US3490990A - Digestion of lignocellulosic materials with an organomercaptan and a hydrotrope - Google Patents

Description

United States Patent 3 490,990 DIGESTION 0F LIGNOCELLULOSIC MATERIALS WITH AN ORGANOMERCAPTAN AND A HYDROTROPE Carl A. Johnson, Toledo, Ohio, assignor to Owens- Illinois, Inc., a corporation of Ohio No Drawing. Filed Dec. 30, 1966, Ser. No. 606,024 Int. Cl. D21c 3/20, 3/04 US. Cl. 162-76 25 Claims ABSTRACT OF THE DISCLOSURE Methods of pulping lignocellulosic material with an organomercaptan by digesting the lignocellulosic material with a treating liquor of an organomercaptan and a hydrotrope agent and continuing the digestion at a temperature and for a period of time to convert the material to a treated material which at least initially contains organomercaptan-reacted lignin.

This invention relates broadly to the art of treating lignocellulosic materials. More particularly it is concerned with such a treating or so-called pulping process wherein a lignin-reactive organomercaptan, e.g., thioglycolic acid (TGA) HSCH COOH, is employed in conjunction with a hydrotrope agent, that is, in a hydrotroping system, to cook or digest wood or other lignocellulosic material. The thioglycolic acid and/ or other organomercaptan are used under differing conditions whereby one can obtain, merely by varying the treating conditions, chemical cellulose, a moderate yield pulp (e.g., 60-69%) of good quality, or a high-yield pulp (e.g., 70-80%) as desired or as may be required by the particular end-use. Surprisingly and unobviously the isolated lignin resulting as a by-product of the process is characterized by a form which is very similar to the orientation or configuration that lignin is believed to possess when it is in its natural or unisolated state in the wood.

In the usual overall process of pulping lignocellulosic material, e.g., wood, the steps generally include 1) the initial step of treating the wood in chip or other subdivided form with a solvent to remove extractives and to leave a solid residue of lignin-holocellulose (lignocellulose); and (2) treating the resulting lignocellulose with a solvent that selectively dissolves lignin and leaves holocellulose (and usually also some lignin) as a solid residue or pulp.

The known pulping processes may be classified as:

(A) Mechanical pulping wherein separation of lignin from holocellulose is eflFected by grinding to give mechanical pulp (groundwood) in high (90-95%) yield.

(B) Chemical pulping, which involves cooking the wood with highly reactive inorganic chemicals to convert the lignin to water-soluble derivatives containing such solubilizing groups as -ONa, SNa and SO Na. Typiv cal chemical processes are:

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(C) Semi-chemical pulping in which a first mechanical treatment and a second chemical treatment are used.

(D) Bjorkman pulping and hydrotrope pulping wherein lignin solubilization is achieved by a chemical treatment but without the chemical bonding of solubilizing groups to the lignin. In Bjorkman pulping lignin is removed by milling the wood with toluene and extracting the residue with dioxane and water. In conventional hydrotrope pulping, a salt, e.g., sodium xylene sulfonate (SXS), is used (specifically in the form of an aqueous solution) to increase the Water-solubility of the lignin. The nature of the salt-lignin interaction is unknown, but chemical bonding is not involved.

The treating or pulping method of the present invention falls into no single category or classification of the conventional pulping classes such as those outlined above. In marked contrast it is a unique and unobvio-us combination of (1) a specific form of a chemical treatment and (2) a conventional hydrotrope agent such as a solution of SXS and/or a hydrotrope-like agent, e.g., ethylene glycol and dimethylsulfoxide. For ease in description the term hydro-trope agent is used herein specifically as well as generically to include hydrotrope-like agent unless it is clear from the context that the latter meaning (namely, a specific form of hydrotrope agent) is intended. By hydrotrope-like agent is meant a treating agent that performs the same function as a conventional hydrotrope agent in a wood-pulping process.

It was known prior to the present invention to pulp wood, specifically spruce sawdust, by treatment with an organomercaptan, more particularly TGA. See, for example, Ingeni-tirs Vetenskaps Akademien, Proceedings No. 103, pp. (1930), The Mercaptans of Pine Wood, by Bror Holmberg. Holmbergs procedure was to treat, for instance, spruce sawdust with a TGA solution containing hydrochloric acid. In a second step the mercaptanreacted lignin was extracted by treating the TGA-digested wood with an aqueous solution of caustic soda, specifically at room temperature.

The present invention is based on my discovery that a hydrotrope system containing an organomercaptan, e.g., (a) TGA; (b) a hydrotrope agent, e.g., SXS; and (0) water (when a. conventional hydrotrope agent, i.e., one of the aqueous salt type is employed) provides a more specific delignification process having a wider degree of flexibility as to the yield and character of pulp obtained than a system containing TGA, water and hydrochloric acid.

In practicing the present invention any raw lignocellulosic material (that is, any wood or woody material, or mixtures thereof in any proportions) may be cooked or digested with ingredients including an organomercaptan and a hydrotrope agent, with or without first removing the extractives by treating the lignocellulosic material in subdivided form (e.g., in the form of sawdust, shavings, wafers and/or chips) with an organic solvent capable of extracting the organic solvent-soluble components of the material. Such lignocellulosic materials include softwoods, hardwoods and fibrous annual plants. Examples of softwoods are balsam fir, Eastern hemlock, jack pine, Eastern white pine, red pine, black spruce, red spruce, white spruce, tamarack and cypress. Examples of hardwoods are black gum, quaking aspen, mixed tomahawk, American beech, paper birch, yellow birch, Eastern cottonwood, sugar maple, silver maple, yellow poplar, black cherry and white oak. Examples of fibrous annual plants are bagasse, hemp and jute. Mixtures of woods or other lignocellulosic materials of diiferent origin may be used if desired, e.g., mixtures of different softwoods, or of different hardwoods, or of one or more softwoods and one or more hardwoods.

THE ORGANOMERCAPTAN REACTANT Illustrative examples of organomercaptans that may be used in conjunction with a hydrotrope agent in digesting wood in accordance with this invention are those embraced by the general formula wherein R represents a divalent radical, more particularly a divalent hydrocarbon radical, Y represents a monovalent substituent bonded directly to R, and n represents a numeral ranging from up to the combining power (i.e., a value that will completely satisfy all valences) of the divalent radical represented by R.

Illustrative examples of divalent radicals represented by R in Formula I are divalent hydrocarbon radicals and, more particularly, divalent aliphatic, especially divalent saturated aliphatic, e.-g., ethylene, propylene (trimethylene), butylene, isobutylene, pentylene, isopentylene, decylene, etc., including divalent cycloaliphatic, especially divalent saturated cycloaliphatic, e.g., cyclopentylene, cyclohexylene, cyclohepthylene, etc.; divalent aromatic, e.g., phenylene, naphthylene, etc.; divalent aliphatic-substituted aromatic, e.g., 2,4-tolylene, ethyl 2,5 phenylene, isopropyl 3,4 phenylene, 1 butyl 2,4 napthylene, etc.; divalent aromatic-substituted aliphatic, e.g., phenylethylene, phenylpropylene, naphthylisobutylene, xylylene, etc.; and radicals that may be classed either as divalent aromatic-substituted aliphatic or divalent aliphatic-substituted aromatic, e.g., 4-,alpha-tolylene, 3, betaphenyleneethyl, 4,alpha xylene, 2,gamma phenylenebutyl. etc. Thus R may represent a divalent hydrocarbon radical represented by the general formula where Ar represents an arylene radical and R represents an alkylene radical. Preferably the divalent hydrocarbon radical represented by R contains not more than carbon atoms, more particularly from 1 to 8 carbon atoms.

Preferably, also, the divalent radical represented by R in Formula I is free from olefinic or acetylenic unsaturation either in a straight chain or in a side chain.

It is not essential that the divalent radical represented by R be composed solely of carbon and hydrogen atoms. For example, the chain of carbon atoms, whether straightchain aliphatic or carbocyclic, may be interrupted in the chain by other atoms, e.g., by oxygen and/or sulfur and/ or nitrogen atoms bonded directly to carbon atoms of the chain.

Illustrative examples of substitutents represented by Y in Formula I are functional groups such as OH; -CN; SH; COOH; -COOR', wherein R is a monovalent hydrocarbon radical corresponding to the divalent hydrocarbon radicals represented by R in Formula II; COOM, wherein M is a salt-forming cation, e.g., N I-I or Na, K, Li or other alkali metal, a salt-forming amine such as a mono-, di-, or tri-(hydrocarbon-substituted) or -(hydroxyhydrocarbon-substituted) amine, or other salt-forming cation and especially those which yield watersoluble salts when present in the particular thio compound. Or, Y may be radical represented by wherein R" and R' are members of the group consisting of hydrogen and monovalent hydrocarbon radicals corresponding to the divalent hydrocarbon radicals represented by R in Formula I.

