WO1994018382A1

WO1994018382A1 - Method for producing chemi-thermomechanical pulps (ctmp)

Info

Publication number: WO1994018382A1
Application number: PCT/FR1994/000138
Authority: WO
Inventors: Christian De Choudens; Michel Petit-Contil; Jean-Pierre Zumbrunn
Original assignee: L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 1993-02-09
Filing date: 1994-02-07
Publication date: 1994-08-18
Also published as: FR2701274A1; DE4490578T1; NZ261328A; CA2117799A1; FI944696A; SE9403227L; BR9404036A; FR2701274B1; FI944696A0; SE9403227D0; JPH07505930A

Abstract

A method for producing chemi-thermomechanical pulps (CTMPs), wherein wood chips are dipped in chemical reagents; the chips are mechanically defiberized (primary refining) in a pressurised steam atmosphere to give a raw pulp; and said pulp is refined (secondary refining). The method is characterized in that oxygen is fed into the reaction medium containing said chips or said raw pulp during at least one of the two refining steps.

Description

Process for the production of icothermic-echo paper pulp (CTMP)

The invention relates to an improved process for the manufacture of chemothermal mechanical pulp (CTMP). As is known, there are essentially three main types of pulp, which take into account the way in which the fibers are released in the individual state.

In so-called chemical pulps, wood chips are dissolved in an aqueous medium containing appropriate reagents, such as sodium sulfide in the presence of soda, sodium bisulfite, to remove lignin and hemicelluloses.

In so-called mechanical pulps, the chips are ground in the absence of chemical reagents.

In recent years, we have developed a process called "chi icother omécanique", designated by the abbreviation "CTMP", which consists in drying wood chips at a temperature above

100 ° C, in particular by steam. Once baked, these chips are subjected to a chemical impregnation or soaking carried out under steam pressure. The main purpose of this impregnation is to soften the chips and modify the lignin in order to impart chemical and mechanical properties to the pulp subsequently obtained.

In particular, it is not intended to delignify or defibrate the shavings. The latter is carried out mechanically, during a primary refining which leads to obtaining a raw paste. Finally, after a possible washing, the raw dough is subjected to a secondary refining which makes it possible to complete the mechanical defibering of the primary refining.

The CTMP pastes thus obtained have intermediate properties between the chemical pulp and the mechanical pulp. These pastes are generally more resistant and have better whiteness than mechanical pastes. In addition, they have a higher opacity and a better light scattering coefficient than chemical pastes.

However, these CTMP pastes have the disadvantage of turning yellow when exposed to light. In this way, they are mainly used in applications where Ton requires good absorbency, such as for example baby diapers or for incontinence or for the manufacture of printing or writing papers, and cardboards. US Patent 4,288,288 describes a process by which the chips are digested by chemical treatment so as to delignify them.

Additional defibration can then be carried out in two successive refiners. In the second of these refiners, it is

. 5 possible to add oxygen to the dough obtained.

It is also known from US Pat. No. 4,534,397, a process for the preparation of chi icomechanical pulp according to which wood chips are chemically treated by impregnation with sodium hydroxide in the presence of oxygen. This treatment results in a partial delignification of said chips. These are then defibrated mechanically in the presence of oxygen. This process is reputed to allow obtaining a pulp yield greater than 80%.

The methods described in the two US patents 4,288,288 and 4,534,397 are not CTMP methods as defined> 15 above. They cannot therefore be used in existing CTMP pulp factories, except in the event of a major transformation of the installations of these factories, in particular so as to provide devices for chemical delignification of the chips.

The invention relates to a method for improving the quality of the '20 CTMP pastes, in particular their whiteness, while avoiding excessive consumption of the reactive products, and for reducing the energy consumption. According to the process of the invention, these advantages can be obtained without having to modify the existing installations in factories producing CTMP pastes. This process for manufacturing the CTMP chemothermal-mechanical pulp which consists of:

- first of all, soaking wood chips in chemical reagents;

- then to mechanically defibrate (primary refining) these ' ³ o chips under an atmosphere of pressurized steam, so as to obtain a raw paste; and

- finally, in refining said raw pulp (secondary refining), in order to obtain the CTMP pulp, is characterized in that, during at least one of the refining phases, we introduce

• ³ 5 oxygen in the reaction medium comprising said chips or said crude paste. In other words, the invention consists in one of the two refining phases, primary or secondary, or even during these two phases, in introducing oxygen into the reaction medium. Preferably, oxygen is introduced during the defibration phase,

> 5, that is to say during the primary refining while the reaction medium is under an atmosphere of pressurized steam, then the secondary refining is then carried out in a known manner, in particular at atmospheric pressure.

