FI56710C - REFERENCE TO A CELLULOSE MATERIAL IN THE MATERIALS OF AN ALKALIS OMGIVNING UNDER ANVAENDNING AV SYRE - Google Patents

Description

r01 .... ADVERTISEMENT v JXg ^ G lJ (11) UTLÄCGNINGSSKRIFT 56710 • SS? C (45) Patönit 1 issued 10 03 1930 uWgjy Patent oeddelat (51) Kv.lk. * / Lnt.CI. * D 21 C 3/02 D 21 <E 9/10 FINLAND — FI N LA ND (21) Patent application —Pit «nuns4knlnf 3013/7 ^ (22) Hakemlspllvl — AnsAknlngsdtg 15.10.7 ^

(23) Alkupilvl — Glltl | hetsdag 15.10.7U

(41) Became Public — Bllvit offentllg 19 · θ8 · 75

National Board of Patents and Registration of the Finnish Patent and Registration Office

(32) (33) (31) Privilege claimed— Begird prloritet 18.02.7U

Japan-Japan (JP) U9-19287 (71) Toyo Pulp Co., Ltd., No. 8-2, 1-chome, Marunouchi, Chiyoda-ku,

Tokyo, Japan-Japan (JP) (72) Tadashi Nagano, Tokyo, Saisei Miyao, Hiroshima-ken, Katsuhiko Takeda, Hiroshima-ken, Japan-Japan (JP) (7U) Berggren Oy Ab (5U) Method for delignification of cellulosic material in temporal under conditions of oxygen - Förfarande för delignifiering av cellulosahaltigt material i alkalisk omgivning under användning av syre

As is well known, an example of oxygen oxidative delignification in the pulp and paper industry has been oxygen bleaching, where delignification is performed at a pulp consistency of more than 18% by weight of the weight of the mixture of pulp and alkaline aqueous medium, in other words in the gas phase. The reason why such a high pulp consistency is necessary is that the degree of solubility of oxygen and solubility in alkaline liquid is low. Therefore, the pulp must be flocculated in a reaction vessel at a high pulp density to expand the surface area of the pulp and to obtain an alkaline liquid on the surface of the pulp fibers only in a thin layer. When oxygen gas is brought into contact with such flocculated pulp through a thin layer of alkaline liquid, delignification occurs efficiently.

In high-density delignification as described above, in a case where the amount of residual lignin is small, it is possible to control the process without risk of an explosion caused by heating due to lignin decomposition, if the reaction is carefully controlled, because the rate of exothermic lignin decomposition is not On the other hand it? to delignify high-yield pulps with a high lignin content, there is a high risk of explosion if standard monitoring equipment is used, because lignin generates a lot of heat when it decomposes. There are now essential basic solutions to this problem.

On the other hand, many studies have been performed on oxidative delignification at relatively low pulp densities, for example in the liquid phase. In general, oxidative delignification is considered to be a heterogeneous surface reaction in which the decomposition of lignin proceeds when the cellulosic substance is in contact with an alkaline liquid and oxygen. Therefore, contact and reaction conditions such as temperature, pressure, time, and alkali used have a significant effect on delignification, especially oxidative delignification in the liquid phase. Therefore, the selection of optimal conditions for delignification is so difficult that oxidative delignification in the liquid phase has not become a practical method ·

It is therefore an object of the present invention to provide a new method for delignifying cellulosic materials so that the disadvantages of previously used methods can be avoided and both high lignin pulp and also wood chips, as well as chemical pulp, can be efficiently delignified.

Another object of the present invention is to provide a new method for delignifying a cellulosic material without the risk of explosion due to heat generation due to lignin decomposition.

It is a further object of the present invention to provide a process for delignifying cellulose in which the contact between the cellulosic substance, the aqueous alkaline solution and oxygen is effectively effected, thereby providing efficient delignification and shortening the reaction time.

The present invention further relates to a novel process for delignifying cellulosic material in which high-yield pulp can be produced.

Referring to the invention, there is briefly provided a method of delignifying cellulosic material with oxygen and an alkaline liquid at elevated temperature in a pressurized reaction vessel, including dissolving oxygen in said alkali, contacting the cell with the consistency of said cellulosic material is maintained such that agglomerates of cellulosic material are formed and that the alkali liquid has no gas spaces, removing some or a substantial portion of the effluent from the vessel while simultaneously adding supplemental fresh oxygen-containing alkaline liquid to the vessel.

These and other advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which: Figure 1 is a schematic diagram of a preferred apparatus for carrying out the invention; and Fig. 2 is a graph showing the relationship between the reaction time and the Kappa number obtained with the pulp obtained by the process of the invention as well as the conventional process.