4 It will be understood, of course, by those skilled in the art that when n in Formula I represents zero (0), then there are no radicals represented by Y in the formula which latter then becomes (III) HSR wherein R represents a monovalent radical, more particularly a monovalent hydrocarbon radical corresponding to the divalent hydrocarbon radicals represented by R in Formula I. Illustrative examples of mercapto compounds embraced by Formula III are the alkyl (including cycloalkyl), aralkyl, aryl and alkaryl mercaptans, more particularly those which contain from 1 through 10 carbon atoms and especially those having not more than about 8 carbon atoms.

The relatively low water-solubility of the unsubstituted hydrocarbyl mercaptans embraced by Formula III makes them much less suitable for use than substituted hydrocarbyl mercaptans having one or more polar or solvating substituent groups. However, if water-solubility of the mercapto reactant is unimportant, e.g., when it is to be used in undiluted state, or in solution in an organic solvent (e.g., ethanol) or in a mixture of water and an organic solvent in which mixture the unsubstituted hydrocarbyl mercaptan is adequately soluble, then a mercaptan within the scope of Formula III may be employed as a treating agent.

Particularly useful in practicing the present invention are organomercaptans represented by the general formula wherein Z represents an alkylene (including cycloalkylene) radical containing from 1 through 10 and preferably from 1 through about 8, carbon atoms; R represents a member of the group consisting of (a) hydrogen, (b) alkyl radicals containing not more than about 10 carbon atoms and preferably a lower alkyl radical (e.g., an alkyl radical containing from 1 through about 6 carbon atoms); and (c) a salt-forming cation, examples of which have been given hereinbefore with reference to M in the grouping COOM which may be a substituent represented by Y in Formula I; and n represents an integer from 1 up to that of the combining power of the alkylene radical represented by Z. The alkylene radical represented by Z may be straight-chain, branchedchain or cyclic as in, for example, cyclopentyl, cyclohexyl and the like.

More specific examples of mercapto compounds embraced by Formula IV are monocarboxylic and polycarboxylic acids such as those having the formulas (v1) HSCHCH2-COOII coon (v11) ns-cn-c o 011 (VIII) sumo-coon (IX) rrs-o oHn-cHT-c 0 on (x) ns-cn-co on Hr-COOH wherein n represents an integer from 1 to 6, inclusive, more particularly from 1 to 4, inclusive, and R has the same meaning as given above with reference to Formula IV. Thus, compounds embraced by Formula XI may be the thio acid itself or a salt (especially a water-soluble salt) or an ester of such an acid. Of these compounds thioglycolic acid and the water-soluble salts and the lower alkyl esters thereof are the more preferred sub-group. Mixtures of acids and/or salts and/0r esters embraced by Formula XI may be used if desired.

Instead of using organomercaptan compounds that are within the scope of Formula XI, one may employ those wherein the -COOR group in that formula has been replaced by other hydrolyzable or solvating groups such wherein R" and R' in the last two groups are hydrogen or a monovalent hydrocarbon radical corresponding to one of the divalent hydrocarbon radicals represented by R in Formula I.

THE HYDROTROPE AGENT Conventional hydrotrope agents (hydrotropic solutions) have been defined as those aqueous salt solutions which effect decidedly greater solubility of slightly soluble substances than does pure water at the same temperature [referencez McKee, Use of Hydrotropic Solutions in Industry, Ind. and Eng. Chem., 38, 4 (1946)]. McKee describes this phenomenon as being the reverse of the common salting-out effect following the addition of many electrolytes to aqueous solutions of numerous solutes This salting-in, as opposed to salting-out, effect is best shown by concentrated aqueous solutions of very soluble salts of organic acids, with organic substances as solutes which have a low solubility in water Typical of these hydrotropic salts are the alkali or alkaline earth salts of the sulfonates of toluene, xylene, or cymene, the alkali benzoates, thiocyanates, and salicylates, and, for some compounds (particularly inorganic), even such common salts as the alkali bicarbonates, oxalates, and thiocyanates.

Among the conventional hydrotrope agents that are particularly useful in carrying the present invention into effect are the alkali-metal salts, especially the sodium salt, of xylene-sulfonic, cymenesulfonic and benzoic acids; and, of these, the sodium salt of xylenesulfonic acid is preferred.

Illustrative examples of hydrotrope-like agents, in addition to the aforementioned ethylene glycol and dimethylsulfoxide, that may be employed are: n-hexyl Cellosolve (ethylene glycol mono-n-hexyl ether), n-hexyl Carbitol (diethylene glycol mono-n-hexyl ether), di-n-butyl Carbitol [bis(beta-n-butoxyethyl) ether], isophorone, n-butanol, Z-ethylhexanol, pyridine, dimethyl-formamide and dimethylacetamide.

Instead of using a single conventional hydrotrope agent, one may employ a plurality (2, 3, etc.) of such agents; or a plurality of hydrotrope-like agents in place of only a single such agent; or a mixture of one or more conventional hydrotrope agents and one or more hydrotrope-like agents in any proportions.

The hydrotrope-like agents, numerous examples of which have been given hereinbefore, are not the full equivalent of conventional hydrotrope agents, e.g., sodium xylene sulfonate (used in the form of an aqueous solution), in practicing the present invention.

6 TREATMENT OF RAW LIGNOCELLULOS IC MATE- RIAL WITH A COMBINATION OF AN ORGAN- OMERCIAPTAN AND A HYDROTROPE AGENT The treatment of raw lignocellulosic material with an organomercaptan is described in, for example, the aforementioned Holmberg publication. Other methods of treating wood and other lignocellulosic materials with an organomercaptan are described in, for instance, the copend ing application of William E. Fisher and Shibley A. Hider, Ser. No. 605,978, filed concurrently herewith, assigned to the same assignee as the present invention, and which by this cross-reference is made a part of the disclosure of the instant application.

The treating liquor used in practicing this invention contains a reactive agent comprised of at least one organomercaptan, preferably TGA and/or a water-soluble salt thereof, dissolved or dispersed in a liquid reaction medium comprised or consisting essentially of a hydrotrope agent. The concentration of the organomercaptan in the aforesaid liquid reaction medium cannot be stated with precision since it is dependent upon so many different influencing factors including, for example, the kind of wood or other lignocellulosic material being digested; the nature of its subdivided form; the ratio between the organomercaptan and the lignocellulose; the temperature and pressure of digestion; type of digester employed; and other influencing factors. Generally, however, the organomercaptan constitutes, by weight, from about 1% to about 14%, more particularly from about 2% to about 6%, of the weight of the liquid reaction medium containing the hydrotrope agent.

The digestion may be carried out (or initiated and then continued) under acid, neutral or alkaline conditions. Thus, the treating liquor during the period of digestion may vary within the pH range of from about 2.0 to 14.0; or the liquor may have an alkalinity greater than a pH of 14.0, in which case the alkalinity may be expressed in terms of the percentage of the particular basic substance in the liquor or in any other suitable terms.

The alkalinity of the treating liquor is adjusted to the desired level by adding any suitable acid or base in the amount required to attain the desired level if it is not already at that point. Thus one may use such inorganic acids as, for example, hydrochloric, sulfuric, sulfurous or phosphoric acids; or organic acids such as benzoic acid, benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, cymenesulfonic acid, or a chloroacetic acid including diand trichloroacetic acids. Or, when required, one may employ for alkalinity-control (specifically pH-control) purposes an alkali-metal hydroxide, preferably sodium hydroxide, or other suitable inorganic base.

Chemical treatment of raw lignocellulosic material with a treating liquor comprising an organomercaptan and a hydrotrope agent may be effected at a temperature within the range of, for instance, from 70 C. (preferably at least about 100 C.) to 200 C., more particularly from about to 190 C., and still more particularly at from about -180 C. The time of treatment varies, for example, from A2 to usually 4 or 5 hours but which sometimes may be 6 or 8 hours or more. This time period and the reaction temperature depend upon such influencing factors as, for instance, the type and degree of sub-division of the lignocellulosic material being treated, the chosen organomercaptan and hydrotrope agent, the amount and concentration of the organomercaptan compound, whether or not the initial digestion period is to be followed by a second extraction-stage whereby lignin is extracted from the Wood, the type of product desired, the type and size of digester used, and other influencing factors.

The concentration of organomercaptan, e.g., TGA, in the treating liquor with respect to the oven-dried (O.D.) lignocellulosic material should be at least about 5% by weight thereof. Thus, it may be, for example, from about 5% to about 100%, more particularly from about 10% to about 50%, by weight of the OD. lignocellulosic material charged to the digester.

The organomercaptan component (i.e., a single organomercaptan or a plurality of different organomercaptans) may be the only reactive agent used in conjunction with a hydrotrope agent to constitute the treating liquor; or, the said organomercaptan component may be employed in the form of an admixture with a minor amount (less than 50% by weight of the admixture) of an inorganic thio reactant, e.g., sodium sulfhydrate (NaSH), sodium sulfide, sodium polysulfide, etc.

One of the advantages of the method of the instant invention is the flexibility with which it lends itself to the obtainment of highor moderate-yield pulps or alphacellulose merely by changing such operating parameters as pH, time and temperature of digestion, and amount of TGA and/or other organomercaptan employed. Furthermore, the method makes possible the recovery of a relatively high proportion of the organic material that is left in the treating liquor.

