CA1036723A - Method or reducing the emission of organic substances from cellulose plants - Google Patents

Abstract

A METHOD OF REDUCING THE EMISSION OF ORGANIC SUBSTANCES
FROM CELLULOSE PLANTS

ABSTRACT OF THE DISCLOSURE

A method of purifying aqueous waste liquors from cellulose plants is provided, in which organic substances are sorbed on water-insoluble polymers, preferably cross-linked polymers, and recovered by elution, which comprises contacting with at least one organic anion exchanger a first aqueous waste liquor having a low content of inorganic anions such as sulphate and chloride and containing organic acids and organic nonionized substances and sorbing thereon organic acids and organic nonionized substances; and contacting a second aqueous waste liquor having a high chloride content and containing aromatic compounds, for example, waste liquor from chlorinating and chlorine dioxide bleaching stages, with at least one adsorption resin and sorbing aromatic compounds thereon while the chloride ions remain in the solution; eluting organic acids and organic nonionized substances by contacting the anion exchanger with an aqueous alkali solution; and eluting aromatic compounds by contacting the adsorption resin with an aqueous alkali solution. The same solution is utilized for each elution, in either order. The regenerated anion exchange and adsorption resins can then be re-used.

Description

1036q23 SPECIFICATION

In recent years concern over the contamination of lakes, streams, coastal waters, and even the open sea, by the emission products of cellulose plants has greatly increaqed.
At present the spent cooking liquors from the digesters of cellulose plants are being used to an ever increasing extent as fuel and for other useful purposes. However, diluted wash waters from chip digestion and pulp screening plants, and waste liquors and wash water from the bleaching planes, may still be diccharged to streams and lakes, and the open sea.
It has been suggested by Sanks, TAPPI, 8th Water and Air Conference, April 7, 1971, Boston, Massachusetts, and Brodderall, Llndberg and Ljungquist, German Offenlegungsschrift ~o. 2,243,141, publichsed March 22, 1973, that prior to such discharge, colored subst~ances, primarily lignin, can be removed by a weakly basic type anion exchanger, such as Duolites~, which is regenerated by elution with an alkaline solution which is subsequently dried and the residue burned. The chloride ions in the bleaching waste liquors are bound very strongly by the ion exchanger, and to`avoid an excessively high concentration of chloride in the eluate, it is necessary to subject the chloride ` ions to a separate elution process, using sodium sulphate, or to effect an activation of the ion exchanger, converting it to bisulphite form, before contacting it with the waste liquor.
As a result, the cost for the chemicals used is very high.
Moreover, the recovery of other ions present in the waste liquors and bound more loosely than chloride is prevented.

1(1367Z3 I)uring elution with sodium sulphate, these ions are dissolvecl in the eluate, which is discharged to waste. Consequently, the purification process is largely linlited to the removal of lignin. Other substances, for exal~lple, organic acids which are formed by the carbohydrates, such as formic acid, glycolic acid, aldonic acids, uronic acids and saccharinic acids, are discharged to the surroundings.
As is evident from articles published on the subject, the method is suitable for waste liquors originating from the extraction stage in sulphate plants, but is unsuitable for other waste liquors obtained from the bleaching section of a sulphate plant. In the case of sulphate plants, however, the major portion of the colored substances are obtained from the waste liquors in the extraction stage, and in the case of sulphate plants where the body of water receiving the discharge is only sensitive to colored substances, the method has obvious advantages. The major portion of the organic substances in waste liquors from the bleaching section, however, passes through the waste discharge system, when this method is applied, despite the very high costs involved in carrying out the process. In the case of sulphite plants, the results are inferior, partly because a large quantity of the lignin is normally obtained in other process stages.
Alternatively, Paleos, U.S. patent No. 3,652,407, dated March 28, 1972, proposed that adsorption resins having no anion exchanging properties can be used for removing aromatic products such as lignin and degradation products of lignin.
It has also been proposed to use porous resins of the type containing phenolic hydroxyl groups for separating ligninsulphoniç

~036!7~3 acid from other non-adsorbable compounds in sulphite waste liquor, such resins being used on a labnratory scale for decolorizing bleaching waste liquors. Although positive results have been reportedJ it would not appear from the literature that tests have been carried out on a large scale. The main reason for this ~Yould seem to be that the purifying effect obtained is not considered to justify the costs involved thereby.
Also, this method does not render carbollydrate degradation products innocuous.
In accordance with the present invention, a method of purifying aqueous waste liquors from cellulose plants is provided, in which organic substances are sorbed on water-insoluble polymers, preferably cross-linked polymers, and recovered by elution, which comprises contacting with at lèast one organic anion exchanger a first aqueous waste liquor having a low content of inorganic anions such as sulphate and chloride and containing organic acids and organic nonionized substances, and sorbing thereon organic acids and organic nonionized substances; and contacting a second aqueous waste liquor having a high chloride content and containing aromatic compounds, for example, waste water from chlorinating and chlorine dioxide bleaching stages, with at least one adsorption resin and sorbing aromatic compounds thereon while the chloride ions remain in the solution; eluting organic acids and organic nonionized substances by contacting the anion exchanger with an aqueous alkali solution; and eluting aromatic compounds by contacting the adsorption resin with an aqueous alkali solution~ The same alkali solution is utilized for each elution, in either order~ The regenerated anion exchange and adsorption resins ~0367;23 can th~n be reused. The ali solution can be recycled to replenish sodium losses in a cellulose treatment process~
The method according to the invention affords a much better purifyillg effect at an operational cost which is surprisingly much lower than kno~vn lllethods. FurtherlYlore, the major portion of the eluted orgallic substances that are recovered can be used for a useful purpose, for example as fuel.
The process of the invention utilizes two aqueous waste liquors, portions or fractions, one with low chloride and sulfate (Fraction A) and one with high chloride (Fraction B). These are selected as liquors, portions or fraction~ from the available waste liquors. The following is an exemplary selection.
Normally, one or more alkaline extraction stages or alkaline refining stages, for example, hot-alkali refining and, less frequently, cold-alkali refining, are included in or precede a bleaching process. These are called E-stages. If an E-stage is placed before a bleaching stage in which a chlorine-containing bleaching agent is used, the waste liquor from an E-stage can be obtained practically free from both chloride and organically bound chlorine. This is particularly

2~ suitable when bleaching sulphite pulp, where a markeddelignification, removal of resin and dissolution of carbohydrates is obtained in a first E-stage, and where the risk of corrosion by the introduction of chloride into the recovery system is much higher than in processes where the liq.uors are more al~aline. The waste liquor from such an E-stage may be treated either as Fraction A or as Fraction B in the process according to the invention.

