SU717197A1 - Method of bleaching pulp for chemical processing - Google Patents

Description

1 The invention relates to the pulp industry of the bulk industry and can be used in the bleaching of cellulose D for chemical processing. A known method of bleaching sulfite cellulose, which includes a chlorination stage, hot refining, is carried out with alkali at a temperature of 80-120 ° C for 120150 minutes, and hypochlorite treatment at a temperature of 35-40 ° C for 120-180 minutes 1. A disadvantage of the known method Cellulose bleaching for chemical processing, is a large loss of cellulose fiber at the stage of hot refining, depending on the content of cellulose, 20-30% by weight of absolutely dry cellulose. It has been established that for each percent increase in os-cellulose, 3-4% cellulose hair is lost: / The closest to the technical essence. The proposed method includes the SG1OSO6 bleaching section, in which, in order to reduce chemical losses, it is envisaged to carry out a round reclamation with a Suitcase solution of alkali and hypochlorite 2. The method consists in that cellulose after chlorination (X) enters hot fencing,; is carried out with alkali with added sodium hypochlorite (GO + H), at t -98-ioO ° C for 120150 min, alkali consumption 10% by weight of absolutely dry cellulose (a. sec. c.),, J and hypochlorite consumption 0.5-3% to m CCE a.c.li. This is followed by the second stage of chlorination (X), then two stages of hypochlorite (G) and Kislovka (X- (GO + G) -X-G-G-K). The consumption of sodium hypochlite in the first stage is 1% by weight, as ac., The processing time is 180 minutes, the temperature. The consumption of hypochlorite at the second stage is 0.6% to the mass of an ac.cts, will continue. 180 min, temperature 40 ° C. Adding hypochlorite in the process of hot refinement allows. to increase the yield of cellulose by 2-7% with the preservation of the content of ot-cellulose within the limits of the norm of GOST No. 5982-75 (see 1 tab. 1).

Change in os-cellulose content, viscosity and chemical loss of cellulose depending on the treatment according to the known and proposed methods

Table 1

383

87.1 87.8 345 420 94.5

Hot refinement with the addition of hypochlorite (a known method)

X- {10 + G. „. ) 93.5 392 80.5 19.5 2.05

92,: 4,308 82.6 17.4 4.10

X- () X- (GO + Gz9) 90.7 224 86.2 13.8 7.67

Hot refining with pretreatment with alkali and hypochlorite (proposed method)

However, the chemical losses in this treatment method are still quite high, obviously, due to the fact that the pulp supplied to the hot refining

Changes in the carbonyl and carboxyl groups in cellulose depending on the degree of bleaching by the known method

11rZ, 12.7 1.09

4.55 4.2

97.5

2.5 78.46 21.54

after chlorination, it contains a rather large amount of carbonyl groups of 12 mmol (100 g of cellulose), which are responsible for dissolving it in hot alkali (see tab. 2 and 3).

. Table 2

The change in the content of carbonyl and carboxyl groups in cellulose, depending on the bleaching runoff according to the proposed method. Carbonyl groups 11.3 12.7 8.68 7.9 Carboxyl groups 5.07 4.55 4, / 7 5.17 The purpose of the invention is to reduce chemical losses cellulose, an increase in its yield while maintaining the purity of the final product, as well as a decrease in the amount of organic pollutants in waste waters. This goal is achieved by the fact that, after chlorination, before hot refining, sequential operations are performed to treat the cellulose with alkali and then with hypochlorite at a flow rate of 0.5–4.0% by weight of absolutely dry cellulose for 60–120 minutes. In contrast to the known method, in which chlorinated cellulose goes directly to hot refining, in the proposed method, after chlorination, the cellulose is additionally treated with alkali at: t ° 40-60 ° C for 60-120 minutes and the change in car content in cellulose is dependent on hypothesis.

Duration of treatment with hypochlorite

9.64

5.34 8.93 5.22 7.14 5.16 6, 34 8.93 9.29 6.66

T a

faces

6.34

5.75

 7.62 6.29 5.48 5.97 6.77 5.58

.5,33 6,81 5,41 6,12 5,96 7,1 6,72 7,25 5,96 0,89 0,5 0,38 6,72 7,1 5,32 6,3 6 , 65 alkali consumption of 0.5-1.5% by weight of absolutely dry cellulose. This treatment reduces the carbohydrate content. cellulose from 12 to 8.7 mmol / lpO g of cellulose (see. Table 3). The following difference of the proposed method from the well-known one is that after this alkaline treatment, the cellulose is treated with hypochlorite with the consumption of the latter from 0.5-4% by weight to absolutely dry cellulose at t 40-45 ° C for 60-120 minutes. The most preferable hypochlorite treatment time at this stage is 90 minutes, since after this time carbonyl groups begin to accumulate in the cellulose and continue processing further, it is unreasonable to see table 4}. A table of length and carboxyl groups of its length. Reducing the processing time of hypochlorite over overeating (GO) is also a distinctive feature of the proposed method compared to the known, where the usual hypochlorite bleaching lasts for 120-150 minutes. Example 1. Unbleached cellulose, for example, sulphite viscose is chlorinated, as usual, at a temperature of 60 minutes and the consumption of active chlorine is 1.0-1.5% by weight of a.s.c. After washing, chlorinated cellulose is subjected to alkaline treatment at t for 120 min and alkali consumption 1.0% by weight of a.s.c

