FI70439C - REFERENCE FOUNDATION FOR TRAEMATIC MEDIA WITH AN ALKALISK KOKVAETSKA SOM VAESENTLIGEN ICKE INNEHAOLLER SVAVELHALTIGAFOERENINGAR - Google Patents

Description

ANNOUNCEMENT nnA1LQ

® B 11 UTLÄG G NIN GSSKRI FT 704 39 (45)? t; Λ · '"It ύ:.): .O: g (51) Kv.lk.4 / lnt.CI.4 D 21 C 3/02 FINLAND— · FI NLAND (21) Patent application- Patentansökning 781352 (22) Application date - Ansökningsdag 02 05 78 (Fh '' (23) Start date - Giltighetsdag 02.05.78 (41) Has become public - Blivit offentlig 0 ^ j ^ yg

National Board of Patents and Registration Date of publication and publication. - 27 0, o,

Patent and registration authorities Ansökan utlagd och utl.skriften publlcerad '· *' (86) Kv. application Int. ansökan (32) (33) (31) Privilege claimed - Begird priority 02.05 * 77 Australia-Australien (AU) PC 9939/77 (71) Australian Paper Manufacturers Limited, k South Gate, South Melbourne, Victoria, Austral ia-Australien ( AU) (72) Alan Farrington, Donvale, Victoria,

Vernon Taylor Henderson, West Preston, Victoria,

Peter Frederick Nelson, Kew, Victoria, Australia-Australien (AU) Oy Koi ster Ab (5 ^) A method for removing lignin from wood material with an early cooking liquid that is substantially free of sulfur-containing compounds -Förfarande för delignifiering av trämaterial med en aikai isk The present invention relates to pulping processes in which lignin is removed from a lignocellulosic material to produce a pulp that can be used to make paper and board. In particular, the invention relates to high-yield semi-chemical pulps, although the process is also suitable for the production of full-chemical pulps.

The sulphate method has been widely used due to the excellent properties of the pulp obtained by it. However, for some purposes, such as the production of component pulps for coating corrugated paper and board, relatively high strength values obtained by the sulphate process may not be required, in which case the relatively low yield and high cost of the sulphate process are disadvantages. It has therefore been proposed to use variants such as the "high yield sulfate method" as well as various sulfite methods for these purposes. The most widely used of these high-yield methods is the so-called Neutral 70439 2 Semi-chemical sulphite process (NSSC) capable of obtaining pulp yields in the range of 65 to 85%, with pulp properties suitable for the manufacture of corrugated paper and as an important ingredient in the manufacture of paperboard coverings and packaging and wrapping papers.

Increasingly stringent environmental protection regulations place great emphasis on a chemical recovery system that recovers pulp cooking chemicals and decomposes dissolved wood, as these chemicals and materials would otherwise be too burdensome on the environment. Recovery methods suitable for NSSC pulp cooking are complex and expensive.

One solution is sometimes to incinerate NSSC waste liquor in a sulfate plant recovery system. However, this presupposes that the NSSC plant is close to the sulphate plant, which is not always the case. In addition, chemicals obtained from the sulfate system are not suitable for use in the NSSC plant and must first be reprocessed at considerable cost. If the environmental protection regulations are so strict that the sulfur-free method must be used, then the NSSC method is in any case inappropriate.

The present invention provides a pulping process in which the chemical recovery is simple and the results obtained in terms of high yield, good color and sufficient strength properties are similar to those in the NSSC process.

Semi-chemical pulps can be prepared by the soda process using sodium hydroxide as the active pulp cooking chemical; however, this is often not used because the strength properties and color of the pulp are not as good as in the NSSC process, and the chemical costs are higher than when using sodium carbonate or sodium carbonate-sodium hydroxide in semi-chemical processes.

The importance of color cannot be overemphasized, as this factor prevents the use of semi-chemical soda-based pulps, for example, in the surface layer of paperboard and in packaging and wrapping papers.

