JPH0672384B2 - Braunstock cleaning method - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to a method for removing and recovering spent or excess cooking chemicals and pitch from raw or primary cellulosic fibers. More specifically, the present invention is an improved method of cleaning Brownstock for enhancing the recovery of spent cooking chemical residues, excess cooking chemicals and non-cellulosic materials such as lignin, fatty acid soaps and resin acids. Regarding

BACKGROUND OF THE INVENTION Raw cellulose fibers made from hardwood or softwood logs are subjected to a number of treatments and are ready for papermaking. In a typical pulping process, logs are cut into wood chips and fed to a digester. A chemical liquid obtained from a washing step described below and dissolved and remaining, a cooking chemical residue used, a cellulosic impurity and a white liquor which is another by-product of the pulping method is supplied to a digester. Cooking chemicals are also added. This cooking chemical will be described later.

The contents of the digester are at a relatively high temperature and pressure, eg, about 177.7 ° C at a pressure of about 110 pounds per square inch.
(350 ° F). Under these conditions, wood chips are digested in a digester to pulp. Typically,
Under these conditions, the chips are cooked for about 1-5 hours.
Cooking is carried out in a batch digester or a continuous digester.

The digested wood pulp in the aqueous medium is called Braunstock. Brownstocks generally consist of two layers, a pulp and a liquid or liquid phase. However, after cooking, too large chips or chips with insufficient cooking, that is, knots remain.
These components are removed from the brown stuff by a knotter with a coarse screen.

It is generally considered necessary to separate the pulp from the chemical solution before further processing the pulp. In order to clean the pulp, it is also necessary to remove as much spent or excess cooking chemicals as possible, and to remove and recover pitch impurities.

After cooking, following removal of the oversized chips, the brownstock is sent to the washer for the washing process. The washing process involves a series of washing machines, where pulp and chemicals are separated,
The pulp is further washed by subsequently removing the cooking chemistry, cooking chemistry residues and non-cellulosic impurities.

Several methods can be used to carry out the cleaning method. In the past, Brownstock was filtered in an auxiliary bottom tank or diffuser. The chemical liquid was discharged therefrom, and the pulp was washed by gravity displacement between the chemical liquid and washing water. Other types of washers are also known, such as pressure washers.

Currently, rotating vacuum drums or cylinders or vacuum washers are commonly used. A vacuum washer is a wire cylinder or drum that rotates in a large butt containing a brown stock (ie a mixture of pulp and chemicals). The lower part of the drum etc. is immersed in the brown stock. A vacuum is applied to the inside of the rotating drum in the Brownstock. The chemical is discharged inward from the surface of the air-ear drum, leaving a layer of pulp on the outer surface. The layer of pulp is held in place by the vacuum force.

As the dipping portion of the drum rotates in the brownstock, a pulp layer grows to form a mat or sheet. Due to the pressure difference between the vacuum in the cylinder and the external atmosphere, the chemical liquid continues to be discharged from the pulp or fiber mat.

The cleaning action is achieved by a shower located above the pulp sheet. Water is sprayed on the pulp sheet and the sheet is replaced with the liquid chemical as the drum rotates. A vacuum force draws water into the sheet where it is replaced with the drug solution.
The chemicals are discharged into the cylinder from the opposite side of the sheet, stored in a filtrate storage tank and reused as wash water for the more contaminated sheet in, for example, another of the series of washers.

Finally, the pulp sheet is removed from the surface of the wire drum with a doctor blade.

Since the wash water has a high chemical concentration while passing through the sheet, the surface of the sheet on the side where the wash water is applied is cleaner than the sheet in contact with the cylinder at the bottom of the sheet. When using a series of washer, the pulp sheet from the first vacuum washer is repulped before being sent to the second washer to obtain a more evenly clean pulp. It is common. This repulping process is repeated between each vacuum washer.

In the repulping process, pulp fibers are agitated with low consistency (pulp is very lean). The dissolved solids will be low in concentration and then the pulp will be collected in a washer. Low consistency repulping promotes the diffusion of contaminated liquids from the pulp.

