SK281290B6 - Process for the chlorine-free bleaching of pulps - Google Patents

Abstract

Chlorine-free bleaching of pulp, esp. artificial fibre pulp e.g. hardwood pulp, with initial kappa values of 15-1, pref. 4-1, or paper pulp, e.g. softwood pulp, with initial kappa values up to 30, pref. up to 10, is carried out with O3 by contacting a pulp suspension at 15-80, pref. 40-70 deg C and pH 1-8, pref. 2-3 with gas (I) contg. 20-300, pref. 50-150 g/cum. O3, using max 2, pref. 0.05-0.5 wt% O3 w.r.t. abs. dry pulp, with vigorous mixing. The novel features are that the suspension has a pulp density of 3-20, pref. 5-20, esp. 7-15 wt% and (I) is introduced at 1-15, pref. 1.1-10 bar. The (I):liquid vol. ratio is 1:U.5-8, pref. 1:1-8. (I) is compressed with a cooled compresser, pref. a water ring pump. Mixing is carried out with a high shear mixer. Several consecutive bleaching stages are used, opt. with intermediate alkaline extn. Bleaching with (I) pref. is carried out after extn. enhanced with O2 and/or peroxide and opt. an alkaline peroxide stage and followed by a peroxide stage and alkaline extn..

Description

The invention relates to a process for bleaching pulp, in particular chemical pulp, into synthetic fibers, for example hardwood pulp, with a starting value of 15 to 1, preferably 4 to 1, or paper pulp, for example coniferous pulp, having a starting value of 30 to 30. preferably up to 10, by means of ozone, in which the pulp suspension is contacted at a temperature of 15 to 80 ° C, preferably 40 to 70 ° C, and at a pH of 1 to 8, preferably 2 to 5, with vigorous stirring or mixing, % with ozone-containing gas, wherein the ozone-containing gas contains up to 300 g / m ³ , preferably 50 to 150 g / m ^{3, of} ozone and in which a maximum of 2 wt. % ozone, preferably 0.05 to 0.5 wt. ozone relative to absolutely dry pulp.

BACKGROUND OF THE INVENTION

Numerous patents have already been granted for chlorine-free bleaching processes which are environmentally friendly and can be processed into paper and fibers by ozone; these differ mainly in the range of substance density and reaction conditions.

In principle, two different technologies are promoted: (HC) and low-consistency (LC) technologies.

Highly consistent ozone bleaching (RC-ozone bleaching) (HC-ozone bleaching) is performed at substance densities above 25%, generally at 35 to 40%.

Since ozone bleaching is not normally used alone, but in combination with other bleaching stages, and conventional bleaching is difficult to perform with such broad substance density ranges, it is necessary to invest in expensive drainage equipment. The reaction of ozone with pulp is a two-phase reaction that proceeds quickly and perfectly.

In addition to the investment costs of the dewatering device, the disadvantage is also the non-homogeneous and cellulose-depleting ozone attack in the HC region, especially at low starting kappa values (referring to US-P 4,229,292, column 2). Therefore, it is even discouraged in the literature to perform HC-bleaching with ozone at values below 10. (Lindholm C.-A. "Effect of pH consistency and pH in ozonbleaching", Part 4, Papers and Puu-Paper and Timber 2/1989; Lindholm C: A. "Effect of pH consistency and pH in ozonbleaching". Part 2 , 1987 Int Oxygen Delignification Conference, San Diego, June 7-11, 1987, Procedings, p. 155; Lindholm C.-A. "Effect of pH Consistency and pH in Ozone Bleaching" Part 3, Nordic Púlp and Páper Rcsearch Joumal, No. 1/1988).

Even worse cellulose damage occurs when cellulose is already bleached with oxygen prior to ozone HC-bleaching.

As an alternative, according to the prior art, only LC-bleaching with ozone is proposed to avoid the use of environmentally harmful chlorine-containing compounds. However, compared to HC-bleaching with ozone, more ozone is consumed, the process is more complicated and very much stirring energy is consumed. Furthermore, the reaction volumes are larger and the amount of impurities is also greater.

In the case of cellulose, low consistency (LC) is usually understood to mean substance densities of up to 5 or 6%. In ozone bleaching, however, the unanimous belief prevails that usable results can be achieved only up to 1%, up to a maximum of 2%.

