DE2450608A1 - METHOD OF DELIGNIFICATION OF CELLULOSE MATERIAL IN ALKALINE MEDIUM USING OXYGEN - Google Patents

Description

Dr. F. Zunriötöln & β <ι. - Dr, E. Assmann Dr. R. Koenlgsberger - Dlpl.-Phys. R. Holzbauer - Dr. F. Zumsteln Jun.

PATENT LAWYERS

TELEPHONE: COLLECTIVE NO. 22 53 41 β M Ü N C H E N 2. TELEX 529979 BRÄUHAUSSTRASSE 4 TELEGRAMS: ZUMPAT CHECK ACCOUNT: MUNICH 91139-809, BLZ 700 100 80 BANK ACCOUNT: BANKHAUS H. AUFHÄUSER

ACCOUNT NO. 397997, bank code 70030600

97 / n '.

Case 156

TOYO PULP CO., LTD., Tokyo / Japan

Process for the delignification of cellulose material in an alkaline medium using oxygen

The invention relates to an improved method for delignification or lignin destruction of cellulose materials using an oxidative reaction with oxygen in the presence an alkaline aqueous medium. In particular, the invention relates to a new method for delignifying cellulosic materials, in which a high delignification is achieved within a short time and not just chemical pulp and pulp of semi-chemical quality can be bleached, but wood chips can also be converted into pulp.

An example of the application of oxidative delignification with oxygen in the pulp and paper industry is known to be bleaching with oxygen, with delignification with a pulp consistency or with a pulp content of more than about 18% by weight, based on the mixture of pulp and an alkaline aqueous medium, i.e. in the vapor phase.

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The reason why such a high pulp consistency is necessary is that the solubility level and the Dissolution rates of oxygen in an alkaline aqueous medium are small. Because of this, the pulp should fluffed in the reaction vessel at a high pulp consistency to increase the surface area of the pulp and to allow the alkaline aqueous medium to be thin around the surface of the pulp fiber Layer is present. By contacting oxygen gas with such fluffed pulp runs through the thin layer of the aqueous alkaline medium effectively abolishes delignification. With such a delignification with a high pulp consistency, as described above In the event that the residual lignin in the pulp is low, the system can be used without the risk of explosion Safe to operate due to the heat generated during lignin degradation if the reaction is carefully controlled is, because in this · case 'the exothermic reaction of lignin degradation is not violent by oxygen. In the case of delignification of high yield pulp with high In the lignin content, on the other hand, there is a high risk of explosion due to the heat generated by lignin degradation when making use of the control method in use. It is therefore essential to have some to get fundamental solutions to this problem.

On the other hand, many studies have been carried out on oxidative delignification with a relatively low pulp consistency, i.e. in the liquid phase. In general, oxidative delignification is seen as a heterogeneous surface reaction viewed in which the degradation of lignin through contact with cellulosic materials. alkaline aqueous medium and oxygen is draining. Hence, practice the bringing-in-contact conditions and the reaction conditions such as reaction temperature, pressure, time and type of used Alkalis have a significant influence on delignification, in particular on oxidative delignification in liquid Phase. For this reason, the choice of the optimal

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conditions for delignification so difficult that oxidative Liquid phase delignification has never been fully used in practice until now.

It is therefore an object of the invention to provide a new method for delignifying cellulosic materials, in which the above-described disadvantages of the prior art are overcome and a pulp with high lignin content and also wood chips and chemical pulp can be effectively delignified.

Another object of the invention is to provide a new method for delignifying cellulosic materials, in which there is a risk of explosion due to the build-up of heat the degradation of lignin is significantly reduced.

Another object of the invention is to provide a new process for the delignification of cellulosic materials, in which the contact of cellulosic materials, alkaline aqueous medium and oxygen is made effective to perform an effective delignification and to reduce the response time considerably.

Another one. The aim of the invention is to provide a new method for the delignification of cellulosic materials, after which pulp of high quality can be produced.

Briefly, a method for delignification is provided according to the invention of cellulosic materials with oxygen in the presence of an alkaline aqueous medium at an increased Temperature created in a pressure reaction vessel, 'which comprises that the oxygen containing the dissolved oxygen is dissolved beforehand or initially in the alkaline aqueous medium alkaline medium contacted with the cellulose materials in the reaction vessel in order to achieve the oxidative delignification of the cellulosic materials to be carried out, the consistency of the cellulosic materials being kept so that agglomeration of cellulose materials is formed and the alkali

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Lische aqueous medium has no gas space therein, one part or a substantial part of the during the The waste liquid formed by delignification is drained from the vessel while the fresh one is added or added alkaline aqueous medium containing dissolved oxygen is introduced into the vessel, thereby displacing the waste liquid by the fresh, dissolved oxygen-containing aqueous medium continuously throughout the delignification is carried out or operated.

