FI67104B - OIL ALKALISK SULFIT SULPHIDE COCKTAIL FOR FRAMSTAELLNING AV MASS FOR LIGNUM CELLULOSE FLOWER MATERIAL - Google Patents

Description

67104

The present invention relates to a process for the production of pulp from a lignin-containing wood raw material according to the preamble of claim 1 to 5. The present invention relates to a process for producing pulp from a lignin-containing wood raw material according to the preamble of claim 1.

Such a process generally involves breaking down the cellulosic feedstock into chips, pretreating it, cooking the chips in an alkaline sulfite-sulfide broth, and grinding the delignified fibrous material to a suitable permeability.

The invention also relates to the composition of the alkaline sulphite-sulphide cooking broth used in such a process.

15 Industrially implemented cellulose broths are known to require technical functionality and economic viability. The most important technical goals are high yields, short cooking times and the fact that the mass produced has good optical and mechanical properties.

20 Economic profitability requires, among other things, that the investment costs arising from the equipment solutions required by the process are as low as possible and that the raw materials used in the process are cheap. It is precisely the high investment costs that currently weigh on sulphate processes, which are the most common cooking process, which is why efforts have been made to find alternative, especially alkaline, cooking processes in recent decades. The oldest and most widely used of these processes is the so-called neutral sulphite method (NSSC), in which sodium sulphite is used as the cooking chemical and in which sodium carbonate and bicarbonate are added to the broth to adjust the pH. The NSSC process is generally implemented as a semi-chemical process, i.e., a process in which the chemical treatment of a raw material is combined with its mechanical treatment to obtain a pulp having the desired properties. Hard wood grades such as birch are used as raw material for this process and have been found to be poorly suited for softwood lignin removal.

The so-called alkaline sulphite process, which is described, for example, in U.S. Pat. No. 3,630,832, is better suited for the treatment of softwood raw material than the neutral sulphite process.

5 It uses sodium sulphite and sodium hydroxide as cooking chemicals. However, lignin removal in this process is not as rapid as in the sulfate process, and other disadvantages of the process include high cooking chemical concentration, difficulty in recovering chemicals, and low yields. Recovery systems combine the complexity of sodium recovery with the causticization required for alkali recovery and the combustion of soda ash.

However, the alkaline sulphite process offers the possibility of producing an easy-to-bleach pulp with good strength properties, which is why efforts have been made to develop it with various modifications.

Some publications have suggested the use of sulphide in alkaline sulphite cooking, thus obtaining a sulphite-sulphide broth in which the active chemicals of a conventional sulphite and sulphate soup are present simultaneously. In his article (TAPPI 53 (1970) No. 8, pp. 11 + 51-1 ^ 57), Shick proposes the addition of sulphide or hydrosulphide to ordinary neutral sulphite cooking broth, whereby a pulp with better properties than the corresponding pulp prepared by the sulphate process can be obtained.

Hinrichs has studied the simultaneous use of sulphite and sulphide as cooking chemicals (Svensk Papperstidning 73 (1970) No. 5, pp. 122-131 *, TAPPI 5 ^ (1971) No. 7, pp. 1105 "1113) and found that the maximum a strength mass of 30 is obtained when sulfite is present in the broth 28 # and sulfide 12 # by weight of dry wood.He also notes that other additives such as hydroxide and carbonate have a detrimental effect on the properties of the pulp.

Pulps made by sulphite-sulphide soups invariably have better strength properties than pulps produced by sulphate, soda, alkali sulphite and sulphide processes. They are also easier to bleach.

However, the sulfite-sulfide processes proposed above have not yet been implemented e.g. due to the following drawbacks which make their application on an industrial scale difficult: 1) The methods require high concentrations of cooking chemicals in order to produce a pulp that meets the quality requirements.

2) Cooking chemicals must be introduced into the solution as pure substances. It has been found that recycled chemicals cannot be used, but that they inhibit the cooking process. This factor, of course, further increases the cost of chemicals.

3) Recovery of chemicals requires expensive and complex equipment.

In addition to the above, it would be desirable to be able to use carbonate in the broth as well, as it has a known effect of reducing the stick content of the pulp.

