FI85726B - FOERFARANDE FOER DELIGNIFIERING AV CELLULOSAMATERIAL. - 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 materials 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 soda.

Description

85726

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.

A known disadvantage of most pulping processes currently in use is that they generate significant amounts of polluting emissions.

Efforts have long been made to improve the cooking efficiency of some non-contaminated methods by bringing it to the same level as in sulphate cooking.

In this context, it has been proposed to impregnate cellulosic materials with a solution containing a peroxide compound before cooking.

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

EUCEPA Symposium "The Delignification Methods of The Future", vol. II, No. 7-18 Helsinki, 2-5. July 1980, the manuscript (Pekkala, pp. 14/1 - 14/19) shows that pretreatment of wood chips with alkaline hydrogen peroxide accelerates delignification in soda soup to the level of sulphate cooking, but also significantly reduces carbohydrate yield (pp. 14/7, lines 10-12). ).

A further disadvantage of all these known methods is that they give a pulp which is further digested, i.e. a lower viscosity and a weight yield generally 2 85726 lower 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 10, the first step of treating the cellulosic material with an acid, the second step of treating the cellulosic material of the first step with hydrogen peroxide in a basic medium and the third step of boiling the basic cellulosic material of at least one chemical is from the group of alkali or alkaline earth metal hydroxides.

By the phrase "cellulosic materials" according to the invention is meant fragments of lignin-containing plants which are used as raw material in the paper industry. Examples of such materials are fragments obtained from: wood, annual herbaceous plants such as forage, monocotyledonous plants, e.g. straw from cereals, bamboo, esparto, reeds and reeds and sugar cane, in particular its waste or bagasse from sugar extraction after. The invention is particularly applicable to wood fragments. Suitable for 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.

30 Resin wood chips and sawmill waste are particularly suitable.

In the process according to the invention, the function of the acid treatment is to separate the metals which they normally contain from the cellulosic materials. Suitable in the form of an aqueous solution are all inorganic or organic acids alone or as a mixture. Strong inorganic acids such as 3,85726 sulfuric acid or hydrochloric acid are suitable. The first step is suitably carried out in the presence of a metal ion complexing agent. Particularly suitable are mixtures of said strong inorganic acids and organic acids selected from the group consisting of aminopolycarboxylic or aminopolyphosphonic acids or their alkali metal salts, which are capable of chelating metal ions. Diethylenetriaminepentaacetic acid (DTPA) is recommended. Examples of suitable aminopolycarboxylic acids are diethylenetriaminepentaacetic acid, ethylenediaminetetraacetic acid, cyclohexanediamine tetraacetic acid and nitrilotriacetic acid. Examples of aminopolyphosphonic acids are diethylenetriamine pentamethylenephosphonic acid, ethylenediaminetetra (methylenephostone) acid and nitrilotri (methylenylene phostone) acid. Diethylenetriamine pentamethylene phosphonic acid (DTMPA) is recommended.

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

The acid and its amount of use must generally be chosen so that the pH of the medium is 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.

25 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 a tank and from 1 to 120 minutes when processing on a percholization column. ingredients are packaged.

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

4,85726

The purpose of the peroxide used in the second step of the process according to the invention is to accelerate the delignification of the cellulosic materials and to slow down the decomposition of carbohydrates in the next cooking step. The optimum amount of hydrogen peroxide 5 depends on the source of 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 from 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 dry matter.

Hydrogen peroxide can be used as an anhydrous or, preferably, an aqueous solution, e.g., a commercial aqueous solution of hydrogen peroxide-15 having a weight of 25 to 90 g of pure hydrogen peroxide per 100 g of solution, or as a dilute aqueous solution of hydrogen peroxide obtained by electrochemical reduction of oxygen.

In the process of the invention, the cellulosic materials 20 may be treated with alkaline hydrogen peroxide in the presence of additives such as hydrogen peroxide stabilizing and degradation inhibitors. Such additives are, 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 cellulose chains from depolymerization, activators or corrosion inhibitors. The amount of additives generally does not exceed 1% by weight of the cellulose-30 ingredients. The amount is in most cases 0.5% by weight of these ingredients.

