WO2005118923A1

WO2005118923A1 - Method for producing cellulose shaped bodies

Info

Publication number: WO2005118923A1
Application number: PCT/AT2005/000170
Authority: WO
Inventors: Herbert Sixta
Original assignee: Lenzing Aktiengesellschaft
Priority date: 2004-06-02
Filing date: 2005-05-20
Publication date: 2005-12-15
Also published as: ATA9542004A; AT413820B

Abstract

The invention relates to the use of a chemical conversion pulp that is produced by methods including an acidic bisulfite pulping method and at least one cold alkali refining step and one hot alkali refining step of the chemical pulp, for producing cellulose shaped bodies in an amine oxide method.

Description

Process for the production of cellulosic moldings

The present invention relates to a process for producing cellulosic shaped articles by the amine oxide process.

As an alternative to the viscose process, a number of processes have been described in recent years in which cellulose is dissolved in an organic solvent, a combination of an organic solvent with an inorganic salt or in aqueous salt solution without the formation of a derivative. Cellulose fibers which are produced from such solutions are called "solvent-spun" fibers and have been given the generic name Lyocell by the BISFA (The International Bureau for the Standardization of man-made Fibers). BISFA defines a cellulose fiber as lyocell, which is made by a spinning process is obtained from an organic solvent. “Organic solvent” is understood by BISFA to be a mixture of an organic chemical and water. "Solvent spinning" is intended to mean dissolving and spinning without derivatization.

To date, however, only a single method for producing a solvent-spun cellulose fiber has become established until industrial implementation. In this process, a tertiary amine oxide, in particular N-methylmorpholine-N-oxide (NMMO), is used as the solvent. Such a method is e.g. in US-A 4,246,221 and provides fibers which are characterized by high strength, high wet modulus and high loop strength.

Other shaped bodies, such as e.g. Cellulose films are made. In the following, the shaped bodies that can be produced by means of an amine oxide process are referred to as “Lyocell shaped bodies”.

An important criterion for the economy of the amine oxide process and the quality of the end products is the selection of a suitable pulp as the starting product.

The publications WO 97/23666, WO 98/58102 and WO 98/58103 describe pulps which are suitable for the amine oxide process.

The production of chemical pulps is dominated by the acidic bisulfite digestion process and the pre-hydrolysis power process. In particular, the acid bisulfite digestion process is due to the high yield and good Possibilities to utilize by-products and waste products or to use them for energy generation represent a very environmentally friendly technology.

For the production of lyocell moldings, in particular lyocell fibers with high strengths, cellulose is particularly suitable which has been obtained by means of a pre-hydrolysis-force disruption.

It has so far not been possible to economically refine pulps based on an acidic bisulfite pulp in such a way that they can be used to produce lyocell fibers with strengths similar to those of a pre-hydrolysis kraft pulp.

The object of the present invention is to provide a chemical pulp which can advantageously be used in the amine oxide process and which, when used in the amine oxide process, in particular results in cellulose moldings with high strengths.

The object of the invention is achieved by using a chemical pulp in the amine oxide process, which is produced by means of a process which

- an acidic bisulfite digestion process and

- Includes at least one cold alkali extraction and one hot alkali extraction of the pulp.

Alkaline extraction is usually used to remove short-chain carbohydrates from wood pulp and to produce highly reactive chemical pulps. The pulp is treated with lye and then squeezed out.

Basically, two methods are known for this, namely cold alkali extraction (CCE) and hot alkali extraction (HCE). The cold alkali extraction usually carried out at temperatures just above room temperature essentially causes physical changes in the pulp, while the hot alkali extraction causes a large number of chemical reactions at typical temperatures from 70 ° C. to 120 ° C.

It has now surprisingly been found that a combined application of a cold alkali extraction and a hot alkali extraction in pulps from an acidic bisulfite pulp leads to the fact that these pulps are outstandingly suitable for use in the amine oxide process. The strength properties of Lyocell fibers produced using such pulps are in the same range as those of fibers from a pre-hydrolysis kraft pulp. This was previously not possible when using a pulp derived from an acidic bisulfite process.

The process for producing the chemical pulp used according to the invention preferably comprises, in a manner known per se, treatment steps before, between and / or after the cold alkali extraction and the hot alkali extraction.

In particular, washing steps and / or bleaching steps can be used as further treatment steps.

As is known per se from WO 97/23666, it is advantageous if a pulp is used for the bleaching of which a TCF bleaching sequence is used.

The chemical pulp used according to the invention can first be subjected to a cold alkali extraction and then, if necessary after further treatment steps, to a hot alkali extraction.