1~)367~3 This waste liquor can also contain to advantage residues of dig~ester waste liquors, for example, sulphite waste liquor or black liquor, the recovery of these being integ~rated in the recovery process according to the invention. This method is particularly suitable when a closed screening section is positioned between the digester and the E-stage, although it can also be used if the pulp is unscreened prior to the E-stage, or screened in a conventional screening section.
An integratlon of the recovery of cooking waste liquor residues affords particular advantages when the first chemical treatment process after the digester comprises an E-stage, or some other treat-ment stage without chlorine-containing bleaching agent, such as an oxygen bleaching stage. It can also be used however, to advantage when the first stage contains chlorine-~ontaining bleaching agents.
Even when the E-stage is placed after a treatment stage with chlorine-containing bleaching agent, such as chlorine and chlorine oxides, e. g. chlorine dioxide, the waste liquor from the E-stage according to the invention may normally be included wholly or partially in Fraction B. It may also be included wholly or partially in Fraction A;
in this case it is suitable to mal~e use of known means to maintain the chloride content of the waste water at a low level, e. g~ by washing and pressing prior to the E- stage, and/or by using chlorine dioxide in the stagè used prior to the E-stage, and when using chlorine to adjust the conditions so that the chlorine content is as low as possible in the -subsequent E-stage.
According to a preferred embodiment, Eraction ~
contains waste liquor from an alkaline bleaching stage in which an 1036~723 o~idation process is employed. Examples of such bleaching stages include oxygen-alkali bleaching, and E-stages with additions of peroxide or other peroxy compounds, or conventionalbleaching~ stages using peroxide. It is particularly suitable to employ an oxygèn-alkali bleaching process as the first bleaching stage after the digester, wherein either all of the waste liquor from said stage or part of said liquor is }ncorporated in Fraction A.
In accordance ~vith a particularly suitable embodiment, the waste liquor from the oxygen-alkali bleaching process is used to displace cooking waste liquor in a manner known per se, while another portion, which may have a lower concentration, is incorporated in Fraction A.
Some waste liquor may optionally be returned to the actual bleaching stage, so that the solids content is as high as possible.
By means of such a method the recovery of solids from the oxygen bleaching stage can be effected practically completely, while in the case of previously known methods the recovery is only efficient to approximately 50%, if the recovery process is effected solely by displacement of waste digesting liquor.
As mentioned above, Fraction A is treated with at least one anion exchanger to remove therefrom organic acids including mono and polyhydroxy mono and polycarboxylic acids such as saccharic, dihydroxy butyric, 2, 5-dihydroxy valeric,glyceric, 2-hydro~ propansic,

3-hydroxy propansic, glycolic, acetic, for~ic, oxalic, tartronic and deoxyaldaric acids, and organic nonionized substances, including lignin, degraded lignin, phenolic compounds, waxes, fats and sterols.

~036qZ3 It is ~;nown that compounds having a very high molecular weight, for example, high molecular weight li~nin sulphonic acids, are adsorbed very poorly or possibly not at ~l on gel-type anion exchanoers having~ a llig~l~ deg~ree of cross-linking and prepared without precautions to introduce macropores ("non-porous" ion exchang~ers).
To enable such compounds to be adsorbed, I:he anion exchanger must contain at least a proportion of pores within the range from about 30 to about 2000 A, preferably from about 50 to about 1000 A, so that the high molecular weight compounds can penetrate into the polymer matrix.
Several types of anion exchangers having such pores are known (Kunin et al, J. Am Chem. Soc. 84 308 t1962))and are commercially available under the designations "macroporous" or "macroreticular" and as "moderately porous" anion e~changers.
The porosity of these resins can be varied and sorne anion exchangers are of moderate porosity. The resin matrix can be prepared by suspension copolymerization of sty~ene and divinylbenzene in the presence of a liquid which is a good solvent for the monomers but a poor swelling agent for the polymer ( = macroreticular resins).
Another type of macroporous resins of low or moderate porosity are those prepared by copolymerization of styrene and divinylbenzene in the conventional way (used for gel resins) with a low percentage of divinylbenzene e. g. 1-4~c and subsequent additional cross-linking of the copolymer by methylene bridging in a swollen .. ~
state e.g. by treatment with chloromethylether, such as Dowex 21 k.
I it is desired to remove organic substances from Fraction A in a single stage, and to obtain practically complete sorption of the high molecular weight acids and nonionized substances, 1036~Z3 an anion exchanger of at least such porosity must be used. Such porous anion exchangers when used in accordance with the invention may have a short useful life, in comparison with collventional gel type anion exchangers and anion exchangers of lower porosity. However, the puriication effect with the latter types is unsatisfactory, when the requirF3ments for color removal are high.
Strongly basic anion exchange resills are dissociated even in aqueous alkaline medium. The most important type contains quaternary ammonium groups, most commonly linked to a styrene-divinylbenzene resin~ Weal~ly basic anion exchange resins are virtually non-dissociated in a strongly alkaline medium, e. g. above pH 10. The most important types contain primary, secondary and tèrtiary amino groups, which are linked to a resin chain which can be aromatic or aliphatic.
In accordance with another embodiment of the invention, Fraction A is treated with a combination of both an anion exchanger and an adsorption resin. In this way noticeable advantages are obtained, not only with respect to the removal of color, but surprisingly, also with respect to the economy of the process. When this combination treatment is used, gel-type anion exchangers and anion exchangers having pores of less than 30 A, i. e. of low porosity, can be used to advantage.
The treatment with adsorption resin is normally effected before the treatment with anion exchanger. In this way, the useful life of the anion exchanger is considerably lengthened. ~he combined treatment produces similar purification results, however, if the adsorption resin is subsequent to the anion exchanger. When the purification 1036!7Z3 requiremellts are ~ery high, a first adsorption resin is used prior to the anion exchallger, and a second adsorption resin, preferably of a different type, is used after the anion exchal~ger~
One par~ic~llar àdvantage afforded with this embodiment is that the eluate obtained from the regeneratioll oE the anion exchanger can be used for regellerating the ad~orption resin.
The Fraction A treatment with an anion exchanger and optionally an adsorption resin can be used either wholly or partially for preparing cooking liquor, bleaching liquor, and/or as washing liquor, or to provide or replace water in so~ne othèr way at any part of the pulping and bleaching process.
In certain instances, it is of economic importance to recover metal cations, preferably sodium ions, present in the waste liquor, or to prevent such metal cations from being discharged. This can be effected by contacting the treated waste liquor, preferably after treatment with anion exchanger, with a cation exchanger in hydrogen form (free acid form), to remove metal cations, e.g. sodium ions.
So that Fraction A can be purified effectively, using certain types of anion exchangers, preferably of the weakly basic type, and also adsorption resins,the pH of the liquor is reduced to less than 9.
Pre~erably, the pH of Fraction A is reduced to within the range from about 1 to about 8, suitably` from 2 to 7, still more preferably 2 to

4. The pH can suitably be reduced by adding an acidic liquor, such as `
diluted acid waste digestion liquor, for example, wash water from a sulphite cooking process, and aqueous SO2 - containing and/or acetic acid-containing solutions, such as condensates~ Carbon dioxide and solutions from acid bleaching stages, e . g . chlorine dioxide bleaching stages, can also be employed.

