DE1947931B2 - Process for bleaching lignocellulosic material - Google Patents

Description

Lignocellulose pulp made by the sulfate or sulfite process is common to many Applications are too dark in color and must therefore be bleached. The dark color is due to the Causes lignin component of the pulp. Bleaching is especially necessary for sulphate pulps, the larger ones Lots of residual lignin contained as sulphite pulps. The remaining lignin of the sulphate pulps speaks moreover, for structural reasons, it is less susceptible to chemical treatment. In general, chlorine is used used to initiate the bleaching of lignocellulose pulps, followed by extraction of the Chlorine treated pulps by means of an alkali such as sodium hydroxide. On these treatments in turn, one or more oxidation and extraction treatments follow. For sulphate pulps it is usually necessary to use at least five stages, with a wash after each stage follows to make a fully bleached pulp. The sequence chlorination-alkali extraction-chlorine dioxide treatment-alkali extraction-chlorine dioxide treatment (abbreviated C-E-D-E-D) is typical of the current practice. There will be too other sequences are used, including hypochlorite and alkaline hydrogen peroxide treatments be made. There are many variations on the chlorine bleaching process, the main ones being aim to increase the degree of bleaching and reduce pulp degradation by the bleaching agents. However, chlorine is still used in the initial treatments of the pulp. The chlorine bleaching Unfortunately, it has the disadvantage that the reaction of chlorine with the pulp causes formation of chlorine aromatic materials, due to their toxicity and their high C.O.D. Contamination problems arise. However, chlorine is the preferred bleach because it is readily available and is cheap.

It has now been found that this improves the chlorine bleaching of a lignocellulose pulp can be that the chlorine treated pulp in the presence of an alkali base at superatmospheric Pressure treated with gaseous oxygen, the reaction products then from the Pulp to be washed out. A lignocellulose pulp treated in this way can by one or several bleaching stages can be further bleached to a high brightness without significant degradation entry. The new bleaching process reduces the C.O.D. of polluted sewage and only produces minimal amounts of toxic chlorinated aromatic materials.

The object of the present invention is to provide a method for bleaching lignocellulose pulp on a to create high brightness, soft process improved brightness stability and sufficient strength properties results and is also cheaper overall than the known methods and also to create a bleaching process whose wastewater is only slightly contaminated.

The process according to the invention for bleaching lignocellulosic material contains the following initial work steps: (1) Treatment of the lignocellulosic material in an aqueous suspension of a consistency of 3 to 7 percent by weight at room temperature with a chlorine-containing reagent with a chlorine equivalent of 2 to 8 percent by weight for 10 to 60 minutes and (2) Contacting the chlorine-treated lignocellulosic material with 2 to 3 percent by weight of an alkaline medium, whereupon the alkaline material in aqueous suspension has a consistency of 3 to 12 percent by weight with oxygen or an oxygen-containing gas under a pressure of 2.1 to 14 kg / cm ² at a temperature of 100 to 200 ° C. for 10 to 30 minutes and the lignocellulose material is washed with water after the completion of work step (1) and / or (2).

The process is characterized in that the chlorine-containing reactant of stage (1) from a mixture of chlorine and chlorine dioxide or of chlorine dioxide with subsequent chlorine treatment without intermediate washing or consists of hypochlorite with subsequent chlorine treatment.

The wood pulp can be washed at the end of step (1), whereby the amount of required in stage (2 alkali base is reduced In step (1, it is advantageous ^e. Add .ne small amount of chlorine dioxide Odei ammonia or an ammonium salt, wi " this is also done in the known process to preserve the viscosity of the pulp. In step (2) it is advantageous to use magnesium carbonate or magnesium oxide together with the alkali base during the oxygen treatment. The use of these reagents is, however, optional.

At the end of the two stages of the process, the lignocellulose pulp is deliged to a greater extent nified as one according to the appropriate levels;

I 947 931

conventional process, which manifests itself in a lower permanganate number and a higher brightness. The pulp is in a condition that it can be easily bleached to an even higher brightness. The additional bleaching treatment required depends on the type of pulp and the concentration of chlorine used in stage (1). When bleaching sulphite wood pulp, a single additional treatment, such as treatment with chlorine dioxide, is sufficient, even after conventional chlorination / alkali extraction, to achieve a brightness of 90. However, after a chlorination / alkaline oxygen treatment plus a single additional chlorine dioxide step, the brightness of a sulfite pulp is higher and more stable for the same amount of chemicals used; Conversely, the concentration of chlorine can be reduced in order to achieve the same brightness value. When bleaching sulfate wood pulp using concentrations of chlorine in step (1). which are similar to a conventional process (e.g. 5 to 6 "" based on the pulp) and after chlorination / alkaline oxygen treatment

(CO-) using the conventional DED levels, the pulp is bleached to an exceptional brightness value, for example 92.5 to 93.0, with an exceptionally small inversion of 0.5 to 1.0. The sole use of a single chlorine dioxide level COD results in a brightness of 89 to 91 with a slight inversion of 1.0 to 2.0.

Alternatively, after chlorination, the pulp can be subjected to an alkaline oxygen treatment (C-O-) The specified sequences are subjected to further treatments: chlorination, alkaline Oxygen treatment, hypochlorite treatment; Chlorination, alkaline oxygen treatment, peroxide treatment; Chlorination, alkaline oxygen treatment, hypochlorite treatment, chlorine dioxide treatment; or chlorination, alkaline oxygen treatment, hypochlorite treatment, chlorine dioxide treatment, Alkali extraction, chlorine dioxide treatment.

Alternatively, the amount of chlorine used in step (1) can be reduced to 50 "" of its conventional value (for example 2 to 3 ""), and if at C-O- the combination D-E-D where the chemical concentrations are otherwise the same, then the brightness value is the same and the brightness stability is then better than a conventional process that uses the larger amount of chlorine. the high brightness values can be achieved without severe pulp degradation occurring (e.g. Viscosities from 15 to 25).

When the procedure on the bleaching of sulfathokpuipe is applied, the working conditions are typically as follows:

Sulphate wood pulp in aqueous suspension with a consistency of 3 to 7% is made at room temperature treated with 2 to 8% chlorine for 10 to 60 minutes. The percentages are expressed in weight and based on Oven dried pulp sourced. The maximum amount of chlorine depends on the lignin content of the unbleached Pulp and usually exceeds the concentration of chlorine used in conventional bleaching.

The wood pulp treated with chlorine can optionally be washed with water. If it is washed, then the wood pulp with 2 to 3 ° / "sodium hydroxide and optionally with 3" _o Magnesiumearbonat or Magnesiunioxyd being treated. If S is not washed, the wood pulp with ausi is-calibrating treated sodium hydroxide to neutralize the acidity and to provide an excess of 2 ° _o sodium hydroxide. if desired, 1% magnesium carbonate or magnesium oxide is added. the washing step may be omitted when lower concentrations of chlorine are used in the first chlorine treatment. the omission of the washing has the advantage that at this stage The alkaline pulp with a consistency of 3 to 12% is then (preferably) heated to a maximum of 130 ° C. under an oxygen pressure of 3.4 atm and with stirring in an autoclave for a period of 2 to 3 minutes ^{It is kept at 130 °} C. for 10 minutes under an oxygen pressure of 3.5 atm.

