FI85725C - Process for delignifying cellulose material - Google Patents

Abstract

1. Process for the delignification of cellulosic materials characterized in that in a first step the cellulosic materials are treated with an acid under regulated conditions to effect a decontamination of the cellulosic material of the metals which they contain, in a second step the cellulosic materials of the first step are treated with hydrogen peroxyde under alcaline conditions and in a third step the cellulosic materials of the second step are boiled in the presence of sulphite or sulphate.

Description

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The present invention relates to a process for delignifying ligno-cellulosic materials to produce a pulp for use in papermaking. In particular, it relates to chemical pulps prepared by cooking cellulosic materials in the presence of delignifiable chemical reactants.

Efforts have long been made to improve the cooking efficiency of cellulosic materials by impregnating the cellulosic material with a solution containing a peroxide compound prior to cooking.

DE-A-873 649 (Degussa) discloses that pretreatment of cellulosic materials with an aqueous solution containing a peroxide compound before cooking sulphite or bisulphite-15 improves the brightness of the pulp obtained. To achieve the same pulp brightness, this pretreatment also allows cooking under cellulose-sparing conditions not at a lower temperature or for a shorter time (page 2, lines 51-59).

BE patent 678 022 (Degussa) discloses 20 similar processes in which the pretreatment of cellulosic materials with an aqueous solution containing a peroxide compound is carried out in a strongly basic medium. According to this patent, said technique promotes a chemical cooking process after pretreatment while maintaining the weight yield of the pulp 25 (page 3, last paragraph and page 4, lines 1-13).

At the source Przeglad Papierniczy, vol. 33, August 1977, W. Mroz and W. Surewicz, "Modification of the kraft Pulping process aimed at improving the color of the pulp" (pp. 277-30 280) mentions that in sulphate-type alkaline soup, pretreatment of cellulosic materials with a peroxide compound only slightly improves the brightness of the pulp and said source show that the results are improved by pre-treatment with impregnation with reducing agents, in particular hydrazine-35a and not oxidants.

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But the disadvantage of all these known methods is that they give a pulp which is further digested, i.e. a lower viscosity and a generally lower weight yield compared to the viscosities and yields of conventional chemical pulps with the same degree of delignification.

The invention eliminates these disadvantages of the known methods by providing a new method for delignifying cellulosic materials, which makes it possible to achieve a high degree of delignification while maintaining the most important quality properties of the cellulose and the weight yield of the pulp.

Accordingly, the invention relates to a process for delignifying cellulosic materials, the first step of which is to treat the cellulosic material with an acid, the second step is to treat the cellulosic material from the first step with hydrogen peroxide in a basic medium and the third step to boil the cellulosic material from the second step in the presence of from the group containing sulfur compounds and oxygen.

The term "cellulosic materials" according to the invention means fragments of lignin-containing plants used as raw material in the paper industry. Examples of such materials are fragments obtained from: wood, annual grasses such as fodder-25 Lane, monocotyledonous plants, e.g. straw from cereals, bamboo, esparto, reeds and reeds, and sugar cane, especially its waste or bagasse after sugar extraction. The invention is particularly applicable to wood fragments. Suitable in the method according to the invention are all types of resin trees (conifers) or deciduous trees (deciduous trees) which can be used in the paper industry. Especially suitable are resin wood chips and waste generated in the sawmill industry.

In the process according to the invention, the function of the acid treatment 35 is to separate the metals which they normally contain from the cellulosic materials. Suitable in the form of an aqueous solution 3 85725 are all inorganic or organic acids alone or in a mixture. Strong inorganic acids such as sulfuric acid or hydrochloric acid are suitable. The first step is suitably carried out in the presence of a metal ion complexing agent 5. Particularly suitable are mixtures of said strong inorganic acids and organic acids selected from the group consisting of amino-polycarboxylic or aminopolyphosphoric acids or their alkali metal salts which are capable of chelating metal ions. Examples of suitable aminopolycarboxylic acids are diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, cyclohexanediamine tetraacetic acid and nitrilotriacetic acid. Diethylenetriaminepentaacetic acid (DTPA) is recommended. Examples of aminopolyphosphonic acids are diethylenetriaminepentamethylenephosphonic acid, ethylenediaminetetra (methylenephosphonic) acid and nitrilotri (methylenephosphonic) acid. Diethylenetriaminepentamethylenephosphonic acid (DTMPA) is recommended.

The operating conditions in the first step of the method 20 according to the invention are not decisive. The conditions must be determined in each individual case, depending on the type of cellulosic material and the processing equipment.

