FI123309B - Process for making pulp and pulp - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to a process for the production of paper pulp. The invention further relates to the use of the pulp produced by the process and to the use of the pulp produced by the process as a raw material for paper and board.

BACKGROUND OF THE INVENTION PCC is a chemically precipitated calcium carbonate, CaCO 3. It can be prepared, for example, from burnt lime CaO, which is quenched by reacting it with water. When the Ca (OH) 2 of the calcium 15 hydroxide obtained by the quenching reaction is reacted with a precipitating agent, typically carbon dioxide CO 2, Precipitated Calcium Carbonate (PCC) is formed. By varying the process conditions, for example, the crystalline and granular form of PCC can be changed.

The precipitation of calcium carbonate is generally carried out in a batch process by introducing carbon dioxide into a calcium hydroxide aqueous slurry, i.e. milk of lime, to precipitate calcium carbonate. Precipitated calcium carbonate (PCC) can also be produced continuously in a stream of fiber or water by introducing lime milk and carbon dioxide into the stream. One method for precipitating calcium carbonate bona fate among a fibrous paper raw material is disclosed in European Patent EP1297220.

(M

i

C/O

PCC is commonly used in paper making both as a filler and as a coating pigment e.g. to improve many of the paper's features, including optical £ 30 and printing qualities. Additive filler

CL

The design also allows the use of a smaller amount of fiber in the papermaking process, whereby the resulting cost savings are typically significantly greater than the cost of the filler additive. Therefore, it is a general tendency to add as much filler as possible to the fiber suspension used in papermaking. However, the increase in filler content is limited by e.g. degradation of paper strength properties.

2

In order to increase the filler amounts of paper clearly, binders should also be added to the fiber suspension in significant amounts. However, binders are typically expensive, which makes it difficult to raise the filler content cost-effectively.

5

Summary of the Invention Ivhvt

The present invention discloses a novel and inventive method for producing pulp. In addition, the paper pulp produced by the process and the use of the pulp produced by the process as a raw material for fine paper and board are disclosed.

The present invention makes it possible to produce paper pulp in a cost-effective manner. The raw materials used to make the pulp in the invention are typically inexpensive because it is possible to use inexpensive additives, such as sodium hydroxide (NaOH), carbon dioxide (CO 2) and calcium hydroxide (Ca (2)) instead of expensive binders and fillers. ). The present invention provides a novel process for the production of paper pulp which comprises both a filler, a binder and a fibrous material.

The process according to the invention comprises one or more of the steps listed below: - xylan is extracted from the cellulose fibers into the extraction solution with sodium hydroxide, - extraction of the xylan in the extraction solution with carbon dioxide,

C/O

0 - Add calcium hydroxide to the mixture to precipitate calcium carbonate 01 £ 30 - Remove sodium hydroxide from the mixture (Wash and precipitate

CL

of the mixture), and $ - recycle the sodium hydroxide removed from the mixture

LO

for example, the xylan extraction step.

δ C \ l 35 Due to the sodium hydroxide used in the extraction, xylan is sufficiently solubilized in the extraction solution and significantly better compared to, for example, the dissolution of xylan with calcium hydroxide. As a result, the hardwood pulp used in the invention from which xylan is extracted may be non-pulverized or slightly pulverized chemically fibrous wood fiber. According to one example, said chemically fiberized hardwood SR 5 (Schopper-Riegler) has a number between 10 and 40, for example between 15 and 30.

The bleached birch pulp containing xylan and precipitated calcium carbonate produced by the process of the invention can be used, for example, as a raw material for paper and board, preferably as a raw material for fine paper.

The process for producing the pulp according to the invention is disclosed in claim 1. The pulp according to the invention is disclosed in claim 8. The use of the pulp according to the invention is disclosed in claims 9 and 10.

The process according to the invention provides several advantages. The following are some of the advantages that may be achieved by using the process of the invention.

20 - The solution of the invention makes it possible to increase the bulk potential of the pulp, since the reduction in the amount of xylan from the inner fibers of the process according to the invention typically increases the bulk of the product made from said pulp compared to the methods used to produce pulp.

