NZ261328A - Production of chemi-thermomechanical pulp (ctmp) in which wood chips are first dipped in chemical reagents and are then mechanically defiberised using pressurised steam, the pulp then being refined; oxygen being added to the chips and/or raw pulp - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £61 3£8 New Zealand No. 2 61328 International No. PCT/FR94/00138 TO BE ENTERED AFTER ACCEPTANCE AND PUBLICATION Priority dates; ^ \ ^ International fifing date: "J J *2) ;Classification: \Pc(o\ D2\&1) l(o ;Publication date: 2<f OCT 1996 ;Jour al No.: IM-O^ ;NEW ZEALAND PATENTS ACT 1953 ;COMPLETE SPECIFICATION ;Title of invention: ;Method for producing chemi-thermomechanical pulps (CTMP) . ;Name, address and nationality of ' ;applicant(s) as in international application form: ;L'AIR LIQUIDE, SOCIETE ANONYME POUR L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE, of 75 quai d1Orsay, 75321 Paris Cedex 07» France ;<X ;-1 - FOLLOWED BY PAGE 1 A) ;261328 ;Process for the production of chemi-thermomechanical pulps fCTMP^ ;The invention relates to an improved process for the production of chemi-thermomechanical pulps (CTMP). ;As is known, there exist essentially three principal types of paper pulps, according to the manner in which the fibers are freed from each other. ;In so-called chemical pulps, the wood chips are dissolved in an aqueous medium containing appropriate reagents, such as sodium sulfide in the presence of soda, sodium bisulfite, to eliminate lignin and hemicelluloses. ;In the so-called mechanical pulps, the chips are ground in the absence of chemical reagents. ;For several years, there has been developed a process called "chemi-thermomechanical", designated by the abbreviation "CTMP", which consists in heating the wood chips to a temperature greater than 100°C, particularly with steam. Once heated, these chips are subjected to impregnation or chemical immersion effected under pressurized steam. This impregnation has for its principal object to soften the chips and modify the lignin so as to impart chemical and mechanical properties to the pulp eventually obtained. It particularly does not aim to delignify or defiber th^ chips. This latter is effected mechanically, during a primary refining which results in a raw pulp. Finally, after possible washing, the raw pulp is subjected to a secondary refining which permits completing the mechanical defibering of the primary refining. ;Zlo\l2h ;The CTMP thus obtained have properties intermediate between chemical pulp and itiechanical pulp. These pulps are generally more resistant and have better brightness than mechanical pulps. Moreover, they have a greater opacity and better coefficient of diffusion of light than chemical pulps. ;However, the CTMP's have the drawback of yellowing when exposed to light. Because of this, they are essentially used in applications in which a good absorbent power is not used, such for example as layers for babies or incontinent persons or for the production of printing or writing papers, and cardboard. ;U.S. patent No. 4,288,288 describes a process according to which the chips are digested by chemical treatment so as to delignify them. ;A supplemental defibering can then be effected in two successive refiners. In the second of these refiners, it is possible to add oxygen to the obtained pulp. ;There is also known from U.S. patent No. 4,534,3 97, a process for the preparation of chemi-thermomechanical pulp according to which wood chips are treated chemically by impregnation with soda in the presence of oxygen. This treatment results in a partial delignification of said chips. These latter are defibered mechanically in the presence of oxygen. This process is said to permit obtaining a pulp output greater than 80%. ;The processes described in the two U.S. patents Nos. 4,288,288 and 4,534,397 are not CTMP processes, as defined ;It 132% ;above. They can however be used in existing CTMP plants, except for important changes in the installations of these plants, particularly so as to provide devices for chemical delignification of the chips. ;The invention seeks to provide a process to improve the quality of the CTMP's, particularly their brightness, while avoiding excessive consumption of reactive products, and to reduce the consumption of energy. According to the process of the invention, these advantages can be achieved without having to modify existing installations in plants producing CTMP's. ;This production process of thermomechanical paper pulps CTMP which consists: ;- first in immersing wood chips in chemical reagents; ;-* then mechanically defibering (primary refining) these chips under a steam atmosphere under pressure, so as to obtain a raw pulp; and finally, refining said raw pulp (secondary refining), to obtain the CTMP, is characterized in that, during at least one of the refining phases, there is introduced oxygen into the reaction medium comprising said chips or said raw pulp.

