EP0485150A1

EP0485150A1 - Pulping processes, extraction of lignin and composition of matter for use in such processes

Info

Publication number: EP0485150A1
Application number: EP91310190A
Authority: EP
Inventors: William Heckrodt; Norman Thompson
Original assignee: Biodyne Chemicals Inc
Current assignee: Biodyne Chemicals Inc
Priority date: 1990-11-06
Filing date: 1991-11-05
Publication date: 1992-05-13
Also published as: CA2055040A1

Abstract

The pulping process involves digesting vegetable matter in a digesting liquor having an effective pH, during the digesting phase, of no more than about 7; the vegetable matter is digested in the presence of a catalyst comprising electron donor moieties and hydrophobic moieties, the catalyst concentration being at least 0.05 equivalents per litre of digesting liquor.

A family of catalysts, which comprise electron donor moieties and hydrophobic moieties, is provided for use in the digesting liquor. The catalysts increase the strength of sheets made from the pulp, as evidenced by increased tear strengths and, in some embodiments, increased burst strengths. The use of the catalysts produce novel pulps, and permit novel sheets to be made with the pulps, and novel lignins can be recovered from the digesting liquor.

Description

This invention relates to pulping processes, extraction of lignin and composition of matter for use in such processes.
More particularly, the invention relates to improvements in production of cellulose pulp from vegetable matter, such as wood, bamboo, bagasse, and the like. In such processes, as commercially practiced, generally the vegetable matter is digested in a digesting liquor with the objective of recovering the cellulose which is useful in making a variety of products, notably paper and paper-related products.
Known digesting liquors generally fall into two classes.
In the first class, the digestion of the vegetable matter is related primarily to chemical reactions between the lignin in the vegetable matter and the digesting liquor, whereby the chemical make-up and chemical and physical properties, of especially the lignin polymer, are significantly changed. In this class, the digesting liquor is generally based on sulfur, sulfur oxides, their derivatives, or a combination thereof.
In the second class, the digestion of the vegetable matter is more related to solvation of the lignin in a solvent composition, wherein the occurrence of true chemical reactions between the lignin and the digesting liquor are less frequent, and wherein the lignin polymer so extracted is generally available in the same, or chemically and physically similar, form as in the vegetable matter. Pulping using this second class of liquors is generally known as solvent pulping.
Solvent pulping is generally preferred for environmental reasons over sulfur-based pulping. With the recent increased emphasis on environmental concerns, there is now increased desire to use solvent based pulping for new pulp mill construction.
The principles of using solvents to separate lignin from cellulose in vegetable matter is well known in the pulping art, and processes have been proposed to utilize the known principles, e.g. Diebold et al United States Patent 4,100,016, herein incorporated by reference in its entirety. However, such processes have limitations, in that the papers produced from pulps made with such solvent processes have comparatively weak tear strengths.
Further, the sulfur-based pulping processes which operate in an acid medium produce pulps which have some reduction in tear strength compared to pulps produced in a similar, but alkaline, medium.
So, while pulping processes which operate in an alkaline medium produce pulps having comparatively greater tear strengths in the paper produced therefrom, pulping processes which operate in a generally neutral (pH 7) or acid medium, and especially solvent-based processes, tend to operate with fewer inherent risks to the environment. Accordingly, it would be desirable to provide a pulping process which is both friendly to the environment (environmentally friendly processes now being characterized by solvent-based processes in neutral and acid media) and which produces pulp having high tear strength in paper produced with such pulp ( processes which produce high tear strength products now being characterized by sulfur-based processes in alkaline media).
This invention is directed toward the improvement of pulping processes, including the solvent-based processes, and at least some of the sulfur-based processes.
It is an object of this invention to provide novel improved pulping processes which yield pulps wherein paper sheets made therefrom have comparatively higher tear strengths.
More particularly the invention aims to provide solvent pulping processes which produce pulps which can be made into a variety of products including paper sheets having higher tear strengths, dissolving pulps, parchment, fillers, and the like, and which processes are friendly toward the environment.
The invention provides a family of catalysts, for incorporation into the digesting liquor, use of which catalyst results in pulps which exibit the desired higher strength, without the traditional higher threat to the environment by the pulping process.
The invention further provides novel compositions of matter, for use as the start-up digesting liquor in the pulping operation.
Especially with respect to pulping processes which operate in an acid medium, it is an object to provide improved processes which yield novel and stronger pulp fibers than are produced in conventional pulping processes which operate in an acid medium.
The invention thus comprises, within its inventive contribution to the art, novel pulps made by the processes of the invention, novel sheets made with the pulps of the invention, and novel lignins produced by the processes of the invention.
The invention is now explained in more detail in the following non-limitative description.
Some of the objects of the invention are obtained in a first family of pulping processes wherein the process comprises the step of digesting vegetable matter in a digesting liquor having an effective pH, during the digesting step, of no greater than about 7, in the presence of a catalyst which is present in the lignin in an amount of at least about 0.05 equivalent, preferably between about 0.1 and about 1.5 equivalents, per liter of the digesting liquor. The catalyst comprises electron donor moieties and hydrophobic moieties, and preferably has a dissociation constant of at least about 10⁻⁷.
In some embodiments, the process includes selecting, as the catalyst, a compound comprising a cation. The cation preferably has up to three valence units, and has an ionic radius at least as great as the radius of a lithium ion.
The digesting liquor generally comprises a liquid which incorporates thereinto the catalyst and one or more active reagents, such as an acid or an alcohol, which active reagents provide a primary digesting function, essentially by a solution mechanism. The process preferably includes selecting at least one active reagent and the catalyst, in combination, such that the active reagent and the catalyst comprise a solvent-solute combination wherein one comprises the solvent a!d the other comprises the solute, and wherein the solute is substantially dissolved in the solvent in the recited amount in the digesting liquor at the digesting conditions.
In some embodiments wherein the digesting liquor comprises an acid, the process includes selecting the acid and the catalyst such that both the acid and the catalyst comprise a common polar moiety, which polar moiety is disposed toward exhibiting a negative charge, and is preferably an anion.
In preferred embodiments, the catalyst is selected from the group consisting of esters, alcohols, aldehydes, and ketones, which group includes salts such as potassium acetate, ammonium acetate, calcium acetate, magnesium acetate, sodium acetate, lithium acetate, and acetone, alkyl alcohols having one to four carbon atoms, and mixtures of the above recited catalysts. It is believed that the catalyst can be essentially any salt which has the electron donor characteristics and the hydrophobic characteristics, and which can be essentially uniformly dispersed in the digesting liquor.
In some embodiments, it is preferred that the digesting liquor include an alkyl ester in an amount of greater than 0% to about 25% by weight, the alkyl group comprising C₁ to C₆ and the ester group comprising C₁ to C₄.
Preferably, the digesting liquor comprises about 50% to about 100% by weight acetic acid, about 0% to about 25% by weight alkyl acetate, and about 0% to about 35% by weight water, the composition percentages being based on the sum of the weights of the acetic acid, the alkyl acetate, and the water; into which the catalyst has been incorporated, the catalyst being soluble in the composition at the operating conditions of the digesting step.
