EP1268556A1

EP1268556A1 - Method and device for continually producing a suspension of cellulose in an aqueous amine oxide

Info

Publication number: EP1268556A1
Application number: EP00979396A
Authority: EP
Inventors: Ralf-Uwe Bauer; Uwe Kind
Original assignee: Alceru Schwarza GmbH
Current assignee: Alceru Schwarza GmbH
Priority date: 2000-03-20
Filing date: 2000-09-29
Publication date: 2003-01-02
Also published as: DE10013777C2; CN1451018A; AU2001216916A1; WO2001070819A1; DE10013777A1; CN1235912C; US7115187B1

Abstract

The invention relates to a method for continually producing a suspension of cellulose in an aqueous tertiary amine oxide for the use according to the lyocell method. According to the inventive method, (a) a cellulose suspension is produced by means of cellulose and an amine oxide-free aqueous phase at a mass ratio ranging from 1:3 to 1:40, (b) the cellulose suspension is dewatered to form a material having a cellulose content ranging from 20 to 80 mass- % and (c) the moist cellulose material is mixed with water-containing amine oxide and is conveyed through a horizontal shear zone in such a way that a suspension having an amine oxide content in the liquid phase is produced after mixing, whereby said content ranges from 70 to 80 mass- % and the suspension essentially completely fills the available conveying cross-section in the shear zone. The inventive method is characterised in that, in step (c), water-containing amine oxide in the finely dispersed form is added to the moist cellulose material in a fall zone which is only partially filled by the cellulose material and that the cellulose material which is mixed with the amine oxide is inserted into the shear zone. The invention also relates to a device for carrying out said method that requires comparatively few apparatuses for producing the suspension. The throughput of the cellulose material can be increased, whereby said throughput is related to the volume of the shear zone.

Description

Method and device for the continuous production of a suspension of cellulose in a water amine oxide

The invention relates to a process for the continuous production of a suspension of cellulose in a water tertiary amine oxide for use in the Lyocell process. The invention also relates to a device for performing this method.

It is known to produce cellulosic molding and spinning masses from solutions of cellulose in ammoxides, preferably in N-methylmorpholine-N-oxide, and a non-solvent for cellulose, preferably water. By deforming the solution, stretching and regenerating the cellulose, products with a variety of uses in the textile and non-textile sector are obtained, see W. Berger, possibilities and limits of alternative cellulose dissolution and deformation, Lenzmger reports 74 (1994) 9, pp. 11-18 , Fibers produced in this way were given the generic name "Lyocell" by BISFA.

From WO 94/28217 a batch process for the production of a suspension of cellulose in water amine oxide is known. Crushed cellulose and an amine oxide solution are mixed in a horizontal mixing chamber by a rotor with radial stirring elements. The time period for a batch is 21 minutes. This mode of operation is disadvantageous because two such mixing chambers have to be operated in parallel because of the continuous loading of the following batch stage. In addition, the complete emptying of the mixing chambers is difficult.

It is also known from WO 96/33221, a cellulose suspension to produce in aqueous N-methylmorpholine-N-oxide (NMMO) by mixing the comminuted cellulose directly with the aqueous, for example 75% by mass NMMO in a ring layer mixer. The suspension formed is dissolved in a separate film truder. A disadvantage of the annular layer mixer is that only a comminuted, essentially dry cellulose can be used. If the cellulose contains water, the layer formation in the mixer is made more difficult by the mixing with the separately added NMMO solution. The water must be thermally separated. The soluble constituents of the pulp get into the spinning solution and lead to disadvantageous properties of the cellulose products. Since the suspension is transported as a layer, the throughput related to the cross-section of the apparatus is low.

From DE 198 37 210.8 it is known to suspend the pulp in water before the formation of a suspension in amine oxide solution and to partially separate it again from the suspending agent after a certain time. The moist cellulose material is then conveyed through a horizontal shear zone, first in the absence of amine oxide and then together with amine oxide. This method of operation requires a relatively long shear zone and thus a considerable outlay on equipment. The formation of a uniform suspension is made more difficult by the fact that the aqueous amine oxide is fed into a cellulose material which completely fills the available apparatus volume.

The present invention has for its object to provide a method and an apparatus for the continuous production of a suspension of cellulose in an aqueous tertiary amine oxide with reduced equipment expenditure for the formation of suspensions and cellulose activation for use in the Lyocell process. In particular, the throughput of the cellulose material, which is based on the volume of the shear zone, is to be increased and the manufacturing time of the suspension is to be reduced. Further advantages result from the following description. The invention accordingly proceeds from a process for the continuous production of a suspension of cellulose and an aqueous tertiary amine oxide for use in the lyocell process, in which (a) cellulose and an amine oxide-free aqueous phase have a mass ratio in the range from 1: 3 to 1 : 40 forms a cellulose suspension, (b) the cellulose suspension is dewatered to a material with a cellulose content in the range from 20 to 80% by mass, and (c) the moist cellulose material is mixed with as much water-containing amine oxide and is passed through a horizontal shear zone, that after the mixture there is a suspension with an ammoxide content in the liquid phase in the range from 70 to 80% by mass, the suspension essentially completely filling the available cross section of the shear zone.