In US-P 4 126 654, a range of substance densities is claimed up to only 0.7%. However, such a range of substance densities poses high demands on closed water management and thus additional investment. In this patent, LC technology is tested systematically for kraft pulp, and it is noted that the reaction of ozone with pulp is indicated by two barriers: the transfer of ozone from the gas phase to the liquid phase and the transition of the liquid phase to the solid phase, i.e. to fibers. From the minimum mixing capacity of 11 kW / m ³ , only the second passage is decisive according to this patent.

A method of this kind is known from U.S. Pat. No. 4,080,249. The mixing energy according to claim 5 of this document is a maximum of 18 kWh / t pulp suspension. The bubble size of the ozone-containing gas is a maximum of 3 mm. In this patent, only densities of between 1 and 2% are described in all examples, so it is clearly an LC method. In this patent, however, it is apparently claimed to prevent circumvention - a range of substance densities of up to 10%, but according to claim 6 of this document substance densities below 3% are preferred; apparently, at unsatisfactory values, only unsatisfactory results can be achieved.

The same applies to US-P 4,372,812. Here, ozone bleaching is generally referred to as a substance density of between 1 and 40%. In the exemplary embodiment, only the LC area is used here at a density of 1% (see Table 3 of this patent). The patent itself deals with a multi-stage bleaching process in which ozone is used in one or more stages, and not by ozone bleaching alone.

SUMMARY OF THE INVENTION It is an object of the present invention to use said method in the range of medium consistency (MC), of course, to achieve good results when compared to LC-technique.

SUMMARY OF THE INVENTION

This problem is solved by a method of bleaching pulp without chlorine, in particular chemical pulp for synthetic fibers, for example hardwood pulp with a starting value of 15 to 1, or paper pulp, for example coniferous pulp, having a starting value of up to 30, by means of ozone, in which the pulp suspension is introduced with intensive stirring or mixing at a temperature of 15 to 80 ° C and at a pH of 1 to 8, in contact with the ozone-containing gas, the ozone-containing gas containing 20 to 300 g / m ^{3 of} ozone and wherein a maximum of 2 wt. ozone with respect to absolutely dry pulp, the essence of which is that the pulp suspension has a substance density of 5 to 20 wt. and the ozone gas is introduced at a pressure of 0.1 to 1.5 MPa into the pulp suspension.

According to a preferred embodiment of the process according to the invention, ozone is introduced at a pressure of 0.11 to 1 MPa into the pulp suspension.

The range of medium consistencies offers the advantage that the reaction tanks can be made smaller in comparison to the LC technique, but no expensive drainage devices are required as with the HC technique. By applying pressure with vigorous stirring or mixing, good results are now achieved even in the MC region; a homogeneous and gentle but effective reaction of the pulp with ozone occurs. The required stirring energy is lower than that of LC. The reaction of ozone with pulp is more homogeneous than HC. Cellulose damage is measured on viscosity and DF distribution - even at very low kappa values, apparently lower than NC and at least a comparator2

SK 281290 s6 with LC. Specific ozone consumption 03 - consumption for the eliminated drop point (significantly lower than LC). The current devices are relatively easy to convert in addition to the pH-regulated acidification (which would also be necessary for LC and HC technology), it is only necessary to invest in the MC pump and MC mixer. The return of waste water and the reuse of reaction gases with a residual ozone content are possible, so that the process works favorably with respect to the environment. On the whole, it is observed that the process is very economical (the necessary mixing energy, the amount of ozone used and the necessary equipment).

A further advantage results from the use of the process according to the invention in multi-stage bleaching as an ozone step. Since the most common ozone-bleaching stages (for example, oxygen bleaching) work most often in the HC region, it is not necessary, as previously, to change the pulp consistency between the stages, so that the overall process is more economical.

Although it is already known from AT-P 380 496 that ozone bleaching is carried out under pressure, in this method the pulp suspension in the LC region (2.5 to 4.5% of the fabric density) is fed intensively under pressure (in the exemplary embodiment). 0.4 MPa) in contact with the ozone-containing gas. Finally, the pulp is drained to a fabric density of 10 to 30%, maintaining the same pressure and temperature at least 20 minutes thereafter. According to this patent, the reaction is then carried out, which is conditioned by the close contact of the LC pulp with the ozone-containing gas (see page 3, lines 41-45 of the patent). In contrast, according to the present invention, it has been found that MC pulp can also be successfully processed directly and with ozone-containing gas while it is under pressure while being vigorously mixed or mixed. Therefore, diluting and dewatering the pulp suspension, as is done according to AT-P 380 496 (see page 3, lines 15 to 20 and 30 to 36).