However, it is also possible that the chemical pulp is first subjected to a hot alkali extraction and then, if appropriate after further treatment steps, to a cold alkali extraction.

As part of the cold alkali extraction, the treatment of the pulp with lye is preferably carried out at a temperature of less than 50 ° C., preferably less than 25 ° C.

The treatment of the pulp with lye is preferred at a consistency of more than 5% by weight, preferably 10% by weight of cellulose (based on the mass of the entire suspension), and at a concentration of the lye of more than 5% by weight

9% by weight (based on the mass of the solution).

A particularly interesting embodiment of a cold alkali extraction is that during the treatment of the pulp with the alkali, the consistency to more than

10% by weight, preferably more than 30% by weight. Is brought pulp, an alkali content of less than, 7 wt.% Based on solution is adjusted and the solution to temperatures is cooled from less than -10 ° C, preferably -15 ° C to -20 ° C. This method is referred to below as "freeze purification".

This method is based on the phenomenon that water crystallizes out of the alkali lye when it freezes, which means that the remaining lye is more concentrated. The lye concentration can thereby be significantly reduced without the cleaning effect being impaired.

In the hot alkali extraction, the treatment of the pulp with lye is advantageously carried out at a temperature of more than 80 ° C., preferably 110 ° C.

The treatment of the pulp with lye is preferred at a consistency of more than 5% by weight, preferably 10% by weight of cellulose (based on the mass of the entire suspension), and at a concentration of the lye of more than 3% by weight more than 5% by weight (based on solution).

The invention also relates to lyocell moldings, in particular fibers and films, which are obtainable by the process according to the invention.

Lyocell moldings according to the invention are also characterized in particular by a significantly lower proportion of hemicelluloses. The pentosan content in the lyocell moldings according to the invention is preferably 1.5% by weight or less, particularly preferably 1% by weight or less.

The pulp used for the production of Lyocell moldings can preferably have a viscosity of 350-550 ml / g, preferably 350-450 ml / g, a pentosan content of less than 2% by weight), preferably less than 1% by weight, and an R18- Have a content of more than 94% by weight, preferably more than 95% by weight.

The person skilled in the art understands the “R18 content” as the residue that can be filtered off after treatment with 18% strength alkali (in accordance with DIN 54355).

It has further been shown that, in particular, the process economy in the production of the pulp used according to the invention can be significantly improved if at least some of the alkalis obtained in the alkaline extraction steps after pressing are recycled to the treatment of the pulp and at least a part of this recycled lye, the beta-cellulose content is reduced before the pulp is treated again.

The term “beta-cellulose” is understood by those skilled in the art to mean that portion in a cellulosic material which (in contrast to alpha-cellulose) is soluble in a 17.5% solution of NaOH at 20 ° C., but when the solution is acidified with 4.75M H ₂ SO ₄ (in contrast to gamma cellulose) fails again.

It has now been found that a return of the alkali resulting from the pressing of the pulp to the alkali treatment of the pulp and thus a significant reduction in the amount of fresh liquor required can be achieved if the content of beta-cellulose in the press liquor is reduced. Obviously, an increased beta cellulose content in the recycled liquor leads to a deterioration in the result of the alkali extraction. Surprisingly, it was found that, on the other hand, the content of gamma cellulose is less important in this context.

To reduce the content of beta-cellulose, at least part of the recirculated alkali is preferably treated by means of a membrane separation process. The membrane separation process is preferably a nano or an ultrafiltration process.

The separation of hemicelluloses from liquids contaminated with thread molecules with molecular weights of at least 10,000 daltons by means of nanofiltration is known per se from WO 97/23279.

To carry out nanofiltration, membranes with a cut-off of are preferred

<2000 g / mol, in particular <1000 g / mol used. This means that 100% of the beta cellulose and more than 50% of the gamma cellulose can be removed, preferably more than 70%. The ratio between retentate and permeate is set between 2 and 5, preferably between 4 and 5.

To carry out ultrafiltration, membranes with a cut-off of are preferably used

<50,000 g / mol, in particular <20,000 g / mol used. This means that 100% of the beta cellulose and more than 10% of the gamma cellulose, preferably more than 30%, can be removed. The ratio between retentate and permeate is set between 2 and 5, preferably between 4 and 5. The permeate from the membrane perming process can be supplied in whole or in part to the liquor tank, from which the liquor used to treat the pulp is removed.

Another possibility for reducing the content of beta-cellulose is that at least part of the recycled alkali is treated thermally. That part of beta-cellulose, which (like e.g. xylan) has no branched structures, is broken down into gamma-cellulose.

