CN1873090A - Method for consecutive blanching flax paper pulp in high whiteness through multiple stage - Google Patents

Abstract

A continuous multisection bleaching method of high whiteness flax paper pulp applies bleaching process as chlorinating-alkali treatment-activation pretreatment-hydrogen peroxide bleaching. In the method, bleaching whiteness value of single hydrogen peroxide bleaching section can be increased by 20-30% ISO.

Description

Method for consecutive blanching flax paper pulp in high whiteness through multiple stage

Technical field

The present invention relates to a kind of dioxde pulp bleaching process of pulp and paper industry, be specifically related to the high whiteness continuous multi-stage method for bleaching of the flax paper pulp in a kind of careless class paper pulp.

Background technology

Flax belongs to the long especially straw or like vegetable fibrous raw material of fiber, this class raw material is in the pulping bleaching process, on links such as treatment process, paper pulp streaming, dewatering of pulp washing, very big difference is arranged with general straw or like vegetable fibrous raw material (as wheat straw, straw, reed etc.).Existing flax paper pulp method for bleaching is to adopt hypochlorite (H) single hop, clearance-type method for bleaching, and mainly there are the following problems for this method for bleaching:

(1) bleached pulp whiteness low (75%ISO is following), can't accomplish high whiteness (more than the 85%ISO), brightness reversion is serious, the high-grade paper product of can't manufacturing paper with pulp, improve the apparent whiteness of paper pulp, must add fluorescent whitening agent, and fluorescent whitening agent is the chemicals that carcinogenesis is arranged, use in the paper field in health care, packaging for foodstuff etc. now, all ban use of.

(2) owing to adopt the clearance-type bleaching, production efficiency is low, and the quality index fluctuation is big, and labor strength is big, and the water of finished product per ton, electricity, vapour and chemicals consumption are big, cause very high production cost.

(3) waste water can't be realized circulating and recovering, and discharge capacity is big.

Do not produce the bleaching technology of high whiteness (more than the 85%ISO) in the existing flax paper pulp method for bleaching, do not have the mode of production of continuous bleaching, do not have pre-activated to handle (S), do not have pre-activated to handle the combination of bleaching with hydrogen peroxide (P).

Summary of the invention

The objective of the invention is to defective, a kind of high whiteness (more than the 85%ISO) method for consecutive blanching flax paper pulp in high whiteness through multiple stage is provided at existing flax paper pulp bleaching technology existence.

Flax paper pulp continuous multi-stage method for bleaching flow process of the present invention is: chlorination (C)---alkali treatment (E)---pre-activated is handled (S, the preliminary treatment of a kind of S activator)---hydrogen peroxide bleaching (P) (being called for short CESP, down together), and concrete steps are as follows:

(1) chlorination (C)

Weight concentration is to add the chlorine that accounts for paper pulp weight 2～3% in 2～5% the paper pulp, enters the paper chlorination tower, and the chlorination tower is a upflow tower, stops in tower 30～50 minutes, and temperature is a normal temperature in the tower, and tower top pressure is a normal pressure.Paper pulp is after chloridized, and residual lignin is transformed into chlorlignin in the paper pulp, after washing is removed, remainder dissolves in alkali treatment (E) process subsequently to be removed in chlorination in a part of chlorlignin, and lignin removing rate reaches about 60% in the chlorination section.

(2) alkali treatment (E)

Paper pulp after the chlorination is 6～10% through washing concentrating to weight concentration, add the NaOH that accounts for paper pulp weight 2～3%, feed steam and be warming up to 50～70 ℃, enter downflow tower, dwell time in the tower is 1～2 hour, chlorination paper pulp is after alkali treatment, and the paper pulp residual lignin can reach more than 30% with respect to the clearance that enters the lignin before the bleaching process, and chlorination like this (C) and the total delignification rate of alkali treatment (E) can reach more than 90%.

(3) pre-activated is handled (S)

The paper pulp of washing concentrating to weight concentration is 5～8%, add to account for the activator of paper pulp weight 0.3～1.0% and feed steam and be warming up to 40～50 ℃, enter the reduction pretreater, dwell time in the tower is 40～60 minutes, and diluted pulp to weight concentration is 2.5～3.5% at the bottom of the tower.

Described activator is a class multicomponent organic compound, for example dimethyl butyl ester, sweet mellow wine, pears sugar alcohol etc., because the related activity group has activation to main component lignin and the chromophoric group that influences pulp brightness, thereby has improved the bleaching effect of follow-up hydrogen peroxide.