In continuous process operations, the process preferably includes maintaining at least a nearly saturating amount of the released lignin in the digesting liquor, drawing a recycle stream from the digesting liquor and recovering lignin from the recycle stream. Alternatively, the lignin can be burned as in conventional pulping operations.
Other objects of the invention are obtained in a second family of pulping processes, wherein the processes comprise the step of digesting vegetable matter, comprising lignin and cellulose, in a digesting liquor which has a first component selected from the group consisting of alcohols having one to four carbon atoms, acetone, glycol, and glycerol, in an amount effective to separate the lignin from the cellulose in the pulping process; as a second optional component, water; and as a third component, a catalyst comprising electron donor moieties and hydrophobic moieties in amounts effective to produce a pulp having at least one strength property of increased magnitude compared with the same strength property when the pulp is produced in a corresponding digesting liquor but without use of the catalyst. In preferred embodiments, the first component of the start-up digesting liquor comprises an alkyl alcohol, the alkyl alcohol being present in an amount of at least about 20% by weight of the digesting liquor. In those compositions where water is not used, the catalyst is, of course, the second actual component.
The process of the invention can include selecting the composition of the digesting liquor and the vegetable matter, in combination, such that the material separated from the vegetable matter by the pulping process is effective to control the pH of the digesting liquor, at steady state conditions, at no more than about pH 7.
Some objects of the invention are obtained in a pulping process which includes selecting for use, in the digesting liquor, along with the catalyst, a compound comprising sulfur oxide moieties in sufficient amount to effect the digesting of the vegetable matter, and sufficient cationic neutralizing agent to establish, in the digesting step, pH of no more than about pH 7.
Other objects of the invention are obtained in pulping processes as above, wherein lignin is received into the digesting liquor in the digesting step, which processes use, as the catalyst, a compound comprising an inorganic moiety (e.g. potassium) which is recoverable as either a liquid or a solid, in elemental or oxide form, after a reduction burning process in a furnace. The steps of these particular pulping processes include (i) digesting the vegetable matter in digesting equipment, (ii) removing a recycle stream of liquor, containing the lignin and catalyst, from the digesting equipment, (iii) concentrating the removed liquor by removing the volatiles, thereby producing a cake residue, (iv) burning the residue in a furnace and thereby combusting the lignin and reducing the catalyst to its inorganic moieties as either elemental material or an oxide thereof, (v) recovering the inorganic moieties from the furnace, (vi) treating the inorganic moieties recovered from the furnace with sufficient reagent to thereby reform the inorganic moieties back into the catalyst form, and (vii) returning the reformed catalyst to the digesting step.
The step of concentrating the removed liquor preferably comprises distilling the removed liquor and thereby removing, from the removed liquor, an aqueous stream comprising mainly water and an organics stream comprising one or more primary organic digesting reagents, which organics stream is returned, as needed, to the digesting step as make-up liquor. In those embodiments wherein acetic acid is used as a primary digesting reagent, it is preferred that the organics stream from the distilling step, and which is returned to the digesting step, comprise at least 50% by weight acetic acid.
The purpose of the recycle stream is primarily to control the composition of the equilibrium digesting liquor by removing excess lignin and water, from the digesting liquor, and by controlling the amount of active reagent in the digesting liquor. In some embodiments, and preferably, the recycle stream is sufficiently large that only part of the recycle stream is removed from the pulping process by removing the water, the lignin, and the organics streams from the recycle stream; whereby the recycle stream, which is depleted in lignin, water, and the components of the organics stream, can be and is returned to the digesting step.
In other, less preferred, embodiments, the only material, from the recycle stream, which is returned to the digesting step is the organics stream, which may include a catalyst component where the catalyst is readily volatized. Accordingly, all other components of the recycle stream are disposed of outside the digesting step. They can, of course, be used elsewhere in the pulping operation. For example, water separated from the recycle stream can be used as wash water.
Still other objects of the invention are obtained in a composition of matter which is use.d as the start-up digesting liquor in the processes of this invention, and which composition of matter comprises, as a first component, about 50% to about 98% by weight acetic acid; and as a second component about 2% to about 50% by weight a alkyl acetate, the alkyl group comprising C₁ to C₆; into which composition a catalyst, as described above, has been incorporated and dispersed in an amount of at least about 0.1 equivalent per liter. The catalyst is preferably soluble in the combination of the first and second components, in the amounts of the first and second components and the catalyst which are used, and is dissolved therein.
The composition may include, as a third component, along with the acetic acid and the alkyl acetate, greater than 0% up to about 35% water.
A preferred composition (for the liquid components of the start-up liquor), for some embodiments, comprises about 75% to about 98% by weight of the acetic acid, about 2% to about 15% by weight of the alkyl acetate, and about 0% to about 15% by weight of the water, and the composition of the catalyst comprises a compound selected from the group consisting of acetates, acetone and aliphatic alcohol: having one to four carbon atoms.
A highly preferred composition for the start-up liquor comprises a high fraction of the acetic acid, such as at least 90% by weight (not considering the catalyst), and the catalyst. The amount of water if any, is 10% or less in the start-up liquor. Preferably, water is 0% to 8%, and alkyl acetate, if any, is about 2% to about 8% by weight.
The invention further comprehends novel pulps made with the processes of the invention, novel sheets made with the novel pulps, and the novel lignins recovered from the vegetable matter using the processes of the invention.
The invention will now be described in more detail by way of example with reference to the accompanying drawings, in which:
FIGURE 1 is a graph illustrating the affect of pulping time on the yield and the Kappa Number of hand sheets made with pulps produced according to the invention.
FIGURE 2-8 are graphs illustrating the affect of various pulping parameters in tear strength and burst strength of hand sheets made with pulps produced according to this invention.
FIGURE 9 is at block diagram illustrating the general flow of materials in the pulping process of the invention, and
FIGURE 10 is a 3-phase diagram illustrating a separation process used in this invention.
This invention pertains to methods of recovering fibers and chemicals from vegetable matter, and to the materials recovered thereby. The illustrated embodiments are confined to examples of pulping wood, primarily for the purpose of recovering cellulosic fibers therefrom. However, other applications of the invention are contemplated, and are intended to be within the scope of this invention. For example, other raw materials (vegetable matter) are contemplated, such as bagasse, straw and other raw materials from which pulp is derived, e.g. for making paper. As another example, this invention provides novel processes for extracting lignin, and other chemicals, from lignin-containing vegetable matter; and all such chemicals and the related extraction processes are contemplated.
In this invention, the vegetable matter (e.g. wood chips) is digested in a pulping/digesting liquor which operates in an acidic or neutral medium. A preferred digesting liquor is based on acetic acid and comprises, as a start-up liquor composition, glacial acetic acid, in the presence of a catalyst in the amount of at least 0.05 equivalent per liter of the digesting liquor. The catalyst has electron donor moieties, such as are typically identified with oxygen atoms, nitrogen atoms, or like electron donor moieties. The catalyst is further characterized as comprising hydrophobic moieties such as alkyl groups. In some embodiments, the catalyst is a salt of an organic acid, in which case the salt cations are at least as large as a lithium ion.
A secondarily preferred family of start-up digesting liquors comprises:

(i) about 50% to about 98% acetic acid;
(ii) about 2% to about 50% alkyl acetate, especially ethyl acetate or butyl acetate, and
(iii) 0% to about 35% water,
also including the above defined catalyst.

