EP1077282A1

EP1077282A1 - Improved chemical pulping process

Info

Publication number: EP1077282A1
Application number: EP00117065A
Authority: EP
Inventors: Russel Allen Elms; James Habermehl; Kenneth Christopher Fey
Original assignee: Dow Corning Corp
Current assignee: Dow Silicones Corp
Priority date: 1999-08-16
Filing date: 2000-08-09
Publication date: 2001-02-21
Also published as: JP2001064889A

Abstract

The use of an oxyalkylene-modified organopolysiloxane in combination with an alkylpolyglycoside as chemical pulping additives is disclosed. The pulping additives utilized in accordance with the chemical pulping process of the invention improve the physical properties of wood pulp and products produced therefrom.

Description

The present invention provides additives which are useful for pulping wood chips. More particularly, the invention uses at least one oxyalkylene-modified organopolysiloxane and at least one alkylpolyglycoside as additives for digestive treatments of wood chips in aqueous cooking liquors.

Chemical pulping is the chemical processing of wood chips or the like to remove significant amounts of lignin therefrom. Pulps produced thereby can often be further subjected to bleaching and purification operations in a bleach plant, including further delignification of the pulp.

Lignin is the major noncarbohydrate constituent of wood and, prior to chemical pulping, usually comprises one-quarter of the raw material, functioning as a binder for the cellulosic fibers. The lignin is dissolved by cooking liquor in the manufacture of wood pulp. The character of the pulp produced is dependent on the extent of lignin removal from the wood chips and hence on the residual lignin content of the final pulp.

Significant quantities of lignin are removed during chemical pulping to form the fibrous pulp. However, substantial quantities of lignin often remain after conventional chemical pulping processes are complete, generally 2 to 6 weight percent of the pulp. Chemically, lignin is a complex structure which varies depending on the species of wood and is characterized by the presence of repeating phenol propane units.

It is known that in the conventional processes for manufacturing wood pulp that the wood can be treated with a variety of chemicals such as alkaline earth metal salts, weak acids, or sulfuric acid in an aqueous solution. These processes have several disadvantages, in particular the need to continue the cooking of the wood chips for 6 to 12 hours for the lignin digestion to be complete. In order to accelerate the delignification of the chips, it is necessary to operate at a temperature of 150°C. to 180°C. and under pressure of several atmospheres.

It is also known that in conventional processes of chemical pulping, wood can be treated with chemicals such as anthraquinone and anthraquinone derivatives in an aqueous solution.

It has also been disclosed that surface active agents can be used in the production of wood pulp by the sulfate pulp process. For example, Parker et al. in U.S. Patent 3,909,345, teach that surface active agents having the general formula R{(C₂H₄O)_n(C₃H₆O)_m}_yH wherein R is the nucleus of a reactive hydrogen compound selected from various glycols. diols, amines, piperazines, amides and acids, can be used as additives to sulfate cooking liquor for the purpose of obtaining higher yields of pulp from a given wood chip charge and that these agents permit a greater effectiveness of the cooking process relative to chips which prior to that invention were considered rejects and not pulpable.

Blackstone et al. in U.S. Patent 4,906,331 disclose that compounds having the general formula HO(C₂H₄O)_a(C₃H₆O)_b(C₂H₄O)_cH where a, b and c have a value of at least one, increase the yield of chemical pulping processes and decrease the level of rejects. Chen et al. in U.S. Patent 4,952,277 disclose a process for making paper or linerboard, the process comprising cooking wood chips in a Kraft liquor to form a Kraft pulp, the liquor excluding anthraquinone and including a surface active agent having the general formula C_nH_2n+1-C₆H₄-O(C₂H₄O)_xH where n is an integer from 8 to 12, and x is a positive integer from 1 to 100, the surface active agent being present in the cooking liquor in an amount effective to increase the yield of pulp. Ling et al. in U.S. Patent 5,250,152 teach a method for enhancing the penetration of cooking liquor into wood chips to form a Kraft pulp which comprises adding to the cooking liquor specific surfactants such as ethoxylated dialkylphenols and ethoxylated alcohols.

Pease in U.S. Patent 5,464,502 teaches a method for removing lignin and spent cooking chemicals from pulp which comprises adding, within the washing operation, from 0.1 to 1000 parts per million parts of pulp of an anionic sulfonate surfactant wherein the removal of lignin and spent cooking chemicals occurs at a temperature of from 30°-100°C.

It has also been disclosed that in chemical pulping processes which produce wood pulp that the wood can be treated with various silicones or siloxanes prior to addition to a digester unit or may be added directly to the digester before or after the digester has been filled with wood chips and liquor. For example, Simmons et al., in U.S. Patent 3,147,179, disclose that various silicones and siloxanes are useful as digestion aids in Kraft, soda or sulfite chemical pulping processes.