(4) hydrogen peroxide bleaching (P)

Paper pulp is 6～15% through washing concentrating to weight concentration, adds to account for the NaOH of paper pulp weight 0.25～2.5%, 2.0～3.0% Na ₂SiO ₃, 0.05～0.2% MgSO ₄, feeding steam, paper pulp feeds the hydrogen peroxide that accounts for paper pulp weight 2.0～4.0% down at 90～95 ℃, enters and falls streaming hydrogen peroxide bleaching tower, and paper pulp stopped in tower 90～360 minutes, and diluted pulp to weight concentration is 2.5～3.5% at the bottom of the tower.

More than various chemicals consumptions all with respect to oven dry stock.

The present invention adopts chlorination (C) and alkali treatment (E) to form the delignification mode of residual lignin in the flax paper pulp efficiently on bleaching process, and its residual lignin clearance is very high, can reach more than 90%.The overwhelming majority of residual lignin is removed in the paper pulp, produces high whiteness (more than the 85%ISO) bleached pulp for the following bleaching section good prerequisite is provided.Adopting activator S that paper pulp is carried out pre-activated before hydrogen peroxide (P) bleaching handles, residual lignin and chromophoric group are to the reaction activity of hydrogen peroxide bleaching in the reduction paper pulp, improve hydrogen peroxide bleaching efficiency so greatly, the increment of single hop hydrogen peroxide bleaching whiteness can reach 20～30%ISO.Compare with existing flax paper pulp method for bleaching, the present invention has following advantage:

One, improve pulp quality and class, can be used for producing high-grade paper product:

(1) pulp brightness was no more than 75%ISO after existing hypochlorite (H) single stage bleaching method was floated, and adopted the present invention, floated the back pulp brightness and can bring up to more than the 85%ISO, because pulp brightness improves, paper product need not to add poisonous fluorescent whitening agent again;

(2) pulp strength improves about 20% than existing H single stage bleaching, can satisfy the high-speed paper machine pulping requirements;

(3) pulping brightness reversion rate is very low, adopts the present invention, and pulping brightness reversion rate only is 20% of a H single stage bleaching.

Two, adopt the continous mode bleaching production technique:

(1) the continous mode bleaching process is than the production efficiency height of clearance-type, the pulping stay in grade:

(2) waste water adopts the circulating and recovering mode, and wastewater discharge is few, and ambient pollution burden is low;

(3) control of DCS system is adopted in system control, controls easyly, and labour intensity is low.

Three, pre-activated is handled and is improved the hydrogen peroxide bleaching effect:

By adopting activator that paper pulp is carried out preliminary treatment, the main component lignin and the chromophoric group that influence pulp brightness in the paper pulp have been activated, improve the bleaching efficiency of follow-up hydrogen peroxide, the whiteness increment is brought up to more than 20～30%ISO, breaks general hydrogen peroxide bleaching whiteness increment only in the traditional concept below 10%;

Four, construction investment is few:

Because chlorination (C), alkali treatment (E) and pre-activated are handled (S) and are adopted low dense system, dense system during hydrogen peroxide bleaching (P) adopts, the equipment of whole system all can domesticize, so whole construction investment is very low.

Description of drawings

Fig. 1 is a process chart of the present invention.

The specific embodiment

The specific embodiment one: in conjunction with Fig. 1, the flax paper pulp continuous multi-stage method for bleaching of present embodiment comprises the steps:

One, boiling, washes mill

After the boiling of flax raw material process alkali sulfite process, through washing grinding machine the boiling disposed slurry is fully washed, cuts off, through screening, cleaning equipment removes impurity, the slurry of removing behind the impurity is adjusted to the concentration that is suitable for storing through decker, puts into the half stuff Buffer Pool.

Two, chlorination (C)

The slurry that process is washed after mill, screening, the purification enters the chlorination tower with chlorine after fully mixing, residual lignin reaction in chlorine and the slurry, lignin degradation becomes the fragment of water-soluble or sig water, pulp viscosity after the chlorination reduces, carbohydrate is subjected to degraded to a certain degree, the acid solution that the chlorinated lignin that forms after the chlorination forms when only some can be dissolved in chlorination, some is insoluble in chlorinated lignin and needs to dissolve in hot alkaline solution.

Three, alkali treatment (E)

Slurry after the chlorination through 1# vacuum cleaning pulp grinder washing back and alkali lye after helical feed, blender fully mix, enter caustic tower (downflow tower) and carry out alkali treatment, the purpose of alkali treatment is to remove the chlorinated lignin of indissoluble, and stripping part resin, under the alkali treatment condition of gentleness, to the not influence of paper pulp reinforcement degree.