The primary function of the acetic acid is to extract the lignin from the wood. The primary function of the alkyl acetate solvent is to hold the extracted lignin in solution in the liquor. The primary function of the catalyst is not understood, but the result of its use is improved properties, including increased tear strength in hand sheets made with pulp so produced. There are also preliminary indications that the catalyst enhances fiber yield and Kappa Number. The primary function of the water is (i) to accelerate the rate at which the acid extracts lignin from the wood and (ii) there are preliminary indications that small amounts of water in the start-up liquor may enhance the effectiveness of the catalyst.
The invention is first illustrated using the above secondarily preferred digesting liquor.
The above composition percentages of the recited elements (i), (ii), and (iii) are based on the sum of solely the acetic acid, the alkyl acetate and the water. Having a limited amount of water present in the digesting liquor increases the rate of digestion, and appears to increase the strengthening affect of the catalyst. However, the amount of water in the start-up liquor is preferably kept small (e.g. 10% by weight or less) because the wood chips digested in the digesting step contain, and in the digesting step release into the digesting liquor, more water than can be effectively used in the digesting step, especially if the liquor is recycled or reused. However, some water may be desired in the start-up liquor in order to obtain an efficient start-up rate of digestion in the start-up liquor as the process is started up, and before significant amounts of water are released into the liquor by the wood chips.
Using the above composition of acid, acetate, water, and catalyst as the start-up digesting liquor, wood chips can be digested, to produce pulp, over a temperature range of about 110 to about 300 degrees C. Digesting time can vary from about 1 minute to about 24 hours. Typical such pulping temperatures range from about 160 degrees C. to about 230 degrees C. Typical pulping time under these conditions is about 30-120 minutes. Compared to pulping processes which use the same digesting liquor and the same digesting conditions, but without the catalyst, using the catalyst does not greatly affect the required pulping temperature; and it does produce higher strength pulps and pulps which can be used to make higher strength paper.
In preferred embodiments of the acetic acid-based liquors which include alkyl acetate, the start-up digesting liquor composition comprises:

(i) 75% to 98% by weight acetic acid,
(ii) 2% to 15% by weight alkyl acetate, and
(iii) 0% to 15% by weight water,
to which has been added 0.05 to 2.0 equivalents per liter (e.g. 0.05 to 2.0 Normal) of catalyst.

A most preferred composition based on acetic acid and alkyl acetate is:

(i) at least 90% by weight acetic acid,
(ii) 2% to 8% by weight alkyl acetate, and
(iii) 0% to 8% by weight water,
to which has been added 0.2 to 1.5 equivalents per liter of catalyst.

