BACKGROUND OF THE INVENTION

The invention relates to pulp production and somewhat more particularly to the process of preparing pulp from a lig- noσellulosic material, such as coniferous or deciduous wood.

Production of pulp from lignocellulosic materials is well known and may involve mechanical, chemical, and thermal processes, or a select combination of such processes to pro¬ duce cellulosic fibers which can be manufactured into various products, for example, paper. Particularly economically at¬ tractive processes typically involve chemical pulping, semi- chemical pulping and/or chemi-thermomechanical pulping, due to high pulp yields.

Typically, in chemical pulping processes, shredded or chipped lignocellulosic materials are subjected to chemical re¬ agents that remove at least partially, as by dissolving, ex¬ tracting, dispersing or the like, lignin, hemicellulose, gums, carbohydrates, fatty materials, etc., collectively referred to as ^•• resins" from, for example, wood chips to release cellulose fibers during a digestion process. A presently dominant chemi¬ cal pulping process in the U.S. and certain other regions of the world is a so-called "Kraft" process. In a Kraft or sulfate process, sodium hydroxide and sodium sulfite typically comprise the principal cooking or digestive chemicals, which, when admixed with water, are generally referred to as alkaline pulping liquor or white liquor. The alkaline reagents react with the lignin and other resin molecules, breaking them into smaller segments whose sodium salts are soluble or dispersable in the cooking liquor.

In a Kraft pulping process, a select amount of, for ex¬ ample, wood chips, optionally pre-treated with steam or water that may also include chemical reagents, are charged to a

digester vessel, along with alkaline pulping liquor to attain a select chemical- or liquid-to-wood ratio and this material charge is then subjected to controlled heat and pressure over a select period of time. Both batch and continuous digestion processes are known. In batch processes, the material charged may be held under select temperature/pressure condition for a calculated period of time to attain a desired pulp characteris¬ tic and then discharged or "blown" into a holding tank so as to yield a pre-calculated amount of pulp suitable for further processing, such as chemical and/or heat recovery, washing, further digestive-type processing, bleaching, etc., prior to, for example, paper manufacturing. In a continuous digestion process, the material charge is controllably moved through zones of select temperature/pressure to a regulated discharge point, (i.e., a valve) to continuously yield pulp having de¬ sired characteristics (i.e., reduced "resins'* content, a se¬ lect Kappa number or range, water drainability, etc.).

A primary object of a pulping or digestion process is to reduce the amount of "resins" present in pulp fibers without deleteriously affecting paper-forming characteristics while maintaining an economically viable process and product (pulp) costs. An emphasis has been placed in pulping processes in¬ volving chemical means to provide chemical reagents compatible with the digestion conditions and cooking chemicals and which aid deresination. For example, U.S. Patent No. 2,716,058 de¬ scribes the use of ethoxylated phenols and tall oil as deresin¬ ation agents. U.S. Patent No. 2,999,045 describes the use of copolymers of polyethyleneoxide and polypropyleneoxide as de¬ resination agents. Organic solvents, such as kerosene, methan- ol, etc. and various emulsifiers such as certain sulfonated fatty acids (see U.S. Patent No. 4,673,400) and solubilizing a- gents, such as C ₁₂ alpha-olefin sulfonates (see U.S. Patent No. 4,426,254) have also been suggested as deresination a- gents. In addition, anthraquinone and certain derivatives thereof have been suggested as additives or catalysts useful in cooking liquors for deresination of lignocellulosic mate-

rials (see U.S. Patent No. 4,012,280). However, the various additives, solvents, catalysts, etc., tend to exhibit various drawbacks, including high chemical costs, excessive processing time, incompatibility with typical alkaline processing param¬ eters, etc.

It is therefore an object of the invention to provide an improved method of producing pulps, such as paperboard pulps, containerboard pulps, linerboard pulps, corrugated medium pulps, Kraft or sulphate market pulps, etc., by adding a diges¬ tion additive to alkaline pulping liquor in a pulping process to attain a reduced H-factor, reduced material rejects, reduc¬ ed "fresh" pulping liquor requirements, and reduced cooking or digestion periods relative to heretofore practiced pulping pro¬ cesses.