Four, pre-activated is handled (S), hydrogen peroxide bleaching (P)

Slurry after superchlorination and alkali treatment, most of chlorinated lignin dissolves, but some need pass through post-bleach, could further improve whiteness.After slurry washs through the 2# vacuum pulp washing machine, enter pretreater and carry out post-bleach, this moment, pulp brightness did not also reach the whiteness of technological requirement, must be through the 4th section hydrogen peroxide bleaching, hydrogen peroxide is used for the bleaching of chemical pulp, be mainly used in the final stage of multistage bleaching, hydrogen peroxide is water white liquid, the aqueous solution is faintly acid, the reaction of hydrogen peroxide and lignin building unit phenyl ring, destroy the coloured lignin quinoid structure that forms in the digestion process, make its other structures that become colorless, cause phenyl ring oxidation cracking, form a series of dicarboxylic acids and aromatic acid at last, simultaneously, the various free radicals that form in the hydrogen peroxide bleaching process also can with lignin reaction, the size degradation lignin makes its stripping, reach the purpose that improves pulp brightness, slurry after the bleaching is sent into the slip casting tower and is stored through the abundant washing of 4# vacuum pulp washing machine, and paper feeding subsidiary factory uses.

The specific embodiment two: with over dry flax raw material 3000kg, sulphite, NaOH and a certain proportion of water are packed in the boiling vessel, under 168～170 ℃ of temperature, boiling through certain hour, do not floated flax pulp, after washing mill, screening, purifying, behind chlorination (C), alkali treatment (E), preliminary treatment (S), four sections continuous bleachings of hydrogen peroxide (P), produce high whiteness flax pulp (more than the whiteness 85%ISO), actual conditions is as follows:

1, conditions of cooking (table 1):

Table 1

Pot		1	2	3	4
						The dress pot time (h)		2.0	2.0	2.0	2.0
The raw materials quality situation	Boon content (%)	4.6	4.6	4.6	4.6
						Short fibre content (%)	14.3	14.3	14.3	14.3
	Average suede long (mm)	53	53	53	53
						Alkali is than (%)		10	10	10	10
Liquor ratio (%)		2.9	2.9	2.9	2.9
						Idle period (h)		1.5	1.5	1.5	1.5
A heating-up time (h)		1.0	1.0	1.0	1.0
						The vapour pressure that once heats up (MPa)		0.45	0.45	0.45	0.45
The little steam bleeding time (min)		10	10	10	10
						The secondary temperature elevation time (h)		0.5	0.5	0.5	0.5
Temperature retention time (h)		8.0	8.0	8.0	8.0
						Insulation vapour pressure (MPa)		0.65-0.75	0.65-0.75	0.65-0.75	0.65-0.75

The big steam bleeding time (h)	2.0	2.0	2.0	2.0
					Hardness (kappa)	13.2	11.2	13.8	11.9
Residual alkali (g/L)	5.00	5.04	6.30	6.30
					The copper valency	0.47	0.47	0.67	0.67

2, conditions of bleaching:

(1) C section:

Chlorine dosage: 2.0～3.0% (to oven dry stocks);

Slurry concentration: 2.0%～3.0%;

Time: 30～40 minutes;

Temperature: normal temperature;

PH value :≤2

(2) E section

Alkali charge: 2.0～3.0% (to oven dry stocks);

Slurry concentration: 6.0～7.0%;

Time: 60～90 minutes;

Temperature: 60 ± 5 ℃;

NaOH compound concentration: 30 ± 2g/l;

PH value: 11～12;

Liquid level: 70～80%;

(3) M section

Activator level: 1.0% (to oven dry stock, available from the south China Institute of Technology);

Slurry concentration: 6.0～8.0%;

Time: 40～60 minutes;

Temperature: 40～45 ℃;

PH value: 〉=8 (outlets);

Liquid level: 70～80%;

(4) P section

Slurry concentration: 6.0～8.0%;

NaOH consumption: 0.25% (to oven dry stock);

Waterglass consumption: 2.0～3.0% (to oven dry stocks);

Magnesium sulfate consumption: 0.1～0.2% (to oven dry stock);

H ₂O ₂Consumption: 4.0% (to oven dry stock);

NaOH compound concentration: 30 ± 2g/l;

H ₂O ₂Concentration 〉=27.5% can not dilute;

Concentration of sodium silicate: dilute 3～4 times, 50～60 ℃ of dilution water temperature;

Magnesium sulfate compound concentration: 10～30g/l, heat-clearing water (50～60 ℃ of temperature) preparation;

Time: 2.5h;

Temperature: 〉=85 ℃

3. result's (table 2):

Table 2

Sequence number	The 4# vacuum pulp washing machine
						Beating degree	Weight in wet base	The GB whiteness	Dust	The copper valency
	1	45	5.5	85.5	275						0.6
2						50	4.5	86.0	94	0.67
	3	50	6.5	86.5	176						0.74
4						48	5.0	85.7	0	0.67
	5	48	5.0	85.0	268						0.80
6						46	5.5	86.3	111	0.80

The specific embodiment three: what present embodiment and the specific embodiment two were different is that concrete process conditions are as follows:

1, cooking schedule:

Dress pot amount: 3200 ± 100kg;

NaOH: 4.0%, dosage: 128kg;

