FI63793C - ALKALIPRESSNING AV CELLULOSAMASSA - Google Patents

Description

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Patent- och rafittaratyralaan 'Anteiun uthfd och uti-skiirun pubUnnd ^ 9-04.03 (32) (33) (31) Requested «TuoikMi-B ^ ini priority 29 - 09.72

Canada (CA) 152905 (71) Pulp and Paper Research Institute of Canada, 570 St. John Boulevard,

Pointe Claire 720, Quebec, Canada (CA) (72) Norman Liebergott, Laval, Quebec, Canada (CA) (7 * 0 Berggren Oy Ab (5 ^) Alkaline compression of cellulosic pulp -Alkalipressning av cellulosassa f a process for the preparation of cellulose for the preparation of pretreated paper, e.g. after treatment with elemental chlorine or an oxidizing agent, e.g. chlorine monoxide, chlorine dioxide, hypochlorites, chlorites, peroxides, chlorates, dichromates, nitrogen oxides, nitrogen oxides, permanganate 12%, by mixing cellulose with an aqueous solution of an alkali, e.g. sodium hydroxide, sodium carbonate, calcium hydroxide, ammonia, etc., at a temperature of 40-90 ° C.

Lignin removal and bleaching are a continuation of the cooking process in which the lignin material and the colored substance remaining in the chemical pulp are selectively removed by minimizing the value of the cellulosic fiber. In this case, it has previously been difficult that in order to achieve a degree of whiteness while maintaining strength, maintaining a degree of whiteness and making bleaching economical, the reaction products resulting from such lignin removal by oxidative bleaching should be removed by alkaline extraction. Sodium hydroxide is the preferred substance, but 2,6793 other alkalis (e.g., ammonia, sodium carbonate, calcium hydroxide, etc.) have been proposed and used.

Alkaline extraction must be separated from alkaline purification. Alkaline extraction is a method of making cellulose for paper. Alkaline purification is a method of making a dissolving mass. Paper pulp is characterized by the retention of strength, the stability of the degree of bleaching and the economics of bleaching. Dissolving pulps also have a high degree of purity, e.g. they contain essentially no hemicellulose, e.g. pentosans or resins, and an alpha-cellulose content of more than 91%. · This is achieved by enhancing conventional alkaline extraction in two applications known as hot base purification and cold alkali purification. tuksena. These methods will now be described with reference to the drawings, in which:

Figure 1 is a schematic flow diagram of a conventional known alkali extraction when making cellulose for papermaking, Figure 2 is a schematic flow diagram of a previously known hot base purification for producing soluble cellulose and Figure 3 is a schematic flow diagram of a prior art cold base purification for solubilizing.

In the conventional alkali extraction shown in Figure 1, the operating conditions vary, with the amount of NaOH per cellulose being 0) 5-3.0% temperature 4o-70 ° C, time 60-120 minutes and pulp thickness 3-16%, with high values considered to be economical for the economical use of steam and space. In particular, in Figure 1, the wood pulp is chlorinated in a chlorinator 10 and washed and thickened in a thickener 11. In this case, cellulose with a consistency of up to 12% is obtained.

The thickened cellulose is mixed in a mixer 12 with steam, water and NaOH, the amount of NaOH being about 2-5% based on the cellulose. The consistency of the mixture is about 10% and the temperature is generally in the range of 60-70 ° C. The mixture is passed to reaction atom 13, where the residence time is about 1-2 hours. After this time, the cellulose is washed in the wash tower 14 and removed at 15 ° C when the NaOH is substantially completely used.

In hot base cleaning, the amount of NaOH used for the cellulose is between 0.5-2%, the consistency of the cellulose is generally between 10-22%, the temperature is generally between 50-145 ° C and the treatment time is generally from a quarter to 4 hours. In Figure 2, the cellulose is chlorinated in a chlorinator 20 and washed and thickened in a thickener 21. This gives cellulose with a consistency of up to 12%.

63793

The thickened cellulose is mixed in a mixer 22 with water and NaOH up to 16% of the amount of cellulose. The consistency during mixing is 12-18% and the temperature is 70-120 ° C or even higher. The mixture is introduced into the reaction tower 23, where the residence time is 1 or 2 hours or more.

The product is then pressed in a press 26 to a consistency of 25-35% and removed in step 27. The pressed cellulose still contains residual NaOH.

In cold base cleaning, operating conditions are generally based on the use of 6-8% sodium hydroxide solution at a consistency of 3%, a time of 30-60 minutes and a temperature of 30-40 C. In Figure 3, cellulose is chlorinated in a chlorinator 30 and washed and thickened in a 31 with a consistency of up to 12%.