In the second step of the process according to the invention, an alkaline medium is formed by adding soluble, basic substances. In general, ammonia, inorganic carbonates of alkali or alkaline earth metals and hydroxides such as sodium, potassium or calcium carbonate and sodium, potassium or calcium hydroxide can be used. Alkali or alkaline earth metal oxides or peroxides, such as Na 2 O, Na 2 O 2 'CaO and CaO 2, may also be suitable, and the peroxides may partially replace the amount of hydrogen peroxide added to the second step 5 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 stage 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 in the second step with hydrogen peroxide in an alkaline medium is generally carried out for a period longer than 2 minutes but not exceeding 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: 1-2: 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.

In this preferred embodiment, the cellulosic material is soaked in a hydrogen peroxide solution prior to the reaction, generally for up to 5 minutes. However, the soaking time cannot usually be less than 30 seconds. The temperature of the peroxide solution is in most cases chosen to be 5-20 ° C higher than the temperature in the reactor, which is maintained for 15-20 minutes by means of a heating mantle. A suitable reaction temperature is 37 to 87 ° C (310 to 360 K).

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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 alkali and alkaline earth metal hydroxides. Preferred examples of such chemical reactants are sodium hydroxide and calcium hydroxide.

In the third step of the process according to the invention, some known delignification additives can be added. These additives are generally used to improve delignification during early cooking. Organic compounds are preferred, e.g. anthraquinone and its derivatives such as 1-methylanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-methoxyanthraquinone, 2,3-dimethylanthraquinone, 2,7-dimethylanthraquinone, 1,4,4a, 5,8,8a, 9a, 10a-octahydroanthraquinone and 1,4,4a, 9a-tetrahydroanthraquinone, * hydroquinones such as p-hydroquinone; certain anthracene derivatives such as 9-nitroanthracene, 9,1O-nitroanthracene and 9-nitro-10-chloro-9,1O-dihydroanthracene; certain heterocyclic compounds such as 6,11-dioxo-1H-anthra [1,2-c] pyrazole] polycytic compounds such as 1,2-benzanthraquinone and phenanthrene quinone; nitrobenzene; amines such as monoethanolamine and ethylenediamine; alcohols such as resorcinol and pyrogallol. Examples of inorganic compounds are hydrazine and alkali metal borohydride. The most effective additives are anthraquinone and its derivatives. Anthraquinone is recommended. These additives are preferably used in amounts not exceeding 2% by weight of the dry cellulosic material. The amount of additives is generally kept below 1% by weight of the cellulosic material.

The optimum operating conditions of the third step 35 of the method according to the invention depend on various parameters, in particular the source of the cellulosic material, and are 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 5 works advantageously when reducing agents are added 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 the need for oxidation of reducing agents.

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 biggest advantage of this is the considerable reduction in the size of the cooking equipment, i.e. space and cost savings are achieved 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 maintaining the degree of delignification 20. This results in significant savings on chemical reactants.

Finally, 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 following practical implementation examples are intended to illustrate the invention.

Experiments 1 to 6R, described below, were performed to demonstrate the improvement in chemical cooking performance of lignocellulosic materials provided by the invention.

Test 1; (according to the invention)

First phase; 300 g of Loblolly pine (Pinus taeda) was added to a jacketed glass reactor equipped with a liquid-tight lid of 8,857,726. The lid had two openings so that one was connected to a vacuum pump and through the other a tubular probe could be inserted into the bottom of the reactor. This probe was connected to a storage tank of reactants 5, which in turn was connected to the outside air or to a vacuum pump via a three-way tap.

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 this vacuum piping. The weight of the aqueous solution used was 8 times the weight of the dry wood. After four hours of impregnation, the chips were washed in three washing cycles, each lasting two hours, with washing water 8 times the weight of the dry wood. Chips 15 were centrifuged between cycles.

Second phase:

An aqueous solution of 0.3 M H 2 O 2, 0.5 M NaOH and 0.001 M Mg ++ ions was then added to the reactor and preheated to 50 ° C (323 K). The solution was used in a weight of 20 times 6 times the weight of dry wood. After two minutes of impregnation, the excess cooking liquor was sucked out of the reactor via a tubular probe. The reaction was then allowed to proceed on steam for 45 minutes by heating the reactor through a jacket with water at 50 ° C (323 K).