Anthraquinone derivative: 0.05%, dosage: 1.6kg;

Liquor ratio: 1: 2.6, add water: 7.8T;

Fluid temperature: 75～80 ℃

Boiling curve:

Dry run: 90 minutes

Once heat up: 60 minutes 0～0.45Mpa

Little steam bleeding: 10 minutes 0.45～0Mpa

Secondary temperature elevation: 30 minutes 0～0.65Mpa

Insulation: 2.5 hours 0.65～0.75Mpa

Hardness :≤6 (Kappa values), residual alkali: only check and do not control;

2, conditions of bleaching:

(1) C section:

Chlorine dosage: 1.0% (to oven dry stock);

Slurry concentration: 2.0%～3.0%;

Time: 30～40 minutes;

Temperature: normal temperature;

PH value :≤2;

(2) E section:

Alkali charge: 2.0% (to oven dry stock);

Slurry concentration: 6.0～7.0%;

Time: 60～90 minutes;

Temperature: 60 ± 5 ℃;

NaOH compound concentration: 30 ± 2g/l;

PH value: 11～12

Liquid level: 70～80%

(3) M section

Activator level: 1.0% (to oven dry stock, available from the south China Institute of Technology);

Slurry concentration: 6.0～8.0%;

Time: 40～60 minutes;

Temperature: 40～45 ℃;

PH value: 〉=8 (outlets);

Liquid level: 70～80%;

(4) P section

Slurry concentration: 6.0～8.0%;

NaOH consumption: 0.25% (to oven dry stock);

Waterglass consumption: 2.0～3.0% (to oven dry stocks);

Magnesium sulfate consumption: 0.1～0.2% (to oven dry stock);

H ₂O ₂Consumption: 3.0% (to oven dry stock);

NaOH compound concentration: 30 ± 2g/l;

H ₂O ₂Concentration 〉=27.5% can not dilute;

Concentration of sodium silicate: dilute 3～4 times, 50～60 ℃ of dilution water temperature;

Magnesium sulfate compound concentration: 10～30g/l, heat-clearing water (50～60 ℃ of temperature) preparation;

Time: 2.5h;

Temperature: 〉=85 ℃

3, result's (table 3):

Table 3

Sequence number	The 4# vacuum pulp washing machine
						Beating degree	Weight in wet base	The GB whiteness	Dust	The copper valency
	1	40	6	86.2	0						0.6
2						42	6.5	87.0	111	0.67
	3	37	6	85.3	0						0.74
4						35	6	85.3	568	0.67
	5	35	6	86.0	96						0.47
6						36	6.5	85	0	0.67

Claims (4)

1, method for consecutive blanching flax paper pulp in high whiteness through multiple stage is characterized in that described method carries out according to following steps:

(1) chlorination:

To weight concentration is to add the chlorine that accounts for paper pulp weight 2～3% in 2～5% the paper pulp, enters the paper chlorination tower then, stops 30～50 minutes in the tower;

(2) alkali treatment:

Paper pulp after the chlorination is 6～10% through washing concentrating to weight concentration, adds the NaOH that accounts for paper pulp weight 2～3%, feeds steam and is warming up to 50～70 ℃, enters downflow tower, and the time of staying is 1～2 hour;

(3) pre-activated is handled:

Paper pulp after the alkali treatment is 5～8% through washing concentrating to weight concentration, add to account for the activator of paper pulp weight 0.3～1.0% and feed steam and be warming up to 40～50 ℃, enter the reduction pretreater, stopped 40～60 minutes diluted pulp weight concentration to 2.5～3.5% at the bottom of the tower in the tower;

(4) hydrogen peroxide bleaching:

Activating pretreated paper pulp is 6～15% through washing concentrating to weight concentration, adds to account for the NaOH of paper pulp weight 0.25～2.5%, 2.0～3.0% Na ₂SiO ₃, 0.05～0.2% MgSO ₄, feeding steam, paper pulp feeds the hydrogen peroxide that accounts for paper pulp weight 2.0～4.0% down at 90～95 ℃, enters and falls streaming hydrogen peroxide bleaching tower, stops 90～360 minutes in the tower, and diluted pulp to weight concentration is 2.5～3.5% at the bottom of the tower.

2, method for consecutive blanching flax paper pulp in high whiteness through multiple stage according to claim 1 is characterized in that temperature is a normal temperature in the chlorination tower, and tower top pressure is a normal pressure.

3, method for consecutive blanching flax paper pulp in high whiteness through multiple stage according to claim 1 and 2 is characterized in that described chlorination tower is a upflow tower.

4, method for consecutive blanching flax paper pulp in high whiteness through multiple stage according to claim 1 is characterized in that described activator is one or more the mixture in dimethyl butyl ester, sweet mellow wine, the pears sugar alcohol.

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