The solution according to the invention also enables paper pulp

C/O

9 increasing the strength potential, since transferring the xylan of the fibers from the inner parts of the fiber to the outside of the fiber, preferably to the surface of the fiber, improves the strength characteristics of the product typically formed from said fibers.

CL

In comparison with those typically used in the manufacture of paper pulp.

LO

The process of the invention also makes it possible to improve the binding and retention of the precipitated calcium carbonate by means of xylan in a pulp suspension.

4 - The invention also makes it possible to use a cheap binder naturally present in the fibers to replace expensive synthetic binders.

The recyclability of the sodium hydroxide according to a preferred embodiment of the invention provides additional advantages to the process according to the invention.

The invention makes it possible to produce a so-called composite pulp, that is to say, a paper pulp which contains all the main paper raw materials, i.e., filler, fibrous material and binder.

10

Description of the drawings

In the following, the invention will be explained in more detail with reference to the accompanying drawing, in which Figure 1 shows a system for producing pulp according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION In this application, reference is made to Figure 1, which uses the following reference numerals: 1 Bleached cellulose fibers, chemically fiberized from hardwood, 25 mm. comprising bleached cellulosic fibers and dissolved xylan

CM

i- seos, o ^ 3 mm. comprising bleached cellulosic fibers and precipitated xylan

C/O

9 alloy, c \ j 4 mm. a blend of bleached cellulose fibers, precipitated xylan and precipitated g 30 calcium carbonate,

CL

5 alkali extraction, $ 6 xylan precipitation, tn 7 calcium carbonate precipitation, ° 8 pulp washing and precipitation, and 35 10 pulp.

In this application, the term "pulp 10" refers to a mixture containing precipitated calcium carbonate (PCC) as a filler, xylan as a binder and chemically fiberized cellulose fibers from hardwood as a fiber raw material. Most preferably, the pulp fibrous raw material comprises chemically fiberized and bleached cellulose fibers from birch, since birch has a particularly high xylan content. Chemically fiberized cellulose fibers 1 used as a fiber feedstock may have been prepared and bleached by a technique known in the art. Preferably, the pulp according to the invention is a raw material of paper or paperboard, more preferably 10 raw materials of fine paper.

By the term cellulosic fiber is meant hardwood pulp, especially birch pulp, which in other words is made from hardwood by a chemical pulping process.

15

Xylan naturally occurs in e.g. Inside the hardwood cellulose fibers. Xylan is inherently a good binder, therefore transferring xylan from the interior of said fibers to the fiber surfaces and / or the fiber suspension increases the strength properties of the product formed from said fibers.

The cellulose fibers 1 according to the invention may comprise non-milled, low-milled and / or highly-milled cellulose fibers. According to a preferred example, the cellulosic pulp SR (Schopper-25 Riegler) used as the fiber raw material has a number between 10 and 40, for example between 15 and 30. When using low-milled cellulosic fibers as a fiber raw material, the cost of manufacturing the fiber raw material is typically reduced compared to more milled cellulose fibers.

C/O

o lulose fibers. This is due to reduced milling costs. According to a preferred example, the degree of refining of the cellulosic fibers is determined according to the desired properties of the g pulp being produced.

According to a preferred example, the preparation of the pulp according to the invention is carried out integrated with the pulp mill, δ

CM

The process according to the invention comprises one or more of the following steps: 6 - Alkaline pulping extraction 5, whereby xylan is extracted with sodium hydroxide from cellulose fibers to 1 extraction solution.

- Xylan precipitation 6, in which step xylan in the leach solution is precipitated with carbon dioxide.

5 - Precipitation of calcium carbonate 7, at which step calcium hydroxide is added to the mixture to precipitate calcium carbonate, - Washing of the mass mixture and precipitation 8, at which step sodium hydroxide is removed from the mixture. For example, a filter may be used for precipitation. The washing and / or precipitation cycles may be one or more. Sodium hydroxide is removed from the mixture formed during this step.