The thickened cellulose is mixed in a mixer 32 with water and NaOH of 9-16%, the consistency of the cellulose being 50%, and the temperature is ambient temperature. The mixture is passed to a purifier comprising a plurality of reaction towers 33 and presses 36, so that the basic reaction has many steps in the reaction tower and press. The total cleaning time is 1-2 hours. The compressed cellulose still contains residual NaOH.

Thus, in the past, no attempt has actually been made to address the issue of improving the alkali extraction step, although many of the proposals made for rapid bleaching are based on a rapid bleaching step that possibly takes into account the low degree of post-bleaching alkali extraction as a degree. ("Degree" as used herein comprises the step of starting and adding a chemical to cellulose and ending with washing the cellulose.) Examples of these include: WH Rapson's "Dynamic Bleaching", TAPPI, Vol. 49, No. 8 ^, p. 324 -344, 1966; AW Brinkley, Jr. et al., U.S. Patent No. 3,575,795, issued April 20, 1971; Allan G. Jamieson, Canadian Patent No. 881,406, issued September 21, 1971; N. Liebergott and FH Yorston, "Experiments in Rapid High Density Bleaching," TAPPI Vol. 48, No. 1, pp. 20-24, 1965.

According to the present invention, it is proposed to extract cellulose for the production of rapid and thoroughly pretreated paper by an alkaline extraction process; providing an extraction technique that is of ecological interest due to the water protection effect, and providing an extraction technique that makes the extracted cellulose very thick so that it is suitable for trituration and treatment with a gaseous reagent in the next bleaching step.

According to the present invention there is provided a process for the alkaline extraction of paper pulp, e.g. after treatment with elemental chlorine or oxidizing agents such as chlorine monoxide, chlorine dioxide, hypochlorites, chlorites, peroxides, chlorates, dichromates, nitrogen oxides, permanganates, etc. %, by mixing the mass with an aqueous solution of an alkali, e.g. sodium hydroxide, sodium carbonate, calcium hydroxide, ammonia, etc. at a temperature of 40 ° C to 90 ° C, where the mass / alkali mixture is formed by rapidly mixing the mass with an alkali of 0.5-5% by weight and the process is characterized in that such a mixture is rapidly compressed by 18-40%. The rapid compression extraction is preferably performed in one compression step. The real practical result obtained with this invention is the reduction of the time required for alkaline extraction. As described above, the time required for alkaline extraction has previously been 50-120 minutes. According to the present invention, the alkali extraction including the stirring time can be performed in 6 minutes.

The pretreated cellulose, e.g., chlorinated and washed cellulose, is rapidly mixed (usually complete in five minutes) with an aqueous alkali solution (usually sodium hydroxide) at a NaOH concentration relative to the Kappa number of the cellulose according to the following table:

Cellulose% NaOH per cellulose after chlorination or oxidation treatment

Hardwood kraft pulp

Kappa No 10-20 0.5 - 2

Softwood kraft pulp

Kappa No 20-40 2 - 4

Bisulfiittimassa

Kappa No 30-50 3 - 5 when the consistency is 4-12% and the temperature is 40-90 ° C. The stirring temperature is preferably 60-80 ° C.

The present invention is particularly suitable for improving a bleaching process in which comminuted pulp for papermaking is bleached and the bleached cellulose is then washed with water and further rapidly at a consistency of 4-12%, e.g., complete mixing in 5 minutes etc., however, preferably sodium hydroxide, which is preferably used up to a saturation concentration relative to the Kappa number of the cellulose according to the following table: 5 63793

Cellulose% NaOH per cellulose after chlorination or oxidation treatment

Hardwood kraft pulp

Kappa No 10-20 0.5 - 2

Softwood kraft pulp

Kappa No 20-40 2 - 4

Bisulfiittimassa

Kappa No. 30-50 3 to 5 at a temperature of 40-90 ° C and preferably at a temperature of 60-90 ° C. In this case, the process is characterized in that a certain type of cellulose / alkali mixture thus formed is rapidly compressed, e.g. so that the compression takes place completely in 1 minute, to a consistency of 18-40%, preferably to a consistency of 20-40%.

In one such embodiment of the invention, the bleaching is carried out in papermaking cellulose which has been compressed to a consistency of 30% and is in pulverized form as fibers and the fiber in agglomerates, the bleaching agent being chlorine gas. In another such embodiment of the invention, the bleaching is carried out on paper pulp having a consistency of 3.5% and the bleaching agent being chlorine dissolved in water. In a third embodiment of the invention, the bleaching is carried out in cellulose for papermaking with a consistency of 12% and chlorine dioxide is used as the bleaching agent.

The present invention is also applicable to multi-stage processes in which a rapid compression extraction step is performed between two oxidation steps. In one embodiment of the present invention, no water washing step is required after the compression extraction step. And in yet another application, the oxidizing agent for both stages is chlorine dioxide.