German Patent Application No. DE 4440186 discloses a process for obtaining pulp from fibrous materials in which organosilicon compounds such as oxyalkylene-modified organopolysiloxanes are added to the chemical pulping process, wherein the fibrous materials are reacted with a chemical pulping liquor in the presence of the organosilicon compounds.

Saint Victor et al. in U.S. Patent 5,728,265 discloses an improved pulping process which comprises contacting wood chips with a liquid mixture comprised of white liquor and at least one surfactant selected from the group consisting of a polymethylalkylsiloxane containing ethylene oxide and optionally propylene oxide groups, a co- and terpolymer of silicone and a polyhydric alcohol, an alkoxylated aryl phosphate, an alkoxylated branched alkyl phosphate, an alkoxylated branched alcohol, an alkyl polyglycoside, an alkoxylated alkyl polyglycoside, a mixture of alkali metal salts of alkyl aromatic sulfate, a sulfosuccinate, and a silicone, and combinations thereof for a residence time effective to extract resinous components without substantial degradation of cellulose and thereafter heating at least a portion of the resulting mixture and wood chips. The polymethylalkylsiloxane of Saint Victor et al. is a compound having the formula

wherein A = (CH₂)_x-O-(C₂H₄O)_y-(C3H6O)_z-R; R is an organic moiety having from 1 to 8 carbon atoms, m is a number from 1 to 100, n is a number from 0 to 100, x is an integer from 1 to 3, y is a number from 1 to 100 and z is a number from 0 to 100.

The present invention uses at least one oxyalkylene-modified organopolysiloxane and at least one alkylpolyglycoside as additives for digestive treatments of wood chips in aqueous cooking liquors.

It has been discovered in chemical pulping processes which involve the digestion of wood chips in liquors that the subsequent properties of the wood pulp are improved if small amounts of at least one oxyalkylene-modified organopolysiloxane and at least one alkylpolyglycoside are added to the liquors employed in the digestive treatments.

It is an object of the present invention to improve the strength of the cooked, washed pulp in chemical pulping processes by the addition of at least one oxyalkylene-modified organopolysiloxane and at least one alkylpolyglycoside to wood chips, cooking liquor or a digester.

This object is attained by a chemical pulping composition comprising

(A) wood chips;

(B) an aqueous cooking liquor;

(C) at least one oxyalkylene-modified organopolysiloxane compound having the formula R¹R₂SiO(R₂SiO)_a(RXSiO)_bSiR₂R¹ wherein R is a monovalent hydrocarbon group having from 1 to 20 carbon atoms, X is a polyoxyalkylene group selected from -R²(OC₂H₄)_cOR³, -R²(OC₂H₄)_c(OC₃H₆)_dOR³, -R²(OC₂H₄)_c(OC₄H₈)_eOR³, -R²(OC₃H₆)_d(OC₄H₈)_eOR³ and -R²(OC₂H₄)_c(OC₃H₆)_d(OC₄H₈)_eOR³ wherein R¹ is R or X, R² is a divalent hydrocarbon group having from 1 to 20 carbon atoms, R³ is selected from a hydrogen atom, an alkyl group, an aryl group, or an acyl group, a has an average value of at least 120, b has an average value from 1 to 500, and c, d, and e independently have an average value from 1 to 150; and

(D) at least one alkylpolyglycoside and by a chemical pulping process comprising the steps of:

(I) forming the above defined composition

(II) heating the mixture of step (I) to a temperature of at least 150°C. for a period of time sufficient to substantially delignify the wood chips (A) so as to form a pulp therefrom;

(III) maintaining the heated mixture of step (II) at a pressure sufficient to prevent boiling of aqueous cooking liquor (B) during step (II); and

(IV) recovering the pulp from said mixture.

Furthermore the present invention refers to the pulp obtainable by said method and to the use of the combination of the above oxyalkylene-modified organopolysiloxane compound and alkylpolyglycoside in chemical pulping.

Our chemical pulping process comprises the steps of (I) forming a mixture comprising (A) wood chips, (B) an aqueous cooking liquor, (C) at least one oxyalkylene-modified organopolysiloxane compound having the formula R¹R₂SiO(R₂SiO)_a(RXSiO)_bSiR₂R¹ wherein R is a monovalent hydrocarbon group having from 1 to 20 carbon atoms, X is a polyoxyalkylene group selected from the group consisting of -R²(OC₂H₄)_cOR³, -R²(OC₂H₄)_c(OC₃H₆)_dOR³, -R²(OC₂H₄)_c(OC₄H₈)_eOR³, -R²(OC₃H₆)_d(OC₄H₈)_eOR³ and -R²(OC₂H₄)_c(OC₃H₆)_d(OC₄H₈)_eOR³, wherein R¹ is R or X, R² is a divalent hydrocarbon group having from 1 to 20 carbon atoms, R³ is selected from a hydrogen atom, an alkyl group, an aryl group, or an acyl group, a has an average value of at least 120, b has an average value from 1 to 500, and c, d and e independently have an average value from 1 to 150; and (D) at least one alkylpolyglycoside, (II) heating the mixture of step (I) to a temperature of at least 150°C. for a period of time sufficient to substantially delignify the wood chips (A) so as to form a pulp therefrom, (III) maintaining the heated mixture of step (II) at a pressure sufficient to prevent boiling of aqueous cooking liquor (B) during step (II), and (IV) recovering the pulp from said mixture.