The addition of oxygen to the reaction medium is known ιo in the manufacture of chemical pulps. The invention however aims to introduce this oxygen into the manufacture of CTMP pastes, at a precise stage, namely during one of the refining phases and, preferably, during primary refining, and only at this stage.

Unexpectedly, the introduction of oxygen, at the stage

15 precise defibration operation or primary refining, in the substantial absence of air, on shavings still impregnated with chemicals, increases the synergistic effect of these products and allows on the one hand, to improve whiteness and, on the other hand and above all, to appreciably save the energy necessary for

20 defibration, while being accompanied by a reduction in the rate of chemical reagents, during the subsequent pulp bleaching phases.

As is known, in the CTMP pulp manufacturing process, the most generally starting from wood in the form of chips. Both softwood and hardwood can be used. These

25 shavings are then parboiled, in particular by steam, to allow the humidity and temperature to be homogenized, and to expel the air. In practice, this steaming step is carried out in a known manner at a temperature below 200 ° C., preferably between 110 and 160 ° C.

³⁰ After steamed, the chips are subjected to a chemical impregnation, in particular by dipping or impregnation of cellulosic lignin reagents for modifying lignin. Conventionally, chemical reagents are used, in particular reducing agents, such as sodium sulfite (Na ^ SO.,), Bisulfite of

> ³⁵ sodium (Na ₂ HSO-J or sodium dithionite (Na _^ S _^ O.). These compounds can be used alone or in combination with soda or sodium carbonate. As chemical reagents, mention may also be made of oxidizing agents, such as hydrogen peroxide, preferably in an alkaline medium, or percarbonates. This impregnation is also carried out in a known manner under saturated steam pressure, at a temperature between 80 and 140 ^β C, preferably in the vicinity of 120 ^β C. The CTMP pastes thus obtained are then washed, then classified to eliminate residual chemical reagents as well as coarse particles of lignocellulosic material. These pastes treated according to the process of the invention can be subsequently bleached, for example with hydrogen peroxide in an alkaline medium in one or more stages in the presence of soda and / or sodium hydrosulfite and co-plexing and stabilizing agents. to achieve high whiteness levels. Advantageously, in practice:

the oxygen is pure industrial oxygen, at a pressure higher than the pressure prevailing in the shredder, and preferably at a pressure lower than 10 bar, preferably at a pressure of 2 to 5 bar, and the more generally around 3 bar; - Toxygene is introduced into the eye of the defibrator, that is to say just upstream of the point where the screw which brings the chips enters the stator;

- The amount of oxygen introduced is between 1 and 5%, preferably between 1.5 and 2.5% of the weight of the dough (expressed as dry matter).

Unexpectedly, CTMP pastes treated in this way have good physical and optical characteristics as well as improved whiteness (from two to five points depending on the base material used and the chemical reagents used during the impregnation. In addition , the consumption of hydrogen peroxide during the subsequent pulp bleaching step is unexpectedly reduced up to 15. Finally, the incorporation of oxygen at this stage of defibration leads to a reduction in the energy consumption required to drive the shredder discs, of the order of 10 to 25%, which translates into an appreciable gain, since on an industrial level, the electrical consumption of such a shredder is frequently of the order of 1000 to 1500 kwh / ton. Finally, the pulp yield is improved, which results in a reduction in the polluting load and the fibers have a better surface condition.

The manner in which the invention can be implemented and the advantages which ensue therefrom will emerge more clearly from the embodiments which follow in support of the appended figures.

Figure 1 is a schematic sectional representation of a conventional defibrator said defibrator or primary refiner, for the manufacture of CTMP pasta. 0 Figures 2 to 5 illustrate the variation of different properties of the doughs treated according to the invention.

In the examples, the following characteristics are measured as follows:

- rupture length LR in meters (m) according to standard NF Q03-002 5 - resistance index: IR

Burst x tear according to NF Q03-053 standards

NF Q03-011

- whiteness Bl of the unbleached pulp in% ISO according to standard NF Q03-039

- pulp yield (R in%) ratio of the weight of the 0 dry pulp to the weight of dry wood in%

Unless otherwise indicated, these weight percentages are expressed relative to the dry paste.