SUMMARY OF THE INVENTION

The invention provides an improved method of producing pulp from lignocellulosic material such as wood, straw, ba¬ gasse, etc., by subjecting such material to an alkaline pulp¬ ing process wherein a cooking or digestive additive selected from the group consisting essentially of alpha-sulfo alkyl es¬ ters, alkaryl sulfonates (i.e., hydrotropes) , alkyl sulfates, alkyl sulfosuccinates, alkanolamides, alkyl polyoxyalkylene glycol ethers, and mixtures thereof is added to an alkaline pulping liquor in a pulping process whereby a reduction of white (alkaline) liquor requirements, a reduction in H-factor, a reduction in percentage of pulp material rejects, and a re¬ duction in cooking or digestion time for a select Kappa number range is attained, relative to similar pulping processes with¬ out such digestive additive.

The above anionic additives are neutralized with a mono- valent or divalent cations and preferably the cation is select¬ ed from the group consisting essentially of Na, K, NH ₄ , sub¬ stituted ammonium, Ca, Ba, Mg, and mixtures thereof.

In certain preferred embodiments of the invention, the a- mount of digestive additive added to alkaline pulping liquors ranges from about 0.001% up to about 10% by weight, based on a 100% total weight basis of dry pulp produced.

The inventive process is particularly useful to produce Kraft or sulphate pulps, such as paperboard pulps, contain- erboard pulps, linerboard pulps, market pulps, etc. However, the principles of the invention may also be utilized to pro¬ duce other grades or types of pulps, such as, for example, a so-called dissolving pulp utilized in the manufacture of rayon and derivatives thereof.

The inventive process is particularly useful to produce paperboard pulps having a Kappa number ranging from about 30 to about 110 via an alkaline pulping proces with a reduction in H-factor, a reduction in pulp-yielding material rejects, a reduction of fresh cooking liquor (white liquor) requirements and a reduction in cooking or digestion time period, relative to heretofore conventional paperboard pulping processes.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention provides an improved method of producing pulps from any available lignocellulosic material source, such as coniferous or deciduous wood, straw, bagasse, etc. , or mix¬ tures thereof, by subjecting such material to a pulping pro¬ cess involving chemical means whereby a digestive additive is added to alkaline cooking or digestion liquors so as to pro¬ vide a reduced white liquor requirement, a reduced H-factor, a reduced percentage of pulp material rejects, and a reduced cooking or digesting time period, yielding a more economical pulp, relative to heretofore available pulping processes.

In accordance with the principles of the invention, a digestive additive selected from the group consisting essen¬ tially of alpha-sulfo alkyl esters, alkaryl sulfonates, alkyl

sulfates, alkyl sulfosuccinates, alkanolamides, alkyl polyoxyalkylene glycol ethers, and mixtures thereof is added to an alkaline cooking liquor whereby reduced processing parameters including reduced chemical requirements, reduced cooking and time periods, reduced H-factor, reduced material rejects, and improved pulp yields are attainable.

The above anionic additives are neutralized with a onovalent or divalent cation and preferably the cation is selected from the group consisting essentially of Na, K, Ca, Ba, Mg, NH ₄ , substituted ammonium (including HOCH ₂ CH ₂ ) ₃ NH, (HOCH ₂ CH ₂ ) ₂ NH ₂ ) , and mixtures thereof.

Examples of alpha-sulfo alkyl esters include moieties having the formula:

0

II

I -HCOIl-

(I)

SO- _j M

wherein R is alkyl or alkenyl group containing from about 4 to about 18 carbon atoms; R' is an alkyl or alkenyl group containing from 1 to about 18 carbon atoms, and M is a monovalent and/or divalent cation.

Examples of alkaryl sulfonates include moieties having the formula:

SUBSTITUTE SHEET

wherein R, R' and R" are each independently selected from the group consisting of H, C - C ₁₈ alkyl or alkylene groups and including both linear and branched chain entities, and M is a monovalent and/or a divalent cation.

Examples of alkyl sulfates include moieties having the formula:

ROSO ₃ M (III)

wherein R is a C ₄ to C ₁₈ alkyl or alkylene groups and M is a monovalent and/or a divalent cation.