In other words, the operating parameters can be varied to obtain lignin and/or pulp or cellulose residue having the desired properties. The conditions can be varied to produce pulp (hence also paper) having a wide range of physical properties; and, additionally, a recoverable lignin having a wide range of utility. For example, the recovered lignin can be utilized as a thermosetting resin, as a coating material or as a component of coating compositions, as a starting material for making chemical compounds and various chemical compositions, and for many other purposes.

Surprisingly it was found that the organomercaptanreacted lignin not only can be readily separated from the wood, thereby permitting easier defibration of the wood chips; but also that the isolated lignin derivatives can be hydrolyzed in an alkaline ethylene glycol medium whereby there is obtained a higher percentage of water-soluble material of lower molecular weight than heretofore could be obtained by conventional pulping processes. In other words, the method of this invention makes it possible to isolate lignin polymer in a non-condensed state such that it is amenable to controlled hydrolysis to smaller units. Thus, the present invention provides a pulping technique whereby the lignin polymeric material is protected or prevented from reacting with itself during its isolation and under conditions that yield a good grade of pulp.

It has been indicated hereinbefore that the initial digestion period may be followed by a second extraction stage whereby lignin is extracted from the wood. Whether or not a one-stage or a two-stage pulping technique is carried out depends mainly upon such influencing factors as the pH of the treating liquor, the time and temperature of the reaction (especially the temperature), and the type of product desired, e.g., alpha-cellulose, or a moderateor high-yield pulp best adapted for the particular end-use. Highly alkaline cooks (i.e., when the digestion is initiated at a pH not less than 11.0) at higher temperatures, e.g., 120-200 C., generally may be efnployed when it is desired to effect pulping in a single stage. Cooks may be carried out at an acidic pH, e.g., at a pH of from about 2.0 to about 4.0 or 5.0, and at a temperature substantially above 100 C., e.g., about 120-200 C. Such operating parameters may be employed when, for example, as under the aforementioned highly alkaline conditions, it is desired to provide a onestage pulping method wherein the organomercaptanreacted lignin dissolves in the liquid reaction medium more particularly in a liquid hydrotrope agent consisting essentially of a concentrated aqueous solution of a very water-soluble salt of an organic acid, and specifically SXS.

Cooks also may be carried out, as indicated in one of the examples that follows, under neutral or approximately neutral conditions (e.g., at a pH of from about 6.5 to about 7.5) and at temperatures of from 80 to 200 C.

When the raw lignocellulosic material has been elfectively digested or pulped in a one-stage technique, the charge is blown or otherwise removed from the react r into a suitable draining or filtering unit, e.g., a wash pit, wherein the liquor is removed from the solid product. The resulting fibrous pulp is washed free of liquor, e.g., with hot water, and screened. Bleaching and/or drying steps are optional depending upon the end-use. If bleaching is to be effected, it is usually done before dying of the pulp. If the raw lignocellulosic material has been cooked under strongly alkaline conditions then, prior to the bleaching step, the crude pulp may be washed With a dilute aqueous solution of an inorganic acid, e.g., a 5% aqueous HCl solution, thereby to insure a more complete and eflicient bleaching action than when bleaching is effected in the absence of such a dilute acid wash. The pulp, with or without further treatment as maybe required for the particular end-use, is then suitable for utilization in making any desired cellulosic product including, for example, paper and related products, cellulose acetate, cellulose xanthate, regenerated cellulose, ethyl cellulose, etc.

TWO-STAGE PROCESS In a two-stage process the excess liquor is preferably removed (e.g., by draining) from the reactor or digester at the end of the cooking period, and the residue is washed, e.g., with hot water.

The washed, subdivided wood containing organomercaptan-reacted lignin is then either transferred to an extraction vessel, the type of which will vary with the particular extraction conditions that are deemed necessary or advisable; or the digester in which the initial cooking was carried out may be used as the extraction vessel.

Organomercaptan-reacted lignin retained by the washed residue is extracted by contacting the said residue with an organic or inorganic extractive agent for the said lignin thereby to form a cellulosic pulp. This extractive agent may be an extractive amidogen compound, e.g., an amine such as monoethanolamine, aniline, and the like; or an amide, e.g., urea, dimethylformamide, etc. Or, the extractive agent may be a solution (including dispersion), preferably an aqueous solution of an inorganic base, e.g., an aqueous solution containing from Arm 4 or 5 weight percent of sodium hydroxide or of a hydroxide of any other alkali metal or of an alkaline-earth metal.

Crude commercial mixtures of amidogen compounds, e.g., mixtures of amines may be used, if desired, as the lignin-extracting agent. Alkaline inorganic agents, e.g., NaOI-I, Na CO Na s, NaSH, etc., may be employed, if desired, in combination with an amine or other nitrogenous extractant.

In extracting the organomercaptan-reacted lignin from the raw lignocellulosic material that has been digested with a treating liquor of the kind used in practicing this invention, the extraction temperatures may range, for instance, from ambient temperature (about 2030 C.) to about 200 C., more particularly from about 50 .or C. to about 180 C., while the extraction time may range, for example, from about A to about 4 or 5 hours or longer, as desired or as conditions may require. Thus, the extraction temperature and time may be -170 C. for from 1 to 2 hours, more particularly when the extractant is a dilute aqueous solution of sodium hydroxide containing, for example, from about 1 to about 2 weight percent of NaOH.

Several examples of extractive amidogen compounds that may be employed (singly or a plurality thereof) as an extractant of the organomercaptan-reacted lignin have been given hereinbefore. Other examples of such amidogen compounds of the amide type include thiourea, diurea, diethylenetriurea, methylurea, phenylthiourea, asymmetrical diethylurea, guanidine, dicyandiarnide, guanylurea, guanylthiourea, biguanide, monophenylbiguanidine, l-aminoguanidine (guanylhydrazine), and the like.

Still other examples of extractive amidogen compounds that may be used include:

The mono-, diand trimethylthrough -dodecylamines (both normal and isomeric forms) wherein the secondary and tertiary amines are either symmetrical or unsymmetrical, e.g., N-ethyl-N-butylamine.

The mono, diand triphenylamines, the mono-, diand tritolylamines, the mono-, diand tribenzylamines, the mono-, diand tri(cyclohexyl)amines, and wherein the secondary and tertiary amines are either symmetrical or unsymmetrical.

The diand triethanolamines, the mono-, diand trin-propanoland -isoprpanolarnines and higher members of the homologous series, wherein the secondary and tertiary amines are either symmetrical or unsymmetrical.

Amines such as 2 amino 4 methylpentane [CH CHNH CH CH(CH3)2] and 3-amino-5-methylpentane.

The alkylenepolyamines (polyaminoalkanes), e.g., Ethylenediamine (1,2,-ethanediamine) 1,2-diaminopropane (propylenediamine) 1,3-diaminopropane (NH CH CH CH NH 3-diethylaminopropylamine (C H NCH CH CH NH 1,3-diaminobutane (NH CH CH CHNH CH 1,3 bis ethylaminobutane [C H NHCH CH CHNH- 2 5) 3l 1,4-diaminobutane 1,5-diaminopentane 1,6-diaminohexane 1,7-diaminoheptane 1,8-diaminooctane Diethylenetriamine (NH CH CH NHCH CH NH Triethylenetetramine v [-NH (CH CH NH CH CH NH Tetraethylenepentamine Pentaethylenehexamine temperature, or it may be employed in the form of a' solvent solution thereof, e.g., dissolved in water and/or methanol, ethanol, isopropanol or other lower alkanol and/ or other organic solvent for the said extractant.

Certain organic solvents free from an organic or inorganic base of the kind hereinbefore described also may be used to extract the organomercaptan-reacted lignin from the treated lignocellulosic material. Examples of such solvents are dimethylsulfoxide and ethylene glycol, both of which, however, are not as effective extractants as monoethanolamine; and dioxane, which is much less effective than ethylene glycol, dimethylsulfoxide and monoethanolamine, but more effective than pyridine and N,N-dimethylacetamide under the same extraction conditions.

Organic solvent-type extractants containing a dissolved or dispersed organic or inorganic base also may be used as the extractant.

Extractions may be carried out under reflux conditions, or they may be effected under superatmospheric pressure sufficient to liquify the extractant (e.g., an amidogen compound of the low-boiling amine type) if Otherwise it would be in gaseous state at the extraction temperature.

At the end of the extraction period the residue or pulp is treated to remove the organic or inorganic extractant containing organomercaptan-reacted lignin. For example, the residue or pulp may be drained and screened to separate the solids which are then defibrated and washed with water or other suitable solvent. When the extractant is, for instance, a water-soluble amidogen compound such as a water-soluble amine, or a water-soluble inorganic base such as sodium or other alkali-metal hydroxide, the solid residue is advantageously washed with hot water. With extractive amidogen compounds such as aniline, substantially pure aniline itself may be used as the washing agent; or a different organic solvent, preferably a water-soluble organic solvent, e.g., methanol, ethanol or dioxane, may be employed. The recovered extraction liquors and washings may be either concentrated, if necessary, and reused in the process; or, they may be treated to recover valuable organomercaptanreacted lignin and to purify the unreacted extractant. Only a small amount of the extraction agent is consumed in the extraction, and the extraction liquor may be repeatedly recycled in the process before any losses need to be replaced. Any ligneous material that precipitates may be removed by any suitable means, e.g., by filtration.