The acid and its application rate must generally be selected so that the pH of the medium will be below 7, e.g. in the range 0.5 to 6.5; particularly preferred pH values are in the range of 1.0 to 4.0.

Temperature and pressure are not critical and ambient temperature and normal pressure are generally suitable. The duration of the treatment can vary widely depending on the type of equipment used, the choice of acid, the temperature and the pressure, e.g. from 30 minutes to several hours when soaking the cellulosic materials in the tank, and from 1 to 120 minutes when the treatment takes place on a percolation column, in which the cellulosic ingredients are packaged.

In an alternative embodiment of the process according to the invention, the cellulosic materials can be treated with 4,85725 steam before the first step. This treatment aims to improve the following impregnation operations.

The function of the hydrogen peroxide used in the second step of the process according to the invention is to accelerate the delignification of the cellulosic substances and to slow down the decomposition of carbohydrates in the next cooking step. The optimum amount of hydrogen peroxide depends on the source of the cellulosic materials. Generally, more than 0.1 g of hydrogen peroxide per 100 g of dry cellulosic material must be used. Amounts of hydrogen peroxide greater than 3 g / 100 g of dry cellulosic material are rarely necessary to achieve rapid delignification. The amounts of hydrogen peroxide used are generally 0.5 to 2 g / 100 g of dry matter. The best results have been obtained with peroxide amounts of 0.7 to 1.5 g / 100 g of dry matter.

Hydrogen peroxide can be used as an anhydrous or, preferably, aqueous aqueous solution, e.g., a commercial aqueous hydrogen peroxide solution having a weight of 25 to 90 g of pure hydrogen peroxide per 100 g of solution, or as a dilute aqueous alkali solution of hydrogen peroxide obtained by reducing oxygen with electrochemistry.

In the process of the invention, the cellulosic materials can be treated with alkaline hydrogen peroxide in the presence of additives such as hydrogen peroxide stabilizing and degradation inhibitors. Such additives include, for example, inorganic or organic chelating agents for metal ions, such as magnesium salts, aminopolycarboxylic acids or water-grade sodium silicate. Other useful additives include surfactants, wetting agents, agents capable of protecting the cellulose chain from 30 and depolymerization, activating agents or corrosion inhibitors. The amount of additives generally does not exceed 1% by weight of the cellulosic materials. The amount is in most cases 0 to 0.5% by weight of these ingredients.

In the second step 35 of the process according to the invention, an alkaline medium is formed by adding soluble basic substances. In general, ammonia, alkaline earth metal or inorganic carbonates and hydroxides of alkaline earth metals such as sodium, potassium or calcium carbonate and sodium, potassium or calcium hydroxide can be used. Alkali or alkaline earth metal oxides or δ-peroxides such as Na 2 O, 2 2 ^ 2, CaO and CaCl 2 may also be suitable, and the peroxides may partially replace the amount of hydrogen peroxide added to the second step of the process. Sodium hydroxide is usually recommended because it is readily available and inexpensive. The amount of the basic substance used is selected so that the pH of the peroxide solution can be adjusted to a range of 11 to 13.5, preferably 12 to 13.

The operating conditions in the second step of the process according to the invention can also vary within wide limits, in particular depending on the type of cellulosic material and the type of equipment used. Thus, the pressure in the second stage can range from 2 kPa to 10 MPa and the temperature from 17 to 107 ° C (290 to 380 K). The treatment with the second phase oxide in an alkaline medium is generally carried out for a period longer than two minutes but not exceeding 20,180 minutes.

In one embodiment of the invention, the cellulosic material is treated with alkaline hydrogen peroxide in a weight ratio of liquid to wood of not more than 2.5: 1 and preferably 1: 1 to 2: 1. In this preferred embodiment, the cellulosic material obtained from the first step is impregnated in a closed reactor with a preheated hydrogen peroxide alkali solution and then the excess solution which has not impregnated the cellulosic material is removed from the reactor, which is then heated to the reaction temperature patient.

In this preferred embodiment, the cellulosic material is soaked in a hydrogen peroxide solution prior to the reaction, generally for up to five minutes. However, the soaking time cannot usually be less than 30 seconds.

The temperature of the peroxide solution is in most cases 5 to 20 ° C higher than the temperature of 6 85725 in the reactor, which is maintained for 15 to 120 minutes by means of a heating mantle. A suitable reaction temperature is 37 to 87 ° C (310 ° to 36 ° C).

The best results were obtained at 50 ° C (323 K) with a reaction time of 45 minutes.

