FI60735B - FOERFARANDE FOER FRAMSTAELLNING AV DISSOLVINGMASSOR - Google Patents

Description

FSSr ^ l ΓΒΐ M ANNOUNCEMENT, Λ?, Σ

Ma lbj utläggnincsskrift oU / od C (45J Patent ay imetty 10 03 1932 Patent meddelat ^ V (51) Kv.lk?/Int.CI.3 D 21 C 9/12 SUOMI-FINLAND (21) Patent application - Patentanaeknlng 1772/73 (22) Hakamltpilvl - AnaOknlngadag 31.05-73 '' (23) AlkupUvi — GHtlghetsdag 31.05.73 (41) Interpreters - Bllvlt offentllg 20.12.73

Patent and Registration Office .... . ..,. . .... u '(44) Nihtlvikslpanen | -

Patent and Registration Office v. An * ök »n utlagd och utl.tkrlften publkend 30.11.81 (32) (33) (31) Privilege requested —Begird priority 19. 06.72 USA (US) 263951 * (71) ITT Industries Inc. 320 Park Avenue, New York 22, NY, USA (72) Romeo John Conca, Shelton, Washington, Herbert Lawrence Hergert,

Madison, New Jersey, Lawrence Frank Maranville, Shelton, Washington,

Albert Marian Hughes, Shelton, Washington, USA (7U) Oy Kolster Ab (5I1) Method for the production of soluble pulps - Förfarande för framställning av dissolvingmassor

The invention relates to a process for the preparation of soluble pulps suitable for use in the production of viscose ion, in which unbleached sulphite pulp is bleached and ground, the treatment steps including chlorination, alkaline hypochlorite treatment and alkaline extraction.

Until now, it has been standard practice to use highly delignified, soft unbleached pulps from "acid-sulfite" pulp to multi-stage bleaching mills for use in the production of rayon silk. These sets of bleaching and refining have normally comprised one or more extraction steps performed under high pressure with a hot base; this has resulted in very high quality soluble pulps. However, a continuing problem with these conventional methods has been that the overall yield of soluble pulps is low and the equipment and operating costs are relatively high. In addition, the high toxicity and B0D (biochemical oxygen demand) content of effluent solutions from hot alkali extraction steps from hitherto used bleaching and refining series used to process unbleached pulps into soluble pulp have required expensive chemical recovery and waste disposal systems. to protect the environment. As a result of these factors, conventional solutes for use in the manufacture of viscose-rayon silk have been relatively expensive.

Therefore, a new and improved process for the production of bleached and ground viscous soluble pulps with relatively low capital requirements and operating costs while increasing the total soluble pulp yield would be highly desirable and economically important. This applies in particular to the need to produce a correspondingly higher demand for relatively high quality, substantially cheaper soluble pulp for processing into tapuli fibers, which are used to make nonwovens and disposable products.

To date, considerable research has been devoted to developing a method for producing bleached and ground pulps with the necessary processability properties and at the same time relatively cheap, so that the yarns made from them are competitive in the nonwovens and disposable products markets.

It is therefore an object of the present invention to provide a process for the production of high yield, relatively inexpensive bleached and ground soluble pulps. A related object is to provide a process for the production of bleached and ground soluble pulps which, both physically and chemically and also commercially, are suitable for use in the manufacture of nonwovens and disposable products.

Another object is to provide a process for the production of relatively inexpensive, viscous grade soluble pulps without the formation of highly toxic scavengers as a by-product of the hot base extraction during pulp bleaching and milling.

It is a further object to provide a multi-stage bleaching and milling process for processing unbleached sulphite pulps into viscous grade soluble pulps.

It is a further object of the invention to provide a process for the production of relatively high quality bleached and ground soluble pulps which requires a relatively low capital cost for operating and environmental protection equipment.

Other objects, unless specifically indicated herein, will become apparent to those skilled in the art from the following detailed description of the invention.

In general, the process of the present invention comprises a new and improved four-stage bleaching and milling series for processing unbleached sulfite pulps into bleached and ground viscous grade pulps having the desired physical and chemical properties. The pulps produced by this method are particularly well suited for use in the manufacture of viscose fibers and staple fibers for the manufacture of nonwovens and disposable fabrics. In addition, 60735 bleached sulfite-viscose pulps prepared by this method are obtained in substantially better yields compared to prior art methods. In addition, this method does not require a hot base extraction step during grinding. Thus, the high-volume, expensive high-pressure grinding equipment required so far is unnecessary, and the formation of highly toxic removers from hot alkali extraction and the associated disposal problems are avoided.

