Method of bleaching pulp

 

(57) Abstract:

Use: manufacture of bleached pulp by bleaching with ozone pre-treatment of unbleached pulp with oxygen in an alkaline environment. The essence of the invention: method of bleaching pulp, comprising processing the original pulp in two stages, the first of which carry water with alkaline solution and the selection part of the aqueous alkaline solution between stages of processing, further processing of the pulp with oxygen at elevated temperature and pressure, flushing of the mass and subsequent ozonation mass, the second step of processing the original pulp hold water in an amount to provide a concentration of mass 7 - 15%. Selection of the part of the aqueous alkaline solution is carried out until the concentration of 18 - 25%. 1 C.p. f-crystals, 3 tables.

The invention relates to the pulp and paper industry and can be used in the production of bleached pulp by bleaching with ozone pre-treatment of unbleached pulp with oxygen in an alkaline environment.

There is a method of bleaching pulp, comprising processing the original pulp aqueous alkaline solution, thickening treated Mascia 28% and subsequent peroxide bleaching of the mass [1].

When this processing within 1-15 min aqueous alkaline solution is carried out at a mass concentration of 10%, using to dilute the pulp to a specified concentration of the liquid obtained at the stage of condensation. Characteristics of the aqueous alkaline solution is as follows: the concentration of the alkaline agent 20-120 g/l; temperature of solution 90-150oF.

The known method is an environmentally friendly way ozone bleaching of lignocellulosic material.

However, the disadvantage of this method of bleaching pulp are low quality bleached pulp. Reduced level of mechanical strength is laid on the stage oxygen-alkali treatment and continued to decline in subsequent ozonation.

The closest analogue to the technical nature of the invention and the achieved effect is a method of bleaching pulp, comprising processing the original pulp in two stages, the first of which carry water with an alkaline solution, the selection part of the aqueous alkaline solution between stages of processing, further processing of the pulp with oxygen at elevated pressure and temperature, rinse the mass and subsequent ozonation polucen is m follows:

(a) the initial mass concentration of < 10% (optimalm= 1-4,5%) treated with an aqueous alkaline solution in the amount of 55-90% of the total solution, running on both stages of processing;

b) then treated mass is thickened by selecting part of the aqueous alkaline solution to a concentration of 18% (optimalm= 25-35%);

in) weight with a concentration of 18% is fed to the second stage treatment with an alkaline agent, the total amount of alkali is 0.8-7.0 percent by weight.with. mass.

Ozonation mass is carried out at a mass concentration of 18% (optimalm= 25-35%). The resulting white mass is 59%.

However, this modified oxygen-alkali treatment does not give the optimal combination of achieved performance of whiteness and strength of the target product.

The invention aims to improve the quality of the target product while reducing alkaline reagent.

This is achieved by a method for bleaching pulp, comprising processing the original pulp in two stages, the first of which carry water with alkaline solution and the selection part of the aqueous alkaline solution between the steps, and less the total ozonation of the mass, according to the invention the second step of processing the original pulp hold water in an amount to provide a concentration of mass 7-15%.

Selection of the part of the aqueous alkaline solution is carried out until the concentration of mass 18-25%, and two-stage processing of the original pulp is as follows.

(a) the initial mass concentration of 2-12% treated with an aqueous alkaline solution, the total amount of the alkaline agent is 2-18% of A. C. weight;

b) then treated mass is thickened by selecting part (20-90%) of aqueous alkaline solution to a concentration of 18-25%.with. weight;

C) after the condensation mass is treated with water in an amount to provide a concentration of mass 7-15%.

As the alkaline reagent in the method can be used caustic soda or white liquor, and the processing of oxygen can be carried out in the presence of hydrogen peroxide.

The number of selected alkaline solution depends on the concentration of the mass of the cellulose is mixed with the alkaline reagent: at low concentrations taken more than 50 vol.%, when the average concentration of no more than about 60. %.