The permanganate number of the wood pulp after completion of the oxygen treatment depends on that in the chlorine concentration used for the first chlorine treatment. At the chlorine concentrations, as they are at Using conventional methods, the C-O modification gives im permanganate numbers Range from 0.5 to 1.5. With a chlorine concentration of approximately 40 to 50 "·" the normal Permanganate numbers ranging from 3.0 to 4.5 were obtained.

The oxygenated wood pulp is then washed with water to remove the reagents and Separate reaction products. The washed wood pulp is then at a consistency of 12 ",, treated with 1 "" chlorine dioxide for 3 hours at 80 C.

The brightness value after the end of the chlorine dioxide treatment achieved depends on the concentration of chlorine used in the first chlorine treatment away. When the chlorine concentration is the same as the C-B sub-sequence. then results in C-O modification brightness values in the vicinity of 90 with only a slight inversion.

If little chlorine is used and if other conditions are kept constant, then the brightness will be lower and an additional bleaching step may be required. Even at the highest brightness value ^{P "v} 'the viscosity of the pulp is acceptable in the range of 15-20.

The Redt used in the üv, - f stage of the bleaching process: ν normally chlorine. However chlorhaiL _e "can; Compounds such as chlorine dioxide, sodium hypochlorite or calcium hypochlorite partially or completely replace the chlorine in the first stage. The chlorine dioxide / chlorine treatment can be carried out either simultaneously or sequentially. The first stage is carried out under acidic conditions.

The alkali base used in the second stage of the process is usually sodium hydroxide. It however, potassium hydroxide or sodium or potassium carbonate or calcium hydroxide would also be suitable. The magnesium carbonate optionally used in the second stage helps to delay the Degradation of lignocellulose pulp. In step (1) ammonia can be used to break down the To delay pulp.

The treatment of the alkaline lignocellulose pulp with oxygen is carried out at a pressure in the range from 2.1 to 70 atm in a container. The wood pulp is oxygen treatment during ^Q, lasts 10 to 30 minutes, maintained under stirring at a temperature in the range of 100 to 200 C ^r. The lignocellulose pulp is mixed with water so that a consistency of 3 to 12% is obtained.

Λη place of pure oxygen can air at one appropriate pressure should be used, i.e. the pressure should be five times as high as when purer Oxygen is used. Furthermore, the addition of oxygen to the extraction stage can be carried out chemically Bound form take place, so that oxygen is created in statu i.ascendi during the treatment. For example, the oxygen can be added in the form of metal peroxides.

It is clear to one skilled in the art that the conditions for treatment According to the type of lignocellulose pulp that must be selected in order to get the optimal treatment obtain. At the beginning of the oxygen treatment it can be, depending on the pressure vessel used It may be useful to preheat the pulp at less than the maximum oxygen pressure.

When treating the lignocellulose pulp with gaseous oxygen, it is preferred to use the pulp To treat the alkaline pulp with an alkaline material, gaseous oxygen under pressure suspend and finally bring the reaction mixture to the reaction temperature. It was found, that this sequence results in less degradation of the lignocellulose pulp than if the pulp \ before the Oxygen addition is heated.

The higher dissolution of the lignin in the lignocellulose pulp. by the method according to the invention is achieved by an interaction of the first chlorine treatment and the subsequent one alkaline oxygen treatment. When the use of oxygen in the second stage is omitted, so that the well-known sequence of chlorine / alkali extraction results, then has the Permanganate number of a sulfate wood pulp (which in the unbleached state has a permanganate number of 18 to 20) at the end of the extraction stage with a first chlorine treatment with 5 to 6 "" a value of 4 to 6 and with a first chlorine treatment with 2 to 3% a value of more than 9. Comparable: values for permanganate numbers of sulphate wood pulps which have been treated according to the invention 1.0 to 1.5 or 3.0 to 4.5. When the chlorination stage of the present process is omitted, so that only the alkaline oxygen treatment remains, then a sulfate wood pulp treatment achieves a permanganate number of about 7, at the same time pulp degradation occurs, as is expressed in a viscosity value of around 10.

In the description, under the expressions »brightness«, »permanganate number« and »viscosity« meant characterizing values for wood pulps obtained by the following standard procedures will:

Brightness: - -TAPPI Standard T 217 m, 218m. Permanganate number: - TAPPI Standard T 214 m. Viscosity: - TAPPI Standard T 230 s: m (0.5 0

The brightness inversion is expressed in brightness values that are determined after the brightness plate Has been heated to 105 C for 1 hour.

example 1

A sulphate wood pulp obtained from conifers

was (mainly spruce and balsam fir) and the

S has a permanganate number of 18.4 and a viscosity

of 27.8 was subjected to the sequence of 5 bleaching stages given below:

1. The wood pulp, which had a consistency of 3.5 ", was treated with 2.0% chlorine at 20 ^° C. for 45 minutes

long treated. The wood pulp was then washed with water.

2. The chlorine-treated wood pulp with a consistency of 7.0% was treated with 5.0% sodium hydroxide and placed in an autoclave. The alkaline wood pulp was then treated with oxygen under a pressure of 11.2 at and at a temperature of 100 ^{° C. for 30 minutes.} The wood pulp was then washed. At the end of this stage, the wood pipe had a permanganate number of 4.0 and a viscosity of 21.2 cps

3. The oxygenated hobpulp, which had a consistency of 12.0%, was then mixed with 1.0 "" treated with chlorine dioxide for 3 hours at 70 ° C. The wood pulp was then washed.

4. The Hobn'-lpe that a consistency of 12.0 "had ,, then for 1.5 hours with 0.5" extracted at 6O ⁰ C ,, sodium hydroxide. The wood pulp was then washed.

5. The wood pulp, which had a consistency of 12.0 ", was then treated with 0.3% chlorine dioxide at 70 ° C Treated for 3 hours. The wood pulp was then washed with water. The bleached product had a brightness of 87.9 and a viscosity of 18.4c. p.s.

Example 2

A sample of sulphate wood pulp obtained from conifers (mainly spruce and balsam fir) and which had a permanganate number of 18.4 became the sequence given below subjected to five bleaching stages:

1. The wood pulp was at a consistency of 7 "" in polyethylene bags with hand stirring for 10 minutes long chlorinated.

2. Sufficient sodium hydroxide solution was added to the unwashed pulp so that a complete Reaction with the chlorine added in stage 1 resulted and an excess of 3.0% sodium hydroxide remained. The wood pulp was stirred for 2 minutes and placed in an autoclave. While In a preheating period, an oxygen pressure of 6.3 atm was generated in the autoclave. The oxygen treatment was then done at 11.2 atm for 30 minutes. The pulp was then washed with water and then subjected to three further stages according to Example 1.

3. Pulp consistency 12.0%, chlorine dioxide 1.0 ", for 3 hours at 70 ° C.

4. Alkali extraction with 0.5% sodium hydroxide for 1.5 hours at 6O ⁰ C and a consistency of 12%.

5. pulp consistency 12.0%, 0.3% chlorine dioxide for 3 hours at 70 ⁰ C. The wood pulp was washed after the end of stages 3, 4 and 5 respectively with water.

The reagents of the first two stages and the reaction conditions and the properties obtained of the wood pulp are given in Table I.

Table I.