The process according to the invention is characterized in that after chlorination a combined treatment is carried out, first an alkaline hypochlorite treatment and then a mild first base extraction without intermediate washing, and after the combined treatment a second base extraction is carried out, followed by a second alkaline hypochlorite treatment.

It has been found that particularly desirable sulfite pulps for use in this process are relatively inexpensive, high yield, easily bleached sulfite wood pulps for paper. Particularly preferred are unbleached paper-grade sulphite pulps prepared by cooking sulphite-cookable wood chips under relatively mild conditions with an acidic sulphite or bisulphite cooking solution which dissolves. In the production of these wood pulps, the soluble cooking solution used in the so-called "acid sulphite" process has a total SO 2 content of about 6.0-8.5% and a combined high SO 2 content of 0.8-1, 2% by weight of the solution. Pulping is normally continued for about 5 ~ 7 hours at about 130-150 ° C and pH 1-2. The cooked mass is then pushed out of the digester, washed and dewatered by conventional methods. Another preferred raw material for use in this process is a paper grade sulfite pulp prepared by a so-called "bisulfite" process in which the total SO 2 content of the cooking liquor is normally about 3.5-5.0% and its combined SO 2 content is about 1 , 75-2.5% The pulping time is about 5-7 hours, the pH is about 3-6 and the temperature is about 150-165 ° C. The pulp is then pushed out of the digester, washed and dewatered by conventional methods. Both of the above methods for preparing the preferred starting materials for this process give an easily bleachable paper grade pulp with minimal damage and loss and maximum yield.

According to a preferred embodiment of the invention, the unbleached sulphite pulp is initially treated in the chlorination step to a consistency of about 3%, based on the oven dry pulp, of about 1-5 $ 5 chlorine. This chlorination step is carried out at a pH not exceeding U.0, preferably between about pH 1.5-3.5, at a temperature of about 5-30 ° C, preferably at about 20-30 ° C, the treatment time being sufficiently long, that the reaction would be essentially complete. This time varies depending on various factors, such as the specific pulp to be treated and the process conditions used, but will normally not exceed about 60 minutes, preferably being about 10-30 minutes.

I: '4 60735

After the chlorination step, the pulp is washed with water and the aqueous pulp suspension is subjected to a combined hypochlorite-mild base extraction step, in which the alkaline hypochlorite treatment is immediately, without intermediate washing, followed by a mild base extraction at high consistency. In the hypochlorite phase of this treatment, alkaline hypochlorite, for example alkali metal or alkaline earth metal hypochlorite, for example sodium or calcium hypochlorite, is added to the washed pulp suspension at a pulp consistency of about 9-17 l, based on the oven-dry pulp, preferably about 12 l. to provide about 2-3 l of available chlorine, based on the weight of the pulp, together with the excess sodium hydroxide added to maintain the pH at about 10-11 when the hypochlorite is consumed. This treatment is continued until all the hypochlorite has been consumed, preferably for about 1-2 hours at a temperature between about 30-70 ° C and preferably about 35 ° C. After completion of the treatment with hypochlorite and without intermittent washing, the pulp is subjected to a slight base extraction with a sufficient amount of sodium hydroxide to ensure an excess of sodium hydroxide at the end of the treatment. Preferably, this mild base extraction is performed at atmospheric pressure with the addition of less than about 4 L of sodium hydroxide (based on the weight of the pulp) and at a temperature below 70 ° C for about 1-4 hours depending on the conditions used. The final pH of this mild base extract is again maintained between about 10-11.

The suspension obtained in the combined hypochlorite-mild base extraction step is then washed with water and dewatered. The pulp is then subjected to a cold base extraction step with aqueous sodium hydroxide solution at low pulp consistency to remove hemicelluloses and other carbohydrate impurities. The cold alkali extraction is carried out at a temperature of about 15-50 ° C, preferably at about 15-25 ° C, at atmospheric pressure with a base concentration of about 4-11 l (based on solution) and preferably at a consistency of about 7 i and about 3 i * n (calculated mass) in about 3-20 minutes.

After the cold base extract has been washed and dehydrated, an alkaline hypochlorite solution such as sodium or calcium hypochlorite with about 2 l of available chlorine (based on the weight of the pulp) is added to the pulp and a sufficient amount of sodium hydroxide is added to maintain the pH at least 7 * and preferably about 11. A pulp consistency of about 9-17, preferably 12-13, is also maintained. The temperature is maintained between 30-70 ° C and preferably about 55 ° C and the treatment is continued until the pulp has the desired intracuous viscosity (about 3-6 I.V.) and whiteness (about 90-94 ELB). Normally this takes about 45-120 minutes depending on factors such as the pulp used, the process conditions used, etc. The bleached and ground pulp obtained is dewatered, washed, treated with O 2 O and dried by conventional methods.