In other words, the invention consists, during one of the two refining stages, primary or secondary, or even during these two phases, in introducing oxygen into the reaction medium. Preferably, oxygen is introduced during the 3 Sefibering stage, which is to say during primary refining while the reaction material is under a steam atmosphere under pressure, then the secondary refininc, is effected in known manner, particularly at atmospheric pressure.

The addition of oxygen into the reaction medium is known in the production of chemical pulps. The invention contemplates however introducing this oxygen into the production of CTMP pulps, at a precise point, namely during one of the refining phases and, preferably, during primary refining, and solely during this stage.

As a surprising result, the introduction of oxygen at the precise stage of defibering or primary re. tiling, in the absence of substantial air, into the chips already impregnated with chemical products, increases the synergetic effect of these products and permits on the one hand improving brightness and on the other hand and above all saving appreciably the energy necessary for defibering, while achieving a reduction in the weight of chemical reagents, during the bleaching phases of the ultimate pulps.

As is known, in the process for the production of CTMP, one begins generally with wood in the form of chips. Evergreen trees can be used as well as deciduous trees. These chips are then heated, particularly with steam, to permit homogenizing the humidity and temperature, and driving off air. In practice, this heating stage is effected in known manner at a temperature below 200°C, preferably between 110 and 160 °C. 4 Once heated, these chips are subjected to chemical impregnation, particularly by immersion or impregnation, with lignocellulosic reagents adapted to modify the lignin. In known manner, recourse is had to chemical reagents, particularly reducing agents, such as sodium sulfite, (Na2S03) , sodium bisulfite (Na2HS03) or sodium dithionite (NA2S204) . These compounds can be used alone or in combination with soda or sodium carbonate. As chemical reagents can also be mentioned oxidizing agents, such as hydrogen peroxide, preferably in alkaline medium, or percarbonates. This impregnation takes place also in known manner with saturated steam under pressure, at a temperature comprised between 8 0 and 140°C, preferably about 120°C. The CTMP's thus obtained are then washed, then classified to eliminate residual chemical reagents as well as the large particles of lignocellulosic material.

These pulps treated according to the process of the invention can eventually be bleached for example with hydrogen peroxide in alkaline material in one or several stages in the presence of soda and/or sodium hydrosulfite and complexing and stabilizing agents to achieve a high degree of brightness.

Preferably, in practice: - the oxygen is pure industrial oxygen, at a pressure greater than the pressure which prevails in the defibrator, and preferably at a pressure less than 10 bars, preferably at a pressure of 2 to 5 bars, and more generally about 3 bars; - the oxygen is introduced into the aperture of the defibrator, which is to say just upstream of the point at which the screw which provides the chips enters the stator; - the quantity of oxygen introduced is comprised between 1 to 5%, preferably between 1.5 and 2.5% by weight of the pulp (expressed as dry material).

In a surprising manner, the CTMP's treated in this way, have good physical and optical characteristics as well as improved brightness (from 2 to 5 points according to the base material used and the chemical reagents employed during impregnation. Moreover, the consumption of hydrogen peroxide during the ultimate bleaching stage of the pulp is, in a surprising manner, reduced by about 15%. Finally, the incorporation of oxygen at this stage of defibering, gives rise to a reduction of the consumption of energy necessary to drive the disks of defibrator, of the order of 10 to 25%, which translates to an appreciable gain because on an industrial scale, the electrical consumption of such a defibrator is frequently of the order of 10 to 15 kwh/ton. Finally, the pulp output is improved, which translates into a decrease of pollutants and the fibers have a better surface condition.

The manner in which the invention can be carried out and the advantages which follow from it, will become apparent from the examples of embodiment which follow with respect to the accompanying drawings. 2,u32& Figure 1 is a schematic view in cross section of a conventional so-called defibrator or primary refiner, for the production of CTMP's.

Figures 2-5 show the variation of different properties of the pulps treated according to the invention.

In the examples/ the following characteristics are measured: - length of rupture LR in meters (m) - index of resistance: IR Bursting x tearing - brightness Bl of the raw pulp in ISO % - pulp output (R in %) according to the standard NF Q03-002 according to standards NF Q03-053 NF Q03-011 according to the standard NF Q03-039 ratio of the weight of the dry pulp to the weight of the dry wood in % Unless otherwise indicated, these weight percentages are expressed relative to the dry pulp.

