JPH0217675B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing chemical-thermomechanical pulp. More specifically, chemicals suitable for bleaching using hydrogen peroxide in an alkaline aqueous medium.
The present invention relates to a method for producing thermomechanical pulp.

BACKGROUND OF THE INVENTION To produce pulp, cellulosic materials such as wood chips are subjected to mechanical, chemical or thermal effects, alone or in combination.

Groundwood pulp or high yield pulp is, for example,
It is produced by mechanically grinding lignocellulosic material in a grindstone grinder, disk grinder or disk refiner.

The chemical-thermomechanical pulp produced according to the present invention can be produced at a temperature of 100°C or higher.
By combining the above method with a non-destructive digestion carried out under saturated vapor pressure in the presence of sodium sulfite or sodium hydrogen sulfite, or more commonly a mixture of sulfur dioxide SO ₂ and sodium hydroxide NaOH. can get.

Hereinafter, the chemical-thermomechanical pulp will be abbreviated as CTMP pulp. In addition, in the following explanation, Na ₂ SO ₃ , NaHSO ₃ or SO ₂ −
NaOH is referred to as sulfite without distinction.

The CTMP pulp is of industrial interest because it is an effective compromise between mechanical and chemical pulps.

For example, the yield of CTMP pulp is typically greater than 85%, and often greater than 90%, based on the weight of dry starting material, which is the dry pulp weight. In this respect, this pulp is more like a pure mechanical pulp, and this is where the term non-destructive cooking comes from.

Problems to be Solved by the Invention However, there is a problem in that the degree of bleaching of this CTMP pulp does not reach the value required from the quality required in the field of products manufactured from this pulp. Thus, for example, bleaching carried out using hydrogen peroxide in an alkaline medium does not give satisfactory results, since the lignocellulosic material is subjected to harmful thermal effects during the above-mentioned digestion.

This can be seen, for example, in James P. “Pulp and Paper Chemistry and Chemical Technology” by James P. CASEY
Chemical Technology) 3rd edition, Volume 1, 1980
, p. 242-250, 654, 655.

The purpose of the present invention is to use hydrogen peroxide H ₂ O ₂ to
At least 80
The purpose of the present invention is to provide a method for bleaching CTMP pulp suitable for bleaching up to 80°. This whiteness can be less than 80° under some special conditions that will be obvious to those skilled in the art.

Several methods for producing this pulp have already been proposed, and the whiteness of the pulp is satisfactory when sulfites are used.

For example, in French patent no. 1150451, in the presence of sulfite and dithionite in acidic medium,
It is recommended to cook at temperatures below 150°C.
The method disclosed in this patent allows for simplified subsequent bleaching, which will not be discussed further.

French Patent No. 1389308 discloses that in the presence of sodium borohydride instead of dithionite,
Bisulfite ions are removed before acid treatment, which is carried out using sulfite and not under saturated vapor pressure.
Another acid treatment using SO ₃ H ⁻ is described. However, the presence of sodium borohydride together with sulfite in the initial treatment is detrimental and the results obtained are worse than those obtained when no sodium borohydride is used at all. The brightness results when bleaching refined pulp according to the optimum conditions described in this patent are:
Even when using _H2O2 , it is much lower _than 80%.

In addition, U.S. Patent No. 3,981,765, which is based on French Patent No. 2,186,984, describes the initial pH of the medium in which sodium borohydride and sulfite are allowed to act.
It describes how to do this with 13 or more.
The addition of borohydride and sulfite is carried out before or preferably after the addition of an acidic aqueous solution, such as a SO ₂ solution or a solution of sodium bisulfite. In practice, the method of this invention is limited to the treatment of hardwood. This patent describes the alkaline treatment of pulp described in the above patent.
There is no mention of any synergistic effect due to H ₂ O ₂ alkali treatment.

In the prior art, it is believed that an acidic step is necessary whenever CTMP pulp is produced using sulfites and reagents such as hydrosulfite (sodium dithionite) or sodium borohydride. Ta.

From unbleached pulp made using sulfites
Since it became possible to obtain highly white pulp using H ₂ O ₂ , the industry is no longer interested in the combined action of sulfites with reagents such as hydrosulfites and hydrogen borides. I'm starting to not have it anymore. In fact, the above combinations result in process complexity, increased usage of SO ₂ or bisulfite, and increased pollution.