Ordinary area., Accommodation: XHD94.5

Famous

the way

X- (GO + G,) 93.5

The proposed method H-Shch-Tso / d-GO 93.3

As follows from the data of table 5, the implementation of the proposed method of bleaching pulp by further processing it before hot refining with alkali and hypochlorite, with a consumption of the last 1% and a processing time of 90 minutes, allows reducing chemical losses to 16.1% instead of 19, 5% by a known method. (Scheme X- (GO + G). Chemical losses during normal refining (X-GO scheme) without the addition of an oxidizing agent are even greater and are 21.54%

The content of C-cellulose according to the proposed method of bleaching is within the limits of GOST. .

P r and I r 2. Unbleached pulp sulfite viscose is chlorinated, as in example temperature

420

78.46

21.54

80.5

19.5

392

83,87

314

16,1

within 60 minutes and consumption of active chlorine 1.0-1.5% by weight of a.s.ts.

Chlorinated cellulose after washing is subjected to alkaline treatment at t for 120 minutes and consumption of alkali 1.5% by weight of a.s.c.

Next, the cellulose is fed to the hypochlorite bleaching. Hypochlorite treatment is carried out at. t 40 ° C, the consumption of hypochlorite is 2.0% by weight of an ac.ct., processing time is 90 min.

After the hypochlorite bleaching, the cellulose enters the hot refining, which is carried out without the addition of an oxidizing agent, at t 98–100 ° C, with an alkali consumption of 10% by weight a.s. within 130 min.

The pulp is then bleached in the usual way,. . Table-6 Next, the pulp is fed to hypochlorite bleaching. Hypochlorite treatment is carried out at t 40 ° С, hypochlorite consumption is 1% by weight of a.s.c. processing time 90 min. After the hypochlorite bleaching, the cellulose is fed to the stage of ordinary hot refining, which is already carried out without the addition of an oxidizing agent, at a temperature of 98-100 ° C, with an alkali consumption of 1% by weight of an ac. within 130: min. . The next stage of bleaching can be either hypochlorite treatment with the latter consumption of 0.6% by weight of an ac / c, or bleaching with chlorine dioxide in the usual way. The proposed method of bleaching, as a rule, completes kislovka ,. Table 5 It follows from the data in Table 6 that the pretreatment of hypoklorit cellulose at a consumption rate of the last 2% will cause chemical losses during a hot area of about 12.3%, compared with the {known method, the loss is 17.4%. The content of o-cellulose. At this, it remains practical without Schme tHeHHft. ; In addition, the analysis of wastewater after gbr of which the cyjifc trimming of viscous pulp was improved.

| la; gIye water sulfite sulfide high living hydration zone | shnby pulp

 Example 3. Unbleached sulphite viscose base 1pu is chlorinated as in examples 1 and 2.

Chlorinated nOeite cellulose washes under cellulite (Delphine 6By Kyo at t 40 ° C for 120 MIN and alkali consumption 1.5% by weight. C.

Then the pulp comes Ya tgypochlorite processing, The second process takes place at t, the flow rate is known method

X-th + r o /

 /but

Proposed

the way

X-C-D su-go

3 / o

Rita 3.0% by weight of a.s.c. Processing time is 90 min.

After the hypochlorite treatment, the cellulose is fed to a hot blender, which carried out 5bt without oxidizer at t 98100 C with an alkali consumption of 10% by weight a.s.c, for 130 min.

Next, the pulp is bleached in the usual way.

Table 8

86.2

224

13.8

212

12.24

87.76 that the bleaching of cellulose according to the proposed & mu method significantly reduces the content of organic pollutants in them. Comparative results of the analysis of wastewater after hot improvement: Vanj Celleoui according to the known and proposed method. tJC) promoted with; isl with bu. . T a b l and c a 7

  From the data in the table it follows that the pretreatment and, using the UI11bhl6 |) b, the amount of the past 3% will reduce chemical losses to 12.2%, while maintaining the sbdor sayiyos cellulose. A further increase in pacxt flia sodium hypochlorite in the treatment of cellulose is impractical because at the same time, patjaib viscosity begins, which can lead to the destruction of cellulose fiber a.

Thus, the proposed. The method of cellulose bleaching for chemical and kKott processing provides the opportunity to produce high quality, cellulose with b (the best output, which essentially reduces the consumption of wood 1 ton of pulp.

Reducing the content of organic pollutants in wastewater is an additional credit: 1 The method of the proposed method, as compared with the known method of pulp bleaching for chemical processing. , /;

Further development of the proposed method of pulp bleaching will be aimed at introducing it into the industry, in particular,

The Priozersk Pulp Mill and other enterprises that produce sulphite pulp for chimperer- processing. .

Claims (2)

1. The protein of cellulose. Monograph Tuppy. Edited by FP Komarov. United States, 1957, p. 65-68,160-163. 2. US patent number 3817825, ml. 162-89, 1974 (prototype).