EP0743991B1 - Process for producing shaped cellulose bodies - Google Patents

Abstract

The invention is concerned with a process for the production of cellulose moulded bodies wherein a suspension of cellulose in an aqueous solution of a tertiary amine-oxide is transformed into a mouldable solution, said solution being extruded by means of a forming tool and conducted into a precipitation bath. The process is characterized in that at least part of the materials in devices and pipes for the transportation and processing of the solution, which material is in contact with the mouldable solution contains at a minimum of 90% up to a depth of at least 0,5 mu m, preferably more than 1 mu m, at least one element of the group consisting of titanium, zirconium, chromium and nickel in elementary form and/or in the form of compounds provided that the remaining of the material does not contain any of the elements of the group consisting of copper, molybdenum, tungsten or cobalt. By means of the use of certain elements and compounds according to the invention, it is possible to control the occurrence and the extent of exothermal degradation reactions in the cellulose solution.

Description

The invention relates to a process for the production of cellulosic moldings, in which a suspension of cellulose in an aqueous solution of a tertiary amine oxide is converted into a moldable solution which is extruded through a shaping tool and passed into a precipitation bath.

In recent decades, due to the environmental problems of the known viscose process for the production of cellulosic fibers, intensive efforts have been made to provide alternative, more environmentally friendly processes. A particularly interesting possibility has emerged in recent years to dissolve cellulose in an organic solvent without the formation of a derivative and to extrude moldings from this solution. Such spun fibers were given the generic name Lyocell by BISFA (The International Bureau for the Standardization of man made fibers), whereby an organic solvent means a mixture of an organic chemical and water.

It has been found that a mixture of a tertiary amine oxide and water is particularly suitable as an organic solvent for the production of Lyocell fibers or other shaped bodies. N-Methylmorpholine-N-oxide (NMMO) is predominantly used as the amine oxide. Other suitable amine oxides are disclosed in EP-A 0 553 070. Methods for producing cellulosic molded articles from a solution of cellulose in a mixture of NMMO and water are disclosed, for example, in US Pat. No. 4,246,221. Fibers produced in this way are characterized by a high fiber strength in the conditioned and in the wet state, a high wet modulus and a high loop strength.

One problem in the production of cellulosic shaped articles by dissolving the cellulose in a mixture of NMMO and water is the stabilization of the moldable solutions obtained in this way. It has been shown that when the cellulose is dissolved in NMMO, the cellulose is broken down, which leads to an undesirable decrease in the degree of polymerization of the cellulose and to the formation of low-molecular decomposition products when the solution is subjected to prolonged thermal stress at temperatures above 100 ° C.

In addition, amine oxides, and especially NMMO, have limited thermal stability, which varies depending on the structure. The monohydrate of the NMMO melts at temperatures of approx. 72 ° C, the anhydrous compound melts at 172 ° C. If the monohydrate is heated, severe discolouration occurs at temperatures above 120/130 ° C. Such temperatures are quite common in processes for the production of cellulosic moldings. Above 175 ° C there are strong exothermic reactions that can take an explosive course. In the course of these reactions, NMMO is thermally degraded primarily to N-methyl-morpholine, morpholine, formaldehyde and CO ₂ .

Since the compounds which form are essentially gaseous at the prevailing temperatures, high pressures arise during the exothermic decomposition of NMMO, which can lead to damage to apparatus parts.

It is known that the breakdown of cellulose in solutions in NMMO and the thermal breakdown of NMMO are clearly related. In fact, there is still no clarity about the actual mechanisms of these undesirable phenomena.

However, the causes of the sometimes sudden degradation phenomena were examined several times, and in particular it was found that metals in the moldable solution obviously show the decomposition temperatures of the NMMO belittle. Such results are listed, inter alia, in an article by BUIJTENHUIS et al., Papier 40 (1986) 12 , 615-618. It is shown that iron and copper in particular accelerate the decomposition of NMMO. However, other metals, such as nickel or chromium, also have a negative effect according to this publication. These effects are mainly attributed to traces of metal ions formed from the metals.

Numerous proposals for stabilizing the moldable solution of cellulose in NMMO / water have also been published. Most of these suggestions, e.g. EP-A 0 047 929, PCT-WO 83/04415 or Austrian patent application A 1857/93 (corresponding to WO-A-9508010) deal with the addition of certain ones which slow down the degradation reactions of both cellulose and amine oxide chemical substances to the process.