In the accompanying drawings, Fig. 4 is a schematic flow diagram of an alkali extraction according to the present invention for making pulp.

In the rapid compression extraction according to the present invention shown in Fig. 4, the pulp is chlorinated in a chlorinating apparatus 40 and washed with water and thickened in a thickener 41. This results in a mass with a consistency of up to $ 12.

The thickened mass is mixed in a mixer 42 with steam and 0.5-5% NaOH, the amount being calculated from the mass, and the mixing takes place when the consistency is less than 12%, preferably 4-12%. The temperature is between 40-90 ° C, preferably 60-80 ° C. Stirring is generally complete in about 5 minutes, and no longer reaction time is required. The mixture is then about immediately compressed in a press 46 to a consistency of about 18-40%, preferably 20-40%. Compression is usually complete in about 1 minute. The cellulose is removed at 45 and requires little or no water washing and no residual NaOH.

The following examples demonstrate the surprising and truly practical results obtained by the method of this invention compared to previously known methods. Before the examples, five pretreatment methods are described.

Pre-treatment method (I)

Unbleached softwood sulphate cellulose with Roe chlorine No. 5.6, Kappa No. 38.1 and 0.5% CED viscosity 24.2 was compressed to a consistency of 30%. The pulp was comminuted into fibers and fiber joints using the apparatus described in U.S. Patent No. 3,630,828. The pulp was then treated with chlorine gas for 1 minute (4.5% chlorine for oven dry pulp), the pK of the chlorinated pulp was 1.0. The pulp was diluted to 16% consistency with deionized water and compressed to 30% consistency. One device suitable for the rapid compression method of this invention is a hydraulic press, but other types of devices, such as a screw press or rollers, may be used as well. The main components of one type of press are an upright cylinder frame with a removable perforated base, a tightly fitted piston inside and devices for accommodating loads on the piston. Pressures of the order of 7 kg / cm are sufficient.

10 gram samples of the prepared cellulose were treated as follows.

Pre-treatment method (II)

Unbleached softwood cellulose with a Roe-chloro-No of 4.6, a Kappa-No of 26.3 and a 0.5% CED viscosity of 24.6 cps was chlorinated at a consistency of 3.5% for one hour at 25 ° C . Chlorine consumption 011 5.1% chlorine per oven dry pulp. After chlorination, the pulp was washed with copious amounts of deionized water and made up to 12% consistency with a Biichner funnel covered with a 100 mesh screen. Samples of the prepared pulp were treated as follows. Pre-treatment method (III)

Unbleached sulphate hardwood cellulose with a Roe-chloro-No of 1.3, a Kappa-No of 13.7 and a 0.5% CED viscosity of 20.2 cps was chlorinated under standard conditions at a consistency of 3.5% for 45 minutes. ° C. Chlorine consumption was 3.0%. After chlorination, the pulp 7 63793 was washed with copious amounts of water using deionized water and brought to a consistency of 12% by draining through a Buchner funnel coated with a 100 mesh screen.

Pretreatment method (IV)

Unbleached softwood sulphite cellulose with Roe-chloro-No 7.6, Kappa-No 38 and 0.5? The CED viscosity was 28.2 cps, compressed to a consistency of 30%. The pulp was comminuted into fibers and fiber bundles using the apparatus described in U.S. Patent 3,630,828. The pulp was then treated with chlorine gas for 1 minute (5.2% chlorine per oven dry pulp), the pH of the chlorinated cellulose was 0.9. The cellulose was then diluted to 1% consistency with deionized water and compressed to 30% consistency.

Pre-treatment method (V)

Sulfate cellulose from South USA, Roe-chloro-No 3.8, Kappa-No 21.1 and CED viscosity 17.0, was chlorinated, washed, extracted, treated with chlorine dioxide and washed to a degree of bleaching according to these standard processing methods. after was 82.4. The pulp was then brought to a 12% consistency by draining through a Biichner funnel with a 100 mesh screen.

Example 1 - Compression extraction of chlorinated pulp by pressing several times Example IA

A portion of the chlorinated washed mass from pretreatment method (I) was extracted with dilute sodium hydroxide (3.5% NaOH per 10% consistency mass over 1 hour at 60 ° C), and then washed with deionized water to a concentration of 1%. The washings were removed from the pulp and color, BOD and COD were measured experimentally. Test sheets were made by hand from the pulp and Kappa number and CED viscosity were measured.

The results obtained are shown in Table I.