Examples of alkyl sulfosuccinates include moieties having the formula:

0 O

II 11

R _OCC HCH ₂ COM _(ιv)

SO ₃ M

wherein R is a C ₄ to C ₁₈ alkyl or alkylene groups and each M is independently a monovalent and/or a divalent cation.

Examples of alkanolamides include the moieties having the formula:

O CH ₂ CH ₂ (OC ₂ H ₄ ) _χ OH RCH ₂ CN _{v)

CH ₂ CH ₂ (OC ₂ H ₄ ) _y OH

wherein R is a C ₄ to C ₁₈ alkyl or alkylene group, and x and y are each integers independently selected and ranging from 0 to about 6.

- -

Examples of alkyl polyoxyalkylene glycol ethers include moieties having the formula:

R -

R _(0C H _2C IH) _χ (0CH _2C IH) _y 0H (vi)

wherein R is a C ₂ - C _ιg alkyl or alkenyl group, R' and R" are H or CH ₃ and are the same or different, and x and y are integers independently selected with a ration of x:y ranging from about 1:1 to about 7:1, with the sum of x and y ranging from 0 to about 50.

In the above examples of suitable moieties, M, the monovalent or divalent cations, are preferably selected from alkali metal, alkaline earth metal, ammonium, substituted ammonium, and mixtures thereof. Specific preferred cations include those of Na, K, Ca, Ba, Mg, NH ₄ , (HOCH ₂ CH ₂ ) ₃ NH, (HOCH ₂ CH ₂ ) ₂ NH ₂ , and mixtures thereof.

The synthesis of the foregoing digestive additives is well known and forms no portion of this invention.

The amount of digestive additive to be added in accordance with this invention to alkaline pulping liquor varies considerably and, principally for economical reasons, amounts up to about 10% by weight, based on the weight of pulp produced, may be added to alkaline pulping liquors. Preferably, the amount of digestive additive admixed with the alkaline pulping liquor will range from about 0.001% up to about 10% by weight, based on a 100% total weight basis of dry pulp produced. More preferably, it ranges from about 0.01% up to about 5% by

wmmi SHEET

weight on the same basis. In typical pulp mill operations, the amount of digestive additives utilized is calculated on a pounds of chemical per ton of wood or other raw material utilized and under this system, the amount of digestive ad¬ ditives ranges from about 0.1 to 5 pounds per ton and more pre¬ ferably from about 1 to 2 pounds per ton of wood.

The digestive additives of the invention are generally biodegradable and thus are environment compatible. Further, they may be considered relatively low foam generating materi¬ als or at least compatible with typical paper chemical defoa - ers, such as nonionic block copolymers available under the trade names PLURONICS ^R or TETRONICS ^R and other like defoam- ing materials, i.e. silicon-based materials.

Thus, in accordance with the principles of the inven¬ tion, the improved method of producing select pulps having a predetermined Kappa number or Kappa number range from a ligno¬ cellulosic material, such as coniferous or deciduous wood chips or mixtures thereof, comprises (a) feeding an amount of, preferably substantially uniformly particulated, lignocellulo¬ sic material to a digester capable of yielding a given amount of at least partially delignified cellulosic pulp, (b) adding a sufficient amount of an aqueous alkaline pulping liquor to the digester to substantially cover the lignocellulosic materi¬ al therein (i.e. provide a select liquor-to-wood ratio), with the pulping liquor including therein an amount up to about 10% by weight, based on a 100% by weight basis of adry weight a- mount of substantially delignified cellulosic pulp, of one or more digestive additives as described above to obtain an aque¬ ous mixture of materials in the digester and subjecting such aqueous material mixture to select temperatures and pressures over select time periods so as to obtain a reduction of white liquor requirements, a reduction of H-factor, a reduction of material rejects and a reduction of digestion time, relative to white.liquor requirements, H-factor, reject percentages and digestion times typically obtainable in similar alka-

line digestion processed without the digestive additive, and (c) displacing the materials from the digester in such a manner as to attain at least some delignified cellulosic pulp and spent black pulping liquor (a portion of at least some chemicals therein may be recovered and/or a portion of such spent liquors may be recycled) . As will be appreciated, in making up typical pulping liquor for a digester, an operator may blend fresh alkaline liquor with spent or black liquor (or other recovered/recycled liquor) to obtain the economical bene¬ fits of reduced chemical costs but at some detriment to diges¬ tive action, unless the additives of the invention are util¬ ized. With the principles of the invention, more black liquor may be utilized so that a reduction of white liquor require¬ ments is readily achieved.