Chlorine,% Chlorination time, sodium Temperature of
Oxygen loading Permanganate-
number after the Brightness at Viscosity am Reversal of min hydroxide,% plot, "C 2nd stage end End, cP Final brightness 1.0 60 4.14 100 10.07 65.75 16.23 3.1 1.0 10 4.14 100 7.1 83.7 13.6 2.6 1.0 10 4.14 110 7.3 81.1 14.3 2.6 2.0 60 5.28 100 6.45 84.1 15.88 3.3 2.0 10 5.28 100 6.1 86.2 14.4 1.4 2.0 10 5.28 110 5.5 87.1 14.8 3.0 3.0 60 6.42 100 4.55 89.7 15.75 2.7 3.0 10 6.42 100 4.2 90.2 15.1 1.9 3.0 10 6.42 110 3.8 89.0 14.8 1.6

Example 3

A sulphate wood pulp obtained from conifers (mainly spruce and balsam fir) and which had a permanganate number of 18.4 became the basic stages of the bleaching process subjected, namely, chlorination and alkaline oxygen treatment. There were six separate ones Tests carried out. Samples (6) of a washed one weighing 13.1 g Pulp with 5.25% consistency was mixed with various amounts of chlorine for 10 minutes long treated. The wood pulp was not washed, but treated with sufficient sodium hydroxide to so that after neutralization of the acidity an excess of 4.0% remained. The ones with sodium hy Wood pulp treated with hydroxide was stirred for 2 minutes. 1.0% magnesium carbonate was then dei Wood pulp added, which was stirred for an additional minute. Each sample was taken separately for 30 minutes in an autoclave with oxygen at 11.2 at pressure treated. Two temperatures were used in the oxygen treatment, namely 120 unc 130 ° C. After completion of the oxygen treatment, the wood pulp was washed with water, and the ( Permanganate number was determined. The results are given in Table II.

Added chlorine

Added sodium hydroxide

Oxygen treatment temperature

Permanganate number according to the
Oxygen treatment ..

1.34%

5.53%

120 ° C

9.0

Tables

2.68%

7.05%

120 ° C

5.1

4.0% 1.34% 2.68% 4.0% 8.56% 6.9% 7.05% 8.56% 120 ^c C 130 ° C 130 ° C 130 ° C 2.8 5.8 4.2 2.3

It can be seen that at a concentration of 1.34% chlorine during the chlorine treatment, a wood pulp is obtained with a relatively high permanganate number.

Example 4

A sulphate wood pulp obtained from conifers (mainly spruce and balsam fir) and which had a permanganate number of 18.4 was subjected to a bleaching sequence with six separate Tests were used.

A. 13.1 g of wood pulp with a consistency of 5.25% was chlorinated with 5.35% chlorine for 10 minutes with hand stirring. The wood pulp was then washed twice with I ^1/2 liters of water and crumbled in a Hobart mixer. 4.0% sodium hydroxide was added to the wood pulp and this was stirred for 2 minutes before being placed in an autoclave. The wood pulp was treated in the autoclave for 30 minutes under an oxygen pressure of 11.2 at 100.degree. The permanganate number of the pulp was then determined.

B. 22.0 g of wood pulp with a consistency of 11.3% were treated with 4.0% chlorine for 10 minutes with hand stirring at room temperature. The wood pulp was then washed twice with 1/2 liter of water. The wood pulp was then crumbled and treated with 2.4% sodium hydroxide for 2 minutes with stirring. The wood pulp was then ^{treated in an autoclave at 100 °} C. for 30 minutes with oxygen at a pressure of 11.2 at. The pulp was an oxygen pressure of 6.3 untei at vorbehan punched at 100 ⁰ C. The permanganate was then measured The wood pulp was then be in a third stage a consistency of 12% with 0.8% Chlordioxyc for 3 hours at 70 ⁰ C treated. The treated with chlorine dioxide the pulp was extracted next in Einei fourth stage at a consistency of 12% with 0.4 °, sodium hydroxide I ^1/2 hours at 6O ⁰ C The extracted wood pulp was then subjected to a fifth treatment at 12% consistency with 0 , 3% Chlordi

oxide for 3 hours at 70 ⁰ C subjected. The brightness of the wood pulp was then determined.

C. 22.0 g of wood pulp were subjected to the bleaching sequence before sample B, with the difference that in dei first stage 3.18% chlorine was used.

D. 17.5 g of wood pulp with a consistency of 7.0 "were treated with 4.0% chlorine for 10 minutes with hand stirring at room temperature. The wood pulp was then _{washed twice with 1 1/2} liters of water

and crumbled in a Hobart mixer. 2.0 "" Sodium hydroxide was then added and the wood pulp was stirred for 2 minutes and placed in an autoclave. The wood pulp had a consistency of 7.0%. The wood pulp was autoclaved for 12 minutes at an oxygen pressure of 6.3 at preheated and then heated for 30 minutes under an oxygen pressure of 11.2 at to 100 ° C. The wood pulp was then _{washed twice with 1 l 1} liter of water. The permanganate number of the wood pulp was then determined. The pulp was then subjected to the three stages 3, 4 and 5 of sample B, except that 1.0% chlorine dioxide was used in the chlorine dioxide treatment in stage 3 and 0.5% sodium hydroxide in stage 4. At the end of the fifth stage, the brightness was measured.

E. 17.5 g of wood pulp were subjected to the bleaching sequence of sample D, with the difference that in Stage 1 5.0% chlorine was used.

F. 17.5 g of wood pulp were subjected to the bleaching sequence of Sample D, with the difference that in Level 1 6.0%, chlorine was used.

The indices of the bleaching sequence are given in Table III.

Table III

sample

Used chlorine

Used sodium hydroxide

Permanganate number according to

Level 2

Brightness after level 5 ...

5.35%

4.0%

2.83

4.0% 2.4%

4.6

87.7

3.18%
2.4%

4.95
85.5

D. E. 4.0% 5.0% 2.0% 2.0% 6.1 4.15 85.3 90.0

6.0%
2.0%

3.7
90.5

Example 5

A sulphate wood pulp obtained from conifers (mainly spruce and balsam fir) and which had a permanganate number of 18.4 subjected to six separate bleaching tests. 17.5 g (oven dried) wood pulp were mixed with various Amounts of chlorine chlorinated for 10 minutes at room temperature and at a consistency of 7%. Sodium hydroxide was added and stirred in for 2 minutes at room temperature. 1% magnesium carbonate was added and stirred in for 1 minute. The wood pulp was then placed in an autoclave introduced and at various temperatures for 30 minutes under an oxygen pressure of 11.2 at heated. The permanganate number and viscosity of the wood pulp were then determined.

The bleaching sequence indexes are shown in Table IV.

Table IV

Added chlorine 1.0% 2.0% 3.0% 1.0% 5.0% 6.0% Added sodium hydroxide 4 14% 5 28% 642% 4 14% 3 0% 3 0% Temperature of the sour fabric treatment 120 C 120 C 120 C 123 C 120 C 120 C Permanganate number 10.6 6.9 4.9 7.1 2.4 2.9 viscosity 22.9 cP 21.7cP 21.7cP 20.3 cP 22.0 cP 21.5 cP

It can be seen that a low concentration of chlorine gives, on average, higher permanganate numbers.

Example 6

A sulphate wood pulp obtained from conifers (mainly spruce and balsam fir) and which had a permanganate number of 18.4 subjected to five separate bleach tests. 52.5 g (oven dried) pieces of wood pulp were added twice Washed with 4 liters of water and then at a consistency of 3.0 "" for 10 minutes at room temperature chlorinated with different concentrations of chlorine. During the chlorination, the wood pulp became mechanically stirred. The wood pulp was then washed twice with 3 liters of water. The washed one Pulp was broken up in a Waring mixer at 3% consistency and on a Filter funnel concentrated to a consistency of 7%. 3.0% sodium hydroxide and 1.0% magnesium carbonate were then added to the wood pulp over 3 minutes with vigorous hand stirring.