The thermal treatment is preferably carried out at a temperature of more than 50 ° C., preferably more than 70 ° C., for a period of 10 minutes to 300 minutes, preferably 30 minutes.

The press liquor is preferably treated both by means of a membrane separation process and thermally.

Before the measures to reduce the content of beta-cellulose, the press liquor can be pre-cleaned using a filter to remove undissolved particles.

When carrying out a cold alkali extraction as well as a hot alkali extraction in the process according to the invention, it is advantageous if the content of beta-cellulose in the alkali used to treat the pulp is less than 20 g / 1, preferably less than 5 g / 1 , based on liquor (ie liquor plus water contained in the pulp).

Furthermore, the gamma-cellulose content in the liquor used for the treatment of the pulp is advantageously less than 40 g / 1, preferably less than 20 g / 1 liquor.

These contents can be adjusted by a suitable mixture of fresh alkali and recycled, according to the invention cleaned or also not cleaned alkali.

The process according to the invention can be carried out advantageously in particular if an acid bisulfite process is used as the digestion process.

Due to the savings in the amount of fresh storage required with the method according to the invention, a pulp obtained with an acid bisulfite digestion can now be economically cleaned by means of cold and / or hot alkali extraction. The invention is explained in more detail below with the aid of examples.

example 1

An unbleached beechwood pulp obtained by means of an acid bisulfite process (hereinafter referred to as "UBABD" pulp) was subjected to the following treatment and bleaching sequences: CCE-W-HCE / O-Z-P or HCE / O-W-CCE-Z-P

"CCE" a cold alkali extraction "W" an intermediate wash "HCE" a hot alkali extraction "O" an oxygen delignification "Z" an ozone bleaching stage and "P" a peroxide bleaching stage.

For comparison, the same ÜB ABD cell substance was treated using an (E / O) -Z-P sequence. Here, "E" means a hot alkali extraction which is comparable to the HCE mentioned above, but is carried out under milder conditions.

The (E / O) -Z-P sequence was carried out under both standard (i.e. mild) and enhanced conditions.

In addition, a commercially available sample of eucalyptus pre-hydrolysis kraft pulp ("PHK") was used.

The conditions used for treatment and bleaching are summarized in the following table:

*) H ₂ S ₄ dosage in er - do a rec The following table summarizes the most important properties of the cellulose produced in this way:

Pulp Whiteness Viscosity R18 RIO ΔR Pentosan Cu GPC

Category bleaching sequence% ISO ml / g%%%%% Mn M DP50 DP200 DP2000

Beech sulfite EO-Z-P (standard) 94.4 419 93.3 85.7 7.6 2.9 1.9 42.8 5.2

Beech sulfite EO-Z-P (HCE reinforced) 95.0 408 95.3 87.7 7.6 2.1 1.2 37.4 3.6

Eucal ptus-PHK *) OO-A-Z-P (standard) 90.9 405 97.4 93.6 3.8 2.6 0.3 51.0 130.4 1.7 14.3 7.3

Beech sulfite CCE-W-HCE / O-Z-P 93.7 397 95.0 91.5 3.5 0.8 1.2 48.2 217.1 3.0 15.3 19.0

Beech sulfite HCE / O-W-CCE-Z-P 91.9 371 94.6 89.9 4.7 0.9 1.3 42.1 195.1 3.8 17.1 17.6

From the tables above it follows that the CCE treatment is more selective (ie leads to higher yields than an increased HCE treatment) and is also more efficient with regard to the cleaning effect than an increased HCE treatment (recognizable by the low pentosan content and comparatively high) RIO content for a given viscosity).

In a comparative experiment, the pulp was also processed according to the sequence CCE-W-HCE / OZP, but the alkali used for the CCE treatment was (a) with 20 g / 1 gamma-cellulose or (b) with 20 g / 1 beta -Cellulose contaminated.

In case (a), no significant differences in properties were found compared to the pulp which was treated with the same sequence but without contamination of the CCE liquor. In case (b), however, the properties deteriorated.

The pulps were processed in a manner known per se to lyocell fibers with a titer of 1.3 dtex.