The term "chemical pulp" as used herein, refers to the product of manufacture of wood pulp from raw wood primarily by chemical means. Chemical pulps are formed by the removal of lignin from raw wood by chemical action to form a fibrous pulp.

Wood chips (A) can be in the form of whole tree chips including bark, branches, hardwood chips, softwood chips, sawdust, or combinations thereof. The wood chips can be prepared by a de-barking operation in which bark is removed from the logs, and the logs are then shredded or cut into chips of suitable small size to facilitate their digestion. Whole tree chips do not need to be de-barked prior to shredding or chipping. The wood chips (A) of this invention may also be "presteamed". Presteamed wood chips are prepared by preheating the wood chips in a steaming vessel to drive out air and open the wood pores of the chips which allows the aqueous cooking liquor (B), described hereinbelow, to more easily penetrate into the wood. This steaming process can be carried out in a continuous cooking operation or in a batchwise fashion for batch digester operations.

The aqueous cooking liquor, Component (B), can be selected from Kraft cooking liquors, soda cooking liquors and sulfite cooking liquors. The aqueous cooking liquor (B) can also further comprise at least one ingredient selected from black liquor, polysulfide and anthraquinone-containing compounds. Thus a combination of two or more of these optional ingredients can also be used. The anthraquinone-containing compounds are exemplified by anthraquinone, anthraquinone-2-carboxylic acid, anthraquinone-1,5-disulfonic acid disodium salt hydrate, anthraquinone-2,6-disulfonic acid disodium salt, and anthraquinone-2-sulfonic acid sodium salt monohydrate. It is believed that the addition of an anthraquinone-containing compound to the aqueous cooking liquor significantly contributes to the removal of lignin.

The Kraft cooking liquors comprise sodium hydroxide and sodium sulfide as the active cooking components of the liquor. It is preferred that the aqueous cooking liquor to wood ratio is from 2:1 to 6:1. The percentage of total active alkali in aqueous cooking liquor (B) depends on the species of wood to be pulped and on the desired degree of delignification of the wood. For example, if a "board" grade of pulp with moderate delignification is desired or a "bleaching" grade of pulp with as much delignification as possible without severe degradation to the cellulosic components is desired, the concentration varies from 12-25% total active alkali, and preferably from 10-30% as Na₂O based on the oven dry weight of the wood chips. The Na₂O represents both the amount of NaOH and Na₂S to be used. The Na₂S used will furnish 15-25% of the total Na₂O while the remainder is furnished by NaOH. In actual practice, some of the aqueous cooking liquor may be circulated so that the total Na₂O content may include salts such as sodium carbonate, sodium hydrosulfate, sodium sulfate and sodium thiosulfate. This is due to the addition of some black liquor to the freshly prepared aqueous cooking liquor prior to its addition to the wood chips. The black liquor may comprise 10 to 50 percent of the aqueous cooking liquor added to a fresh charge of wood chips. The sulfide content of the aqueous cooking liquor (B) is expressed as sulfidity, i.e. the percentage ratio of Na₂S expressed as Na₂O, to the total active alkali is preferably from 10-40%.

As used herein to describe Component (C), the oxyalkylene-modified organopolysiloxane, it is understood that the various siloxane units and the oxyethylene, oxypropylene and oxybutylene units may be distributed randomly throughout their respective chains or in respective blocks of such units or in a combination of random or block distributions.

The term "oxyalkylene-modified organopolysiloxane compound," standing alone, encompasses a number of compounds, including those based upon cyclic, branched and resinous siloxane compounds. While cyclic, branched and resinous oxyalkylene-modified siloxanes can be used in combination with alkylpolyglycosides they are comparatively expensive and thus, are not as cost effective as the particular oxyalkylene-modified organopolysiloxane compounds used in accordance with the present invention.

In the above formula for Component (C), R is a monovalent hydrocarbon group having from 1 to 20 carbon atoms exemplified by alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, octyl and decyl, cycloaliphatic groups such as cyclohexyl, aryl groups such as phenyl, tolyl, and xylyl, and aralkyl groups such as benzyl and phenylethyl. It is preferred that R is selected from methyl or phenyl. The several R radicals can be identical or different, as desired.

