EP0777780A1

EP0777780A1 - Sulphite fusion process

Info

Publication number: EP0777780A1
Application number: EP95928394A
Authority: EP
Inventors: Karl Fuchs; Albert Huber; Hans-Ludwig Schubert
Original assignee: Impco-Voest-Alpine Pulping Technologies GmbH
Current assignee: Impco-Voest-Alpine Pulping Technologies GmbH
Priority date: 1994-08-26
Filing date: 1995-08-25
Publication date: 1997-06-11
Anticipated expiration: 2015-08-25
Also published as: ATE173517T1; EP0777780B1; ID15812A; WO1996006974A1; DE59504281D1; CN1160426A; FI970707A; BR9508634A; ZA956506B; ATA165194A; FI970707A0; RU2124083C1; ES2126305T3; CA2198485A1; AT401068B

Abstract

The present inventon relates to a sulphite fusion process for the production of celluloses using alkaline monosulphite solutions, organic solvents and quinone derivatives. The raw material to be fused is treated in a special impregnation step with either a solvent-free monosulphite solution or a solvent-water mixture.

Description

Sulphite digestion process

The present invention relates to a sulfite digestion process for the production of cellulose using alkaline monosulfite solutions, organic solvents and quinone derivatives.

The most important chemical processes for the production of cellulose are the sulfite and sulfate digestion. In addition, processes using sodium hydroxide solution and chlorine or nitric acid are known, but are not very widespread on an industrial scale.

In the sulfite digestion process, the raw materials (shredded wood) are introduced into an acidic or neutral cooking acid and these lignocellulosic materials are boiled with solutions of hydrogen sulfites or sulfites. If the hydrogen sulfite solutions additionally contain sulfur dioxide, one speaks of "acid bisulfite processes".

Frequently used methods are the calcium bisulfite method and in particular the magnesium bisulfite method. A detailed summary of the various known sulfite exclusion methods can be found in Ingruber and Allard (1973) "Alkaline Sulfite Pulping for Kraft Strength", Pulp and Paper Magazine of Canada 1974, pages 354-369.

An alkaline sulfite digestion solution generally consists of a sulfite and carbonates or bases; the specific digestion variant, however, always depends on the type of wood used.

It is known that a sulfite digestion process in which a sodium sulfite solution, ie a pure monosulfite solution, is used and in which methanol and / or anthraquinone is further added to the cooking solution, achieves an increased rate of delignification and an increased digestion efficiency can be (Tappi-Journal, 65 (10) (1982), 29). A particularly advantageous method is described in EP-Bl-0 205 778. In a sulfite digestion process, carbonate and / or hydroxides are added to the digestion solution, which has a predominant proportion of monosulfite solution, in addition to methanol and a quinone derivative. This process is referred to as the ASAM process (Alkaline Sulphite Anthraquinone Methanol Process).

EP-A1-0 538 576 and AT-B-398 992 each disclose methods for recovering the chemicals used for pulping from the waste liquor according to the ASAM method. For this purpose, the waste liquor is burned in a caustic combustion boiler, the slag or ash is drawn off, dissolved in water, converted to H ₂ S and burned, sodium sulfite being recovered from the waste gases formed during the combustion.

The object of the present invention is to provide a sulfite digestion process which is further improved compared to the prior art described and which enables more efficient digestion of the raw material, improved recovery of substances used and process simplification of the process.

According to the invention, this object is achieved by a sulfite process for lignocellulose-containing raw material using water-soluble alkaline monosulfite solutions, organic solvents and at least one quinone derivative, in which the raw material is subjected to an impregnation step at a temperature before the actual digestion of the raw material. which is below the temperature required for the digestion reaction, the impregnation solution being composed only of a part of the chemical constituents which are necessary for the actual digestion step.

The impregnation step can either be carried out solvent-free by the raw material containing the alkaline monosulfite solution. solution is impregnated, or by means of a solvent / water mixture.