In the third step of the process according to the invention, the cellulosic material obtained from the second step is initially boiled in the presence of at least one chemical reactant. The term "chemical reactants" refers to acidic or basic sulfur-containing materials, e.g., those used in known soups in the pulp industry, known as sodium or magnesium sulfite, sodium, magnesium or calcium bisulfite, sodium, magnesium or as a calcium hydrogen sulfite and sodium sulfate soup, or kraft soup. Oxygen soups are also included in soups by chemical reactants.

The optimum operating conditions of the third step of the method according to the invention depend on various parameters, in particular on the source of the cellulosic material, and can be easily determined in each individual case.

In a preferred embodiment of the method according to the invention, the cellulosic material is washed with water between the second and third steps. Said embodiment works advantageously when sulfur-containing reactants are used in the third step. The purpose of this washing is to remove at least some of the water-soluble material formed in the second stage from the cellulosic material and to extract the remaining hydrogen peroxide residues, thus avoiding unnecessary oxidation of the sulfur-containing reactants used in the third stage, i.e. cooking.

The process according to the invention makes it possible to considerably accelerate the delignification of the cellulosic material to be treated, which results in a shortening of the third stage, i.e. cooking with chemical reactants. The main advantage of this is a significant reduction in the size of the cooking equipment, i.e. a saving of space and costs, or, alternatively, a higher production efficiency is achieved with a given cooking equipment.

The invention also makes it possible to significantly reduce the amount of chemical reactants in the cooking step while keeping the degree of delignification the same. This results in significant savings in chemical reactants and reduces environmental pollution, especially with gaseous and liquid, sulfur-containing wastes when using sulfur-containing chemical reactants.

Finally, it should be noted that the invention can produce chemical pulps with a higher viscosity than pulps produced by prior art methods with improved weight yields and thus lower costs.

The object of the following practical embodiments is to illustrate the invention.

First set of tests (tests 1 - 6R)

The purpose of Experiments 1 to 6R, described below, is to demonstrate the advantages of the invention achieved in the chemical cooking of cellulosic materials.

Experiment 1: (according to the invention)

Wood flour obtained from Loblolly pine (Pinus taeda) (particle fraction which, using the Tyler standard sieve series, passes through a 40 mesh screen and remains on a 60 mesh screen) was treated with hydrochloric acid by soaking the wood flour in 0.1 M HCl for four hours at ambient temperature. The weight of the aqueous solution used was 40 times the weight of the treated wood flour (first step).

The wood flour from the first step, corresponding to 10 g of dry matter, was fed to a 200 ml reactor coated on the inside with polytetrafluoroethylene. After the reactor was preheated to 50 ° C (323 K) in a polyethyl eniglycol bath, 150 g of a water-35 solution of 0.04 M hydrogen peroxide, 0.5 M sodium hydroxide and 0.001 M Mg ++ was added to the reactor. . Reactor 8 8 S · v 5 was then heated to 80 ° C (353 K) in 30 minutes and maintained at this temperature for 15 minutes. The reactor was then cooled and the wood flour was washed (second step).

Sulfate cooking was then performed, in which the wood flour obtained from the second stage and the aqueous Na 2 S and NaOH solution were boiled in a 450 ml stainless steel laboratory autoclave equipped with a stirrer (third stage). The cooking conditions were: active alkali in cooking liquor 20 g 10 Na 2 O / liter cooking liquor, cooking liquor sulphidity 25%, cooking liquor to dry wood flour weight ratio 40: 1, temperature and duration: heating from ambient temperature to 170 ° C (443 K) 90 minutes, holding 170 At ° C (443 K) for 52.5 minutes.

Experiment 2R (Comparative) 15 The conditions in this comparative experiment were the same as in Experiment 1, except that the first treatment step was not performed.

Experience 3R (comparison)

Same as Experiment 1 except that the second treatment-20 step was not performed.

Experiments 4r and 6R (comparison) These were conventional sulphate soups. Steps 1 and 2 were not performed, but the operating conditions were otherwise the same as in Experiment 1. However, in Experiments 5R and 6R, the cooking time at 170 ° C (253 k) was extended to 60 and 75 minutes, respectively.

At the end of the cooking step, three quantities were analyzed from the obtained mass: number of pieces, total weight yield and viscosity. The following standard methods were used in the analyzes:

Number of pieces: TAPPI standard T236,

Viscosity: TAPPI standard T230.

The results obtained are shown in Table I.

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Table I

Experiment Operating conditions The mass of the obtained mass is characterized by 5 ------- 1. 2. 3. vai- 3. vai · Kappa- Size- Visco-phase stage they featured figure females.

