von Lignin in einem mit Wasser mischbarenorganischen Losungsmittel, dadurch gekennzeich-net, daS man die Lignin enthaltende Losung mit Was-ser und einer Saure verdunnt zur Bildung einerverdunnten waSrigen Losung mit einem pH von weni-gerals 3, einem Gehaltan organischem Losungsmit-tel von weniger als 30 Vol.-% und einer Temperatur

von weniger als 75C.

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EP 0 224 721 B1 121Schwarzlauge mit der waBrigen Saure, um eine ver-diinnte Schwarzlauge zu bilden, aus der Lignin aus-gefallt wird, Zuriicklassen einer uberstehendenSchwarzlauge ; Entfernen des organischen Losungs-mittels aus der uberstehenden Schwarzlauge, um ei-ne restiiche uberstehende Schwarzlauge zuerzeugen ; und danach Rezyklisieren eines Teils derrestlichen uberstehenden Schwarzlauge zur Verwen-dung als waBrige Saure beim Verdunnen derSchwarzlauge.15. Verfahren nach Anspruch 14, dadurchgekennzeichnet, daB man als organisches Losungs-mittel einen niederen aliphatischen Alkohol mit 1 bis4 Kohlenstoffatomen verwendet.16. Verfahren nach Anspruch 15, dadurchgekennzeichnet, dad man die verdunnte Schwarz-lauge mit einem pH von weniger als 2,5 vorsieht.17. Verfahren nach Anspruch 16, dadurchgekennzeichnet, daB man die verdunnte Schwarz-lauge mit einer Temperatur von weniger als 60C vor-sieht.18. Verfahren nach Anspruch 15, dadurchgekennzeichnet, dad man die verdunnte Schwarz-lauge mit einem Alkoholgehalt von 10 bis 25 Vol.-%vorsieht.19. Verfahren nach Anspruch 18, dadurchgekennzeichnet, dad man die verdunnte Schwarz-lauge mit einem pH von 1,5 bis 2,5 und einer Tempe-ratur von weniger als 60C vorsieht.20. Verfahren nach Anspruch 19, dadurchgekennzeichnet, daB man die verdunnte Schwarz-lauge mit einer Temperatur von 35 bis 55C und ei-nem Alkoholgehalt von 12 bis 21 Vol.-% vorsieht.21. Verfahren nach Anspruch 14, gekennzeich-net durch den Umstand, daB die Schwarzlauge Was-ser enthalt, bevor sie mit der rezyklisierten waBrigenSaure verdunnt wird.22. Verfahren nach Anspruch 21, gekennzeich-net durch den Umstand, daB die Schwarzlaugegriindlich und rasch mit der rezyklisierten waBrigenSaure vermischt wird zur Bildung der verdunntenSchwarzlauge.23. Verfahren nach Anspruch 15, dadurchgekennzeichnet, daB man die verdunnte Schwarz-lauge mit einer Temperatur von 70 bis 95C und dierezyklisierte waSrige Saure mit einer Temperatur vonweniger als 50C vorsieht.24. Verfahren nach Anspruch 23, dadurchgekennzeichnet, daB man die verdunnte Schwarz-lauge mit einer Temperatur von 80 bis 92C und dierezyklisierte waSrige Saure mit einer Temperatur von25 bis 40C vorsieht.25. Vorrichtung zum AufschlieBen von Holz oderanderem fasrigen Pflanzenmaterial mit einem mitWasser mischbaren organischen Losungsmittel, umeine Schwarzlauge als Nebenprodukt zu erzeugenund zum nachfolgenden Gewinnen des Losungsmit-tels aus der Schwarzlauge, gekennzeichnet durch :