, 1036qZ3 Alternatively, the pH of the liquor can be reduced by contacting Fraction A with a cation exchanger in hydrogen form, preferably of the carboxylic acid type. Ion exchangers of the sulphonic acid type can also be used, especially in sodium-based sulphite mills, where the sodium ions are eluted and used for acid preparation in a manner known per se.
Cation exchange resins, as is well known, have a synthetic resin base molecule to which are attached the active groups to which the resin owes its cation exchange capacity.
These active groups include sulfonic~ carboxylic, phenolic hydroxyl, phosphonous, phosphonic, and phosphoric acid groups.
As the base resin molecule, there are usually used polystyrene, copolymers of styrene and divinyl benzene, poly-methacrylic acid, polyacrylic acid, phenol-formaldehyde poly-condensates, and processed coal. Cation exchange resins that are commercially available, and all of which are trademarks, include Amberlite IR-120, IR-122, IR-124, XE-100, Dianion SK, Dowex 50 (Nalcite HCR), Dowex 50 W, Duolite C-20, Duolite C-25, Imac C-12, Lewatit S-100, Ionac C-240, (Permutit Q), Permutit RS, Permutit C 50 D, Wofatit KPS 200, Zerolit 225 (Zeo-Karb 225), which are of the sulfonated polystyrene type, or styrene-divinyl benzene copolymer; Amberlyst 15 is also of this type, and is macroreticular; Duolite C-3, Duolite C-10, Ionac C-150 (Zeo-Karb), Lewatit KS, Lewatit KS~, Wofatit K (Ks), Wofatit P, Zerolit 215 (Zeo-Karb 215), which are of the sulfonated phenol-formaldehyde type; Amberlite IRC-50 and IRC-84, Amberlite XE-(89 H), Duolite CS-101, Ionac C-270 (Permutit H-70), Lewatit C, Lewatit CNO, Zerolit 226 (X-2.5 and ~ l/,`i~ -10-1036~23 X-4 . 5), Wof~tit C, which are of the polymethacrylic acid and polyacrylic acid carboxylic acid type; and Duolite ES-62, Duolite ES-63, and Duolite ES-65, which are of the p~osphonous, pllosphonic and phosphoric acid types, respectively.
These cation exchange resins can be used in any par-ticulate form~ Beads and granules are available. The highest surface area is preferred.
It has been found of particular advaneage to effect the treatment with cation exchangers in two stages: (1) cation exchangers of the carboxylic acid type, in free acid form (2) cation exchangers of the sulphonic acid type in free acid form.
Irrespective of whether cation exchangers of the carboxylic acid type are used alone or in combination with other methods to lower the plI, it is suitable to effect the regeneration process with water containing CO2 under pressure, the resulting bicarbonate solution being used to advantage to replace sodium losses and water in part of the pulping process, e.g. in the digester, washing system, chemical recovery system, or bleaching system.
In a sodium-based sulphite mill, the embodiment utilizing strong acidification of Fraction A, for example, to a pH equal to 2 or lower, and with subsequent treatment using anion exchangers o-f the weakly basic type, affords a rational and effective method of rendering the organic substances in Fraction A innocuous and simultan-eously of utilizing said substances. In this instance, the acidification is effected by means of a cation exchanger, preferably of the carbox~lic acid type, and the cation exchanger is regenerated with an S02-con-taining aqueous solution, eluted sodium ions being passed to the acid system of the millO

. 1036q23 In a sulphate n~ill, this method can be effected in a manner such that the regneration of cation exchangers is effected, for example, with acid solutions obtained by scrubbing waste gases and optionally admixed with acid, eg. waste sulfuric acid from a chlorille dioxide production process, and/or chlorine-alkali manufacturing processes~ Other acid solutions, such as hydrochloric ~cid or acetic acid, may also be used.
Irrespective of the type of plant concerned, the treat-ment lnUSt be adapted to the puriication requirelllents and the energy costs and the chemical losses (primarily sodium and sulphur losses) which need be covered during the manu~acturing process. The more effectively the sodium ions and other metal c~tions are removed by cation exchange, the ~ore effectively the adsorption of organic acids with a weakly basic anion exchanger can be made.
When the organic substances must be removed practically completely from Fraction A, it is possible to use a strongly basic anion exchanger. This method is particularly suitable in those cases where no acids are available for regenerating a cation exchanger, or cheap acids are not available to a sufficient extent. The prime disadvantage with a strongly basic anion exchanger is that it requires a considerable excess of alkali for the regeneration process.
In accordance with the method of the invention, this problem is resolved by using the eluate from the ion exchanger to re-generate the adsorption resin or resins. It is often expedient to combine the use of a strongly bàsic anion exchanger with the use of a weakly basic anion exchanger, the eluate from the strongly basic anion exchanger normally being used for eluting the weakly basic anion exchange~, and the eluate from the weakly basic ion exchanger being used to regenerate the adsorption resin.

1036~Z3 In the case of a treatment process using the weakly basic anion exchanger, sodium ions are removed from the solution by means of a cation exchanger, for example, in accordance with one of the aforementioned methods. Those wea~ly basic anion exchangers prevlously described with reference to the sorption of sulphite waste liquor and of colored substances in the waste fronl a bleaching section can be used~ The structure of ehese wQakly basic anion exchangers is not known in detail, snd there is much to indicate that the sorption of many substances, for example, substance containing phenolic groups, is not the result of a pure ion exchange, but that other interactions which take place are of critical importance.
Of particular interest are the phenol~formaldehyde resins described in Offenlegungsschrift No. 2,243,141. These are weakly basic anion exchangers, previously used in con~unction with the removal of lignin from pulping waste liquors. They have as the base polymer chain a phenol-formaldehyde polymer unit, and on the phenol ring there are one or more tertiary or secondary amino groups, and also possibly primary amino and quarternary ammonium groups. Exemplary available resins of this type include Duolite~ A-4F, Duolite~ A-6, Duolite~ A-7~ and Duolite~ S-37. All of tbese resins are phenol-formaldehyde base polymers. Duolite~ A-4F and Duolite~ A-6 contain functional groups which are primarily tertiary amines, Duolite~ A-7 functional groups which are primarily secondary amines, and Duolite~ S-37 a mixture of primary and secondary amino groups.
Suitable anion exchangers of the type envisaged are found described in the literature and are commercially available, for example under the trade names AMBERLYST~ (Rohm and Haas Co.) and DUOLITE~ (Chemical Process Co.).