In purifying the extraction agent and recovering the mercaptan-reacted lignin, the extraction liquor may be treated with, for example, CO or a dilute mineral acid such as HCl; an inorganic salt; or an extractant-compatible liquid in which the lignin is insoluble, e.g., alcohol, in order to precipitate the ligneous material for recovery. Dialysis also may be employed to separate the lignin from the extraction liquor. Or, the liquor containing the dissolved lignin may be passed through an anion-exchange resin in free-base form thereby selectively to adsorb on the resin anionic materials contained in the liquor while the lignin in purified form passes through the resin for subsequent evaporation of the eluate and recovery of lignin. This latter technique is more fully described and broadly and specifically claimed in the copending application of William H. Greive and Karel F. Sporek, Ser. No. 418,872, filed Dec. 16, 1964, now abandoned and assigned to the same assignee as the present invention.

If the extractant is a volatile amidogen compound with a relatively low-boiling point, it may be recovered by distillation from the lignin-containing liquor in which it is present and reused in the process. Higher boiling extractive amidogen compounds may be recovered from this liquor by extraction with low-boiling solvents. After distilling off the low-boiling solvent, bleaching and/or drying steps, as well as acidification to insure a more efiicient bleaching action, may be carried out as previously has been described with reference to the one-stage process.

In order that those skilled in the art may better understand how the present invention can be carried into effect, the following examples are given by way of illustration and not by way of limitation. All parts and percentages are by weight unless Otherwise stated.

EXAMPLE 1 This example illustrates the digestion under acidic conditions of a softwood, specifically isopropanol-extracted cypress, in a treating liquor comprising an organomercaptan, more particularly TGA, and a hydrotrope agent, specifically a concentrated (about 36%) aqueous solutionof SXS.

The procedure employed'to'extract the cypress in chip form involves a vapor extraction of the chips with a reboiler wherein the extractives are accumulated and the solvent, isopropanol, is flashed off. Isopropanol (about 1.5 liters) is employed to extract 1 kg. of cypress chips. (The same apparatus and procedures are used in removing extractives from chips of pine, green aspen, and other woods which are processed in practicing the present invention.)

In a specific pulping procedure a total of 300 g. (ovendry basis) of isopropanol-extracted cypress chips is added to a 2100 ml. water solution in a 3-liter reaction kettle. This water solution contains (a) 36% sodium xylene 11 sulfonate (SXS), (b) 300 g. thioglycolic acid (TGA) and (c) a concentration of 1.8 N p-toluenesulfonic acid 12 Corrected D.P. values given in the table are calculated on the assumption that no lignin goes into solution.

TABLE I.PULPING OF ISOPROPANOL-EXTRACTED CYPRESS CHIPS Pulp Time, Pulp Klason Corrected No. hours 'lemp., 0. 11+ TGA 1 yield lignin P.P. D.P

1-A 4. 102 l. 8 N 100 42. 7 0. 8 289 286 l-B- 4. 0 90 l. 8 N 50 55. 1 9. 9 370 335 1-0. 2.0 92 1. 8 N 100 57. 7 10. 6 383 344 1-D 4. 0 101 0. 9 N 50 52. 0 7. 6 397 367 1E 2.0 101 0.9 N 100 65. 4 13. 6 414 361 1-F. 2.0 90 0.9 N 50 71. 7 28. 1 1-G- 4. 0 92 0. 9 N 100 47. 1 4. 8 305 291 1H 2. 0 102 1. 8 N 50 57. 0 12. 4 383 340 1 TGA in approximately a 36% aqueous solution of SXS.

EXAMPLE 2 Same as in Example 1 with the exception that the wood which is pulped is a hardwood, specifically black gum chips.

The details of the operating parameters for the individual runs, together with the pulp yields, Klason lignin values, and corrected and uncorrected D.P. values of the pulp are given in Table II.

TABLE II.-PULPING OF ISOPROPANOL-EXTRACTED BLACK GUM CHIPS.

Pulp Time, Pulp Klason Corrected No. hours Temp, 0. 11+ TGA 1 yield lignin P.P. D.P

4. O 103 1. 8 N 100 43. 5 0. 6 279 276 4. 0 90 1. 8 N 50 45. 9 1. 8 433 424 2. 0 103 0. 9 N 100 45. 4 l. 8 459 449 4. 0 102 0. 9 N 50 43. 5 0. 8 410 407 2. 0 91 l. 8 N 100 44. 3 5. 1 456 433 2. 0 90 0. 9 N 50 49. 6 10. 6 354 318 4. 0 91 0. 9 N 100 50. 3 4. 0 462 443 I TGA in approximately a 36% aqueous solution of SXS.

30 C.). The chips defibrate into a fine, white pulp.

The white pulp is filtered off from the brown liquor, and 40 washed with water until neutral to litmus paper. The yield of pulp is 51%; Klason lignin value, 6%. (The Klason lignin value is determined as described in, for example, TAPPI Standard Test Method T13 m54.)

EXAMPLE 3 Same as in Example 1 with the exception that a different softwood is employed, specifically chips of Valdosta pine.

The details of the operating parameters for the individual runs, together with the pulp yields, Klason lignin In a manner similar to that described in the preceding values, and corrected and uncorrected D.P. values are paragraph, four variables in the operating parameters are given in Table III.

TABLE I.-IULPING OF ISOPROPANOL-EXTRAOTED VILDOS'IA PINE CHIPS Time, Pulp Klason Corrected hours Temp., 0. 11+ TGA 1 yield lignin P.1. D.P

4. 0 103 1. 8 N 100 42. 6 0. 4 346 343 2. 0 103 1. 8 N 47. 0 3. 0 436 425 4. 0 102 0. 9 N 50 46. 1 8. 4 482 464 2. 0 102 0. 9 N 100 51. 1 4. 2 466 446 4. 0 91 0. 9 N 100 56. 7 10. 3 403 364 2. 0 90 1. 8 N 100 58. 3 11. 5 485 432 4. 0 89 1. 8 N 50 50. 0 10. O 479 436 2. O 90 0. 9 N 50 60. 5 18. 6 219 181 1 TGA in approximately a 36% aqueous solution of SXS.

are run at two levels. A constant liquor level of 700 ml. is

used in each run. The variables and levels are as follows:

EXAMPLE 4 Same as in Example 1 with the exception that two A B different conditions are employed and, before digestion, 1. Hydrolysis time, hours 4 the yp ip re soaked for av prolonged period, 2. YdrolySiS t p i 1 ,Q-( DD J specifically 66 hours, in the treating liquor at ambient fit r lil fif"???it???31????33???. 0 9 N 1 8 N temperature (about 2040 C.). TGA concentration 100 chips 50 100 The details of the operating parameters for each run,

The details of the operating parameters for the individual runs, together with the pulp yields, Klason lignin values and corrected and uncorrected D.P. (degree of polymerization) values of the pulp are given in Table I.

The uncorrected D.P. value of the pulp is determined as described in SCAN-C15z62 (Scandinavian Pulp, Paper together with the pulp yields and Klason lignin values, are given in Table IV. For ease of comparison there is 70 included in this table the corresponding data on pulp Nos. l-B and l-E from Table I. It will be noted that in each case there was a lowering of the pulp yield and of the Klason lignin content by the 66-hour presoaking and Board Testing Committee), Tables 1-3 and 7. The treatment in the treating liquor.

' Ethylene glycol.

TABLEIV.-HOTPULPINGOFISOPROPANOL-EXTRACTED CHIPS AFTER SOAKING FOR 66 HOURS AT AMBIENT TEMPERATURE EXAMPLE This example illustrates the relative effectiveness of various organic solvents as extractants of organomercaptan-reacted lignin' from black gum wood chips that have been digested under acidic (PTSA) conditions in a treating liquor comprising TGA in approximately a 36% aqueous solution of SXS. The operating parameters for the digestion correspond to those given for pulp No. 2-A inTable-II.

The organic solvents tested include monoethanolamine (MEA), dimethylsulfoxide, ethylene glycol, dioxane, pyridine and 'N,N-dimethylacetamide. The black gum chips (50 g., O.D. basis) are refluxed in about 300 ml. of the solvent for 2%. hours, mechanically stirred to de fiber the chips in fresh solvent at ambient temperature, filtered, and washed with fresh solvent at room temperature for 5 minutes. The filtered pulps are suspended in a blender With water to remove the solvent employed in the individual run.

Below are shown the reflux temperatures of extraction with each solvent, and the percent of Klason lignin in the extracted pulp.

Refiux temper- Percent Klason E xtraction Solvent lignin Monoethanolamine Dimethylsulfoxide.

Dioxane ridlne N, -dimethylaceta.mide

' Another run is made, as described above, using monoethanolamine as an extractant but limiting the reflux time to one hour. "The resulting pulp is white, and con- EXAMPLE 6 The same general procedure is followed as described in the third paragraph of Example 1 with the following exceptions:

Three large digestions or cooks using" 300 g. of isopropanol-extracted O.D. cypress chips are run at reflux 14 chips are extracted with monoethanolamine at reflux temperature (129*133 0).

