Method of bleaching of sulphate pulp

 

(57) Abstract:

Way concerning the technology of bleaching of sulphate pulp from deciduous or coniferous wood, or a mixture thereof. The pulp is treated with oxygen in a reactor in the presence of alkali. Lepromatous cellulose is treated with additional oxygen, or hydrogen peroxide, or mixtures thereof, or a peroxide compound in an alkaline medium in the mixer at a pH of 9.5 to 12.1 with subsequent storage in the storage tank at atmospheric pressure for 20-120 minutes at the same time as peroxide compounds used peroxomonosulfate acid, or peroxidizing acid, or sodium salt of one of these acids in an amount of 0.01-1,50% by weight of the abs.dry. the pulp. The first stage of processing chlorine dioxide is carried out in the presence of sulfuric acid at pH 3-5. Then perform the first processing pulp with chlorine dioxide, the treatment with oxygen in the presence of alkali, hydrogen peroxide and protector of magnesium sulfate in the bleaching tower with upward flow of the pulp. Followed by a second treatment with chlorine dioxide. After the second stage of processing pulp chlorine dioxide can additionally be bucking with subsequent treatment with chlorine dioxide. what tatom of the proposed method is to reduce the consumption of chlorine dioxide, reducing the pollution reduction process, as well as increasing the strength characteristics of the pulp at the expense of increasing the selectivity of oxygen delignification. 3 C.p. f-crystals, 2 tab.

The invention relates to the field of pulp and paper production and concerning the technology of bleaching of sulphate pulp from deciduous or coniferous wood, or a mixture thereof.

There is a method of bleaching of sulphate pulp by two-step processing of its two reactors with oxygen under pressure in the presence of hydrogen peroxide in the second stage, from pre-feed chemicals into the mixer (US, 5916415A, D 21 C 9/16, N. CL 162-65, 29.06.1999,)

However, this method does not allow to obtain a pulp with a high mechanical strength due to the significant degradation of cellulose treated her under pressure in the second reactor. In addition, this method is very expensive.

The closest analogue of the present invention is a method of bleaching of sulphate pulp, comprising the successive stages of processing pulp with oxygen in a reactor in the presence of alkali, the first treatment with chlorine dioxide, treatment with oxygen in the presence of alkali, hydrogen peroxide and protester, N206560 A2, D 21 C 9/10, 30.12.1986 year).

According to this method, both stages of treatment with oxygen is carried out in the presence of hydrogen peroxide. About the use of sulfuric acid during treatment with chlorine dioxide in the description is not specified.

This method allows to reduce the scheme bleaching on the main stages up to 4 stops.

However, this method leads to a significant consumption of chlorine dioxide, thereby causes the increase of environmental pollution.

In addition, the known method in the bleaching process can lead to poorer preservation of the strength properties of bleached pulp.

New technical result from the use of the present invention is to reduce the consumption of chlorine dioxide, leading to the reduction of environmental pollution and the cost of the process, as well as increased strength characteristics of the pulp at the expense of increasing the selectivity of oxygen delignification.

This result is achieved in that in the method of bleaching of sulphate pulp, comprising the successive stages of processing pulp with oxygen in a reactor in the presence of alkali and tread or without him, the first treatment with chlorine dioxide is a tower with an ascending stream of pulp and second processing chlorine dioxide, according to the invention after treatment with oxygen in the reactor before the first stage of processing of chlorine dioxide lepromatous pulp is further treated with oxygen or hydrogen peroxide, or mixtures thereof, or a peroxide compound in an alkaline medium in the mixer at a pH of 9.5 to 12.1 with subsequent storage in the storage tank without pressure (at atmospheric pressure) for 10-120 minutes at the same time as peroxide compounds used peroxomonosulfate acid (H2SO5), or peroxidizing acid (H2S2O8), or sodium salt of one of these acids in amounts of from 0.01 to 1.50% of the mass of absolutely dry pulp, and the first stage of processing chlorine dioxide is carried out in the presence of sulfuric acid at pH 3-5.

The treatment of pulp with oxygen in the reactor can be conducted in the presence of hydrogen peroxide at the rate of the last of 0.1 to 1.0% by weight of absolutely dry pulp, and without it, and the treatment of pulp with oxygen in the bleaching tower is necessarily carried out in the presence of hydrogen peroxide at the rate of the last 0.5 to 1.5% by weight of absolutely dry cellulose, the treatment with oxygen in the bleaching tower is carried out at a flow rate of hydrogen peroxide in excess of its expenses is led by chlorine her optionally be bucking and subsequent treatment with chlorine dioxide, especially when bleaching the hard pulp.

The second stage of processing chlorine dioxide is carried out in the presence of sulfuric acid at a pH of 4-6.

The authors of the present invention, it was found that the efficiency of this process is determined precisely by the combination of four-stage bleaching, comprising the successive stages of processing cellulose in the reactor with oxygen, the first treatment with chlorine dioxide, processing oxygen in the bleaching tower and a second stage treatment with chlorine dioxide, with in-depth delignification, which expose the pulp after the first of these stages by processing lepromatous pulp in the mixer oxygen-containing compound in an alkaline medium at a pH of 9.5 to 12.1 with subsequent storage in the storage tank pulp at atmospheric pressure. In fact, this invention has the same four-step process, as in the prototype, but with a deep delignification in the first stage, which leads to increase the degree of delignification and the selectivity of the process. This in turn leads to lower consumption of whitening chemicals in the later stages of bleaching and pollution runoff.

Processing of cellulose in the reactor is carried out prabodh pulp with oxygen in the bleaching tower is performed under hydrostatic pressure, equal to the height of the column of the tower at a flow rate of alkali from 0.8 to 3.0% by weight of absolutely dry pulp.

The invention is illustrated by the following examples of its implementation.