The foregoing objects and features of the present invention will become apparent from the following description in conjunction with the drawing, in which

Fig. 1 schematically illustrates the apparatus used in a preferred embodiment of the invention and

Fig. 2 is a diagram showing the relationship between the reaction times and the kappa numbers of the pulp obtained according to the invention and by a conventional method.

To provide a new and improved process whereby pulp of any lignin content can be delignified and the above-mentioned problem of vapor phase treatment can be eliminated have been made by the applicant various methods of oxidative delignification of cellulose materials with oxygen in the liquid phase at a comparatively low consistency of cellulosic materials of about 5 to about 20% by weight, based on the mixture of cellulosic materials and the alkaline aqueous medium, investigated. As a result of this investigation was found for the delignification of cellulose materials with oxygen in the liquid phase:

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Ι) The oxidative degradation of lignin takes place in alkaline water Medium under certain temperature and pressure conditions. decreases very quickly, while the resolution and transfer or Transfer rate of oxygen gas in the alkaline aqueous medium are low. For this reason it is subject the ambient zone of the reaction continuously or constantly a "lack of dissolved oxygen" · Because of this "oxygen starvation", the Delayed response. In order for the reaction to proceed quickly, it is therefore necessary to have constant contact between the dissolved oxygen-containing alkaline aqueous medium and the cellulosic materials.

2) On the other hand, soluble salts of organic acids, which are formed by the oxidative breakdown of lignin, tend to accumulate in the intermediate layer between the alkaline aqueous medium and the cellulosic materials. Not only does this decrease the solubility of oxygen in the alkaline medium, but also adversely affects the Kgntakt reaction of oxygen with the cellulosic materials due to a kind of Donnan membrane equilibrium. It is therefore preferred to use such salts of organic pigments, Ren, which arise as by-products, for an effective delignification with oxygen from the intermediate layer remove. -

The present invention is based on the above findings regarding the delignification of cellulosic materials with oxygen in an alkaline aqueous medium.

According to the invention, oxygen is first or beforehand dissolved in the alkaline aqueous medium, and the waste alkaline medium Medium or the used alkaline medium is continuously replaced by a fresh, dissolved oxygen-containing medium displaced, whereby a constant contact of the dissolved oxygen-containing alkaline aqueous medium with the Cellulosic materials is maintained.

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To further remove the salts of organic acids from the intermediate layer the alkaline medium, which contains dissolved oxygen, is removed by the pulp or cossette suspension, -Mat, -layer or the like conducted, whereby the so-called Donnan membrane equilibrium breaks down.

The consistency of the cellulose materials to be used according to the invention should be in the range in which the alkaline medium can easily be displaced. That is, it is necessary to select a range of consistency in which the agglomeration of the cellulosic materials in the alkaline medium retains its shape as if it were a mat or a layer or the like without any gas space therein. However, since pulp fibers have a good affinity for water compared to non-defibrated cellulosic materials such as wood chips, the consistency of pulp-like materials for forming the agglomeration of cellulosic materials and alkaline medium as a fiber mat, layer or bed is lower than that from or for wood chips. Thus, the preferred consistency will vary depending on the cellulosic materials used. In general, a cellulosic consistency of from about 5 to about 15% by weight based on the mixture of cellulosic materials and alkaline aqueous medium is preferred for chemical and semi-chemical grade pulp and from about 10 to about 20% for wood chips.

According to the method of the invention, cellulosic materials are treated at a relatively low consistency, so that there is a lot of medium to absorb the heat of reaction generated. The absorbed heat is therefore always along with the medium, which is continuously drained from the reaction vessel during the entire delignification by medium displacement is discharged. As a result, there is no risk of explosion or overheating in the reaction vessel as in Case of delignification of high consistency pulp.

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According to the invention, alkaline chemicals, such as sodium hydroxide, carbonate and bicarbonate, can be used as the alkaline medium be used. However, it is preferable from the viewpoint of recovery in the case of delignification of the frayed Materials wherein the rate of alkali penetration into the materials is a small factor, a sodium carbonate solution to use. On the other hand is sodium hydroxide Applied to wood chips where rapid and effective penetration of the alkaline medium in the schnitzel is necessary.