Example 1: Evergreen wood chips (epicea) are preheated to 110°C for 20 seconds, then heated while impregnating it with a solution of sodium sulfite of 100 g/1 to 125°C for ten minutes. These chips are then defibered in a disk defibrator under a relative pressure of 1.7 bar commonly used for the production of CTMP's shown in Figure 1. This defibrator comprises essentially a first body l heated if desired, in 7 2U3ZS which is introduced the chips 2 which advance under the influence of a rotating screw 3, to enter the inlet 4 of the defibrator itself 5, comprising a fixed stator 6 and a rotor 7 fixed to a shaft 8 coupled to a motor 10. The defibered pulp P leaves by the opening (11).

This pulp P is then washed and refined to a draining index of 100 ml CSF (standard CPPA - CI: 62 or SCAN-C21:65).

The characteristics of the obtained pulp are as follows: - LR: 4190 - IR: 48.8 - Bl: 58.8 - R : 92.8 Example 2: The defibrator of Figure 1 is modified by including a tubing (12) disposed adjacent the inlet 4, closed by a valve 13 connected to a source 14 of oxygen under pressure. The pulp treated with a quantity of oxygen of about 2.5% relative to the pulp and under a pressure of 5 bars, has the following characteristics: - LR: 3900 (as against 4190) - IR: 47.3 (as against 48.8) - Bl: 59.7 (as against 58.8) - R : 93.7 (as against 92.8).

Moreover, it is noted that the consumption of energy of the motor 10 is reduced by about a quarter, namely by about 250 kwh/ton. 8 ^U3ZS Example 3: In known manner, the two pulps of Examples l and 2 are bleached with 3% hydrogen peroxide, 3% soda, 3% sodium silicate, 0.3% DTPA (diethylene triamine penta-acetic acid), and 0.1% of magnesium sulfite. This bleaching is effected at a pulp concentration of 16% for three hours at 70°C.

With the pulp of Example 1, there is obtained a brightness of 75.5 and with the pulp of Example 2, a brightness of 77.0.

The gain of brightness observed in Example 2, is increased by a final stage of bleaching with hydrogen peroxide. Thus, to achieve the same brightness of 7 5.5 with the pulp of Example 1 treated with hydrogen peroxide, but with a pulp treated with oxygen according to Example 2, there is a saving of 8.7% of hydrogen peroxide, which amounts to a substantial saving.

Example 4: Example 1 is repeated with poplar chips by impregnating the chips in a mixture of sodium dithionite at 64.2 g/1 and soda of 20 g/1. The CTMP obtained has the following characteristics: - LR: 4460 - IR: 27.2 - Bl: 60.4 2. U 3 2-8 Example 5: Example 4 is repeated by including oxygen under pressure, according to Example 2 above. There are obtained the following characteristics: - LR: 4260 (as against 4460) - IR: 29.7 (as against 27.2) - Bl: 62 (as against 60.4) - R : 91.5 (as against 90.4).

The process according to the invention therefore permits improving the brightness by two points, increasing the output by one point and effecting a reduction of energy consumption for defibering, of about 15%.

After bleaching with hydrogen peroxide, under the same conditions as in Examples 3 and 4, there is observed a brightness of: - without oxygen: 79.4 - with oxygen: 80.0.

For the same brightness, the saving of hydrogen Example 6: Example 1 is repeated, but replacing the 100 g/1 of sodium sulfite by 82 g/1 of sodium bisulfite. There are obtained the following results: peroxide would be of the order of 3%.

Bl LR IR R Without Qxvaen 4500 35-9 54.2 91.7 With Qxvaen 4380 35.3 59. 0 92.2 / Ua l3 Zh It will thus be seen that there is an increase of brightness of 5 points with increased output of 0.5 point and a reduction of energy consumption during defibering in the presence of oxygen of 18%.

After bleaching, in a single step with 3% peroxide, the brightness improves from 75.6 to 78.0, namely a saving of hydrogen peroxide of 12%.

Example 7: There is introduced into the inlet of the defibrator 4, not only oxygen, but also a solution of hydrogen peroxide comprising 3% of peroxide and 2% of sodium carbonate, 2% of sodium silicate and 0.2% of DTPA. The reaction is allowed to proceed for about 30 minutes after defibering. There is obtained an increase of brightness of 0.5 point, an increase of output of one point and a noticeable improvement of the length of rupture LR (3800 as against 3130) and of the ♦ bursting index IR (32.7 as against 31.4).