For optimum results, it is expedient that the gas: liquid volume ratio is 1: 0.5 to 1: 8.

Preferably, the gas: liquid volume ratio is 1: 1 to 1: 6.

A refrigerated compressor, preferably a water ring pump, is preferably used to compress the ozone-containing gas. A high-shear mixer is used for intensive mixing or mixing.

High-shear mixers are known and often used for a variety of purposes, for example for the production of paint dispersions (DE-A 24 06 430), for the production of powdered PVC resins (US-A 3 775 359) and for the manufacture of semi-solid emulsions (US- No. 3,635,834), it is already known that they are used for the preparation of pulp suspensions (JP-A 6 309 9389).

The high-shear mixer has plates with elevations that are located at a distance from each other. This does not mean grinding but perfect mixing. It is expedient if the process is carried out several times in succession, wherein an alkaline extraction is carried out between the individual steps. The alkaline extraction can be carried out using oxygen or peroxide. This multiple embodiment can simply be ensured in practice by removing a portion of the pulp downstream of the reactor and feeding it once more to the high-sher mixer, so that a cycle is formed.

Advantageously, the process is carried out after extraction with oxygen and / or peroxide, and then ozone gas at a pressure of 1 to 5 bar is introduced into the pulp suspension.

Advantageously, after the extraction with oxygen and / or peroxide, an alkaline peroxide step is introduced and then ozone gas at a pressure of 0.1 to 1.5 MPa is introduced into the pulp suspension.

After introduction of ozone at a pressure of 1 to 5 bar, a peroxide stage or an alkaline extraction may be used.

Finally, it is also expedient if all or part of the waste water filtrate which is removed during the ozone treatment is fed to the pulp suspension before it is brought into contact with the ozone gas, whereby the necessary acid is supplied together with the waste water filtrate. , particularly sulfuric acid, to adjust the desired pH. Since the waste water filtrate is acidic, acid can be saved in this way; at the same time, the waste water filtrate is expediently used so that it does not have to be disposed of or discharged while destroying the environment.

If the pulp of coniferous wood with initial values of up to 30 or up to 10 is subjected to the process according to the invention, values below 10 or below 5 are achieved.

If the pulp of deciduous trees with a starting value of 15 to 1 or 4 to 1 is subjected to the process according to the invention, then a kappa value of 12 to 0.5 or 1.5 to 0.5 is achieved. The initial brightness is 50 to 80% and 70 to 80%, respectively, and this is increased to at least 65 to 90% and 75 to 90%, respectively.

In the process according to the invention, it is advantageous that the molecular weight distribution of chemical pulps into synthetic fibers can be determined. In addition, by varying the pH, the amount of ozone used and the temperature, the viscosity required for the further use of the pulp, as well as the DP distribution and the reactivity measured at the filter value required for the further use of the pulp, can be achieved. J *, vl * y

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail with reference to FIG. la a lb. Fig. show a device suitable for carrying out the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The device has a pulp supply 1 for ozone bleaching from one of the preceding bleaching stages, such as bleaching with oxygen and / or peroxide and subsequent alkaline extraction. The acid wastewater filtrate 14, which falls off at the end of the ozone bleaching stage, is added to the pulp suspension to adjust the density of the substance and utilize the residual liquid content. Simultaneously, the addition of acid 2 to adjust the pH value determines the pH value. By means of the MC pump 3, the pulp suspension is conveyed to the mixer 4, which is preferably a high-shear mixer.

The ozone-containing gas 7 is compressed in the compressor 8 and introduced under pressure into the MC-mixer 4. In the MC-mixer 4, the suspension and the ozone-containing gas 7 are thoroughly mixed rapidly.

The reaction is further carried out under pressure in the reactor, which is formed as reaction tube 5. At the end of the reaction tube 5, there is a return line 9 (in the form of a tube and a pump) to the reaction mixture, so as to optionally undergo the pulp suspension several times in the process according to the invention.