The principles of the invention are particularly useful in Kraft pulping procedures to produce Kraft or sulphate (mar¬ ket) pulps, as well as paperboard pulps, containerboard pulps, linerboard pulps, etc. However, the principles of the inven¬ tion may also be utilized to produce other grades or types of pulp, such as, for example, a dissolving pulp utilized in the manufacture of rayon or a derivative thereof.

A pulp mill or pulp line or other lignocellulosic materi¬ al processing facility typically seeks to produce a maximum a- mount of pulp at the lowest cost possible. Thus, a pulp mill typically adjusts a variety of chemical/processing parameters in an attempt to achieve maximum throughput of select quality of pulp. Thus, for example, a pulp mill may elect to utilize a somewhat higher cost processing chemical if the cook time will be reduced while yielding a comparable quality pulp, i.e. a higher chemical cost can be offset by a greater amount of pulp produced. Similarly, the addition of a further or adjunc- tive chemical to more traditional cooking chemicals may reduce processing times and reduce material rejects so as to provide a greater overall pulp through-put such as tons per day (tpd) over a given period of time, or reduce energy requirements to

obtain the same quality of pulp, thus providing a lower cost per unit of pulp. Thus, pulp mills seek to balance operat¬ ing/output parameters, typically expressed as Kappa number (de¬ gree of delignification) , percentage of pulp-yielding material rejects, cooking or digestion parameters (temperature, pres¬ sure, time, etc.) including reduction in white liquor require¬ ments, reduction of H-factor (defined as the relative reaction rate between the cooking chemical and the "resins" in the lig¬ nocellulosic material, graphically expressed as cooking time versus temperature) . Improvements in any one or more of these and other variables can lead to either greater throughput in a pulp mill or a lower cost per unit of pulp.

By practicing the inventive method, a pulp mill can readily achieve a more economical operation by adding the di¬ gestive additives to a pulping process and reducing white or fresh cooking liquor requirements, reducing H-factor, reducing rejects and reducing cooking time whle maintaining a desired Kappa or range. Of course, if desired, the Kappa number or range may be reduced from that typically attainable at a given digester while keeping the processing parameters (H-factor, cooking time, etc.) relatively constant.

Further, as will be appreciated, the adjunctive chemical additives of the invention have utility not only in the ' ini¬ tial digestion process (whether such involves a single or ul- tistep digestion process) of lignocellulosic materials but al¬ so in further refining processes, as sometimes are utilized to produce cellulosic materials having a high or higher alpha cel¬ lulose content, such as may be required to produce rayon or a derivative therof.

The digestive additives utilized to produce pulps in ac¬ cordance with the principles of the invention function in a manner not presently fully understood. It may be that these digestive additives provide aspects of surfactants/wetting agents/emulsifiers/dispersants/penetrants/solubilizers, etc. ,

to the pulping process and function via numerous mechanisms, including, for example, wetting the surface of, for example, wood chips to allow the cooking chemicals to more rapidly pene¬ trate into the interior layers thereof, and diffuse throughout the capillaries therein, solubilizing or emulsifying the "res¬ ins" or lignin by-products, etc.

Specific presently preferred anionic digestive additive materials useful in the practice of the invention comprise so¬ dium alpha-sulfo methyl laurate, (which may include some alpha- sulfo ethyl laurate) for example as commercially available un¬ der the trade name ALPHA-STEP ^tm - M:40; sodium xylene sulfo- nate, for example as commerciallly available under the trade name STEPANATE ^R - X; triethanolam onium lauryl sulfate, for example as commerciallly available under the trade name STEPA- NOL ^R - WAT; diosσdium lauryl sulfosuccinate, for example as commerciallly available under the trade name STEPAN ^R - Mild SL3; further blends of various digestive additives may also be utilized, for example a 50% -50% or a 25% - 75% blend of the a- foresaid ALPHA-STEP™ and STEPANATE ^R materials, or a 20% - 80% blend of the aforesaid ALPHASTEP™ and STEPAN0L ^R mate¬ rials (all of the aforesaid commercially available materials may be obtained from Stepan Company, Northfield, Illinois) .