The pulps were then placed in an autoclave and used under the following conditions Oxygen Treated:

Preheating for approximately 13 minutes at an oxygen pressure of 6.3 atm and then Treatment with stirring for 30 minutes at a pressure of 11.2 at and at the indicated pressure Temperature. After the completion of the oxygen treatment, the permanganate number and the viscosity were determined the wood pulp determined.

In three of the tests (labeled C, D and E) the oxygen treated wood pulp passed Subjected to bleach tests.

C. In step 3, 0.4% chlorine dioxide was added to 12.5 g wood pulp with a consistency of 12%, and the pulp was treated for 3 hours at 70 "C. The brightness and inversion of the wood pulp were then measured after a 5 minute sulfur dioxide treatment.

The wood pulp, which had a consistency of 12%, was then extracted ¹ I ₂ hours with 0.5% Nalriumhydroxyd at 60 ⁰ Cl

In stage 5 the wood pulp, which has a consistency of. 2%, 3 hours at 70 ° C with 0.3 '.' · ■ "Chlorine dioxide treated. The brightness and inversion were observed after 5 minutes of treatment the wood pulp measured with sulfur dioxide. The viscosity of the wood pulp was also measured. D. A 12.5 gram sample of the oxygen treated wood pulp underwent three rapid bleaching stages subjected, each lasting 10 minutes, each being vigorously stirred:

Level 3: 1.0 ° ₀ chlorine dioxide, 4% consistency,

Temperature 70 ° C.
Level 4: 0.5% sodium hydroxide, 4% consistency,

Temperature 60 ° C.
Level 5: 0.3% chlorine dioxide, 4% consistency,

Temperature 70 ° C.

The brightness and transformation of the wood pulp after 5 minutes of treatment with Sulfur dioxide and the brightness and transformation of a wood pulp without such treatment would be measured.

E. In stage 3, 1% chlorine dioxide was mixed with 12.5 g wood pulp, which had a consistency of 12%, Mixed for 3 hours at 70 ° C. The brightness after 5 minutes of treatment with sulfur dioxide and the lightness conversion were then measured.

In the fourth Srufe the wood pulp, which had a consistency of 12%, I ¹ Z extracted with 0.5% sodium hydroxide for ₂ hours at 60 ° C. In

In stage 5, the wood pulp was treated with 0.3% chlorine dioxide at a consistency of 12% for 3 hours at 70 ° C. The brightness after the treatment with sulfur dioxide, the brightness conversion and the viscosity were then measured. The ratios of the bleaching sequences are shown in Table V.

Table V

sample A. B. C. D. E. Chlorine used in the first stage
Applied in the second stage
Sodium hydroxide
Oxygen treatment temperature.
Permanganate number after the second stage
Viscosity after the second stage
Brightness after the third level
(SO ₂ -treated wood pulp)
Brightness inversion after the third level
Brightness (SO ₂ -treated pulp)
the fifth stage
Brightness inversion (S (^ -treated
Pulp) after the fifth stage
Brightness, untreated pulp, after
the fifth stage
Lightness inversion (untreated pulp)
after the fifth stage
Viscosity after the fifth stage 5.0%
3.0%
150 ° C
1.0
11, OcP 6.0%
3.0%
150 ° C
0.85
10.7 cP 5.0%
3.0%
143 ° C
0.65
13.7 cP
90.4
1.5
92.6
0.7
12.5 cP 6.0%
3.0%
140 ° C
0.75
13.1 cP
89.5
1.4
88.2
1.1 6.0%
3.0%
130 ° C
0.85
15.1 cP
90.3
1.9
92.8
1.0
12.65cP

It can be seen that Example 6 was carried out on the concentrated chlorine. The sodium hydroxide and 1.0% treatments a brightness of 90 after level 3 50 magnesium carbonate were the chlorine-treated

can be obtained.

Example 7

Pulp, which had a consistency of 7%, was added over 3 minutes with vigorous hand stirring. the Oxygen treatment was carried out at a pressure of 11.2 at, with preheating at a

A sulfate wood pulp obtained from conifers with a pressure of 6.3 atm. In four of the bleaching processes

(mainly spruce and balsam fir) and which had a permanganate number of 18.4 subjected to five separate multi-stage bleaching processes. The initial chlorinations were made as in a treatment with chlorine dioxide was used in a third stage. The key figures of the bleaching treatments are given in Table VI below.

Table VI

sample A. B. C. D. E. Chlorine used in stage 1
Applied in level 2
Sodium hydroxide
Temperature of the oxygen treatment .. 6.0%
3.0%
147 ⁰ C 5.0%
3.0%
144 ° C 6.0%
3.0%
140 ° C 5.0%
3.0%
140 ⁰ C ^l 6.0%
3.0%
135 ° C

continuation

sample

Preheating time (min)

Time of oxygen treatment

11.2 at (min)

Permanganate number after the second stage Viscosity after the second stage (cP) .. Applied in the third stage

Chlorine dioxide

Brightness after the third level

Brightness inversion after the third level Viscosity after the third level (cP) ..

14th

20 1.0 11.8

12th

10
1.8
15.8

1.0
90.7

1.7
13.3

12th

10
1.5
15.9

1.0
90.45

1.75
13.4

10
5
18.3

1.0
90.0

2.1
15.4

2.4
17.9

1.0
90.3

1.9
15.3

Example 8

A sulphate wood pulp obtained from conifers (mainly spruce and balsam fir) and which had a permanganate number of 18.4 was subjected to six separate three-stage bleaching processes. Samples of the wood pulp weighing 52.5 g (dried in the oven) were treated after washing to a consistency of 3% with 10 ml of 2% ammonium chloride solution and 5 to 6% chlorine. The chlorine treatment was carried out at room temperature for 10 minutes with stirring. The wood pulp was then washed twice with 3 liters of water. To the wood pulp, 1.0% magnesium carbonate and 3.0% sodium hydroxide were then added while stirring for 3 minutes. The wood pulp was then placed in an autoclave and preheated under an oxygen pressure of 6.3 atm, followed by treatment for 30 or 20 minutes under an oxygen pressure of 11.2 atm. In a third stage, the wood pulp, which had a consistency of 12%, was ^{treated with 1.0% chlorine dioxide at 70 °} C. for 3 hours. The plates for the determination of brightness were made using a treatment with sulfur dioxide. The indices of the bleaching processes are given in Table VII.

Table VII

sample

Chlorine used in stage 1

Sodium hydroxide applied in stage 2

Preheating time (min)

Oxygen treatment temperature. Oxygen treatment time (min) ..

Permanganate number according to level 2

Level 2 viscosity (cP)

Level 3 brightness

Brightness inversion

5.0%

3.0%

130 ° C 30 U 18.1 88.6 1.5

6.0%

3.0%

130 ^c C
30th
0.85
17.4
89.9
1.3

5.0%

3.0%

120 ⁰ C
30th
1.3
19.1
88.6
1.6

6.0%

3.0%

120 ⁰ C
20th

1.35
20.03
89.4

1.6

5.0%

3.0%

110 ⁰ C
30th

1.4

20.0

89.0

1.5

6.0%

3.0%

110 C
30th

1.15
20.0
89.7
1.8

Example 9

A sulphate wood pulp obtained from conifers (mainly spruce and balsam fir) and which had a permanganate rating of 18.4, underwent six separate three-step bleaching processes subject.