The group R² is a divalent hydrocarbon group having from 1 to 20 carbon atoms which is exemplified by alkylene groups exemplified by methylene, ethylene, propylene, butylene, pentylene, trimethylene, 2-methyltrimethylene, pentamethylene, hexamethylene, 3-ethyl-hexamethylene, octamethylene, -CH₂(CH₃)CH-, -CH₂CH(CH₃)CH₂-, -(CH₂)₁₈- and cycloalkylene radicals such as cyclohexylene, arylene radicals such as phenylene, combinations of divalent hydrocarbon radicals such as benzylene (-C₆H₄CH₂-), and oxygen containing groups such as -CH₂OCH₂-, -CH₂CH₂CH₂OCH₂-, -CH₂CH₂OCH₂CH₂-, -COOCH₂CH₂OOC-, -CH₂CH₂OCH(CH₃)CH₂- and -CH₂OCH₂CH₂OCH₂CH₂-. Preferred alkylene groups have from 2 to 8 carbon atoms.

The group R³ can be a hydrogen atom, an alkyl group, an aryl group, or an acyl group. The alkyl groups are exemplified by methyl, ethyl, propyl, butyl, hexyl, octyl and decyl. The aryl groups are exemplified by phenyl, tolyl and xylyl. The acyl group can have from 1 to 20 carbon atoms and include groups such as acetyl, propionyl, butyryl, isobutyryl, lauroyl, myristoyl and stearoyl 3-carboxypentadecanoyl. Preferably the acyl group is a group having the formula -OCR⁴ wherein R⁴ denotes a monovalent hydrocarbon group. The monovalent hydrocarbon groups of R⁴ are as delineated above for R. It is preferred that R⁴ is a lower alkyl group such as methyl, ethyl or butyl.

In the above formula for Component (C), preferably a has an average value of at least 120, b has an average value from 1 to 500, and c, d and e independently have an average value from 1 to 50. It is especially preferred that a has an average value from 120 to 260, b has an average value from 5 to 50, and c, d, and e independently have an average value from 1 to 36. It is highly preferred that a has an average value from 140 to 220.

Preferably Component (C) is an oxyalkylene-modified organopolysiloxane compound having the formula Me₃SiO(Me₂SiO)_a(MeXSiO)_bSiMe₃, wherein X is selected from -(CH₂)_n(OC₂H₄)_cOH, -(CH₂)_n(OC₂H₄)_c(OC₃H₆)_dOH, -(CH₂)_n(OC₂H₄)_cOCH₃, -(CH₂)_n(OC₂H₄)_c(OC₃H₆)_dOCH₃, -(CH₂)_n(OC₂H₄)_cOC(O)CH₃, and -(CH₂)_n(OC₂H₄)_c(OC₃H₆)_dOC(O)CH₃ wherein Me denotes methyl, a has an average value from 120 to 260, b has an average value from 1 to 50, n has a value of 2 to 10, c has an average value of 1 to 36, and d has an average value of 1 to 36. In a preferred embodiment of this invention, a has an average value from 140 to 220. Component (C) can also comprise a mixture of the above delineated oxyalkylene-modified organopolysiloxanes.

The wood chips (A), aqueous cooking liquor (B), oxyalkylene-modified organopolysiloxane compound (C) and alkylpolyglycoside (D) may be added to a digester in any order. For example, the oxyalkylene-modified organopolysiloxane compound (C) and alkylpolyglycoside (D) of this invention may be added directly to the digester before or after the digester is charged with chips and cooking liquor, or may be added to the cooking liquor or chips prior to addition of the cooking liquor or chips to the digester. Preferably, the oxyalkylene-modified organopolysiloxane (C), and alkylpolyglycoside (D), are added to cooking liquor (B) before it is circulated through the wood chips (A) in a digester.

The term "digester" as used herein, refers to a cylindrical metal vessel, used chiefly in the preparation of wood pulp for papermaking, in which lignin is separated from cellulose by chemical means. Standard commercial digesters are 12 feet in diameter and 45 feet high with a wall thickness of 2 inches. These types of digesters hold 20 cords of wood. Elevated pressure and temperature are applied to the mixture to separate, by dissolution, as completely as possible, the lignin content of the cellulosic fibers of the wood. Usually, steam to heat and pressurize the digester is supplied through a pipe to the digester (i.e. direct steam injection). The heat can also be supplied by circulating steam and a heat exchanger. The oxyalkylene-modified organopolysiloxane (C) and alkylpolyglycoside (D) can be used in Kraft pulping using either a continuous or a batch digester, continuous digestion Kraft pulping with extended delignification using staged alkali addition and countercurrent final cooking, batch digestion Kraft pulping with extended delignification using rapid liquor displacement and cold blowing techniques, or Kraft-anthraquinone pulping to achieve enhanced delignification using either a continuous or batch digestion stage.

Usually the concentration of oxyalkylene-modified organopolysiloxane compound (C) and alkylpolyglycoside (D) ranges from 50 to 1,000 weight parts per million (based on dry weight of wood chips), more preferably from 50 to 500 parts per million, and most preferably from 50 to 300 parts per million.