It is advantageous that according to the method of the invention the reaction time is significantly reduced, so that when the present invention is applied to the bleaching of a chemical Pulp is applied, the bleaching can be accomplished within 10 minutes while, applied to delignification of pulp of semi-braid quality or of Schnitzel materials, the delignification is achieved in about 20 to about 40 minutes, which is quite a short time compared to the prior art methods. Another advantage of the invention is that a Good quality pulp can be obtained because the oxidative degradation of cellulose fibers, the less the shorter the required response time.

The reaction temperature can generally be about 80 to 160 ° C, preferably about 100 to 150 ° C, depending on the type the cellulosic materials and the degree of delignification. The partial pressure of oxygen under the oxygen in the alkaline aqueous medium prior to admission Dissolved into the reaction vessel can be at least about 4 kg / cm, and preferably more than about 7 kg / cm, if a high level of delignification is desired.

It may therefore be necessary that the overall reaction ■ pressure during delignification more than the partial pressure of oxygen, previously used to dissolve oxygen in the alkaline aqueous medium is.

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When carrying out the method according to the invention, both a continuous as well as a batch system can be used. Fig. 1 shows schematically a device, which is suitable for a preferred embodiment of the method according to the invention in which the delignification is continuous is carried out. Defibrated or non-defibrated cellulosic materials are continuously fed into a pressure reaction vessel 1 introduced from the upper part of the same. The alkaline aqueous medium in which oxygen previously in one Oxygen dissolving tank 2 has been dissolved also becomes continuous into the vessel, its pressure at the same pressure or at a pressure higher than the partial oxygen pressure is held in the oxygen dissolution tank, inserted through a central tube 3, which has a plurality of holes or gaps arranged lengthwise on the surface thereof. Containing dissolved oxygen alkaline aqueous medium is then passed radially through the central tube over the cellulosic materials that are in the vessel were introduced, distributed. This is how the cellulosic materials come into contact with the dissolved oxygen alkaline aqueous medium and the delignification process occurs during this contact. The during Waste liquid formed during the delignification is continuously drained or drawn off through suction pipes 4 and 5 or extracted, and at the same time supplementary fresh alkaline aqueous medium containing dissolved oxygen, continuously introduced or charged into the vessel from the tank 2 through the central pipe 3. The consistency of the Cellulosic materials in the reaction vessel is controlled by controlling the volume of the medium fed through the tube 3 and the waste liquid withdrawn through the pipes 4 and 5 kept constant. The lignin content of the cellulosic materials gradually increases with the migration of the cellulosic materials downward in the reaction vessel, and so the delignified pulp obtained is discharged from the lower part of the vessel taken through a blow valve 6.

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Part of the waste liquid that is from the relatively initial or earlier stage of delignification is taken through the upper suction pipe, can be transferred to a chemical recovery system (not shown) are transferred. The alkaline chemical obtained with the help of the recovery system can dem Tank 2 can be returned for reuse. Another part of the fluid produced by the later stage of delignification is drained through the lower suction pipe 5, can be recycled to the tank 2, where the liquid with the alkaline aqueous solution obtained from the recovery system and, if desired, mixed with fresh solution and oxygen is thoroughly dissolved under pressure in the mixed solution. The regenerated or retreated Solution thus obtained is reintroduced into the reaction vessel and reused as a supplemental fresh alkaline aqueous medium containing dissolved oxygen.

In this embodiment, there were two stages of delignification considered, namely an earlier stage and a later stage. However, it may be possible in another embodiment multiple multiple stages of delignification to consider and multiple multiple layers differentiated Correspond to degrees of delignification of the cellulose materials in the reaction vessel by removing the To get waste liquid from each layer in the reaction vessel. By using one described above Multi-layer system, it is possible to use different types of alkali and different p "values of the alkaline aqueous medium to use simultaneously in a single reaction vessel.

For example, when wood chips are used as cellulosic materials in the invention Method used, it is preferred, in order to obtain a good quality pulp, the wood chips with a sodium hydroxide solution of. relatively high p "value in the relatively initial stages or layers in the vessel to treat and then with a sodium carbonate solution of

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low ρ - value in the later stages or layers, where delignification has progressed to some extent. It may also be possible both the delignification of the cellulose materials and the washing of the pulp obtained in a vessel Treatment of the pulp obtained with hot water instead of the alkaline aqueous solution in the final stage or -Layer to carry out in the vessel. When the fluid withdrawn from the later stages of delignification after the thorough dissolution of oxygen therein is recirculated to the relatively initial or early stages in the vessel the process can be carried out in a countercurrent on this occasion. By using such a countercurrent system, the total volume of the alkaline aqueous medium used is kept small, and consequently, a waste liquid having a higher concentration of organic substances is obtained. This is preferred from the standpoint of chemical recovery.