EP-A 0 356 419 presented a process by means of which a moldable solution is obtained in one step from a suspension of cellulose in an aqueous tertiary amine oxide in a continuous manner. Since this process works very quickly, thermal degradation reactions during solution preparation can be minimized in this way.

Nevertheless, the malleable solution usually has to be transported through pipelines before spinning or e.g. are temporarily stored in buffer containers in order to be able to compensate for differences between the supply of new solutions and the demand from the spinning apparatus. There is a high risk of degradation reactions in particular at locations of these pipelines and apparatuses where the moldable solution comes to a standstill or is moved at a low speed.

PCT-WO 94/02408 and PCT-WO 94/08162 describe that stainless steel is used in the apparatuses published there without further specification.

PCT-WO 94/28210 describes the use of stainless steel with AISI code 430 for a perforated plate of a spinneret and stainless steel according to AISI code 304 for the side walls of this spinneret.

In the literature, "stainless steel" or "stainless steel" refers to iron-based materials which are obtained by adding other metals, in particular chromium, but also e.g. Molybdenum or nickel have increased corrosion resistance. This is largely attributed to the formation of protective oxide layers of the added metals, which passivate the surface of the material. The presence of the alloy components thus results in an additional passivation of the material surface and at the same time restrains the corrosion of the base metal iron, which is usually present in excess, to a certain extent.

The compositions of the common stainless steels are specified in various standards, e.g. in the AISI codes of the American Iron and Steel Institute, e.g. in KIRKOTHMER, Encyclopedia of Chemical Technology, 2nd Edition (1969), Volume 18, pages 789 ff., or in the DIN standards listed in STAHLSCHLÜSSEL 1986 (Verlag StahlKey Wegst GmbH).

In investigations by the applicant it has now been found that, despite the use of stainless steel, thermal degradation reactions of the cellulose and the amine oxide cannot be ruled out.

The object of the present invention is to take measures to minimize the above-mentioned degradation reactions and to avoid the catalytic effects mentioned in the process for the production of cellulosic moldings from a solution of the cellulose in a mixture of a tertiary amine oxide and water.

This object is achieved in that at least part of the material in contact with the moldable solution of apparatus and piping for transporting and processing the solution to a depth of at least 0.5 µm, preferably greater than 1 µm, calculated from the surface, contains at least 90% at least one element from the group of titanium, zirconium, chromium and nickel in elemental form and / or in the form of compounds, with the proviso that the rest of the material does not contain any of the elements copper, molybdenum, tungsten or contains cobalt.

The invention is based on the knowledge that decomposition reactions can occur on the surface of the materials in contact with the moldable solution, which are catalyzed by the material itself, and that it is therefore possible to provide material surfaces that are in contact with the malleable solution do not have the catalytic effects listed above and therefore neither induce nor accelerate thermal degradation reactions.

Surprisingly, it has been shown that the use of elements or compounds in parts of the system in contact with the solution can minimize thermal degradation reactions of the solution in accordance with the composition according to the invention, i.e. that the degradation reactions in the formable solutions which wash around the surfaces composed according to the invention do not start much faster or more violently than in solutions which are not in contact with any technical material. In particular, the measures according to the invention show significantly better effects compared to materials known from the prior art, such as Stainless steels according to AISI codes 304 and 410.

The elements or connections used according to the invention are therefore not only corrosion-resistant, so that essentially no entry of metal traces or traces of Metal ions occur in the moldable solution, but also do not have the catalytic effects observed with conventional stainless steel. The elements or compounds used in parts in contact with the solution according to the invention are therefore referred to below as essentially "non-catalytic" for the purpose of differentiating from other materials on which catalytic effects can be observed.

It has surprisingly been found that from the area of known materials or material components only a relatively small selection of elements or compounds shows non-catalytic effects with regard to the moldable solution. Surprisingly, these elements come from various groups in the periodic table of the chemical elements. It has been found that elements from the same group of the periodic table have completely different effects with regard to the stabilization of the moldable solution.

For example, Chromium in elemental form or in the form of compounds or as an essential component of a material as non-catalytic, while the molybdenum in the same group of the periodic table, which is known as an alloy component that increases corrosion resistance, in contact with formable solutions, the occurrence of exothermic reactions significantly accelerated.

Very negative effects with regard to exothermic reactions show e.g. also the elements cobalt and tungsten, which are often used in other areas of chemical process engineering in elemental form or in the form of compounds.

It is also surprising in this respect that, for example, the elements chromium and nickel, which in the literature (BUJTENHUIS et al.) Are said to have a negative influence on the stability of the solution, in the process according to the invention produce excellent results with regard to exothermic reactions, ie obviously have no negative influence on the solution.