The preferred alkyl acetate is butyl acetate with a secondary preference for ethyl acetate.
One family of preferred catalysts for use with the acetic acid-based liquor is the salts of organic acids, which salts include a cation selected from those cations commonly used in the pulping industry, preferably potassium. Examples of preferred catalysts are potassium acetate and magnesium acetate.
The reactivity of the lignins dissolved in pulping processes using the above described solvent digesting liquors is not inhibited the same way as reactivity of the lignins is inhibited in conventional sulfur-based pulping processes. So the lignin dissolved in the above solvent digesting liquors can potentially, re-condense back onto the fiber. Thus it is important that the solvation system be effective to hold the lignin in solution without substantial re-condensation back onto the fiber. The alkyl acetate, in combination with the acetic acid and water, is used primarily for that purpose of holding the solvated lignin in solution, and is effective to hold the lignin in solution in the liquor, and thereby to maintain a substantial load of dissolved lignin in the liquor. The process can be operated without the alkyl acetate or other lignin holding solvent, albeit with less lignin-holding capacity.
A high concentration of acetic acid (at least 50%) is used in the start-up liquor which is based on acetic acid, in order to achieve a preferred yield quantity of the pulp, as well as other benefits disclosed hereinafter. For example, in 6 liter "M and K" batch digesters operating at 50% acetic acid and up, in the start-up liquor, the pulp yield is good when the other appropriate conditions are met. The Kappa Number, however, which can be relatively high when the start-up liquor in the batch digesters is 50% acetic acid, depending on what material is being pulped, typically drops to about Kappa 20 when the start-up liquor is 60% acetic acid, and can be under 20 at 70% acetic acid.
For a given higher level (e.g. 50% or greater) of acetic acid in the start-up liquor in the batch digesters, as the amount of water is increased, the rate of the pulping reaction is accelerated; both the rate of delignification and, adversely, also the rate of cellulose degradation.
The following Examples 1-5 in Table 1 represent a first set of experiments using "M and K" six liter batch digesters in pulping of aspen chips. These experiments experimented with the affect of addition of potassium acetate (granular solid) catalyst to two liquor compositions. Liquor composition No. 1 was 70% acetic acid, 15% ethyl acetate, and 15% water. Liquor compsition No. 2 was glacial acetic acid. Liquor compositions are percent by weight, based only on the liquid fraction of the contents of the digesters. Wood chip size was nominally 1/4-1/2 x 3/4-1 x 1/8-1/4, all in inches. Liquor to wood ratio was maintained at 7/1. Come-up time to reach the operating temperature in the digesters was 35-45 minutes.
As seen in Table 1, yield was generally increased by use of the catalyst, while Kappa Number was generally maintained in an acceptable range. Especially Examples 3 and 4, with 0.25 to 0.50 equivalents of catalyst addition, produced high yields and desirably low Kappa Number.
Examples 6-10 in Table 2, following, were performed in the same batch digesters as indicated, and, along with Examples 1-3, illustrate the affect of various digesting parameters on the yield and Kappa Number when pulping Aspen chips. Liquor composition No. 3 was about 95% acetic acid, no alkyl ester, and about 5% water. Catalyst in Examples 6-10 was potassium acetate in the amount indicated.
The Kappa No. and Yield are illustrated graphically in FIGURE 1, wherein it is seen that yield reaches a low (constant catalyst amount) and increases with digesting time; and that Kappa Number generally decreases with digesting time.
Pulps illustrated in Tables 1 and 2 were refined for various periods in a commercial Waring Blender Model 5011.
After refining, the pulps in Examples 1-4, and 6-10 (Tables 1 and 2) were used to produce hand sheets, and the hand sheets were tested for burst strength and tear strength. FIGURE 2 graphically illustrates the burst strengths. FIGURE 3 graphically illustrates the tear strengths.
The refining and sheet forming processes were as follows.
Pulp samples weighing ten grams oven dry were placed in the Waring Blender with sufficient water to fill the blender three quarters full. The blender was then used to disintegrate the fiber bundles and to mechanically treat the fibers. The treated pulp was then diluted with water tp approximately 0.25% consistency and stirred at low speed. 500 ml portions were removed and used to make handsheets on a TAPPI standard handsheet mold. The handsheets were pressed and dried on a dryer under restraint.
The physical properties of handsheets made using this process generally compare well with hand sheets made using the standard Valley Beater process for treating the pulp. The major difference is indicated to be about a 10-20% greater tear strength and a 10-20% lower bursting strength with hand sheets made from pulp which was treated using the Waring Blender.
FIGURE 2 shows that short digesting time (Example 6, Table 2) produces a lower burst strength. At low refining levels, the bursts of some of the other catalyzed samples (e.g. Exs. 3 and 9) were approximately equal to the similar uncatalyzed control, Comparative Example 1. However three of the higher yielding samples (Examples 7, 8, and 10) had higher initial burst strengths, and the relative burst strengths were generally maintained with refining time. The large increase in burst strength of the uncatalyzed Comparative Example 1 at 15 minutes refining time is not understood and may represent errant data. In any event, FIGURE 2 and Table 2 suggest, in combination, that the catalyzed digesting process (e.g. Ex. Nos. 8 and 10) can produce the combination of high yield (over 60%), low Kappa No. (e.g. 17-24), and higher burst strength than the similar but uncatalyzed digesting process (Comp. Ex. No. 1) under at least some conditions descriptive of the pulp digestion, refining, and sheeting processes.
Referring to FIGURE 3, hand sheets made with a pulp having short digesting time (Example 6) also have lower tear strengths. The other catalyzed pulps , after refining, produced hand sheets having better tear strength than the hand sheets made with the uncatalyzed pulp of Comparative Example 1. The hand sheets of all the catalyzed pulping examples except Example 6 had better tear strengths after refining in the blender than uncatalyzed Example 1. Example 10 had better tear strength overall than either of the Comparative Examples 1 or 2. Accordingly the representation in FIGURE 3 indicates that pulp produced with the catalyst produces sheets with higher tear strength than similar pulp produced without the catalyst. Example No. 10, which had the highest tear strength, as illustrated in FIGURE 3, had catalyst concentration of 0.5 equivalent per liter. Accordingly, FIGURE 3 suggests that greater than 0.25 equivalent per liter of catalyst in the start-up liquor is preferred where high tear strength in the resulting hand sheets is preferred.
In Example 11, pulp was prepared as in uncatalyzed Comparative Example 1, except that potassium acetate catalyst was used at the rate of 1 equivalent per liter. The pulps (Examples 1 and 11) were then refined in a standard Valley Beater for the times shown in FIGURE 4, and the burst strengths and tear strengths of subsequently made hand sheets were measured. FIGURE 4 shows the results. The actual burst strengths and tear strengths, as shown in FIGURE 4, were generally lower for the catalyzed pulps. However, when the curves were mathematically adjusted for yield differences, also shown in FIGURE 4, such that the respective hand sheets, so produced, hypothetically contained the same number of fibers, the tear strength of hand sheets made with the catalyzed pulp was greater than the tear strength of hand sheets made with the uncatalyzed pulp; and the catalyzed versus uncatalyzed burst strengths were closer together. This generally indicates the relative tear strengths of the sheets as imparted by average fibers, reducing the indicated effect of the number of fibers in the sheet. Thus FIGURE 4 suggests that the catalyzed pulping process yields pulp fibers which are individually stronger than the pulp fibers produced by pulping processes which are the same except for the use of the catalyst.
Examples 12 and 13 were prepared as illustrated in Table 3, using Aspen chips sized as above.
The pulps so prepared were then refined in a standard Valley Beater for various times. Handsheets were made with the refined pulps, and were tested for burst strengths and tear strengths. The burst and tear results are given in FIGURE 5 wherein it is seen that the catalyzed pulps of Example 12 produced hand sheets having both higher actual tear strengths and higher actual burst strengths, than the pulps of Comparative Example 13, which did not use catalyst, both without refining of the pulps and at all levels of refining tested.
The pulps of Example 12 and Comparative Example 13 were also beaten to a variety of Canadian Standard Freeness levels, made into hand sheets, and tested for burst and tear strengths at the comparative Canadian Standard Freeness levels. The comparative burst and tear strengths are illustrated in FIGURE 6. Again, it is seen that both the burst and tear strengths of hand sheets made from the catalysed pulps of Example 12 were greater than the respective strengths of hand sheets made from the uncatalyzed pulps of Comparative Example 13.
Canadian Standard Freeness, as used herein, is obtained according to TAPPI Standard T-227, om-85.
Beating in the Valley Beater was performed according to the Laboratory Process of Pulp Beating Methods, T-200, om-85.
Forming of handsheets for Physical Determination of Pulp was performed according to TAPPI Standard T-205, om-88.
Physical Testing of Pulp Handsheets was performed according to TAPPI Standard T-220, om-88.
As seen in the above examples, the use of the potassium acetate catalyst can provide pulps which can be made into hand sheets having higher tear strengths and higher burst strengths than pulps made with digesting liquor which does not incorporate the catalyst.