The following examples illustrate the invention without restricting it.

example 1

Unbleached Kraft pulp made from Douglas fir (douglas fir) with a kappa number of 32.8 was used for delignification treated according to the invention.

100 g of the pulp were placed in the middle of an 8 liter autoclave brought by fastening between two wire mesh plates, so that a pulp consistency between two wire mesh plates of about 7% by weight is obtained when placed in an alkaline one aqueous medium is immersed.

The alkaline solution containing sodium carbonate and sodium hydroxide (Na ₂ CO ₃ / NaOH = 4 / l) and having an alkali concentration of 5 g / l as sodium oxide was used as an alkaline medium for cooking.

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With the alkaline medium in which oxygen had previously been dissolved under an oxygen partial pressure of 8 kg / cm, the autoclave was quickly filled at a temperature of 110 ° C. Then it was filled into the vessel a fresh alkaline medium containing dissolved oxygen, in addition and continuously from the lower part The same was pumped in at a rate of 1 l / minute for 5 minutes, while the overflowing excess liquid was removed from the upper part of the vessel. According to this procedure, part of the alkaline cooking medium was continuously passed through during the delignification the fresh alkaline aqueous medium containing dissolved oxygen is displaced.

The delignified pulp obtained had a kappa number of 6.8 and a brightness of 46.7 (GE).

From the above results, it follows that the above well applied to the first stage of a conventional bleaching process in the bleaching of kraft pulp can be.

Example 2

Eucalyptus wood chips were stored at a temperature of 180 C for 1 hour, in an alkaline solution of sodium carbonate in an amount of 15% by weight - as sodium oxide -, based on the wood, cooked and then shredded with the help of a Schexben fiberizing machine. The obtained raw Pulp had a kappa number of 132 for a yield of 68.4%. . ■

The raw pulp was delignified in the same manner and under the same conditions as in Example 1, but with the following was used:

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Oxygen partial pressure: 12 kg / cm Temperature: 140 C

Response time: 10 minutes

Magnesium carbonate with a concentration of 0.1 g / l mixed in.

For comparison purposes, the same schnitzel were after a usual Kraft method under the following conditions delignified:

Alkali Load: 22% as Na ₂ O based on

wood

Sulphidity: 31.6 %

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

The data obtained by the method of the invention and by the Kraft method are shown below Comparison of table.

Sieved
Pulp
yield
% Kappa
number Bright
speed Fractional ⁴ "*
length
mm Burst +)
factor Zer- ⁺ )
tear
factor Invent
dungs
according to 47.7 7.6 50.2 6.53 5.46 116 Force-
Pulp 42.6 10.6 29.5 5.74 5.57 115

PFI mill 400 ecm freedom

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As can be seen from the table, the quality is the after The pulp obtained according to the invention is superior to that of the Kraft pulp, with a better yield and better gloss can be achieved, and in the physical parameters, like breaking length, bursting and tearing factor, equivalent-

Example 3

Raw pulp with a kappa number of 126 was made from hardwood chips by boiling the schnitzel with a sodium carbonate solution and then fiberizing the softened chips with a yield of 69.5. % manufactured·

The raw pulp thus obtained was processed in the same manner and under the same conditions as in Example 1, the following conditions being used:

Oxygen partial pressure: 12 kg / cm Temperature: 140 ° C

The relationship between the kappa number of the deli The modified pulp and the reaction time are shown in curve A in FIG.

The delignification in the same was used as a comparative experiment Manner and under the same conditions as described above, with the difference that an alkaline aqueous Medium was used in which oxygen had not previously been dissolved, and * oxygen directly into the vessel below an oxygen partial pressure of 12 kg / cm was blown. The relation obtained is also curve B of FIG remove. ·.

From these two curves it follows that more than 80% delignification was obtained within 5 minutes in the case of "A" in which oxygen was previously dissolved. On the other hand, the same delignification as in "A" could not even after 30 minutes can be obtained in case "B" where oxygen gas enters it directly Vessel was initiated. '■ ■

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Example 4

Shredded Douglas fir shavings were stored for 30 minutes at a temperature of 170 ° C. in an alkaline solution of Sodium hydroxide in an amount of - as sodium oxide - 15%, based on the weight of the wood, cooked to remove non-frayed materials with a kappa number of 128 in a yield of 62.8%.