In the preferred embodiment of the invention, the amount of oxyalkylene-modified organopolysiloxane compound (C) ranges from 10 parts to 90 parts, by weight, and the amount of alkylpolyglycoside, Component (D) ranges from 90 parts to 10 parts, by weight, per 100 parts of the combined weights of (C) and (D). In the process of the invention, it is even more preferred that the amount of Component (C) ranges from 25 parts to 75 parts, by weight, and Component (D) ranges from 75 parts to 25 parts, by weight, per 100 parts of the combined weights of (C) and (D).

Component (D) of the present invention is an alkylpolyglycoside. Those skilled in the art will appreciate that the term alkylpolyglycoside encompasses numerous compounds including alkylpolyglucosides, alkylpolymannosides and alkylpolygalactosides.

The alkylpolyglycosides of this invention are exemplified by a compound or a mixture of compounds having the formula R⁵O(R⁶O)_x(Z)_y wherein R⁵ is a monovalent organic radical having from 4 to 40 carbon atoms, R⁶ is a divalent alkylene radical having from 2 to 4 carbon atoms, Z is a saccharide residue having 5 or 6 carbon atoms, x is a number having a value from 0 to 12, y is a number having a value from 1 to 6. Preferably, x has a value of 0, R⁵ is an alkyl group having from 8 to 16 carbon atoms, Z denotes C₆H₁₁O₅, and y has a value of 1 to 4, inclusive.

The preferred alkylpolyglycosides are characterized in that they have increased surfactant properties and an HLB in the range of 10 to 16 and a non-Flory distribution of glycosides, which is comprised of a mixture of an alkyl monoglycoside and a mixture of alkylpolyglycosides having varying degrees of polymerization of 2 and higher in progressively decreasing amounts, in which the amount by weight of polyglycoside having a degree of polymerization of 2, or mixtures thereof with the polyglycoside having a degree of polymerization of 3, predominate in relation to the amount of monoglycoside, said composition having an average degree of polymerization of 1.8 to 3. Such compositions, also known as peaked alkylpolyglycosides, can be prepared by separation of the monoglycoside from the original reaction mixture of alkylmonoglycoside and alkylpoly-glycosides after removal of the alcohol. This separation may be carried out by molecular distillation and normally results in the removal of 70-95% by weight of the alkyl monoglycosides. After removal of the alkylmonoglycosides, the relative distribution of the various components, mono- and poly-glycosides, in the resulting product changes and the concentration in the product of the polyglycosides relative to the monoglycoside increases as well as the concentration of individual polyglycosides to the total, i.e. DP2 and DP3 fractions in relation to the sum of all DP fractions.

Other alkylpolyglycosides which can be used in the process of this invention are those in which the alkyl moiety contains from 6 to 18 carbon atoms in which and the average carbon chain length of the composition is from 9 to 14 comprising a mixture of two or more of at least binary components of alkylpolyglycosides, wherein each binary component is present in the mixture in relation to its average carbon chain length in an amount effective to provide the surfactant composition with the average carbon chain length of 9 to 14 and wherein at least one, or both binary components, comprise a Flory distribution of polyglycosides derived from an acid-catalyzed reaction of an alcohol containing 6-20 carbon atoms and a suitable saccharide from which excess alcohol has been separated.

Alkylpolyglycosides of the type described are commercially available from Henkel Corporation, Ambler, Pa. 19002 sold under the tradenames APG®, GLUCOPON®, or PLANTAREN® surfactants. Examples of such surfactants include but are not limited to APG®225 Surfactant: an alkylpolyglycoside in which the alkyl group contains 8 to 10 carbon atoms and having an average degree of polymerization of 1.7, APG®425 Surfactant: an alkylpolyglycoside in which the alkyl group contains 8 to 16 carbon atoms and having an average degree of polymerization of 1.6, APG®625 Surfactant: an alkylpolyglycoside in which the alkyl groups contains 12 to 16 carbon atoms and having an average degree of polymerization of 1.6, APG®325 Surfactant: an alkylpolyglycoside in which the alkyl groups contains 9 to 11 carbon atoms and having an average degree of polymerization of 1.6, GLUCOPON®600 Surfactant: an alkylpolyglycoside in which the alkyl groups contains 12 to 16 carbon atoms and having an average degree of polymerization of 1.4, PLANTAREN®2000 Surfactant: a C_8-16 alkylpolyglycoside in which the alkyl group contains 8 to 16 carbon atoms and having an average degree of polymerization of 1.4. PLANTAREN®1300 Surfactant: a C_12-16 alkylpolyglycoside in which the alkyl groups contain 12 to 16 carbon atoms and having an average degree of polymerization of 1.6, and GLUCOPON®220 Surfactant an alkyl polyglycoside in which the alkyl group contains 8 to 10 carbon atoms and having an average degree of polymerization of 1.5. Other commercially available alkylpolyglycosides which are suitable for use in this invention are sold by Henkel Corporation. Emery Group/CD, of Cincinnati, Ohio, sold under the name Glucopon® with product designations of 220 UP, 225 DK 425, 600 UP, 625 CSUP and 625 FE.