HCl H2 ° 2 phate duration yield (mPa.s) cooking min 10 1 yes yes yes 52.5 34.5 46.1 19.4 2R no yes yes 52.5 28.3 41.5 9.4 3R yes no yes 52.5 53.8 48.4 22, 1 4R no no yes 52.5 54.4 48.1 18.6 5 R no no yes 60 45.2 46.9 16.4 6R no no 75 30.5 45.3 15.1

A comparison of the results of Experiment 1 and the results of Experiments 2R, 3R and 4R shows an unexpected synergistic effect on the viscosity of the pulp after the last cooking step using the first and second steps of the invention. It is further found that the successive use of the first two steps of the process according to the invention also makes it possible, quite surprisingly, to prevent a significant reduction in the viscosity of the pulp due to the use of an oxidant. Comparing test 1 with test 4R, it can be seen that the viscosity of the pulp prepared according to the process of the invention has even improved.

Experiments 5R and 6R were comparative experiments in order to determine the weight yield and viscosity of delignified pulps only in the cooking step (according to the prior art method) when the degree of delignification (measured in pieces) was the same as in Experiment 1. An advantage of the invention is immediately apparent from the chemical cooking time.

It is also apparent that the process 10 85725 of the invention produces pulps with better viscosity and higher weight yield.

Second set of tests (tests 7 - 11R)

It is also the task of Experiments 7-11R, described below, to demonstrate the effect of the invention on the chemical cooking performance of cellulosic materials.

Experiment 7 (according to the invention) In these experiments, 300 g of wood chips obtained from Loblolly pine (Pinus taeda) were placed in a jacketed glass reactor equipped with a liquid-tight lid. The lid had two openings so that one was connected to a vacuum pump tree and through the other a tubular probe could be inserted into the bottom of the reactor. This probe was connected to a reactant storage tank, which in turn was connected to the outside air or to a vacuum pump via a three-way faucet.

The chips were then immersed at ambient temperature in an aqueous solution of 0.003 M Na 2 DTPA and 0.1 N sulfuric acid by suctioning the solution into the reactor using the vacuum generated by the vacuum piping. The amount of weight-20 of the aqueous solution used was eight times the weight of dry wood. After four hours of impregnation, three washing cycles, each lasting two hours, were performed with a wash water weighing eight times the weight of the dry wood (first stage).

An aqueous solution of 0.3 M was then added to the reactor

1 H 2 O, 0.5 M NaOH and 0.001 M Mg ++ and preheated to 50 ° C (323 K). The solution was used in a weight amount that was six times the weight amount of dry wood. After two minutes of impregnation, the excess cooking liquor 30 was sucked out of the reactor via a tubular probe. The reaction was then allowed to proceed under steam for 45 minutes by heating the reactor with water circulating through the jacket and thermostated to 50 ° C (323 K) (second step).

35 The chips from the second stage were then subjected to conventional sulphate cooking in the liquid phase in an 11 85725 stainless steel reactor, to which heat was supplied by placing the reactor in an oven. The operating conditions for the sulphate cooking were: total active alkali content in the cooking liquor calculated as 20% Na 2 O, 5 cooking liquors 25%, weight ratio of cooking liquor to dry wood 5: 1, temperature and duration: heating to 170 ° C (443 K) in 90 minutes and then for 45 minutes at 170 ° C (443 K).

Experience 8R (comparison)

The conditions were the same as in Experiment 7 for Erol-10 la that the first treatment step was not performed.

Experience 9R (comparison)

Same as Experiment 7 except that the second treatment step with hydrogen peroxide was not performed.

Experiments 10R and 11R (Comparative) In these experiments, only the third step, i.e. conventional sulfate cooking, was performed under the same conditions as the third step in Experiment 7. However, in Experiment 11R, the proportion of active alkali was increased to 26% Na 2 O.

At the end of the cooking step, the mass obtained was analyzed for the same quantities and by the same methods as in Experiments 1 to 6R, except for the viscosity.

The results are shown in Table II.

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Table II

Experiment Operating conditions The mass of the obtained pulp is characterized by 5 ------ 1. 2. 3. vai- Active Kappa- Total phase stage they sul- alkali number yield DTPA H2 ° 2 long. 3. (% by weight) cooking step; you % ! 10 | i _____I_ 7 yes yes yes 20 34.9 46.4 8R no yes yes 20 42.9 45.0 9R yes no yes 20 52.2 48.2 10R ci ci yes 20 60.3 50.2 1 1R no no yes 26 34,3 45,5 »- f --- r _ 1 1 _-I --- - 1_ 20 A comparison of the results of test 7 carried out according to the method of the invention with the results of test 11R shows that when the degree of delignification is the same, the method according to the invention gives sulphate pulp with a higher weight content after cooking.

