JP2582838B2 - Method for adjusting pH of cellulose pulp using carbon gas and apparatus therefor - Google Patents

Description

The present invention relates to the preparation of cellulose pulp and, more particularly, to the chemical treatment of alkali cellulose pulp prior to treatment in a papermaking device.

(Prior Art) At present, the digestion of cellulosic materials is mainly performed using any of the soda method, the sulfate method, the sulfite method or the neutral sulfite method, and is frequently performed by the batch method. In the batch process, relatively small flaky or chip-like finely divided cellulose materials are introduced into a pressure cooker or digester where the mixture is raised to a delignification temperature and then discharged as thick pulp and wastewater for further processing operations. Offer. The continuous method is also known. Processing data that defines delignification conditions, such as the strength, time and temperature of chemicals, is often determined from actual experience rather than from laboratory data. This is because the severity of the chemical attack on the charged cellulosic material varies considerably between grades.

The delignified cellulosic material is introduced from the digester into a blow tank for dilution, diluted to a pumpable consistency of 1.5 to 4 percent solids to decompose and recover the cooking chemicals, and then refined to a cellulose pulp slurry As well as further processing, Fourdrin
ier) machine.

Various chemicals are added to the cellulose pulp slurry to impart suitable and / or desired physical properties to the paper, paper board or the like formed by such machines, or otherwise deficient. Improve one or more properties. For example, use sizing agents to impart resistance to the penetration of certain liquids to the paper, and use clay and other pigments to improve whiteness, opacity and printability; Starches and gums to improve; various synthetic polymers to provide wet strength;
Dyes and color pigments to give the desired hue; absorptive, convert self-sizin
g) Use surfactants to improve and reduce foaming and pitch problems.

Generally, treatment of the cellulose pulp slurry with such additives is advantageously performed at a pH of about 4.5 to 7.0. The pH of the cellulose pulp produced by the alkaline pulping method is about 12.0 to 10.0, and firstly, the cellulose pulp is treated with sulfuric acid to adjust the cellulose pulp to an appropriate pH range of 9.5 to 7.5 so that the treatment with the additive is effective. , Comprehensive chemical treatment is needed.

SUMMARY OF THE INVENTION One object of the present invention is to provide an improved method for adjusting the pH of alkaline cellulose pulp before paper formation.

It is another object of the present invention to provide an improved method by which the pH of an alkaline cellulose pulp can be easily adjusted to a desired pH level by a simple method.

Yet another object of the present invention is to provide a method for adjusting the pH of alkaline cellulose pulp, thereby improving the physical properties of the paper.

Yet another object of the present invention is to provide an improved method of adjusting the pH of alkaline cellulose pulp so that pulp drainage is better, thereby enabling papermaking with reduced drying energy.

It is a further object of the present invention to provide a method of adjusting the pH of an alkaline cellulose pulp, thereby improving the operation of a papermaking machine.

It is yet a further object of the present invention to provide an improved method for adjusting the pH of alkaline cellulose pulp, thereby providing improved papermaking operations and concomitantly reducing rejected paper.

It is a still further object of the present invention to provide an improved method of adjusting the pH of alkaline cellulose pulp and reducing the required amount of certain additives (such as alum or aluminum sulfate).

It is yet a further object of the present invention to provide an improved method for adjusting the pH of alkaline cellulose pulp during the refining process.

(Means for Solving the Problems) The above and other objects of the present invention are to adjust the pH of the pulp stream before introduction into the pulp refiner to about 8.5 to 6.5 and to maintain the pH at that pH. By introducing gaseous carbon dioxide into alkaline cellulose pulp. At pH above about 8.5 it is less effective, and at pH below about 6.5 it requires an excessive amount of carbon dioxide. A pH in the range 8.5 to 7.5 is preferred. Pulp flow before introduction to papermaking equipment
It is also preferred to introduce gaseous carbon dioxide into the refined pulp under conditions that adjust the pH to about 7.0 to 5.5 and maintain that pH. More preferred is a pH in the range of 6.0 to 5.5.

Further objects and advantages of the present invention will become apparent from the following detailed description, taken using the schematic flow diagram of the present invention.