One aspect of the present invention is the finding that the good color of the chemical or semi-chemical pulp depends on the high amount of residual alkali in the waste broth due to the high pH at the end of cooking 70439 in 3 stages. This is achieved by using an excessively strong alkali in the pulping process. It is already known that there is a relationship between good color and yield, but the present invention is based on the finding that using an excess of alkali gives a better color in equally good yield.

Similarly, in different yields, the lower yielding pulp may have similar color properties to the higher yielding pulp if an excess of alkali has been used in the production of the lower yielding pulp. Although excess alkali used causes high residual pH in buffered pulp cooking systems, large differences in alkali amounts do not necessarily cause changes in residual pH, especially if the pH is high. Previous processes using sodium sulfite, sodium carbonate or sodium carbonate-sodium hydroxide could not obtain a high residual pH, nor could high yield soda processes obtain a high residual pH because the first two cases do not use a sufficiently strong alkali, while the two in the latter, the amount of alkali is usually insufficient. This is especially true for high-yield or semi-chemical processes, where the aim has been to utilize the alkali used as accurately as possible, resulting in a low residual pH. The strong alkali used in excess in the present invention gives a high residual pH of 9-14, preferably 12-13.

It is an object of the present invention to provide a process for removing lignin from a lignocellulosic material, which process is characterized in that the lignocellulosic material is boiled with a pulping liquid containing mainly sodium, potassium, magnesium, calcium or ammonium hydroxide or carbonate and a hydroxide excess.

The method according to the invention can be used in both batch and continuous cookers and regardless of whether the latter operate in the same or opposite direction. The method is not limited to conventional cooking utensils, but can also be used for so-called "in explosive pulping, where chemically treated wood chips are defibrated by rapid or explosive reduction of pressure.

70439

The method is suitable for all types of wood, including both softwood and hardwood, as well as non-wood materials such as straw, bagasse, etc. When wood is used, it can be peeled or unpeeled and may contain branches, roots, twigs and leaves, such as so-called "Täyspuuhake".

Conventional semi-chemical soda processes generally use temperatures of 165-180 ° C, and the pH of the waste liquor is normally in the range of 9-10. Also disclosed in U.S. Patent No. 3,954,553, which discloses a process similar to conventional semi-chemical sulfite processes, sodium hydroxide and sodium carbonate are used and have a cooking temperature of 190 ° C.

According to another aspect of the present invention, it has been found that better pulp strength can be achieved by alkaline cooking at lower than normal temperatures. Thus, the invention provides a process for removing lignin from a lignocellulosic material, which process is characterized in that the lignocellulosic material is boiled with a pulping liquid containing mainly sodium, potassium, magnesium, calcium or ammonium hydroxide or carbonate at a temperature of up to 160 ° C.

In the process according to this aspect, the cooking temperatures can range from up to 160 ° C, although the preferred temperatures are above 100 ° C, and the most preferred temperature range is 210-150 ° C. There are many benefits to working at temperatures up to 160 ° C. An unexpected advantage is that the strength of the resulting mass is higher at lower temperatures. It has also been shown that in some cases a better color is obtained, and of course lower cooking temperatures generally mean energy savings. In a preferred form of the invention, the excess alkali used and the low cooking temperature are combined to give pulps with a high residual pH and good color and strength properties.

This method has been found to give masses with properties, including color, similar to those of an NSSC mass. Using the method, it has further been found that in a preferred embodiment of the invention, the cooking rate can be further accelerated, and thus either lower the reaction temperature or shorten the reaction time by adding small amounts of quinone or hydroquinone compounds to the chips or broth. Such additions can be made when the chips and / or the liquid are introduced into the digester, or as a separate pretreatment. The addition of quinone or hydroquinone compounds is particularly useful when low cooking temperatures are used, whereby the addition of these compounds and the low cooking temperature provide improved strength in a shorter cooking time.