Example IB

An aliquot of the treated pulp from pretreatment method (I) was mixed rapidly (30 seconds) with aqueous sodium hydroxide solution (3.5% of the oven-dry pulp) at 60 ° C. The consistency of the resulting mixture was 10%. The mixture was immediately compressed to a consistency of 31%, and the pressing liquid was removed from the pulp, and its color, BOD and COD were measured by appropriate experiments. The pulp was then washed with deionized water to a concentration of 1% and test sheets were prepared by hand and the Kappa number and CED viscosity were measured.

The results are shown in Table I.

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Example 1C

A batch of the pulp treated by the pretreatment method (I) was mixed with an aqueous solution of sodium hydroxide (3.5% of the oven-dry pulp) at 60 ° C. The consistency of the mixture was 10%. The mixture was immediately compressed to a consistency of 30%. The pressing liquid was rapidly remixed a second time so that the consistency was again 10%, and the mass was immediately recompressed to 29. The compressed liquid was removed from the pulp and the color, BOD and COD were determined. The pulp was then washed with deionized water to a consistency of 1%, and test sheets were prepared by hand, the Kappa number and CED viscosity of which were measured.

The results are shown in Table I.

Example ID

A batch of the cellulose treated by the pretreatment method (I) was rapidly mixed with an aqueous solution of sodium hydroxide (3.5% by oven dry mass) at 60 ° C. The consistency of the mixture was 10%. The mixture was then suddenly compressed to a consistency of 30%. The press liquid was then mixed with the press cake to a consistency of 10% and immediately re-pressed to $ 30. The liquid was mixed again with the press cake to a consistency of 10%, and then the mixture was immediately pressed to a consistency of 32%. The compression fluid was removed from the pulp and its color, BOD and COD were determined experimentally. The pulp was then washed with deionized water to a consistency of 1 # and test sheets were prepared by hand, the Kappa number and CED viscosity of which were measured.

The results obtained are shown in Table I.

Example IE

A batch of chlorinated, washed cellulose treated by pretreatment method (I) was extracted with dilute sodium hydroxide (3.5% NaOH per mass at a consistency of 10% for 1 hour at 80 ° C), and then washed with deionized water at a consistency of 1%. . The washings were removed from the pulp and its color, BOD and COD were determined. Test sheets were then made by hand from the pulp and their Kappa number and CED viscosity were measured.

The results obtained are shown in Table I.

Example 1F

A batch of the cellulose treated by the pretreatment method (I) was mixed rapidly (30 seconds) with an aqueous solution of sodium hydroxide (3.5% of the oven-dry mass) at 80 °. The consistency of the resulting mixture was 10%. The mixture was immediately compressed to a consistency of 20% and the compression solution was removed from the pulp and its color, BOD and COD were determined. The pulp was then washed with deionized water to a consistency of 1%, and 9,637,933 manual test sheets were prepared from which Kappa number and CED viscosity were measured.

The results obtained are shown in Table I.

Example 1G

A batch of the cellulose treated by the pretreatment method (I) was rapidly mixed with an aqueous solution of sodium hydroxide (3.5% by oven-dry mass) at 80 ° C. The consistency of the mixture was 10%. The mixture was immediately compressed to a consistency of 20%. The pressing liquid was rapidly remixed a second time so that the consistency was again 10%, and the pulp was pressed again to 18%. The compression fluid was removed from the pulp, its color, BOD and COD were determined. The pulp was then washed with deionized water to a consistency of 1%, and test sheets were prepared by hand, the Kappa number and CED viscosity of which were measured.

The results obtained are shown in Table I.

Example 1H

A batch of the cellulose treated by the pretreatment method (I) was rapidly mixed with an aqueous solution of sodium hydroxide (3.5% of the oven-dry mass) at 80 ° C. The consistency of the mixture was 10%. The mixture was then immediately compressed to a consistency of 20%. The press liquid was then mixed with the press cake to a consistency of 10% and immediately re-pressed to $ 20 pound. The liquid was remixed with the press cake so that the consistency of the mixture was 10%, and then the mixture was immediately pressed to 22%. The compression fluid was removed from the pulp and its color, BOD and COD were determined. The pulp was then washed with deionized water to a consistency of 1%, and test sheets were prepared by hand, the Kappa number and CED viscosity of which were measured.

The results are shown in Table I.

63793 10

Table I

Effect of temperature and number of compressions on Kappa number.

