Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
A PROCESS FOR THE PRODUCTION OF SULPHATE PULP
Document Type and Number:
WIPO Patent Application WO/2001/021882
Kind Code:
A1
Abstract:
A process for the production of chemical pulp, in which wood is treated with a cooking liquor essentially not containing any polysulphide, and in which, prior to the treatment, the cooking liquor does essentially not contain any carbonate, and the concentration of added hydroxide ions in the cooking liquor is < 0.2 M, and that the cooking liquor also contains anthraquinone and/or derivatives thereof.

Inventors:
TORMUND DISA (SE)
BERTHOLD FREDRIK (SE)
OLM LEELO (SE)
LINDSTROEM MIKAEL (SE)
Application Number:
PCT/SE2000/001824
Publication Date:
March 29, 2001
Filing Date:
September 20, 2000
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
SVENSKA TRAEFORSKNINGSINST (SE)
TORMUND DISA (SE)
BERTHOLD FREDRIK (SE)
OLM LEELO (SE)
LINDSTROEM MIKAEL (SE)
International Classes:
D21C3/02; D21C3/22; (IPC1-7): D21C3/02
Foreign References:
SE309530B1969-03-24
Other References:
HASAN JAMEEL ET AL.: "Extending delignification with AQ/polysulfide", TAPPI JOURNAL, vol. 78, no. 9, September 1995 (1995-09-01), pages 151 - 160, XP002936137
V.R. PARTHASARATHY ET AL.: "Application of anthraquinone in extending the delignification of kraft and polysulfide pulps", TAPPI JOURNAL, vol. 78, no. 2, February 1995 (1995-02-01), pages 113 - 125, XP002936138
Attorney, Agent or Firm:
Grip, Joakim (Stockholms Patentbyrå Zacco AB Box 23101 S- Stockholm, SE)
Download PDF:
Claims:
Claims
1. A process for the production of sulphate pulp, in which wood is treated with a cooking liquor essentially not containing any polysulphide, c h a r a c t e r i s e d in that prior to the treatment, the cooking liquor does essentially not contain any carbonate and the con centration of added hydroxide ions in the cooking liquor is < 0.2 M, and that the cooking liq uor also contains anthraquinone and/or derivatives thereof.
2. A process according to claim 1, c h a r a c t e r i s e d in that the concentra tion of added hydroxide ions in the cooking liquor is < 0.15 M.
3. A process according to claim 1, c h a r a c t e r i s e d in that the cooking liq uor does essentially not contain any added hydroxide ions.
4. A process according to claim 1, c h a r a c t e r i s e d in that the cooking liq uor does not contain any polysulphide.
5. A process according to claim 1, c h a r a c t e r i s e d in that the cooking liquor contains up to about 1 weight% anthraquinone.
6. A process according to claim 1, c h a r a c t e r i s e d in that the cooking liquor contains up to about 0.020.25 weight% anthraquinone.
Description:
A process for the production of sulphate pulp The present invention relates to a process for the production of sulphate pulp.

Prolonged delignification in the cooking process and oxygen delignification is of great importance when performing bleaching according to modem technology. It is also of growing importance with regard to the trend of pulp production process systems becoming increasingly more closed. However, prolonged delignification suffers from the drawback of impaired pulp yield, and thus of higher wood costs.

The pulp yield decrement in the sulphate pulping process is primarily caused be alkaline peeling, as discussed in SE 9704273-3. Anthraquinone has been used in combination with polysulphide to counteract alkaline peeling, as disclosed in US-A-4,012,280. The use of polysulphide taken alone, i. e. without anthraquinone, in sulphate pulping processes has also shown a positive impact on the pulp yield, see US-A-3,874,991. Anthraquinone used alone in sulphate pulping processes, however, seems to have a rather limited effect, at high sulphide concentrations, on the pulp yield.

It would be desirable to provide a process for the production of sulphate pulp, in which wood is treated with a cooking liquor, which contains anthraquinone, but essentially no polysulphide, which process provides for a higher pulp yield, particularly when the process involves or is combined with prolonged delignification and/or oxygen delignification.

Thus, one problem to be solved by the present invention is to provide such a process. This problem is solved by means of the process as defined by appended claim 1.