Those skilled in the art will appreciate that commercially available alkylpolyglycosides are often diluted with fairly substantial quantities of water (up to 50%, by weight). The preferred ranges for the use of Components (C) and (D) as set forth above are based upon "solids" content, exclusive of such water content.

In manufacturing operations, it is preferable to add the oxyalkylene-modified organopolysiloxane compound (C) and an alkylpolyglycoside (D) as an aqueous solution so as to facilitate the admixture of the additives with the liquor during digestion. The mixture of Step

(I) is generally formed at temperatures of below 80°C.

Step (II) in the chemical pulping process of this invention comprises heating the mixture of step (I) to a temperature of at least 150°C. for a period of time sufficient to substantially delignify the wood chips (A) so as to form a pulp therefrom. Preferably the mixture of Step (I) is heated to temperatures of from 150 to 180°C. This temperature is then maintained for a period of time sufficient to substantially delignify the wood chips (A) so as to form a pulp therefrom, generally from 0.5 hours to 6 hours, preferably from 0.5 hours to 3 hours.

Step (III) in the chemical pulping process of this invention comprises maintaining the heated mixture of step (II) at a pressure sufficient to prevent boiling of aqueous cooking liquor (B) during step (II). Generally steam is allowed to enter the digester until a maximum pressure of from 100 to 150 psi (6.89 x 10⁵ to 1.03 x 10⁶ Pa) is reached. This pressure is then maintained from 0.5 hours to 6 hours, preferably from 0.5 hours to 3 hours.

Step (IV) in the chemical pulping process of this invention comprises recovering the pulp from said mixture. The pulp can be recovered by any process known to those skilled in the art. Typically the pulp is recovered by a process comprising discharging the cooked chips from a digester under pressure, the mechanical force of which breaks up the wood chips into individual fibers, producing pulp which contains fiber and exhausted liquor which is black in color, washing the black liquor from the pulp, and then screening the pulp to remove uncooked chips and other large fragments.

It should be pointed out that organopoly-siloxanes are also employed for suppressing foam in the washing stages of some Kraft mills. As such, and because of normal black liquor recycle procedures, trace amounts of organopolysiloxanes may have been known to inadvertently enter a digester with the recycled black liquor. The trace amounts of organopolysiloxane have produced no recognizable benefits to the Kraft pulps and accordingly the small amounts of organopolysiloxane compounds employed in accordance with the present invention are distinguishable from the trace amounts which inadvertently enter a digester through the normal use of certain organosilicon compounds for foam control in the pulp washing phases of the processes.

The combination of oxyalkylene-modified organopolysiloxane compound (C) and alkylpoly-glycoside (D) improve the physical characteristics of pulp treated therewith, especially the tensile and tear strength of the produced pulp.

The Kappa number associated with a delignified pulp represents a measure of residual lignin content. Kappa number are generally measured in accordance with TAPPI Classical Method T 236 cm-85. Those skilled in the art will appreciate that the degree of delignification which is desirable for a given chemical pulping process is directly related to the desired end product. For instance, if the desired end product is unbleached Kraft liner, the target Kappa number generally ranges from 65 to 115, indicating a fairly high level of residual lignin. Whereas in bleached Kraft pulp, suitable for use in fine paper, such as writing paper, the desired Kappa number target may be from 25 to 35, indicating a much higher degree of delignification. Thus, in accordance with the present invention, the heating step (II) is limited such that the mixture is heated to a temperature in excess of 150°C. for a period of time sufficient to substantially delignify the (A) wood chips so as to form a pulp therefrom. As used herein, the term "substantially delignify" means that the delignification has taken place to the desired extent, depending upon the desired end product.

The performance of the chemical pulping additive of this invention was compared to the performance of a cook completed with the prior art invention and a standard Kraft cook (no additives). The cooks were carried out under typical Kraft pulping conditions utilizing a laboratory scale digester equipped with temperature and pressure monitoring devices.

The wood chips utilized in this study were conventional Southern Pine softwood chips obtained from a commercial pulping operation. The moisture content of the chips was measured and the wood chips were loaded into the laboratory digester on a dry weight basis. Thereafter, an aqueous cooking liquor in the form of a white liquor with an effective alkali content of 16.5% by weight (expressed as Na₂O) and a sulfidity of 25% by weight (expressed as Na₂O), in accordance with that hereinabove described, was added to the digester. The weight ratio of the white liquor to wood chips was 3.8:1.

The first run series, RUN1, was completed with no addition of any additive to the white liquor. The second and third run series, RUN2 and RUN3, were completed with the addition of a mixture of 45.0 weight parts of oxyalkylene-modified organopolysiloxane, 45.0 weight parts alkylpolyglycoside and 10.0 weight parts water added to the white liquor each at a level of 550 ppm prior to addition to the digester.

