A method of obtaining a bleached sulfite pulp on magnesium base

 

(57) Abstract:

The method applies to the pulp and paper industry and can be used in the manufacture of bleached sulfite cellulose magnesium base for the production of paper with the increased demand for white. The method includes a preliminary two-stage treatment of a suspension of cellulose, the first stage of which is carried out by acid, and the second magnesium-containing compound, with intermediate washing between steps; wash before bleaching. The bleaching is carried out by treatment of a suspension of pulp without chlorine bleaching reagent on the basis of hydrogen peroxide in the presence of a suspension of magnesium hydroxide. In the first stage pre-treatment as acid use sulfite cooking solution of magnesium base at a flow rate total SO20.5 to 1.5%. In the second stage pre-treatment as a magnesium-containing compounds are used magnesium hydroxide in the amount of 0.5-2.0%% MgO by weight of absolutely dry pulp. This bleached without chlorine reagent on the basis of hydrogen peroxide and magnesium hydroxide suspension of cellulose further treated with one hydrogen peroxide at pH of 10.5 and use hydrogen peroxide or a mixture of hydrogen peroxide and oxygen. After washing, the suspension of pulp processed in the first processing stage, is subjected to chelation at a flow rate of chelate compound in an amount of 0.1-0.3% of the mass of absolutely dry pulp. The chelate compounds are used Trilon B. Technical result is to increase the efficiency of the process with the increased demand for white. 3 C.p. f-crystals, 1 table.

The invention relates to the pulp and paper industry and can be used in the manufacture of bleached sulfite cellulose magnesium base for the production of paper with the increased demand for white.

There is a method of bleaching lignocellulosic wood pulp, involving pre-treatment of the pulp by acid (pH 1-7) in the presence of compounds of magnesium, washing, and bleaching peroxide-based compound (see EN 2072014 C1, MCI D 21 C 9/16, publ. 29.10.82).

At the same time as the magnesium compounds can be used the following compounds: magnesium sulfate, magnesium chloride, magnesium carbonate or magnesium nitrate and the conditions for their use in the processing phase of the slurry should be such that the alkaline earth metal was dissolved in the suspension of the pulp.

Kacha is obtained as chemical (sulphate process cooking, sulfite method of cooking, cooking with organic solvents or Sadovyi ways), and mechanical treatment.

The known method provides a higher degree of whiteness of the finished cellulose significant reduction of the Kappa number.

However, this method of bleaching cellulose is effective only up to a certain limit and does not provide pulp for paper with high demand for white.

The closest analogue of the present invention to the technical essence and the achieved result is a method of obtaining a bleached sulfite pulp on magnesium base, including a preliminary two-stage treatment of a suspension of cellulose, the first stage of which is carried out by acid, and the second magnesium-containing compound, with intermediate washing between steps, washing before bleaching, and bleaching by treating the suspension of pulp without chlorine bleaching reagent on the basis of hydrogen peroxide in the presence of a suspension of magnesium hydroxide (see EN 2039141, MCI D 21 C 9/147, publ. 30.04.91).

At the first stage of processing of a suspension of cellulose using an inorganic acid selected from the group of sulphur, cellulose as magnesium-containing compounds are used magnesium sulfate, or magnesium chloride, or a mixture of magnesium chloride with calcium oxide, or a mixture of magnesium chloride with calcium chloride.

The known method has allowed to increase the whiteness of the pulp with reduced consumption of hydrogen peroxide.

However, to achieve white more than 88% of the known method does not work, as follows from the presented data.

New technical result is to increase process efficiency in the production of pulp for paper production with increased demand for white.