Example 1: 5 Softwood shavings (spruce) are pre-oven at 110 ° C for twenty seconds, then oven oven and then impregnated with a 100 g / l sodium sulfite solution at 125 ° C for ten minutes. These shavings are then defibrated in a disc shredder under a relative pressure of 1.7 bar in common use for the manufacture of CTMP pasta shown in FIG. 1. This shredder essentially comprises a first body 1 possibly heated, in which introduces the chips 2 which advance under the effect of a rotary helical screw 3, to penetrate into the eye 4 of the defibrator proper 5, comprising a fixed stator 6 and a rotor 7 secured 5 to a shaft 8 coupled to a motor 10. The defibrated paste P comes out through the opening (11). This paste P is then washed and then refined to the drip index of 100 ml CSF (CPPA standard - Cl: 52 or SCAN-C21.65).

The characteristics of the dough obtained are as follows:

- LR: 4190 5 - IR: 48.8

- Bl: 58.8

- R: 92.8 Example 2:

The defibrator of FIG. 1 is modified by incorporating therein an ιo tubing (12) disposed in the vicinity of the eye 4, closed by a valve.

13 connected to a source of oxygen 14 under pressure. The pulp treated with an amount of oxygen approximately 2.5% relative to the pulp and under a pressure of 5 bar, has the following characteristics:

- LR: 3900 (against 4190) 15 - IR: 47.3 (against 48.8)

- Bl: 59.7 (against 58.8)

- R: 93.7 (against 92.8).

In addition, it is observed that the energy consumption of the motor 10 is reduced by almost a quarter, or approximately 250 kWh / ton. 20 Example 3:

In a known manner, the two pastes of Examples 1 to 2 are bleached with 3% hydrogen peroxide, 3% soda, 3% sodium silicate, 0.3% DTPA (diethylene triamine penta-acetic acid), and

0.1% magnesium sulfate. This bleaching is carried out at a

• 25 dough concentration of 16% for three hours at 70 ° C.

With the paste of Example 1, a whiteness of 75.5 is obtained and with the paste of Example 2, a whiteness of 77.0.

The gain in whiteness observed in Example 2 is increased by a later stage of bleaching with hydrogen peroxide. Thus, for ^{1 3} o reach the same whiteness of 75.5 with the paste of Example 1 treated with hydrogen peroxide, but with a paste treated with oxygen in accordance with Example 2, 8.7% of peroxide is saved hydrogen, which translates into significant savings.

Example 4: ^"35 was repeated Texemple 1 with poplar chips by impregnating the chips in a mixture of sodium dithionite in 64.2 g / 1 and sodium hydroxide 20 g / 1. The CTMP paste obtained has the following features:

- LR: 4460

- IR: 27.2

- Bl: 60.4 - R: 90.4

Example 5:

Example 4 is repeated while incorporating oxygen under pressure, in accordance with Example 2 above. The following characteristics are obtained: - LR: 4260 (against 4460)

- IR: 29.7 (against 27.2)

- Bl: 62 (against 60.4)

- R: 91.5 (against 90.4)

The method according to the invention therefore makes it possible to improve the whiteness of two points, to increase the yield of one point and to achieve a reduction in consumption of defibration energy by approximately 15%.

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

- with oxygen: 80.0.

For equal whiteness, the gain of hydrogen peroxide would be of the order of 3%.

Example 6: Example 1 is repeated, but replacing the 100 g / l of sodium sulfite with 82 g / l of sodium bisulfite. The following results are obtained: without oxygen with oxygen LR 4500 4380 IR 35.9 35.3

Bl 54.2 59.0

R 91.7 92.2

There is thus a gain in whiteness of five points with a higher yield of 0.5 point and a reduction in energy consumption of defibration in the presence of oxygen by 18%.

After bleaching, in a single stage with 3% peroxide, the whiteness goes from 75.6 to 78.0, ie a gain in hydrogen peroxide of 12%. Example 7:

Is introduced into the eye of defibrator 4, not only oxygen, but also a solution of hydrogen peroxide comprising 3% peroxide and 2% sodium carbonate, 2% sodium silicate and 0.2 % of DTPA. The reaction kinetics are allowed to develop for approximately thirty minutes after defibration. We obtain a gain of whiteness of 0.5 point, an increase in yield of one point and a notable improvement in the length of rupture LR (3800 against 3130) and in the burst index IR (32.7 ° against 31 , 4).