In FIG. 1a and 1b, the combination of a gaseous suspension of a substance in a conventional bleaching tower 10 is shown. This is not absolutely necessary according to the invention. There is a distinction between ascending and descending towers. With the ascending tower (Fig. 1a), a suspension of the gas and the pressurized substance is conveyed to the

Bleaching tower 10, with or without throttling 6, where there may still be a post-reaction. In the discharge area, the pressure is released and the waste gas is discharged through the waste gas line 11. The pulp slurry released from the pressure is topped up with dilution water 12 and dried from the bleaching tower 10 to the wash filter 13. The waste effluent filtrate 14 is fed to the pulp supply 1 via the waste water return line 15.

Using the descent tower (Fig. 1b), the gasified suspension of the substance coming from the reactions of the tube 5 is passed through the throttle valve 6 and then released to atmospheric pressure in the gasifier. The discharge of the substance to the bleaching tower 10 is also effected by the addition of dilution water 12. The ozone-poor waste gas is also passed through the waste gas line 11, for example a catalytic or thermal ozone decomposition plant.

The oxygen leaving in the waste gas line 11 can be used in the oxygen bleaching step and the excess oxygen can be returned to the ozonator after appropriate purification. If oxygen is not used in the oxygen bleaching stage, then everything can be returned after the necessary purification steps.

By recirculating the waste water and waste gas, some energy can be saved, especially at the high temperatures used in the air flow.

In all cases, the retention of the pulp suspension in the reaction tube 5 and in the bleaching tube 10 is less than 3 hours, normally less than 1 hour, preferably even less than 5 minutes.

In the following examples, the beech chemical pulp for synthetic fibers or spruce paper pulp is subjected to the ozone bleaching of the invention after the usual peroxide-enhanced oxygen extraction.

Example 1

The pulp has the following characteristic values after the peroxide-enhanced oxygen (EOP) extraction:

kapa nepranej : 2,1 drip washed : 1,9 lightness : 76% (Elrepho) viscosity CSB-accompanying waste 255 mP (= 25.5 mPa, s) Water : 5 g / kg of absolutely dry pulp It is subjected to ozone bleaching with the following parameters: pressure : 0.52 MPa substance density : 12% temperature : 46 ° C pH : 2,3 spec. use of O ₃ : 1.82g / kg spec. The consumption of ozone concentration of ₃ : 1.69 g / kg fresh gas ozone concentration in : 76.8 mg / Nl waste gas : 3.2 mg / Nl reaction time : 120 s mixing time : 20s in _g / v, high-shear- : 1 / 3.2 (at 0.52 MPa) -miešačky : 1700 / min.

Bleached pulp values: kappa delta kappa consumption O ₃ / delta kappa has the following characteristics: 0, 9: 1,85: 0,9i lightness delta lightness viscosity delta viscosity by means of: pressure substance density temperature pH value spec. use of ozone spcc. ozone consumption ozone concentration in fresh gas ozone concentration in waste gas reaction time mixing time

Vg / Vi speed of high-shear mixer

Bleached pulp values: kappa delta kappa consumption O ₃ / delta kapota size delta size viscosity delta viscosity

Example 3: viscosity drops the degree of lightness

It is subjected to ram bleaching: pressure fabric density temperature pH value spec. Application O ₃ spec. O ₃ consumption ozone concentration in fresh gas ozone concentration in waste gas reaction time mixing time I / O, speed of high-shear mixers

Bleached pulp values: kappa delta kappa consumption Oj / delta kappa: 83.5%: 7.5%: 214 mP (= 21.4 mPa.s): 41 mP (= 4.1 mPa.s)

Example 2

The pulp has the same characteristic values as in Example 1, with the following exceptions: Unwashed: 2.9

The pulp is subjected to ozone bleaching with the following pa: 0.52MPa: 9.5: 50 ° C: 2.5: 1.60 g / kg: 1.57 g / kg: 79.7 mg / Nl: 1.3 mg / Nl: 120 sec: 20s: 1/2, 6 (at 0, 5 MPa): 3.200 / min.

has the following characteristics: 1.25: 1.65: 0.95: 82.5%: 6.5%: 227 mP (= 22.7 mPa.s): 28 mP (= 2.8 mPa.s)

Pulp has the following characteristic values:

: 1.9: 255 mP (= 22.5 mPa.s): 76% ozone with the following parameters: 0.5 MPa: 10: 50 ° C: 5.0: 1.5 g / kg: 1.13 g / kg: 78 mg / Nl: 17 mg / Nl: 120 S: 20s: 1 / 2.6 (at 0.5 MPa): 3.200 / min.