This method is characterized according to the invention in that in stage (c) finely divided aqueous amine oxide is added to the moist cellulose material in a falling zone which is only partially filled by the cellulose material, and the cellulose material mixed with the amine oxide is introduced into the shear zone. Deviating from the process according to DE 198 37 210.8, the first part of the shear zone is omitted, through which the cellulose material is required and homogenized in the absence of NMMO. In addition, the water-containing amine oxide is not introduced into the shear zone, which is essentially completely filled by the suspension, but into the upstream drop zone. The cellulose material only partially fills the drop zone, so that with the feeding of the ammoxide, a pre-distribution of the ammoxide in the moist cellulose material is achieved. This pre-distribution of the ammoxide makes it possible to shorten the shear zone adjoining the falling zone to form a uniform suspension for the subsequent solution formation. Compared to the method according to DE 198 37 210.8, this shortens the shear zone by about 1/3 and saves investment costs by 10 to 15%. According to the preferred embodiment of the process according to the invention, the water-containing amine oxide is dusted into the drop zone. As a result, the falling particles of the moist cellulose material are coated with the water-containing amine oxide, and there is a good premix which allows the subsequent homogenization section to be shortened in the shaving apparatus. Dust-N-methylmorphol-N-oxide monohydrate is preferred in the fall zone.

Surprisingly, despite the reduction in the process stages and the production time of the suspension, an improved quality of the mash was found, which can be determined from the very good swelling state of the cellulose particles in the three-component cellulose / NMMO / water at the end of the shear zone. This is due to the fact that the distance distribution of the amine oxide in the drop zone shortens the time required until the NMMO solution attacks the cellulose particles, so that the swelling of the particles as a whole has already progressed further at the end of the shear zone. The amount of water-containing ammoxide added in the drop zone is matched to the amount of cellulose used so that the amine oxide content in the liquid phase of the suspension formed is in the target range of 70 to 80% by mass.

In step (a) above, the supplied pulp (roll or sheet form) can be whipped with water in a pulper or homogenizer. In this stage, the reactivity or accessibility of the cellulose chains for the amine oxide can be improved by adding enzymes. Dewatering in stage (b) can be achieved using a belt press, screw press, roller filter or centrifuge. It is preferable to dewater to a cellulose content in the range of 45 to 55% by mass. The slightly fluctuating water content after dewatering can be evened out on the transport to the weighing device. Since the water-containing amine oxide used is often a reprocessed solution prepared from a used waste bath, Fall bath regeneration can aim at the formation of an ammoxide concentrate of the required concentration. The short-term and short shear zone ensures sufficient comminution and homogenization of the cellulose particles, which is not possible with the known ring-layer mixer. In general, a water-containing amine oxide with a molar ratio of amine oxide to water in the range from 1: 1 to 1: 2.2 can be used according to the invention. The most concentrated ammoxide, namely in particular NMMO monohydrate, will be used in water-containing cellulose which, for example, has been broken down with water and / or pretreated enzymatically or thermally before the suspension according to the invention.

The preparation of the mash is conveniently carried out at a temperature in the range from 75 to 100 ° C. At these temperatures, the cellulose breakdown and the decomposition of the ammoxide are low; on the other hand, the homogenization and uniform mixing of the moist cellulose with the ammoxide are favored by the elevated temperature. The temperature-controlled suspension can be brought to a solution in a subsequent step by evaporation of water under vacuum without a significant change in temperature.

According to the preferred embodiment of the process according to the invention, the mashing is carried out in a continuous pass and the suspension is continuously drawn off at the end of the shear zone and passed into a loose stage. Since the process runs continuously, the suspension formed can run continuously into the batch stage without the need for an intermediate container.

It is preferable to work in the shear zone with a residence time in the range from 5 to 30 mm, in particular in the range from 10 to 15 mm.

The process can be carried out with the addition of additives such as stabilizers. These additives can also be found in be added to the falling zone together with the amine oxide.

The invention is also based on a device comprising (a) a mixing apparatus with mixing elements, supply nozzle for cellulose and aqueous suspension medium and discharge nozzle for the suspension, (b) a separator connected to the mixer for partial separation of the suspension medium from the cellulose and ( c) a shaving apparatus with horizontal shafts equipped with shearing tools, a loading device for the cellulose material from the separating apparatus at one end of the shaving apparatus and a discharge pipe for the suspension at the other end of the shaving apparatus.