Another advantage of using additives is the improved strength of the pulp produced. As can be seen from the examples, the strengths of the pulps prepared by the process of the invention are better than the strengths of the NSSC pulps obtained in the same yield.

Suitable quinone and hydroquinone compounds have been found to be anthraquinones (AQ) and anthrahydroquinones and their tautomers and derivatives, naphthoquinones and naphtho hydroquinones and their tautomers and derivatives and benzoquinones and benzohydroquinones and their tautomers and derivatives. Examples of tautomers of anthrahydroquinone are 10-hydroxyanthrone and 1,4-dihydroanthraquinone and, for example, a naphthohydroquinone derivative is 1,4,4a, 9a-tetrahydroanthraquinone. Such compounds are described in more detail in Applicant's respective Australian Patent Applications 25519/77 and PC 9939/77, which are incorporated herein by reference.

These compounds are preferably used in an amount of 0.001 to 1.0% by weight and most preferably 0.01 to 0.3% by weight of the dry wood used.

Since many of the preferred compounds are substantially insoluble in water, they are preferably used in finely divided form, i. ground into small particles. In some cases, it is preferable to use a dispersant or surfactant such as Teepol or Comprox (trademarks).

The treatment of the lignocellulosic raw material according to the invention with a quinone / hydroquinone compound or a tautomer thereof may vary according to the requirements of the method used in each case. For example, the quinone / hydroquinone compound or tautomer thereof may be present in the pretreatment liquid in which the lignocellulosic feedstock is dipped or impregnated prior to addition to the cooking liquor in the digester to complete lignin removal; or the compound may be premixed in the cooking liquid and lignocellulosic raw material before being added to the digester under various conditions; 70439 or the compound can be added directly to the cooking liquor and lignocellulosic raw material in the digester either in one portion or in several portions in different cooking steps or continuously throughout the cooking.

In practicing the process of the present invention, it may be advantageous to use more readily soluble hydroquinone compounds which can be formed in situ by reacting the corresponding quinone compounds with a reducing agent in a solution added to or to be used as a cooking liquid. Inorganic or organic reducing agents may be used, of which organic compounds or compositions are more preferable.

Suitable inorganic reducing agents for use include, for example, sodium or zinc dithionite (hydrosulfite), sodium borohydride or zinc powder, and sodium hydroxide. Preferred organic reducing agents include, for example, carbohydrates such as glucose, xylose, mannose and other monosaccharides, sucrose, cellobiose, maltose and other disaccharides, oligosaccharides such as raffinose, or polysaccharides such as starch, dextrin, dextrin. or xylan; amines or alkanolamines such as ethylenediamine or diethylenetriamine or ethanolamines; or aldehydes such as vanillin.

The reducing agent in the cooking liquid may sometimes evaporate or decompose during the cooking process, as a result of which the reducing effect is substantially reduced or completely eliminated. It has been found that in such cases it is advantageous to add the reducing agent in small amounts from time to time by injecting it with lignocellulose soups, whereby the amount of hydroquinone compound in the cooking liquid can be kept sufficient throughout the cooking.

The pretreatment of the cellulosic feedstock with a quenching fluid containing a quinone or hydroquinone compound to pre-impregnate the cellulosic feedstock with these compounds can be performed before the cellulosic feedstock is introduced into the digester to complete lignin removal. The purpose of this pretreatment or pre-cooking of the lignocellulosic raw material is to cause the quinone compound to better penetrate or diffuse into the lignocellulosic raw material before cooking the pulp in order to obtain the beneficial effect of the quinone or hydroquinone compound on the lignocellulosic raw material.