The pulp medium and the washing liquid are arranged in a continuous washing machine so that they are in an alternating current. Fresh water is used to wash the pulp sheet in the final washer. The filtrate that has passed through the pulp sheet in each washing machine is used for washing the pulp in the preceding washing machine. This minimizes the dilution of the chemicals separated from the pulp from which the cooking chemical or its residues should be recovered.

The cooking chemicals used in pulping mills are known in the art. Cooking systems are generally Kraft or sulfite processes. Other cooking systems are also known.

The Kraft system uses sodium hydroxide and sodium sulfide in a digester to break down wood fibers to produce pulp. Sodium is supplied as sodium sulfate, sodium carbonate, or similar sodium compounds. The sulfite system uses SO and magnesium, calcium, sodium or ammonia. Black liquor is produced in craft mills, while it is called red liquor in sulfite mills. As used herein, "chemical liquor" means a liquid layer of both red liquor and black liquor, as well as pulp mixtures obtained from other pulp treatment processes as described below.

Some pulping mills form pulp from wood without the use of cooking chemicals. Such pulping methods are known and include mechanical methods such as the groundwood method, the use of tofiners to make refiner mechanical pulp, or the use of heat to make thermomechanical pulp. Many of these methods break wood fibers by heat and mechanical action. Other methods, such as the NSSC method, rely on both chemical and mechanical action. Although these mechanical, thermomechanical, or semi-chemical methods do not include a washing step, the method of the present invention can be used to clean pulp and recover organic impurities if a washing step is used.

Uncleaned brown stocks contain many impurities from the pulping process, such as excess cooking chemicals and used cooking chemicals (if chemicals are used for pulping), and similar acids derived from resin acids, fatty acid soaps and wood. It includes various organic inclusions such as substances. This inclusion is entangled in pulp fibers and is present in the water phase of Brownstock. In general, the contents of black liquor and corresponding pulp have been found to be alkaline lignin, hydroxy acids, lactones and sodium. Generally, black liquor is acetic acid, formic acid, sulfur, tractives,
And also includes methanol. Red liquor (obtained from the sulfite method)
And the corresponding pulps are lignosulphonates, monosaccharides (mannose, xylose, galactose, glucose and arabinose), poly and oligosaccharides, calcium, aldonic acids, sugar-sulphonates, extracts, acetic acid, methanol and glucuronic acid. including. These materials are substantially different from the materials encountered in deinking or dewaxing repulping processes, where the inclusions are inorganic materials and very different organic materials.

It is highly desirable to recover cooking chemical residues for reuse and reduce the amount of chemicals required in the mill.
These residues that remain in the pulp are generally not recoverable and remain in the pulp product. These residues carried by the drug solution can be recovered. Therefore, it is advantageous to reduce the amount of chemicals in pulp and increase the amount in chemicals. Particularly, it is preferable to transfer the chemical from the pulp to the chemical liquid.

Such transfer can be accomplished considerably by washing the pulp.
However, a huge amount of wash water is required for washing at the manufacturing level to obtain a large amount of pulp of high quality, that is, high purity. Since recovery of chemicals involves distillation or evaporation of aqueous components,
Recovering a drug from a very dilute solution can be very expensive and outweigh the cost of recovery. Accordingly, there is a need for a method of washing raw pulp that is capable of substantially removing excess and spent cooking chemicals from the pulp and cleaning the pulp without undue dilution.

In addition to the problem of recovering inorganic chemicals for cooking, there is a second problem due to lignin and other organic substances present in wood chips, such as resin acids and fatty acid soaps. If they are of economic or market value, such as when recovered as tall oil, then recovery is desirable. The bleaching process is costly because more chemicals are required to bleach pulp that leaves high levels of such substances. It is desired to provide a method for washing raw pulp by minimizing the dilution amount, that is, the amount of washing water, and recovering a larger amount of organic substances to obtain a pulp having high brightness.