jl/J' -13-According to a preferred embodiment, Fraction A is divided into two fractions, the first raction (i) having a very low chloride content (e. g. liquor from a~ stage or an oxyg~en bleaching stag~e which has been incorporated before the pulp has been treated with chlorine-colltaining a~ents) and a second raction (ii) having a higher chloride content (e. g. from an E-stage after a chloxinating or ClO2 treatment stage). The first fraction (i) is subjected to a treatment process with a strongly basic anion exchanger in hydroxide form to take up organic acids. The second fraction (ii) is treated with a wealdy basic anion exchanger, prePerably subsequent to acidification by one of the aforementionèd methods.
When a weakly basic anion exchanger is used, it is possible, when necessary to activate the anion exchanger, to reduce the chioride ions in a separàte fraction, when necessary, for example, to reduce corrosion risk.
Anion and cation exchange resins have been reviewed by Wheaton and Hatch in Ion Exchange 2 Editor Marinsky published by Dekker, New York 1969 (316 references). The number of exchange groups is from about 1 to about lQ equivalents per kg of anion exchanger or cation exchanger. Adsorption resins are lacking or virt~lally lacking in ionogenic groups. ~dsorption resins can be made hydrophilic by the introduction of a very small amount of cationic ex- -change groups. Their capacity is only from 1 to 10~C of the capacity of conventional cation exchangers.
Examples of adsorption resins are macroreticular p styrene-divinylbenzene copolymer (Amberlite XAD-2) which retains extractives and most of the lignin, and cross-linked acrylic ester 1~367Z3 esin (Amberlite~ XAD-8) which removes polar degradation products from lignin e.g. phenols and aromatic acids, more effectively, and is also used for the uptake of lignin breaking through the first resin bed.
The adsorption resins used can be of the types pre-viously used for the adsorption of lignin, or other adsorption resin types which, as far as is known, have not been used for this purpose but which are suitable for the sorption of non-polar compounts andtor aromatic compounds from dilute aqueous solutions.
The adsorption resin normally comprises a polymer cross-linked with covalent bonds, although other water-insoluble polymers may be used.
Among the adsorption resins that can be used are those deqcribed in Offenlegungsschrift No. 2,243,141 having a baslc polymer chain of phenol-formaldehyde units but not ionic groups.
In place of ionic groups of the amine type, there can be present free phenolic groups on the phenolic ring. An example of this type is Duolite~ S-30 which is a phenol-formaldehyde resin having free hydroxyl groups on the phenol ring.
Also useful are the adsorption resins described in U.S. Patent No. 3,652,407, column 3, line 24 to column 4, line 70.
These are macroreticular polymers of an aliphatic or aromatic character, containing from 2 to 100 weight percent polymerized or copolymerized therewith of a polyethylenically unsaturated monomer such as a polyvinyl benzene monomer including divinyl benzene, trivlnyl benzene, alkyl divinyl benzenes with from one to four aklyl groups substituted on the benæene ring, the alkyl groups having one or two carbon atoms, or an alkyl trivinyl benzene having from one to three alkyl groups substituted on ~ -15-1036~723 the benzene ring, the alkyl ~roups having one or two carbon atoms.
The preparation of such polymers is described in British patent No. 932, 126.
Exemplary alkyl substituted di or trivinyl benzene monomers or similar vinyl toluene monomers includes divinyl xylene, divillyl ethyl benzene, 1, 4-divinyl-2, 3, 5, 6 - tetra-methyl-benzene, 1, 3, 5-trivinyl-2, ~, 6-trimethy~benzene, 1, 4-divinyl-2, 3, 6-triethy~benzene, 1, 2, 4-trivillyl- 3, 5-fliethy~benzene, or l, 3, 5-trivinyl-2-1nethyl-benzene.
Other types of polyethylenically unsaturated monomers include divinyl pyridine, divinyl naphthalene, di-allyl phthalate, ethylene glycol diacrylate, ethylene glycol methyl acrylate, divinyl sulfone, polyvinyl or polyallyl ethers of ethylene glycol, glycerol, pentaerythritol; or monothio or dithio derivatives of glycol or resorcinol; divinyl ketone, divinyl sulf-ide, allyl acrylate, diallyl maleate, diallyl fumarate, diallyl succinate, diallyl carbonate, diallyl malonate, ~iallyl oxalate, diallyl adipate, diallyl sebacate, divinyl sebacate, diallyl tartrate, trially~tri-carballylate, triallyl aconitate, triallyl citrate, triallyl phosphate, N, N'-methylene dimethylacrylamide, N, N'-ethylene.diacrylamide, trivinyl naphthalene and polyvinyl anthracene.
Also useful are monomers prepared from aliphatic materials such as trimethylolpropane trimethacrylate and acrylonitrile~
Exemplary are metal acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, tertiary butyl acrylate, ethyl hexyl acrylate, cyclohexyl acrylate, isobornyl acrylate, benzyl acrylate, phenyl acrylate, alkyl phenyl acrylate, ethoxymethyl acrylate, ethoxyethyl acrylate, ethoxypropyl acrylate, propoxymethyl acrylate, propoxy ethyl acrylate, propoxyprowl acrylate, ethoxyphenyl acrylate, ethoxybenzyl acrylate, ethoxycyclohexyl acrylate and 1036~23 similar esters of methacrylic acid; ethylene, propylene, isobutylene, diiso~utylene, styrene, vinyl toluene, vinyl chloride, vinyl acetate, vinylidene chloride, and acrylonitrileO These materials can be copolymerized with isoprene, butadiene and chloroprene, for example~
. .
Other useEul adsorption resins al~e polyvinylpyrrolidone, polyalrlides such as condensation polymers obtained by polymerization oî caprolactam or by copoymerization of adipic acid and hexamethylene-diamine.
It is particularly suitable to use a cross-linked polymer lQ containing proton-accepting groups, e.g. groups `which participate in hydrogen bonding with protons e. g. phe nolic protons in the solutes to be adsorbed, ester groups and/or carbonyl groups. The proton-accepting ability of chemical compounds of this type can be amplified by synthesizing the compounds in a manner such that the nitrogen atom is placed in the 1~ vicinity of es~er and/or carbonyl groups, for example, so that the nitrogen atom is bound to the same carbon atom as the carbonyl oxygen.
Particularly advantageous results have been obtained when using adsorption resin containing a heterocyclic ring which includes one or more nitrogen atoms. Examples of such groups are pyrrolidone groups. An exaTnple of adsorption resin of this type is polyvinyl pyrrolidone~ The cross-linking agent used may be any unsaturated compound containing two or more vinyl groups or other groups which are l~iown to give cross links, such as divinyl benzene, trivinylbenzene, trivinylnaphthalene, divinylnaphthalene, chloromethylether, and epichlorohydrin. Resins of this type are sold by the General Aniline lE ~ Company under the name of POLYCLA~) ~ .

