RU2491379C1 - Method of producing sulphate pulp from mixture of chips from different species of wood - Google Patents

Abstract

FIELD: textiles, paper.

SUBSTANCE: method for producing sulphate pulp from a mixture of chips from different species of wood includes the use of three batch cookers sequentially interconnected by liquid phases, their loading with a mixture of chips from different species of wood, including wood of larch, pine, spruce, birch, aspen, preliminary two-stage treatment of the mixture with water extraction at the first stage and black liquor at the second, removal of the extract from the cooker, supply to the cooker of cooking liquor, recycling the extract to obtain arabinogalactan. Both extraction treatments are carried out in three cookers interconnected by liquid phases by their sequential filling with each of the liquid phases with the removal of the aqueous extract by its replacement from the cookers by black liquor and the removal of the black liquor by its displacement by the cooking liquor.

EFFECT: alignment of the characteristics of chips from all types of wood and increase in the concentration of arabinogalactan in the aqueous extract.

4 cl, 1 tbl, 3 ex

Description

The invention relates to technologies for the production of pulp by the sulfate method of cooking and can be used in the pulp and paper industry.

It is known that the optimal regimes of cooking chips from different wood species in the production of cellulose, for example, with the same value of the Kappa number, differ significantly in the duration and / or temperature of the cooking and / or consumption of cooking chemicals, as well as in the degree of influence of the pre-treatment technology on the specified pulp parameter chips, for example, by steaming, removing some substances from the chips by extraction with water or another extractant, impregnation with black liquor, etc. Therefore, when cooking a mixture of wood chips from different types of wood, one should select such a technology of preliminary processing of the mixture that would average the characteristics of the whole chip to the maximum extent. This is especially important if the mixture contains larch wood. In this case, it should be noted that this wood contains arabinogalactan (AG), which, on the one hand, makes it difficult to cook the chips containing it, and on the other, it is a very valuable product. Accordingly, in the pretreatment technology, provision should be made for the production of AH at reasonable costs.

A known method of producing sulfate cellulose in a batch boiler, including its loading with wood chips, its preliminary treatment with black liquor at a temperature of 130-145 ° C for 10-30 minutes, pulping (SU, No. 1838487, D21C 3/02, publ. 30.08 .1993). Chip processing liquor is taken from another boiler after cooking in it by displacement with washing liquor. The purpose of using such a pretreatment scheme is to intensify the cooking process, simplify equipment for heat recovery of hot black liquor, and reduce the consumption of steam for cooking. In the examples, the species composition of the chips is not indicated, but it is obvious that in the presence of larch chips in the mixture of chips of different breeds, it is practically impossible to obtain AG by this method.

The closest analogue to the proposed method is a method for producing sulfate cellulose from larch chips (SU, No. 1595977, IPC D21C 3/02, 1/02, publ. 09/30/1990). This method using a batch boiler includes loading it with chips from larch wood, water treatment of chips at a temperature of 100-120 ° C, removing the spent solution from the boiler, processing it to produce arabinogalactan, feeding the boiler with a cooking solution, boiling wood chips, removing it from the boiler cooking products.

In essence, the aqueous medium directed to the processing of wood chips can be called an extractant, the processing operation is the extraction of wood chips, and the aqueous medium after processing is called an extract.

This method is intended for the production of cellulose for various purposes from larch wood chips, as well as AG and flavonoids extracted from wood chips.

The disadvantage of this method is that when processing a mixture of wood chips, including larch, the effectiveness of water treatment, in terms of leveling the characteristics of wood chips of all species in the mixture before cooking, is negligible. In addition, the concentration of AG in the extract is small and it is economically unprofitable to extract it from the extract.

New technical results from the use of the invention are to increase the uniformity and quality of cellulose due to the equalization of the characteristics of wood chips from different wood species during the preliminary processing of the mixture, as well as to simplify and reduce the cost of the processing of the extract to obtain AG due to the increase in its concentration in the extract.

These results are achieved by the fact that in the method for producing sulfate cellulose from a mixture of wood chips of different types of wood, including the use of a boiler of periodic action, loading wood chips from a number of species containing larch, the level of extraction of wood chips by treating it with an aqueous medium at an elevated temperature for a specified time to obtain the extract, removing it and processing it to produce arabinogalactan, feeding the cooking liquor to the boiler, cooking chips, removing cooking products from the boiler, according to the invention tenyu, a number of species additionally includes wood of pine, spruce, birch, aspen, the mixture of chips after treatment with an aqueous medium is additionally treated with hot black liquor, while both treatments are carried out in three boilers connected by liquid phases by sequentially filling each of the liquid phases with the withdrawal of the aqueous extract by its displacement from boilers with black liquor and the withdrawal of black liquor by displacement with a cooking solution. The share of larch wood chips in the total mass of chips is 20-80%. Chips are treated with water and black liquor at a temperature of 95-98 ° C. The extract is used to process fresh wood chips.