The present invention solves the drawbacks of the above conventional methods, and
This method improves the whiteness of the known method for producing bleached pulp using H ₂ O ₂ to a high value.

Means for Solving the Problems The present invention features mechanical pulverization, a mixture of sodium sulfite, sodium hydrogen sulfite or sulfur dioxide and sodium hydroxide, and a reducing agent having lower electronegativity than sulfite ions. using 100
In a method for producing chemical-thermomechanical pulp from lignocellulosic material in combination with non-destructive cooking carried out at a temperature of 0.degree. using hydrogen peroxide in an alkaline aqueous medium by simultaneously acting on the lignocellulosic material with the mixture and a reducing agent that is less electronegative than the sulfite ion and bringing the initial pH of the medium from 7 to 12.5. The point is that the pulp is suitable for bleaching.

The reducing agent is usually selected from thiourea dioxide or formamidine sulfinic acid, sodium borohydride and sodium hydrosulfite or sodium dithionite.

For example, on December 6, 1985, Odile CHALMIN
``Reducing properties of sodium dithionite under phase transition conditions'' by Claude Bernard (LOUIS-ANDRE) submitted to the University of Lyon 1.
sodium dithionite under phase transfer
You can check the electronegativity of sodium dithionite and thiourea dioxide by referring to ``conditions''.

The amount of reducing agent used can vary depending on its type. In the case of thiourea dioxide or dithionite it usually ranges from 0.1 to 5%. This amount, as well as other amounts in this specification,
Even if not specified, it is expressed as a weight percent based on the weight of the dry lignocellulosic material. Sodium borohydride 0.01 to 0.5%
used at a rate of This reducing agent is preferably used in the form of an aqueous solution containing 12% by weight of sodium borohydride, such as that sold under the trade name BOROL by the company VENTRON.

The temperature of the cooking process according to the invention can be increased up to 200°C. Usually about 120℃ to 160℃
Select a range of ℃.

The pressure is actually equal to the pressure corresponding to the vapor pressure at the cooking temperature.

During the cooking process, the amount of atmospheric oxygen, especially molecular oxygen, such as oxygen contained in lignocellulosic materials, must be minimized. This is a known method,
For example, especially the aforementioned James P. This can be accomplished by steam or pressure, as described on page 213 of the work of James P. CASEY. On pages 219 to 229 of this document there is a description of equipment, in particular pressure-resistant equipment, suitable for the production of CTMP pulp.

The amount of sodium sulfite, sodium hydrogen sulfite or _SO2 -NaOH mixture used is the amount normally used in known processes suitable for producing CTMP pulps that do not contain the components of the invention. Therefore,
Expressed as _SO2 , it ranges from 0.1 to 10%, most often from 1 to 6%.

The cooking according to the invention can be carried out before, during or after the grinding or mechanical refining process.

For example, the cooking process of the lignocellulosic starting material, such as wood chips, according to the present invention can be carried out prior to grinding, which is carried out at atmospheric pressure and low temperature.

For example, wood chips are impregnated with a cold aqueous solution of the reactants necessary for carrying out the invention,
It is then cooked according to the invention and ground as described above.

For example, cooking according to the invention can be carried out in a grinder or mechanical refiner containing the lignocellulosic starting material, e.g. wood chips, or material already pulped by grinding for further processing if necessary. Start with.

The cooking method according to the invention can be applied, for example, to pulp after crushing/refining a lignocellulosic starting material such as wood chips.

The consistency, ie, the weight percent of lignocellulosic material in the mixture calculated in the dry state, is not a critical factor in practicing the invention. In practice, in embodiments of the invention, the consistency is between 5 and 50%, typically between 5 and 25% in the case of already ground material.

Cooking times according to the present invention will vary depending on other implementation parameters, including the type of equipment used. Usually it does not exceed 1 hour. More generally, the number
It ranges from 10 seconds to 30 minutes.

The invention also relates to a method for bleaching the pulp produced as described above. This bleaching
The process consists of washing the pulp to remove as much sulphite ions and reducing agents as possible and reacting the washed pulp with hydrogen peroxide in an alkaline aqueous medium.