The quinone derivative can be present during the impregnation of the pipe material or is added before the digestion step with the other components still missing for the digestion. The quinone derivative accelerates delignification in alkaline digestion processes as a redox catalyst and stabilizes the reducing ends of the carbohydrates against an alkaline "peeling-off". A preferred quinone derivative is anthraquinone.

If the impregnation step is solvent-free, the organic solvent is only added to the alkaline monosulfite solution after this impregnation step; in the case of impregnation with a solvent / water mixture, the remaining inorganic digestion chemicals required are added after the impregnation.

If the raw material is impregnated with the alkaline monosulfite solution, the said raw material is impregnated with the alkaline monosulfite solution for a period of 5 to 360 min, preferably 15 to 60 min. The temperatures usually used here are between 60 and 150 ° C., preferably between 100 and 130 ° C.

The impregnation with the alkaline monosulfite solution can be ended by adding the organic solvent or the solvent / water mixture to the impregnation solution. In this process, the ionic strength of the impregnating liquor should be adjusted to the concentration required for the digestion by introducing the organic solvent or the solvent / water mixture.

The solvent, for example low-boiling alcohols, such as methanol, can be introduced into the digestion system under pressure after the digestion material has been impregnated. Then the digestion material with the complete digestion solution is transferred to the Reaction required temperature heated, or the impregnation is replaced by modern displacement technology with a complete digestion solution containing the solvent.

Particularly preferred in this modification of the process is an impregnation solution which has a higher ion concentration than the actual digestion solution. This requires a faster and more homogeneous distribution of the alkaline and monosulfitic digestion chemicals in the digestion material.

The impregnating liquor can either be used in comparison with the amounts required for the cooking with an excess of inorganic chemicals and liquid amounts, or with the chemical amounts required for the digestion with a reduced liquid volume compared to the boiling.

In the first case, part of the amount of liquid with the amount of chemicals still present therein after impregnation must either be withdrawn or displaced from the digestion system before the solvent is introduced into the digestion system. The solvent or solvent-water mixture can be used as a displacement medium. The displaced or withdrawn displacement liquor can be strengthened to the initial concentration with fresh chemicals and reused.

The solvent used for the displacement can be mixed with water, so that the chemical and solvent concentration required for the digestion can be set variably. Energy savings due to the lower requirements for the purity and concentration of the recovered solvent become possible.

Alternatively, the impregnation can be carried out with less liquid than is necessary for the digestion itself. However, it must be ensured that all digestion material is soaked. This can be done, for example, by pumping the gnier solution can be achieved. In the impregnation, the digestion material absorbs the inorganic digestion chemicals. At the end of the impregnation, the chemical concentration of the digestion solution is adjusted to the concentration required for the digestion by replenishing the solvent or the solvent / water mixture, or is achieved by displacing the impregnation solution with complete digestion solution.

This process design has the technological advantage that the solvent-containing lye circuit remains limited to the areas of the digestion system, the black liquor management up to the separation of solvents and parts of the brown liquor washing. The white liquor remains solvent-free, which increases the solubility of the inorganic digestion chemicals.

It is a feature of this modification of the process that conventional digestion systems for the digestion material can be used in continuous digestion systems since the impregnation liquid is solvent-free.

Special features of this aspect of the invention are the acceleration of the digestion process and the improvement of the digestion homogeneity, which is particularly noticeable in a reduction in the amount of sliver. The qualities of the pulps produced in this way remain at the level of those produced according to the standard ASAM process with somewhat higher cellulose yields and lower splinter contents.

Impregnation of wood with a mixture of water and a solvent, preferably a low-boiling alcohol, such as methanol, has the advantage that such a solution has a much lower viscosity, is less polar, and is easier to penetrate into the internal structure of the wood can and by dissolving hydrophobic substances, such as resins, improves the mobility of the wood. If the impregnation is carried out at higher temperatures, besides the effects mentioned, cleavage of lignin-carbohydrate bonds is also achieved, so that this also facilitates the subsequent digestion. The presence of the solvent component, in particular the alcohol, at the same time protects the carbohydrates from very intensive degradation. Appropriate pretreatment of the wood enables shorter digestion times or lower maximum digestion times.