The following table summarizes the strengths of the conditioned fibers made from the pulps:

Pulp Min. Titer Titer FFc FDc

Category bleaching sequences dtex dtex cN / tex%

Beech sulfite EO-Z-P (standard) 0.80 1.26 34.2 10.0 Beech sulfite EO-Z-P (HCE finished) _ 0.76 1.24 35.1 11.0

Eucalyotus-PHK | OO-AZP (standard) ^' 0.53 1.29 41.0 11.9 Pulp Min. Titer Titer FFc FDc

Category bleaching sequences dtex dtex cN / tex%

Beech sulfite CCE-W-HCE / O-Z-P 0.51 1.10 42.7 11.5 beech sulfite HCE / O-W-CCE-Z-P 0.44 1.16 41.4 11.1

Min. Titer Minimally spinnable titer

FFc fiber strength in conditioned condition

FDc fiber elongation in a conditioned state

Surprisingly, lyocell fibers which have been produced from a UBABD pulp treated with both CCE and HCE have strengths which are comparable to those of the eucalyptus PHK pulp. These strengths are significantly higher than those achieved with UBABD pulp fibers made without CCE treatment. The combination of a CCE and an HCE treatment results in UBABD pulps that can be used excellently for the production of Lyocell fibers, which fibers have strengths that were previously only achievable by using pre-hydrolysis Kraft pulps.

Fibers made from a pulp treated with a gamma-cellulose-contaminated CCE liquor according to case (a) above showed no significant deviation in strength. On the other hand, a Lyocell fiber made from a pulp treated with a CCE liquor contaminated with beta-cellulose (case (b) above) has a lower strength.

Example 2 - Reduction of the content of beta-cellulose in press liquor by the CCE process

An unbleached beech pulp (UBABD pulp) obtained by means of an acid bisulfite pulp was dewatered to a consistency of 35% by weight and subjected to a cold alkali extraction reactor (100 g / 1 NaOH.) In a cold alkali extraction reactor (CCE reactor) , 25 ° C, residence time 30 min). The chemical properties of the starting pulp are described in the following table:

Pulp unit value

Kappa 5.7 intrinsic viscosity ml / g 519 Pulp Unit Value Alpha Cellulose% 92.6 Beta Cellulose% 6.1 Gamma Cellulose% 1.3

After leaving the CCE reactor, the alkaline pulp suspension was pressed to a consistency of 32% by weight.

The return of the press liquor to the CCE reactor and the necessary additions of fresh liquor were simulated using a computer simulation (process simulation software SimeX) using the following scenarios:

* Calculated assuming a 50% level of beta-cellulose to gamma-cellulose.

The results of the computer simulation are given in the tables below:

* Comp. = Simulation of a test without any measures for cleaning the press liquor

As can be clearly seen, the use of nanofiltration to reduce the content of beta-cellulose can significantly reduce the amount of fresh lye (NaOH make-up) required.

With a combined application of nanofiltration and thermal treatment, the necessary amount of fresh liquor can even increase by 409 kg NaOH / t otro pulp in the case of a target concentration of <1 g / 1 beta-cellulose (example 2c compared to example 2a) or by 276 kg NaOH / t otro pulp in the case of a target concentration of <5 g / 1 beta. Cellulose (Example 2f compared to Example 2d) can be reduced.

Example 3

Combination of a cold alkali extraction with "freeze purification" and a thermal treatment of the press liquor:

In the course of a CCE treatment of a pulp with a consistency of 10% by weight and a concentration of 70 g / 1 NaOH, the suspension became a press cake of 30-40% by weight. Consistency drained, cooled to -15 ° C for 30 to 60 minutes, then thawed and washed. The result of this purification is equivalent to a CCE treatment with 100 g / 1 NaOH.

The following table demonstrates the effect of this lower alkali concentration on the alkali balance, in particular on the necessary addition of fresh alkali based on a target content of less than 5 g / 1 beta-cellulose in the treatment liquor, with simultaneous application of a thermal treatment of the press liquor:

It can be seen from this table (in comparison to Example 2f) that by means of the "freeze purification" the amount of fresh liquor required can be further reduced from 242 to 171 kg / t of dry cellulose without in this case treating the press liquor by means of nanofiltration would be necessary.

Claims

claims:

1) Use of a chemical pulp which is produced by a process which

- an acidic bisulfite digestion process and

- Contains at least one cold alkali extraction and one hot alkali extraction of the pulp, for the production of cellulosic moldings by the amine oxide process.

2) Use according to claim 1, characterized in that the method for producing the chemical pulp comprises further treatment steps before, between and / or after the cold alkali extraction and the hot alkali extraction.

3) Use according to claim 2, characterized in that washing steps and / or bleaching steps are used as further treatment steps.

4) Method according to claim 3, characterized in that a TCF bleaching sequence is used.

5) Use according to one of the preceding claims, characterized in that the chemical pulp is first subjected to a cold alkali extraction and then, optionally after further treatment steps, a hot alkali extraction.

6) Use according to one of claims 1 to 4, characterized in that the chemical pulp is first subjected to a hot alkali extraction and then, optionally after further treatment steps, a cold alkali extraction.

7) Lyocell moldings, in particular fibers or films, obtainable by the method according to one of the preceding claims.