The oxyalkylene-modified organopoly-siloxane used in RUN2 was a random rake copolymer having the general formula: Me₃SiO(Me₂SiO)_a(MeR¹SiO)_bSiMe₃ wherein Me denotes methyl, a has an average value of 169, b has an average value of 23, and R¹ has the general formula: -(CH₂)₃(OC₂H₄)_c(OC₃H₆)_dOH and c has an average value of 18 and d has an average value of 18.

The alkylpolyglycoside used was an alkylpolyglycoside supplied by Henkel Corporation and sold under the name Glucopon® 600 UP. The alkylpolyglycoside is described by Henkel Corporation as having the following general formula: R⁵-O(C₆H₁₁O₅)_h(C₆H₁₁O₅) wherein R⁵ is an alkyl group having from 12 to 16 carbon atoms and h is predominantly from 0 to 3, inclusive.

The oxyalkylene-modified organopoly-siloxane used in RUN3 was a random rake copolymer having the general formula: Me₃SiO(Me₂SiO)_a(MeR¹SiO)_bSiMe₃ wherein Me denotes methyl, a has an average value of 25, b has an average value of 6 and R¹ has the following general formula: -(CH₂)₃(OC₂H₄)_c(OC₃H₆)_dOH and c has an average value of 10 and d has an average value of 4. The alkylpolyglycoside used was an alkylpolyglycoside supplied by Henkel Corporation and sold under the name Glucopon®600 UP as described hereinabove.

Each of the pulping additives (mixture of oxyalkylene-modified organopolysiloxane and alkylpolyglycoside) were added separately to the digester. The contents of the digester were then heated to a cooking temperature of 170 °C. The time to obtain the specified cooking temperature was 60 minutes and once obtained, the cooking temperature was held constant for 80 minutes such that the H-factor for each of the laboratory cooks was 1450. The pressure during each digester cook reached a maximum of 110 psi (7.58 x 10⁵ Pa). After the cook was completed, the pressure in the digester was released to atmospheric pressure. The cooking conditions were sufficient to substantially delignify the wood chips and form a pulp therefrom. Residual active alkali and effective alkali concentrations were measured on the black liquor discharged from the digester. The cooked pulp removed from the laboratory digester was screened on an 8-cut flat screen to measure screened yield, rejects and total yield. The KAPPA number was measured on the screened pulp.

The screened pulp from each run series was subjected to mechanical treatment (beating) in accordance with TAPPI Classical Test Method T 248 wd-97, until approximate target Canadian Standard Freeness values of 725, 675, 550,425, 300 and 250 mls were obtained. Five standard 60 g/m² handsheets were cast from each pulp at each target freeness in accordance with TAPPI Official Test Method T 205 sp-95. The handsheets were then conditioned and tested for tensile strength, tearing resistance and tensile energy absorption in accordance with TAPPI Official Test Method T 220 sp-96.

The strength indexes reported in Tables 2-4 were calculated from the conditioned weight of the handsheet and represent the numerical average obtained from the five handsheets.

	RUN 1	RUN2	RUN3
Residual Effective Alkali (g/l as NaOH)	14.6	14.3	14.9
Residual Active Alkali (g/l as NaOH)	18.4	19.8	19.8
Total Yield (%)	45.8	46.2	45.6
Screened Yield (%)	45.2	45.6	44.8
Rejects (%)	0.67	0.64	0.79
KAPPA Number	31.7	31.8	32.2

RUN 1
PFI Revolutions	0	4000	6000	7000	8000	10000
Canadian Standard Freeness (mls)	744	633	499	432	351	257
Tear Index (mN·m²/g)	28.7	19.8	17.3	17.8	16.4	15.4
Tensile Index (N·m/g)	36.3	78.1	77.0	75.6	77.2	82.2
Tensile Energy Absorption (J/m²)	23.1	103.4	108.6	115.5	101.1	113.0

RUN 2
PFI Revolutions	0	4000	6000	7000	8000	10000
Canadian Standard Freeness (mls)	741	625	527	453	367	287
Tear Index (mN·m²/g)	28.4	19.3	17.6	18.1	17.0	17.1
Tensile Index (N·m/g)	33.6	77.7	82.2	80.7	83.5	79.2
Tensile Energy Absorption (J/m²)	21.0	98.6	120.5	132.4	129.2	126.1

RUN 3
PFI Revolutions	0	4000	6000	7000	800	10000
Canadian Standard Freeness (mls)	754	620	487	427	362	261
Tear Index (mN·m²/g)	25.9	18.6	16.3	15.9	15.4	14.3
Tensile Index (N·m/g)	32.2	74.0	77.1	80.0	82.3	79.9
Tensile Energy Absorption (J/m²)	19.1	100.0	110.8	111.8	123.7	109.4

Referring now to Table 1, it can be seen that the use of the pulp digester additive in accordance with the present invention (RUN2) provides both increased Total Yield and Screened Yield relative to both conventional Kraft pulping (RUN1) and that of the prior art process (RUN3). Because a typical mill may process up to 2,000 (1.81 X 10⁶ Kg) tons of wood chips per day, a one percent increase in yield represents an increased output of 20 (1.81 x 10⁴ Kg) tons of pulp. Accordingly, what appear to be small increases in yield can have dramatic effects on the profitability of chemical pulping operations. Further, as shown in Table 1, the pulp digester additive in accordance with the present invention (RUN2) improves, or lowers, the KAPPA number relative to the prior art process (RUN3).