Such pretreatment or pre-cooking can be performed on the lignocellulosic feedstock according to one of the following methods (A), (B), (C) or (D): (A) the lignocellulosic feedstock is impregnated at normal pressure or positive pressure (hydraulically or pneumatically supplied) or negative pressure ( vacuum) with an alkaline solution of a quinone or hydroquinone compound at temperatures from room temperature to 120 ° C, which alkaline solution may be a normal cooking liquid or other liquid of suitable composition, which is removed after impregnation and replaced with a normal cooking liquid; or (B) increasing the time normally required to raise the temperature of the lignocellulosic feedstock and the cooking liquid containing the quinone or hydroquinone compound from room temperature to the maximum cooking temperature to a maximum of about 150 ° C; or (C) the cooking liquid containing the lignocellulosic raw material and the quinone or hydroquinone compound is maintained at a temperature in the range of 100 to 120 ° C for 15 to 60 minutes, after which the temperature is raised at a normal rate to a maximum cooking temperature of about 150 ° C; or (D) the spent or partially used cooking liquid from a previous cooking or one or more steps of a multi-stage process or at some point in a continuous cooking process, usually near the top of such a digester, is passed to a pre-impregnation step which can be performed either batchwise or continuously.

In step (A) above, the impregnation time may be up to one hour before the start of cooking, which can be carried out at a temperature of up to 150 ° C for 0.5 to 5 hours. In method (B), the extension time may be up to 2-3 hours before the start of the cooking process as in (A) above. In method (C), the time to reach a temperature of 100-120 ° C may be 0.5-2 hours, while the cooking time after a delay of 15-60 minutes at 100-120 ° C may be 0.5-5 hours as in the above method. (A). In some cases, the time required to reach the cooking temperature is sufficient to obtain a satisfactory pulp yield, so the cooking time required is 8 70439 in this case 0. The method (D) described above, which can improve the pulp quality by recycling the additive, is an economically advantageous use of additives.

When the conversion of an insoluble or sparingly soluble quinone compound to a hydroquinone compound is accomplished by reduction as generally described above, and when working at low liquid circulation rates, the surfactant added to the liquid may keep the compound suspended, more easily reduced to a hydroquinone compound, and the amount of cooked ingredients in the mass obtained.

In some cases, especially when using batch digesters, it is advantageous to work using higher than normal cooking liquid recirculation rates in the digester, e.g., by circulating the cooking liquid at a rate of up to 10: 1 compared to normal speed. Thus, when, under normal conditions, the circulation rate of the cooking liquid is 6-10 whole liquid cycles per hour, it has been found advantageous in the method according to the invention to use pumps in which the whole liquid is circulated 60-100 revolutions per hour. However, this is not essential in all cases, and excellent results can also be obtained at normal rotational speed.

The absence of sulfur in the process according to the invention not only means that the disgusting odor caused by sulfur-containing substances in the art collection system is avoided, but that a relatively simple recovery method can be used. Suitable methods include, in addition to the normal incineration method, fluidized bed incineration, wet incineration and in Australian patent application no. 73885/74 and in English patent publication no. Wet incineration and other processes mentioned in 1407272.

The practical examples shown in the following table illustrate a preferred method according to the invention. The table, drawings and further examples show the preferred methods according to the invention. In all cases, 4Q0 g of oven-dried (aperture or pine) was boiled in a rotary electrically heated cooker using a cooking liquid-wood ratio of 3.5: 1 and a heating time of 1.5 h from room temperature to cooking temperature. Other conditions are seen in the table and examples. The properties of the pulp were determined

II

9 70439 after grinding in Lampen Mill. The properties of pulps made from mixed species and Ash-type eucalyptus were evaluated at grinding levels of 400 and 200, respectively (Canadian Standard Freeness).

In Example 1, instead of NaOH solution, an NSSC cooking solution containing 9.8% sodium sulfite and 2.3% sodium bicarbonate from the amount of wood described in the furnace is used.

In the table and elsewhere in this application, color refers to the reflection coefficient of tristimulus green.

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The following comparison of the figures in the table illustrates the invention.

1. A comparison of Example 3 and Example 4 shows a clear effect of the excess alkali used on the color of the pulp. Example 3, where the residual pH is higher due to the excess alkali used, has a better color than Example 4.