Third step:

The chips from the second step were then subjected to conventional soda-anthraquinone cooking in the liquid phase in a stainless steel reactor which was heated by placing the reactor in an oven. The cooking conditions used were: total active alkali content in the cooking liquor calculated as 20% Na 2 O, anthraquinone 1 g / kg wood, 5: 1 weight ratio of liquid to dry wood, temperature and duration: heating to 170 ° C (443 K) in 80 minutes and then 70 minutes at 170 ° C (443 K).

Experiment 2R: (comparison) 85726

The conditions were the same as in Experiment 1, but the first step was omitted.

Experiment 3R: (comparison) 5 Same as Experiment 1, but no second treatment step with hydrogen peroxide was performed.

Test 4R; (comparison)

Chips as in Experiment 1, but the first and second steps were omitted and the third step of Experiment 10 1 was immediately performed under the same conditions.

Experiment 5R: (comparison)

The conditions are the same as in Experiment 4R, except that the chips were kept at 170 ° C (443 K) for 100 minutes during cooking. Experiment 6R: (comparison)

The conditions are the same as in Experiment 3R, except that the chips were kept at 170 ° C (443 K) for 100 minutes during cooking.

At the end of the cooking step, four quantities were analyzed from the pulps: lump number, lignin content, total weight yield, and viscosity. The following standard methods were used in these analyzes: number of pieces: TAPPI standard 20 T236, lignin content: TAPPI standard T222, viscosity: TAPPI standard T230.

Total weight yield was determined gravimetrically by weighing the samples before and after the experiments.

The total carbohydrate content was also calculated by subtracting the lignin content from the total weight yield.

The results obtained are shown in the following table.

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Experiment Operating conditions Characterization of the obtained mass No. 1. 2. Step 3 3. ‘or- Kap- Size. Lign. Hiilih. Viscos 5 step step soda ash precipitation pit. a bonfire. sit.

H2SO4, H2O2 AQ boiling point Number (wt%) (wt%) yield (mPa.s) to min (wt%) 1 saturated yes 70 33.1 46.3 4.9 41.4 15, 9 10 2Ä no cyl yes yes 70 34.9 45.8 5.3 40.5 16.1 3R <above no yes 70 41.2 48.2 6.2 42.0 18.9 4R no no 70 44, 9 48.0 6.7 41.3 19.0 5R no no 100 35.0 46.6 5.3 41.3 16.2 6R cop no yes 100 34.5 46.2 5.2 41.0 15.4 15

A comparison of the results of Experiment 1 and the results of Experiments 2R, 3R and 5R shows the synergistic effect of the combined use of the first and second steps of the invention on delignification and carbohydrate retention at the end of the cooking step following these steps. In addition, it can be seen that the successive use of the first two steps of the method according to the invention makes it possible to reduce the duration of the third, i.e. cooking step, by at least 30%, which correspondingly reduces the size and cost of the cooking equipment.

Claims (10)

11 85726 A method for delignifying cellulosic materials, characterized in that in a first step 5 the cellulosic material is treated with an acid, in a second step the cellulosic material obtained from the first step is treated with hydrogen peroxide in a basic medium and in a third step the basic second stage cellulosic material is boiled in at least one chemical reactant - being from the group consisting of alkali or alkaline earth metal hydroxides. Process according to Claim 1, characterized in that the first step is carried out at a pH of 1 to 4. Process according to Claim 1 or 2, characterized in that the first step is carried out in the presence of an inorganic acid. Process according to one of Claims 1 to 3, characterized in that the first step is carried out in the presence of a metal ion complexing agent. Process according to one of Claims 1 to 4, characterized in that the chemical reactant of the alkali broth is an aqueous solution containing sodium hydroxide and a compound from the group consisting of anthraquinone and anthraquinone derivatives. Process according to one of Claims 1 to 5, characterized in that the second step is carried out at an initial pH of 12 to 13. Process according to one of Claims 1 to 6, characterized in that the second step is carried out at a temperature of 40 to 80 ° C (313 to 353 K) for 10 to 60 minutes. Process according to one of Claims 1 to 7, characterized in that the second step is carried out with an amount of hydrogen peroxide of 0.5 to 2 g / 100 g of dry cellulosic material and in a weight ratio of cooking stove to wood of 1: 1 to 2: 1. 12 85726 Process according to one of Claims 1 to 8, characterized in that hydrogen peroxide is used in the second step as an aqueous solution. Process according to one of Claims 1 to 9, characterized in that the cellulosic material is wood chips which are resin wood chips. 13 85726