This has confirmed the advantage of the present invention that bleaching with improved whiteness is possible.

Washing to remove sulfite ions and reducing agents to the maximum extent is carried out by known methods such as dilution with water and compression. This method may or may not be repeated. Etsuchi. Kruger (H.KRUGER), H.KRUGER. You. Syus (H.
Tappi 1982 International Sulphite Pulp Manufacturing Conference (U.SUSS)
Pulping Conference), Toronto,
The importance of cleaning can be confirmed by referring to "October 20-22", 1982, pp. 143-148.

Bleaching reduces the consistency by 10-30%, e.g.
in the presence of about 1 to 6% sodium silicate solution with a density of 1.33, at a pH of about 9 to 11, at a temperature of about 40 to 100°C, for 0.5 to 2 hours.
It is carried out in a known manner using hydrogen peroxide in an amount of 10%. The bleaching solution may contain additives such as one or more complexing or sequestering agents, such as diethylenetriaminepentaacetic acid and ethylenediaminetetraacetic acid in the form of their sodium salts. The amount usually ranges from 0.1 to 1%. The pulp produced by the method of the invention may also be treated with a bleaching agent and the above-mentioned complexing or sequestering agents. Depending on the type and amount of complexing or sequestering agent, this treatment is preferably carried out at temperatures between 20 and 100°C, so that the rate of complexation or sequestration is sufficiently fast that there is no need to operate under pressure. is 50
to 100°C, more preferably from 50 to 95°C, with a consistency ranging from 5 to 30% and a time varying from 5 minutes to 2 hours. It is then preferably washed and, for example, compressed.

It is also possible to carry out treatment of the lignocellulosic material with complexing or sequestering agents of the type described above prior to digestion according to the invention. In that case, the consistency is in the range of 5 to 50%, unless the material to be treated has been previously subjected to a grinding action and has not exceeded about 25 to 30%. Such treatment makes it possible to further increase the inherent effects of the present invention on the final brightness and effectiveness of the hydrogen peroxide action.

The lignocellulosic material can also be contacted with a complexing or sequestering agent during the cooking process according to the invention.

EXAMPLES The advantages of the invention will become clearer with the following examples. However, these examples are not intended to limit the invention in any way.

In these examples: - Amounts are expressed in weight percent based on dry lignocellulosic material, even if not specified.

- If, before cooking, a treatment with complexing or sequestering agents is carried out, hereinafter referred to as sequestering treatment, this treatment is carried out at 90 °C for 15 minutes, unless otherwise indicated. , with a consistency of 10% and a titer of 40 for the sodium salt of diethylenetriaminepentaacetate, hereinafter referred to as DTPA.
It is carried out using a 0.5% aqueous solution by weight.

- the initial PH of the cooking medium according to the invention and of the impregnating aqueous solution optionally containing sulphite and reducing agent is between 7 and 12.5;

- Sodium borohydride is BOROL
used in the form of The amount displayed is the amount in this form.

-Silicate means an aqueous sodium silicate solution with a density of 1.33.

−Whiteness is KARL ZEISS
ELREPHO manufactured by
(457 nm).

Example 1 Ground wood chips with a brightness of 53.7% were heated in an autoclave at 120° C. under saturated vapor pressure to a brightness of 0.5%.
Over time, at a consistency of 20%, sodium sulfite Na ₂ SO ₃ 5.9%, hydrosulfite 2.5
% and 2% sodium hydroxide.

After cooking, it is washed with water to remove sulfite ions and reducing agents. Next, the obtained CTMP pulp was heated at 90°C for 2 hours to a consistency of 20%.
%, hydrogen peroxide H ₂ O ₂ 5%, sodium hydroxide 2
%, using 4% silicate and 0.5% DTPA,
to bleach.

The whiteness thus obtained is 82.8%.

For comparison, no hydrosulfite was used, and 5% sodium bisulfite and 1.2% NaOH were used so that the SO ₂ /NaOH ratio in this case was the ratio considered to be the practical optimum. Operating as above but carrying out the cooking using
Consumes 1.05 times more H ₂ O ₂ .