Experiments 7, 8R, 9R and 10R show, like the first series of experiments, that the combination of the first two steps provides an unexpected synergistic effect in the method according to the invention.

Third Set of Experiments (Experiments 12 and 13) The purpose of Experiments 12 and 13, which are both in accordance with the invention, is to demonstrate the advantages of a particular embodiment of the invention in which there is a water wash of the cellulosic material between the second and third steps of the process.

The first and second steps of the method were the same as in the second set of experiments described above.

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In Experiment 12, the third step of the process was carried out immediately, but in Experiment 13, three washing cycles with hot water were performed so that each cycle was two hours long and the amount of water used was eight to 5 times the weight of dry wood.

In the third step, it was impregnated with sulphate cooking liquor so that the operating conditions were as follows: active alkali expressed as 20% Na 2 O, sulphidity 25%, weight ratio of cooking liquor to dry wood 5: 1, temperature and duration: heating to 170 ° C ( 443 K) in 80 minutes and then for 30 minutes at 170 ° C (443 K).

The mass obtained at the end of cooking was analyzed as in the first series of experiments of the examples. The results are shown in Table III.

15 Table III

Experiment Operating conditions The mass of the obtained pulp is characterized by 1. 2. Intermediate 3. Kappa- Total Viscose 20 step step washing step number yield sit.

DTPA H 2 O 2 sulfl (% by weight (mPa.s) soup 25 -------- 12 yes yes no yes 47.1 47.6 45.8 13 yes yes yes yes 43.1 47.9 47.6 These results highlight the advantages of the intermediate washing operation between the second and third steps of the method according to the invention.

The results show the beneficial effect of the intermediate wash on the increase in the degree of delignification, while the weight yield and the viscosity of the pulp can be maintained more efficiently.

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Fourth set of experiments (experiments 14 - 16)

The purpose of experiments 14-16 according to the invention is to demonstrate the effect of pH during the hydrogen peroxide treatment in the second step of the process according to the invention. These experiments were performed with wood flour obtained from Loblolly pine (Pinus taeda) under the same operating conditions as in the first series of experiments, except that the amounts of NaOH were varied in the second stage so that the pH varied in this range from 10.1 to 12.9 at the start of the reaction.

10 The results are shown in Table IV.

Table IV

Experiment Operating conditions Particle number characterization of the obtained mass ^ 1. 2. | Step 2 Step 3 Total number of steps step by step they yield acid starting sulf. (% by weight) pH soup 20 ------- 14 yes yes 10.1 yes 44.8 46.9 15 yes yes 11.8 yes 38.2 46.7 16 yes yes 12.9 yes 35, 5 46.2 __1 1 __ 25 The most preferred number of pieces was obtained in Experiment 16, where the pH was 12-13 in the second step. The increase in pH did not significantly reduce the yield.

Claims (10)

A process for delignifying cellulose material, characterized in that the cellulose material is treated with an acid in a first step, the cellulose material from the first step in a second step is treated with hydrogen peroxide in an alkaline medium and the cellulose material from the second step of a third step is boiled in the presence of at least one chemical reactant which is from the group of sulfur-containing materials and oxygen. Process according to claim 1, characterized in that the first step is carried out at a pH of 1 - 4. A process according to claim 1 or 2, characterized in that the first step is carried out in the presence of an inorganic acid. Method according to any of claims 1-3, characterized in that the first step is carried out in the presence of a metal ions complexing agent. 20 Process according to any one of claims 1-4, characterized in that the third stage consists of sulphate boiling. Method according to any of claims 1-5, characterized in that the second step is carried out at an initial pH of 12-13. Process according to any of claims 1-6, characterized in that the second step is carried out at a temperature of 40 - 80 ° C (313 - 353 K) and lasts 10 - 60 minutes. 30 Process according to any of claims 1-7, characterized in that the second step is carried out with a hydrogen peroxide amount of 0.5 - 2 g / 100 g of dry cellulose material and having a weight ratio of 1: 1 -2: 1 between cooking liquor and wood. 17 85725 9. A process according to any one of claims 1-8, characterized in that hydrogen peroxide in the second step is used as aqueous solution. 10. A process according to any of claims 1-9, characterized in that the cellulose material consists of wood chips which are resinous wood chips.