An essential component of the method according to the invention is that the elements or compounds used according to the invention form a layer of at least 0.5 μm, but preferably greater than 1 μm, on the surface of the materials in contact with the moldable solution.

It is known from the prior art that, when used as a material, many metals form layers of their respective oxides on their surface, which passivate the material against corrosive attack. Such protective layers are e.g. also, as already described above, formed on the surface of stainless steel. However, these layers, e.g. in "Corrosion and Corrosion Protection", Springer Verlag 1985, p.86, only a few molecular layers, e.g. in the size range of 3-5 nm thick. If this extremely thin protective layer is broken through at one point, a local element is formed and thus a corrosion attack occurs, in which catalytically active materials come into contact with the medium to an increased extent.

Due to the requirement of the method according to the invention, which are to be used as essentially non-catalytic elements or compounds at a depth of at least 0.5 μm, suddenly better effects in terms of avoiding thermal decomposition reactions compared to materials with a lower protective layer thickness could be achieved. e.g. Stainless steel.

It is also essential that the top layer provided according to the invention contains a maximum of 10% other elements which may have catalytic effects. It is particularly advantageous if the layer is practical consists entirely of the non-catalytic elements and only traces of other elements are contained. However, material mixtures which, for example, consist only of 90% of the non-catalytic elements, also prove to be favorable in the process according to the invention. However, the elements copper, molybdenum, tungsten and cobalt must not be contained in such material mixtures.

It has proven to be advantageous if the layer provided according to the invention contains not only a non-catalytic element or a compound, but rather mixtures of a non-catalytic element and its compounds or also mixtures of a plurality of non-catalytic elements or their compounds.

The process according to the invention is advantageously designed such that the oxides, carbides, nitrides, borides and / or silicides contained in the materials in contact with the moldable solution as compounds of the non-catalytic elements.

Particularly preferred compounds are e.g. the oxides of chromium, zirconium, titanium and nickel as well as chromium boride, chromium nitride, chromium carbide, titanium carbide and titanium nitride.

A further preferred embodiment of the invention is characterized in that the part of the materials in contact with the moldable solution is at least partially constructed in layers, the topmost layer in contact with the solution being at least 90% of at least one of the non-catalytic elements in elementary form Contains form and / or in the form of connections and this layer is applied to a material that may contain more than 10% other elements and / or connections.

It has been found that even thin layers applied to materials with a negative effect on the solution of the non-catalytic elements or compounds reduce the risk of thermal decomposition reactions, provided that the thickness of the layer exceeds 0.5 µm, of course. This variant of the method according to the invention contributes to the economics of the method because only small amounts of the sometimes relatively expensive non-catalytic elements or compounds are required and less expensive materials, such as stainless steel, can be used as the base materials for the coating.

A further advantageous embodiment of the invention is characterized in that the materials in contact with the solution in those parts of apparatus and pipelines contain the at least one non-catalytic element in a depth of at least 0.5 µm in which the moldable solution stands or is stationary only moved at low speed.

Particular sources of danger in the process for the production of moldings from solutions of cellulose in tertiary amine oxides are the so-called "dead spaces", that is to say those spaces in which there is little or no movement of the moldable solution. At these points, e.g. in filtration devices or in shut-off devices such as ball valves and the like. the solution has a long service life at elevated temperature, which naturally leads to an increased risk of thermal decomposition reactions.

It has been shown that the occurrence of thermal decomposition reactions can be reduced very efficiently if layers of the non-catalytic elements or compounds are used only in these locations. This enables a particularly economical use of the non-catalytic substances.

The object of the present invention is further achieved by using at least one element from the group of titanium, zirconium, chromium and nickel in elemental form and / or in the form of compounds in materials of apparatus and piping in contact with a moldable solution of cellulose in a mixture of a tertiary amine oxide and water in the surface layer which is in contact with the moldable solution in a proportion of at least 90 % dissolved to a depth of at least 0.5 µm, preferably greater than 1 µm.

The invention is explained in more detail with the following examples, in which formable solutions with a cellulose content of approximately 15% were used to compare the influence of different substances on the induction of thermal decomposition reactions.

1) Sample preparation:

Mouldable cellulose solutions of cellulose in aqueous N-methylmorpholine-N-oxide (NMMO) with 15% cellulose and 500 ppm propyl gallic acid (GPE) and 500 ppm hydroxylamine (based on the process produced in EP-A 0 365 419) Cellulose) as stabilizers were finely ground in a solid, crystallized state in a laboratory mill.