Many oxidative delignification methods have been studied which can be applied to cellulosic material using oxygen in the liquid phase at relatively low cellulosic material consistencies, 5 ~ 20%, providing a new and improved method for delignifying pulp of any lignin content and avoiding the above gas phase treatment. As a result of the study, the following information has been obtained: in the event that the cellulosic material is subjected to oxygen gas dissolution in the liquid phase.

1) The oxidative decomposition of lignin occurs very rapidly under temporal liquid conditions under certain temperature and pressure conditions, although the dissolution of oxygen-gas and the transition to alkaline solution is slow. Therefore, there is a lack of dissolved oxygen in the zone surrounding the reaction. Due to the depletion of oxygen, the reaction sought is slowed down. Therefore, in order to keep the reaction progressing rapidly, it is necessary to maintain a constant contact between the alkali solution containing dissolved oxygen and the cellulosic material.

2) On the other hand, the soluble salts of organic acids formed during the oxidative decomposition of lignin tend to accumulate in the intermediate layer of the cellulosic material and the alkali solution. This lowers the solubility of oxygen in the alkaline solution and adversely affects the reaction of oxygen with the cellulosic material under the influence of Donnan's film equilibrium. It is therefore advisable to remove such salts of organic acids, which are formed as a by-product, from the interlayer in order to achieve more efficient oxygen delignification.

The present invention is directed to the above areas for delignifying cellulosic material with oxygen in temporal aqueous solutions.

According to the present invention, oxygen is pre-dissolved in an aqueous alkaline solution and the waste alkali liquid is continuously removed by displacement with fresh alkaline liquid, thereby maintaining constant contact between the alkaline aqueous solution containing dissolved oxygen and the cellulosic material.

Further, in order to remove salts of organic acids from the intermediate layer, an oxygen-dissolved alkali solution is passed through a suspension, mat, layer or the like of the pulp or chips to disturb the so-called Donnan membrane equilibrium.

The consistency of the cellulosic material used in the present invention should be determined at values at which displacement of the alkaline liquid can easily occur. This means that it is necessary to select a consistency range where the accumulation of cellulosic material in the alkaline liquid retains its shape if it were a mat or layer or the like without the gas spaces contained therein. However, since the pulp fibers have a good affinity for water compared to non-fibrous cellulosic materials such as wood chips, the consistency of the cellulosic material becomes smaller when forming cellulosic material and alkaline liquid agglomerates as a nonwoven, fibrous layer or mattress than wood chips. Thus, the recommended consistency will vary depending on the cellulosic material used. In general, the consistency of the cellulosic material varies between 5-15% by weight of the cellulosic material and the alkaline liquid with chemical and semi-chemical pulps and between 10-20% with wood chips.

In the process of the present invention, the cellulosic material is treated at a relatively low consistency so that a large amount of medium is present which absorbs the heat of reaction formed. The absorbed heat 5 56710 is therefore always dissipated together with the medium which is continuously removed from the reaction vessel during delignification by displacing the medium. Accordingly, there can be no risk of explosion or overheating in the reaction vessel as is the case with delignification at high pulp densities.

Alkali chemicals such as sodium hydroxide, carbonate and bicarbonate can be used as the alkaline medium in the invention. However, it is more preferable to use sodium carbonate solution due to regeneration considerations when delignifying the defibrated material, where the penetration of alkali into the material is a small factor. On the other hand, sodium hydroxide is preferably used for wood chips, which require rapid and efficient alkali penetration into the chips.

It is preferred that the present invention significantly reduces the reaction time, so that when the process of the invention is applied to bleaching chemical pulp, bleaching is performed in about 10 minutes, while when applied to delignification of semi-chemical pulp or chips, delignification is achieved in about 20-40 minutes, which is relatively short. compared to previously implemented methods. A characteristic advantage of the invention is that benign pulp can be obtained, because the shorter the required reaction time, the less oxidative degradation of cellulose occurs.

As for the reaction temperature, it may generally be about 80 to 160 ° C, preferably 100 to 150 ° C, depending on the quality of the cellulosic material and also on the degree of delignification. The partial pressure of oxygen, where the oxygen is dissolved in the alkaline solution before being introduced into the reaction vessel, can be at least 4 kg / cm 2, and preferably more than 7 kg / cm if a high degree of delignification is desired.

Therefore, the total reaction pressure in delignification may be required to be greater than the oxygen partial pressure previously used to dissolve oxygen in an alkaline solution.