More particularly, the present invention relates to a process for the production of sulphate pulp, in which wood is treated with a cooking liquor essentially not containing any polysulphide, whereby prior to the treatment, the cooking liquor does essentially not contain any carbonate and, also prior to the treatment, the concentration of added hydroxide ions in the cooking liquor is < 0.2 M, and that the cooking liquor also contains anthraquinone and/or derivatives thereof.

By the expression"essentially no polysulphide"is meant that the process may involve minor amounts of polysulphide, such as trace amounts of polysulphide or polysul- phide impurities; this applies, mutatis mutandis, also to the expression"does essentially not contain any added hydroxide ions".

By the expression"added hydroxide ions"is meant any hydroxide ions that have been added, when preparing the cooking liquor, to the hydroxide ions already present in the water of the cooking liquor.

By the expression"cooking liquor"is meant any such liquors that are common in cooking liquors for the production of sulphate pulp, as long as requirements set out by the features in claim 1 are fulfilled.

In one embodiment, said concentration of added hydroxide ions in the cooking liquor is < 0.15 M. In another embodiment, the cooking liquor does essentially not contain any added hydroxide ions. In a particular embodiment, the cooking liquor does not contain any added hydroxide ions.

In a particular embodiment, the cooking liquor does not contain any polysul- phide.

The present invention is advantageous in that, among other things, the pulp yield obtained in a sulphate pulping process can be increased without having to use any polysul- phide.

The cooking liquor contains anthraquinone and/or derivatives thereof.

Preferably, the cooking liquor contains up to about 1 weight-% anthraquinone, in particular about 0.02-0.25 weight-%. The amount of used anthraquinone in the cooking liquor can be decreased by means of the present invention, while retaining the pulp yield at least unchanged, or even increased. This is of great economic significance, as anthraquinone is an expensive substance, and as the use of polysulphide is associated with certain technical draw- backs.

The cooking liquor used according to the present invention may contain, apart from anthraquinone, any such substance, in any such amount, that are common in cooking liquors for the production of sulphate pulp, as long as requirements set out by the features in claim 1 are fulfilled. Exemplary of such substances is hydrogen sulphide compounds such as sodium hydrogen sulphide, and sodium hydroxide. When hydrogen sulphide compounds are used, the HS-concentration is about 0. 05-1M, preferably about 0. 1-0. 5M.

The wood treatment of the present process is preferably carried out at a tem- perature of about 70-160°C, particularly in the range of 130-150°C.

The present invention is described in more detail below by means of certain ex- amples, the purpose of which in no way are to limit the scope of the invention, but are merely provided to illustrate the same.

Examples Example 1. Sulphate pulping at various hydroxide ion concentrations in the treatment. 300 grams (oven dry) water impregnated pinewood chips were charged in auto- claves and the treatment liquor was added. The liquor-to-wood ratio was 4: 1. The autoclaves

were placed in a glycol bath for 10 minutes at 100°C and heated at a rate of 2°C/min to 130°C. The treatment time was 60 minutes. After the treatment, the autoclaves were cooled and hydroxide ions were added to the treatment liquor. After hydroxide ion addition, the auto- claves were placed in a glycol bath for 10 minutes at 130°C and heated at a rate of 2°C/min to 170°C. The H-factor at 170°C was 1800. The total effective alkali charge was 18%, calculated on the wood, and the hydrogen sulphide ion concentration in the treatment liquor was 0. 3 mole/1. The treatment conditions and pulping results are given in Table 1 below.

Table 1. The pulp yield and pulp viscosity at kappa number 30 for a reference sulphate cook andfor sulphate cooks according to the invention with different hydroxide ion concentration in the treatment liquor. The hydroxide ion concentration in the beginning of the reference sulphate cook, cook no. 1, was 1. 0 molell.

Cook No. [OH~] initialS Yield, Viscosity, mole/1 % on wood ml/g 1 1. 0 47. 0 1150 2 0 48.5 1110 3 0 48.3 1120 4 0.1 47.2 1140 5 0.2 47.0 1170 Table 1 shows the pulp yields at kappa number 30 for various hydroxide ion concentrations in the treatment liquor. In the reference cook, the initial hydroxide ion concen- tration in the treatment liquor was 1 mole/1. As shown in Table 1 the pulp yield at kappa num- ber 30 increases with decreasing hydroxide ion concentration in the treatment. Cook 2 and 3, where no hydroxide ions were added to the treatment liquor, gave the highest pulp yield, 1. 5 %-units, calculated on the wood, compared to the reference cook.