2. Verfahren nach Anspruch 1, dadurch gekenn-zeichnet, daB man den Gehalt an organischemLosungsmittel der verdunnten waBrigen Losung inForm eines niederen aliphatischen Alkohols mit 1 bis4 Kohlenstoffatomen vorsieht. 53. Verfahren nach Anspruch 2, dadurch gekenn-zeichnet, daB man die verdunnte waBrige Losung miteinem pH von weniger als 2,5 bildet.4. Verfahren nach Anspruch 3, dadurch gekenn-zeichnet, daS man die verdunnte waBrige Losung mit 10einer Temperatur von weniger als 6PC bildet.5. Verfahren nach Anspruch 4, dadurch gekenn-zeichnet, daB man die verdunnte waSrige Losung miteiner Temperatur von 35 bis 55C bildet.6. Verfahren nach Anspruch 2, dadurch gekenn- 15zeichnet, daS man die verdunnte waBrige Losung miteinem Alkoholgehalt von 10 bis 25 Vol.-% bildet.7. Verfahren nach Anspruch 6, dadurch gekenn-zeichnet, daB man die verdunnte waBrige Losung miteinem Alkoholgehalt von 12 bis 21 Vol.-% und mit 20einer Temperatur von weniger als 65C bildet.8. Verfahren nach Anspruch 6, dadurch gekenn-zeichnet, daB man die verdunnte waBrige Losung miteiner Temperatur von weniger als 60C und einem pHvon 1,5 bis 2,5 bildet. 259. Verfahren nach Anspruch 8, dadurch gekenn-zeichnet, daB man die verdunnte waBrige Losung miteiner Temperatur von 35 bis 55C und einem Alkohol-gehalt von 12 bis 21 Vol.-% bildet.10. Verfahren nach Anspruch 1, dadurch gekenn- 30zeichnet, daB man als Wasser zum Verdunnen derLignin enthaltenden Losung Wasser verwendet, daszu dem bereits in der Losung vorhandenen Wasserzusatzlich hinzukommt.11. Verfahren nach Anspruch 10, dadurch 35gekennzeichnet, daB man die Lignin enthaltendeLosung grundlich und rasch mit einer Mischung ausder Saure und dem zusatzlichen Wasser mischt zurBildung der verdunnten waBrigen Losung.12. Verfahren nach Anspruch 1, dadurch gekenn- 40zeichnet, daS man als Lignin enthaltende Losung eineLosung verwendet, die erhalten wird, durch Kontak-tieren von Holz oder einem anderen fasrigen Pflan-zenmaterial mit dem organischen Losungsmittel beierhohter Temperatur und erhohtem Druck, um eine 45Cellulosepulpe und eine Schwarzlauge zu erzeugen,die Lignin und das organische Losungsmittel enthalt,und Abtrennen der Pulpe von der Schwarzlauge.13. Verfahren nach Anspruch 12, dadurchgekennzeichnet, daS man die Saure und Wasser in 50einer Mischung verwendet, die ebenso Hemicellulo-sen, andere Saccharide, Extraktionsmittel und Ligninmit einem Molekulargewicht von weniger als 400g/Mol enthalt.14. Verfahren nach Anspruch 13, dadurch 55gekennzeichnet, daB man als die Saure- und Wasser-mischung eine rezyklisierte waBrige Saure verwen-det, die erhalten wird durch Verdunnen der

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15 EP 0 224 721 B1 16cede consiste adonnerune teneuren alcool de 10 a ger rapidement et intimement le liquide noir avec25% par volume au liquide noir dilue. I'acide aqueux.19. Conformement a la revendication 18, ce pro-cede consiste a donner un pHde 1,5 etune tempera-ture de moins de 60C au liquide noir dilue. 520. Conformement a la revendication 19, ce pro-cede consiste a donner une temperature de 35 a 55Cet une teneur en alcool de 12 a 21% par volume auliquide noir dilue.21 . Conformement a la revendication 14, ce pro- 10cede se caracterise par le fait que le liquide noircontient de I'eau avant d'etre dilue avec I'acideaqueux retraite.22. Conformement a la revendication 21 , ce pro-cede consiste a melanger intimement et rapidement 15le liquide noir avec I'acide aqueux retraite afin d'obte-nir un liquide noir dilue.23. Conformement a la revendication 15, ce pro-cede consiste a donner une temperature de 70 a 95Cau liquide noir dilue et une temperature de moins de 2050C a I'acide aqueux retraite.24. Conformement a la revendication 23, ce pro-cede consiste a donner une temperature de 80 a 92Cau liquide noir dilue et une temperature de 25 a 40Ca I'acide aqueux retraite. 2525. Un appareil a pulper le bois ou toute autreplante fibreuse avec un solvant organique miscibledans I'eau pour produire un liquide noircomme deriveet recuperer par la suite le solvant contenu dans leliquide noir, et caracterise par : 30a) une technique de dilution de liquide noir avecun acide aqueux afin d'en precipiter la lignine et

obtenir un surnatant depourvu de lignine ;b) une technique permettant de separer par lasuite le precipite de lignine du surnatant depourvu 35de lignine ;c) une technique permettant d'extraire par la suitele solvant du surnatant depourvu de lignine pourobtenir un surnatant depourvu a ia fois de solvantde lignine ; et 40d) une technique permettant de retraiter une par-tie du surnatant depourvu de solvant et de lignineafin de I'utiliser comme I'acide aqueux employedans la technique de dilution.26. Conformement a la revendication 25, cet 45appareil se caracterise par le fait que la technique dedilution est associee a un systeme d'extraction d'unepartie du solvant du liquide noir avant la dilution de cedernier.27. Conformement a ia revendication 26, cet 50appareil se caracterise par ('association de la techni-que de retraitement avec une technique permettantd'ajouter un acide fort soluble dans I'eau au surnatantdepourvu de solvant et de lignine avant de le retraiterpour I'utiliser dans le systeme de dilution. 5528. Conformement a la revendication 25, cetappareil se caracterise par lu fait que le systeme dedilution comprend un procede qui permet de melan-

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