There is moreover noted a reduction in the energy consumption of 20%.

After bleaching in a hydrogen peroxide step, there is observed an improvement of brightness of 1.6 point by incorporation of oxygen, which translates for the same level of brightness, into a saving of 10.7% of hydrogen peroxide.

Example 8: Example 7 is repeated, by impregnating however the epicea chips with a solution comprising: 11 -LU32& - hydrogen peroxide: 2% relative to the dry chips - sodium carbonate: 2% relative to the dry chips instead of 2% of sodium carbonate - sodium silicate: 2% relative to the dry chips - DTPA: 0.2% relative to the dry chips.

There are obtained the following characteristics: Without Oxygen With Qxvaen LR 3630 3530 IR 33.9 34.1 Bl 58.8 59.9 R 95.1 95.5 There is therefore observed a gain of brightness of one point, an output improved by 0.5 point, for identical pulp properties.

After bleaching with hydrogen peroxide, the brightness Bl increases from 75.5 for a process without oxygen to 77.5 in a process with oxygen, which, for a level of brightness of 75.5, permits a saving of 11.4% of hydrogen peroxide.

Example 9: Example 6 is repeated, using variable quantities of oxygen; the bleaching with peroxide is however not repeated.

The results obtained are shown in Figures 2-5, in which on the abscissa there is shown the quantity of oxygen introduced as a weight percent and on the respective ordi-nates: - in Figure 2, brightness Bl, 12 - in Figure 3, defibering energy in kwh/ton, - in Figure 4, the index of resistance Ir, - in Figure 5, the length of rupture LR in meters.

The brightness increases with the percentage of oxygen introduced. Beyond 2.5% oxygen, the gain of brightness stabilizes, but the surplus oxygen has a beneficial influence on the energy consumption in the defibering stage (the values correspond to the energy consumed by a primary refiner 3 0 cm in diameter). The rupture length and the index of resistance decrease linearly with the oxygen load. The rupture length decreases more quickly than the index of resistance.

As already said, the process according to the invention which consists in introducing selectively oxygen under pressure during mechanical defibering under an atmosphere of steam under pressure, has numerous advantages relative to the production processes for CTMP's known until now. There could be cited: - the fact that it is not necessary to modify the existing installations; - a gain of brightness Bl which can be as much as 5 points; - an appreciable energy saving for defibering or primary refining of the order of 10 to 2 5% according to the nature of the chemical reagents and of the wood chips used; - an appreciable reduction of the weight of chemical reagents, particularly of hydrogen peroxide in the final stages of treatment. 13

Claims (9)

WHAT WE CLAIM IS: 261328

1. Process for the production of chemi-thermomechanical pulps CTMP, which consists: first, in immersing wood chips in chemical reagents; - then mechanically defibering these chips (primary refining) under an atmosphere of steam under pressure, so as to obtain a raw pulp; and finally, refining said raw pulp (secondary refining), to obtain the CTMP, characterized in that during at least one of the two refining stages, oxygen is introduced into the reaction medium comprising said chips or said raw pulp.

2. Process according to claim 1, characterized in that the oxygen is introduced during the primary refining stage (mechanical defibering).

3. Process according to claim 1 or 2, characterized in that the oxygen is introduced at a pressure between 2 and 5 bars.

4. Process according to any one of claims 1 to 3, characterized in that the oxygen is introduced into the inlet of the defibrator. 14 261328

5. Process according to any one of claims 1 to 4, characterized in that the quantity of oxygen introduced is comprised between 1 and 5% by weight relative to the pulp (expressed as dry material).

6. Process according to any one of claims 1 to 5, characterized in that the chemical reagents are reducing agents alone or in mixture with soda or sodium carbonate. that the reducing agent is sodium sulfite, sodium bisulfite or sodium dithionite. characterized in that the chemical reagents are oxidizing agents. that the oxidizing agent is hydrogen peroxide or a percarbonate. 10. Process according to claim 9, characterized in that the hydrogen peroxide is used in an alkaline medium. 11. Process according to any one of claims 1 to 10, characterized in that after secondary refining, the CTMP is bleached. 12. Process for the production of chemi-thermomechanical pulps according to any one of claims 1 to 11, substantially as herein described.

7. Process according to claim 6, characterized in

8. Process according to any one of claims 1 to 5

9. Process according to claim 8, characterized in P obtained by the practice of the process CTte of claims 1 to 12. 15