Several publications have suggested the use of additives in alkaline cooking processes to speed up cooking and increase yield. Among these additives, mention may be made, for example, of polysulphides and borohydrides. However, they are so expensive that the economic benefits of using them have been quite questionable. Quinone, hydroquinone and anthraquinone and related quinones and their derivatives have proven to be quite promising additives in recent years. It has been shown that in basic cooking liquors, the end groups of cellulose molecules oxidize to aldonic acids and thus stabilize the polysaccharides against hydrolysis, while maintaining a high degree of cellulose polymerization. They also speed up the removal of lignin, thus shortening the cooking time.

35 Kettunen et al. have studied the use of anthraquinone and the like in the alkaline sulphite soup of U.S. Pat. No. 3,630-32 and found that it accelerates cooking and reduces the amount of cooking chemicals required by 15-30 ° (Paper and Wood 61 (1979) No. 11, p. 685 (5,700). The recovery of cooking chemicals was also facilitated. However, the process they propose is slower than the ordinary sulphate process, its yield is low and the pulp produced with it has poor brightness. The investment costs associated with carrying out the process are not less than the costs of the sul-10 fate process.

As can be seen from the above, the current cellulose cooking processes do not meet the criteria for an industrial process set out at the outset.

It is an object of the present invention to provide a process in which the pulp is prepared by alkaline sulphite-sulphide cooking. The process according to the invention makes it possible to eliminate both the technical and economic disadvantages of previous processes and to provide an alkaline sulphite-sulphide cooking process which is economically viable and industrially feasible and which has good strength properties, low stick content and good brightness.

Upon closer examination of the simultaneous use of sulphite and sulphide as cooking chemicals, it has been possible to establish e.g. the following: The formation of thiosulphate in the broth occurs as a result of a reduction reaction in which sugars or organic acids are oxidized by sulphite, whereby the sulphite is reduced to thiosulphate (reaction 1).

30 2HSO ~ + HCOOH -> S ^ 2 '+ CO2 + 2H2O (1)

Thiosulfite is also formed by the reaction of sulfite with dissolved sulfide (hydrosulfide).

35 H HaHSO 3 + 2 NaHS -> 3 NagS ^ + 3 HgO (2) δ 67104

Thiosulfate has been found to have several adverse effects in cooking broth, including the following: Thiosulfate reacts with sulfite to reduce the amount of effective sulfite to form inert sulfate, which reduces cooking efficiency, according to the following reaction: 5 S2032 "+ k HS03" + 6 H + —- > 6 S2032 "+ 2 SO ^ 2" + 8 H + + H 2 O (3)

Thiosulfate also causes condensation of dissolved lignin, which increases the viscosity of the waste liquor and makes it difficult to handle. The reaction of thiosulphate with lignin easily results in a so-called black soup.

It has been found that the above factors tend to increase the total amount of Kemi-15 cabbages required in sulfite-sulfide cooking and thus increase the cost of chemicals and make their recovery more difficult.

The present invention is based on the fact that anthraquinone and the corresponding oxidation-reduction catalysts added to sulfite-sulfide soup have been found to have a completely new and surprising effect, which significantly improves the technical functionality of the process and its economic profitability.

It has been found that the above-mentioned formation of thiosulfate from bisulfite and sulfite (reaction 2) does not occur under alkaline conditions if an oxidation-reduced s-catalyst such as e s im is present in the cooking solution. ..ant ra-quinonia. Apparently, thiosulphate is not formed as a result of the reduction of organic substances, respectively (reaction 1), and thus there is no danger of the cooking being interrupted or of the so-called black cooking.

On the other hand, it has been found that sulphite-sulphide soups containing anthraquinone or the like do not necessarily use pure chemicals, but e.g. sulphide can be introduced into the broth as a white liquor obtained from the Kemi-35 cabbage cycle of sulphate soup, At the same time, the white liquor replaces some of the NaOH needed to adjust the pH of the solution to a clearly alkaline value of 9 to 13.0, which has been found to be the most preferred pH range for sulfite-sulfide cooking.

5 Due to the protective effect of anthraquinone and similar compounds, carbonate, which is known to have a stick-reducing effect, can now also be added to cooking broth as cooking chemicals. The polyra-difference-reducing effect of the carbonate carbohydrates, which is usually observed as a reduction in the tear and tensile strength of the pulp, is not apparent due to said additives.

In the alkaline sulphite-sulphide cooking broth according to the invention, alkali sulphite, alkali sulphide, alkali carbonate and alkali hydroxide are also used simultaneously as cooking chemicals, as well as quinone derivatives which also act as oxidation-reduction catalysts.

More specifically, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1.

The composition of the broth according to the invention is in turn characterized by what is set forth in the characterizing part of claim 2.