The drawings schematically show a papermaking machine such as a fold linear machine. The papermaking machine (shown generally at 10) has a headbox 12 for distributing papermaking pulp material on a moving screen 36 of the fold linear machine 10. The cellulose pulp material produced by the standard alkaline pulping method is introduced into a blow tank (not shown), washed and stored in the chamber 14, and the white water in the line 16 is added to the solid pulp to obtain a solid content of about 1.5 to 5.0.
A pumpable consistency of percent, typically about four percent, is passed in line 18 to the suction side of pump 20.

The pulp slurry entering the line 22 from the discharge side of the pump 20 is brought into contact with the carbon dioxide gas from the line 21 by the injection device 25 to form a combined flow of the line 26. The amount of carbon dioxide added is sufficient to bring the pH in the combined pulp stream to about 8.5 to about 6.5. This combined pulp stream is passed through a refiner 28 to fibrillate the cellulose pulp material.

In a preferred embodiment, in line 30 downstream of the refiner 28, there is a second injector 60 for contacting the refined pulp stream with the additional carbon dioxide from line 21. The amount of carbon dioxide added is sufficient to allow the combined stream in downstream line 62 to have a pH of about 7.0 to 5.5.

The pulp from line 62 is mixed with the white water in line 46 to a consistency of about 0.4 percent solids, and pump 32 and line 34
Through the headbox 12 via. Generally, a sizing precursor such as alum is introduced into the pulp by the alum introduction means 48. The alum is introduced as a liquid into line 30, line 46 or directly into headbox 12 (as shown). The pulp in the headbox 12 is a fold linear machine.
Dispensed on ten wire woven dressing belts 36. While passing over the wire-woven endless belt 36, a liquid (previously "white water")
Is discharged and passed through a further processing step (generally in roll form) of the pulp sheet into a dry finished paper. White water 40 discharged from cellulose pulp while being distributed on a wire-woven endless belt 36
Are collected in a liquid reservoir 38 of the fold linear machine 10 and passed through a mixing tank 42 called a wire pit. Other additive chemicals needed to make specific paper products
Add from 44 to the mixing tank. A white water purge stream is generally withdrawn from line 45 to maintain chemicals, such as sulfate ions, at a predetermined level in the recirculated white water stream in line 46.

Typical pressure of carbon dioxide in line 21 is about 276 to 1378 kPa (40 to 200 psig) gauge pressure, and is preferably 69 to 138 kPa (10 to 20 psi) higher than the pressure of cellulose pulp in line 22. Carbon dioxide injector 25 is a porous metal sparger, preferably in combination with a static mixer that disperses the gas well and maximizes transport efficiency. Suitable spargers and static mixers are commercially available from a number of manufacturers. With the proper addition of carbon dioxide gas, it quickly and rigorously mixes into the cellulose pulp, at a point downstream from the discharge side of the pump 20 the pH of the line 26 reaches a uniform predetermined level and then to the next unit operation, e.g. be introduced. The pH of the treated pulp slurry is measured by a meter 50 having a pH probe 52 in line 26. The meter output generates a feedback control signal to actuate valve 56 in line 21 and is used to regulate the flow of carbon dioxide in line 24 to bring the pH of the pulp stream to a desired level.
Line 24 has a check valve 27.

The second carbon dioxide injection device 60 is a porous metal sparger, and is appropriately mixed without the second static mixer. A second meter 64 having a pH probe 66 in line 62 measures the pH and generates a control signal to activate a second valve 68. The second valve is connected to a line 70 between the carbon dioxide gas line 21 and the second injector 60. Line 70 also has a check valve 72. The pressure of the carbon dioxide gas in the line 21 is about 69 to 13 in gauge pressure more than the pressure of the purified pulp stream in the line 30
Preferably, the pressure is 8 kPa (10 to 20 psig) higher.

Examples The following examples illustrate the conditions of the method of the present invention and should not be construed as limiting the scope of the present invention.