Western softwood sulphate cellulose, Roe-chloro-No 5.6,

Kappa No 38.1, CED viscosity (0.5%) 24.2 cps, pentanes 6.7%, alpha-cellulose 89.2%

Pre- NaOH- Thermal- Pulp se- Consistency pH Extraction- Pulp characteristic% mass The extraction time of the extraction after washing was washed from about ° C during the time I remained. Kappa 0.5 i% keen No CED viscosity cps IA 3.5 60 10 - 10.5 - 7.9 24.6 IB 3.5 60 10 31 10.9 0.75 7.9 25.0 1C 3.5 60 10 29 10.5 0.75 7.5 26.3 ID 3.5 60 10 32 10.1 0.75 7.5 25.7 IE 3.5 80 10 - 10, 3 0.75 7.5 25.2 1P 3.5 80 10 20 10.6 0.75 7.2 24.1 1G 3.5 80 10 18 10.3 0.75 7.1 24.8 1H 3 , 5 80 10 22 10.0 0.75 6.3 24.3

Pre-pulp properties- Liquid properties 1 H? 0 marks after washing Off- Color COD BOD removed / ton no. Pento- Alpha-clarified APHA- ppm ppm cellulose received cellulose volume and%% ropes ml Mg / Pt / 1 465 Mu IA 6.7 90.3 917 3.028 589 115 83ΟΟΟ IB 6.8 88.9 68 33.216 5870 1430 6210 1C 6.7 90.1 65 35.693 6325 1500 5940 ID 6.7 90.2 69 36,170 7388 1550 6300 IE 6.6 90.4 917 3.121 618 115 83ΟΟΟ 1P 6.7 89.2 51 33.248 6128 1500 4630 1G 6.7 89.9 45 43.211 6692 1550 4θ8θ 1H 6.7 90.2 55 48.327 8683 2050 5020 after acidic clone treatment.

As can be seen from Table I, a significant advantage in the compression extraction of chlorinated pulp seems to be that rapid, preferably single extraction (usually lasting less than one minute) can reduce the Kappa number in chlorinated cellulose to a value similar to conventional treatment with the same amount of alkali. when used, at the same temperature, but in a much shorter period than the usual 60 minute period, obtained. The results obtained in Examples IB, 11 63793 1C and ID show that two or three compression extractions do not significantly reduce the Kappa number from that obtained after the first compression extraction, and this result is surprising. It should be noted that the content expressed in liquid color units, COD units and BOD units is higher for compression-extracted cellulose; this means that a larger amount of impurities enters a smaller amount of water, which increases the concentration of such impurities, so the removal or purification operation can be much simpler.

Example 2 - Effect of mixing consistency on compression extraction of chlorinated cellulose

The following examples are intended to show the effect of reducing the Kappa number on mixing chlorinated and washed cellulose with dilute sodium hydroxide solutions at different mixing consistencies (5 and 10%>), which mixture is then immediately compressed by a simple compression step to 20-40% consistency.

Example 2A

A portion of the chlorinated washed compressed pulp from pretreatment method (I) was mixed rapidly (two minutes) with an aqueous solution of sodium hydroxide (3.5% per oven-dry pulp) at 60 ° C. The consistency of the resulting mixture was 5%. The mixture was immediately compressed to a consistency of 21% in 0.39 minutes and the compression liquid was separated from the pulp. The pulp was then washed with deionized water at a consistency of 1% and test sheets were prepared from it, the Kappa number and CED viscosity of which were measured.

The results are shown in Table II.

Example 2B

A batch of chlorinated washed compressed cellulose from pretreatment method (I) was mixed rapidly (two minutes) with aqueous sodium hydroxide solution (3.5% by oven dry mass) at 60 ° C. The mixture was pressed to a consistency of 31% in 0.52 minutes and the pressurized liquid was removed from the pulp. The pulp was then washed with deionized water at a consistency of 1% and test sheets were prepared by hand, the Kappa number and CED viscosity of which were measured.

The results are shown in Table II.

Example 2C

An aliquot of chlorinated washed compressed pulp from pretreatment process (I) was mixed rapidly (two minutes) with aqueous sodium hydroxide solution (3.5% of the oven-dry pulp) at 60 ° C. The mixture was immediately compressed to a concentration of 38% (compression time 1.15 minutes), and the compression fluid was removed from the cellulose. This was then washed with ion-free water at a consistency of 1% and test sheets were prepared by hand, the Kappa number and CED viscosity of which were determined.

The results are shown in Table II.

Example 2D

A batch of chlorinated washed compressed cellulose from pretreatment method (I) was mixed rapidly (two minutes) with aqueous sodium hydroxide solution (10% by oven dry mass) at 60 ° C. The mixture was immediately compressed to a consistency of 22% (compression time 0.33 minutes) and the compression fluid was removed from the pulp. The pulp was then washed with deionized water at a consistency of 1% and test sheets were prepared by hand, and the Kappa number and CED viscosity were determined.

The results obtained are shown in Table II.

Example 2E

A batch of chlorinated washed compressed cellulose from pretreatment method (I) was mixed rapidly (two minutes) with aqueous sodium hydroxide solution (10% by weight) at 60 ° C. The mixture was immediately compressed to a consistency of 30% (compression time 0.5 x 5 minutes), and the compression liquid was removed from the pulp. The pulp was then washed with deionized water to a consistency of 1%, and prepared into test sheets by hand, and the Kappa number and CED viscosity were measured.