In stage 1, the wood pulp, which had a consistency of 3%, was used for 10 minutes at room temperature 0.1% ammonia and 5 or 6% chlorine treated.

In stage 2, 1.0% magnesium carbonate and various amounts of sodium hydroxide were added to the wood pulp added, after which the wood pulp was then stirred for 10 minutes before being placed in an autoclave 140 ° C was introduced. The wood pulp came first preheated under an oxygen pressure of 6.3 atm and then under an oxygen pressure for 30 minutes treated by 11.2 at.

In stage 3, the wood pulp, which had a consistency of 12%, was ^{treated with 1.0% chlorine dioxide at 70 °} C. for 3 hours. The permanganate number and

the viscosity of the wood pulp was determined after completing step 2, and the brightness was measured after Completion of stage 3 measured. The characteristics of the bleaching processes are shown in Table VIII.

Table VIII

Pr; .öe A. B. C. D. E. F. Chlorine used in stage 1
Sodium applied in stage 2
hydroxide 5.0%
2.5%
1.6
11.9
85.05 6.0%
'2.5%
2.0
16.0
89.0 5.0%
2.0%
1.3
15.6
86.6 6.0%
2.0%
1.8
88.75 5.0%
1.5% *)
1.3
85.4 6.0%
1.5% *)
2.0
86.1 Permanganate number after level 2
Viscosity after level 2 (cP)
Brightness after level 3

*) pH of extraction liquids about 6.0.

Example 10

A sulphate wood pulp obtained from conifers (mainly spruce and balsam fir) and which had a permanganate number of 18.4 was subjected to a three-stage bleaching treatment, wherein a sequential treatment with chlorine dioxide and chlorine was carried out in the first stage.

1. Two 3 "" consistency pulp samples weighing 52.5 g (oven dried) were obtained at room temperature first with chlorine dioxide (0.4 g, 0.48 g) and then for 30 seconds with chlorine (1.62 g, 1.89 g) treated according to 5 or 6 ° “chlorine. The samples were washed twice with 3 liters of water and weighed in 17.5 g (oven-dried) Portions divided.

2. For each of the six 17.5 g samples

3.0% sodium hydroxide and 1% magnesium carbonate were added. Each serving was in one Autoclave placed and 1 to 4 minutes under an oxygen pressure of 6.3 at and then Heated for 10 minutes under an oxygen pressure of J 1.2 at different temperatures. The wood pulp was then washed, and the permanganate number and viscosity were measured.

3. The wood pulp, which had a consistency of 12 "", was ^{treated for 3 hours with 0.6% chlorine dioxide at 70 °} C. The pulp was then washed. Before brightness measurements were made, the pulp was treated with sulfur dioxide Viscosity was also measured and the characteristics of the bleaching processes are shown in Table IX.

Table IX

sample

Chlorine-containing compound added in stage 1 (as chlorine equivalent)

Oxygen treatment temperature.

Permanganate number according to level 2

Level 2 viscosity (cP)

Level 3 brightness

Brightness reversal after level 3

Level 3 viscosity (cP)

5.0%
130 ⁰ C

1.3
21.7
90.4

2.0
19.5

6.0%
C.

1.2
21.4
89.8

1.9
39.0

5.0%
120 ⁰ C

i, 2
22.0
90.4

1.9
19.7

6.0%
120'C

1.1
21.4
90.5

1.6
18.6

5.0%
11OC

1.4
22.9
90.0

1.9
19.9

6.0%
110'C

1.3
22.6
90.0

1.8
20.2

Example 11

In Examples 11-18 the cost of the chemicals used in bleaching the wood pulp taken as a criterion for the effectiveness of the bleaching process. The calculations were based on 1 ton of oven dried (OD) material based on 100% yield. The cost of each Chemicals were as follows:

Chlorine 3.25 c / lb

Chlorine dioxide 20.0 c / lb

Sodium hydroxide 3.25 c / lb

Sulfur dioxide 2.8 c / lb

A sulphate wood pulp obtained from conifers (mainly spruce and balsam fir) and which has a kappa number of 28.0 and a viscosity of 35.0 c. p.s. exhibited became the conventional one Bleaching sequence C-E-D-E-D, a variation the same (DC) -E-D-E-D and the sequential chlorination, alkaline oxygen treatment, chlorine dioxide treatment, C-O-D, subject.

Sequence DEDED
Chlorination

Three samples of 100 g each of a pulp with a consistency of 3.0% were given 4.5%, 5.5% and 10%, respectively 6.5% chlorine containing 0.1% chlorine dioxide over a period of 10 minutes at room temperature chlorinated.

Alkali extraction

The chlorinated pulp, which had a consistency of 12 ", was extracted with 4.0% sodium hydroxide true 1V? Hours at 6O ⁰ C.

Chlorine dioxide treatment

The pulp, which has a consistency of 12 ", like; was treated with 0.6 "" chlorine dioxide for 3 hours b (70 ° C.

Alkali extraction

Chlorine dioxide treatment

The pulp had a consistency of 12 _"O, was extracted with 0.4% sodium hydroxide I ^1/2 hours at 6O ⁰ C.

Chlorine dioxide treatment

The pulp had a consistency of 12 ° _o, was treated with 0.25% chlorine dioxide for 3 hours at 70 ⁰ C.

The pulp characteristics and the chemical cost are summarized in Table X. The pulp, which had a consistency of 12%, was treated with 0.75% chlorine dioxide for 3 hours 8 ° C treated. . .

The results of the two bleaching tests are u Table XII given.

End
bright
speed Tabel: K Costs. OD
unce pale.
"J Chlorine concentrations
tration,% 87.1
89.6
90.4 Final light
reversal Final viscosity
cP 9.88
J 0.54
11.19 4.5
5.5
6.5 3.2
3.2
3.1 25.6
26.7
27.2

Table XII 10
Final brightness Final brightness
reversal Final viscosity.
cP Costs. O. D "
unbleached.
S. 90.1
15 89.7 Ol Ol 22.0
22.5 7.79
7.79

(DC) -E-D-E-D sequence

The first stage of this sequence consisted of treating the wood pulp to a consistency of 3%, with chlorine dioxide for 5 minutes at room temperature and from a subsequent treatment for 5 minutes with chlorine at room temperature, the reaction mixture then 50 minutes was left to stand at room temperature. The reaction mixture was maintained throughout the stage touched.

The conditions used in the following stages -E-D-E-D were the same as for that Sequence C-E-D-E-D.

The results of the bleaching tests are shown in Table XI.

Calcium hydroxide as base chlorination

Four pulp samples weighing 100 g and having a consistency of 3% were ^{treated with 4.0% chlorine containing 0.1% chlorine dioxide at 20 °} C. for 10 minutes.

Oxygen treatment

The pulp, which had a 3% consistency, was treated with various amounts of calcium oxide and mixed with magnesium oxide or magnesium carbona. The pulp was then irradiated for 10 minutes a reactor exposed to an air pressure of 14 atm while stirring.