Example I A concentrated pulp stream of pH 11, 15 percent solids, produced by kraft processing of softwood, was diluted with white water at Plato producing 600 tons of paper per day to obtain a consistency of 4 to 5 percent solids and Bring to a pH of 10.5. This diluted pulp stream is introduced into the suction side of the pulp pump 20 and passed therethrough at a speed of 2100 GPM (trim dilution if necessary).
From the pulp pump to the dilute pulp stream in a conduit downstream 3.
4 kg / min (7.5 lb / min) of carbon dioxide is added, resulting in a dilute pulp stream having a pH of 7.0 when introduced into the refiner 28 for processing. The refined pulp stream does not add carbon dioxide.

4.72 kg / min (10.4 pounds / minute)
Add alum). The pulp stream thus treated and refined is further diluted with white water, and the solid content is reduced before being introduced into the bed box 12 of the fold linear machine 10 for papermaking.
Bring the pH to about 4.5 and the pH to about 4.5.

The method of introducing carbon dioxide gas in such a controlled manner before the refining step improves the refining as compared with the method of adjusting the pH by introducing sulfuric acid before the refining step, resulting in a stronger paper.

Example II In a plant producing 1500 tons of paperboard / day,
Kraft pulping from softwood and softwood produces a dilute pulp stream of about 4 to 5 percent solids.
The dilute softwood pulp stream and the dilute hardwood pulp are combined to form a first line pulp stream for refining, which is diluted with white water to form a dilute pulp stream having a solids content of about 0.4 percent;
Introduced to the first head box of the paper machine.

The dilute softwood pulp stream having a solids content of 4 to 5 percent and a pH of 10.5 is passed through the suction side of the pulp pump at a speed of 3000 GPM (including trim white water). The dilute pulp stream (4% solids content) in the downstream conduit leaving the pulp pump,
Add 4.72 kg / min (10.4 lb / min) of carbon dioxide.
The resulting pulp stream at pH 7.0 is introduced into a first refiner and then combined with a dilute hardwood pulp stream at pH 7.0 in a second refiner.

A dilute softwood pulp stream having a solids content of 4 to 5 percent and a pH of 10.5 is passed through the suction side of the pulp pump (including the trim white water) at a rate of 900 GPM. Lean hardwood pulp in the downstream conduit from this pulp pump (4% solids content)
1.4 kg / min (3.1 lb / min) carbon dioxide gas to pH 7.0
And then into the second refiner. The combined pulp stream from the second rifuina was further diluted with white water (recovered from a paper machine wire pit and acidified with sulfuric acid) to a solids content of 0.4 percent and a pH of about 4.5 before being fed to the first headbox. Introduce. Add 13.5 pounds / minute of alum to the first headbox.

650GPM on suction side of pulp pump (with trim white water)
From the dilute hardwood pulp stream having a solids content of 4 to 5 percent formed in the discharge pipe of the pump. To this lean pulp stream, add 1.2 kg / min (2.6 lb / min) carbon gas to pH
A 7.0 dilute pulp stream is passed through the first and second refiners sequentially. The pulp stream (pH 7.0) thus purified is withdrawn from a second refiner and mixed with white water (recovered from a paper pit of a paper machine and acidified with sulfuric acid) to give a solids content of 0.4%, pH About 4.5
And then into the first headbox with 0.95 kg / min (2.1 lb / min) alum.

If carbon dioxide gas is introduced under control instead of sulfuric acid before the purification process, the dilution tank and the corrosive liquid piping can be omitted. Furthermore, since the amount of carbon dioxide is easily adjusted and has a self-buffering ability, the deviation of pulp pH, which causes a decrease in strength during aging, is eliminated, and the physical properties of the resulting paper product are marked. To improve.

EXAMPLE III In a plant producing 1400 tons / day of paper, a consistency of 4 to 5 percent solids and its consistency in thick pulp of pH 11.0, 15 percent solids, produced by kraft processing of softwood and hardwood, The resulting dilution is to a pH of 10.5. This diluted pulp stream is introduced and passed through the suction side of the pulp pump 20 at 2000 GPM (trim dilution if necessary). 1.5 kg / min (3.3 lb / min) of carbon dioxide gas is added to the dilute pulp stream in the downstream pipe 26 from the pulp pump,
When introduced into the refiner 28 for processing, a dilute pulp stream of pH 8.0 is used.