The soluble pulps prepared by the process of the invention have been found to be reactive and xanthate easily to easily filter viscous solutions suitable for spinning rayon filaments, which are particularly useful in the manufacture of nonwovens and disposable fabrics. In addition, the bleached and refined viscose solute pulps prepared by this process can be recovered in substantially higher yields and at lower cost than the conventional fibers produced by previous processes.

The following examples are presented only to illustrate the method of the invention and the properties of the products obtained and are not intended to limit the invention in any way.

Example I

This example is shown to demonstrate the advantages of using the process of the invention on unbleached paper grade sulphite wood pulp over the prior art conventional viscose type bleaching and milling process used on the same unbleached paper grade pulp.

A batch of Western hemlock wood chips was prepared and pulped into a fairly crude paper grade pulp by conventional methods using a sodium-based acid sulphite cooking solution. An unbleached pulp with an intrinsic viscosity (I.V.) of 11.1 and a permanganate number (KNo.) Of 20 was obtained in a screened yield of 46 * 5/6 (based on the oven-dry pulp).

Two samples (3 kg each) of this pulp were bleached and ground by the following methods:

Method (l) - Normal bleaching and grinding method previously used in the production of viscose grade soluble pulps

First step - The unbleached mass was chlorinated by conventional means for 20 minutes at 20 ° C with 4% chlorine added. The consistency of the pulp was $ 3 based on the oven-dry pulp. The mass was washed and dewatered and transferred to the next lie.

Second step - The pulp from the previous step was extracted - with 7 # sodium hydroxide solution with a pulp consistency of $ 17 (counting maesaeta) for 45 minutes at 110 ° C. It was then washed, dehydrated and transferred to the next step.

Third step - The pulp from the previous step was treated with an alkaline sodium hypochlorite solution containing 2.2 μl of available chlorine and 1.0 μl of sodium hydrochloride uk. by calculating the mass. The treatment lasted 95 minutes at 60 ° C with a consistency of the pulp of $ 15. · The bleached pulp was washed and dehydrated, treated with SO 2 to pH 2.8 and dried by conventional methods.

Samples of the resulting soluble pulp were then xanthated by conventional methods into an 8.5 / 5.25 / 32 (pulp / NaOH / CS2) viscose spinning solution to determine its viscous 6,60735 spinning properties. The results obtained are summarized in Table 1.

Process (2) Process according to the invention for bleaching and grinding pulps for the production of viscose-grade soluble pulps

First step - The unbleached pulp was chlorinated in exactly the same manner as above in the corresponding part of method (1). Chlorination was continued for 20 minutes at 20 ° C using 4% added chlorine at a pulp consistency of 3 ° / o uk. by mass. The mass was then washed, dehydrated and transferred to the next step.

Second step - The pulp from the previous step was treated with an alkaline solution of sodium hypochlorite containing 2.2 l of available chlorine and 1.6 ° of sodium hydroxide from the uk. The consistency was 14% and the treatment was continued for 103 minutes at 35 ° C · Between washes and in the same vessel was then added 1-3 $ NaOH, the temperature was raised to 40 ° C and the treatment was continued for another 105 minutes. The mass was then washed, dehydrated and transferred to the next step.

Third step - The pulp from the previous step was extracted for 15 minutes at 25 ° C and a mass consistency of 3 n (based on the pulp) with 7 * 5/6 * sodium hydroxide solution. It was then washed, dehydrated and transferred to the next step.

Fourth step - The pulp from the previous step was treated with an alkaline sodium hypochlorite solution containing 2.2% available chlorine and 0.9 sodium hydroxide uk. by mass. The treatment was continued for 70 minutes at 55 ° C and the consistency of the pulp, based on the pulp, was 15. The bleached pulp was then washed, dehydrated, treated with Stella to pH 2.8 and dried by conventional methods.

Samples of the resulting soluble pulp were then xanthated to a 8.5 / 5.25 / 32 viscous spinning solution by conventional methods to determine its viscous spinning properties. The results obtained are summarized in Table I, where the chemical additions are calculated from the UK mass, unless otherwise stated.