This result is achieved in that in a method of producing bleached sulfite pulp on magnesium base, including a preliminary two-stage treatment of a suspension of cellulose, the first stage of which is carried out by acid, and the second magnesium-containing compound, with intermediate washing between steps, washing before bleaching, and bleaching by treating the suspension of pulp without chlorine bleaching reagent on the basis of hydrogen peroxide in the presence of a suspension of magnesium hydroxide, on the first level pre-processing as acid use sulfite cooking solution of magnesium base at a flow rate total SO20.5 to 1.5%, and ve in the amount of 0.5-2.0% in units MgO by weight of absolutely dry pulp, with bleached without chlorine reagent on the basis of hydrogen peroxide and magnesium hydroxide suspension of cellulose further treated with one hydrogen peroxide at a pH of 10.5 to 12.0, the temperature of 75-85oC, concentration of mass 7-20% for 180-240 minutes

The first stage pre-treatment of cellulose is carried out at a pH of 1.2 to 3.0, the mass concentration of 5-12%, the consumption of SO20.5-1.5 percent to absolutely dry fiber, a temperature of 15-50oC and a duration of 0.5-1.0 h, and the second stage pre-treatment of cellulose is carried out at a pH of 8.0 to 9.5, and a temperature of 20-100oC, concentration of mass 5-12%, the consumption of magnesium hydroxide 0.5 to 2.0% in units of MgO and duration of 0.2-1.5 h, and as a bleaching agent in the first stage of pulp bleaching using hydrogen peroxide or a mixture of hydrogen peroxide and oxygen at the flow rate of 0.5-2.0% of absolutely dry mass. The consumption of hydrogen peroxide in the second bleaching stage is 1-4% of absolutely dry mass.

Possible processing chelate compound washed pulp after treatment with acid, the consumption of chelate compounds is 0.1-0.3% of the mass of absolutely dry pulp, and as chelate soedinenii sulfite pulp on magnesium base.

Example 1. A method of obtaining a bleached sulfite pulp on the magnesium base is carried out by two-step processing suspension sulfite softwood pulp with Kappa number 20, in this case:

- on the first stage of a 5% suspension of cellulose treated with sulfite cooking solution of magnesium base at a flow rate total SO21.5% by weight of the absolutely dry fiber, the concentration of SO24,5%, the MgO content of 0.1% and a pH of 1.2. Processing time is 0.5 hours at a temperature of 15oC;

- at the second stage, 12% suspension of cellulose is treated with a suspension of magnesium hydroxide with a flow rate of 2% to absolutely dry fiber at a pH of 9.5. The processing time is 90 minutes at a temperature of 100oC.

Between the first and second stage processing suspension of cellulose washed with water.

The pulp suspension with a concentration of mass to 7% after the second stage of processing is bleached with hydrogen peroxide in the presence of magnesium hydroxide. Technological parameters bleaching following: the consumption of hydrogen peroxide 4% by weight of the absolutely dry fiber, the consumption of magnesium hydroxide 2% by weight of the absolutely dry fiber, temperature 80oC, pH of 9.0, the duration of the bleaching 120 minutes

The next step otelleri bleaching following: the consumption of hydrogen peroxide 1% by weight of the absolutely dry fiber, the consumption of sodium hydroxide and 0.7% by weight of the absolutely dry fiber, the temperature of the 75oC, pH of 10.5, the duration of the bleaching 180 minutes

Qualitative indicators of cellulose in the table.

Example 2. A method of obtaining a bleached sulfite pulp on magnesium base carried out analogously to example 1 with the only difference that:

- at the first stage the pulp suspension is treated with sulfite cooking solution of magnesium base at a temperature of 30oC;

- on the second level of 5% suspension of cellulose is treated with magnesium hydroxide with a flow rate of 0.5% to absolutely dry fiber at pH 8.0. The processing time is 12 min at a temperature of 20oC;

after the first stage processing and washing the pulp is subjected to chelation by Trilon B at the expense of its 0.2 percent to absolutely dry fiber in the presence of sulfuric acid. Process parameters: pH 4.0, temperature 50oC, the mass concentration of 5%, the duration of 60 minutes;

- the first stage of pulp bleaching was carried out with a mixture of oxygen, hydrogen peroxide and magnesium hydroxide under pressure of 0.4 MPa.

Process parameters: flow rates of hydrogen peroxide 2% of absolutely dry fiber, the consumption of magnesium hydroxide 2BR> - the second stage of pulp bleaching was carried out with hydrogen peroxide in the presence of sodium hydroxide. Technological parameters bleaching following: the consumption of hydrogen peroxide 4% of absolutely dry fiber, the consumption of sodium hydroxide 1.5% of absolutely dry fiber, pH 12,0 temperature 85oC, concentration of mass to 7%, duration: 240 minutes

Qualitative indicators of cellulose in the table.