has the following characteristics: 1.1: 0.9: 1.25

SK 281290 Β6 lightness delta lightness viscosity delta viscosity: 82,0%: 6,0%: 210mP (= 2,1 mPa.s): 37 mP (= 3,7 mPa.s)

Example 4

The same pulp as in Example 3 is subjected to ozone bleaching with the following parameters:

EOP-Z ₁ -PE ₁ -Z ₂ -PE ₂ (POP = alkaline peroxide-enhanced oxygen treatment, Z = ozone treatment; PE = alkaline peroxide treatment).

a) The EOP pulp batch steps were carried out in an MC mixer under the following conditions:

pressure substance density temperature pH value spec. Application O ₃ spec. O ₃ consumption reaction time mixing time ozone concentration in fresh gas ozone concentration in waste gas VA.

high-shear mixer speed

Bleached pulp values: kappa delta kappa consumption O ₃ / delta kapota size delta size viscosity delta viscosity: 0,5 MPa: 10,7%: 23 ° C: 2,5: 1,6g / kg: 1,2g / kg: 120 s: 120 s: 83.2mg / Nl charge NaOH charge H ₂ O ₂ use O ₂ substance density residence time temperature: 2.0% (absolute dry substance): 2.0% (absolute dry substance): 0.2 MPa: 10%: 3h: 80 ° C

The following pulp parameters were obtained:

: 21 mg / Nl: 1 / 2.6 (at 0.2 MPa) kappa lightness viscosity tear length

WRA overpressure strength: 3.200 / min.

has the following characteristics: 6.6: 75.5%: 1498 mPas 10: 7800 m (24oSR); 8300 m (37oSR);

: 810 mNm / m (24 ° SR); 1057 mNm / m (37 ° SR);

: 3.3 kg / cm ² (24 ° SR);

3.5 kg / cm ² (37oSR)

With this EOP pre-bleached substance, the residual sequences of Z ₁ -PE ₁ -Z ₂ -PE ₂ were performed in three different ways V _b v ₂ , v ₃ .

0.60

1.3

0.91

86.3%

10.3%

228 mP (= 22.8 mPa.s) mP (= 2.8 mPa.s)

(b) ozone grade -1 (Z))

The parameters of the first ozone bleaching and the characteristic pulp numbers after the first ozone bleaching were as follows:

The differences between the properties of the substances of Examples 3 and 4 can only be attributed to the altered pH and the altered temperature.

The pH is therefore suitable for adjusting the viscosity.

The following examples 5 and 6 relate to spruce paper sulphite pulp. The following test samples were used for substance parameters:

MARKET LENGTH ENORM L 1114

WRA = resistance to further tearing viscosity

DIN53 115 Zelleheming IV / 30/62 readings in m readings in mNm / m readings in mPas.10

parameters VI V2 V3; - substance density (?) 8.5 8.2 9 pressure (MPa) 0.56 0.56 $ 0.5 temperature (’C] 20 31 ⁴⁴ · \ pH 2.5 2.5 2,5R ~ mixing time (s) 15 15 15 reaction time (s) 120 120 120 number of revolutions (min) 3200 3200 3200 special ozone feed (kg / t) 1.85 1.78 1.94 special ozone consumption (kg / t) 1.80 1.70 1.86 Vi / V, (at 0,56 MPa) 1.1 2.87 2.61 kapa 4.9 4.5 4.0 degree of lightness (?) 73.0 73,4 73.2 viscosity (mPas.10) 1048 971 976

Example 5

The raw material had the following values: kappa (Tappi 236 os-76) viscosity degree of lightness (Elrepho) market length (24 oSR) market length (41 oSR) WRA (24 oSR) WRA (41 oSR) overpressure strength (24 oSR) strength under pressure (41 oSR) initial characteristic: 20,4: 1500mPaa.l0: 49,7: 8900 m: 9200 m: 1143 mNm / m: 1010 mNm / m: 4,4 kg / cm ² : 4,2 kg / cm ²

c) PE level;

The parameters of the first alkaline peroxide treatment and the characteristic pulp values after treatment were as follows:

NaOH charge parameter (% relative to

VI V2 V3 for absolutely dry pulp) 1.0 charge H ₂ O (?, Relative to absolutely dry pulp) 0.7 substance density (%) residence time (h) temperature ('C) kappa

1.0

1.0

0.7

0.7

10 10

65

3.2 3.2

2.7. bleaching

Bleaching was performed using the following sequences:

degree of lightness (%) viscosity (mPas.10)