Example 2 The same lignocellulose starting material as in Example 1 is sequestered and washed with water. Next, processing is performed in the same manner as in Example 1.

When hydrosulfite is reacted simultaneously with sulfite during cooking before bleaching, the final whiteness obtained is 83.3%. For comparison, when cooking was carried out under the same cooking conditions as in the comparative example of Example 1, the whiteness was only 81%. Furthermore, the consumption of H ₂ O ₂ is
Increases by 1.12 times.

Example 3 The procedure is analogous to Example 2 for the simultaneous reaction of hydrosulfite and sulfite. However, the cooking temperature should be 140℃ instead of 120℃.

The whiteness obtained in this way is always high and
It is 82.6%.

Example 4 The lignocellulose starting material of Example 1 was sequestered, washed with water and treated with 1.5% BOROL and 5.9% sodium sulfite at 120° C. for 0.5 hours at a consistency of 20%. Cook in the presence of water and wash with water to remove sulfites and reducing agents. The resulting CTMP pulp is bleached in the same manner as in Example 1 after co-reacting hydrosulfite with sulfite.

The whiteness thus obtained is 84.5%.

The amounts of H ₂ O ₂ , NaOH, and silicate were each 2%,
When bleaching is carried out by changing to 1% and 3%, the whiteness becomes only 82%.

Example 5 Example 4 except that the amount of BOROL was changed from 1.5 to 1% and the sodium sulfite was replaced with hydrosulfite and a 5% amount was used.
Operate in the same way.

The resulting CTMP pulp is bleached in the same manner as in Example 1 after the simultaneous reaction of hydrosulfite with sulfite. The whiteness thus obtained is 82.7%.

Example 6 The procedure is as in Example 5, except that 3% of BOROL is used instead of 1%.
The whiteness obtained is 83.8%.

Example 7 250 kg/hour of crushed resinous wood chips, 90
consistency using DTPA 0.5% at °C.
40%, then washed in a press, and simultaneously reacted in an autoclave under saturated vapor pressure with 1.5% BOROL and 2.5% sodium bisulfite neutralized with sodium hydroxide. and cook. Cooking at 140℃ for the first 5 minutes
and then at a temperature of 100° C. for 1 hour. After washing with water to remove sulfite ions and reducing agents, the resulting CTMP pulp was treated at a consistency of 28% at 80°C for 1 hour.
H ₂ O ₂ 5.1%, NaOH 2%, silicate 4% and
Bleach using DTPA 0.5%.

After refining and schooling with a disc-type refiner, the whiteness of the obtained CTMP pulp is 80.
%. The tensile strength, or breaking length, is
It is 3.835m.

When operating in the above manner except without using BOROL, the whiteness is only 77% even when using 5.4% H ₂ O ₂ , and at this time, the tearing length is also
It will only be 3.290m.

After grinding/refining without any reagents, the starting material chips have a whiteness of 55.5% and a fracture length of 2.755 m.
It is.

Example 8 A procedure similar to that described in Example 7 except that the digestion of CTMP pulp was carried out by simultaneously reacting 2.5% hydrosulfite, 5% sodium bisulfite neutralized with NaOH, and 1% NaOH. Bleaching was carried out as in Example 7, except that the method of the invention was carried out and only 4.7% H ₂ O ₂ was used.
The whiteness of CTMP pulp is 78.5%, and the breaking length is
It is 3.525m.

Example 9 The same lignocellulosic starting material as in Example 1 is sequestered and washed with water. next,
At 120℃, over 0.5 hours, consistency 20%
So, 1% thiourea dioxide and sodium sulfite
Cook in the presence of 5.9%.

After cooking, it is washed with water to remove sulfite ions and reducing agents. At 90°C, as in Example 1 after co-reacting hydrosulfite with sulfite,
H ₂ O ₂ 5 at a consistency of 20% for 2 hours.
%, sodium hydroxide 2%, silicate 4% and
Bleach the resulting CTMP pulp using DTPA 0.5%.

The whiteness thus obtained is 83.5%.