Example 3. A method of obtaining a bleached sulfite pulp on magnesium base carried out analogously to example 1 with the only difference that:

- at the first stage the pulp suspension is treated with sulfite cooking solution of magnesium base with the following parameters: flow total SO20.5% of absolutely dry fiber, pH 3.0, the content is just SO23.5%, the MgO content of 1.7%, temperature 50oC, concentration of mass 12%, duration: 60 min;

- at the second stage, 7% suspension of cellulose is treated with magnesium hydroxide with the consumption of 1% to absolutely dry fiber at a pH of 9.0, a temperature of 60oC and a duration of 30 minutes;

after the first stage processing and washing the pulp is subjected to chelation by Trilon B at the rate of 0.1% to absolutely dry fiber in the presence of the si 12%, temperature 80oC, 30 min;

- the first stage of pulp bleaching was carried out with hydrogen peroxide in the presence of magnesium hydroxide. Process parameters: flow rates of hydrogen peroxide 2%, the consumption of magnesium hydroxide 1% of absolutely dry fiber, pH 7.5, temperature 110oC, concentration of 20 mass% and a duration of 30 minutes;

- the second stage of pulp bleaching was carried out with hydrogen peroxide in the presence of sodium hydroxide. Process parameters: flow rates of hydrogen peroxide 3%, the consumption of sodium hydroxide 0.8% of absolutely dry fiber, pH of 11.2, temperature 80oC, concentration of 20 mass% and a duration of 240 minutes

Qualitative indicators of cellulose in the table.

Example 4. A method of obtaining a bleached sulfite pulp on magnesium base carried out analogously to example 1 with the only difference that:

- at the first stage slurry of pulp is treated at a temperature of 30oC and the concentration of total SO24%;

after the first stage processing and washing the pulp is subjected to chelation analogously to example 2;

- the first stage of pulp bleaching was carried out with a mixture of oxygen at a pressure of 0.1 MPa, hydrogen peroxide and hydroxy is dry fibre, temperature 80o, pH 7.5, the concentration of mass 5%, 30 min;

- the second stage of pulp bleaching was carried out with hydrogen peroxide as in example 3.

Qualitative indicators of cellulose in the table.

Example 5 (contr.). A method of obtaining a bleached sulfite pulp on magnesium base carried out analogously to example 1 with the only difference that:

- at the first stage slurry of pulp is treated at a pH of 3.2, and a temperature of 130oC, the mass concentration of 4%, the total consumption SO20,4%, MgO content of 1.8%, the processing time 20 min;

- on the second level, 13% suspension of cellulose is treated with magnesium hydroxide with a flow rate of 0.4% to absolutely dry fiber at a temperature of 18oC, pH 7.8 and duration 10 min;

- the first stage of pulp bleaching was carried out with hydrogen peroxide in the presence of magnesium hydroxide. Process parameters: flow rates of hydrogen peroxide 18%, the consumption of magnesium hydroxide 0.8% of absolutely dry fiber, pH 7.3, temperature 78oC, the concentration of mass of 6.5% and a duration of 25 minutes;

- the second stage of pulp bleaching was carried out with hydrogen peroxide in the presence of sodium hydroxide. Process parameters: flow perox the situation of the mass of 6.5%, the duration of the bleaching 170 minutes

Qualitative indicators of cellulose in the table.