1036q23 A particularly favorable result has been obtained with macroporous resins. These are in macroreticular form, having a particle width or diameter within the range from 0.15 to 1.19 mm, and in some case~s the particles can be as small as about 0. 037 mm. The preparation of this type of resin is well known from the literature concerning the preparation of macroporous and so-called macroreticular ion exchangers, and a number o~ types o macroporous resins are ~>
commercially available under the name AMBERLITE XAD (R~hm and Haas Co. ). Such a resin AMBERLITE XAD-8, which contains ester groups bound to an acrylate resin, has been found particularly sultable for use for purifying Fraction B and also, subsequent to acidi~ying Fraction ~ with a cation exchanger, for removing aromatic products from Fraction A prlor to the treatment process with an anion exchanger.
This and other adsorption resins of preferred types have the property whereby adsorbed compounds of the types existing in waste water are readily desorbed in aLkalin2 medium. ~n the other hand, the adsorption process should be effected in the vicinity of the neutral point or in an acid environmentO
Fraction 13 normally contains an acidic waste liquor, for example, waste liquor from a chlorination and/or chlorine dioxide treatment process, but it may also contain a waste liquor from an aLkaline stage, such as hypochlorite-and chlorine-containing liquors from an E-stageO The waste liquor from the alkaline stages is normally neutralized or acidified with waste from the acid-bleaching stages.
~5 Acidification, however, can also be effected in other ways, for example, such ways as those mentioned with respect to Fraction A~

1036~723 If it is required to use an adsorption resin having a very high chemical resistance, it is an advantage to use such a resin which substantially laclis polar groups. E~amples of such a resin having~ aromatic structure include a porous (macroreticular) styrene-divinyl benzene resin. Such resins are commercially available (AMBERLITE XAD - 2 and 4). The purification effect obtained with the use of solely this type of adsorption resin is not, in itself, satis-factory, but in combination with ion exchangers according to the method of the invention, a result is obtained which fulfills the stringent requirements regarding the removal of both colored and uncolored substances, and this is at an extremely moderate cost.
The sorbability onto non-polar macroreticular adsorption resins, for example, those which comprise a porous matrix of styrene-divinyl benzene and resins obtained by a copolymerization of other non-polar aromatic compounds such as ethylvinylbenzene, and isobutyl-vinylbenzene can in-many cases be made more effective if a small number of polar groups is incorporated in conjunction with the process of polymerization, and/or by subsequent treatment. Examples include the addition of from 2 to lO~c acrylic acid in the polymerization of nonpolar vinyl compounds, such as divinylbenzene, divinylnaphthalene, and trivinylnaphthalene, preferably in mixture with monovinyl compounds such as styrene and ethylvinylbenzene, or a weak sulphonation, so that approximately 1 to 10% of the aromatic nuclei become sulphonated.
According to these examples, the adsorption resins acquire cation exchange properties, although their capacity in this respect is very low in comparison with commercially available cation exchangers.
The sorption thus does not result from an ion exchange but from an 103~723 adsorption in the widest meaning, and hence the products have been classified as adsorption resins.
Resins other than the aforementioned polar-type adsorption resins can also be usecl. For example, resins containing phenolic hydroxyl g~roups can be used, as can also resins containing amide linkag,es (e.g~ polyacrylamide), both for treating Fraction B
and in coml~ination with an anion exchanger for Fraction A .
When the purification requirements are high, it is particularly suitable to use two or more different types of adsorption ~0 resin, either in mixture, e.g. in a mixed bed, or in separate units, e.g. stationarybeds or movable beds. The combination of a non-polar resin with a resin containing proton-accepting ester groups or a macroporous resin of cross-linked polyvinyl pyrrolidone has been found to be surprisingly effective .
The adsorption resins and ion exchangers are most simply used in the normal manner, in stationary beds, which are re-generàted in accordance with a chosen time schedule, or subsequent to analyses which are carried out automatically or manually. In both cases, the switch between sorption and ~egeneration can be effected manually or automatically. Intermediate washing stages and also the partial return of used eluting agent and buffer containers can be incorporated in a manner known to one skilled in this art.
As with other ion exchange and adsorption methods, the process can be effected continuously, eOgO by moving beds of the solid polymers, in accordance with known methodsO Both the ion exchangers and adsorption resins are sensitive to mechanical contamination, eOg.
with fibers, particles of clay and resin, which may be present in the waste liquor to be treated in accordance with the invention. Consequently, ~l~3~
the waste liquor should be subjected to an effective mechanical purification process in a known manner, Eor example, by filtering with known filters, such as sand filters, fine-mesh net or textile or ceramic filters. The mechanical purification process is effected before the method of the invention is commenced.
When stationary beds of ion exchangers and adsorption resin are used, the beds should be provided with flushing~ means, e. g. water flushing xneans, for flushing away mechanical contaminants in a known nlanner. A trap should be provided for the adsorption resin and ion ex-changers, to prevent losses.
Although generally unnecessary, when local conditions so require a flocculating process and/or chemical treating process with lime may also be carried out.
With regard to the useful life of the polymers, it is important that said polymers are not subjected to significant quantities of active oxidants, for example, chlorine, chlorine dioxide and peroxide. This can be avoided by mixing waste liquor containing active oxidizing agents with agents which react~with these active oxidation agents, so that the oxidizing agents are destroyed. Thus, waste from a chlorinating or chlorine ~dioxide stage, which often contains active chlorine, can be mixed with a suitable quantity o~ the waste liquor from an E-stage and/or with the waste liquor from`a washing stage after the digester, or condensate. The mixture should be stored for a period of time sufficient to ensure that the active chlorine is consumed. Also, SO2 and/or SO2-water can be used for rendering oxidizing agents innocuousO
A suitable storage time is from 0.5 to 2 hours.