Specific presently preferred nonionic digestive addi¬ tives useful in the practice of the invention comprise cocodi¬ ethanolamide, such as commercialy available under trade name NINOL ^R - 11CM; alkyl polyoxyalkylene glycol ethers, such as relatively high molecular weight butyl ethylenoxide - propylen- oxide block copolymers commerically available under the trade name T0XIMUL ^R - 8320 from the Stepan Company. Additional al¬ kyl polyoxyalkylene glycol ethers may be selected, for exam¬ ples, as disclosed in U.S. Patent No. 3,078,315. Blends of the various nonionic additives may also be utilized, for exam¬ ple a 50% - 50% or a 25% - 75% blend of the aforesaid NIN0L ^R and T0XIMUL ^R materials.

Specific presently preferred anionic/nonionic digestive additive blends useful in the practice of the invention in¬ clude various mixtures of the above materials, for example a 50% - 50% blends of the aforesaid ALPHA-STEP™ and NINOL ^R materials or a 25% - 75% blend of the aforesaid STEPANATE ^R and T0XIMUL ^R materials.

Preferably, the various digestive additive blends util¬ ized in the practice of the invention have a solids content up to about 100% by weight and preferably have an active content ranging from about 10% to about 80%. Of course, other blends or other solids (active) content may also be utilized and these digestive additives may also be utilized with known pulp¬ ing chemicals such as, for example, anthraquinone and deriva¬ tives thereof and/or other typical paper chemicals, such as caustics, defoamers, and the like.

The digestive additives of the invention are readily sol¬ uble in hot and cold aqueous solutions and are stable at typi¬ cal digestion parameters, i.e. at typical digestion tempera¬ tures ranging from about 120 to about 180 ^" C. , typical diges¬ tive time periods typically ranging from about 15 minutes to about 4 hours or more, typically digestive pressures ranging up to about 5 to 10 kg/cm ² , and typical cooking liquor pH levels up to about 13 or more. Further, unlike anthraquinone, the digestive additives of the invention are readily soluble in aqueous solutions and may thus be sprayed, or the like, on¬ to wood chips prior to charging the same into the digester.

With the foregoing general discussion in mind, a number of detailed examples are presented which will illustrate, to those skilled in the art, the manner in which the indention is carried out. However, these examples are not to be construed as limiting the scope of the invention in any way but are pro¬ vided merely to point out the efficacy of the invention in at¬ taining exemplary economical pulping production and to demon¬ strate a preferred utility of the digestive additives of the

invention.

EXAMPLE

The pulping conditions utilized and the residual liquor analysis data are set forth in Table I below. All pulping runs were carried out in uniform size laboratory digesters. In each run, 2,000 grams of O.D. (oven dry) soft wood (south¬ ern pine) chips passing through a 3/4 inch screen and retained on a 1/4 inch screen were charged into the digester and white liquor containing the selected digestive additive in specified amounts was added to a digester to attain a selected liquor-to- wood ratio. The liquor was continuously circulated during each entire cooking cycle, which was made using indirect steam.

Constant pulping conditions were adopted for each run and were as follows: liquor-to-wood ratio = 4:1; time period to rise to cooking temperature = 15 minutes; cooking tempera¬ ture = 340 ^β F (about 171"C); time period at cooking tempera¬ ture = 65 minutes. At the end of each cooking cycle, the cooks were blown at 90 psig (about 6 kg/cm ² ) and subsequent¬ ly washed with ambient temperature water until substantially free of chemical. After washing, the pulps were defiberized in a laboratory refiner in one pass at 0.25 inch clearance with a continuous flow of water. The pulps were screened on a 10-cut screen after defiberization. The pulps from each cook were subjected to screened Kappa numbers, percent rejects, yields and residual liquor analysis.