The cooking chemicals used in the process affect the wood raw material as follows: 25 - Alkali sulphite sulphonates the lignin and promotes its dissolution.

Alkali sulfide keeps the molecular weight of dissolved lignin low and prevents it from condensing. Alkali carbonate lowers the stick content.

30 - The oxidation-reduction catalyst prevents the hydrolysis of wood and promotes delignification. At the same time, it prevents the formation of thiosulfate. Alkali hydroxide is present in the cooking broth to adjust the pH to clearly alkaline.

The simultaneous use of alkali sulphite, sulphide and oxidation-reduction catalyst 7 67104 significantly contributes to the dissolution of lignin, thus speeding up the cooking process.

The overall economy of alkaline pulp production is improved by the process according to the invention due to the following positive features:

The required sodium sulfide is introduced into the broth as a white liquor, which at the same time replaces part of the hydroxide and is more advantageous to use than pure chemicals, thus reducing the total cost of the cooking solution.

The treatment of the resulting waste liquor is substantially facilitated. It has been found that the waste liquors obtained from the process according to the invention can be concentrated in a multi-stage evaporator to a dry matter content of at least 65% and generally up to 60%. Only certain effluents can be concentrated to a dry matter content of 6θ-62/6: η. This fact greatly improves the stability of the soda combustion and facilitates the treatment of the waste liquor and the recovery of the chemicals.

The same recovery and regeneration systems as for sulphate processes can be used. It has therefore been found that it is most economically viable to place the process operating according to this method in conjunction with a conventional sulphate process, in which case the same recovery and regeneration systems can be used in both processes. This, of course, means a significant reduction in investment costs.

The following examples illustrate the invention:

Example 1 (Soup A) 2

In a factory digester with a capacity of 300 m, βθ t (abs. Dry) spruce chips were packed with steam. The digester 8 67104 was then charged with an alkaline sulphite cooking solution to which white liquor from the chemical cycle of the sulphate plant had been added so that the total chemical dose was 17 # Na 2 O based on wood. The digester temperature was raised to 188 ° C in 5 120 minutes using indirect heating connected to the digester forced circulation. The temperature was maintained at 168 ° C for 300 minutes to ensure that all active chemical had reacted. The composition of the cooking solution as well as the properties of the pulp are shown in Table 1 below. After cooking, the pulps were sampled to determine the number of pieces, the stick content with a laboratory sorter with a slit plate and the brightness.

Example 2 (Soup B) 15

Using the embodiment and apparatus of Example 1 and the same spruce chip, cooking was performed with a Na sulfite / Na hydroxide solution supplemented with 0.50 g / l anthraquinone as a catalyst.

20

Example 3 (soups C, D and E)

Using the procedure, apparatus and the same six chips of Example 1, cooking C was performed. Anthraquinone was added to cooking solution 25 before the addition of the sodium sulfide-containing white liquor so that after the addition of the white liquor, the AQ content of the finished cooking solution was as shown in Table 1.

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Claims (2)

10 67104 A process for preparing pulp from a lignin-containing cellulosic raw material, in particular wood raw material 5, which process comprises: - decomposing the cellulosic raw material into chips, - treating the chips into a suitable raw material for cooking, - U00 g sodium sulphite / kg dry wood, 35 to 110 g sodium sulphide / kg dry wood, 20 to 150 g sodium carbonate / kg dry wood and the quantity required. Sodium hydroxide to raise the pH of the broth to 9 to 13, add 0,05 - 0.3j of anthraquinone to the amount of wood to speed up cooking, reduce the concentration of cooking chemicals and prevent the formation of thiosulphate, and 20. the delignified fibrous substance is ground to a suitable permeability, characterized in that sodium 2. Alkaline sulphite-sulphide cooking broth for the removal of lignin from cellulose raw material, in particular wood raw material, which broth contains: - 70 to 1 * 00 g of sodium sulphite / kg of dry wood ,. - 35 to 110 g of sodium sulphide / kg of dry wood, 30 to 20 to 150 g of sodium carbonate / kg of dry wood, - the amount of sodium hydroxide required to raise the pH of the broth to 9 ~ 13 and - 0,05 to 0,3ί of anthraquinone or a derivative thereof for accelerating cooking, lowering the concentration of cooking chemicals and preventing the formation of thiosulfate, characterized in that sodium sulfide and at least part of sodium hydroxide are added to the broth in the form of white liquor 5 obtained from the chemical cycle of the sulphate process.