1036~7Z3 In addition to the effect of mechanical contaminants and the effect of oxi~ation, the efficiency of ion exchangers and adsorption resins can be reducecl as a result o~ specific substances being more or less irreversibly bound thereto. Examples of such substances are fats and wax-like substances, which are incorporated in the so-called resin in the wood, and which are often modified, for example, chlorinated, during the pulping and bleaching process. Unknown aromatic compounds may also be bound so strongly that no elution can be ef~ected at reasonable cost using normal methods.
. In such cases, the polymers can be reactivated by treatingwith suitable organic solvents, e.g. methanol, ethanol, dichloromethane and/or cymene. Such a reactivation may be effected either in the apparatus (for example, the bed) in which the polymer is used, or by removing the polymer. The reactivation is suitably carried out at intervals of e.g. 0.5 -12 months, depending on the composition of the waste water.
A s the active alkali, sodium hydroxide is often preferred to, for example, sodiumbicarbonate and/or sodium carbonate. It has been surpri~ingly found that, in the case of many types of mills or systems, it is possible to achieve a thorough purification both with respect to colored products and uncolored organic acids by supplying to the regeneration only that quantity of sodium hydroxide which is required to cover the aL~ali losses in the systemO
This is made possible in accordance with the invention by 2~ using sodium hydroxide in at least two stagesO In general, it is most suitable for the sodium hydroxide to be used first for regenerating used anion exchangers and then for regenerating adsorption resin. When a very effective purification result is required, and particularly when the sodium losses have been reduced by different recovery llleasures, it may be necessary and suitable to also use active allcali recovered, for exarnple, subsequent to the combustion of cool~ing~ waste liquors or bleaching waste liquors or mixtures thereo. This is particularly simple with sulphur-freè cooking, for example, oxygen coo~ing and soda cooking, where sodium carbonate is obtained in ash form, or subsequent to wet combustion. Sodium carbonate and/or bicarbonate may also be recovered in a manner known per se from the melt from sulphate and sulphite plants. These compounds can then be used as active alkali for the regeneration of ion exchangers and adsorption resin.
In the case of sulphate mills for which there is a high requirement on the reduction of the biochemical oxygen demand, it is suitable to causticize the recovered sodium carbonate. In the case of a sulphite plant, the recovery and direct use of sodium carbonate or sodium bicarbonate as active alkali for the regeneration (and the sodium hydroxide required to cover the alkali losses) is to be preferred.
Previously known methods for purifying the waste liquors from bleaching sections with anion exchangers have been connected to weakly basic anion exchangers. With the method according to the in vention there is used to advantage a strongly basic anion exchanger in those cases where an effective removal of organic acids is required~
In order to reduce the required quantity of regenerating agent, preferably sodium hydroxide, it is suitable to use those anion exchangers which can be easily rege~erated with alkali. Thus, in the case of normal , ion exchangers containing quaternary ammonium ions (-N ~lR2R3) wherein Rl, R2 and R3 are selected from the group consisting of hydroxyalkyl and alkyl having from one to four carbon atoms. It is preferred that at least one of the three substituents ~l~ R2 and R3 contains a hydroxyl group, e. g. comprises a llydroxyethyl or hydroxypropyl group, the remaining substituents ma~r comprise, for example, methyl, ethyl, propyl or butyl groups.
In accordance with a further embodiment of the invention which has been found to provide particularly advantageous results there is used both a weakly basic and a strongly basic anion exchanger, sodium hydroxide being used first to regenerate 1:he strongly basic anion ex-changer and then to regenerate the weal~ly basic anion exchanger and finally to reg~aerate one or more adsorption resins. When proceeding in this manner the purification effect can be equally as good as that when using solely a strongly basic anion exchanger, while considerably reducing the cost of the regeneration.
Irrespective of how the invention is applied, it can be suitable for the active alka.li used for the regeneration to have the form of waste liquor obtained from an oxygen bleaching and/or alkaline refine-ment and/or extraction stage, optionally made up with sodium hydroxide.
This embodiment is particularly suitable when the eluate from the ion exchanger and adsorption resin is to be burned or vaporized or wet-burnedO E waste liquor from a hot-alkali extraction stage or normal oxygen bleaching stage is used, suitable quantities of alkali, for example, sodium hydroxide, should be added to improve the elution, while when cold-alkali refinement waste liquor is used, make up with active aLkali is generally unnecessaryO

`- ~036723 A suitable portion of the eluate obtained after the regenera-tion of anion exchanger may be optionally returned to the system, and used for further elution of anion exchangers, prlor to bemg used wholly or partially for the regeneration of adsorption resin or resins. The

5 eluate can then be used, except for evaporation and combustion or wet-combustion, separately or in mixtùre with cooking waste liquor as a ~rash water, e.g. for a lime-sludge washing process, and for dissolving ash obtained subsequent to a combustion process, or for adding~ water to the pulping and bleaching process in any other way so that the organic 10 substance is directly combusted or combusted in a later stage. A
typical example in this respect is the use of the eluate for displacing cooking waste liquor subsequent to the termination of a cooking process.
Between the regeneration stage and a subsequent sorption stage it is suitable to wash both the anion exchanger and the adsorption 15 resin with water or diluted aqueous solution. The whole or part of the weak liquor thus obtained can be returned and, subsequent to make up with active alkali, can be used for regeneration purposes~ The weak liquors may also be fractionated and used in accordance with the counterflow principle, so that the losses are low and the concentration as high as 20 possible. Weak liquors (used wash water)can be used to replace water in the pulping and bleaching process, e.g. for washing pulp, lime-sludge or for similar purpqes.
The invention will now be illustrated by means of a number of Examples, which represent preferred e~odiments of the invention~ -~0367~3 Example 1 In a sodium-based sulphite mill there was manufactured both paper pulp and hot-alkali refined rayon pulp, according to the sy~tem shown in Figure 1. The wood was digested in a digester 1, and the resulting pulp wa.s washed in a washer 2, so that 97~c of the solids was recovered.
5 The washed pulp was then passed to a closed screening station 3, from which there was no discharge. The pulp was passed ~rom the screening station 3 to a press 4, in which it was squeezed to a solids content of 30%.
The pulp was then transferred to a.n alkaline extraction sta.ge 5, which 10 comprised the first bleaching stage in the bleaching section,where the pulp wa.s all~ali extracted. In the bleaching section the pulp was then chlorinated in a chlorinating stage 6, and then subj ected to a mild extrac-tion in an extraction stage 7, treated with chlorine dioxide in a chlorine dioxide treating stage 8, and with hypochlorite in a hypochlorite stage 9.
Waste liquor from the extraction stage 5 was recycled thereto, and was also used in aknownmanner for washing the un-bleached pulp.
In this way there was utilized approgimately 20% of the solids content as fuel, in conjunction with the combustion of the 20 sùlphite waste liquor, and a corresponding recovery of alkali used in the extraction stage 5 was obtained.
The remaining portion of the waste liquor from the a~ali extraction stage 5 together with the wash water from the washer 2, which could not be returned, comprised Fraction A in accordance with the in-25 vention, and was passed to the container A
In the bleaching section B, washing was effected betweenstages in a manner such that the quantity of waste~water was moderate, ~;Q367Z3 without jeopardizino~ the quality of the pulp. In this respect counterflow washingwas.-applied, in a. manner known per se. The mixed waste liquors from the bleaching sta.ges and the washing stages was passed to container B, this mixed waste liquor comprising~ Fraction B, in a.ccordance with the invention.
Fraction A, which had a pH of approxima.tely 10, was passed from container A to a sand filter 10, and, subsequent to passing through sa.id filter, to a bed al of a weakly acid cation ex-changer of the carboxylic acid type in free acid form (AMBERLITE
, . .
IRC-50 Rohm and Haas Co. ) produced by copolymerization of acrylic acid and divinylbenzene, the pH being lowered to approximately 3. The acidified fraction was then passed through a bed a2 of an adsorption resin (Macroporous styrene-divinyl benzene resin, AMBERLITE XAD-4, Rohm & Haas Co.) where approximately 50% of the colored substance in the faction was sorbed, while more than 90% of the substance which exhibited a biochemical oxygen demand (BOD7 ) passed through. The effluent from the adsorption resin bed a2 was passed through a strongly acid cation exchanger a3 of the sulphonic acid type, substantially in hydrogen form (DOWEX 50X-8, Dow Chemical Process Co. obtained by sulphonation of a copolymerizate of styrene and divinylbenzene (8%
divinylbenzene), sulphonated to obtain an exchange capacity of about 5 equivalents of per kg dry resin = 5 mmol sulphonic acid groups per kg dry resin). The majority of the remaining sodium ions were removed in this way.
The effluent from the cation exchanger a3 was passed through a macroporous anion exchanger a4 containing weakly basic groups (amino groups) and having a structure such that colored sub-stances of the lignin type were bound by the ion exchanger (DUOLITE A6, 1~36~23 Diamond Sllamrock Chemical Co. a macroporous anion exchange resin with phenolic matri~ containing mainly NH2-groups as anion exchanging groups~ said ion exchanger having been previously described as suitable for sorption of sulphite waste li~uor and for colored substances in waste li~uor from the bleaclling section~ Unlike effluent which had been treated solely with ~dsorption resin, or solely with anion e~changer, the effluent from the bed a4 could be used for preparing cooking acid, which affords considerable advantages.
During this treatment, there was removed a total of 10` approximately 95% by weight of the colored substances, primarily lignin, and approximately 90% by weight of the total organic substance in Fraction A arriving from the bleaching section. Sugar present in Fraction A, said sugar originating practically totally from the cooking waste liquor, was still present in the effluent from the anion exchanger a4. If desired, this sugar can be eliminated by adsorption on a strongly basic anion exchanger, not shown in Figure 1. The sugar present in the effluent from the anion exchanger a4, however, was not deleterious when the thus-purified Fraction A was used for cooking acid preparation process.
The color of the effluent was determined automatically and the volume of the resin bed chosen so that 50 bed volumes of ~action A
were puriied before breakthrough the bed reached an average level of 5%.
Fraction B was passed through two series-connected buffer containers 11 and 12, the resident time of the Fraction B in said containers being of such duration that active chlorine present in said Fraction B was destro~7ed. Suitable residence times in this respect are from 0. 5 to 2 hours. The Fraction 13 was then passed through a sand filter 13, and through two series-connected beds of 1036!723 adso~ption resin. The first bed bl contained a non-polar macroporous adsorption resin of the styrene-divinyl benzene type (~MBERLITE
~ 1~ 1t XAD-4 Rohm & Haas Co.), while the second bed b2 contained a macroporous adsorption resin of t~ie acrylic ester type (AMBERLITE X~D-8, Rohm & Haas Co.). The conditions were so adjusted that approximately 90%
by weight of the colored substances in Fraction B was adsorbed. In this way more than half of the chemical o~ygen demand was eliminated, while the eEfect on the biochemical oxygen demand was lower. The volume of the resin beds was chosen so that 200 bed volumes of Fraction B were lO purified before an average breakthrough the bed reached 10%. The effluent from the bed b2 was rich in chloride, and was allowed to pass to waste.
The sodium ions taken up by the cation exchangers _1 and a3 wère used in the process in a manner known per se for preparing 15 cooking acidO Instead of fresh water being used, the flow from container a4 was also used for preparing the SO2-water in container 15 used for the regeneration of cation exchangers al and _3 The path travelled by the eluted liquid is marked by dashed lines in Figure 1 O The fresh SO2-water was caused to pass first through the strongly acid catidn 20 exchanger of sulphonic acid type _3 and then through the weakly acid cation exchanger of carboxylic acid type _1 After make-up with sodium ions and SO2 or SO2-containing solution, the eluate from al was used as a cooking acid.
The regeneration of the anion exchanger _4 and adsorp~ion 25 resin bed a2 was effected by means of aqueous sodium carbonate ~olution obtained by separating sodium sulphide and sodium carbonate from the melt obtained in the combustion of waste liquor by a fractionated water leaching process, wherewith sodium carbonate was obtained in solid form and sodium sulphicle in aqueous solutionO The sodium carbonate soiution, which was ~repared in container 14 from solid sodium carbonate and returned wash ~vater, and contained 100 grams of Na2CO3 per liter, 5 ~vas passed to the bed of weakly basic anion exchanger a4.
The first portion of the eluate from a4 was used to re-generate the adsorption resin beds a2, bl and b2, in that order, while the latter portion of the éluate rom a4was returned and used in the next elution cycle, as a first elution agent for the anion exchanger _4 and the 10 adsorption resin beds a2, bl and b2, followed by fresh sodium carbonate solution.