TABLE I

SUMMARY OF ALKALINE COOKING DATA

COOK NO. 1 2. 3 Additive* Control ALPHA-STEP TOXIMUL STEPANATE-X NINOL-11CM 8320 50/50 BLEND

Conditions: Chip moisture,% 51.1 51.1 51.1 51.1 Liquor: ood Ratio 4:1 4:1 4:1 4:1 Chip Charge, O.D.,g 2000 2000 2000 2000 Total Liquid, ml 8000 8000 8000 8000 Time Up, min. 15 15 15 15 Time At, min. 65 65 65 65 Temperature, *F 340 340 340 340 Pressure, psig 90 90 90 90

Chemicals: White Liquor, grams AA 00 300 300 300 Active Alkali, % ** 15 15 15 15 Sulfidity, % 25 25 25 25 Additive, lbs./ton on O.D. Wood

Residual Liσuor:

Active Alkali, g/1** 13.64 5.19 13.64 14.57

Eff. Alkali, g/1** 7.13 8.37 7.13 7.75 pH 12.8 3.1 13.0 13.0

Pulp Results: Total Yield, % 55.2 54.0 54.4 54.5 Screened Yield, % 50.1 50.5 50.1 51.1 Screened Kappa No. 77.0 62.4 69.1 69.2 Rejects, % 9.2 6.5 7.9 6.3

COOK NO. 5 6 2 8

Additive* STEPANOL STEPAN ALPHA-STEP ANTHRA¬

WAT MILD SL3 QUINONE

Conditions:

Chip moisture,% 51.1 51.1 51.1 51.1

Liquor:Wood Ratio 4:1 4:1 4:1 4:1

Chip Charge, 0.D. , g 2000 2000 2000 2000

Total Liquid, ml 8000 8000 8000 8000

Time Up, min. 15 15 15 15

Time At, min. 65 65 65 65

Temperature, "F 340 ^' 340 340 340

Pressure, psig 90 90 90 90

Chemicals:

White Liquor, grams AA 300 300 300 300

Active Alkali, % ** 15 15 15 15

Sulfidity, % 25 25 25 25 Additive, lbs./ton on O.D. Wood 2 1.34

Residual Liquor:

Active Alkali, g/1** 16.43 15.81 16.59 14.88

Eff. Alkali, g/1** 8.06 8.37 8.53 6.51 pH 13.0 13.0 12.7 12.45

Pulp Results:

Total Yield, % 53.8 53.7 53.9 56.6

Screened Yield, % 49.7 49.7 49.8 52.6

Screened Kappa No. 66.5 66.7 70.4 68.4

Rejects, % 7.2 7.4 7.6 7.0

♦Trademark materials identified earlier herein.

**Active and effective alkali concentrations are expressed as

Na ₂ 0.

As shown by the above data, the digestive additives of the invention provide beneficial results in comparison to a typical alkaline pulping (control) run or cycle and in compari¬ son to anthraquinone. Thus, under substantially uniform pulp¬ ing conditions, all of the exemplary inventive additives test¬ ed in the above Example provided lower Kappa numbers in compar¬ ison to the control, similar or lower rejects as anthraquinone (and, of course, substantially lower than the control) , and greater total pulp yield to that of the control and similar to that attained with anthraquinone. Further, it is pointed out that anthraquinone is difficult to work with due to its rela¬ tive insolubility and this material is relatively expensive, being about 2.5 to 5 times more expensive than the inventive additives. Yet further, in instances where a pulp mill seeks to produce a pulp having a given Kappa number or Kappa number range and elects to utilize the digestive additives of the in¬ vention, a substantial reduction in H-factor (graphical rela¬ tion between cook time versus temperature) , a reduction in al¬ kaline (fresh) liquor requirements, a reduction of reject per¬ centage, and a reduction of cook times can be attained at a very low additional cost.

.As is apparent by the foregoing specification, the pres¬ ent invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specifi¬ cation and description. For this reason, it is to be fully understood all of the foregoing is intended to be merely illus¬ trative and is not to be construed or interpreted as being re¬ strictive or otherwise limiting of the present invention, ex¬ cept as set forth in the hereto appended claims.