Similar two-hour cooks at 100 C. are also madeon isopropanol-extracted cypress and approximately a 50/50 by weight mixture of isopropanol-extracted cypress and isopropanol-extracted black gum. The chips are cooked in the same formulation of treating liquor described above. Lignin is extracted from the digested chips by treatment with a 4% aqueous solution of NaOH at room temperature.

Details of the pulping conditions for the individual runs, and yields and properties of the pulps are given in Table V-a. Also shown in this table are the percent pulp yields and percent Klason lignin contents of pulps resulting from simulated kraft cooks of cypress and of pine in an autoclave. The cook formulation and cooking procedure employed in making these kraft cooks are given below. The cooks differed only as to the type of wood used; that is, cypress chips were employed to obtain Pulp No. V-F, and pine chips in making Pulp No. V-G.

(I) Cook formulation Chip charge: 150.0 g. (O.D. weight) of air-dried chips;

pre-extracted with 1:2 alcoholbenzene Liquor composition: 14.4 g.p.l. Na CO (7.6% as Na O on the OD. wood); 41.9 g.p.l. NaOH (29.3% as Na O on the OD. wood); 18.4 g.p.l. Na s (13.1% as Na O on the OD. wood) Liquor active alkali as Na O: 47.1 g.p.l. (42.4% on the OD. wood) Liquor total alkali as Na Oz 55.5 g.p.l. (50.0% on the OD. wood) Liquor sulfidity: 26.3% of the total alkali Liquor-to-wood ratio: 9: 1

Total liquor volume: 1350 ml.

The above liquor was prepared by dilution of concentrated mill White liquor. The active alkali concentration of 47.1 g.p.l. as Na O is the same as that of a mill cook at 16% active alkali on the wood and 3.4 liquor-to- Wood ratio. As a result of the high liquo'r-to-wood ratio required in these cooks (9:1), the active alkali on the wood was at a high level (42.4%) compared to mill pulping.

(II) Cooking procedure The charge of chips and liquor was cooked with stirring in a stainless steel, electrically heated and Water cooled, one-gallon autoclave under the following condition-s:

Max. cook temperature: 338 F. (170 C.) Time at temp. (338 F.): 26 min.

Time to temp. (338 F.) min.

Cooling time to F.: 25 min.

The resultant digested wood was recovered by filtration, then washed thoroughly with hot water. After defibering the cooked Wood in a Sprout-Waldron refiner, the pulp was refined and paper sheets Were made for testing.

Table V-a follows.

TABLE Va.PULPIN'G CONDITIONS, YIELDS AND PROPERTIES OF PULPS FROM TGA-SXS COOKS Time, Temp., Yield, K.L., Corrected Wood hrs. 0. Extraction treatment percent percent D. P D. Pfl

2 100 15 Ext. in RT 1 aqueous N aOH 51. 3 5. 96

2 102 1 hr. Ext. in 131 C. MEA, 45. 5 2. 32 288 295 1% 100 1 hr. Ext. in 133 C. MEA 50.0 3. 47 331 341 101 1 hr. Ext. in 129 C. MEA. 51. 8 3. 35 426 440 1 R.I.= Room temperature (about 25-30 0.).

2 K.L.=Klason lignin (reL: TAPPI Standard T13 m-54). 3 D.P.=Degree of polymerization.

4 Simulated standard Kraft cook in autoclave.

(III) Refining, sheetm-aking and testing The procedures used in these steps were essentially the same as those described in the aforementioned Fisher et :al. copending application Ser. No. 605,978 with the following exception. In the case of Pulp Nos. V-F and V-G only one refining was possible because of the small amount of pulp obtained from the cooks. Only one refining also was carried in the production of the other pulps. Additional details on refining technique, and sheetmaking and testing of the handsheets, follow:

The wet cellulosic pulp produced as hereinbefore described was dried to 20-30% solids. A portion, based on the OD. weight of the wet pulp, was refined with water at 1% consistency in a Mead Laboratory Refiner (manufactured by The Bauer Bros. Company, Springfield, Ohio). The degree to which the pulp was refined, as determined by measuring the dnainage time (TAPPI Standard T221) of the pulp in a Slowness Tester (manufactured by Williams Apparatus Company, Watertown, N.Y.), was controlled so as to refine, as closely as possible, to a Williams Slowness of 55 seconds.

The handsheets were formed in an 8" x 8" Williams sheet mold from aliquots of the pulp slurry that were measured volumetnically so as to obtain sheets corresponding as nearly as possible to 2'6 lb./MS-F sheets, i.e., 4.6 grams of O.D pulp per sheet. The pulp consistency on forming the sheets was adjusted to 0.05% by further dilution of the pulp aliquot in the mold. The seven or more sheets (wet webs) formed from each batch of pulp slurry were couched from the wire of the mold onto standard 12" x 12'' TAPPI blotters, then stacked between blotters with six blotters separating the sheets. The stack was then pressed for minutes at 150 p.s.i. gauge pressure on a Williams press (manufactured by the Williams Apparatus Company). The pressed sheets, retained on the couch blotters, were dried at 260 -280 F. on a steam-heated Noble and Wood drier, with the sheet contacting the drum for approximately twominutes. After removing the blotters, the dried sheets were conditioned at 50% relative humidity and 72 F. for a minimum of 24 hours before testing.

The results of tests on papers (handsheets) made from the pulps identified in Table V-a are given in Table V-b. The values for the paper characteristics listed under the various column headings in the latter table are the results obtained when the respective handsheets are tested using apparatus and procedures described, for example, in the following TAPPI Standard Testing Methods:

Test: TA-PPl standard Caliper T411 Tear T414 ts-64 Stretch T457 Tensile T404 os-61 Ring crush T472 rn-Sl Mullen T403 ts-63 Brightness T452 m-58 Table V-b follows.

than those made from the latter. The digested woods from the TGA-SXS cooks also were much easier to refine as compared with those resulting from the kraft cooks. The team values for the handsheets made from the pulps of the TGA-SXS cooks are low because the acidity of the treating liquor was not optimized to obtain optimum tear properties. (As tear values increase, tensile values decrease depending upon the refining time.) Handsheets made from some of the pulps (e.g., V-E) of the TGA-SXS cooks were comparable in tensile and ring crush values with those of handsheets from the two kraft cooks.

It is also to be noted that higher temperatures (170 C.) were required for the kraft cooks, in order to obtain the pulps from which handsheets having the described properties were obtained, as compared with only 102 C. for the TGA-SXS cooks.

EXAMPLE 7 This example illustrates the use of higher temperatures, specifically about 150 C., in the initial digestion of isopropanol-extracted cypress and black gum chips using a ratio of 100 g. of TGA per 100 g. of isopropanolextracted O.D. chips. The liquid reaction medium is a concentrated (about 36%) solution of SXS in aqueous 1.8 N PTSA (p-toluenesulfonic acid).

The aqueous PTSA-SXS solutions used are prepared as follows: The SXS is dissolved in the water by stirring with a magnetic stirrer, and to this solution the PTSA is added with stirring. The TGA is weighed out and added to about 300 ml, of the PTSA-SXS solution in a graduated cylinder. Additional SXS solution containing PTSA is then added to bring the total volume to 1400 ml. This liquor is added to 200 g. of the extracted chips and cooked in a one-gallon autoclave. The autoclave is brought to a temperature of 150 C. and immediately cooled. The total time ranges from to minutes.

At the end of the cooking and cooling period, the autoclave is opened, the chips are filtered off, and the clave is rinsed with fresh SXS solution. The liquor and rinsings are combined, and then diluted with water in the ratio of 3 parts water to 1 part of the combined liquor and rinsings in order to precipitate the lignin dissolved in the spent liquor.

The chips are placed in 1 liter of 4% aqueous NaOH, stirred for 15 minutes, then filtered and washed. The NaOH extract is acidified with 18% aqueous HCl to precipitate the lignin. The precipitated lignin is filtered off. If the lignin is to be analyzed, it is washed thoroughly with distilled water and air-dried prior to analysis.

The yields of pulp and percentage Klason lignin therein are tabulated below:

Percent PS OF TABLE V-a Dry Ring Bright- Caliper, Tear, Stretch, tensile, crush, Mullen, ness, Pulp No Wood mils g./16 sh. percent lbs/in. lbs. p.s.i. percent; Cypress 7. 2 s3. 0 1. 2 37. 5 57. 5 55. 4 50 Black gum plus cypress- 8. 4 70. 5 1. 1 35. 5 54. 6 50. 3 53 7. 9 104. 9 0. 9 32. 5 59. 4 66. 5 50 7. 7 123. 8 0. 2 47. 2 51. 0 75. 9 45 7. 4 6. 4 14. 4 48. 4 62. 6 S1. 1 45 V-F -do 9. 2 181 50 62 21 V- G Pine 8. 2 53 60 20 1 Ring crush, lbs.=Short column ring crush, lbs.l6-in. circumference. 2 Brightness, percent=Photovolt brightness, percent reflectance.