The results obtained are shown in Table II.

Example 2F

A batch of chlorinated washed compressed cellulose from pretreatment method (I) was mixed rapidly (two minutes) with aqueous sodium hydroxide solution (10% by weight) at 60 ° C. The mixture was immediately compressed to a consistency of 38% (compression time 1.0 minutes), and the compression fluid was removed from the pulp. The pulp was then washed with deionized water to a consistency of 1%, and prepared into test sheets by hand and the Kappa number and CED viscosity were measured.

The results obtained are shown in Table II.

13 63793

Table II

Effect of mixing and compression consistency during alkaline compression extraction

Softwood sulfate cellulose, Roe chlorine No. 5.6, Kappa No. 38.1, 0.5% CED viscosity cps. 24.2; pentosans 6.7%> alpha-cellulose 89.2% *

Pre- NaOH Heat- Mass consistency pH extract- Extraction time mark-% mass Stir- Extraction residues.

of residual ° C of residual no. chicken 2A 3,5 60 5 21 11,2 0,39 2B 3,5 60 5 31 11,1 0,52 2C 3,5 60 5 38 10 .8 1.0 2D 3.1 60 10 22 11.0 0.33 2E 3.5 60 10 30 10.9 0.45 2F 3.5 60 10 38 10.7 1.0

Pre- _Mass properties_ __After washing _____ No. Kappako 0.5% CED- Pentosans Alpha-cellulose viscosity-%% ti cp 2A 7.9 25.0 6.8 88.9 2B 7.7 24.7 6.8 88.7 2C 7.4 24.9 6.7 89.2 2D 8.2 24.8 6.8 89.6 2E 7.9 25.1 6.7 89.9 2F 7.4 24.9 6.7 89 , 9 ^ after acidic chloride treatment.

As can be seen from Table II, the Kappa number was very little affected by the fact that the consistency of the pulp during mixing is in the range of 5 ~ 10% or when the consistency of the pulp after pressing is in the range of 21-38%.

Example 3 - Effect of conventional chlorination on the compression extraction of chlorinated pulp

The following example is intended to demonstrate the use of the process of this invention in a pulp chlorinated by conventional treatment in aqueous solution.

Example 3A

A batch of chlorinated washed pulp from pretreatment process (II) was extracted with dilute sodium hydroxide (2.0% NaOH per oven dry 63793 14 pulp with a consistency of 10% over 1 hour at 60 ° C), and then washed with deionized water at 1 #. . The pulp was then made into test sheets by hand and the Kappa number and CED viscosity were measured.

The results obtained are shown in Table III.

Example 3B

A portion of the treated pulp from pretreatment method (II) was mixed rapidly (3 minutes) with aqueous sodium hydroxide solution (2.0% of the oven-dry pulp at 60 ° C). The consistency of the resulting mixture was 10%. The mixture was compressed to a consistency of 30% and the liquid was removed from the pulp. The pulp was then washed with deionized water to a consistency of 1%, and test sheets were prepared by hand and the Kappa number and CED viscosity were measured.

The results obtained are shown in Table III.

Example 3C

An aliquot of the treated pulp from pretreatment process (II) was stirred rapidly (2 minutes) with aqueous sodium hydroxide solution (2.0% NaOH per oven-dry pulp) at 60 ° C. The consistency of the mixture is 011 10%. The mixture was immediately compressed to a consistency of 30%. The pressing liquid was rapidly remixed so that the consistency was again 10%, and the mass was pressed again to 30%. The compression fluid was removed from the pulp. The pulp was then washed with deionized water to a consistency of 1%, and test sheets were prepared by hand and the Kappa number and CED viscosity were measured.

The results obtained are shown in Table III.

63793 15

Table III

Softwood sulphate pulp from the East, Roe-chloro-No 26.5, 0.5% CED viscosity 24.6 cp, conventional chlorination, 5.1% Cl per kiln-dry pulp, pentosans 9.9%> alpha-cellulose 87.5% *

Pre- NaOH Temperature Mass consistency_ pH of extraction- Extraction-% of oven- ° C Stir- After extraction time ki dry after its time min.

of mass 3A 2.0 60 10 to 11.3 3B 2.0 60 10 30 11.5 0.75 3C 2.0 60 10 30 11.3 0.75

Pre-_Massage properties_ mpr'V-, · _ _ After washing_ nf0 Kappa No. 0.5% CED- Pentosa- Alpha-cellulose viscosines%% tea cp 3A 7.1 24.0 8.8 87.6 3B 7.1 24.2 8.9 87.2 3C 6.3 24.1 8.6 87.8 ^ after acidic chloride treatment.