The respective powdered metals or metal compounds were homogeneously distributed into the ground cellulose solutions before the start of the test, a constant volume of metallic additives being used to standardize the surfaces (calculation of the mass via the density).

The addition of powdered metals or

Metal compounds were 0.035 cm ³ powder to 11.5 g cellulose solution in the tests in a SIKAREX oven and 7.5 ∗ 10 ^-4 cm ³ powder to 200 mg cellulose solution in the gas chromatographic tests.

A solution prepared in the same way without any addition of metals or metal compound was used as a comparative sample for determining a blank value (BW).

2) Analytical methods: a) Carrying out the safety calorimetric tests in the SIKAREX furnace:

The tests were carried out in a Sikarex oven (TSC 512) from SYSTAG, the samples being heated in a sealed pressure vessel with a glass insert.

As a temperature program, a step experiment of the standard software was carried out, in which heating was carried out very slowly between two isothermal stages (1st stage 90 ° C, 2nd stage 180 ° C) (heating rate of 6 ° C / h). In the area of interest, this resulted in a dynamic driving style that provided excellent reproducibility with regard to the exothermic events. During this heating, the temperature difference between the temperature of the heating jacket (TM) and the temperature of the sample (TR) was continuously measured. The data collected was processed on a computer.

b) Carrying out the gas chromatographic experiments:

The samples filled in so-called vials were exposed to a thermal load of 120 ° C. for 5 hours in a headspace sampler (HP 7694). The first analysis was carried out after 15 min, then analysis was carried out at hourly intervals.

In each analysis, 150 kPa He overpressure was applied to the vial and the pressure was subsequently released to normal pressure by switching the valve into a loop in the sampler. After an equilibration phase and renewed valve switching, the gaseous products were switched into a He carrier gas stream, which then brings the gas phase via a transfer line to an injector for a gas chromatograph. After splitting the carrier gas stream in a ratio of 1:70, a column (Stabilwax DB + Phenylmethylsilicone deactivation Guard Column, length 30 m; iD [mm]: 0.32; film [µm]: 0.5) was injected and injected Temperature program driven. The detection was carried out via an FID detector.

In the hourly analyzes, the amount of N-methyl-morpholine (NMM), which is one of the essential decomposition products of an NMMO solution, was measured.

3) results

The two measuring methods provide characteristic parameters:

TM bei Δ10

ist jene Mantel- (Ofen)-temperatur, bei der aufgrund eines exothermen Verlaufes in der Probe eine um 10°C höhere Temperatur als im Mantel herrscht

Trials in the SIKAREX oven:

TM at Δ10

is the jacket (furnace) temperature at which the temperature in the sample is 10 ° C higher than in the jacket due to an exothermic course

[NMM]norm

gibt die auf den Blindwert (BW) normierte Aminbildung der mit einem Additiv (Pulver von Metallen oder Metallverbindungen) versetzten Probe an. Ein Wert von 2 bedeutet z.B. 2-fache Aminbildung im Vergleich zum Blindwert.

Gas chromatographic experiments:

[NMM] norm

specifies the amine formation standardized to the blank value (BW) of the sample mixed with an additive (powder of metals or metal compounds). A value of 2 means, for example, double amine formation compared to the blank value.

These parameters clearly show common trends in the tests. Degradation tests with high stability values in the SIKAREX test (e.g. large TM at Δ10) usually show very little amine formation. On the other hand, with decreasing stability data, a clear increase in amine formation is usually found at the same time.

The common course in the results enables a combination of parameters in combined safety parameters, which in an even clearer way Document the influence of materials (additives) on spinning mass.

The following safety parameter Sk2 (10) has been formulated for the following descriptions and is shown in the tables: $$\text{Sk2 (10) =}\frac{\text{(TM at Δ10)}}{\text{[NMM] norm}}$$

The Sk2 (10) value provides clear information about the safety relevance of a material (or its catalytic activity) in the NMMO process, since it determines the temperature behavior (when does an exotherm occur?) And the tendency towards formation that is decisive for almost all metallically initiated degradation reactions key degradation product NMM.

The larger the Sk value, the lower and therefore the more positive the influence of the material on the medium. However, it should be noted that Sk values of different materials can only be meaningfully compared if the grain sizes of the respective materials and thus the respective specific surfaces are as similar as possible.