Example 1. Sulphate pulp from wood of aspen and birch with a concentration of 11% was processed with oxygen in the reactor under a pressure of 0.5 MPa and the flow rate of alkali (caustic soda) 1.5% of the mass of absolutely dry pulp within 60 minutes

On the washed pulp folder consistently serves the protector of magnesium sulfate in amount of 0.2% by weight of absolutely dry cellulose, alkali in amount of 1.5% by weight of absolutely dry pulp is then pumped through a heater (heating lead to a temperature of 95oC) the mass is fed to the mixing with oxygen in the amount of 1.6% by weight of absolutely dry cellulose and hydrogen peroxide in the amount of 0.5% by weight of absolutely dry pulp and then into the reactor. The treatment is carried out in the reactor for 50 min. Pressure at the bottom of the reactor is 0.75 MPa, and in the upper part of the reactor - 0.37 MPa.

Then lepromatous pulp from the digester blow tank for relieving excess pressure and is served by a pump to a mixer for additional processing oxygen in caliche within 60 minutes Alkaline environment in the mixer is created due to residual alkali in the mass.

Then the mass is washed on a vacuum filter and serves on the stage of processing (delignification) chlorine dioxide which is taken in the amount of 2.0% (in units of active chlorine) from the mass of absolutely dry cellulose, pre-acidification weight sulfuric acid. Treatment with chlorine dioxide is carried out at a temperature of 50oC for 120 minutes

Then the mass is washed on a vacuum filter, washed on the folder serves consistently protector of magnesium sulfate in the amount of 0.5% by weight of absolutely dry pulp and the alkali in the amount of 0.9% by weight of absolutely dry pulp. Then the mass through the heater where it is heated to a temperature of 70oC, and the mixer, in which it is treated with hydrogen peroxide in the amount of 0.8% by weight of absolutely dry cellulose and oxygen in the amount of 0.5% by weight of absolutely dry pulp, served by the pump in the bleaching tower with upward flow of the pulp, where treated for 40 minutes at a temperature of 70oC under hydrostatic pressure equal to the height of the column of the tower. The mass moves in the column from the bottom up. From the top of the column saturated with chemicals mass poured into the vacuum filter and served in the second stage of processing chlorine dioxide, which take in the amount of 1.3% (in units of active chlorine) from the mass of absolutely dry pulp. This treatment is carried out without acidification mass at a temperature of 65oC for 180 min at pH 5.5.

Bleached pulp is washed on a vacuum filter.

Modes of obtaining bleached pulp are presented in table 1.

The quality indicators received bleached pulp are presented in table 2.

Examples 2-7. Experiments are performed analogously to example 1. Distinctive features of the parameter values, chemicals and their costs, confirming the validity of the claims presented in table 1.

Indicators bleached pulp are presented in table 2.

Example 8. The experience carried out analogously to example 1, but the processing of oxygen in the reactor is carried out without addition of hydrogen peroxide and magnesium sulfate.

After the second stage of processing chlorine dioxide washed mass additionally leach caustic soda (Y) at a temperature of 60oC for 120 min, the mass is washed and served on the stage of treatment with chlorine dioxide (D2). The treatment is carried out at a temperature of 65oC for 180 min at a flow rate of chlorine dioxide of 0.5% (in units of AK is the storage tank to withstand the weight for 120 minutes

The indicators obtained bleached pulp are presented in table 2

Example 9. The experience carried out as in example 1, but using pulp from softwood (pine and spruce). Additional stage be (Y) and treatment with chlorine dioxide (D2) were carried out as in example 8. In the storage tank to withstand the weight within 20 minutes

Parameter values are presented in table 1.

The indicators obtained bleached pulp are presented in table 2.

Example 10 (the prototype). The experience carried out as in example 1, but without a stage of processing after the processing stage of the pulp with oxygen in the reactor before the first stage of processing of chlorine dioxide and without addition of sulphuric acid at both stages of treatment with chlorine dioxide.

As can be seen from tables 1 and 2, the proposed method can improve mechanical properties of cellulose and its whiteness and reduce pollution (COD and Oh).

1. Method of bleaching of sulphate pulp, comprising the successive stages of processing pulp with oxygen in a reactor in the presence of alkali, the first treatment with chlorine dioxide, treatment with oxygen in the presence of alkali, hydrogen peroxide and protector of magnesium sulfate in otbel the processing of oxygen in the reactor before the first stage of processing of chlorine dioxide lepromatous pulp is further treated by oxygen, or hydrogen peroxide, or mixtures thereof, or a peroxide compound in an alkaline medium in the mixer at a pH of 9.5 to 12.1 with subsequent storage in the storage tank at atmospheric pressure for 20 to 120 min, the peroxide compounds are used peroxomonosulfate acid, or peroxidizing acid, or sodium salt of one of these acids in amounts of from 0.01 to 1.50% of the mass of absolutely dry pulp, and the first stage of processing chlorine dioxide is carried out in the presence of sulfuric acid at pH 3 to 5.

2. The method according to p. 1, characterized in that the treatment of pulp with oxygen in the reactor is carried out in the presence of hydrogen peroxide at the rate of 0.1 to 1.0% by weight of absolutely dry pulp, and the treatment of pulp with oxygen in the bleaching tower is carried out at a flow rate of hydrogen peroxide 0.5 to 1.5% by weight of absolutely dry cellulose, the treatment with oxygen in the bleaching tower is carried out at a flow rate of hydrogen peroxide in excess of its consumption in the processing phase, the oxygen in the reactor is 0.1 - 0.7 percent.

3. The method according to p. 1, characterized in that after the second stage of processing pulp chlorine dioxide additionally leach and subsequent treatment with chlorine dioxide.

4. SPO is s at pH 4 - 6.

 

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