0 to refined pulp in line 30 downstream from the refineer.
Add additional carbon dioxide at 64 kg / min (1.4 lb / min) and add
A combined stream of pH 5.5 is formed in 62.

3.0 kg / min (6.7 lb / min) of alum is added to the refined pulp stream. The pulp stream thus treated and refined is further diluted with white water to a solids content of 0.4% and p
H is set to about 5.0, and then introduced into the head box 12 of the fold linear machine 10 and supplied to papermaking. Do not use sulfuric acid.

In the method of the present invention, carbon dioxide is used to lower the pH of the crude pulp and the refined pulp.
Chemical cost savings are realized by eliminating g / ton (20 pounds / ton) of sulfuric acid. It is also possible to further save costs due to the cost difference between carbon dioxide and sulfuric acid. Furthermore, the method of the present invention also reduces rejected paper.

In the preferred method of the present invention, no sulfuric acid is used, and the amount of carbon dioxide introduced into the crude pulp stream and the refined pulp stream is selected in each case to optimize the operation of the refiner 28 and the paper machine 10. Is done. To optimize the purification process, it is preferred that the pH of the pulp stream in line 26 before entering the refiner be in the range of about 8.5 to about 7.5.
The pH of the white water 40 in the wire pit 42 of the papermaking apparatus is usually in the range of 7.0 to 4.5, typically in the range of 5.5 to 4.5. For this reason, it is preferred that the pH of the pulp stream in line 62 after the refiner be in the range of about 6.0 to about 5.5. The use of carbon dioxide to reduce the pH of the combined stream to a value less than about 5.5 is usually uneconomical due to the increased amount of carbon dioxide required.

Replacing sulfuric acid produces a paper sheet with higher whiteness. Still further, because the pulp is handled in the absence of sulfuric acid and its corrosive effects, the fold linear machine has improved effectiveness and improved operation. The use of carbon dioxide significantly reduces the deposition of barium sulfate (barium is present in the cellulosic feedstock) and significantly reduces the associated paper scale scaling of the papermaking equipment, thereby interrupting the papermaking line. Reduce the frequency of "boil out" recordings that must be made.

The use of carbon dioxide in the processing of recycled paper products has also significantly improved the operation of paper machines and related equipment.

Many modifications and variations of the present invention are possible in light of the above teachings, and, thus, the invention may be practiced other than as specifically described above within the scope of the appended claims.

Embodiments 1) In a papermaking process from cellulose pulp in which the cellulose material is delignified and the delignified cellulose pulp is fibrillated with a refiner to form a papermaking pulp, about 8.5 to about prior to the fibrillation step. A process for making paper from cellulosic pulp, which comprises introducing into the delignified pulp an amount of carbon dioxide that forms a precursor paper forming pulp stream having a pH of 6.5.

2) adjusting the pH of the precursor paper forming pulp stream from about 8.5 to about
The method according to claim 1, wherein an amount of carbon dioxide gas adjusted to a value within the range of 7.5 is added.

3) mixing the stream from the papermaking operation with the delignified cellulose pulp to form the paper-forming pulp having about 4 percent solids content for contacting with the carbon dioxide. 2. The method according to item 1 above.

4) mixing the liquid stream with the delignified cellulose pulp and introducing the mixture to the suction side of a pulp pump; and introducing carbon dioxide gas to the paper-forming pulp discharged from the pulp pump. 4. The method according to the above item 3, characterized in that:

5) The pressure of the carbon dioxide gas is about 276 to 1380 kPa
The method of claim 4, wherein the pressure is between 40 and 200 psig.

6. The method of claim 4, wherein the pressure of the carbon dioxide gas is 69 to 138 kPa (10 to 20 psi) higher than the pressure of the paper-forming pulp stream.

7. The method of claim 6, wherein the pH of the paper-forming pulp stream is measured to adjust the amount of carbon dioxide introduced into the paper-forming pulp.

8) The method of claim 7, wherein the pH is measured before introducing the paper-forming pulp stream into a refiner.

9) The method of claim 1, further comprising introducing an amount of carbon dioxide to the fibrillated pulp to form a precursor paper forming pulp stream having a pH of from about 7.0 to about 5.5.