Final temperatures, low splinter content in the cellulose and easy digestion of difficult to impregnate woods.

In the impregnation stage, the entire amount of the organic solvent required for the digestion is preferably added at a higher concentration than the subsequent digestion solution with a reduced liquor ratio, and possibly the redox catalyst. This increases the impregnation effect, protects the carbohydrates of the wood from degradation and minimizes condensation reactions of the lignin, which would make the subsequent digestion more difficult.

According to a particular embodiment of the process, liquor ratios of 1: 2 to 1: 3.5, preferably of 1: 3 to 1: 3.5, should be used in the case of impregnation with a solvent / water mixture, with a solvent content of the impregnation solution between 20 and 35%. The impregnation itself should in this embodiment, at temperatures of 120 - 150 ° C, preferably 130 - 140 take place ^β C and 20 - 80 min, preferably 60 min, last.

The impregnation step can be ended in both variants - both in the case of solvent-free impregnation and also in the case of impregnation by means of a solvent / water mixture, by replacing (for example by displacing) the impregnation solution with the digestion solution.

After impregnation, an aqueous solution of the inorganic digestion chemicals, possibly together with the quinone derivative to be used, can be introduced into the digester, the digester heated to maximum temperature and the digestion carried out become. The heating-up time can be shortened very much compared to the normal digestion because, because of the improved mobility of the wood, the inorganic digestion chemicals penetrate very quickly into the microstructure of the wood. The cooker's total rotation time is not extended. The maximum digestion temperature can be reduced, for example in the case of softwood, from 180 to 173-170 ", as a result of which the stove pressure is reduced as a function of the solvent content of the digestion solution.

During the digestion reaction, the solvent should preferably be present in an amount between 0.5 and 50 percent by volume of the total amount of liquid.

Sodium sulfite is preferably used in the alkaline monosulfite solutions in an amount between 5 and 40% based on the raw material. Other bases, e.g. Potassium hydroxide or potassium carbonate, but are also suitable.

According to a preferred process form, aqueous solutions of sodium hydroxide and / or sodium carbonate are mixed into the monosulfite solutions, in an amount between 0 and 15% based on the raw material used.

The digestion solution and the digestion material can be brought to the temperature necessary for the digestion reaction directly after or with the introduction of all digestion chemicals still required.

The digestion process can be ended by displacing the digestion solution or by cooling the system.

The processes described can be operated either continuously or batchwise. If a discontinuous process sequence is desired, a preferred process variant consists in that the impregnation step is already carried out in standing, discontinuous cookers in which the liquids are moved by means of pumps and the Raw materials are entered using filling equipment. In this case, the impregnating liquor is preferably introduced into the cooker from a separate impregnating liquor tank.

In the case of a continuous process, the impregnation step is preferably carried out in a separate impregnation tower, and the digestion material is then transported into the cooker with a liquid.

An example of a plant for a continuous process is shown in FIG. 1:

Raw material (1) is heated in a container (2) by means of steam (3, 4) and transferred to the feed system (5), in which the impregnation solution (6), which consists of NaOH, Na ₂ CO ₃ , Na ₂ , is mixed S0 ₃ and anthraquinone exists. The mixture is passed via a heat exchanger (7) into the impregnation tower (8), in which the actual impregnation step takes place. From the impregnation tower, the impregnated raw material is fed into the cooking tower (12) via further heat exchangers (9, 10), the solvent methanol (11) also being added between the heat exchangers (9) and (10) becomes. After the digestion phase, both the pulp (13) and the alkali (14) are led out of the digester and processed or reprocessed.