The pH of the pulp treated with oxygen was then adjusted to 3.0 by adding ν of sulfur dioxide represents. The slurry was then filtered and diluted to a consistency of 1.0%; the pH value was < by adding lime water to a value of 8, (increased.

chlorine Table XI Final light End Costs,
OD. Chloride salary. ability viscosity. unge dioxide- % Finally bright reversal cP bleaches.
S. salary, % 2.4 speed 3.2 29.9 10.55 0.61 3.0 85.4 3.0 27.3 11.59 0.76 3.6 90.0 2.6 27.0 12.61 0.915 91.4

C-O-D sequence

In this sequence, either sodium hydroxide or calcium hydroxide was used as the base in the oxygen stage used.

Sodium hydroxide as the base

Chlorination

Two 100 g samples of the wood pulp, one Consistency of 3% were mixed with 4.0% chlorine containing 0.05% chlorine dioxide for 10 minutes Treated at room temperature.

Oxygen treatment

The chlorinated pulp, which had a consistency of 3%, was treated with 3.0% sodium hydroxide and then exposed to an air pressure of 14 atm ^{at 130 ° C. for 10 minutes with stirring in a reactor.} Chlorine dioxide treatment

The pulp had a consistency of 12% was treated with 0.65% chlorine dioxide for 3 hours at 8O ⁰ C.

The results of four bleach runs are shown in Table XIII.

Table XIII

Added Lime.

2.8
3.5

2.8
3.5

Used
Additive, %

MgO

0.5
MgO

0.5
MgCO ₃

1.0
MgCO ₃

1.0

Finally bright
speed

86.8
90.2
86.2
89.8

Finite-

ability

reversal

1.3 1.9 1.9

1.7

Final viscosity, cP

22.6 19.1 22.4 19.7

Costs. O. D., unbleached, S.

6.20 6.30 6.20 6.30

It should be noted that the mixtures consist of: lime and magnesium additives, which are used as reagents used in dolomite limestone and dolo mitischeni quicklime are present.

Example 12

In the bleaching procedure of this example (C-O-D) calcium hydroxide was used as the base with no magnesium added used.

Chlorination

Three 100 g samples of the vast Sulfatholzpulpe of Example 11, which had a consistency of 3.0 ° ;, were contained 4.0% chlorine, 0.1% chlorine dioxide, 10 min-treated at 2O ⁰ C long.

Oxygen treatment

The pulp had a consistency of 3.0%, was treated with different amounts of lime _{(Cakiumoxyd)! 5} and then at exposed in a reactor under stirring for 10 minutes at 13O ⁰ C a Luftdmck 14 days.

The pH of the slurry was then adjusted as described in the last section of Example 11.

Chlorine dioxide treatment

The pulp, which had a consistency of 12 ^U _O , was treated with 0.65% chlorine dioxide at 80 ^° C. for 3 hours. The results of the three runs are shown in Table XIV.

Table XIV

Final brightness

2.1
1.7
2.1

Final viscosity.
cP

21.3
19.3
15.4

Costs. O. D ..

unbleached.

S.

6.20
6.30
6.40

Example 13

(Samples 1, 3 and 5) or treated with 0.30% chlorine dioxide (Samples 2, 4 and 6).

Alkali extraction

The pulp had a consistency of 12%, was treated 1 ¹ I _{for 2} hours with 0.3% sodium hydroxide at Fi0 ° C.

Chlorine dioxide treatment

The pulp, which had a consistency of 12%, was mixed with 0.20% chlorine dioxide for 3 hours at 80 ° C (Samples 1,3 and 5) or 0.15% chlorine dioxide (samples 2, 4 and 6).

The results are shown in Table XV.

Table XV

35

This example concerns the five-step bleaching sequence C - O - D - E - D, in which either sodium hydroxide or calcium hydroxide is used as the base in the oxygen treatment step.

Sodium hydroxide as the base
Chlorination

Six 100 g samples of the sulfate wood pulp, which was used in Example 11 and which had a consistency of 3%, were treated ^{with 4.0% chlorine containing 0.1% chlorine dioxide for 10 minutes at 20 ° C.}

Oxygen treatment

In Samples 1 and 2, the pulp, which had a consistency of 3%, was made with 3.0% sodium hydroxide treated. For samples 5 and 6, in which the pulp also had a consistency of 3%, treatment with 3.0% sodium hydroxide and 1.0% dolomitic quicklime took place. For samples 3 and 4 the consistency was 7%; these samples were treated with 3.0% sodium hydroxide. All samples were stirred in a reactor for 10 minutes at 130 ° C with air under a pressure of 14 at.

Chlorine dioxide treatment

The pulp, which had a consistency of 12 ", was was for 3 hours at 80 ° C with 0.45 "·" Chlorine dioxide

sample End
brightness Final light
circumspection
change Final viscosity,
cP Costs, O. D,
unbleached, 1
2
3
4th
5
6th 90.1
88.5
91.0
89.7
91.4
90.1 2.0
2.1
1.9
1.7
1.8
1.8 21.6
22.8
18.3
19.2
21.6
22.1 7.95
7.15
7.95
7.15
7.95
7.35

Calcium hydroxide as a base

Chlorination

Two 100 g samples of the sulfate wood pulp, which was used in Example 11 and which had a consistency of 3.0%, were treated ^{with 4.0% chlorine containing 0.1% chlorine dioxide for 10 minutes at 20 ° C.}

Oxygen treatment

The pulp, which had a consistency of 3%, was treated with two mixtures of calcium oxide and magnesium oxide (2.8 g CaO, 0.5 g MgO and 3.5 g CaO, 0.5 g MgO) as shown in the table XVI is shown. The pulp was then in a reactor at 130 ⁰ C for 10 minutes while stirring an air pressure of. 14 at exposed.

The pH of the oxygen treated pulp was then adjusted by two separate methods:

(a) V - he 1 and 3: 15g portions of one each P iv were at a consistency of 1.0%

with .v: 5, · -. o.'ioxyd acidified to a pH of 3.0, and η. ^ - w; n filter off and dilute to one Consistency of 1.0%, the pH was further adjusted to a pH of 8.0 with lime water.

(b) Trials 2 and 4: 15g portions of each sample were adjusted to a consistency of 1.0% slurried and adjusted to a pH of 8.0 by adding sulfuric acid.

Chlorine dioxide treatment

All servings were then at a consistency of 12% with 0.4% chlorine dioxide for 3 hours 80 ° C treated.

Alkali extraction

All portions were then extracted with 0.25% sodium hydroxide at a consistency of 12% at 80 ^° C. for 3 hours.

1 947

ι Il

Chlorine dioxide treatment

" No /", it η? "/ Chlorine dioxide for 3 hours at 80 ° C

All servings were then added at a consistency of 12 _{/ o} with u, J. _{/ o} <~ wu j υ, _

treated.

The results are shown in Table XVI.

Table XVI attempt
No. Added
Lime, g NaOH equiva-
lent of lime,
% MgO, g Final brightness Final wedge
reverse Final viscosity.
cP Cost, OD
unbleached,"
S. 1
3
4th 2.8
2.8
3.5
3.5 4.0
4.0
5.0
5.0 0.5
0.5
0.5
0.5 90.7
92.2
89.9
90.8 1.9
1.6
1.8
1.5 22.1
18.9
22.1
18.9 6.16
6.26
6.16
6.26

Example 14

A sulphate wood pulp made from New Zealand softwood that was unbleached properties

Kappa number 23.8

Viscosity 34.7

was through a conventional C-E-D-E-D sequence and through the sequence C-O-D-E-D bleached.

C-E-D-E-D sequence chlorination

The pulp was at a consistency of 3 "" with 4.24% chlorine containing 0.1% chlorine dioxide, treated for 45 minutes at 25 ° C.