The eluate from the adsorption resin bed b2, which had been diluted with solution remaining in the beds, was evaporated and com~usted together with the coo~ing waste liquorO In order to obtain a 15 more complete elution, a solution containing 50 g of NaOH per liter was also passed through the anion exchanger a4 and the adsorption resin beds a2, bl and b2 in that order . Subsequent to wa shing with water, which was then partially returned to the process, the eluate was burned to-gether with the eluate obtained with the carbonate elution processO The 20 flow rate in the sorption stages was approxim~tely 12 bed volumes per hour in the sorption stages and approximately one bed volume per hour in the regeneration and washing stagesO
Both of the Fractions A and B were, in accordance with this embodiment, purified effectively with respect to colored sub-25 stances, primarily lignin, fromboth the bleaching section and thecooking sectionO The purificatiQn with respect to non-colored organic acids, which were the prime source of BOD of the bleaching sequence, 10367;Z3 was effective in respect of Fraction A, but not in res~)ect of Fraction B, where the major portion of the organic acids passed to waste together with the chloride, as in previously known methodsO
With the method accorcling to the invention, however, 5 the fractions could be selected so that the quantity of organic acids was ~mall in Fraction B, as compared witll Fl~action ~
When al)l)lied to the manufacture o~ rayon pulp in accordance with the foregoing, 90~ or more of the non-colored organic acids were obtained in Fraction A. Approximately 90~ of these acids 10 were recovered, which means that more than 80~ of the total quantity of organic acids were removed. In addition, there was recovered approximately 90~ of the colored substances from the bleaching section and the major portion of the cooking liquor residues, which otherwise normally pass to the discharge system.
Example 2 The method described in Example 1 was repeated with the exception that an extra bed of porous, cross-linked polyvinyl-pyrrolidone resin (Polyclar AT, polyvinyl pyrrolidone cross-linked with divinylbenzene) was arranged after the strongly acid cation exchanger a3, 20 and the po. ous, wea'r~ly basic anion exchanger a4 was replaced by a con-ventional non-porous or low-porous anion exchanger of the weakly basic type, styrene-divinylbenzene resin (8~o divinylbenzene) subjected to chloromethylation and subsequently reacted with a mixture- of polyamines to introduce amine groups. Exchange capacity 5. 5 milliequivalents per g 25 of dry resin, Dowex 3, Dow Chemical Co. An elution process using active alkali was effected in the following order: anion exchanger, PVP-resin, a2,bl and b2. No change was obtained in the purification effect. Although the 1036!723 purification effect remained unchanged and the volume of the anion ex-chantrer was the sallle, the time intervals between the regeneration processes could be increased by 20~, from five hours to six hours.