Referring to Tables 2-4, it can be seen that the use of the pulp digester additive in accordance with the present invention (RUN2) dramatically and surprisingly increases the tensile energy absorption of the pulp compared to both conventional Kraft pulping (RUN1) and that of the prior art process (RUN3). Further, particularly beneficial results are noted when the relationship between tensile index and tear index are examined within each run series. The tensile index : tear index relationship in accordance with the present invention (RUN2) is measurably higher than pulp produced via conventional Kraft pulping techniques (RUN1) and that of the prior art process (RUN3). Finally, it can also be seen from Table 3 and Table 4 that use of the pulp digester additive in accordance with the present invention (RUN2) dramatically and surprisingly increases the tear strength of the pulp relative to pulp produced from the prior art process (RUN3).

Claims

A chemical pulping composition comprising

(A) wood chips;

(B) an aqueous cooking liquor;

(C) at least one oxyalkylene-modified organopolysiloxane compound having the formula R¹R₂SiO(R₂SiO)_a(RXSiO)_bSiR₂R¹ wherein R is a monovalent hydrocarbon group having from 1 to 20 carbon atoms, X is a polyoxyalkylene group selected from -R²(OC₂H₄)_cOR³, -R²(OC₂H₄)_c(OC₃H₆)_dOR³, -R²(OC₂H₄)_c(OC₄H₈)_eOR³, -R²(OC₃H₆)_d(OC₄H₈)_eOR³ and -R²(OC₂H₄)_c(OC₃H₆)_d(OC₄H₈)_eOR³ wherein R¹ is R or X, R² is a divalent hydrocarbon group having from 1 to 20 carbon atoms, R³ is selected from a hydrogen atom, an alkyl group, an aryl group, or an acyl group, a has an average value of at least 120, b has an average value from 1 to 500, and c, d, and e independently have an average value from 1 to 150; and

(D) at least one alkylpolyglycoside.
The composition according to claim 1 wherein (C) is oxyalkylene-modified organopolysiloxane compound having the formula Me₃SiO(Me₂SiO)_a(MeXSiO)_bSiMe₃ wherein Me denotes methyl, X is selected from -(CH₂)_n(OC₂H₄)_cOH, -(CH₂)_n(OC₂H₄)_c(OC₃H₆)_dOH, -(CH₂)_n(OC₂H₄)_cOCH3, -(CH₂)_n(OC₂H₄)_c(OC₃H₆)_dOCH₃, -(CH₂)_n(OC₂H₄)_cOC(O)CH₃, and -(CH₂)_n(OC₂H₄)_c(OC₃H₆)_dOC(O)CH₃, a has an average value from 140 to 220, b has an average value from 1 to 50, n has a value of 2 to 10, c has an average value of 1 to 36, and d has an average value of 1 to 36.
The composition of any of claims 1 and 2 wherein (D) is an alkylpolyglycoside having the formula or a mixture comprising alkylpolyglycosides having the formula R⁵O(R⁶O)_x(Z)_y wherein R⁵ is a monovalent organic radical having from 4 to 40 carbon atoms, R⁶ is a divalent alkylene radical having from 2 to 4 carbon atoms, Z is a saccharide residue having 5 to 6 carbon atoms, x is a number having a value from 0 to 12, y is a number having a value from 1 to 6.
The composition according to claim 3 wherein x has a value of 0, R⁵ is an alkyl group having from 8 to 16 carbon atoms, Z denotes C₆H₁₁O₅, and y has a value of 1 to 4, inclusive.
A chemical pulping process comprising the steps of:

(I) forming the composition of any of claims 1-4

(II) heating the mixture of step (I) to a temperature of at least 150°C. for a period of time sufficient to substantially delignify the wood chips (A) so as to form a pulp therefrom;

(III) maintaining the heated mixture of step (II) at a pressure sufficient to prevent boiling of aqueous cooking liquor (B) during step (II); and

(IV) recovering the pulp from said mixture.
The process according to claim 5 wherein Step (II) comprises heating the mixture of Step (I) at a temperature of 150 to 180°C. for 0.5 hours to 6 hours.
The process according to any of claims 5 and 6 wherein the pressure in Step (III) is from 100 to 150 psi.
A pulp obtainable by the process of any of claims 5-7.
Use of a combination of an oxyalkylene-modified organopolysiloxane compound and an alkylpolyglycoside in chemical pulping wherein said oxyalkylene-modified organopolysiloxane and said alkylpolyglycoside is defined as in any of claims 1-4.