From a consider-anon of the data given m Tables EXAMPLE 8 V-a and especially V-b, it will be seen that the pulps of the TGA-SXS cooks contain much less lignin than those made from the two kraft cooks, and that hand- This example illustrates the use of a different organomercaptan, specifically n-butylmercaptan, in a two-stage technique for pulping black gum chips in accordance sheets made from the former pulps are much brighter 75 with the present invention.

The general procedure is essentially the same as in Example 7 with the exception that 50 g. of n-butylmercaptan per 100 g. of 0.1). 'black gum chips is used in a liquid reaction medium containing a concentrated (about 36%) solution of SXS in aqueous 1.8 N PTSA. The digestion is carried out at atmospheric pressure for 4 hours at a temperature ranging from 79 C. to 97 C. The yield of pulp is 49.7%, and the content of Klason lignin is 8.8%.

EXAMPLE 9 but such control is not always such as to provide three or more refining points bracketing 55 seconds Williams Slowness.

Other details of the operating conditions for the individual cooks, and the percentages of pulp yields and Klason lignin contents thereof, are given in Table VI which follows. Where is designated in the column headed Time, Hrs, it means that the wood chips are heated to the specified temperature (150 C.), and having reached that temperature heating of the autoclave is immediately discontinued, and the digested wood is al lowed to cool to ambient or near-ambient temperature.

Table VI follows.

TABLE VI.-PINE COOKS USING TGA-36% SXS HYDROTROI E AGENT Time, Temp., Initial Final Percent Percent E. or U. hrs. C. 11+ 1 TGA 2 pH pH yield L.

Cook N 0.:

1 From para-toluenesultonic acid (PTSA). 2 TGA in grams per 100 grams of O.D. pine.

3 Unextracted. 4 Extracted.

sure. The. 150. C. cooks-are eifected in an autoclave.

In all cases with the exception ofcook No. 6-E (including 6-E-1), the TGAereacted lignin in the digested chips is extracted by post-treating the chips by immersion in a 4% aqueous solution of NaOH having about the same volume asthe cooking-liquor. This slurry is stirred for one hour at room temperature, filtered, and the isolated solids washed with' hot water. The extracted chips are run through a Sprout-Waldron refiner to defiber them. The extract is acidified with concentrated H SO to precipitate the lignin.

In the case of cook No. 6-E the digested chips are first extracted for minutes at 300F. (followed by cooling to atmospheric pressure over a period of minutes) in an autoclave in about the same volume of dioxane (2400 m1.) as that of the initial treating liquor. The cihps are filtered ofi, washed,fdefibered mechanically, and the yield of pulp determined, retaining a sample of the pulp for a Klason lignin determination. This pulp is then extracted for 1 hour at ambient temperature in a 4% aqueous solution of NaOH, and the yield and lignin content again determined. The pulp on which these determinations were made is identified in Table VI The technique employed in refining the defibered, digested chips is essentially the same as .that described under Example 6 with the exception that the procedure includes pulps wherein aliquots (a minimum of three) 'of 'the experimental pulp, in an amount based on the OD. weight of the wetpulp, are, refined with Water at 1% consistency for varying periods of time in a Mead Laboratory Refiner. The degree to which each pulp aliquot is refin'ed,-as hereinbefore described, is controlled;

Table VII shows the Williams Slowness values to which three aliquots of certain of the pine cooks listed in Table VI were refined, and properties of handsheets made from the corresponding pulps obtained after refining to the indicated degree. All of these pulps were refined for 60, and seconds.

Table VII follows.

TABLE VII.PROPERTIES OF HANDSHEETS MADE FROM TYPICAL PINE COOKS OF TABLE VI AFTER REFINING TO VARYING WILLIAMS SLOWNESS VALUES Properties of Handsheets Williams Density, Dry Ring Tear, Cook slowness, Caliper, lbs/cu. tensile, crush, g./ 16 sh N 0. sec. in. it. p.s.i. lbs.

6-K-1 23. 1 0. 0111 26. 6 2, 170 48 74 6K2 57. 0 0. 0101 29. 7 2, 586 49 77 6-K-3. 404. 0 0. 0084 35. 2 3, 760 49 53 6O1 12. 6 0.0102 36. 2 4, 510 118 6O2 46. 9 0. 0090 38. 1 5, 120 88 6O3 101. 2 0. 0065 51. 8 8, 380 52 6-R-1 7. 1 0. 0130 25. 0 2, 310 61 The data given in- Tables VI and VII show that pulping of lig'nocellulosic material can be effectively carried out, using a treating liquor comprised of an organomercaptan and a hydrotrope agent, under less acidic conditions than thoseqemployed in. prior examples; and, also, under slightly alkaline Cook No. 6-T) or approximately neutral (Cook No. 6-S) conditions. In other words, one

does not need to use the relatively high acid concentraa. much lower concentration of acid than was used in prior examples in order to ascertain desirable conditions for easy defibration. When the cooking temperature was increased substantially above 100 C., specifically 150 C., it was unnecessary to include additional acid in the treating liquor used in the process in order to obtain a satisfactory pulp.

The data in Table VII on handsheets made for Table VI cooks 6-K, 6-0, 6-R and 6-S at three dilferent refining times provide information on the paper-making qualities of the pulps. Note the extremely high tensilestrength development (8380 p.s.i.) and the very compact, dense handsheets (density =51.8 lbs./cu. ft.) obtained from the pulp (58.7% yield) of cook 6O-3 at 120- seconds refining time. Kraft cooks at 52% yield require a refining time of 160 to 180 seconds in order to obtain a pulp from which can be made papers having similar physical properties other than in percent brightness, in which latter property such papers are lower than that of papers made from pulps produced by the method of this invention.

The data in Table VII further show that a better pulp was obtained from cook 6-0 (initial pH 3.5, yield 58.7% than from cook 6-K (initial pH 2.9, yield 76.7% However, as evidenced by the data on handsheets made from pulp 6-R, when the hydrogen-ion concentration is lowered further (i.e., the initial pH value is increased to 5.4), the yield of pulp is increased to 72%; and, from this pulp, one is able to produce handsheets having reasonably good tensile-strength properties and good ringcrush characteristics. The data on handsheets made from the pulp of cook 6-S show that a further lowering of the hydrogen-ion concentration of the treating liquor (i.e., the initial pH value is increased to 6.8), provides a pulp at 76.8% yield and which contains 20.5% Klason lignin. Handsheets made from this pulp have a tensile strength equivalent and a ring-crush value superior to those obtainable from a kraft process. Pulps such as those of cook 6-S would be valuable in the production of corrugating media.

In general, the data presented in Tables VI and VII, especially when condsidered with that presented in the prior examples, show the extreme flexibility of the process of this invention not only with respect to the various types of lignocellulosic materials to which the invention is applicable but also with regard to the simplicity of changing processing conditions so that pulps adaptable for making products having many different end-uses can be produced. For example, cypress, pine or other softwoods or any of the various hardwoods, and all from the 20 the digestion conditions, pulp yields and Klason lignin contents thereof are tabulated below:

TABLE VIII.-HYDROTROPE PULPING OF PINE Time, Initial Final Klason hrs. pH pH Yield lignin The pulps that were produced were w-holly unsatisfactory. The tensile strengths of handsheets made from the pulps could not be measured because of the inadequacies of the pulps, while the ring-crush values of the sheets were only between 35 and 40. Additionally, the defibered, digested pine was very diflicult to refine.

EXAMPLE 10 Essentially the same procedure is followed as described under Example 7 in pulping isopropanol-extracted black gum and aspen chips with the exception that the TGA (100 g. per 100 g. of 0D. wood) is dissolved in approximately a 36% solution of SXS in aqueous 0.009 N PTSA instead of in aqueous 0.9 N PTSA as in Example 7.

The yields of pulp and percentage Klason lignin therein are tabulated below:

Percent Percent Klason yield lignin Black gum pulp 41. 1 4. 25

Aspen pulp 50. 0 4. 56

EXAMPLE 11 This example illustrates the use of a treating liquor comprised of TGA dissolved in approximately a 36% solution of SXS in aqueous 1% concentrated nitric acid (instead of varying amounts of =PTSA). This liquor is employed in treating unextracted pine chips. The liquorto-wood ratio is 10:1. The digestion is carried out in a 1-liter, 3-necked flask provided with a reflux condenser and a thermometer. Digestion is effected for periods of either 2 or 4 hours. In two of the cooks the TGA is omitted to note the effect thereof. The digested chips from two of the cooks are given no post-extraction treatment. The remaining cooks (three in number) are extraeted with a 4% aqueous solution of sodium hydroxide at room temperature as was described under Example 9.

Details of the operating conditions for the individual runs, together with the pulp yields and percentage of Klason lignin in the pulp, are given Table IX.

TABLE IX.-PULPING OF UNEXTRAOT86IE USING A TGA-SXS-HNOa-HzO TREATING Nitric Cook Time, Temp., acid, SXS, Percent Percent No. Wood hrs. 0. percent TGA 1 percent yield K.L. Post treatment IX-A--- Pine 4 104 l 100 36 56. 4 7. 5 R.T. NaOH extn. IX-B do 2 101 1 36 93. 8 30.2 No ext'n. IX-C do. 2 102 1 90 36 70. 3 21. 3 R.T. NaOH extn. IX-D do 2 102 1 0 36 84. 2 33. 7 No extn. IX-E do. 2 102 1 0 36 84.3 32. l R.T. NaOH extn.