Example 3 The method described in Example 1 was repeated, with the exception th~t the strong acid cation exchanger -~ was omitted. The purification effect witll respect to non colored orgallic acids in Fra~tion was reduced by approximately 30~, although surpri singly the sub-stances which prevent the use of a non-anion exchanged Fraction A for the preparation of cooking acid were so completely eliminated that the fraction purified in this way could be recycled for the preparation of cooking acid.
Example 4 In a sulphate cellulose mill employing a bleaching sequence including chlorination in the chlorinating stage 1, extraction in the extraction stag~e 2, hypochlorite in the hypochlorite stage 3, chlorine dioxide in the chlorine dioxide stage 4, extraction in the extraction stage 5, chlorine dioxide in the chlorine dioxide stage 6 according to Figure 2, where the body of water into which wastes were discharged was extremely sensitive to colored substances, but less sensitive to non-colored organic substances, the dischar~e from the first extraction stage 2 was incorporated in Fraction A, in accordance with the inven-tion, and passed to the container A. The fraction was then acidified to pH 3 by passage through a bed al containing a carboxylic acid-type cation ex-B
changer (AMBERLlTE IRC-50, Rohm & Haas Co~) . The fraction was then passed through a bed _2 containing a styrene-divinyl-benzene -~ 36723 type non-polar adsorption resin AMBEP~LITE XAD-4, Rohm & Haas Co.) and a bed a3 of an adsorption resin having ester gl'OUpS (~MBERLlIE@) XAD-8, I~ohm & Haas CoO), and finally through a bed a4 containing a low-porous weakly basic anion exchanger (DUOLITE, Chemical Process 5 Co.).
The discharges from the hypochlorite stage 3, the chlorine dioxide stage 4, the extraction stage 5 and the chlorine dioxide s`tage 6 wère collected in a container B, ànd comprised Fraction B in accordance with the invention. The fraction was filtered and 10 caused to pass through two beds b1 and b2 containing the same adsorp-tion resin as the beds bl and b2 in Example 1. The discharge from b2 was rich in chloride, and was passed to the discharge systemO
By means of the treatment process, about 90~ by weight of the colored substance in Fraction B was ~emovedO This was also 15 effected in respect to Fraction A, but in this case about 50~ of the uncolored organic acids were also removedO
The regeneration process was effected by passing aqueous sodium hydroxide solution from the container 7 to the beds in the order a4, a3, a2, bl and b2. The eluate was combined with the cooking waste 2~ liquor and burned together therewith.
When it was necessary to increase the recovery of non-colored organic substances, Fraction A was acidified with a sulphonic acid type cation exchanger (not shown in Figure 2)o The weakly acid cation exchanger in the bed _1was regenerated with C02-water under 25 pressure, while the sulphonic acid-type cation exchanger was regenerated with waste acid, which thereafter passed to the bed _1 ~bout 80'~ of the organic acids in Fractlon A was removed by these measures.

Example 5 In the sa~ne sulphate mill as tllat rcferred to in Example 4, Fraction A was passed to a bed of strongly basic anion exchanger in hydroxide ~ (DOWEX 2-X8 CH

HOCH~CF~- - ... N

dimethyl-hydroxy-èthylamine). The effluent from the bed was mixed with Fraction B, and the mixture passed to a bed of adsorption resin lU AMBERLITE XAD-8.
The regeneration process was effected with aqueous sodium hydroxide solution, which was first passed mrough the anion exchanger and then the bed of adso~ption resin, and was so adjusted that the take-up of colored substances was efEected to 90%, and the take-up of organic uncolored acids to about 40%.

3~

Claims (22)

Having regard to the foregoing disclosure, the following is claimed as the inventive and patentable embodiments thereof:

1. A method of purifying aqueous waste liquors from cellulose plants, in which organic substances are sorbed on water-insoluble polymers and recovered by elution, which comprises contacting with at least one organic anion exchanger a first aqueous waste liquor having a low content of inorganic anions and containing organic acids and organic nonionized substances and sorbing thereon organic acids and organic nonionized substances; and contacting a second aqueous waste liquor having a high chloride content and containing aromatic compounds with at least one adsorption resin and sorbing aromatic compounds thereon while the chloride ions remain in the solution; eluting organic acids and organic nonionized substances by contacting the anion exchanger with an aqueous alkali solution; and eluting aromatic compounds by contacting the adsorption resin with the same aqueous alkali solution.

2. A method according to claim 1, in which the alkali solution is aqueous sodium hydroxide, which after elution is recycled to replenish sodium losses in the cellulose plant.

3. A method according to claim 1, wherein the first aqueous waste liquor comprises waste liquor from an alkaline extraction stage in the bleaching sequence.

4 . A method according to claim 1, wherein the first aqueous waste liquor comprises waste liquor from an oxygen alkaline bleaching sequence.

5. A method according to claim 1, wherein the first aqueous waste liquor is treated with an adsorption resin in addition to the treatment with anion exchanger.

6. A method according to claim 5, wherein the aqueous alkali solution after contact with the anion exchanger is contacted with the adsorption resin.

7. A method according to claim 1, wherein the first aqueous waste liquor at the conclusion of the purifying process is used at least in part for the preparation of a member selected from the group consisting of cooking liquors, bleaching liquors, and wash liquids in the cellulose plant.

8. A method according to claim 1, wherein the first aqueous waste liquor is in addition contacted with a cation exchanger in hydrogen form for removal of sodium ions.

9. A method according to claim 1, wherein the pH
of the first aqueous waste liquor is brought to within the range from about 1 to about 8, prior to contact with an anion exchanger.

10. A method according to claim 9, wherein the pH
is lowered by contacting the first portion with a cation exchanger in hydrogen form.

11. A method according to claim 1, wherein the first aqueous waste liquor is contacted with a strongly basic anion exchanger.

12. A method according to claim 1, wherein the first liquor is contacted with a strongly basic anion exchanger for taking up organic acids, and the second liquor is contacted with a weakly basic anion exchanger.

13. A method according to claim 1, wherein the adsorption resin is a cross-linked polymer containing proton-accepting groups selected from the group consisting of ester groups and carbonyl groups.

14. A method according to claim 13, wherein the adsorption resin contains nitrogen atoms in addition to ester groups and/or carbonyl groups.

15. A method according to claim 14, wherein the adsorption resin contains nitrogen atoms in a heterocyclic ring.

16. A method according to claim 1, wherein the adsorption resin comprises a porous styrene-divinyl benzene resin.

17. A method according to claim 1, wherein the adsorption resin comprises a non-polar porous matrix of styrene-divinyl benzene having a number of polar groups.

18. A method according to claim 1, wherein two adsorption resins are used.

19. A method according to claim 1, wherein the active alkali in the aqueous alkali solution is sodium hydroxide, which is first contacted with the anion exchanger, and then with the adsorption resin.

20. A method according to claim 19, wherein the anion exchanger comprises a strongly basic anion exchanger and a weakly basic anion exchanger.

21. A method according to claim 1, wherein the active alkali in the aqueous alkali solution is an alkaline waste liquor from an oxygen alkaline bleaching sequence.

22. A method according to claim 1, wherein the active alkali in the aqueous alkali solution is an alkaline extraction stage in a bleaching sequence.