SUMMARY OF THE INVENTION The addition of nonionic surfactants, dispersants, and preferably solvents to the wash water or the Brown Stock itself results in an unexpected improvement in raw pulp cleaning. There was found. According to the present invention, a given amount of wash water surprisingly increases the removal of spent or excess cooking chemicals and organic inclusions, thus diluting the wash process while providing light colored pulp in the wash. It minimizes and facilitates economical recovery of cooking chemical residues and organics.

In the present invention, a nonionic surfactant is used in the washing step in combination with a dispersant, and preferably also with a solvent. The surfactant contains an oxyethylene glycol chain, and one terminal hydroxyl group of this chain is substituted with an ether group selected from an aliphatic ether group and an alkyl aromatic ether group, and the other terminal hydroxyl group is a polyoxypropylene group and It is substituted with a group selected from benzyl ether groups. A typical structure of a preferred surfactant is: R (Ar) _a (CO ₂ H ₄ ) _n (OC ₃ H ₆ ) _m Y, where a is 0 or 1 and Ar is An aromatic residue, preferably monocyclic, R is an aliphatic group, n is about 3 to about 50, m is about 0 to about 50, and Y is a hydroxyl group and a benzyl ether. A benzyl ether when m is 0).

The R group is typically saturated and contains at least 6 carbon atoms. When a is 0, R contains 6 to 24 carbon atoms; when a is 1, R usually contains 6 or less carbon atoms.
The R (Ar) _a group has at least 6 aliphatic carbon atoms and a total of 2
Contains up to 4 carbon atoms.

The above structural formulas include two major classes of surfactants: (a) alkylene oxide adducts of alkylphenols, and (b) alkylene oxide adducts of higher (C and higher) aliphatic alcohols or acids. The acids used to make the surfactants are lauric acid, myristic acid, oleic acid, linolenic acid, palmitic acid, stearic acid. If a fatty acid adduct is used, R typically contains from 6 to 24 carbon atoms and may contain some unsaturation.

The surfactant used is a low foaming agent that does not substantially cause the foaming problem in the system.

These surfactants are based on the Ri filed Nov. 13, 1979.
Chard E. Freis, James E. Maloney and Thomas R. Oakes in detail in US patent application 093,744 entitled "Methods of Deinking Secondary Fibers". The continuation application of this patent application 093,744 was withdrawn on January 17, 1983 and its number is 458,432.

The present invention uses a polyelectrolyte dispersant. The term "polyelectrolyte" means any homo-, co-, terpolymer, etc. of the structural formula: (In the formulae, R ₁ , R ₂ , R ₄ and R ₅ are independent of each other and are hydrogen, C ₁ -C ₄
Lower alkyl, alkyl carboxy (e.g., -CH ₂ COO
H) or a mixture thereof, R ₃ and R ₆ are hydrogen, carboxy, alkylcarboxy or a mixture thereof, and X is carboxy (including a salt, derivative, for example, amine), acetyl, a free radical monomer. hydrocarbon moiety that typically binds (e.g., -C ₆ H ₅ in styrene), a +
The sum of b is in the range 15-1000. ) Examples of substances included in the above formula include polymaleic acid, polymethacrylic acid, polyacrylic acid / itaconic acid copolymers, polyacrylic acid / hydrogenated maleic acid copolymers, polymaleic acid / itaconic acid copolymers, hydrogenated maleic acid / Vinyl acetate copolymer, polyacrylic acid / acrylamide copolymer, polyacrylic acid / methacrylic acid copolymer, styrene / maleic acid copolymer, styrene styrene / maleic acid copolymer, polymaleic acid / methacrylic acid copolymer, maleic acid telomer,
There is a maleic acid / alkyl sulfonic acid copolymer.

A particularly preferred water-soluble polyelectrolyte is a polyacrylate compound. This polyacrylate compound includes polymers and copolymers of the following structural formulas, and derivatives thereof; (In the formulae, R ₂ , R ₅ , X, a and b are as defined above).