1 TGA in grams per grams of O.D. pine.

same forest area, could be used as raw materials in the process of this invention if a stand of one type could not support a single operation of a particular kind.

The unique and unobvious results obtained by using a combination of an organomercaptan and a hydrotrope agent such as, for example, sodium xylene sulfonate, will be better appreciated from a consideration of the results obtained when a 36% aqueuos solution of SXS alone (no TGA or other organomercaptan was present) was similarly used as the treating liquor in digesting pine chips for 2, 3 and 8 hours at C. Other details of 7 contents of EXAMPLE 12 This example illustrates the TGA cooking of isopropanol-extracted pine chips under at least initially alkaline conditions ranging from 8.6 (cook IO-A) to 12.1 (co k 10-H) at liquor-to-wood ratios of 4.5 :1, and with or without a post-treatment of the digested chips with a 1% aqueous solution of sodium hydroxide at 97 or 98 C. In other words, the pulping technique is one-stage when no NaOH post-treatment is applied due to the fact that a large amount of the organomercaptan-reacted lignin has dissolved in the alkaline solution. In all cooks except one, viz, 10-E cook, NaOH in the amount shown in Table X that follows is added to the treating liquor to provide the alkaline conditions. TGA alone in amounts ranging from 6.4 to 19.3 g./100 g. O.D. chips is used in all cooks except 10-I where a combinations of 6.4 g. TGA and 6.05 g. NaSH per 100 g. O.D. chips is employed. The treating liquor consists essentially of the aforementioned ingredients dissolved in a concentrated (about 36%)aq-ueous solution of SXS. The cooking time is varied from /2 to 3 hours and the cooking temperature from 150-160 C. 1

Cypress and black gum chips (cooks 10-] and 10K, respectively) are cooked at nearly neutral initial pH values (7.7 and 6.1, respectively). Cypresscook 10-G is digested at an initial pH of the treating liquor of 12.5 and a final pH of 12.3.

The general procedure for preparing the treating liquor and for cooking the'chips is essentially the same as that given under Example '7 with the exception that a differentratio of liquor-to-wood is employed and cooking is continued atthe maximumtemperatures of 150 r 160 C; for the specified periods of time.

In Table X are'give n details of theoperating conditions for'the' individual cooks and for. the post-treatment (if employed), pulp yields, and pulp analyses for Klason lignin, sulfur and pentosans.

The amount of TGA employed in the aforementioned cypress cook 10-G is 6.4 g./ g. wood. A better pulp is obtained using a higher amount of TGA, specifically 19.3 g. TGA, as evidenced by the following results of tests corresponding to those given above, on pine cook 10C and, in addition, the results of stretch tests. These results are given in the following Table XII.

TABLE XII Williams Density, Dry Mead refining slowness, lbs/cu. tensile, Tear, Stretch time, sec. see. it. p.s.i. g./16 sh. percent The stretch values shown in Table XII are especially significant. These values are comparable to stretch values of similarly made handsheets produced from kraft pulps wherein the pulp yield is only 52%.

With further reference to the data in Table X it may also be pointed out that, at a final pH as low as 9.6 (cooks 10-C and 104D), a post-extraction of the digested wood was not required although only 19.3 g. TGA/ 100 g. O.D. wood was used. A comparison of the data on cooks 10-H and 10-I (Table X) shows that the inclusion of NaSH (cook 10-I) in the treating liquor, which also contains TGA and SXS, provides even greater delignification effect (15.9 vs. 20.4 P.L.) than the use of TGA alone with aqueous SXS.

The method of the present invention provides byproduct lignins having properties dilferent from those of other processes including those wherein an organomercaptan, specifically T GA, is used as a pulping agent in a non-hydrotropic system, more particularly in an aqueous solution which is free from SXS or other salt of an organic acid that is employed to form a conventional hydrotrope agent. This is shown, for example, by the differences in the Water-solubility of the respective lignins after hydrolysis.

Tabulated below (Table XIII) is a comparison of-the TABLE X Extraction conditions Pulp yield and analysis i NaOH Cook Time, Temp., G. TGA/100 NaOH, Initial Final Time, Temp., Cone, Yield, K.L., S, Pentosans 0. hrs. C. g. chips g. pH pH hrs. C. percent percent percent percent percent a 10.T 2 150 6. 4 9. 75 7. 7 4. 8 1 98 1 74. 1 34. 1 10-K l 150 6. 4 9.75 6. 1 4. 6 1 98 1 70.0 22.8

1 Crude TGA. 3 Cypress cook.

3 Black gum cook.

Mead refining times and the Williams Slowness values, as well as the density, tensile strength and tear values of papers (handsheets) made from the pulp of cypress cook 10G, and in which pulp the ratio of lignin to carbohydrateis 0.39, are given in Table XI.'

i TABLE XI Williams Density, Dry slowness, lbs/cu. tensile, Tear, sec. ft. p.s.i. g./16 sh.

Mead refining time, sec i 60.. 5 22 1,400 156 120 11 26 2, 500 147 26 29 3, 200 140 with magnetic stirring for 3 hours at C. The cooled reaction mixture was diluted, in volume, with distilled water by an amount'equal to ten times the weight of the alkaline glycol liquor; then acidified to a pH below 2 with 50% HCl. The acid-insoluble precipitate was col- 23 lected in a tared sintered funnel, washed with distilled water and dried in vacuo at 50 C.

Table XIII Percent water-soluble after hydrolysis Lignin from cypress pulped with acidic TGA 54 Lignin from cypress pulped with acidic TGA in a conventional hydrotrope agent, specifically aqueous SXS 68 Lignin from black gum pulped with acidic TGA in It will be noted from a consideration of the data given in Table XIII that the lignins from the McKee hydrotrope and the kraft processes do not undergo hydrolysis to any great extent while all of the other lignins are hydrolyzed to a high degree, more particularly from about 2 /2 to about ,4 times as much as the kraft and the McKee hydrotrope lignins. It is also pointed out that the lignins obtained from the woods that had been pulped with acidic TGA in aqueous SXS were more readily hydrolyzed under comparable hydrolysis conditions than were the lignins from the woods pulped with a purely aqueous system 6r TGA in water, i.e., in the absence of the hydrotrope agent SXS (68% vs. 54% and 70% vs. 66%).

The following additional advantages concerning the process of the present invention may be pointed out, and related comments made.

By using a hydrotrope agent, e.g., sodium xylene sulfonate, as a component of the treating liquor together with an organomercaptan, lignin is removed from the lignocellulosic material and passes into the treating liquor almost concurrently with the reaction of the organomercaptan with the lignin in the lignocellulose. As a result, the digested wood in chip or other subdivided form is easier to refine than when a hydrotrope agent alone is employed or an organomercaptan alone. In other words, milder conditions can be used in digesting the wood or other lignocellulosic material and in refining the digested chips to a pulp having properties comparable to, or better than, those heretofore obtained by prior processes. It will be understood, of course, by those skilled in the art that the amount of lignin that is removed from the wood in the reaction stage, that is, the stage wherein the organomercaptan reacts with the lignin in the wood, depends upon the type of wood that is to be digested. Thus, in this reaction stage the softwoods give up less lignin than do the hardwoods under the same reaction conditions.

As shown by some of the examples, a simple alkaline extraction was made primarily to assure maximum removal of the lignin from the digested wood so that, when analysis of the pulp was made, the correct ratio of lignin to carbohydrate could be determined. If analytical data on the pulps had not been desired, one could have refined the digested chips without the alkaline extraction and obtained pulps having practically the same properties. However, when an organomercaptan, e.g., TGA, alone is employed in an aqueous system as the treating liquor under otherwise comparable digestion conditions, an alkaline extraction of the digested chips is ordinarily required in order to soften the chips suificiently for refining to a pulp having the desired properties.

As in the use of a hydrotrope agent alone (i.e., in the absence of an organomercaptan in the treating liquor), water can be added tothe used treating liquor containing an undesirably high amount of lignin in order to precipitate the lignin. After separation of the precipitated lignin, e.g., by filtration, the dilute liquor is concentrated for reuse in the process. Additional conventional hydrotrope agent (e.g., SBX) or hydrotrope-like agent (e.g., dimethylsulfoxide, dimethylformamide, dimethylacetamide or others, examples of which have been previously given) and/ or an organomercaptan, e.g., TGA, are added as make-up to the recovered solution, in an amount or amounts as desired or as may be required in order to bring the treating liquor to substantially its original composition for reuse in the process.

From the foregoing description it will be seen that the present invention provides a method of pulping lignocellulosic material (sometimes designated herein as raw lignocellulosic material) which includes the steps of digesting said material with a treating liquor that includes as essential components (I) at least one lignin-reactive organomercaptan, e.g., thioglycolic acid, in an amount corresponding to at least about 5 percent (e.g., from about 5 to about percent) by weight of the oven-dried lignocellulosic material, and (II) a hydrotrope agent; and continuing the said digestion for a period at least sufiicient to convert the lignocellulosic material to a treated material which at least initially contains organomercaptan-reacted lignin.