- Recycling treatment of at least one filtrate formed during washing and precipitation in 8 steps. The sodium hydroxide removed from the mixture is then recycled back to the xylan extraction step, for example.

15

In pulp alkali extraction 5, bleached cellulose fibers 1 are extracted with sodium hydroxide to dissolve xylan from said fibers in the extraction solution. The extraction may be carried out, for example, during or after the final bleaching step of said bleached cellulose fibers. According to a preferred pre-20 example, the extraction is carried out at a fiber consistency of about 10%, for example 3-25% consistency. According to one example, the extraction is carried out at a fiber consistency of 3-5%. According to one example, the extraction is carried out at a fiber consistency of 5-15%.

Preferably, the extraction is performed with 0.25-1.25 M sodium hydroxide (NaOH), more preferably 0.5-1.0 M sodium hydroxide. According to a preferred example, the extraction time at room temperature is about one hour. After the extraction

C/O

The pH of the resulting mixture 2 can be, for example, between about 12 and 13.

CM

In connection with the extraction 5 according to the invention, the xylan is soluble from hardwood fibers in the extraction solution. In this case, the xylan will also dissolve from the interior of the fibers, which has a beneficial effect on the mass of the article made from the pulp. According to one

LO

according to a preferred example, the xylan extraction is continued until 2-100 °, more preferably 5-50% or 5-25% of the xylan in the fiber is extracted from the fibers to the extraction solution.

7

Xylan precipitation 6, at which point xylan typically precipitates to a white polymer, occurs by the addition of gaseous carbon dioxide to the post-extraction fiber suspension 2. The xylan in dissolved form then forms a precipitated xylan. In addition, the reaction results in the formation of sodium carbonate as follows: 2 NaOH + CO 2 (g) -> Na 2 CO 3 (aq) + H 2 O.

The carbon dioxide used to precipitate the xylan preferably has a purity between 10 and 100%. Carbon dioxide is suitably added until the pH of the mixture is between 7.5 and 10. In one example, the precipitation of the xylan is enhanced by the addition of a precipitation enhancing component to the mixture.

The precipitation of the calcium carbonate 7 is carried out with the aid of calcium hydroxide. Addition of calcium hydroxide to the fiber suspension not only precipitates calcium carbonate but also converts the sodium carbonate formed during the precipitation of xylan to sodium hydroxide. The reaction of calcium hydroxide with the formed sodium carbonate to form precipitated calcium carbonate (PCC) and sodium hydroxide is as follows:

Na2G03 + Ca (OH) 2 → 2 NaOH + CaCO3

The precipitated calcium carbonate, precipitated xylan and fiber-containing pulp mixture resulting from the reaction of sodium carbonate with calcium hydroxide typically have a very basic pH (typically> 13).

The reaction conditions under which the particle size and quality of the PCC (including temperature, pH, time, concentration) can be influenced are preferably determined by:

CL

achieving the desired predefined particle size shape of PCC.

SJ

OO

tn

After precipitation of the calcium carbonate, the pulp mixture 4 is thickened and washed 8. Typically, during thickening and washing 8, the greatest amount of PCC is retained in the stock to be thickened. According to one of the 8 preferred examples, the filtration of the pulp mixture and the resulting thickening is carried out by means of a filter and / or a funnel.

According to a preferred example, during thickening and washing 8, the mas-5 mixture 4 is washed with a solution such as water at least once, more preferably at least two or at least three times. Here, according to a preferred example, at least part of the filtrates formed are recovered. Most preferably, the recovered filtrates, or at least some of them, are recycled. Typically, especially the first wash filtrates comprise concentrated sodium hydroxide and may have a pH of, for example, about 13. According to a preferred example, the pulp mixture is washed with the solution until the pH is near neutral.

The sodium hydroxide-containing filtrate recovered from the process may be reused for, for example, xylan extraction, or may be recycled to another process, or may be recovered for further use. Said filtrate recovered from the process may be treated to increase the purity of the sodium hydroxide.