As shown in Table III, the obvious advantage of compression extraction of chlorinated pulp in the usual way appears to be that a single such compression extraction can reduce the Kappa number of chlorinated pulp to the same value that can be obtained by conventional treatment with the same amount of alkali at the same temperature, but achieved here. in a much shorter time than the usual 60 minute period. The results of Examples 3B and 30 show that the two compression extractions did not significantly reduce the Kappa number from the value obtained in the first extraction, and this result is surprising.

Example 4 - Effect of conventional chlorination on the compression extraction of chlorinated pulp

Example 4A

A portion of the chlorinated washed pulp from pretreatment method (III) was extracted with dilute sodium hydroxide (2.0% NaOH per oven-dry pulp at 10% consistency, for 1 hour at 60 ° C) and then washed with deionized water at 1% consistency. The pulp was then made into test sheets by hand and the Kappa number and CED viscosity were measured.

The results are shown in Table IV.

63793 16

Example 4B

A portion of the chlorinated washed pulp from pretreatment method (III) was mixed rapidly (3 minutes) with aqueous sodium hydroxide solution, 2.0% per oven-dry pulp, at 60 ° C. The consistency of the mixture was 10%. The mixture was immediately pressed to a consistency of 30% and the pressing liquid was removed from the pulp. The pulp was then washed with deionized water to a consistency of 1%, and test sheets were prepared by hand and the Kappa number and CED viscosity were measured.

The results obtained are shown in Table IV.

Table IV

Hardwood sulphate pulp from the East, Roe-chloro-No 1.3 »Kappa-No 13.7, 0.5% CED viscosity 20.2 cp, conventional chlorination 3» 0% Cl 2 per kiln-dry pulp, pentosans 22 .3%, alpha-cellulose 86.9% *

Pre- NaOH% Thermal pulp consistency pH Extraction oven fiber Stir- Extraction extraction time ki only ° C then after after min.

n from mass 4A 2.0 60 10 - 11.2 4b 2.0 60 10 30 11.3 0.50

Pre-pulp properties after washing mark- Kappa- 0.5% CED- Pentosans Alpha-cellulose ki figure viscose-%% no. .9 86.6 * ...

after acidic clone treatment.

As shown in Table IV, a single compression extraction according to the present invention is very useful for conventionally chlorinated pulp.

Example 5 ~ Effect of gas chlorination on simple compression extraction

Example 5A

A batch of chlorinated washed compressed pulp from pretreatment method (IV) was extracted with dilute sodium chloride (2.5% NaOH per oven-dry pulp at 10% consistency over 1 hour at 60 ° C) and then washed with deionized water at 1% consistency. The pulp was then made into test sheets by hand and the Kappa number and CED viscosity were measured.

The results obtained are shown in Table V.

63793 17

Example 5B

An aliquot of the treated pulp from pretreatment process (IV) was mixed rapidly (30 seconds) with aqueous sodium hydroxide solution (2.5% per oven dry pulp) at 60 ° C. The consistency of the resulting mixture was 10%. The mixture was immediately pressed and the pressing liquid was removed from the pulp. The pulp was then washed with deionized water to a consistency of 1% and prepared into test sheets by hand, and the Kappa number and CED viscosity were measured.

The results obtained are shown in Table V.

Example 50

An aliquot of the treated pulp from pretreatment process (IV) was mixed rapidly (30 seconds) with aqueous sodium hydroxide solution (2.5% per oven dry pulp) at 60 ° C. The consistency of the mixture was 10%.

The mixture was immediately compressed to a consistency of 30%. The pressing liquid was mixed rapidly a second time so that the consistency was again 10%, and the pulp was immediately re-compressed to a consistency of 30%, and the pressing liquid was removed from the pulp. The pulp was then washed with deionized water and prepared into test sheets by hand, and the Kappa number and CED viscosity were measured.

The results obtained are shown in Table V.

Table V

Softwood sulphite cellulose, Roe-chloro-No 7.6, Kappa-No 38, 0.5% CED viscosity 28.2 cp, gas phase chlorination 5.2% Cl 2 per kiln-dry pulp, pentosans 7.1% t alpha-cellulose 86.8 % 1. NaOH% Thermal pulp consistency pH extraction Extraction time oven fiber After mixing Extraction min.

f1? only ° C during it after kl n '° of mass 5A 2.5 60 10 - 10.5 5B 2.5 60 10 30 10.9 0.75 5C 2.5 60 10 30 10.5 0.75

Pre-pulp properties after washing mark- Kappa-No 0.5% CED-viscos- Pentosans Alpha-cellulose ki No. capacity cp%% 5A 1.2 28.0 6.7 87.2 5B 1.5 28.1 ^ 7.0 86.9 5C 1.3 28.0 6.8 87.0 after acid chloride treatment.