Tabelle 2: Zugabe von Elementverbindungen in pulverförmiger Form: Additiv Teilchengröße SK2 (10) - (Blindwert "BW") - 160,80 Titannitrid < 10µm 161,72 Chromcarbid < 44 µm 149,14 Chromoxid ∼ 1µm 130,25 Chromnitrid < 44 µm 118,80 Chromborid < 44 µm 105,21 Wolframcarbid < 10µm 60,16 Eisensulfid < 149 µm 52,56 Molybdäncarbid < 44 µm 29,30 Wolframsulfid < 2µm 24,83 Molybdänsulfid <1µm 14,43 In the following tables the different measured samples are compared with the particle size on the basis of the determined Sk2 (10) value:

Table 2: Addition of element compounds in powder form: Additive Particle size SK2 (10) - (blank "BW") - 160.80 Titanium nitride <10 µm 161.72 Chromium carbide <44 µm 149.14 Chromium oxide ∼ 1µm 130.25 Chromium nitride <44 µm 118.80 Chromium boride <44 µm 105.21 Tungsten carbide <10 µm 60.16 Iron sulfide <149 µm 52.56 Molybdenum carbide <44 µm 29.30 Tungsten sulfide <2 µm 24.83 Molybdenum sulfide <1 µm 14.43

It can be clearly seen from Tables 1 and 2 that the elements used according to the invention, both in elemental form and in the form of compounds, have a significantly more favorable influence with regard to decomposition reactions than e.g. the elements iron, molybdenum, ruthenium and tungsten. The Sk2 (10) values for the elements used according to the invention are considerably above 100, and significantly less than 100 for catalytically active materials. Particularly when titanium or titanium compounds are used, exothermic reactions only set off just as late and with the same intensity as in a solution without any addition of materials.

It should be mentioned that, as can be seen, the metal compounds listed in Table 2 do not have uniform particle sizes. This makes it an absolute It is not possible to compare the Sk2 (10) values, but Table 2 clearly shows the tendency that the titanium and chromium compounds used according to the invention give significantly better values than other metal compounds, even with the most varied particle sizes.

The following table shows the influence of the use of materials which have catalytic effects per se and which have been coated with non-catalytic substances. In these experiments, washers made of various basic materials were measured. In the case of coatings, the layer thickness was at least 2 μm in each case. Table 3: Adding washers coated / not coated: Basic material Coating Sk2 (10) (Blank value "BW") - 160.80 Structural steel nickel 144.46 Structural steel chrome 141.49 Structural steel NiCr + ZrO ₂ 110.62 Stainless steel 1.4571 - 72.56 Structural steel - 37.82

This table also shows the favorable influence of the elements nickel, chromium and zirconium. The Sk2 (10) value of the coating with NiCr and zirconium oxide, which drops slightly compared to nickel and chrome, is due to a poor coating of the sample.

By coating cheaper materials such as Structural steel with the materials used according to the invention can thus be used in a particularly economical manner to prevent the formation and extent of exothermic reactions in cellulose solutions in aqueous amine oxides.

Claims (5)

1. A process for the production of cellulose moulded bodies wherein a suspension of cellulose in an aqueous solution of a tertiary amine-oxide is transformed into a mouldable solution, said solution being extruded by means of a forming tool and conducted into a precipitation bath, characterized in that at least part of the material of devices and pipes for the transportation and processing of the solution, which material is in contact with the mouldable solution, contains at a minimum of 90% up to a depth of at least 0,5 µm, preferably more than 1 µm, measured from the surface, at least one element of the group consisting of titanium, zirconium, chromium and nickel in elementary form and/or in the form of compounds provided that the remaining of the material does not contain any of the elements of the group consisting of copper, molybdenum, tungsten or cobalt.
2. A process according to Claim 1, characterized in that as compounds of the elements their oxides, carbides, nitrides, borides and/or silicides are provided.
3. A process according to one of the Claims 1 or 2, characterized in that the part of the material in contact with the mouldable solution is arranged at least partly in layers, the top layer being in contact with the solution containing the at least one element at a minimum of 90%, and this layer being applied to a material containing other elements and/or compounds of more than 10%.
4. A process according to one of the preceeding Claims, characterized in that the materials contain the at least one element at a depth of at least 0,5 µm in those parts of devices and pipes in contact with the solution wherein the mouldable solution comes to a standstill or moves only at a reduced rate.
5. The use of at least one element of the group consisting of titanium, zirconium, chromium and nickel in elementary form and/or in the form of compounds in materials of devices and pipes in contact with a mouldable solution of cellulose in a mixture of a tertiary amine-oxide and water at the surface layer in contact with the mouldable solution, at a percentage of at least 90% up to a depth of at least 0,5 µm, preferably more than 1 µm.