Example 6 (CTR.). A method of obtaining a bleached sulfite pulp on magnesium base carried out analogously to example 1 with the only difference that:

- at the first stage slurry of pulp is treated at a pH of 1.1, temperature 52oC, the mass concentration of 12.5%, the total consumption SO21.7%, and the concentration of SO24.7 percent, the MgO content of 0.05%, the processing time of 70 min;

after the first stage processing and washing the pulp is subjected to relativeiy analogously to example 3. Technological parameters: consumption trylon 0.4%, pH of 3.7, the temperature of the 38oC, the concentration of mass of 12.5%;

- at the second stage processing of 12.5% suspension of cellulose conduct of magnesium hydroxide with a flow rate of 2.2% to absolutely dry fiber at a temperature of 102oC, a pH of 9.7, the processing time of 100 minutes;

- the first stage of pulp bleaching was carried out with a mixture of oxygen at a pressure of 0.5 MPa, hydrogen peroxide and magnesium hydroxide. Process parameters: flow of hydrogen peroxide to 2.2%, the consumption of magnesium hydroxide 2.2% of absolutely dry fiber, pH of 9.2, temperature 112oC, the concentration of mass of 15.5%; the duration of the sodium. Process parameters: flow of hydrogen peroxide to 4.2%, the consumption of sodium hydroxide 1.6% of absolutely dry fiber, pH of 12.5, temperature 87oC, the concentration of mass of 20.5%; the duration of the bleaching - 250 minutes

Qualitative indicators of cellulose in the table.

Example 7 (the prototype). A method of obtaining a bleached sulfite pulp on the magnesium base is carried out by two-step processing suspension sulfite softwood pulp with Kappa number 20 this:

- on the first stage of a 10% suspension of cellulose is treated with sulfuric acid at a pH of 1.2, at a temperature of 50oC; the duration of treatment 60 min;

- at the second stage, 20% suspension of cellulose treated in the presence of magnesium sulfate in the amount of 3 kg/t to the mass of absolutely dry pulp at a temperature of 60oC;

the bleaching is performed with hydrogen peroxide at a concentration of 20% and pH 12 (consumption of hydrogen peroxide 2.5% by weight of absolutely dry cellulose), a temperature of 80oC for 120 minutes

Indicators of cellulose in the table.

The analysis of the table shows that the proposed method for the production of bleached sulfite cellulose magnesium base increases the efficiency Proizvodstvo examples 1-4 85-86,5 with high mechanical strength (resistance to fracture 1400-1600 hours D. p.; mechanical strength 8450-8800 m). The achieved level of quality indicators pulp in the proposed method exceeds that of cellulose prototype: white 12 - 13,5%; breaking length at 300 - 500 m; the fracture resistance of 400 - 600 H. p. D.

1. A method of obtaining a bleached sulfite pulp on magnesium base, including a preliminary two-stage treatment of a suspension of cellulose, the first stage of which is carried out by acid, and the second magnesium-containing compound, with intermediate washing between steps, washing before bleaching, and bleaching by treating the suspension of pulp without chlorine bleaching reagent on the basis of hydrogen peroxide in the presence of a suspension of magnesium hydroxide, wherein the first pre-processing stage as acid use sulfite cooking solution of magnesium base at a flow rate total SO20.5 to 1.5%, and the second stage pre-treatment as a magnesium-containing compounds are used magnesium hydroxide in the amount of 0.5 - 2.0% in units MgO by weight of absolutely dry pulp, with bleached without chlorine reagent on the basis of hydrogen peroxide and magnesium hydroxide WM> concentration mass 7 - 20% for a 180 - 240 minutes

2. The method according to p. 1, characterized in that the chlorine-free bleaching agent use hydrogen peroxide or a mixture of hydrogen peroxide and oxygen.

3. The method according to p. 1, characterized in that after washing, the suspension of pulp processed in the first processing stage, is subjected to chelation at a flow rate of chelate compound in an amount of 0.1 - 0.3% of the mass of absolutely dry pulp, at the same time as chelate compounds are used Trilon B.

4. The method according to p. 1, characterized in that the first stage pre-treatment is carried out at a pH of 1.2 to 3.0, concentration, mass, 5 to 12%, the consumption of SO20.5 - 1.5 percent to absolutely dry fiber, the temperature of 15 - 50oC and a duration of 0.5 - 1.0 h, and the second stage is carried out at a pH of 8.0 to 9.5, and a temperature of 20 - 100oC, concentration of mass 5 to 12%, the consumption of magnesium hydroxide 0.5 to 2% in units of MgO and duration 0,2 - 1,5 hours

 

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