There is also a reduction in energy consumption of 20%.

After a whitening in one stage with hydrogen peroxide, an improvement in whiteness of 1.6 points is observed by ⁵ incorporation of oxygen, which translates for the same level of whiteness, by the saving of 10.7 % hydrogen peroxide.

Example 8:

Example 7 is repeated, however impregnating the spruce shavings with a solution comprising: - hydrogen peroxide: 2% relative to the dry shavings

- soda ash: 2% compared to dry shavings instead of 2% sodium carbonate

- sodium silicate: 2% compared to dry shavings

- DTPA: 0.2% compared to dry chips. The following characteristics are obtained: without oxygen with oxygen

LR 3630 3530

IR 33.9 34.1

Bl 58.8 59.9 R 95.1 95.5

There is therefore a gain in whiteness of one point, an improved yield of 0.5 point, for identical pasta properties.

After bleaching with hydrogen peroxide, the whiteness Bl goes from 75.5 in the oxygen-free process to 77.5 in the oxygen process, which, for a whiteness level of 75.5, allows a saving of 11.4% in hydrogen peroxide. Example 9:

Example 6 is repeated, using varying amounts of oxygen; however, peroxide bleaching is not repeated.

The results obtained are collated in FIGS. 2 to 5, in which the quantity of oxygen introduced as a percentage by weight is plotted on the abscissa and is plotted on the ordinate, respectively:

in FIG. 2, the whiteness Bl,

- in FIG. 3, the defibration energy in kWh / ton, - in FIG. 4, the resistance index Ir,

- in Figure 5, the rupture length LR in meters.

The whiteness increases with the percentage of oxygen introduced. Beyond 2.5% oxygen, the whiteness gain stabilizes, but the excess oxygen has a beneficial influence on energy consumption at the defibration stage (the values correspond to the energy consumed by a refiner primary 30 cm in diameter). The breaking length and the resistance index decrease linearly with the oxygen load. The breaking length decreases faster than the resistance index. As already said, the method according to the invention which consists in selectively introducing oxygen under pressure during mechanical defibration under an atmosphere of pressurized water vapor, has many advantages compared to the methods of manufacturing CTMP paper pulp. known to date. We can cite: - the fact that there is no need to modify existing installations;

- a gain in whiteness Bl of up to five points;

- an appreciable gain in defibration energy or primary refining of the order of 10 to 25% depending on the nature of the chemical reagents and the wood chips used;

- a significant reduction in the level of chemical reagents, in particular hydrogen peroxide in the later stages of treatment.

Claims

1. Process for the manufacture of CTMP chemo-thermal paper pulps, which consists of:

- first, to soak wood shavings in 5 chemical reagents;

- then to mechanically defibrate these chips (primary refining) under an atmosphere of pressurized water vapor, so as to obtain a raw paste; and

- Finally, to refine said raw paste (secondary ιo refining), to obtain the CTMP paste, characterized in that during at least one of the two refining phases, oxygen is introduced into the reaction medium comprising said chips or said paste brute.

2. Method according to claim 1, characterized in that> 15 introduces oxygen during the primary refining phase (mechanical defibration).

3. Method according to one of claims 1 and 2, characterized in that the oxygen is introduced at a pressure between 2 and 5 bar. ι 20

4. Method according to one of claims 1 to 3, characterized in that oxygen is introduced into the eye of the defibrator.

5. Method according to one of claims 1 to 4, characterized in that the quantity of oxygen introduced is between 1 and 5% by weight relative to the paste (expressed as dry matter) /

6. Process according to one of claims 1 to 5, characterized in that the chemical reagents are reducing agents such as sodium sulfite, sodium bisulfite and sodium dithionite, alone or in mixture with soda or carbonate sodium.

7. Method according to one of claims 1 to 5, characterized ³⁰ in that the chemical reagents are oxidizing agents such as hydrogen peroxide, preferably in an alkaline medium, or per- carbonates.

8. Method according to one of claims 1 to 7, characterized in that after the secondary refining, the CTMP pulp is bleached.

³⁵ 9. Pulp CTMP obtained by implementing the method according to one of Claims 1 to 8.