Alkali extraction

The pulp had a consistency of 12 ",, was treated for 2 hours with 2.5% sodium hydroxide at 6O ⁰ C 1 '/.

Chlorine dioxide treatment

The pulp had a consistency of 12% was mixed with 0.9% chlorine dioxide for 3 hours at 7O ⁰ C.

treated. ,.

Alkali extraction

The pulp had a consistency of 12%, was / treated with 0.5% sodium hydroxide 1 'for 2 hours at 6O ⁰ C.

Chlorine dioxide treatment

The pulp, which had a consistency of 12%, was treated with 0.5% chlorine dioxide at 70 ° C for 3 hours.

The bleached pulp had a brightness value of 91 and the chemical cost was $ 11.07 / ton.

3P

35

40

45 CODE-D sequence

Chlorination

Four 100 g samples of the pulp with a consistency of 3% were given two concentrations of chlorine of 3.5% (samples 1 and 3) and 3.0% (samples

2 and 4), each chlorine reagent containing 0.1% chlorine dioxide, treated for 10 minutes at room temperature.

Oxygen treatment

The pulp was made at a consistency of 7% with sodium hydroxide or lime, the magnesium oxide at the concentration shown in Table XVII. The pulp was then in one Reactor of 130 ° C exposed to an air pressure of 14 atm for 10 minutes with stirring.

Chlorine dioxide treatment

The pulp was at a consistency of 12% with Treated 0.4% chlorine dioxide for 3 hours at 80 ° C.

Alkali extraction

The pulp was treated to a consistency of 12% for _1/2 hour at 60 ° C with 0.3% sodium hydroxide.

Chlorine dioxide treatment

The pulp was made with a consistency of 12%

Treated with 0.25% chlorine dioxide at 80 ° C. for 3 hours.

In the case of samples 2 and 4, the products of the oxygen treatment were based on sulfur dioxide adjusted to a pH of 3.0, filtered and diluted to a consistency of 1.0% and again with lime water adjusted to a pH of 8.0. These products then underwent chlorine dioxide treatment as described above subject.

The results of the bleaching are shown in Table XVII.

Table XVII

sample Oxygen treatment conditions CaO MgO Final seal Final wedge
reversal Final viscosity,
cP Cost, O. D
unbleached,
S. NaOH - - 1 2.5 2.8 0.5 91.2 1.3 18.9 7.30 2 - - - 90.2 1.5 21.2 6.07 3 2.5 2.8 0.5 91.1 1.3 18.7 6.97 4th --- 89.0 1.8 20.8 5.74

Example 15

Alkali extraction

A sulphate wood pulp made from a hardwood which has the bleached properties' from

Kappa number 15.5

Viscosity 57.3

was bleached by the two sequences C-O-D-E-D and C-E-D-E-D. The oxygen treatments were carried out using an improved reactor, the one heavy load on the reactor, more effective heating and agitation of the pulp, and greater Uniformity and reproducibility of the results allowed. The reactor was used in Examples 15-18.

C-O-D-E-D sequence

20 chlorination

Two 100 g samples of the pulp were at a consistency of 3.0% with 2.4% chlorine (sample 1) and 3.0% chlorine (Sample 2) at room temperature for 10 minutes.

Oxygen treatment

The pulp was treated with a consistency of 7 "" in a reactor and at an air pressure of 14 atm with 2.0 "" sodium hydroxide. The temperature was ^{raised to 130 °} C. with stirring and held at this value for 10 minutes.

Chlorine dioxide treatment (level 3)

The pulp was treated with chlorine dioxide (sample 1.0.6 ""; sample 2.0.4 "/") at 80 ° C. for 3 hours at a consistency of 12%.

Alkali extraction

The pulp was at a consistency of 12% with sodium hydroxide (Sample 1, 0.5% Sample 2 ";, 0.3) 1V ₂ hours treated at 6O ⁰ C.

Chlorine dioxide treatment (level 5)

The pulp was treated at a consistency of 12% with 0.25% chlorine dioxide for 3 hours, and at 8O ⁰ C.

The results are given in Table XVIII.

Table XVTII

sample Brightness at
Level 5 Brightness
reversal at
Level 5 viscosity
at level 5,
cP Cost, O. D
unbleached,
S. 1
2 90.1
90.5 4.6
4.2 26.4
31.2 6.22
6.66

The pulp had a consistency of 12%, was treated IV ₂ hours at 6O ⁰ C with 2.0% sodium hydroxide.

Chlorine dioxide treatment

The pulp had a consistency of 12%, was treated for 3 hours at 8O ⁰ C with 0.7% chlorine dioxide.

Alkali extraction

The, pulp having a consistency of 12%, was treated 1V for ₂ hours at 6O ⁰ C with 5.3% sodium hydroxide.

Chlorine dioxide treatment (level 5)
The pulp had a consistency of 12%, was treated for 3 hours at 8O ⁰ C with 0.3% chlorine dioxide.

The results of the bleaching tests are shown in Table XIX.

Brightness at
Level 5 Table XIX viscosity
at level 5,
cP Cost, OD,
unbleached,
S. sample 90.2
90.4 Brightness
reversal at
Level 5 31.6
29.3 7.32
7.64 1
2 6.0
6.3

55

60

C-E-D-E-D sequence chlorination

Two 100 g samples of the pulp were taken with a consistency of 3% with chlorine (sample 1, 3.0%; sample 2, 3.5%) for 10 minutes at room temperature treated.

30 It is apparent that the same brightness is obtained at two bleaching sequences, but that the sequence CODED gives improved brightness reversion bleaching at lower costs.

Example 16

Two samples of a sulphate wood pulp showing the unbleached properties:

Sample A kappa number 83.4

Sample B Kappa number 59.4

were the conventional C-E-D-E-D bleaching sequence and individually the oxygen bleaching sequences Subjected to C-0-C / D-E-D and C-O-C-O-D.

C-E-D-E-D sequence

CQ

Chlorination

The pulp was treated with chlorine at 3% consistency at room temperature for 45 minutes (Sample A, 15.6%; Sample B, 11.0%).

Alkali extraction

The pulp was at 6O ⁰ C and sodium hydroxide (sample A, 10.0%; Sample B, 7.0%) with a consistency of 12% I ^1/2 hours treated.

Chlorine dioxide treatment

The pulp was treated at a consistency of 12% for 3 hours at 8O ⁰ C with 1.0% chlorine dioxide. . ",.

Alkali extraction

The pulp was extracted to a consistency of 12% for 1 _1/2 hours at 60 ° C with 0.5% sodium hydroxide.

Chlorine dioxide treatment (5th stage)

The pulp is treated with 0.5% chlorine dioxide at a consistency of 12% for 3 hours at 80 ° C.

The results of the bleaching are given in Table XX.

Table XX

sample

brightness
at level 5

89.2
90.0

Brightness

reversal at

Level 5

4.2
3.9

viscosity

at level 5.

cP

32.0
20.3

Cost, O. D.,

unbleached.

23.20
18.20

brightness
at level 5

89.7

Brightness reversal at
Level 5

2.9

Viscosity at

Level 5.

cP

35.8

Cost, O. D ..

unbleached,

15.70

C-O-C-O-D sequence - sample B

Chlorine dioxide treatment (5th stage)

The pulp, which had a consistency of 12%, was for 3 hours at 80 ° C with two different amounts of chlorine dioxide, once with 0.5% and once treated with 0.75%.