2. A comparison of Example 3 and Example 5 confirms the effect of high residual pH. Example 3 (high pH) gives a much better color than Example 5 (low pH), although it has a slightly lower pulp yield.

3. A comparison of Example 6 and Example 8, on the other hand, shows that using a higher amount of alkali and thus a higher residual pH gives a better color, although the yield is lower. The differences in the measured pH values are not large at these alkali levels due to the buffering effect of the waste broth at the end of cooking, but Example 6 has a clearly higher alkali content than Example 8.

4. Example 6 together with Example 7 shows the combined effect of the increased amount of alkali and the reduced temperature (Example 6) with the same mass yield. No large color differences were expected because in both cases the residual pH is high, however, a clear difference can be observed.

5. Example 7 and Example 8 show the beneficial effect of lower cooking temperature on pulp strength. These pulps were boiled using the same amount of alkali at different temperatures, and although in Example 7 (150 ° C) the yield was lower, in Example 8 (140 ° C) the strength is higher. If the pulps are cooked at the same temperatures and otherwise under the same conditions, then the pulp with a lower yield will normally have a higher strength.

6. Example 8 together with Example 9 confirm this result. With the same pulp yield, pulp cooked at a lower temperature has (Example 8) a better strength.

7. A comparison of Example 5 and Example 14 shows an accelerating effect of anthra-quinone addition. Using the same amount of alkali and the same temperature, the yields were 69% with anthraquinone and 73% without anthraquinone. It should be noted that when anthraquinone is added, the cooking time is half the cooking time otherwise required.

8. Example 10 in conjunction with Example 11 shows an improvement in the color of the pulp 12 70439 using anthraquinone when the alkali charge and residual pH are increased and the yield and number of pieces are the same.

9. Example 10 together with Example 14 shows that under otherwise similar cooking conditions at a lower temperature a better color of the pulp is obtained with the same pulp yield. In Example 14, the residual pH is somewhat higher than in Example 10, but below pH 11, this should have little effect on color.

10. Example 2 and Examples 10 and 12 show clear improvements in pulp strength values obtained with anthraquinone addition.

11. Example 15 shows a preferred combination of pulp cooking with a high alkali charge and residual pH, low cooking temperature and anthraquinone addition. The obtained pulp has a very good color and high pulp strength values.

12. Comparing Example 7 to Examples 16 and 17, a significant increase in pulp strength achieved with anthraquinone is observed while the cooking speed is clearly increased.

The above table clearly shows the advantages obtainable by the method according to the invention. As noted above, one advantage is the light colored masses obtained when the residual pH is adjusted. The effect of pH on color is further illustrated in Figure 1, which shows the color of pulps produced at the same cooking temperatures and in similar yields as a function of residual pH. As the pH rises, the color improvement is clear. To date, the technical literature does not show a clear effect of the observed residual pH on the color of semi-chemical soda pulps.

Another advantage of the process according to the invention, which is clear from the examples, is the use of low cooking temperatures. With the process according to the invention, it is possible to use temperatures much lower than those used or considered practical in the production of semi-chemical pulps of the type described so far. The use of such low temperatures results not only in energy savings but also in an unexpected improvement in the strength of the paper made from the pulp (commonly referred to as pulp strength). This is also shown in Figure 2, where the puncture resistance is shown as a function of pulp yield at two different cooking temperatures.

13,, Λ 70439

When comparing 140 ° C cooking to 130 ° C cooking, an increase in the puncture index of 0.1-0.4 units is seen depending on the mass yield.

Figure 2

Examples 18 and 19 show the effect of anthrahydroquinone on pulp cooking. The results were generally similar to those obtained with anthra-quinone (Example 17).

Example 18

Semi-chemical soda cooking method using anthrahydroquinone

Ash-type aperture chips were boiled for 0.25 h at 150 ° C using 15% total sodium hydroxide and 0.1% anthrahydroquinone per kiln-described wood. Anthrahydroquinone was prepared by dissolving 0.4 g of anthraquinone in 200 ml of water containing 8.0 g of glucose and 30 g of sodium hydroxide and boiling the solution under nitrogen.