10) The pH of the precursor paper-forming pulp stream is from about 6.0 to about
10. The method of claim 9 wherein an amount of carbon dioxide adjusted to a value in the 5.5 range is added to the fibrillated pulp.

11) The method of claim 9 wherein the stream obtained from the papermaking operation is mixed with the delignified cellulose pulp to form the paper forming pulp for contact with the carbon dioxide.

12) mixing the liquid stream with the delignified cellulose pulp and introducing it to the suction side of a pulp pump;
And introducing carbon dioxide into the paper-forming pulp discharged from the pulp pump.
11. The method according to item 11.

13. The method according to claim 11, further comprising mixing the liquid stream obtained from the papermaking operation with the fibrillated pulp stream after contacting with carbon dioxide gas.

14) The method according to the above item 13, wherein the pH of the fibrillated pulp stream is measured before the mixing step.

15) In a paper making apparatus in which the delignified pulp is fibrillated with a refiner to form a pulp for paper production, an amount of the precursor paper forming pulp stream having a pH of about 8.5 to about 6.5 upstream of the refiner. An improved paper manufacturing apparatus comprising means for injecting and dispersing carbon dioxide into a delignified cellulose pulp stream.

16. The apparatus of claim 15, further comprising means for measuring the pH of the paper-forming pulp stream and adjusting the amount of carbon dioxide introduced in response to maintain the desired pH.

17) The apparatus according to the above item 16, wherein the means for injecting and dispersing carbon dioxide gas includes a static mixer.

18) The method of claim 1, further comprising injecting and dispersing an amount of carbon dioxide into the fibrillated cellulose pulp stream downstream of the refiner to form a precursor paper forming pulp stream having a pH of about 7.0 to about 5.5. Device according to clause 15.

19) Measure the pH of the precursor paper forming pulp stream both upstream and downstream of the refiner, and adjust the amount of carbon dioxide introduced in response to maintain the desired pH both upstream and downstream of the refiner. Further comprising means for adjusting;
Item 19. The device according to the above item 18.

[Brief description of the drawings]

 The drawings show a schematic flow diagram of the present invention.

Continuation of front page (72) Inventor Walter Kleinberg, Brookside Road, Edison, New Jersey, USA 08817 47 (56) References JP-A-49-30605 (JP, A) JP-A-52-31563 (JP, A) JP-A-55-12881 (JP, A) JP-A-62-110998 (JP, A) JP-B-35-5655 (JP, B1) JP-B-48-39762 (JP, B1)

Claims (3)

(57) [Claims] 1. A method for producing paper from alkaline cellulose pulp produced by delignification of a cellulose material, wherein the alkaline delignified cellulose pulp thus produced is fibrillated with a refiner to produce a paper-forming pulp. Forming, and introducing gaseous carbon dioxide to said delignified pulp, wherein said gaseous carbon dioxide is fibril in an amount such that a precursor paper-forming pulp stream having a pH of 8.5 to 6.5 is formed. A method for producing paper, wherein the method is introduced upstream of the sintering step, and the amount of carbon dioxide introduced is adjusted in accordance with the measured value of the pH of the pulp stream forming the precursor paper. 2. An apparatus for producing paper, having a function of fibrillating delignified cellulose pulp with a refiner (28) to form a paper-forming pulp, and removing gaseous carbon dioxide. An apparatus comprising means (25) for injecting and dispersing a ligninized cellulose pulp stream, said means being located upstream of said refiner (28), whereby carbon dioxide has a pH of 8.5 to 6.5 pH. The formed pulp stream may be injected in an amount to be formed, and the pH of the precursor paper forming pulp stream may be detected, and the amount of carbon dioxide introduced may be adjusted according to the detected pH value to achieve a desired value. Means for maintaining pH (52, 50, 56)
An apparatus for producing paper, comprising: 3. Injecting gaseous carbon dioxide into the fibrillated cellulose pulp stream in such an amount that a precursor paper forming pulp stream having a pH of 7.0 to 5.5 is formed downstream of the refiner (28). Device according to claim 2, further comprising means (60) for dispersing.