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Table 1 Bleaching and Method (l) Method (2) Grinding series Normal viscose used (Comparison)

The chlorination step

Added Clg »$ 4 * 0 4 * 0

Time, t: min. 0:20 0:20 Temperature, ° C 20 20

Consistency, oven dry 3 3

Alkaline hypochlorite (sodium based)

Added Cl2, # 2.2

Added NaOH, $ 1.6

Time, t: min. 1:43 Temperature, ° C 35

Consistency, $ oven dry 14 (no washing)

Emäsuutos

Added NaOH, $ 7 * 0 1.3

Time, t: min. 0:45 1:45 Temperature, ° C 110 40

Consistency, $ oven dry 17 13 * 3

Cold base extract Added NaOH, $ (calculated from solution) 7 * 5

Time, t: min. 0:13 Temperature, ° C 25

Sakeus, ^ uk. 3

Alkaline hypochlorite (Na-based)

Added Cl2, $> 2.2 2.0

Added NaOH, # 1.0 0.9

Time, t: min. 1:35 1:10 Temperature, ° C 60 55

Sakeus, $ uk. 15 15 SOg treatment

Initial pH 2.8 2.8

Total bleached yield 37 * 0 38 · 9

Cuene I.V. 4 · 4 4 · 4

Whiteness, ELB 90.3 91 * 1 8 607 35

Table 1 (cont.)

Viscose, 8.5 / 5 * 25/32

Viscosity, bfs. 47 »2 81.2 p

Plug value, g / cm * 1500 2200 x

Values corrected for viscosity.

As can be seen from the results summarized in the table, a substantial increase in yield is achieved using the method of the present invention compared to the prior art bleaching and milling method. In fact, when using batches of the same easily bleached paper grade sulphite pulp, the process of the invention gives an increase of $ 1.9 to the bleached pulp yield (based on the weight of wood used) compared to the prior art, which corresponds to a 5 n increase in relative total yields. The pulp produced by the method of the invention also has a somewhat better color and a higher (improved) plug value (2200 vs. 1500). In addition, because the process of the invention does not have a hot alkaline, high pressure leaching step, a non-toxic, oxygen-rich, hot scavenger is formed, the disposal of which represents an inherent problem in prior art standard processes.

Example II

This example has been shown to show a very substantial increase in the yield of bleached pulp using the process of the invention in a paper grade sulphite pulp compared to the use of a prior art process in a conventional soluble bleached pulp.

A batch of chips from the Eucalyptus tree was made and divided into several parts. One portion was boiled into a fairly crude paper-grade pulp by KSo. was 18.6 and Cuene I.V. 12.4 * The screened pulp yield was 53 * $ 9 · The other part of the chips was boiled into a fairly soft rayon-grade pulp by KNo. was 8.7 and Cuene I.V. 8.42, with a screened pulp yield of 46.4. Each batch was boiled by the acid sulphite method using soda-based acid sulphite broth. unless otherwise stated.

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Table 2 Pulp used Solubility degree Paper grade bleaching and grinding KNo. 8.7-I. V.. 8.42) KNo. 18.8-1.V. 12.4) ink set Method (l) Method (2)

The chlorination step

Found Cl2, 2.5 4-6

Time, t: min. 0:20 0:20 Temperature, ° C 25 25

Sakeue, and oven dry 3 3

Alkaline hypochlorite (Na-based)

Added Cl 2, i ° 2.0

Added NaOH, 36 1.1

Time, t: min. 1:43 Temperature, ° C 35

Sakeus, i UK. 12 (no washing)

Emäsuutos

Added NaOH, $ 7 * 5 1 * 3

Time, t: min. 0:45 1:45 Temperature, ° C 110 40

Sakeus, i UK. 15 11.8

Cold base extraction

Added NaOH, io (calculated from solution) 7 * 5

Time, t: min. 0:15 Temperature, ° C 25

Sakeus, and UK. 3

Alkaline hypochlorite (Na-based)

Added Cl2, ia 1.7 1.5

Added NaOH, ia 1.0 0.9

Time, t: min. 1:00 2:00 Temperature, ° C 57 55

Consistency, # UK. 16 15 SO ^ treatment

Initial pH 3.0 2.9

Total yield of bleached 36.0 44 * 0

Cuene I.V. 4 * 5 4 · 6

Whiteness, ELB 93 * 6 93 * 6

Viscous

Solutions 7.5 / 6.5 / 34 9.Ο / 5.5 / 28

Viscosity, bfs. 35 · 0 35 · 9 2

Plug value g / cm 1050 2400 10 60735

Of the tabulated results, it should be noted in particular that an absolute increase of $ 8.9 (or a relative increase of $ 22) in the total yield of bleached pulp (based on the weight of wood used) is achieved using the process of this invention applied to paper grade sulfite pulp compared to conventional prior art process. to unbleached pulp. In addition, the soluble pulp prepared according to the method of the invention has equivalent color properties compared to hitherto conventional soluble pulp, and its plug value has been improved.