The pulp was then treated with sulfur dioxide before the final brightness values were determined. The results are shown in Table XXII.

Table XXII

Chlorine dioxide concentration
in stage 5

C - O - C / D - E - D sequence - sample A
Chlorination

The pulp was made to a consistency of 3 "; at room temperature for 45 minutes with 10.0% chlorine treated.

Oxygen treatment

The pulp was at a consistency of 7% for 30 minutes at 130 ° C and at air pressure of 14 at with stirring treated with 6.0% sodium hydroxide.

Chlorine dioxide / chlorine treatment

The pulp was treated to a consistency of 12% for 3 hours at 50 ° C. with a mixture of 1.1 % chlorine and 0.1% chlorine dioxide.

Alkali extraction

The pulp was / extracted with a consistency of 12% l _{'for 2} hours at 60 ⁰ C with 1.5% sodium hydroxide.

Chlorine dioxide treatment (5th stage)

The pulp was treated with 0.75% chlorine dioxide at a consistency of 12% for 3 hours at 80 ° C.

The results of the bleaching are shown in Table XXI.

Table XXI

0.5%
0.75%

Final brightness

90.2
91.4

E-ndhellig-

reversal

2.2
2.2

Final viscosity, cP

23.9 23.0

Cost, O. D.,

unbleached,

13.70 14.70

Example 17

A sulfite wood pulp which has the following unbleached properties

Kappa number 9.0

Viscosity 24.0

was followed by a conventional C-E-D - E-D bleaching sequence, which gave a final brightness of 95 and subjected to a C - O - D oxygen bleaching sequence.

C-O-D sequence chlorination

Chlorination

The pulp, which had a consistency of 3%, was kept at room temperature with stirring for 20 minutes treated with 5.0% chlorine for a long time.

Oxygen treatment

The pulp had a consistency of 7% was treated with 4.0% sodium hydroxide and then subjected to at stirring in a reactor for 10 minutes at a temperature of 130 ⁰ C at an air pressure 14 days.

The third and fourth stages were a repetition of the first two stages.

Two 100 g samples of the pulp were left at 3% consistency at room temperature for 10 minutes long treated with chlorine: sample 1, 2.0% x sample 2 2.5%.

Oxygen treatment

The pulp samples, which had a consistency of 7%, were treated with 2.0% sodium hydroxide (sample 1) and 2.8% calcium oxide (sample 2). The alkaline pulp samples were then in a Reactor exposed to an air pressure of 14 atm at 130 ° C. for 10 minutes with stirring. 50

Chlorine dioxide treatment

The pulp samples which had a consistency of 12% were treated both for 3 hours at 8O ⁰ C with 0.3% chlorine dioxide.

The pulps were then treated with sulfur dioxide before the brightness panels were made. The results are shown in Table XXIII.

«° Table XXIII

sample Finally bright
speed Final light
reversal Final viscosity,
cP Costs. O.D,
unbleached,
S. 1
2 94.2
94.9 1.6
1.4 18.3
17.8 4.00
343

27
Example 18

A semi-chemical neutral sulphite pulp based on sodium, which the unbleached properties

Kappa number 91.0

Chlorine requirement 17.0%

was subjected to the C-O-D bleaching sequence.

Chlorination

Two 35 g samples of the pulp were obtained at 3% consistency with 17.0% chlorine at room temperature Treated for 40 minutes.

Oxygen treatment

The pulp, which had a consistency of 7%, was treated with 5.0% sodium hydroxide and then exposed to an oxygen pressure of 11.2 atm at 130 ° C. for 30 minutes with stirring in a reactor.

Chlorine dioxide treatment

The pulp, which had a consistency of 12%, was treated with 1.0% chlorine ^{at 70 ° C. for 3 hours.}

The results of the bleaching are shown in Table XXIV.

Table XXIV

brightness
at level 2 Finiteness Final brightness
reversal Costs. OD,
unbleached,
S. 62.4
61.8 84.1
83.3 13.5
18.1 18.30
18.30

It can be seen that the use of an oxygen bleach in accordance with the invention is a bleached one Gives wood pulp having a brightness equal to that obtained by a conventional method but the cost of chemicals is lower.

Example 19

Two samples of sulfate wood pulp obtained from conifers became the following Subject to bleaching sequence: chlorination, treatment ίο with alkaline peroxide under pressure, treatment with chlorine dioxide, C-P-D. A third sample served as a comparison. The terms of the treatments were as follows:

_t chlorination

The wood pulp was in aqueous suspension at a consistency of 3% with 4.0% chlorine and 0.1% Treated chlorine dioxide at room temperature for 10 minutes.

Alkaline peroxide treatment

The pulp treated with chlorine, which had a consistency of 3%, was treated for 10 minutes with the reagents shown in Table XXV at a temperature of 130 ^° C. in a sealed reaction container. During the treatment, the pressure reached a maximum value of 3.36 atm. The increase in pressure was a result of the heating of the contents of the reaction vessel.

Chlorine dioxide treatment

The pulp, which had a consistency of 12%,

was treated with different percentages chlorine dioxide, which are shown in Table XXV, for 3 hours at 8O ⁰ C. At this stage the first two samples were each divided into two portions.

The results of the bleaching sequence are shown in Table XXV. It can be seen that alkaline peroxide is below Pressure is an effective source of oxygen for bleaching.

Table XXV

step sample % Chlorine 1 2 3
comparison 1 % Chlorine dioxide 4.0 4.0 4.0 % Sodium hydroxide 0.1 0.1 0.1 2 % Hydrogen peroxide (50%) 5.5 4.0 5.5 % MgSO ₄ • 7H ₂ O 2.0 2.0 - % Na ₂ SiO ₃ (42 Be) - 1.0 - Final pH - 5.0 - Permanganate number 10.3 9.4 10.8 brightness 2.0 1.5 3.2 Viscosity, cP 63.2 68.5 45.3 % Chlorine dioxide 17.0 203 29.6 3 brightness 0.65 0.55 0.5 0.65 - Holiness Reversal 90.9 90.0 89.9 91.9 - Viscosity, cP 1.4 1.6; 1.6 1.4 - - - 18.8 183 -

Claims (2)

Patent claims: 1. Process for bleaching lignocellulosic material, using sulphate, sulphite or semi-chemical neutral sulphite wood pulp including the following initial steps: (1) Treatment of the lignocellulosic material in aqueous suspension with a consistency of 3 to 7 percent by weight at room temperature with a chlorine-containing reagent with a chlorine equivalent of 2 to 8 percent by weight for 10 to 60 minutes; and (2) contacting the chlorine-treated lignocellulosic material with 2 to 3 percent by weight of an alkaline medium, whereupon the alkaline material in aqueous suspension has a consistency of 3 to 12 percent by weight with oxygen or an oxygen-containing gas under a Pressure of 2.1 to 14 kg / cm ^{2 is} treated at a temperature of 100 to 200 C for 10 to 30 minutes and the lignocellulosic material is washed with water after completion of the work step (1) and / or (2), characterized in that the chlorine-containing Reaction center l of work stage (1) consists of a mixture of chlorine and chlorine dioxide or of chlorine dioxide with subsequent chlorine treatment without intermediate washing or of hypochlorite with subsequent chlorine treatment. 2. The method according to claim 1, characterized in that that used in work stage (2) alkaline medium made of sodium hydroxide. Potassium hydroxide, sodium carbonate. Potassium carbonate or potassium hydroxide.