Examples 14-15 were prepared as in Examples 12-13, using glacial acetic acid digesting liquor plus catalyst, as shown in Table 4. The same processes were used, as in Examples 12-13, in pulping the same type of Aspen chips, thus indicating the utility of magnesium acetate catalyst at 1 Normal concentration. Additional experimental parameters are shown in Table 4. The respective tear strengths and burst strengths of hand sheets made with the pulps, after refining of the pulps in the Waring Blender, are illustrated in FIGURE 7.
As seen in the combination of Table 4 and FIGURE 7, handsheets made with the pulps made in the presence of magnesium acetate catalyst had higher tear strengths than handsheets made with similar but uncatalyzed pulps.
Examples 16-18 were prepared as in Examples 14-15, using glacial acetic acid digesting liquor plus catalyst, as shown. The same processes were used, as in Examples 12-15, in pulping Southern Pine chips of the same dimensions as the Aspen chips used for Examples 12-15. Experimental parameters are shown in Table 5. The so-prepared pulps were refined and subsequently used to make hand sheets. The respective tear strengths and burst strengths of hand sheets so made are illustrated in FIGURE 8.
As seen in the combination of Table 5 and FIGURE 8, handsheets made with the catalyzed pulps (acetone or magnesium acetate) had higher tear strengths than hand sheets made with the similar nut uncatalyzed pulp of Comparative Example 16.
The above described family of digesting liquors (e.g. start-up liquors based on acetic acid) and processes, especially when used with the catalyst, is superior to conven-tional solvent processes and liquors because the resulting pulps have a desirable Kappa Number, and because handsheets made with resulting pulps have higher tear strengths, and in some cases higher burst strengths, than hand sheets made with pulps produced with conventional solvent pulps. The pulps made with the above liquors and processes are superior to conventional sulfur oxide based processes which operate in alkaline media, because they avoid the waste disposal problems inherent in alkaline sulfur oxide based pulping processes, whereby the novel processes herein are more friendly to the environment.
However, it is believed that the use of the catalyst as defined herein is not limited to use with pulping processes based on acetic acid. Rather, it is believed that further experimentation will confirm that the herein defined catalyst provides improved tear and burst strengths in a wide variety of digesting liquors and processes, including at least some of the liquors and processes based on sulfur oxides.
The amount of catalyst needed in a given pulping process varies, depending upon other independent variables in the pulping process, and upon the properties which are desired to be obtained in the resulting pulp. As illustrated in the above examples, a preferred amount of catalyst is about 0.25 to about 1.0 Normal concentration of the catalyst. If the catalyst is a solid material, it is preferably soluble in the primary liquid medium of the digesting liquor. It is concurrently recognized that some catalysts are not solids, such as the acetone catalyst in Example 17. In any event, the catalyst should be readily dispersed in the digesting liquor, especially the equilibrium composition of the digesting liquor, described more fully hereinafter, which is the liquor extant in the digesting container at steady state conditions in a continuous pulping operation.
With respect to,the amount of catalyst used, a lesser amount (e.g. 0.25 Normal) is preferred in order to obtain high pulp yield and low Kappa Number. A somewhat higher amount of catalyst (e.g. 0.5 to 1.0 Normal) is preferred in order to obtain pulps which can be used to make hand sheets having higher strengths. Accordingly, practicing artisans will routinely select the amount of catalyst to be used in the digesting liquor in view of their priority objectives with respect to the desired properties in the pulp to be produced.
As the amount of catalyst is reduced below 0.25 Normal, the advantageous improvements in one or more of yield, Kappa No. and strength, over uncatalyzed pulps, are reduced until, at less than about 0.05 Normal catalyst concentration, the beneficial affects of the catalyst are generally not evidenced.
As the amount of catalyst is increased above about 1.0 Normal, the beneficial affects of the catalyst on the above properties of the pulp are not greatly increased, and in some cases are reduced. While catalyst quantities up to about 2.0 Normal may be used in some embodiments, concentrations above 2.0 Normal are generally not used because the benefits produced by the catalyst are generally not improved above 2.0 Normal catalyst concentration; especially when used with liquors and processes which operate in an acid environment at pH no greater than about pH 7.
It is specifically contemplated that conventional acid sulfite and bisulfite digesting liquors and processes will benefit from the addition of the catalyst as herein disclosed, with resultant improvements in one or more of yield or Kappa Number of pulps so produced, or burst strength or tear strength of hand sheets made with the pulps so produced.
Returning now to the preferred acetic acid-based digesting liquor, further benefits thereof are seen in the following description of the pulping system as a whole.
A significant consideration in the planning of any pulping system is the plan for recovery or disposal of the pulping chemicals. FIGURE 9 illustrates, in block diagram form, the main process steps in converting the raw vegetable matter feed (e.g. wood chips) into usable pulp. The solid lines from top to bottom of the diagram indicate the main flow of the fibrous material. The "A" recycle loop, in general separates and removes water, some lignin, and other wood chemicals extracted and produced in the pulping process. A second recycle loop "B" provides primary recovery of lignin from the digesting liquor, wherein a recycle stream 8 from the digesting container 6 is depleted in lignin, which is withdrawn as stream 12, and the balance of depleted stream 8 is returned to the digesting container 6, as depleted recycle stream 10.
Referring to FIGURE 9, wood chips are digested in the cooking/digesting liquor container 6, wherein the start-up liquor preferably has one of the compositions disclosed above, namely
about 50% to 100% acetic acid
about 0% to 25% alkyl acetate
about 0% to 35% water.
The conditions and procedures of the digesting step are selected according to the specific liquor composition and the specific vegetable matter being digested/pulped. Examples of conditions as to time and temperature of the digesting step are disclosed above ant with respect to the Examples.
A further advantage to the preferred digesting liquor composition is seen in the lignin which is recovered from the digesting liquor in recycle loop "B". Lignin compounds produced in conventional sulfur-based pulping are sulfonated, and are also substantially fractionated by cleavage of the lignin polymer molecules, whereby the lignin polymer has undergone substantial chemical and physical change in the pulping process, and wherein sulfur has been chemically bonded to the lignin. The fractionation of the lignin, and the addition of sulfur to the lignin are generally considered to be degradations of the lignin polymers. These degraded, sulfonated lignin polymers have limited utility, and therefore limited value. Significant quantities of the lignin produced in such processes are disposed of by burning, albeit with significant expense in recovery of sulfur compounds from the stack gases.
The lignin produced by digesting the wood chips with the preferred digesting liquor of this invention is not sulfonated and has undergone substantially less polymer cleavage in the pulping process than is experienced in sulfur-based pulping processes. Rather, in this invention, the lignin extracted from the vegetable matter is extracted primarily by a solvation process, and is therefore present in the digesting liquor in generally or nearly its pristine polymeric form, as it was in the wood before the digesting in the digesting step, albeit with somewhat reduced molecular weight due to some moderate amount of polymer cleavage which does occur during the digesting process. Overall, the lignin recovered from digesting liquors used in this invention represents an intermediate, " lightly modified" family of lignins which are somewhat fractionated as compared to truly pristine lignin, but less fractionated than lignin produced by the conventional sulfur-based processes; and is free from additions of sulfur thereto.
Accordingly, the lignins extracted using the processes of this invention have greater utility and therefore greater value than lignins produced by conventional sulfur-based pulping processes. There is thus greater value in recovering the lignin from the digesting liquor, so that its greater value can be realized from the sale thereof.
It is known to recover lignin from a digesting liquor whose start-up liquor composition was 1/3 acetic acid, 1/3 water, 1/3 ethyl acetate, by drawing a recycle stream from the digesting reactor vessel, and diluting the recycle stream with water. Alternatively, in a batch digesting system, the entire amount of the digesting liquor batch can be diluted with water. A dilution ratio of approximately 10/1 (water/ digesting liquor) is typical for good precipitation of the lignin. The lignin precipitate is washed, recovered and dried using conventional processes.
It is also known to recover lignin from alcohol based solvent pulping processes, by addition of diluting water, as disclosed in United States Patent 4,764,596 Lora et al.
A novel process of contacting a digesting liquor, pregnant with lignin, with a cool plating surface and thereby plating the lignin onto the plating surface is taught in US application serial number 07/503,722. It is contemplated that a lignin recovery process similar to the above novel process can be practiced with the pregnant (e.g. equilibrium) liquors produced in the pulping processes of this invention.
It is well known that wood chips and other biomass which are digested to separate pulp fibers from lignin typically contain a significant amount (e.g. 30% to 50% by weight) of water, which is released into the digesting liquor during the digesting process. Further, the biomass also releases, into the digesting liquor, a variety of other chemicals, including acetic acid, alkyl acetates, furfural, sugars and, in some embodiments, some cellulose derivatives. Accordingly, the composition of the digesting liquor changes as the process of digesting the biomass proceeds. Starting with the start-up liquor, e.g.