In particular, the invention enables a clear simplification of the process control of the ASAM process and simplifies its implementation in industrial practice, both with continuous and with discontinuous digestion systems. Improved impregnation reduces the splinter content of the cellulose and increases the yield of accepted material. Examples:

Digestion of spruce wood

Digestion type standard methanol-free

(ASAM process) Impregnation

impregnation

Temp., ° C 120

Heating time, min. 53

Time at T _maχ 60

MeOH,% / fleet 0

Fleet 3: 1

AQ,% / wood 0.1

Information

Temp., ° C 180 180

Heating time, min 100 37

Time at T _maχ 120 150

MeOH,% / fleet 15 15

Fleet 4: 1 4: 1

Max- ^pressure ^bar 14 14

Total alkali (calculated 25 25 as NaOH),% wood

Na ₂ SO ₃ : NaOH 80:20 80:20

AQ,% wood 0.1 0.1

Kappa 22.2 '22.4

Acceptable material yield,% 45.9 50.0

Splinter,% 4.9 2.2

Viscosity, ml / g 1327 1334

Whiteness,% .ISO 45.7 39.6

TABLE 1 2 .: Disruption of pine wood

Digestion type standard methanol / water

(ASAM process) Impregnation

impregnation

Temp., ° C 135

Heating time, min. 40

Time at T _maχ 60

MeOH,% / fleet 28

Fleet 3.5: 1

AQ,% / wood 0.1

Information

Temp., ° C 180 170

Heating time, min 120 80

Time at T _maχ 150 150

MeOH,% / fleet 20 20

Fleet 5: 1 5: 1

Max- ^pressure ^bar 15 11.5

Total alkali (calculated 25 25 as NaOH),% wood

Na SO ₃ : NaOH 70:30 70:30

AQ,% wood 0.1

Kappa 17.9 24

Acceptance yield,% 46.0 50.5

Splinter,% 2.0 0.7 viscosity, ml / g 1240 1480 whiteness,% .IS0 31, 9 34

TABLE 2 3 .: Standard digestion according to the ASAM process conventional and with white liquor impregnation and excess chemicals during the pre-impregnation

3.1 .: ASAM - conventional

Raw material: spruce wood

The digestion was carried out in a 15 l autoclave.

Chemicals: 20% Na ₂ SO ₃ and 5% NaOH calculated as NaOH on otro wood 0.075% anthraquinone on otro wood 15 v / v% methanol

Fleet: 4: 1 (liquid: wood)

Technology: dissolving all chemicals in the fleet

Steaming the digestion material for 20 min

Cook for 90 min 180 min Ready cooking at 180 ° C

Displace cooking liquor for 20 min and empty the cooker

Result: Kappa number: 24.6 Acceptable material yield: 47% splinter 1.2

3.2 .: ASAM - with white lye impregnation

Raw material: spruce wood

The digestion was carried out in a 15 l autoclave.

Chemicals: 130 g / 1 Na ₂ S0 ₃ and 20 g / 1 NaOH (on otro wood)

0.075% anthraquinone in the pre-impregnation 15 v / v% methanol in the boil; is only added after impregnation

Fleet: 6: 1 - (liquid: wood)

Technology: Dissolve the inorganics in the liquor for 20 minutes

Impregnation for 30 min at 110 ° C. 10 min of methanol input and displacement of alkali for 30 min

100 minutes of ready cooking at 180 ° C. For 20 minutes, displace the cooking liquor and empty the cooker

Result: Kappa number: 16.2

Acceptable material yield: 46.6% splinter 0.1

4.: Standard digestion according to the ASAM process with white liquor impregnation without excess chemicals during the pre-impregnation

Raw material: spruce wood

The digestion was carried out in a 10 m ³ cooker.

Chemicals: 17% Na ₂ S0 ₃ , 3% NaOH and 14% Na ₂ C0 ₃ based on wood 0.07% anthraquinone during the impregnation

10 v / v% methanol in the boil is only added after impregnation

Fleet: 3.3: 1 (liquid: wood) during the impregnation 4: 1 (liquid: wood) during the digestion

Technology: Prepare the impregnation liquor for 20 min. Steam the digestion material for 15 min. Impregnate at 122 ° C for 10 min. Methanol input and displacement of the alkali and alkali for 60 min

200 minutes of ready cooking at 180 ° C. For 30 minutes, displace the cooking liquor and empty the cooker

Result: Kappa number: 19.8

Acceptable material yield: 50.8% splinter 1.8

Claims

Claims:

1. sulfite digestion process for lignocellulose-containing raw material using water-soluble alkaline monosulfite solutions, organic solvents and at least one quinone derivative, characterized in that the raw material before the actual digestion of the raw material, an impregnation step at a temperature which is below the temperature required for the digestion reaction ¬ temperature, is subjected, the impregnating liquor being composed only of a part of the chemical constituents which are necessary for the actual digestion step.