The proposed method can be implemented as follows. A mixture of wood chips is prepared from different species of wood, including larch. Determine the content of AG in larch chips. Under laboratory conditions, water treatment of this woodchip is carried out at a temperature of 95-98 ° C, and the duration of effective AG extraction (τ _eff. ), As well as its degree of extraction over this period of time, is determined by the dependence of the concentration of AG in the extract on the duration of extraction. τ _{eff is} taken equal to 25 min, the degree of extraction of AG - 40%. Estimated residual AH content in the chips.

Next, the same portion of the chips is treated with black liquor at a temperature of 95-98 ° C for τ _eff . The degree of AG extraction by this extractant is determined, the final AH content in the chips after both treatments and the degree of “cleansing” of the chips from AG are evaluated. The degree of AG extraction with black liquor is 47%, calculated on its content in the chips after aqueous extraction. The total degree of "cleaning" is 70-72%.

In an industrial process for the production of cellulose, a mixture of wood chips with a known fraction of larch wood chips is loaded with compaction and wetted by spray into three digesters of periodic action, interconnected by liquid phases. Water is supplied to the first boiler at a speed that ensures filling the boiler with wood chips in 25 minutes and in an amount that provides a hydraulic module value of not more than 1: 3, calculated on dry wood chips. After the first boiler is completely filled with water, it continues to be supplied for another three minutes. After that, black liquor begins to be fed into the first boiler at the same speed. A layer of water added over 3 minutes (this is ~ 12% of the volume of the liquid phase in the boiler) serves as a buffer between black liquor and the extract and eliminates its contamination with liquor.

When the first boiler is filled with liquor, its supply is stopped and the cooking solution begins to be fed, which displaces the liquor from the first boiler into the second. In this case, the liquor displaces the extract and the buffer layer of water from the second boiler into the third boiler. When boilers are sequentially filled with cooking liquor, at the output of the third boiler, first extract water, which is sent to the storage tank, then a buffer layer, which can be used, for example, to wash the cooked pulp and, finally, black liquor, which is sent to the cooking regeneration system chemicals.

When the liquid phase is transferred from the boiler to another boiler, each liquid phase is heated to 95-98 ° C.

When filling the third boiler with the cooking solution, its supply is stopped. Boilers are ready for pulping. As a result, the chips in all the boilers went through the same treatment in two stages. As a result of water treatment of a triple volume of chips, an extract with a high concentration of AG is obtained. It is sent to the storage tank. In boilers, wood chips are poured with the same cooking solution. Cellulose is cooked in the same modes with separate recirculation of the cooking solution in each of the boilers. After cooking, the boilers are empty. Part of the black liquor is sent to a storage tank. The rest is sent to the cooking chemicals regeneration system. After emptying the boilers, they begin the second cycle of the boiler. The boilers are reloaded with wood chips. Filtered extract from the storage tank (for example, with the addition of water) is supplied to the first boiler for water treatment. Using this technique allows you to increase the concentration of AG in the extract or to maintain it at a high level, ensuring the maximum degree of extraction of AG from the chips with water and the possibility of selecting part of the extract for processing. Black liquor to the second stage of chip processing is fed from the storage tank. The remaining operations of the pulp production process are similar to those described above.

All subsequent boiler cycles are also identical.

The following examples illustrate the possibilities of the proposed method. When they are used, a laboratory setup is used, which includes an autoclave with systems for recirculating liquid phases, heating the contents of the autoclave and liquid phases to a predetermined temperature, removing each liquid phase from the autoclave by displacing it with another phase, providing the specified parameters of the cooking modes, as well as storage tanks for the extract and black liquor. In all examples, the processing of wood chips before cooking is carried out with a hydraulic module of 1: 3, calculated on dry wood, the temperature of the extractants 95-98 °, the extraction time for each of the extractants is 25 minutes, the moisture content (averaged) of the chips loaded into the autoclave is 50%. Samples processed in two steps of chips are cooked with recirculation of the cooking liquid. Each processing cycle includes sequential processing of three identical portions of chips (a, 6, c). Control boiling of samples of treated chips is carried out in the following mode: raising the temperature from 95 to 140 ° C - 40 minutes, holding at 140 ° C - 40 minutes, raising to 170 ° C - 40 minutes, cooking time at 170 ° C - 90 minutes. The consumption of white liquor calculated on absolutely dry wood, 22%, the value of the hydraulic module during cooking - 1: 4. As parameters for comparing samples of cooked cellulose, its yield, Kappa number, and α-cellulose content are used.

