Method of bleaching of sulphate pulp

 

(57) Abstract:

The method is designed to produce bleached pulp. Hardwood sulphate pulp delignification stabilized hydrogen peroxide solution at pH 100,5. Washed with water and delignification ozone. The delignification hydrogen peroxide is carried out before the rigidity of cellulose 30-60 permanganate units /~5-11% Kappa/. As a stabilizer of hydrogen peroxide using sodium silicate. The delignification hydrogen peroxide is carried out at a temperature of 60-100oC, concentration of 10-20 mass% at a flow rate of hydrogen peroxide is 0.5 to 3.0%. The method allows to increase the selectivity of delignification of hardwood sulphate pulp with ozone and ensures complete dissolution of the reaction products directly in acidic solution due to more complete degradation of lignin. 1 C.p. f-crystals, 1 tab., 1 Il.

The invention relates to the field of pulp and can be used to produce bleached pulp totally free from chlorine (TFC-cellulose).

There is a method of bleaching pulp using ozone, and the ozone used in the first bleaching stage instead of chlorination hardwood sulphate pulp [1].

Known methods bleaching of sulphate pulp using ozone, the ozone treatment is subjected unbleached semi-bleached cellulose or after exposure to oxygen or unstabilized (not containing stabilizers decomposition of H2O2) a solution of hydrogen peroxide, for example, the methods described in [2].

Examples:

1. Ozonation of unbleached sulphate pulp - Z1 (refer to source).

2. Ozonation after the EOp stage-Z1, where EOp - treatment with alkaline hydrogen peroxide and oxygen at high pressure 3 bar (Oxidative bucking).

Such methods using ozone have drawbacks: the ozonation of unbleached hardwood sulphate pulp is accompanied by increased its destruction, and the ozonized lignin is poorly soluble in the acidic environment on the level of ozonation (table, example 1). To a lesser degree, the same disadvantages inherent in the sequence of NaOH/H2O2- OZONE, about half of ozonated lignin in acidic solution in which lead ozonation, does not come (PL. , example 2), which reduces the efficiency of ozonation: lengthening schemes bleaching with ozone or additional consumption of oxidants on when cnice) schemes for bleaching dobesova steps starting with the 5-stage oxidation processing (in the prototype circuit with ozonation was preceded by pretreatment with oxygen spruce sulphate pulp, see table. 11 source). At the level of P comes almost delignification pulp with Kappa number, from 2.8), and the level of ozonation with Kappa number, 1,3.

The objective of the invention was to develop a method of bleaching of sulphate pulp using ozone, which would increase the selectivity of delignification of hardwood sulphate pulp, would ensure complete dissolution of the reaction products directly in acidic solution due to more complete degradation of lignin. This is a new technical result, which is in causal connection with the essential features of the invention.

The essential features are:

before ozone delignification of hardwood sulphate pulp previously subjected delignification processing of stabilized hydrogen peroxide solution at pH 10,50,5 and washed with water; the delignification hydrogen peroxide lead to stiffness 30-60 permanganate units (5-11% Kappa). The delignification hydrogen peroxide is carried out in the presence of the stabilizer - silicate is The proposed method improves the selectivity of delignification of hardwood sulphate pulp with ozone, provides complete dissolution of reaction products directly in acidic solution at the expense of deeper oxidative degradation of lignin. The essence of the method lies in the fact that before anyway, ozonation cellulose pre delignification stabilized hydrogen peroxide solution at pH 100,5 and washed with water.

The effect is due to the impact of hydroperoxide anions (the predominant oxidant-nucleophile in a stabilized hydrogen peroxide solution) conjugate carbonyl-containing structure of the residual lignin (aromatic aldehydes, ketones, quinones), the content of which herewith is reduced and subsequent ozonation is more selectively through the effect on the aromatic nucleus. In the end, for less ozone derived soluble in the acidic environment of the oxidation products of lignin.

The ozonation products of lignin unbleached sulfate cellulose dissolved in an acidic environment 4%; if the ozonation was preceded by oxidative bucking - 50-60%; if ozonation is carried out after partial delignification of stabilized hydrogen peroxide, ozone lignin dissolves completely (table).

the second cellulose, is the greater the selectivity, the smaller the degradation of cellulose ozone because ozone in acidic environment will destroy only significiance cellulose, and the more it contains lignin (see the drawing data of the authors). The minimum level of rigidity of sulphate pulp, which can be achieved without the use of chlorine-containing reagents, i.e., using hydrogen peroxide without prior treatment, is 40-50 VT. units for stable solution and 50-60 VT. units - when using hydrogen peroxide without stabilizers in the so-called oxidative bucking. With various pre-treatments attainable minimum stiffness of the cellulose is reduced in the case of the stabilized hydrogen peroxide solution to 13-20 VT. units for oxidative be" up to 40 VT. units. Degradation of cellulose in alkaline medium increases with increasing pH and in the absence of stabilizers decomposition of hydrogen peroxide.