2. The method according to claim 1, characterized in that the impregnation step is carried out solvent-free in the presence of the monosulfite solution and optionally the quinone derivative.

3. The method according to claim 2, characterized in that the raw material is impregnated with the monosulfite solution for a period of 5 to 360 min, preferably from 15 to 60 min.

4. The method according to any one of claims 2 or 3, characterized gekenn¬ characterized in that the raw material at a temperature between 60 and 150 ° C, preferably between 100 and 130 ° C, is impregnated with the monosulfite solution.

5. The method according to any one of claims 2 to 4, characterized gekenn¬ characterized in that an impregnating liquor with a higher ionic strength than that of the digestion solution is used.

6. The method according to any one of claims 2 to 5, characterized gekenn¬ characterized in that at the end of the impregnation step, the organic solvent or the solvent / water mixture is introduced into the impregnating liquor.

7. The method according to claim 6, characterized in that the ionic strength of the impregnating liquor is adjusted to the concentration required for the digestion by the entry of the organic solvent or the solvent / water mixture.

8. The method according to claim 1, characterized in that the impregnation step is carried out by means of a solvent / water mixture to which a quinone derivative has optionally been added.

9. The method according to any one of claims 1 or 8, characterized gekenn¬ characterized in that the entire amount of solvent required for the digestion with increased concentration compared to the subsequent digestion solution are presented in the impregnation step.

10. The method according to any one of claims 1, 8 or 9, characterized in that the impregnation is carried out at 1: 2 to 1: 3.5 at Fleet ratios.

11. The method according to any one of claims 1 and 8 to 10, characterized in that the impregnation is carried out at a solvent content of 20 to 35%.

12. The method according to any one of claims 1 and 8 to 11, characterized in that the impregnation is carried out at a temperature between 120 and 150 ° C, preferably between 130 and 140 ° C.

13. The method according to any one of claims 1 and 8 to 12, characterized in that the impregnation is carried out for a period of 20 to 80 min, preferably 60 min.

14. The method according to any one of claims 1 to 13, characterized gekenn¬ characterized in that one or more as organic solvents quality alcoholic solvents, preferably methanol, are used.

15. The method according to any one of claims 1 to 14, characterized gekenn¬ characterized in that the solvent is used during the digestion reaction in an amount between 0.5 and 50 percent by volume of the total amount of liquid.

16. The method according to any one of claims 1 to 15, characterized gekenn¬ characterized in that sodium sulfite is used in the monosulfite solutions in an amount between 5 and 40% based on the raw material.

17. The method according to any one of claims 1 to 16, characterized gekenn¬ characterized in that aqueous solutions of sodium hydroxide and / or sodium carbonate are mixed to the monosulfite solutions in an amount between 0 and 15% based on the raw material.

18. The method according to any one of claims 1 to 17, characterized gekenn¬ characterized in that potassium hydroxide and / or potassium carbonate is used as alkali in the monosulfite solutions.

19. The method according to any one of claims 1 to 4 and 8 to 18, characterized in that the impregnation solution for the end of the impregnation step is replaced by the digestion solution.

20. The method according to any one of claims 1 to 19, characterized gekenn¬ characterized in that the impregnation step is carried out in discontinuous digestion systems, the impregnation phase is already carried out in the cookers.

21. The method according to any one of claims 1 to 20, characterized gekenn¬ characterized in that the method is carried out in continuously operating digestion systems, the impregnation phase being carried out in a separate impregnation tower.