DD140747A1 - PROCESS FOR THE PRODUCTION OF VISCOSES - Google Patents

Description

Anwe area of the invention

The invention relates to a process for the production of viscose from pulp.

Characteristic of the "known tech nischen.ösen conditions

In the production of viscose, using pulp as the starting material, the first stage of the process is the production of alkali cellulose. The procedure is generally as follows:

The pulp used as starting material is alkalized either as a mash or as leaves with 17-22% HaOH solution

The excess ITaOH solution is removed by pressing, so that the obtained alkaline cellulose has a NaOH content of 15-17 % . The cellulose content of the alkali cellulose is 30-35 %.

The resulting alkali cellulose is fiberized and exposed at 20 - 60 ⁰ C the oxygen influence of the air until the average molecular size of cellulose by chain cleavages to the desired size decreases.

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The faster at elevated temperature depolymerization can be accelerated by the use of oxidizing agents or catalysts such as cobalt or manganese salts. The disadvantage of such a procedure consists in a considerable proportion of free alkali in the alkali cellulose. As a result, except in the main reaction, the xanthogenation of the carbohydrates, in the side reactions with the free alkali of the alkali cellulose carbon disulfide consumed, which is thus not available for the esterification , In the patent DD 75636 this disadvantage is eliminated by Doppelalkalisierung by after the pre-maturation a further alkalization with a NaOH solution of less than 15 % is connected.

• The disadvantage here, in comparison to the usual method, the necessary double Alkalisieranlage and the associated high investment and operating costs. Furthermore, by dissolving away considerable proportions of the low molecular weight constituents formed during the pretreatment, considerable dive losses can not be avoided. From DE-OS 2208335 it is known that wood is treated prior to digestion with high-energy radiation. The aim of the method is to modify the lignin of the hemicelluloses and the cellulose in the wood. This results in links between the fragments of the long molecular chains and other molecular components of the wood, especially between the lignin fragments and the hemifragments. As a result, an unbleached pulp with an increased yield but also with an increased lignin content is obtained. A disadvantage of this process is an increased consumption of bleaching chemicals in the production of bleached pulp.

In the patents DD 113 581 and DD 125 429 the disadvantage of the increased lignin content in the unbleached pulp by a pre-treatment with BisuIfit- or sulfite solutions before irradiation with. eliminated high-energy rays. The lignin content is further reduced below the previously known level.

Explanation of the essence of the invention

The object of the invention is to achieve a pre-activation by irradiation of the pulp. According to the invention, the object is achieved by a combination of irradiation of the pulp with high-energy rays, preferably high-energy electrons before alkalization and treatment with HaOH solution. and bleaching process the accompanying substance of the wood lignin is removed. which is favored by prior irradiation of the wood as described in patents DD 113 and DD 125 429. Thus, the radial scavenger present in native or vorsulfonierter form in the pulp, so that a targeted depolymerization with simultaneous structure loosening by irradiation of the pulp is possible «

The applied radiation dose is chosen in the range of 1-30 kGy so that the desired average degree of polymerization after alkalization is present. The alkalization is carried out with an ITaOH solution of less than 19%, preferably 16%. The advantages of the method according to the invention are that the irradiation of the pulp leads to a pre-activation with simultaneous structure loosening and incoming depolymerization. This will ensure alkalization at lower liquor concentrations and eliminate the pre-maturity used until then. Further savings will be made on carbon disulfide and caustic soda and sulfuric acid.

The reduced CS ₂ -EseSEZ reduces the environmental impact of HpS and CSp *. Compared to the double-alkalization, lower immersion losses occur. The elimination of the second alkalization plant and its readiness for pre-maturity leads to a reduction of the operating costs. · The capital expenditure is considerably reduced and labor is saved.

Auaführungsbe ispieIe Example 1

Buchensulfitzellstoff with an average degree of polymerisation of 810 is pre-activated by irradiation with electron beams with a dose of 10 kGy and degraded to an average degree of polymerisation of 425. The subsequent Tauchalkalisierung is rn.it NaOH solution having a Konsentration of 16% at 21 ⁰ C performed "after squeezing the excess sodium hydroxide solution is no preripening immediately with the sulfidation a Zeitraum.von 150 minutes, at a temperature of 21-29 ⁰ C rising, started. The resulting xanthogenate is dissolved in a turbo solvent. The composition of the viscose obtained is 8% cellulose, 5.8 % alkali and 28 % carbon disulfide based on cellulose.

The filter value of this viscose is _kw = 967. Since the filter value is not standardized, an estimation can be made according to the following scale

k 800 - 1000 very good filterability k _w 1000 - 1200 good filterability k _w 1200 - 1500 moderate filterability

Example 2

Viscous prepared as in Example 1, but with a carbon disulfide content of 24 %. A filter value of k = 1008 is achieved.

Example 3

Viscous prepared according to Example 1, wherein the carbon disulfide content 27 % and the alkali content is 5 * 3. The achieved filter value is 983 «

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Claims (1)

invention claim A process for producing viscose from pulp, characterized by a combination of irradiation of a pulp with high-energy radiation, preferably high-energy electrons of a radiation dose of 1 to 30 kGy, preferably before alkalization and treatment with KaOH solution below 19 %, preferably 16%.