In the most preferred embodiment, X is --COOZ, where Z is H, or a monovalent cation such as Na ⁺ , K ⁺ , ▲ NH ⁺ ₄ ▼. Thus, the preferred polyelectrolytes are polyacrylic acid, polymethacrylic acid, and acrylic acid / methacrylic acid copolymers (eg, AQUATREAT, commercially available from ALCO Chemical Company).

The polyelectrolyte of the present invention is water soluble. Water-soluble generally means that the polymer must contain sufficient polar groups (eg COOH) that it can interact with polar water molecules. This is in copolymers, terpolymers, tetramers, etc. with unsaturated monomers which are predominantly or wholly hydrocarbon (eg styrene), where there are sufficient polar functional groups to dissolve them in water at room temperature or below. Means that. Generally, at least about 10 mol% of the monomer-containing polymer has a polar functional group (eg, It has the necessary water solubility.

The low molecular weight polyelectrolyte has a molecular weight of about 50,000 or less, preferably about 500 to 25,000, more preferably 750 to 5,
It has a molecular weight of 000. Therefore, the sum of a + b is 5 to 1,0
The range is 00, preferably 10 to 500, more preferably 12 to 450. The substances in the above molecular weight range have a molecular weight smaller than that of a polymer called floculant having a molecular weight of several millions. The action of the flocculant is the aggregation of dispersed particles, as opposed to the desired dispersing action. Therefore, these polymeric substances are used in the opposite manner to the substances of the invention. The low molecular weight substances of the present invention are commonly referred to as dispersants.

In the present invention, various known water-soluble solvents or cosolvents can be used together with the dispersant and the surfactant. The solvent improves the removal of pulp impurities more than expected. Solvents include ethoxylated solvents such as the glycol ethers marketed under the Cellosolve and Carbitol trademarks. Preferred examples are tetrahydrofuran, tetrahydrofurfuryl alcohol and their ethoxylated and propoxylated derivatives. Tetrahydrofurfuryl alcohol is particularly preferred to improve the recovery of spent cooking chemicals and the resulting pulp purity level.

In operation, nonionic surfactants, dispersants and solvents are used in amounts sufficient to increase the recovery of cooking chemicals and soluble organics and to increase pulp purity after washing with a volume of water. Best results are obtained with a surfactant: dispersant ratio of about 0.5: 1 to 2: 1. If a solvent is used, the surfactant:
The effective ratio of solvents is about 0.5: 1: 1.

The desired concentration of specific ionic surfactant is generally about 0.01-30 lbs.
s / ton of dry pulp, preferably 0.1-4 lbs / ton. The concentration of the solvent is about 0 to 25 lbs / ton, preferably 0.1.
~ 4 lbs / ton. In the art, "pound / ton" means pound weight of additive to ton weight of washed oven dried pulp.

Additives are provided at various locations in the pulping system, such as showerheads, wash vats, filtrate storage tanks, digesters, denotters, repulsors, and the like. It has been found to be well distributed in the wash system when fed to the middle of a series of washers, for example the second showerhead in triplicate.

The additives can be added separately, premixed and added as a mixture. Preferably the additives are premixed. In a preferred example, 10-60% nonionic surfactant, 10-60
A mixture of% polyelectrolyte and 0-50% solvent (100% total) is added at a level of about 0.1-50.0 lbs./ton. More preferably, the mixture is 30-50.
% Nonionic surfactant, 20-40% polyelectrolyte, 20-
Contains 40% solvent. In order to achieve a great economic effect, the concentration is about 0.2268-2.268 kg (0.5-5.0 lb) / ton and the mixture is added to the intermediate showerhead of a series of washers.

The temperature of the wash water is in the range of about 37.8-100 ° C (100-212 ° F), preferably about 60-82.2 ° C (140-180 ° F).

The surprising result achieved by the present invention is the result of preventing channeling in the mat, such as permeation of wash water into the mat and effective replacement of chemicals and impurities such as used cooking chemicals and organic substances. it is conceivable that.