Example 10 Pulverized chips of deciduous wood with a whiteness of 59.9% were heated in an autoclave under saturated steam pressure at 120%
°C, at a consistency of 20% over 0.5 h.
BOROL 1.5% and sodium sulfite
Cook in the presence of 5.9%. This is followed by washing with water to remove the sulfite and reducing agent. Next, 90℃
So, for 2 hours, with a consistency of 20%,
H ₂ O ₂ 5%, sodium hydroxide 4%, silicate 4
CTMP obtained using 0.5% and DTPA
Bleach the pulp.

The whiteness obtained is 86.6%.

Operating as above, except cooking without BOROL for comparison, the whiteness obtained was only 84.1%, and _{the H2O2}
Consumed 1.05 times.

Example 11 250Kg/hour of already crushed resinous wood chips
Impregnated with 0.5% DTPA at 90 °C, consistency 20%, washed with water by successive dilution and compression operations, then under saturated vapor pressure, 120 °C
So, in 30 seconds, the consistency was 28%, and the pH was 8.4.
in a mixture of BOROL 1.5% and
React SO ₂ 3% with sodium hydroxide simultaneously,
Digest. This cooking takes place at 100°C for 30 minutes. After cooking, the pulp is washed with water through successive dilution and compression operations to remove sulfite ions and reducing agents, and is then heated to consistency at 80°C for 2 hours.
26.5%, H ₂ O ₂ 5.2%, NaOH 2%, Silicate 4
% and DTPA 0.5%.

After refining and schooling with a double disc refiner, the whiteness of the bleached CTMP pulp is 83.6%.

When operated in the same manner as above, except that BOROL was not used during cooking, the whiteness of the bleached CTMP pulp was only 80.1%;
H ₂ O ₂ is consumed 1.05 times.

Example 12 Deciduous wood chips were used as starting material, except that the cooking was carried out simultaneously with BOROL using 2.45% SO ₂ with sodium hydroxide in a mixture of PH 11.5. Proceed as in Example 11.

The whiteness of the bleached CTMP pulp thus obtained was 87.3%, and the breaking length was 3.235 m.
and the tear index is 352.

If the operation is the same as above except that BOROL is not used, even if the degree of refinement is the same, the whiteness will be only 86% and the fracture length will be 2.885.
m, and the tear index is 310.

Example 13 No sequestration treatment was performed prior to cooking and instead sulfite and borol (BOROL)
The procedure is as in Example 4, except that the cooking is carried out in addition to 0.5% DTPA.

Bleached CTMP thus obtained
The whiteness of the pulp is 86%. Also, if you operate in the same way as above, except without using BOROL, it will only be 84%.

Example 14 Resinous wood chips preheated with steam are impregnated with 3% sodium sulfite, 3% sodium bisulfite, 1.5% BOROL and 0.5% DTPA by simultaneous soaking and drainage. do. It is then digested at 90° C. for 4 minutes under saturated steam pressure in an autoclave, after which it is ground by rapid discharge from the autoclave through a die and refined in a disc refiner.

The CTMP pulp thus obtained is 90
°C for 2 hours at a consistency of 20%.
H ₂ O ₂ 5%, sodium hydroxide 2%, silicate 4
% and DTPA 0.5%.

Although the whiteness of the refined starting material chips is only 56%, the final product obtained in this way
The whiteness of CTMP pulp is 71%.

If you operate as above, except without BOROL, the whiteness will be 66%
It's nothing more than that. The tearing length is also 3.900m in the above case.
However, in this case, the tear index becomes smaller, 3.755 m, without actually changing.

Effects of the Invention The present invention can be used even from resinous wood or soft wood.
Even from deciduous wood, i.e. hardwood, high whiteness can be achieved by reducing H ₂ O ₂ consumption and bleaching.
Not only can CTMP pulp be produced, but the mechanical properties of this bleached CTMP pulp can be maintained,
Furthermore, it can be improved.