The unfiberized materials thus obtained were then delignified in the same way and under the same conditions as in Example 1, but with the following conditions were complied with:

Cellulose material consistency: 10%

Oxygen partial pressure: 12 kg / cm

Temperature: 150 ° C alkaline aqueous medium

during an initial

10 minute period: sodium hydroxide solution

during a later one

10 minute period: mixed solution

from sodium carbonate and hydroxide (Na ₂ CO ₃ / NaOH = 4 / l)

The results obtained were as follows:

Yield of screened pulp: 44.2%

Scrap: 0%

Kappa number: 18.2

Brightness: 38.2 (GE)

As can be seen from the above description and examples, the present invention provides an effective process for the rapid delignification of any type of cellulosic material, such as chemical pulp, semi-chemical quality pulp and wood chips. For the expert there are many changes in detail, the arrangements, the materials and the process stages of course, without thereby departing from the scope of the invention. 5098 3.4 / 05AA

Claims (12)

- 15 claims If a process for delignifying a cellulose material with -J oxygen in the presence of an alkaline aqueous medium at an elevated temperature in a reaction vessel under pressure with a consistency of the cellulose material of about to about 20% by weight, based on the mixture of cellulose material - rial and alkaline aqueous medium, characterized in that the oxygen is dissolved in the alkaline aqueous medium, the alkaline medium containing the dissolved oxygen contacts the cellulose material in the reaction vessel for oxidative delignification of the cellulose material, the consistency of the cellulose material being such that agglomeration of the cellulose material and of the alkaline aqueous medium is formed without gas space being present therein, and from the vessel a part or a substantial part of the waste liquid formed during the delignification drains, while fresh, dissolved oxygen-containing alkaline aqueous medium into the vessel ß is introduced, the displacement of the waste liquid with the fresh alkaline aqueous medium containing dissolved oxygen being carried out during the entire course of the delignification. 2. The method according to claim 1, characterized in that the cellulosic material with unbleached chemical pulp relatively low lignin content. , ' 3. The method according to claim 1, characterized in that the cellulosic material is semi-chemical grade pulp which has a relatively high lignin content. 4. The method according to claim 1, characterized in that the cellulose material consists of wood chips. 5. The method according to claim 1, characterized in that the consistency of the cellulosic material about 5 to about 15% by weight, based on the mixture of cellulosic ma-. materials and alkaline aqueous medium, is and 509834 / 05U the cellulosic material is unbleached chemical pulp or semi-chemical grade pulp. 6. The method according to claim 1, characterized in that the consistency of the cellulosic material is about 10 to about 20% by weight, based on the mixture of cellulose materials and alkaline aqueous medium, is and the cellulosic material consists of wood chips. 7. The method according to claim 1, characterized in that the waste liquid drained from the reaction vessel to recover the alkaline aqueous medium is treated therefrom, in which medium dissolved oxygen and containing the dissolved oxygen thus obtained alkaline aqueous medium is used to displace the waste liquid. 8. The method according to claim 1, characterized in that the waste liquid is separated from different stages taken from the delignification in the vessel. 9. The method according to claim 1, characterized in that the waste liquid is separated from different stages the delignification in the vessel and the fresh alkaline aqueous medium, the dissolved oxygen contains, is also introduced separately in different stages of delignification in the vessel. 10. The method according to claim 7, characterized in that the fresh alkaline aqueous medium, which is separated into different stages of delignification is introduced, consists of different types of alkali. 11. The method according to claim 7, characterized in that the fresh alkaline aqueous medium, which is introduced separately in different stages of delignification, has different p _H ~ values and the aqueous medium, which has different p n values, is used separately 509834/0 544 is to the medium having a relatively high p _H ~ value at a relatively initial stage of the delignification in which the lignin content is high, to introduce, and the medium having a relatively low _pH value at a later stage of the delignification in which the lignin content is relatively low. 12. The method according to claim 7, characterized in that Oxygen in the waste liquid drained from the later stage of delignification in the vessel is, is dissolved and the waste liquid thus obtained, containing dissolved oxygen at a relatively early stage of delignification into the Vessel is introduced as a fresh alkaline aqueous medium to displace the waste liquid, whereby the cellulosic materials and the alkaline aqueous medium are contacted in countercurrent in the vessel. 509834/0544 Blank page