As a criterion of selectivity used A factor equal to the ratio L/SP , where L is the relative reduction in the rigidity of the cellulose, and SP - relative reduction in the degree of polymerization of cellulose.

Example 1. (The prototype is oxene) 1390, weight of 10 g (abs. dry. the fiber after washing with water are placed in a reactor bubbling type, pour a solution of sulfuric acid to pH 2 and passed Ozonesondes mixture with ozone concentration of 0.36 mmol/l at room temperature. The feed rate of the mixture of 0.4 l/DM3. Control of ozone absorption photometric and by chemical analysis (iodometry). After absorption of 0.25% ozone by weight abs. dry. cellulose ozonation stop, the pulp is washed with water, some of it dried and examined for the stiffness in the permanganate units (and photometrically), and the second part is subjected to alkaline extraction at a flow rate of sodium hydroxide 2% by weight of the abs. dry. pulp to a pulp consistency of 10%, duration 1 hour, a temperature of 80oC.

The characteristics of the initial cellulose: after ozonation - hardness 87 VT. units, degree of polymerization of 1200; after ozone and alkaline extraction rigidity 68 VT. units, degree of polymerization 1190.

Share diluted on-stage ozonation (ozone) lignin 4: 23=to 0.17 or 17%.

The absolute reduction in stiffness on stage ozonation - 4 VT. units; relative 0,04.

The selectivity factor on the level of ozonation A=0,3.

2O2, 2% NaOH by weight abs. dry. pulp to a pulp consistency of 10%, a temperature of 100oC) washed with water and placed in a reactor bubbling type, pour sulfuric acid solution with a pH of 2 and is subjected to ozonation in example 1. Consumption of ozone for reaction (absorbed by ozone) is 0.25%.

Indicators pulp before ozonation: the hardness of 64 VT. unit, SP= 960. After ozonation - hardness 50 VT. units, degree of polymerization 830.

The selectivity factor on the level of ozonation A=1,6.

Example 3. (The prototype). The hanging wet hardwood sulphate pulp hardness 90 VT. units, degree of polymerization (TPP catocene) 1200, weight 10 g (abs. dry. the fiber) is treated with hydrogen peroxide and alkali in example 2 with the consumption of hydrogen peroxide 2%, sodium hydroxide 4% by weight of the abs. dry. pulp without stabilizer. The second step is carried out with a flow of ozone to 0.50%.

Indicators pulp before ozonation: rigidity 53 VT. unit, SP=800.

After ozonation - rigidity 34 VT. units, degree of polymerization 690.

Indicators pulp before ozonation: hardness 60 VT. units, SP= 950.

After ozonation - rigidity 34 VT. units, degree of polymerization 830.

The selectivity factor on the level of ozonation A=3,4.

Example 5. (The proposed method). The hanging wet hardwood sulphate pulp rigidity 91 VT. units, degree of polymerization (TPP catocene) 1390, weight 10 g (abs. dry. fiber) after pre-delignification (including before ozonation) stabilized by hydrogen peroxide at pH 10,00,5 in example 4 to hardness 40 VT. units and washing water are placed in a reactor bubbling type, pour sulfuric acid solution with a pH of 2 and is subjected to ozonation in example 1 with the="ptx2">

After ozonation - hardness 20 VT. units, degree of polymerization of 1100.

The selectivity factor on the level of ozonation A=4,7.

Example 6. (The proposed method). The hanging wet hardwood sulphate pulp rigidity 91 VT. unit, the degree of polymerization (TPP catocene) 1390, weight 10 g (abs. dry. fiber) after pre-delignification (including before ozonation) stabilized by hydrogen peroxide at pH 10,00,5 in example 4 to hardness 30 VT. units and washing are placed in a reactor bubbling type, pour sulfuric acid solution with a pH of 2 and is subjected to ozonation in example 1 with the consumption of ozone 0,23%.

Indicators pulp before ozonation: hardness 30 VT. units, SP= 1100.

After ozonation - hardness 12 VT. units, degree of polymerization 990.

The selectivity factor on the level of ozonation A=6,0.

1. Method of bleaching of sulphate pulp, comprising the sequential processing of hydrogen peroxide and ozone in the given modes, characterized in that the ozonation expose hardwood sulphate pulp after the preliminary delignification processing stabilized solution of hydrogen peroxide is permanganate units (~ 5 - 11 units of Kappa).

2. The method according to p. 1, characterized in that the delignification hydrogen peroxide is carried out in the presence of the stabilizer is sodium silicate, at a temperature of 60 - 100oWith the mass concentration of 10 - 20%, at a flow rate of hydrogen peroxide is 0.5 to 3.0%.

 

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