Claims (1)

[Claims] 1. Mechanical pulverization, sodium sulfite, sodium hydrogen sulfite, or a mixture of sulfur dioxide and sodium hydroxide, and a reducing agent with lower electronegativity than sulfite ions at a temperature of 100°C or higher. A process for the production of chemical-thermomechanical pulp from lignocellulosic material in combination with non-destructive cooking carried out at temperature and under saturated vapor pressure, comprising: sodium sulfite, sodium bisulfite or a mixture of sulfur dioxide and sodium hydroxide as described above; A method characterized by simultaneously acting on a lignocellulose material with a reducing agent having lower electronegativity than sulfite ions, and adjusting the initial pH of the medium from 7 to 12.5. 2. Process according to claim 1, characterized in that the reducing agent is selected from among thiourea dioxide, sodium borohydride or sodium dithionite. 3. Claim 2, characterized in that the above-mentioned thiourea dioxide or sodium dithionite is used in an amount of 0.1 to 5% by weight of the dry lignocellulose material.
The method described in. 4. Process according to claim 2, characterized in that the sodium borohydride is used in an amount of 0.01 to 0.5% by weight of the dry lignocellulosic material. 5. Process according to any one of claims 1 to 4, characterized in that the non-destructive cooking is carried out at a temperature not exceeding 200°C. 6. Process according to claim 5, characterized in that the temperature of said non-destructive cooking is in the range from 120 to 160°C. 7. Claim 1, characterized in that the amount of said sodium sulfite, sodium hydrogen sulfite or mixture of sulfur dioxide and hydrogen peroxide is in the range from 0.1 to 10% of the weight of the dry lignocellulosic material, expressed as sulfur dioxide. 6. The method according to any one of 6. 8. Process according to any one of claims 1 to 7, characterized in that the lignocellulosic material is treated with a complexing agent or a sequestering agent before said non-destructive digestion. 9. Process according to any one of claims 1 to 7, characterized in that during said non-destructive digestion the lignocellulosic material is contacted with a complexing agent or a sequestering agent. 10. A method according to claim 8 or 9, characterized in that the complexing agent or sequestering agent is sodium diethylenetriaminepentaacetate. 11. Process according to any one of claims 1 to 10, characterized in that said non-destructive digestion is carried out before, during or after said mechanical comminution. 12 Mechanical grinding and simultaneous application of sodium sulfite, sodium bisulfite or a mixture of sulfur dioxide and sodium hydroxide and a reducing agent less electronegative than sulfite ions to the lignocellulosic material and adjusting the initial pH of the medium. 7 to 12.5
A chemical-thermomechanical pulp is produced from a lignocellulosic material by combining non-destructive cooking under saturated steam pressure at a temperature of 100° C. or higher, and the resulting chemical-thermomechanical pulp is then washed to remove the sulfurous acid. A method for bleaching chemical-thermomechanical pulp, which comprises removing ions and reducing agents, and further bleaching the washed pulp using hydrogen peroxide in an alkaline aqueous medium. 13. The bleaching method according to claim 12, characterized in that hydrogen peroxide is allowed to act on the pulp in an alkaline aqueous medium having a pH of 9 to 11. 14. The bleaching method according to claim 12 or 13, characterized in that 2 to 6% hydrogen peroxide is used. 15. Bleaching method according to any one of claims 12 to 14, characterized in that the reducing agent is selected from thiourea dioxide, sodium borohydride or sodium dithionite. 16. Bleaching process according to any one of claims 12 to 15, characterized in that 0.1 to 5% of the weight of the dry lignocellulosic material is used of thiourea dioxide or sodium dithionite. 17. Bleaching method according to any one of claims 12 to 15, characterized in that the sodium borohydride is used in an amount of 0.01 to 0.5% by weight of the dry lignocellulosic material. 18 Claims 12 to 17, characterized in that the temperature of the non-destructive cooking is in the range of 120 to 160°C.
A bleaching method as described in any one of paragraphs. 19. Claim 12, characterized in that the amount of said sodium sulfite, sodium bisulfite or mixture of sulfur dioxide and hydrogen peroxide ranges from 0.1 to 10% of the weight of the dry lignocellulosic material, expressed in sulfur dioxide. 19. The bleaching method according to any one of 18 to 18. 20. A bleaching method according to any one of claims 12 to 19, characterized in that the lignocellulosic material is treated with a complexing agent or a sequestering agent before said non-destructive digestion. 21. A bleaching method according to any one of claims 12 to 20, characterized in that said non-destructive cooking is carried out before, during or after said mechanical grinding.