(a) 70% acetic acid
(b) 15% alkyl acetate
(c) 15% water
(d) catalyst,

The digestion of biomass can be continued until such time as the chemical composition of the digesting liquor changes so much that the digesting liquor reaches the limit of its capacity to effectively digest the biomass in view of the chemical and physical changes which have taken place in the liquor. It is contemplated that digesting liquors in steady state pulping processes of this invention will generally operate at or near the limits of the digesting liquor, whereby the equilibrium liquor composition will generally coincide with the limits so defined with respect to the wood. chemicals which enter the digesting liquor. In a typical equilibrium liquor composition, derived from the above start-up liquor comprising elements (a) - (d), the elements (a), (b), and (c) are related to each other as follows.

(a) 40% -60% acetic acid
(b) 10% - 20% ethyl acetate
(c) 30% - 40% water,

When the liquor composition reaches its equilibrium composition in a steady state process, or before if desired, a recycle loop "A" is preferably set up to remove from the digesting liquor those components which would inhibit future effective digesting activity. Also a recycle loop "B" is set up, as desired, to recover lignin for other than fuel use. While a variety of components can be, and are, removed, the greatest volumes of material removed in the recycle loops are lignin and water. Generally, the amount of the chemical load which is removed from the equilibrium liquor, using the recycle loops, corresponds to the amounts of those same chemicals which are entering the digesting liquor in the digestion process by way of the incoming biomass. Accordingly, the composition of the equilibrium liquor is controlled and held constant through the use of the recycle loops.
The recycle loop "A" generally comprises a plurality of streams and process steps. Referring to FIGURE 9, the pregnant liquor is withdrawn from the digesting step as stream 14 and is separated into component parts by one or more distillation and/or extraction column. The distillation process typically is employed to only partially fractionate the pregnant liquor stream 14, to produce four streams, namely (1) a water steam 15, (2) a make-up liquor stream 16, of light organic fractions, (3) a bottoms stream 18 essentially saturated with lignin, which is burned for energy, and (4) an intermediate stream 20 of recovered liquor which has been relieved of the components in streams 15, 16, and 18. The light organic fractions in the make-up liquor stream 16 generally include acetic acid, ethyl acetate, and other alkyl acetates. The make-up liquor stream 16 generally contains little, if any, lignin, and substantially reduced amounts of water, preferably no water; and is enriched in acetic acid (compared to the pregnant liquor stream 14). The make-up liquor typically does contain some water, e.g. up to about 10%, which is tolerated because of the cost of further-water separation. However, no water need be added to the equilibrium liquor, since the equilibrium liquor is well supplied with water which enters the digesting step as a component of the in-coming wood chips.
The make-up liquor stream 16, with its enriched level of acetic acid, and its depleted level of water, is well suited for use in the digesting step as make-up digesting liquor, and is added to the digesting liquor in container 6 as needed through stream 22, as shown in FIGURE 9. Any excess amounts of the make-up liquor stream 16 are sold for the chemical content.
The recovered liquor 20 which is left over from the distillation operation in the recycle loop "A" is somewhat depleted in water, lignin, and the light organic fractions, and is returned to the digesting container 6.
Bottoms stream 18 is relatively low in liquid such that it has a semi-solid consistency which the industry generally recognizes as a cake. It is this cake which is burned in the reduction furnace.
In those embodiments wherein an inorganic solid catalyst is used, such as potassium acetate, the inorganic material, e.g. potassium oxide, is recovered from the reduction furnace which burns the cake of bottoms stream 18. The potassium oxide is subsequently reacted with acetic acid from the make-up liquor stream 16 to regenerate the potassium acetate catalyst, which is then re-used in the digesting step as needed.
The basic concept of the recycle loops is to separate, from the streams 8 and 14 enough materials that the digesting step can operate continuously, whereby the chemicals entering the digesting step are removed, through the recycle streams, in streams 12, 15, 16, and 18. The unseparated portions of streams 8 and 14, defined as depleted liquor streams 10 and 20, can be returned to container 6 without overloading the digesting liquor composition with especially water or lignin. In the process of operating recycle loop "A", a sufficient amount of acetic acid typically can be recovered from stream 14, and added as make-up liquor from stream 16, such that the digesting step can be operated continuously without addition of acetic acid from outside sources. Of course, additional quantities of digesting chemicals can be added from outside sources, if needed.
It is preferred to set up recycle loop "A" such that it separates out only easily separated fractions for streams 15, 16, and 18. Thus the preferred process separates, from the stream 14, enough material, in combination with recycle loop "B," to satisfy the compositional needs of the equilibrium digesting liquor without fractionating the entire stream 14. This can be done by taking from container 6 flow streams 8 and 14 having sufficient flow rates to support producing streams 12, 15, 16, and 18 in sufficient flow rates to meet at least the minimum required removal rates for water and lignin, while depleting streams 8 and 14 of these respective components without requiring the entire amount of streams 8 and 14 to be assimilated into the combination of streams 12, 15, 16, and 18. Accordingly, streams 8 and 14 are depleted, but maintain their identities as separate streams. The thus depleted streams are referred to as depleted liquor streams 10 and 20 respectively, and are returned to digesting container 6 as shown in FIGURE 9.
In the alternative, a smaller stream 14 can be taken from container 6 and the entire stream fractionated, whereby no "depleted liquor" stream exists to correspond to stream 20 in the previous example. Rather, the entire mass of stream 14 is disposed of outside the recycle loop "A", except for that portion of the make-up liquor stream 16 which is returned to digesting container 6 and the reconstituted catalyst. The rate of slow of stream 14 which is required to be removed from container 6 under this "entire stream fractionation" embodiment is controlled by the amounts of the primary components, lignin and water, which are entering the digesting step in the biomass. Enough flow rate must be removed in stream 14 that the amounts of water and lignin removed by the recycle streams are at least equal to the respective amounts of the corresponding materials which are entering the digesting step, thereby maintaining a constant mass balance in the digesting step.
Acetic acid removed by the operation of recycle loop "A", using either entire stream fractionation, or partial stream fractionation, can be returned, as needed, as make-up liquor from stream 16. To the extent sufficient acetic acid enters the digesting step from the wood, which sufficient entry can occur, no acetic acid need be added to digesting container 6 from outside sources once the start-up liquor has been provided. Alkyl acetate can also be provided in the make-up liquor, if not otherwise separated from stream 16.
The sum of the lignin removed in both of streams 12 and 18 satisfies at least the required minimum lignin removal rate.
A significant advantage of the preferred digesting liquor, and the process of using it, is that it produces, as by-products of the pulping process, the primary digesting chemical, namely acetic acid. In principle, then, the acetic acid produced in the pulping process is sufficient in quantity to keep the process continuously and adequately supplied with that chemical. Accordingly, once the process has been fully started up and stabilized, the needs of the process for acetic acid are met by the amount of that material which is generated by the instant pulping process. Accordingly, addition of fresh acetic acid from outside sources is generally not required. Minor amounts of such additives as conditioners and buffers may still be needed, and, if so, are provided from outside sources as usual. The catalyst is, of course, added from outside sources as necessary.
In addition to serving as a solvent to hold the lignin in solution, the alkyl ester serves as a vehicle for removal of excess water. See the tertiary phase diagram in FIGURE 10. As acetic acid is removed from the digesting liquor in the recycle loop "A", the composition approaches and eventually enters the two phase envelope at about 20% acetic acid. Inside the envelope, the composition readily separates into an organic phase which is enriched in the alkyl ester and an aqueous phase which is enriched in water. The phase separation is thus conveniently used as a means of separating and concentrating the pulp chemicals. The preferred alkyl ester is butyl acetate, wherein the tie lines in the two phase envelope favor an efficient separation.
The fractionation of lignin referred to herein is not seen to be in conflict with the assertion that the pulping processes of the invention depend on solvation for extraction of the lignin from the biomass. Indeed, the primary extraction process is believed to proceed by a solvation mechanism. However, as seen above, the extraction operation is practiced in a hot acid environment which encourages a variety of chemical activities, and which does result in a degree of chemical activity taking place typically as secondary cleavage reactions which cleave some of the lignin polymer molecules, and thus produce modest changes in the extracted lignin. Accordingly, lignins recovered from pulping processes of the invention are typically "lightly modified" as defined above.
It is believed that the catalyst disclosed herein performs in the capacity of an electron donor which dissociates at least mildly, such as a dissociation constant of at least about 10⁻⁷, in the equilibrium digesting liquor composition which predominates during the digesting step; and that the dissociated catalyst supports maintenance of an acid pH, and thereby provides a readily available active site at the electron donor moiety. The catalysts herein defined also contain an hydrophobic moiety, which can also be described as an "electron poor" moiety. Such moiety is seen in the methyl group on the acetate anion of potassium acetate, or the methyl groups of acetone. The function of the hydrophobic, or electron poor group is not understood, but its presence is observed on the catalysts of the invention. Accordingly, it is believed to play a material, by not yet understood role in the pulping processes of the invention.