83.5 84.3

85.2

1047

981

972

d) ozone level - 2 (Z ₂ )

The parameters of the second ozone bleaching and the characteristic values after the second ozone bleaching are as follows:

parameter VI V2 V3 substance density (¾) 8 Θ Θ pressure (MPa) 0.56 0.56 0.56 temperature (’C) 21 33 45 pH 2.5 2.5 2.5 mixing time (s) 15 15 15 reaction time (s) 120 120 120 mixer speed (minj 3200 1800 3200 special ozone feed (kg / t) 2.70 2.38 2.34 special ozone consumption (kg / t) 2.06 1.85 1.92 Vi / V, at 0.56 MPa 2.5 2.6 2.5 kapa 1, 24 1.19 1.19 delta kapa (consumption 0.95 1.08 0.79 degree of lightness (%) 82.3 83.9 83.5 viscosity (mPas.10) 679 581 631

(e) PE level ₂

The parameters of the second alkaline peroxide treatment and the characteristic pulp values for processing were as follows:

parameter VI V2 V3 NaOH charge (%, relative to for absolute dry pulp) 0.7 0.7 0.7 the H 2 O 3 used (%, relative to to absolute dry pulp) 0.5 0.5 0.5 density of substance P) 10 10 10 temperature (’C) 65 65 65 kapa 0, 6 0, 6 0.6 degree of lightness (¢) 90.0 90, 0 90.0 viscosity (mPas.10) 650 583 577 market length (oSR) m 7600/20 / 7900/20 / 7500/20 / (oSR) m 8000/34 / 8200/36 / 8000/35 / WRA (oSR) mNm / m 1043/20 / 1080/21 / 1060/20 / (oSR) mNm / m 1100/34 / 1040/36 / 1047/35 / overpressure strength (□ SR) kg / cm ^: 3.13 (20) 3.30 (21) 3.27 (20) oSR / kg / cm ² 3.50 (34) 3.37 / 36 3.43 (35)

Strength densities corresponding to the standard bleached pulp ('standard bleached' pulp refer to the sequence C-PE-H-R) despite the extremely high degree (90%) and the low viscosity values refer to C-PE-H-R.

Example 6

The same raw material as in Example 5 was subjected to the EOP-Z-PE bleaching sequences with less lightness requirements. Final bleaching (PE) conditions (V4, V5) have been changed to achieve a degree of brightness greater than 85% at the highest possible strength values.

a) EOP bleaching was performed as in the example

5th

(b) ozone bleaching (Z)

The parameters of ozone bleaching and the characteristics of pulp after bleaching are as follows:

Parameter density of the substance (Sj12 pressure (MPa) 0,62 temperature (° C) 24 pH2,5 stirring time (s) 15 reaction time (s) 120 RPM MC mixer (minj1700 special ozone charge (kg / t) 2.62 special ozone consumption (kg / t2.37)

Vi / V _y 2.56 kappa3.7 delta kappa (OJ1.22 viscosity (mPas.10) 771 degree of lightness (%) 75.7

Example 7

The spruce kraft pulp, after the usual oxygen extraction, was subjected to two different bleaching steps according to the invention. The pulp had the following characteristic values after oxygen extraction:

capacity: 16 whiteness: 27,7 market length: 10, 5 km (17 * SR)

10.7 km (21 * SR)

WRA: 1666 mNm / m (17 * SR)

1620 (21 * SR) rel. burst strength: 7.42 kPam ² / g (17 * SR) 7.13 kPam ² / g (21 * SR)

Bleaching was performed using the sequences Ζ, -ΕΟ-Z ₂ -P as well as the sequence Z _r ECP-Z ₂ -P (Z = ozone treatment, EO = alkaline oxygen treatment, EOP = peroxide-enhanced alkaline oxygen treatment, EOP = peroxide-enhanced alkaline oxygen treatment, P = peroxide treatment).