The digestion may be effected under acidic, approximately neutral or alkaline conditions. Acid conditions may be provided by acidifying the treating liquor with such acids as, for example, an organic sulfonic acid, more particularly a toluenesulfonic acid, and specifically p-toluenesulfonic acid. Or, one may use as the acidifying agent, organic acids the soluble salts (e.g., alkali-metal salts) of which when dissolved in water constitute the aqueous hydrotrope agent, e.g., xylenesulfonic acid, cymenesulfonic acid and benzoic acid. Mineral acids also may be emp oyed as the acidifying agent, e.g., nitric, hydrochloric, sulfuric or phosphoric acid. Alkaline conditions may be provided by any base or baseforming substance, e.g., such readily water-soluble bases as the alkali-metal hydroxides. Preferably sodium hydroxide is employed.

The method of this invention advantageously includes the initial step of treating the lignocellulosic material (e.g., wood) with an organic solvent, e.g., isopropanol, acetone or the like. This pretreatment or pre-extraction step removes extractives (including soluble materials such as those which are components of tall oil, and other resinous bodies). The residue is lignin-holocellulose, or more commonly designated merely as lignocellulose. The pretreatment just described is not essential in practicing the present invention and may be omitted if desired.

The lignocellulose or lignocellulosic material that is converted into a pulp in carrying the instant invention into eifect has sometimes been designated herein as raw lignocellulosic materia This terminology is not intended to diiferentiate between (1) lignocellulosiccontaining material or materials that have been extracted (i.e., given the above-described pretreatment to remove organic-solvent soluble extractives); and (2) those which are unextracted, that is, have not been given such a treatment but instead are in native or virgin form. In other words, the term raw lignocellulosic materia in singular or plural form, as sometimes used in this specification, includes within its meaning both unextracted and extracted lignocellulosic material(s) as these latter terms have just been defined.

As has been indicated hereinbefore, the scope of the present invention includes the method wherein digestion of the lignocellulosic material and extraction of the organomercaptan-reacted lignin therefrom is completed in either one or two stages.

In a typical two-stage method, digestion of lignocellulosic material with a lignin-reactive organomercaptan is initiated and continued under acidic conditions at a'temperature and for a period of time sufiicient to convert the lignocellulosic material to a treated material containing organomercaptan-reacted lignin. The excess treating liquor is then removed (e.g., by drainage from the digestion vessel) from the digested lignocellulosic material and the latter is washed, e.g., with water and, preferably, hot water. Thereafter the organomercaptan-reacted lignin retained by the washed residue is extracted by contacting the said residue with an organic or inorganic extractive agent for the said lignin. This extractive agent may be a solution of an inorganic base, such as an aqueous solution of sodium or other alkalimetal hydroxide and, more particularly, an aqueous solution of sodium hydroxide containing from about 0.5 to about weight percent of NaOH. Or, the extractive agent maybe an extractive amidogen compound such as an alkanolamine, and advantageously monoethanolamine. With extractive agents or solutions thereof boiling below about 200 C., the temperature of extraction is within the range of, for example, from ambient temperature to the reflux temperature of the extraction liquor.

The two-stage process herein described is not limited to processes wherein the first or digestion stage is carried out under acidic conditions. It may also be employed, as desired or as may be required, when the digestion is effected at, for example, approximately neutral conditions throughout the digestion period; or approximately neutral initially and acidic at the end; or under relatively low alkaline conditions (i.e., alkaline pH below about 11.0) which either remain thusly throughout the period of digestion or are approximately neutral or acidic at the end.

In some cases it may not be necessary, in a two-stage process that includes a digestion step and an extraction step, to wash the residue (i.e., digested lignocellulosic material) remaining after the excess liquor has been removed therefrom. For example, when the recovery of treating liquor or of the extractive agent is not unduly complicated by the elimination of this wash, then said wash may be omitted from the above-described two-stage technique.

I claim:

1. The method of pulping lignocellulosic material which includes the steps of (A) digesting said material with a treating liquor that includes as essential components (I) at least one lignin-reactive organomercaptan in an amount corresponding to at least about 5 percent by weight of the oven-dried lignocellulosic material, and (II) a hydrotrope agent, and (B) continuing the said digestion at a temperature and for a period of time at least sufiicient to convert the lignocellulosic material to a treated material which at least initially contains organomercaptan-reacted lignin.

2. The method as in claim 1 wherein the lignin-reactive organomercaptan includes thioglycolic acid, and the amount of the organomercaptan corresponds to from about 5 to about 100 percent by Weight of the oven-dried lignocellulosic material.

3. The method as in claim 1 wherein the treating liquor is acidic and contains an organic sulfonic acid, and the organomercaptan is thioglycolic acid in an amount corresponding to from about 5 to about 100 percent by weight of the oven-dried lignocellulosic material.

4. The method as in claim 3 wherein the organic sulfonic acid is a toluenesulfonic acid.

5. The method as in claim 1 wherein the treating liquor is acidic and contains nitric acid; and the organomercaptan is thioglycolic acid in an amount corresponding to from about 5 to about 100 percent by weight of the oven-dried lignocellulosic material.

6. The method as in claim 1 wherein the lignin-reactive organomercaptan includes n-butylmercaptan, and the 2'6 amount of the organomercaptan corresponds to from about 5 to about percent by weight of the oven-dried lignocellulosic material.

7. The method as in claim 1 wherein the hydrotrope agent is a concentrated aqueous solution of a soluble salt of an organic acid.

8. The method as in claim 7 wherein the soluble salt of an organic acid is at least one member of the group consisting of the alkali-metal salts of xylenesulfonic, cymenesulfonic and benz-oic acids.

9. The method as in claim 8 wherein the alkali-metal salt is sodium xylene sulfonate.

10. The method as in claim 1 wherein the lignocelluosic material is hardwood.

11. The method as in claim 1 wherein the lignocellulosic material is softwood.

12. The method as in claim 1 wherein digestion is initiated and continued under acidic conditions.

13. The method as in claim 1 wherein digestion is initiated and continued under approximately neutral condition-s.

14. The method as in claim 1 wherein digestion is initiated and continued under alkaline conditions.

15. The method as in claim 1 which includes the initial step of treating the lignocellulosic material with an organic solvent to remove organic-solvent soluble material from the said lignocellulosic material.

16. The method as in claim 15 wherein the organic solvent is isopropanol.

17. The method as in claim 1 wherein digestion of the lignocellulosic material and extraction of organomercaptan-reacted lignin therefrom is completed in one stage; the lignin-reactive organomercaptan includesthioglycolic acid; the amount of the organomercaptan corresponds to from about 5 to about 100 percent by weight of the oven-dried lignocellulosic material; the hydrotrope agent is a con centrated aqueous solution of sodium xylene sulfonate; the digestion is effected under alkaline conditions at an initial pH not less than about 11.0; the temperature of digestion is within the range of from about C. to about 200 C.; and the time of digestion is within the range of from about /2 to about 8 hours.

18. The method as in claim 17 wherein the lignocellulosic material is pine wood, and the temperature of digestion is Within the range of about 160 C.

19. The method as in claim 1 wherein digestion of the lignocellulosic material and extraction of organomercaptan-reacted lignin therefrom is completed in two stages; the lignin-reactive organomercaptan includes thioglycolic acid; the amount of the organomercaptan corresponds to from about 5 to about 100 percent by weight of the ovendried lignocellulosic material; the hydrotrope agent is a concentrated aqueous solution of sodium xylene sulfonate; the digestion with the treating liquor is initiated and continued under acidic conditions at a temperature and for a period of time suflicient to convert the lignocellulosic material to a treated material containing organomercaptan-reacted lignin; and the method includes the following additional steps:

(C) removing the excess liquor from the material that has been digested under acidic conditions with the treating liquor and washing the residue; and

(D) extracting organomercaptan-reacted lignin retained by the washed residue by contacting the said residue with an organic or inorganic extractive agent for the said lignin.

20. The method as in claim 19 wherein the treating liquor additionally contains a toluenesulfonic acid.

21. The method as in claim 19 wherein the agent for extracting the organomercaptan-reacted lignin is a solution of an inorganic base.

22. The method as in claim 21 wherein the solution is an aqueous solution of sodium hydroxide containing from about 0.5 to about 5 weight percent of NaOH.

23. The method as in claim 19 wherein the agent for extracting the organomercaptan-reacted lignin is an extractive amidogen compound.

24. The method as in claim 23 wherein the extractive amidogen compound is an alkanolamine.

25. The method as in claim 24 wherein the alkanolamine is monoethanolamine, and the temperature of extraction is within the range of from ambient temperature to the reflux temperature of the extraction liquor.

References Cited Wood Chemistry, Wise & John, 2nd ed., vol. I, pub. by Reinhold Pub. Corp., New York, N.Y., 1952, p. 435 and p. 498.

HOWARD R. CAINE, Primary Examiner U.S. C1. X.R.