In carrying out the process of the present invention, either a continuous or batch process may be used. Figure 1 shows a schematic apparatus useful in implementing a preferred embodiment of the process of the invention, where delignification is performed continuously. The defibrated or non-defibrated cellulosic material is 56710 fed continuously to the pressurized reaction vessel 1 through its top. The alkaline solution to which the oxygen has previously been dissolved in the oxygen dissolution tank 2 is also continuously fed to a vessel whose pressure is adjusted to equal or greater than the partial pressure of oxygen in the oxygen dissolution tank through a central pipe 3 with a large number of openings or slits arranged longitudinally. The alkali solution containing dissolved oxygen is then applied radially from the central tube, across the cellulosic material fed to the reaction vessel. In this case, the contact between the cellulosic material and the alkali solution containing oxygen is good and delignification progresses during this contact. The waste liquor generated during delignification is continuously removed or extracted from the suction tubes 4 and 5 and at the same time a fresh oxygen-containing alkali solution is continuously added to the reaction vessel from the tank 2 via the central tube 3. The consistency of the cellulosic material in the reaction vessel is kept constant by controlling the amount of liquid added and waste liquor removed. The lignin content of the cellulosic material gradually decreases as the cellulosic material travels downward in the reaction vessel, thereby delignifying the pulp from the bottom of the vessel through the butt valve 6.

A portion of the waste liquor removed at a relatively early stage of delignification through the upper suction pipe 4 can be fed to a chemical recovery system (not shown). The alkaline chemical obtained from the regeneration can be led to the tank 2 for reuse. A second portion of the lye, which is removed at a later stage of delignification through the lower suction pipe 5, can be recycled to tank 2, where the lye is mixed with an aqueous alkali solution from regeneration and, if desired, additional solution and oxygen are dissolved in the stirred solution. The regenerated and re-used solution thus obtained is fed back into the reaction vessel and reused as an additional alkaline liquid containing oxygen.

This embodiment has two delignification steps, i.e., an earlier step and a latter step. However, it may be possible that other embodiments have multiple delignification steps. and a plurality of layers corresponding to different degrees of delignification of the delignification of the cellulosic material in the reaction vessel and separate removals of waste liquor from the reaction vessel for each layer. Using such a multilayer system, as described above, it is possible to use different alkalis and different pH with time solutions simultaneously in one reaction vessel 7 56710

For example, when wood chips are used as a cellulosic material in the process of the invention, it is recommended, to obtain good cellulose, to treat the chips with sodium hydroxide solution at relatively high pH in relatively early stages or layers in the vessel, and then sodium carbonate solution at low pH in subsequent stages or layers. . Furthermore, it may be possible to perform both delignification and washing of the pulp with hot water instead of an alkaline solution in the last step or layer in the vessel. When the lye extracted from the later steps is recycled, after the oxygen has been dissolved in it, at relatively early stages in the vessel, in this case, the process can be carried out countercurrently. When implementing such a countercurrent system, the total amount of alkali solution used is lower and the waste liquor has a correspondingly higher content of organic matter. This is recommended for chemical recovery.

The following examples are for illustration only.

Example 1

Unbleached sulphate pulp made from Douglas spruce with a Kappa number of 32.8 was treated by delignification according to the invention.

100 g of pulp was placed in the middle of an 8-liter autoclave by placing the pulp between two wire cloths so that the consistency of the pulp became approximately 7% when immersed in an alkaline solution.

An alkali solution containing sodium carbonate and sodium hydroxide (Na 2 CO 3 / NaOH = 4/1) and an alkali content of 5 g / l as sodium oxide was used as an alkali solution in cooking.

An alkaline solution previously dissolved in oxygen at an oxygen partial pressure of p 8 kp / cm was rapidly introduced and the autoclave was heated to 110 ° C. A freshly alkaline solution containing dissolved oxygen was then continuously fed into the thus filled vessel from the bottom of the vessel at a rate of 1 1 / minute for five minutes, while the excess overflow liquor was taken out of the top of the digester.

By this method, a portion of the alkaline cooking liquor was displaced during delignification with a fresh alkaline solution containing dissolved oxygen.

8 58710

The delignifrdtu pulp obtained had a Kappa number of 6.8 and a brightness of 46.7 (GE).

From the above results, it is apparent that the above treatment is well suited as a first step in a conventional bleaching process for bleaching sulphate pulp.

Example 2

Eykalyptus chips were boiled at 180 ° C for one hour in an alkaline solution of sodium carbonate in an amount of 15% by weight of wood oxide and then defibrated in a plate mill. The coarse pulp obtained had a Kappa number of 132 and a yield of 68.4%.

The crude mass was delignified in the same manner and under the same conditions as in Example 1, except using the following values:

Oxygen partial pressure = 12 kg / cm ^ Temperature = 140 ° C Reaction time = 10 minutes

Magnesium carbonate was added to the alkaline cooking liquid to a concentration of 0.1 g / l.