[Examples] The present invention will be further described by the following examples.

Example 1 A pre-execution, execution, and post-execution were conducted in a sulfite pulping mill equipped with three rotary cylinder vacuum cleaners. Data from previous runs were measured from the mill during 21 days of standard production. The run was carried out for 27 days using the present invention under standard conditions. Subsequent runs were measured about 21 days after implementation during the standard production again without the use of the invention. The pre- and post-run data are standard and are for comparison with the data obtained by use of the present invention.

The implementation method is as follows: The additives used were fed to the second shower. 40 additives
Denatured alcohol ethoxylates with a specific gravity of 0.97% by weight, 30% by weight low molecular weight polyacrylic acid with 100% activity and 48-50% aqueous solution with a PH of 1.5-2.0 at 100%, and a molecular weight of about 10
2, containing about 30% by weight of tetrahydrofurfuryl alcohol having a specific gravity of about 1.0543 at 20/20 ° C. The temperature of the second shower solution was 48.9-71.1 ° C (120-160 ° F).

The results are shown below: The Notch TDS is the total solids dissolved in the liquid layer from the Notter before washing the pulp.

The first washer filtrate TDS is the total solids dissolved in the filtrate recovered from the first washer of the triple washer. Higher values indicate more impurities were washed from the pulp.

The third washer mat TDS is the total solids dissolved in the mat itself formed in the third washer. This was calculated by squeezing the liquid from the mat and testing the liquid for all dissolved solids. It is understood in the art that the composition of the liquid squeegee corresponds to the composition of the mat itself. The lower the value, the more pure the mat is, which is preferable.

The third washer shower flow is gallons per minute of wash water flowing from the third shower head.

Red liquor solids are weight percent of solids based on the total weight of red liquor.
This value shows the presence of impurities such as cooking chemicals and lignin contained in pulp after cooking and removed by washing. A high value means that many impurities are removed from the pulp and can be recovered.

Surge tank solids loss means solids, cooking chemicals, lignin, etc. that are entrained in the pulp and therefore cannot be recovered. The lower this value is, the more preferable.

Total efficiency is expressed in%. A high% indicates a large cleaning effect and is preferable. This is calculated by the following formula: Efficiency = {(TDS 1st Butt) − (TDS 3rd Matt)} × 100 / {(TDS 1st Butt) − (TDS 3rd Shower)} where TDS is All dissolved solids are meant. The TDS 1st batch is the total dissolved solids of the Brownstock in the 1st batch of the washer. The third TDS mat is obtained from an analysis of the squeegee of the mat formed in the third washer. The TDS 3rd Shower is the total dissolved solids of the wash water sprayed from the 3rd Shower Head.

The third washer MAT extractables are the weight percentages of impurities relative to the total weight. This test was performed according to the TAPPI method using toluene and alcohol instead of benzene and alcohol in the extraction process. The smaller this value is, the less soluble organic impurities are in the pulp or mat.

For the data, N is the number of samples tested.
The values obtained were then analyzed via the Student T test,
The values in Table 1 were obtained. S represents the standard deviation in the values obtained. The% in Katsuko is the confidence limit for the value.

Discussion of Results A regression equation was developed using data from all runs as well as data from runs with addition of the mixture described in the examples at the level of 0.6804 kg (1.5 lbs) / ton. All work was performed via multiple linear regressions. The terms contained in the formula are significant at the level of (P = 0.05). The regression equation is as follows: red liquor solid = 9.813 + 1.352 x matt TDS + 1.190 x pound / ton of additive mixture used + 0.077 x first butt TDS-0.16.
7 x cooking (No./day).

R = 0.8102.

Surge tank solid loss = 117.12 + (2.65 x cooking (No./
(Day)) + (0.022 x Notter flow)-(1.78 x efficiency) +
(Manufacturing 0.120 x 1 day). R = 0.5535.

Third mat TDS = 6.552 + (0.030 × notter-TDS)-(0.
066 x efficiency)-(0.041 x pounds / ton of additive mixture used). R = 0.6658.