In its broader scope, the invention is not funded for specific combinations, steps, and described processes, and deviations from them may be made within the scope of the appended claims without departing from the principles of the invention and without sacrificing its main advantages.

Claims (9)

60735 A process for producing soluble pulps suitable for use in the production of viscose ion, wherein the unbleached sulphite pulp is bleached and ground, the treatment steps comprising chlorination, alkaline hypochlorite treatment and alkaline extraction, characterized in that the chlorination is followed by a combined treatment followed by alkaline hypochlorite treatment without intermediate washing, a slight first base extraction, and after the combined treatment, a second base extraction is performed, followed by a second alkaline hypochlorite treatment. Process according to Claim 1, characterized in that the first and second base extractions are cold extractions. carried out below 70 ° C. Process according to claim 1, characterized in that the first alkaline hypochlorite treatment comprises treating the pulp with alkaline hypochlorite at a pulp consistency of about 9-17% (based on oven-dry pulp) in an amount sufficient to give about 2-3% available chlorine ( based on the weight of the pulp) that sodium hydroxide is added in an amount sufficient to maintain the pH at about 10-11 when the alkaline hypochlorite is consumed, that the first hypochlorite treatment is continued for about 1-2 hours at about 30-70 ° C, and that then a first base extraction is performed with up to 1 +% sodium hydroxide (based on the weight of the pulp) at up to 70 ° C for about 1-U hours at a final pH of about 10-11. Method according to Claim 1, characterized in that the combined treatment is carried out at normal pressure. Process according to Claim 1, carried out with a high-yield, easily bleachable pulp of the paper grade, characterized in that the pulp to be bleached and ground is prepared by cooking wood chips in a soluble cooking broth having a total SO 2 content of about 6-8.5% and a combined SO 2 content of 0.8 -1.2% (based on the weight of the broth), for about 5 ~ 7 hours at about 130-150 ° C at a pH of about 1-2. Process according to claim 1, carried out with a high-yield, easily bleached pulp of the paper grade, characterized in that the pulp to be bleached and ground is prepared by cooking wood chips in a cooking broth with a total SOg content of about 3.5 ~ 5% and a combined SOg content of about 1.75 -2.5% (based on the weight of the broth) for about 5-7 hours at about 130-165 ° C at a pH of about 3-6, Process according to Claim 1, characterized in that the chlorination is carried out with a pulp consistency of about 3% (based on the oven-dry pulp) using about 1-5% chlorine at a pH below about k at about 5 ~ 30 ° C for at most one hour that the pulp is then washed with water, the washed pulp suspension is subjected to a first alkaline hypochlorite treatment with a pulp consistency of about 9-17% (based on oven dry pulp) by adding alkaline hypochlorite in an amount sufficient to give about 2-3% available chlorine (based on pulp weight). that the excess sodium hydroxide is added in such an amount that the pH remains at about 10-11 when the alkaline hypochlorite is consumed, that the first alkaline hypochlorite treatment is continued at about 30-70 ° C until the alkaline hypochlorite is consumed, that the first base extraction , which is carried out after the first alkaline hypochlorite treatment without intermediate washing, is carried out li adjusting the amount of sodium hydroxide sufficient to provide an excess of base to the broth after the first base extraction, keeping the temperature of the pulp below 70 ° C for about 1-U hours at a final pH of about 10-11, subjecting the dewatered pulp to a second base extraction with an aqueous solution of sodium hydroxide at about 15-50 ° C at normal pressure with a sodium hydroxide concentration of about U-11% (based on the weight of the solution) and a consistency of the mass of about 3% (based on the mass of the mass) for about 3-20 minutes, washing the extracted mass with water, the pulp is dewatered and the second alkali hypochlorite treatment is carried out by adding to the pulp an alkaline hypochlorite solution with an available chlorine content of about 2% (by weight of the pulp) together with an amount of sodium hydroxide sufficient to maintain a pH of at least about 7 with a pulp consistency of about 9 ~ 17% at a temperature of about 30 ~ 70 ° C, followed by bleached and ground viscose slabs soluble cellulose ot e t aan t alt een. Process according to Claim 7, characterized in that the first alkali hypochlorite treatment is carried out within 1 to 2 hours. Process according to Claim 7, characterized in that the first base extraction is carried out at normal pressure by adding up to 4% of sodium hydroxide (based on the weight of the pulp) to the pulp. 13 60735