(a) ozone treatment (Z _t and Z ₂ ) was carried out under the following conditions:

substance density pressure temperature pH value stirring time reaction time number of turns ozone concentration spec. ozone charge ozone consumption V | / in _g : 10%: 0.8 MPa (Z,)

0.7 MPa (W ₂ ): 52 ° C: 2: 2s: 120 sec: 3200 rpm.

: 100 g / Nm ³ : 4 kg / t absolute dry matter (Zj): 95%: 1.96 (Z ₂ )

b) the EO or EOP step was carried out under the following conditions: substance density temperature NaOH charge peroxide charge: 12%: 90 ° C: 2.0: 0.5 to 3%

(c) peroxide treatment (P) was carried out under the following conditions: substance density NaOH charge: 12%: 70 to 80 ° C: 0.5 to 2.5 g

SK 281290 BŔ peroxide charge 0.5 to 2%

The pulp now had the following characteristics, step by step:

parameter Rev. EO-Rev-P Z _: -EOP-Z _from -P Eo_Z. kapa 12 12 lightness 41 41 before Z _; kapa 7 6 lightness 62 65 po Z _ž kapa 4 3.5 lightness 78 80 to P (Fully Bleached) lightness 85 87 market length (km) 9.8 (15 * SR) 9.7 (15 * SR) 10.9 (23 * SR) 10.6 (22 * SR) rel. tensile strength to (kPa n7g) 7.0 (15 * 5R) 7.4 (15 * SR) 7.5 (23‘SR) 7.6 (22 »SR) WRA (mNm / m) 1816 [14 * SR) 1780 (14 * SR)

Example 8 (comparative example)

For comparison with Example 7, the same pulp was subjected to chlorine bleaching with a bleaching sequence of Z _r EO-Z ₂ -D. (D = chlorine bleaching).

The process conditions of step Z _t , step EO and step Z ₂ were identical to those described in Example 7. The reaction conditions of step D were as follows: substance density: 10-12 temperature: 70 ° C active chlorine: 1

The pulp was now puffy

Other features: E & Z kapa : 12 lightness 41 ored Z ·, kapa 7 lightness : 62 PoZ ₂ kapa : 4 lightness : 78 to D (úolne bleached ^-) lightness : 89 market length (km) : 9.8 (15 * SR) : 11.0 (24 * SR)

rel. compressive strength (kPam ² / g): 7.2 (15 * SR): 7.5 (24 * SR) WRA (mNm / m): 1820 (15 * SR): 1520 (22 * SR)

Examples 7 and 8 show that there are no differences in strength properties between unbleached or chlorine bleached pulp on the one hand and chlorine-free bleached pulp according to the invention on the other hand.

wood, with a starting value of up to 30, by ozone, in which the pulp suspension is fed with vigorous stirring or mixing at a temperature of 15 to 80 ° C and at a pH of 1 to 8, in contact with the ozone-containing gas, % ozone contains 20 to 300 g / m ^{3 of} ozone, in which a maximum of 2 wt. ozone with respect to absolutely dry pulp, characterized in that the pulp suspension has a substance density of 5 to 20 wt. and the ozone-containing gas is introduced into the pulp suspension at a pressure of 0.1 to 1.5 MPa.

The process according to claim 1, characterized in that ozone is introduced at a pressure of 0.11 to 1 MPa into the pulp suspension.

The method of claim 1, wherein the gas: liquid volume ratio is 1: 0.5 to 1: 8.

The method of claim 1, wherein the gas: liquid volume ratio is 1: 1 to 1: 6.

Process according to one of Claims 1 to 5, characterized in that it is carried out several times in succession, wherein an alkaline extraction is carried out between the individual steps.

Method according to one of Claims 1 to 6, characterized in that the extraction is first carried out with oxygen and / or peroxide and then ozone gas at a pressure of 1 to 5 bar is introduced into the pulp suspension.

Method according to claim 7, characterized in that, after the extraction with oxygen and / or peroxide, an alkaline peroxide step is introduced and then ozone gas at a pressure of 0.1 to 1.5 MPa is introduced into the pulp suspension.

Method according to claim 1 or one of the following claims 2 to 8, characterized in that after the introduction of ozone at a pressure of 0.1 to 1.5 MPa into the pulp suspension, a peroxide stage or an alkaline extraction is introduced.

Method according to one of Claims 1 to 8, characterized in that all or part of the waste water filtrate which is removed during the ozone treatment is fed to the pulp suspension before it is brought into contact with the ozone gas, together the required acid, in particular sulfuric acid, is also supplied with the waste water filtrate and the desired pH value is adjusted.

Claims (1)

Method for bleaching pulp without chlorine, in particular chemical pulp for synthetic fibers, for example hardwood pulp with a starting value of kappa 15 to 1, or paper pulp, for example pulp of needles.