Example 1. To obtain cellulose they take a mixture of wood chips from pine, birch and larch with a mass fraction of larch wood chips of 20% and an AH content of 19.8%. With a sequential extraction of 25 minutes in a recycle mode of the extractant of three portions of wood chips (this is an analogue of the process in an installation of 3 boilers), the concentration of AG in the extract reaches 15.05 g / l. The residual concentration of AG in the chips is 9.8%. The same portions of chips are subsequently treated with black liquor. After this treatment, the AG content in larch chips is below 5.0%. After replacing the black liquor with a cooking solution, the content of liquor in the chips is ~ 10%. All three servings (a, b, c) are cooked under the same conditions. The results of measurements of the parameters of cellulose in the samples are presented in the table.

In the second cycle of testing the method, as well as in the subsequent ones, using 3 portions of the same chips, an extract from the first cycle or a mixture of extracts from previous cycles are fed to the water treatment of the first portion. Otherwise, all operations are similar to operations in the first cycle. The concentration of AG in the extract after the second cycle is 29.3 5 g / l, after the third - 42.93 g / l, after the fourth - 55.74 g / l, after the fifth - 64.3 g / l. In the sixth cycle, an extract with the addition of fresh water is fed to the chip processing.

For comparison with the first cycle in terms of the leveling characteristics of the chips in the mixture, all three portions of chips of the fifth cycle (a, b, c) are cooked under the same conditions. The results of the analysis of the obtained pulp samples are shown in the table.

Example 2. To obtain cellulose, a mixture of wood chips from spruce, aspen, and larch is taken with a mass fraction of 50% and an AG content of 13% in it. After the first cycle, an extract is obtained with an AH content of 24.7 g / l, after the second - 48.1 g / l, after the third - 48 g / l. Accordingly, in the following cycles, an extract with the addition of water is fed to the first stage of chip processing.

Samples of chips after the first and third cycle (a, b, c) are cooked according to the above modes. The results of the analysis of cellulose are shown in the table.

Example 3. To obtain cellulose, they take larch chips with an AH content of 6% in it with the addition of 20% birch chips. The extract after the first cycle contains 18.24 g / l AG. The calculated concentration of AG in the water inside the larch chips is 24 g / l. In this case, already in the second cycle, a mixture of extract and water in a ratio of ~ 30:70 is fed to the wood chips. All three servings of chips processed in the first cycle (a, b, c) are cooked, the characteristics of the chips are measured.

Derived from the processes of the extract is processed as follows. First, it is cleaned of resinous substances by filtration or pressure flotation, then concentrated by ultrafiltration to an AG content of 25-26% in water. Then AG is planted in acetone, the precipitate is washed with acetone, dried and pure AG is obtained.

Table Pulp Characteristics Example 1 Example 2 Example 3 Cycle 1 Cycle 5 Cycle 1 Cycle 2 Cycle 1 but b at but b at but b at but b at but b at Exit, % 33.0 33,2 33,2 33.0 33,2 33.1 33.3 33.5 33,4 33.3 33,4 33,4 33.6 33,4 33.5 Kappa number, units 21.0 21,2 21.1 21,2 21,2 21.3 21.3 21.3 21.3 21.0 21.1 21.1 21,2 21.3 21,4 The content of α-cellulose,% 94.03 94.00 94.01 94.01 94.04 95.92 93.84 93.85 93.7 94.01 94.01 93.9 94.65 94.3 94.6

Claims (4)

1. A method of producing sulfate cellulose from a mixture of wood chips of different wood species, including the use of a periodic boiler, loading it with wood chips from a number of species containing larch, extraction of wood chips by treating it with an aqueous medium at an elevated temperature for a predetermined time to obtain an extract, removing its processing with the production of arabinogalactan, supplying a cooking solution to the boiler, cooking chips, removing cooking products from the boiler, characterized in that a number of breeds additionally include wood Pure pine, spruce, birch, aspen, wood chips mixture after treatment with an aqueous medium are additionally treated with black liquor, while both treatments are carried out in three boilers connected by liquid phases by sequentially filling each of the liquid phases with the removal of the aqueous extract by displacing it from the boilers black liquor and the withdrawal of black liquor by its displacement with a cooking solution. 2. The method according to claim 1, characterized in that the proportion of wood chips of larch in the total mass of wood chips is 20-80%. 3. The method according to claim 1, characterized in that the chips are treated with water and black liquor at a temperature of 95-98 ° C. 4. The method according to claim 1, characterized in that the extract is used to process fresh wood chips.