Red liquor solids increased during the run and decreased during the post run.
The regression equation is equal to 0.19% per ton of added mixture. Or
About 0.3 at an average working feed of 0.6804 kg (1.5 lb) / ton
It showed an effect equal to 0%.

The resulting values for all dissolved solids in the first washer were significantly elevated, indicating that the use of the additive mixture significantly improved the washing results. The total knotter dissolved solids also increased during the run.

The total dissolved solids in the third washer mat decreased by 17% during the run compared to the average of the pre-run and the post-run. This value means a surprising effect of solids removal. The regression equation shows that the effect of the additive mixture on the total dissolved solids in the third washing machine is 0.6804 kg.
The use of the additive mixture at (1.5 lb) / ton shows a 0.0615% reduction.

The total efficiency increased significantly. The values of the post-runs are more reliable than the pre-runs due to the smaller sample size of the pre-runs. Efficiency was calculated from all oven dried solids dissolved.

Matte extractables from the third washer 12
%, Which is an unexpectedly large decrease in view of the high production speed of the implementation.

Example 2 Example 2 was performed in the same way as Example 1 using the same standard method on the same sulfite mill.

The first pre-run lasted 8 consecutive days, followed by another 12 days to measure data for standard mill operation. The implementation period lasted 5 days in succession to the previous implementation on 12 days, and continued for 3 days in the subsequent implementation.

The method of implementation of Example 2 is as follows: Squeezing was performed from the third mat at various times during and after the run as indicated in the sample run, and in some cases water soluble by the TAPPI test using toluene and alcohol instead of benzene and alcohol. Inorganic matter was analyzed. The results of the third matsu squeezing analysis are shown below in PPM units: The average of the 3 mat dissolved solids, and in% by weight solids / squeegeeing weight, is as follows: first previous exemplary second before the implementation and rear exemplary implementation 0.48 0.49 0.42 Results third mat Dissolved solids average 0.49% to 0 during the run.
42%, indicating a decrease in soluble inorganic and organic matter. Water analysis of the third mat confirmed a significant reduction of minerals during the run. These results showed that the use of the additive mixture in the second shower tended to unexpectedly reduce the inorganic and organic solids in the third mat.

The above description and examples do not limit the present invention. Those skilled in the art will be able to make various changes and modifications within the scope of the present invention.

Claims (25)