For comparison, the same chips were delignified by the conventional sulfate method under the following conditions:

Alkaline dose - 22% Na 2 O from wood Sulfidity = 31.6

Time to maximum temperature = 70 minutes Time to maximum temperature = 60 minutes Wood-liquid ratio = 1: 5

The comparison results of the pulp obtained by the process according to the invention and the pulp obtained by the sulphate process are shown in the following table.

Screened Kappa- Brightness Breakage + Breakout + Tear yield% number length, km factor multiplier +

Pulp according to the invention 47.7 7.6 50.2 6.53 5.46 116

Sulphated pulp 42.6 10.6 29.5 5.74 5.74 115 (+ PFI milling 400 ml freenes) 9,56710

As can be seen from the table, the quality of the pulp according to the invention is better than that of sulphate pulp in terms of yield and whiteness and equal in terms of physical properties such as burst length burst and tear.

Example 3

The crude pulp with a Kappa number of 126 was prepared from hardwood chips by cooking the chips with sodium carbonate and defibrating the softened chips in a yield of 69.5% - The crude pulp thus obtained was delignified in the same manner and under the same conditions as in Example 1 using the following values: 2

Partial oxygen pressure = 12 kg / cm Temperature = 140 ° C

The relationship between the kappa number and the reaction time on the thus delignified pulp is shown by curve A in Figure 2.

As a comparative experiment, delignification was performed in the same manner and under the same conditions as above, except using an alkaline solution in which oxygen had not been previously dissolved and blowing oxygen gas 2 directly into the vessel with an oxygen partial mass of 12 kg / cm. The relationship obtained is also shown by curve B in Figure 2.

From these two curves, it is evident that more than 80% delignification was achieved in five minutes in case A, where oxygen had been dissolved in advance. On the other hand, the same delignification as in A was not achieved in B after another 30 minutes, in which case oxygen gas was added directly to the vessel.

Example 4

The shredded Douglas spruce chips were boiled at 170 ° C for 30 minutes in an alkaline solution of sodium hydroxide and 15% by weight of wood, calculated as sodium oxide, to give a non-fibrous material with a Kappa number of 128 and a yield of 62.8%.

The non-fibrous material thus prepared was then delignified in the same manner and under the same conditions as in Example 1, applying the following values: 10 56710

Consistency of cellulosic material = 10%. p

Oxygen partial pressure = 12 kg / cm Temperature = 150 ° C Alkaline solution

First 10 minutes = sodium hydroxide solution After 10 minutes = mixture of sodium carbonate and sodium hydroxide (NagCO 2 / NaOH = 4/1)

The following results were obtained:

Screened yield 44.2%

Rejects 0%

Kappa number 18.2%

Brightness 38.2 (GE)

As can be seen from the above processes and examples, the present invention provides an efficient method for delignifying any cellulosic material, such as chemical pulp, semi-chemical pulp, and wood chips. It will be appreciated that numerous changes may be made in the details, apparatus, materials and methods in relation to what is set forth herein to determine the nature of the invention, without departing from the scope of the invention.

Claims (13)

1. A process for delignifying cellulose material with oxygen in the presence of an alkaline aqueous medium in a pressurized reaction vessel by introducing oxygen and the aqueous alkaline medium into the vessel, withdrawing effluent from the vessel during delignification, and re-using the effluent after concentration, characterized oxygen is dissolved in fresh alkaline aqueous medium before being introduced into the vessel, whereupon the dissolved oxygen-containing alkaline aqueous medium is continuously fed into a cellulose material and the aqueous alkaline medium formed in the reaction vessel for oxidizing delignification of the cellular acid, said cellulose material, said cellulose that upon delignification, effluent generated is continuously removed from the vessel, while fresh, dissolved oxygen containing alkaline aqueous medium is continuously fed into the vessel, as a result of which effluent is continuously displaced with fresh, dissolved oxygen containing an alkaline aqueous medium during the process of delignification, and that all the oxygen required for the delignification is supplied to the pressurized vessel with said dissolved oxygen containing alkaline aqueous medium. 2. A process according to claim 1, characterized in that said cellulose material consists of unbleached chemical pulp with relatively low lignin content. 3. A process according to claim 1, characterized in that said cellulose material is a semi-chemical pulp with a relatively high lignin content. Method according to claim 1, characterized in that said cellulose material is made of wood chips. Process according to claim 1, characterized in that said cellulosic material has a concentration of about 5 to 15% by weight of the mixture of the cellulosic material and the alkali solution, and that the cellulosic material consists of unbleached chemical pulp or semi-chemical pulp. Method according to claim 1, characterized in that said cellulose material has a concentration of approximately 10-20% by weight based on the weight of the mixture of cellulose material and alkali solution, and that the cellulose material is wood chips.