Example 2. Sulphate-AQ pulping at various hydroxide ion concentrations in the treatment. 300 grams (oven dry) water impregnated pinewood chips were charged in auto- claves and the treatment liquor together with anthraquinone (AQ) was added. The liquor-to- wood ratio was 4: 1. The autoclaves were placed in a glycol bath for 10 minutes at 100°C and heated at a rate of 2°C/min to 130°C. The treatment time was 60 minutes. After the treatment, the autoclaves were cooled and hydroxide ions were added to the treatment liquor. After hy- droxide ion addition, the autoclaves were placed in a glycol bath for 10 minutes at 130°C and heated at a rate of 2°C/min to 170°C. The H-factor at 170°C was 1600. The total effective

alkali charge was 16%, calculated on the wood, and the hydrogen sulphide ion concentration in treatment liquor was 0. 3 mole/I. The AQ-charge was 0.1%, calculated on the wood. The cooking conditions and results are given in Table 2 below.

Table 2. The pulp yield and pulp viscosity at kappa number 30 for a reference sulphate-AQ cook (cook no. 6) for sulphate cook with no [OH/inib (cook 2) and for sulphate-AQ cooks (cooks 7 and 8) according to the invention, with different hydroxide ion concentration in the treatment liquor. The hydroxide ion concentration in the beginning of the reference sulphate- AQ cook was 1. 0 molell.

Cook No. [OH-] initiai Yield, Viscosity, mole/l % on wood ml/g 6 1.0 47.9 1130 2 0 48.5 1110 7 0 51.0 1080 8 0.1 48.4 1070 Table 2 shows that the pulp yield for the sulphate process according to the in- vention (cook 2) is higher than for the reference sulphate-AQ process (cook 6). Moreover, the pulp yield in sulphate-AQ cook increases with decreasing initial hydroxide ion concentrations in the treatment liquor. As shown in Table 2, cook 7 without initial hydroxide ion addition to the treatment liquor gave the highest pulp yield, 3 %-units, calculated on the wood, to the reference sulphate-AQ cook.

Example 3. Sulphate-AQ pulping at various AQ charges. 300 grams (oven dry) water impregnated pinewood chips were charged in autoclaves and the treatment liquor to- gether with anthraquinone (AQ) was added. No hydroxide ions were added to the treatment liquor. However, the AQ charge on wood was varied according to Table 3. The liquor-to- wood ratio was 4: 1. The autoclaves were placed in a glycol bath for 10 minutes at 100°C and heated at a rate of 2°C/min to 130°C. The treatment time was 60 minutes. After the treatment, the autoclaves were cooled and hydroxide ions were added to the treatment liquor. After hy- droxide ion addition, the autoclaves were placed in a glycol bath for 10 minutes at 130°C and heated at a rate of 2°C/min to 170°C. The H-factor at 170°C was 1700. The total effective alkali charge (EA) and AQ charge on wood were varied according to Table 3. The hydrogen sulphide ion concentration in treatment liquor was 0.3 mole/l. The cooking conditions and results are given in Table 3 below.

Table 3. The pulp yield and pulp viscosity at kappa number 30 for a reference sulphate cook, cook no. 1, and a reference sulphate-AQ cook, cook no. 6, as well as for sulphate-AQ cooks <BR> <BR> <BR> <BR> according to the invention. The total effective alkali charge (EA) as well as the AQ charge on wood was varied.

Cook Total EA, AQ, Yield, Viscosity, No % on wood % on wood % on wood ml/g 1 18 0 47. 0 1150 6 16 0.1 47.9 1130 9 17 0.025 49.4 1070 10 17 0.05 50.1 1090 11 17 0.1 50.7 1110 Table 3 shows that the AQ charge in a sulphate-AQ cook treatment according to the invention can be half the charge of the reference, while retaining the improvement of pulp yield. It should furthermore be noted that a AQ charge as low as 0.025% (cook no. 9) gives a considerable increase of the pulp yield compared to the sulphate reference (cook no. 1).