Thus it is believed that a variety of materials, as defined above, can serve as the catalyst, so long as they can be more or less distributed through the carrying medium of the digesting liquor. Accordingly, there can be mentioned, for the catalyst, such materials as esters, alcohols, aldehydes, and ketones. Examples of catalysts, in addition to the above illustrated potassium acetate, magnesium acetate and acetone, are ammonium acetate, calcium acetate, sodium acetate, are lithium acetate, alkyl alcohols having one to four carbon atoms and mixtures of the above recited catalysts. Although inorganic acids such as hydrochloric acid, sulfuric acid or nitric acid may be present in the digesting liquor, they do not provide the increased strength benefit in hand sheets made with the pulp, and they do not have hydrophobic moieties. Accordingly, such inorganic acids are not included in the definition of the catalysts of the instant invention.
In some embodiments, the catalyst can be generated in situ in the digesting liquor by addition of appropriate compounds which, by themselves are unable to perform the catalytic function. For example, an appropriate amount (equivalents) of potassium hydroxide can be added to an acetic acid-based digesting liquor, whereupon the acetic acid reacts with the potassium hydroxide in a standard acid-base reaction to form the potassium acetate catalyst and water. Such potassium acetate catalyst, when generated in situ, will function, as catalyst, just as well as previously generated granular solid potassium acetate which is dissolved in the liquor liquid medium.
Considering the catalyst as the first element of the digesting liquor, in situ generation of catalyst is typically facilitated when a first component of the desired catalyst is present as a second component of a second element of the digesting liquor. For example, in the above illustration, the acetate component of the potassium acetate catalyst is present as the acetate anion of the acetic acid element of the digesting liquor. It is further necessary that, if the second element has a function other that to react to generate the catalyst, the second element (in this case acetic acid) must be present in large enough quantity that conversion of some of the second liquor element to catalyst will not reduce the amount of the second liquor element below the minimum amount required for its other function.
Similarly, reagents which can be used to form the catalyst in situ in the digesting liquor can be added to the liquor, separately or jointly, to thereby form the catalyst in situ. Thus, using the acetic acid based digesting liquors, there can be mentioned, as examples, the following catalyst components which can be added to the acetic acid digesting liquor to make the noted (acetate) catalyst.
Of the above mentioned catalysts, those based on sodium potassium, magnesium, calcium, and aluminum can be recovered in the reduction furnace as described above.
Catalysts which can be recovered without going through a reduction furnace are economically preferred over the catalysts whose recovery requires use of the reduction furnace. For example, ammonia can be bubbled into a digesting liquor which contains acetate ion, thereby generating ammonium acetate catalyst. The ammonium acetate can subsequently be recovered as ammonia and acetic acid by distillation whereupon the ammonia and acetic acid components can be disposed or used as appropriate. The ammonia gas can, of course, be reused or, in some small and safe amounts, discharged to the atmosphere.
Another catalyst which can be recovered without the catalyst going through a reduction burning operation is acetone, which can be recovered as part of light organics stream 16, and which can then be separated from stream 16.
It is preferred that a primary digesting/extracting reagent (e.g. acetic acid) and the catalyst (e.g. potassium acetate) have a common polar moiety (e.g. acetate ion).
The strengthening affect produced by using the catalyst as herein defined has been identified with digesting liquors which operate in an acid medium as illustrated in the above examples. It is noted herein that the use of the disclosed catalyst system is compatible with use in the conventional alcohol solvent pulping process as disclosed in e.g. 4,100,016 Diebold et al. While it would appear at first glance that the alcohol process is not acidic, it is the "operating pH" at the digesting conditions which is seen to be determinative of the desired acid conditions. While the alcohol based liquor is not generally considered to be acidic, but rather to have a more or less neutral pH of about pH 7, the pulping process does release various chemicals from the wood into the digesting liquor, including acids such as acetic acid which are weakly dissociated and which control the operating pH of the liquor. Accordingly, the operating condition of the alcohol-based digesting liquor composition, when considering the wood chemicals released thereinto, is mildly acidic and therefore compatible with use of the catalysts herein disclosed with respect to acid media, including the use of catalyst components (e.g. potassium hydroxide) which react in situ with chemicals (e.g. acetic acid) released from the wood to generate the catalyst (e.g. potassium acetate). Typically, the alcohol is present in the amount of at least about 20% by weight of the start-up liquor, preferably at least about 40% by weight, with the balance generally comprising water.
In a batch alcohol-based pulping process, the pH of the liquor varies according to the release of wood chemicals into the liquor, and conversion of those chemicals in the liquor, during the digesting step. In a continuous such process, once the start-up phase of the process has been passed, the pH will vary somewhat, but within a relatively closely defined steady state range, depending upon the process used.
Similarly, the use of the disclosed catalyst system is compatible with use in conventional bisulfite and acid sulphite pulping processes, wherein the effective digesting liquor compositions generally operate at pH 6 or less, though up to pH 7 is acceptable for use herewith.
A variety of other liquor pulping compositions, namely start-up liquor compositions, and respective processes are contemplated for use in acid media, in combination with the catalysts disclosed herein. These contemplated compositions include:
Glacial acetic acid and acetone.
Glacial acetic acid and aliphatic alcohol C₁-C₄, plus catalyst.
Glacial acetic acid, aliphatic alcohol C₁-C₄, and a salt neutralized organic acid such as potassium acetate.
Any of the lower alkyl alcohols C₁-C₄, acetone, glycol or glycerol, in combination with an effective amount of the catalyst as herein described.
Any of the start-up liquor compositions herein disclosed can be used in a water medium, or in a medium which is devoid of any water. However, a small amount of water, such as 5% to 10% generally facilitates the initiation of the digesting step, as does at least a mildly acidic pH.
The term "lightly modified" as used herein with respect to extracted lignin, refers to a family of lignin products. This family typically includes (i) a first fraction of pristine lignin which is in its original form as in the wood, and (ii) a second fraction of lignin products which comprise reaction products produced by light and moderate fractionation of the pristine lignin polymer. Generally, these reaction products exhibit the same chemical and physical properties as pristine lignin polymer, except for properties affected by their reduction in molecular weight. The overall reaction product does include (iii) a small fraction of monomeric moieties which exhibit the properties of the respective monomer moieties. The term " lightly modified" lignin does not refer to sulfonated lignins, or to the highly fractionated lignins produced in a sulfur-based pulping process.
The term "start-up liquor" as used herein refers to the composition of the virgin mixture of chemicals which is used to start up the pulping process, for digesting the biomass (e.g. wood chips) to obtain the separation of the cellulosic fibers from the lignin or lignin-type chemicals which bond the biomass material together. "Start-up liquor" does not include, in its definition, any chemicals or water which are released from the biomass; nor does it include chemical compositions which are returned to the digesting container 6 from a recycle loop or a recycle stream.
The term "primary digesting/extracting reagent" means a reagent whose primary role is that of extracting/separating lignin from cellulose in the digesting step. It does not include the catalyst in its definition.
The digesting liquor compositions herein disclosed, and the pulping processes in which they are used, are effective to produce fibrous pulp which can be used to make sheets. The term "sheets" includes handsheets, separate larger sheets, continuous webs such as are made on conventional commercial paper making machines, and the various converted products made with the above sheets and webs.
Thus this invention provides novel compositions and processes, and pulps and sheets made therefrom, all in recovering fibers, chemicals and lignins from pulpable vegetable matter.
Specifically, this invention provides a family of catalysts for incorporation into the digesting liquor, use of which results in improved pulp yields and pulp Kappa Numbers, and wherein hand sheets made with the pulps exhibit improved strengths.
The invention further provides novel compositions of matter for use as the start-up digesting liquor in the pulping operation.
The invention still further provides improved processes which yield novel fibers, and stronger pulp fibers than are produced in conventional pulping processes which operate in an acid medium.
The invention provides novel pulps so made.
The invention provides novel sheets made with the novel pulps.
The invention provides novel lignin compounds produced by the compositions and processes of the invention.
While the invention has been described above with respect to its preferred embodiments, it will be understood that the invention is susceptible to numerous rearrangements, modifications, and alterations, without departing from the spirit of the invention. All such arrangements, modifications, and alterations are intended to be within the scope of the appended claims.