After treatment with oxygen mass is washed, thicken the SS="ptx2">

The necessity of pre-ozonation oxygen-alkali treatment with partial selection of an alkaline reagent and subsequent treatment with water to a concentration of 7-15% caused by the fact that the artificial increase of the gradient of the concentration of the alkaline solution between the effective volume of the fiber and the surrounding solution increases the permeability of the cell wall fiber for oxygen and creates the conditions under which retard the oxidative degradation of cellulose, and the very structure of the fiber end processing oxygen and flushing changes occur, providing the most effective process of ozonization.

Received after the AAT with the selection of the cellulose samples have lower indicators of water retention and mechanical strength is not inferior to the performance of unbleached pulp, which creates the necessary margin of safety before the actual process of ozone at high concentrations, mass.

Example 1. Method of bleaching of sulphate pulp with a hardness of 91 p. E. is as follows.

The initial mass concentration of 12% treated with an aqueous alkaline solution, the total amount of caustic NAT the project so to the selection of the aqueous alkaline solution was 20 vol.%. Then the mass is treated with water in the quantity, ensure the accomplishment of the mass concentration of 11%, followed by treatment with oxygen at a pressure of 0.8 MPa and a temperature of 100oC for 45 min oxygen Flow rate is 3%.

Delignification oxygen mass is washed and ozoniruyut at a concentration of 35 mass% in an environment of sulfuric acid (pH 3) at a temperature of 25oWith over 60 C. the Flow rate of ozone is 1.5 kg/t.with. the pulp.

Physicochemical properties of the bleached pulp are given in table.1.

Example 2. Method of bleaching unbleached sulphate pulp with rigidity 112 p. that is carried out analogously to example 1 with the only difference that: (a) the selection of the aqueous alkaline solution is 40%; (b) condensed mass is treated with water to a concentration of 15 mass%.

Physicochemical properties of the bleached pulp are given in table.1.

Example 3. Method of bleaching unbleached sulphate pulp with a hardness of 96 p. that is carried out analogously to example 1 with the only difference that: (a) selection aqueous alkaline solution of 11% of the mass is 40 vol.%; b) condensed mass is treated with water to a concentration of mass 11%; C) processing the hydrogen in the amount of 3.5%.with. cellulose; d) the ozonation is carried out at a concentration of 40 mass%.

Physicochemical properties of the bleached pulp are presented in table.1.

Example 4. Method of bleaching unbleached sulphate pulp with a hardness of 96 p. that is carried out analogously to example 1 with the only difference being that a) the selection of the aqueous alkaline solution of 11% of the mass is 40 vol.%; b) condensed mass is treated with water to a concentration of 11%.

Characteristics of the bleached pulp are presented in table.3.

Example 5. Method of bleaching unbleached sulphate pulp with a hardness of 96 p. that is carried out analogously to example 1 with the only difference being that a) the selection of the aqueous alkaline solution of 2% by weight is 90 vol.%; b) condensed mass is treated with water to a concentration of 15%.

Characteristics of the bleached pulp are presented in table.3.

Example 6. Method of bleaching unbleached sulphate pulp with a hardness of 96 p. that is carried out analogously to example 1, with the only difference being that a) the selection of the aqueous alkaline solution of 11% of the mass is 40 vol.%; b) condensed mass is treated with water to a concentration of mass to 7%.

Characteristics of the bleached pulp are presented in table.3.

As can be seen from the tables and akov allows to obtain a bleached pulp with high whiteness and strength, improving its quality.

1. Method of bleaching pulp, comprising processing the original pulp in two stages, the first of which carry water with an alkaline solution, the selection part of the aqueous alkaline solution between stages of processing, further processing of the pulp with oxygen at elevated temperature and pressure, flushing of the mass and subsequent ozonation of the mass, wherein the second step of processing the original pulp hold water in an amount to provide a concentration of mass 7 - 15%.

2. The method according to p. 1, wherein the selection part of the aqueous alkaline solution is carried out until the concentration of the mass 18 to 25%.

 

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