Total yield 72%

Chapter number Waste broth pH 12.9 Color 40

Puncture index 5.0 (kPa m ^ / g)

Breaking length 8.7

Example 19

Semi-chemical soda cooking method using anthrahydroquinone

The wood and cooking conditions were the same as in Example 18 except that anthrahydroquinone was prepared by dissolving 0.4 g of anthraquinone in 200 ml of water containing 0.5 g of sodium dithionite and 30 g of sodium hydroxide and boiling the solution under nitrogen.

Total yield 71%

Chapter 110 Waste broth pH 12.9 Color 41

Burst index (kPa m 2 / g) 5.2

Breaking length (km) 8.7 70439 14

Examples 20 and 21 show the effect of 10-hydroxyanthrone and 1,4-dihydroanthraquinone, both tautomers of anthrahydroquinone, on pulp cooking. These compounds are alkali soluble and are thought to be converted to anthrahydroquinone in alkaline solution. They are at least as effective as anthra-quinone (Example 12), and can be advantageously used when it is desired to use a soluble additive that can be easily impregnated into the wood before starting the pulp cooking.

Example 20

Semi-chemical soda mass cooking using 10-hydroxy anthrone

Chips from miscellaneous eucalyptus trees were cooked using 15% sodium hydroxide per oven dried wood and 0.1% 10-hydroxyanthrone per oven dried wood. The cooking time was 140 ° C for 1 h. Total yield 67%

Chapter number Waste liquor pH 12.0 Color 29

Example 21

Semi-chemical soda soup using 1,4-dihydroanthraquinone The wood and cooking method were the same as in Example 20. Total yield 65.5%

Chapter 121 Waste broth pH 12.1 Color 28

Example 22 illustrates 1,4,4a, 9a-tetrahydroanthraquinone using pulp cooking. This compound can be converted in alkaline solution to tautomeric 1,4-tetrahydroanthrahydroquinone, which can also be considered as substituted naphtho hydroquinone.

Example 22

Semi-chemical soda soup using 1,4,4a, 9a-tetrahydroanthraquinone

The wood and cooking conditions were the same as in Example 21. Total yield 65.1%

Chapter number Waste broth pH 12.0 Color 29

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70439 15

Examples 23 and 24 illustrate the application of the method of the invention to pine chips. The pulp prepared with a higher alkali charge and residual pH (Example 23) has a better color in the same yield.

Example 23 Example 24% sodium hydroxide 13% 11%

Cooking time 1.5 h 2.5 h

Yield 74.5% 75.1%

Chapter number 168 164 Residual pH 12.9 12.4 Color 35 30

Claims (6)

A method for removing lignin from a wood material to produce a cellulose pulp of improved color, wherein the wood material is boiled with a cooking liquid substantially free of sulfur-containing compounds and containing mainly sodium, potassium, magnesium and calcium hydroxide or carbonate and optionally quinone or hydroquinone , characterized in that hydroxide or carbonate is used in excess of the amount of lignocellulosic material to ensure that the pH of the waste liquor at the end of cooking is 12-13. Process according to Claim 1, characterized in that the cooking liquid contains mainly sodium hydroxide and / or sodium carbonate. Process according to Claim 1, characterized in that the cooking temperatures are 120 to 150 ° C. Process according to Claim 2 or 3, characterized in that hydroxide or carbonate is used in the cooking liquid in excess of the amount of lignocellulosic material. Process according to Claim 1 or 4, characterized in that a quinone or hydroquinone compound or a tautomer of such a compound is added in an amount of 0.01 to 0.3% by weight, based on the weight of the lignocellulosic material. Process according to Claim 5, characterized in that the additive is chosen from anthraquinones, anthrahydroquinones, naphthoquinones, naphtho hydroquinones, benzoquinones or benzohydroquinones.