Claims

A pulping process, which comprises, digesting vegetable matter in a digesting liquor having an effective pH, during said digesting step, of no greater than about 7, in the presence of a catalyst in said liquor, the amount of said catalyst comprising at least about 0.05 equivalent per liter of said digesting liquor, said catalyst comprising electron donor moieties and hydrophobic moieties.
A pulping process as in Claim 1, said digesting liquor comprising an organic acid, and including generating said catalyst in situ in said digesting liquor by incorporating into said digesting liquor a positively charged component of said catalyst, and reacting said positively charged component with said organic acid and thereby generating said catalyst.
A pulping process as in Claim 2 and including selecting said positively charged component from the group consisting of ammonia and ammonium hydroxide.
A pulping process as in Claim 1 including selecting, as said catalyst, a compound which can be separated from the lignin in said digesting liquor by a fractionation process, said process including the step of separating said catalyst from said digesting liquor using a fractionation process.
A process for extracting lignin from vegetable matter in lightly modified form, said process comprising the steps of:
(a) digesting, in a digesting liquor composition comprising a liquid alkyl acid, into which digesting liquor composition has been incorporated a catalyst comprising (i) an electron donor moiety and (ii) an hydrophobic moiety, in an amount, of said catalyst, of at least 0.05 equivalent per liter, said catalyst being soluble in said liquor composition at the conditions of said digesting step, a sufficient amount of vegetable matter at appropriate conditions to release enough lignin into said liquor composition that said liquor is saturated or nearly saturated, with lignin at the digesting conditions; and

(b) recovering said lignin from said digesting liquor.
A process for extracting lignin as in Claim 5 and including selecting, for said digesting liquor, a composition comprising about 50% by weight to about 100% by weight acetic acid, about 0% to about 25% by weight alkyl acetate, and (iii) about 0% to about 35% by weight water, said composition percentages being based on the sum of the weights of said acetic acid, said alkyl acetate, and said water; into which digesting liquor composition has been incorporated said catalyst.
A pulping process, said process comprising the step of digesting vegetable matter, comprising lingin and cellulose, in a digesting liquor, said digesting liquor comprising a first component selected from the group consisting of alcohol having one to four carbon atoms, acetone, glycol, and glycerol, in an amount effective to separate said lignin from said cellulose in said pulping process; as a second optional component, water; and as a third component, a catalyst comprising an electron donor moiety and an hydrophobic moiety in an amount effective to produce a pulp having at least one strength property or increased magnitude compared with the same said strenght property when said pulp is produced in a corresponding said digesting liquor without use of said catalyst.
A pulping process as in Claim 7 and including selecting, as said catalyst, a compound comprising a cation having up to two valence units, said cation having an atomic radius at least as great as the radius of the lithium ion.
A pulping process as in claim 7 or 8, including selecting said first component and said catalyst, in combination, such that said first component and said catalyst, in said digesting liquor, comprise a solvent-solute combination wherein one of said first component and said catalyst comprises the solvent of said combination and the other of said first component and said catalyst comprises the solute of said combination, and where in said solute is substantially dissolved in said solvent in said recited amount in said digesting liquor.
A pulping process as in Claim 7, 8 or 9 including selecting said alcohol and said catalyst such that both said alcohol and said catalyst comprise a common polar moiety, said common polar moiety being disposed toward exhibiting a negative charge.
A pulping process as in any of Claims 6 to 10, including selecting said catalyst from the group consisting of esters, alcohols, aldehydes, and ketones, said group including potassium acetate, ammonium acetate, calcium acetate, magnesium acetate, sodium acetate, lithium acetate, acetone, alkyl alcohols having one to four carbon atoms, and mixtures of said above recited catalysts.
A pulping process, said pulping process comprising the steps of:
(a) digesting vegetable matter in a digesting liquor, said digesting liquor comprising volatile components, and being contained in digesting equipment, said liquor being effective to separate lignin from cellulose in said vegetable matter, whereby said digesting liquor receives said lignin thereinto, said digesting liquor comprising a catalyst, said catalyst comprising an inorganic moiety recoverable as a liquid or solid, element or oxide from a furnace, said catalyst further comprising electron donor moieties and hydrophobic moieties;

(b) removing liquor, containing said lignin and said catalyst, from said digesting equipment;

(c) concentrating said removed liquor by removing at least part of said volatile components therefrom, and thereby producing a cake residue;

(d) burning said residue in said furnace and thereby reducing said catalyst to said inorganic moiety as either elemental material or an oxide thereof;

(e) recovering said inorganic moiety from said furnace;

(f) treating said inorganic moiety recovered from said furnace with sufficient reagent and thereby converting said inorganic moiety back into said catalyst; and

(g) returning said reformed catalyst to said digesting step.
A pulping process, said process comprising:
(a) digesting vegetable matter in a digesting liquor, said digesting liquor being contained in digesting equipment, said liquor comprising and alkyl acid, said digesting liquor being effective to separate lignin from cellulose in said vegetable matter, whereby said digesting liquor receives said lignin thereinto;

(b) removing liquor, containing said lignin and said alkyl acid, from said digesting equipment;

(c) separating said alkyl acid from said removed liquor; and

(d) returning a portion of said alkyl acid to said digesting step as make-up liquor.
A pulping process, said pulping process comprising the steps of:
(a) preparing a digesting liquor, said digesting liquor comprising a plurality of elements, including (i) an extractive agent for extracting lignin from vegetable matter, and (ii) a catalyst, said preparing of said digesting liquor comprising combining at least one component of said catalyst with at least one other of said digesting liquor elements, and reacting said at least one component of said catalyst with said at least one other of said digesting liquor elements and thereby generating said catalyst; and

(b) digesting vegetable matter in said digesting liquor, whereby said digesting liquor receives said lignin thereinto.
A pulping process as in Claim 14 and including:
(c) selecting said extractive agent from the group consisting of organic acids which are liquid at 73 degrees F.; and

(d) selecting said at least one component from the group consisting of ammonia, ammonium hydroxide, and oxides and hydroxides of sodium, potassium, magnesium, calcium and aluminum.
A pulping process, said pulping process comprising the steps of:
(a) digesting vegetable matter in a digesting liquor in digesting equipment, and thereby receiving lignin into said digesting liquor, said digesting liquor comprising (i) an organic acid selected from the group consisting of those organic acids which are liquid at 73 degrees F., and (ii) a catalyst, said catalyst comprising a catalytically active moiety which is removable from said digesting liquor by liquid fractionation, and which is returnable to and reusable in said liquor as said catalyst;

(b) removing at least a part of said digesting liquor from said digesting equipment; and

(c) fractionating said removed digesting liquor and thereby removing said catalytically active moiety of said catalyst from said removed digesting liquor.
A composition of matter, comprising:
(a) as a first component, about 50% to about 98% by weight acetic acid; and

(b) as a second component about 2% to about 50% by weight alkyl acetate, said alkyl group comprising C₁ to C₆;

in which a catalyst has been dispersed in an amount of at least about 0.1 equivalent per liter, said catalyst comprising electron donor moieties and hydrophobic moieties.
A composition of matter as in Claim 17 said composition comprising about 85% to about 98% by weight of said acetic acid, about 2% to about 8% by weight of said alkyl acetate, and about 0% to about 8% by weight of said water.
A pulping process, said process comprising the step of digesting vegetable matter in a digesting liquor comprising, as the start-up liquor, the composition of matter of Claim 17 or Claim 18.