[Claims] 1. A method for removing spent or excess cooking chemicals or organic impurities from chemically or mechanically produced raw pulp: (a) chemically or mechanically produced raw pulp. And (b) passing an aqueous solution containing a substituted oxyethylene glycol nonionic surfactant and a water-soluble low molecular weight polyelectrolyte dispersant through the fiber mat. 2. The method according to claim 1, wherein the step of passing the aqueous solution through the fiber mat includes applying the aqueous solution to the fiber mat and sucking the aqueous solution in a vacuum through the mat.
Method of terms. 3. The method of claim 2 wherein the step of applying the aqueous solution to the fiber mat comprises spraying the aqueous solution onto the surface of the mat. 4. The method of claim 3 wherein the fiber mat is manufactured using a rotary drum vacuum washer. 5. The temperature of the aqueous solution is about 37.8 to 100 ° C. (100 to 100 ° C.).
212 ° F.), the method of claim 3. 6. The method according to claim 1, wherein the aqueous solution further contains an ethoxylated water-soluble solvent. 7. The method according to claim 1, wherein the aqueous solution contains tetrahydrofurfuryl alcohol, an ethoxylated derivative thereof or a mixture thereof as a water-soluble solvent. 8. The total concentration of substituted oxyethylene glycol nonionic surfactant, low molecular weight water soluble polyelectrolyte dispersant and solvent is about 0.04 per tonne of oven dried pulp.
536 to 22.68 kg (0.1 to 50.0 lbs), with a total concentration of 10 to 60 wt% surfactant and 10 to 60 wt% dispersant
And the solvent comprises 0 to 50% by weight.
Method of terms. 9. The method of claim 8 wherein the total concentration is about 0.5 to 5.0 pounds per ton of oven dried pulp. 10. The method according to claim 1, wherein the polyelectrolyte is a copolymer of maleic acid and vinyl acetate. 11. The method of claim 1 wherein said polyelectrolyte comprises a polyacrylate compound. 12. The polyacrylate compound is 500 to 250.
The method of claim 11 having a molecular weight of 0. 13. The above-mentioned polymer electrolyte is (Wherein R ₁ , R ₂ , R ₄ and R ₅ are independent and are hydrogen, C ₁ -C ₄
Lower alkyl, alkylalkoxy, or a mixture thereof, R ₃ and R ₆ are independently hydrogen, carboxy, alkylcarboxy, or a mixture thereof,
X is carboxy or a salt or derivative thereof, acetyl, a hydrocarbon moiety normally attached to a free radical monomer, COOZ (where Z is H, a monovalent metal ion or ammonium), or a mixture thereof, a + b Is 15 to
It is in the range of 1000. ) The method of claim 1 having the structure 14. R ₁ , R ₃ , R ₄ and R ₆ are hydrogen, and R ₂ and R ₅
Is hydrogen or methyl, and X is carboxy,
The method of claim 13. 15. Used or excess cooking chemicals or organic impurities from an aqueous pulp medium containing chemically or mechanically produced raw pulp and used or excess cooking chemicals or organic impurities. In the method of removal: (a) mixing the aqueous pulping medium with a substituted oxyethylene glycol nonionic surfactant and a water soluble low molecular weight polyelectrolyte dispersant, and (b) raw pulp from the aqueous pulping medium. Substantially separating, and (c) thereafter removing spent or excess cooking chemicals or organic impurities from the aqueous pulping medium. 16. The method of claim 15 wherein the raw pulp is washed in a washing step in the step of substantially separating the raw pulp from the aqueous pulping medium. 17. The method of claim 15 wherein the raw pulp is substantially separated from the aqueous pulping medium and washed in a rotary vacuum cylinder washer. 18. The method according to claim 15, wherein in the step (a), a solvent containing tetrahydrofurfuryl alcohol, an ethoxylated derivative or a mixture thereof is further mixed. 19. The total concentration of the substituted oxyethylene glycol nonionic surfactant, the low molecular weight water-soluble polyelectrolyte dispersant and the solvent is about 0.1 per ton of oven dried pulp.
Claims: 04536 to 22.68 kg (0.1 to 50.0 lbs), the total concentration being 10 to 60 wt% surfactant, 10 to 60 wt% dispersant and 0 to 50 wt% solvent. First
Method of paragraph 18. 20. The method of claim 19 wherein the total concentration is from 0.5 to 5.0 pounds per ton of oven dried pulp. 21. The method according to claim 15, wherein the polyelectrolyte is a copolymer of maleic acid and vinyl acetate. 22. The method of claim 15 wherein the polyelectrolyte comprises a polyacrylate compound. 23. The polyacrylate compound is 500 to 250.
The method of claim 22 having a molecular weight of 0. 24. The polymer electrolyte is (Wherein R ₁ , R ₂ , R ₄ and R ₅ are independent and are hydrogen, C ₁ -C ₄
Lower alkyl, alkylcarboxy, or a mixture thereof, R ₃ and R ₆ are independently hydrogen, carboxy, alkylcarboxy, or a mixture thereof,
X is carboxy or a salt or derivative thereof, acetyl, a hydrocarbon moiety normally attached to a free radical monomer, COOZ (where Z is H, a monovalent metal ion or ammonium), or a mixture thereof, a + b Is 15 to
It is in the range of 1000. ) The method of claim 15 having the structure of. 25. R ₁ , R ₃ , R ₄ and R ₆ are hydrogen and R ₂ and R ₅
Is hydrogen or methyl, and X is carboxy,
The method of claim 24.