As can be seen from Table V, the simple compression extraction of this invention is very useful for pulp chlorinated with gas.

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Example 6

The following examples are intended to show that the extraction or neutralization can be carried out by alkaline compression extraction, with or without washing, following a multi-stage neutralization or extraction method, between the two oxidation steps, oxidizing with e.g. chlorine dioxide, chlorine dioxide (DD) or hypoxide, neutralization or extraction is usually performed to improve the bleaching rate of the final oxidation step. Example 6A

An aliquot of the semi-bleached cellulose from pretreatment process (V) was extracted with dilute sodium hydroxide (1.0% NaOH per oven-dry pulp at a consistency of 10% for 1 hour at 60 ° C), and then washed with deionized water at a consistency of 1%. The pulp was then brought to a consistency of 12% by draining through a Bilchner funnel, and then bleached with 0.5% chlorine dioxide (per oven dry pulp, for 3 hours, at 70 ° C). The pulp was then washed and made into test sheets by hand, and the degree of bleaching obtained was 91 * 1 as measured by an Elrepho whiteness meter.

Example 6B

An aliquot of the semi-bleached pulp from the pretreatment process (V) was mixed rapidly (2 minutes) with aqueous sodium hydroxide solution (1.0% per oven-dry pulp, at 60 ° C). The consistency of the resulting mixture was 10%. The mixture was immediately compressed to a consistency of 30% and the compression solution was removed from the pulp. Without further purification, the pulp was stirred with chlorine dioxide solution (0.5% chlorine dioxide per oven-dry pulp) at a consistency of 10%} for 3 hours, at 70 ° C. The pulp was then washed and prepared into test sheets to determine severity. The severity was 90.8 as measured by the Elrepho whiteness meter. Example 6C

A batch of semi-bleached cellulose from pretreatment process (V) was rapidly mixed with aqueous sodium hydroxide solution (1.0% per oven dry mass) at 60 ° C. The consistency of the mixture was 10%. The mixture was then immediately pressed to a consistency of 30% and the pressing liquid was removed from the pulp. The pulp was then washed with deionized water to a consistency of 1% and then brought to a consistency of 12% by passing through a Bilchner funnel with a 100 mesh screen. The mass was then mixed with a chlorine dioxide solution (0.5% chlorine dioxide per oven-dry mass at a consistency of 10%, for 3 hours, at 70 ° C).

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After washing, test sheets were made from the pulp by hand and whiteness was measured. It was 91.1 on the Elrepho whiteness meter.

As can be seen from the above, it is clear that the compression extraction of the pulp with alkali between the two oxidation steps does not require further washing after the compression extraction treatment according to the invention.

Although the present invention has been shown using sodium hydroxide as an alkaline extractant in the examples, it is also possible to carry out the alkali extraction with calcium hydroxide or sodium bicarbonate, whereby the improvement over the previous processes using these alkalis is the same.

The above examples can be carried out with similar results by substituting the substances and operating conditions mentioned in the descriptions with the substances and conditions mentioned in the various examples.

Claims (6)

A process for the alkaline extraction of a pretreated pulp of paper grade, for example, after treatment with elemental chlorine or oxidative reactants, such as chlorine monoxide, chlorine dioxide, hypochlorite, chlorite, peroxides, chlorate, bichromate, oxides of nitrogen, permanganate, etc. concentration up to 12% by mixing the pulp with an aqueous solution of an alkali, for example an aqueous solution of sodium hydroxide, sodium carbonate, calcium hydroxide, ammonia, etc., at a temperature of 40-90 ° C, forming the mixture of pulp and alkali by rapid mixing of the pulp with an alkali having a concentration of 0.5 - 5%, calculated on the pulp, characterized in that such a mixture is quickly pressed to a concentration of 18-40%. Process according to claim 1, characterized in that the pulp is pretreated in that the pulp is disintegrated in a bleaching treatment and the bleached pulp is subjected to a water wash. 3. A process according to claim 1 or 2, characterized in that the alcohol is NaOH and its concentration is related to the pulp number according to the following table: Pulp% NaOH calculated on pulp after chlorination or oxidative treatment. 2 - 4 Sulfate pulp of softwood, Kappatal 20-40 2 - 4 Bisulfite pulp, Kappatal 30-50 3 - 5 4. A process according to any one of claims 1-3, characterized in that the mixture is substantially complete in 5 minutes and that the rapid press extraction is a single extraction step which is substantially completed in 1 minute. Process according to any of claims 1-4, characterized in that the concentration of the pulp in the mixing step is 4-12%. Process according to any of the preceding claims, characterized in that the temperature during mixing stages is 60-8cPc.