It is essential in the invention that xylan is not attempted to be removed at any stage from the pulp suspension, but that xylan extracted from cellulosic fibers is allowed to remain in the extraction solution in association with the cellulosic fibers. Thereby, when the xylan is precipitated in the pulp suspension, it is possible for the xylan to adhere to the surface of the fibers at the same time. The precipitation of the xylan with carbon dioxide 25 is carried out by starting the precipitation step 6 in a strongly basic extraction solution. As the precipitation proceeds, the pH of the extraction solution decreases due to the addition of carbon dioxide. Preferably, the pH of the mixture is kept basic (pH> 7)

C/O

o throughout the precipitation of xylan.

CM

g 30 The xylan precipitation step is followed by a calcium carbonate precipitation step 7 where

CL

in step 7, calcium hydroxide is added to the mixture. Addition of calcium hydroxide is also carried out throughout the fiber suspension. In this case, a fiber suspension (LT) containing e.g. cellulose fibers, and precipitated xylan, precipitates from calcium-cm 2 of silicon carbonate. Due to the process of the invention, calcium carbonate also precipitates on the fiber surfaces. The xylan extracted and precipitated in the previous 9 steps of the pulp mixture can then act as a binder for the calcium carbonate particles.

According to a preferred example, the pulp produced by the process of the invention is used as a raw material for paper or board, most preferably as a raw material for fine paper.

With the method of the present invention, it is possible to produce, e.g. a pulp suitable for use as a raw material for fine paper containing at least cellulosic fibers, a filler and a binder. In the solution according to the invention, the xylan naturally present in the process is used as a binder, which is effectively used by the process according to the invention. This makes it possible to increase the filler content in a cost-effective manner so that the cost typically remains lower than, for example, using separate, expensive synthetic adhesives.

The invention is not limited to the examples set forth in Figure 1 and the foregoing description, but instead is characterized by what is set forth in the following claims.

20

OJ

δ cv oo cp I '-

C \ J

X

cc

CL

00 uo δ

(M

Claims (10)

A process for the production of paper pulp (10) using bleached, chemically fiberized cellulose fibers (1) derived from hardwood as a fiber raw material, characterized in that the process comprises: extracting (5) xylan from said cellulose fibers with sodium hydroxide (1). , adding carbon dioxide to said cellulose fibers (1), to a mixture containing dissolved xylan 10 and sodium hydroxides (2) to precipitate xylan, adding calcium hydroxide to said precipitated xylan and cellulose fiber containing sodium oxide to form a precipitated calcium oxide, , a mixture of cellulose fibers (1) and calcium carbonate (4), sodium hydroxide. Process according to Claim 1, characterized in that the sodium hydroxide removed from said mixture (4) is recycled for use, for example, in the extraction of xylan. Process according to Claim 1 or 2, characterized in that in the process carbon dioxide is added to precipitate xylan (6) until the pH of the mixture is between 7.5 and 10. C \ J δ Process according to one of Claims 1 to 3, characterized in that the CO 2 process is carried out integrated with a chemical pulping process comprising one or more bleaching steps, wherein said extraction (5) is carried out directly on said cellulosic fibers (1). at or after the final bleaching step. sj- OO tn Process according to one of Claims 1 to 4, characterized in that 5 to 50 to 35% of xylan contained in said cellulose fibers (1) are extracted. Process according to one of Claims 1 to 5, characterized in that, during the removal of sodium hydroxide, said mixture (4) is washed with a solution, preferably water. Process according to Claim 6, characterized in that said cellulosic fibers (1) are ground and that the degree of pulverization of the cellulosic fibers (1) at the start of the extraction, expressed as SR (Schopper-Riegler) number, is between 10 and 40. Paper pulp (10) produced by the method of any one of claims 1 to 7. Use of a pulp (10) produced by the process according to any one of claims 1 to 7 as a raw material for paper or board. 15 Use according to claim 9, characterized in that the pulp (10) is used as a raw material for fine paper. C \ l δ CVJ 00 o CM X cc CL 00 LO δ CM