This device is characterized according to the invention in that the loading device is a downpipe for the formation of a drop zone and is provided with nozzles directed into its interior for the introduction of the water-containing ammoxide into the cellulose material. While according to DE 198 37 210.8 the loading device of the shear apparatus e funnel for introducing the cellulose material present as bulk material is the shear apparatus, according to the invention the loading device is provided for the formation of a falling zone which the pulp material particles fall through and therefore offers the possibility of these particles to spray and wet with the aqueous am oxide so that a premix of the moist cellulose material and the aqueous ammoxide is formed in the drop zone, which is drawn as such into the shaving apparatus. The loading device can be a vertical tube, which can be cylindrical or conical in the direction of the shearing apparatus, narrowing or widening. When this premixing enters the shaving apparatus, the mixing of the cellulose particles with aqueous amine oxide is therefore more advanced than when the ammoxide is fed into the shaving apparatus in the process according to DE 198 37 210.8. The length of the apparatus can therefore be shortened considerably without the swelling state of the cellulose particles in the suspension being impaired thereby. At least one slide equipped with nozzles is preferably arranged in the feed pipe. The aqueous ammoxide is emitted into the downpipe via this pipe. It is advantageous here that the particles or particle aggregates of the moist cellulose material falling through the tube are as small as possible. If desired, the partially dewatered cellulose material can be passed through a shredder before entering the downpipe.

The at least one ring line is expediently connected to a heated inlet line. This prevents the aqueous ammoxide from becoming solid within the lines and nozzles.

A horizontal multi-shaft reactor, such as a multi-screwless machine with self-cleaning heat exchange surfaces, a reactor with 2 to 8 co-rotating, intermeshing screws or a multi-chamber mixer can be used as a shear apparatus.

The invention is described below with reference to the drawing and by the example.

The drawing shows schematically a plant for performing the inventive method. A mixing container 1 is fed continuously through pipe 2 with cellulose and through pipe 3 with water as a suspending agent. The aqueous pulp suspension formed in the container 1 passes via the line 4 to a belt press 5, on which it is dewatered to a liquid content of 50%. The moist pulp material obtained on the screen belt press passes as a fleece through a weighing device 6 in a funnel-shaped downpipe 7 which, in the embodiment shown, has an Rmleitung 8 on the inside with nozzles 9 directed into the interior of the tube. The Rmgleitung 8 is fed with a heated supply line 10 with water NMMO. The moist cellulose material falls through the tube 7 and is thereby wetted and loaded with the emitted aqueous ammoxide, so that at the lower end of the downpipe 7 there is a mixture of water-containing cellulose material and amine oxide which also contains air cushions. The downpipe 7 is followed by a multi-shaft apparatus 11 in which the mixture drawn into the apparatus is further mixed by the shearing and conveying elements (not shown) arranged on the shafts 12 and conveyed to the outlet pipe 13. The air entrained with the mixture through the downpipe 7 and some water vapor are drawn off through the nozzle 14. A connecting device, which is constructed similarly to the multi-shaft device 11, connects to the outlet pipe 13. The cellulose solution is formed in it at elevated temperature. The apparatus 11 as well as the dissolver, not shown, are provided with a heating jacket (not shown), so that the desired mixing or. Dissolving temperature can be maintained.

example

70 kg of dry spruce sulfite pulp (Cuoxam-DP 510; oC cellulose content> 90%) with soft water in a liquor ratio of 1:20 are whipped up and homogenized in a turbo solver. With the help of a thick matter pump, the suspension is pumped into a stock chest and diluted to a stock density of 10 g / 1 at a temperature of 50 ° C. A pulp fleece with a solids content of 50% is produced on a wet fleece plant with subsequent pressing and is continuously introduced into a twin-screw apparatus at a throughput of 33.5 kg / h pulp via a chute. The pulp is homogenized during transport to the weighing device. Via a heated feed line, NMMO monohydrate is added at a rate of 127.3 kg / h via nozzles in the chute. In the following shear and homogenization zone of the twin-screw apparatus, the cellulose / water suspension is mixed uniformly with the NMMO monohydrate. A mash is obtained with an NMMO content of 76%, so that in a subsequent evaporation stage a spinning solution with a 12.9% cellulose content can be prepared.

When assessing the quality of the suspension after the slurry mixer the swelling state of the cellulose particles was measured according to the ASG standard. A maximum of 3 non-swollen cellulose particles per cm ^{2 were found} in the mash, which is classified as very good according to the quality standard.

The quality assessment of the spinning solution formed from the suspension was carried out using a microscope V 300, from Hund, Wetzlar, with an evaluation unit (video camera and printer from JVC). The number of undissolved cellulose particles in the spinning sample is given in each case 1 cm ² . The following quality rating applies: number of undissolved cellulose particles / cm ² rating

0 to 5 1

6 to 10 2

11 to 15 3

15 not spinnable

The spinning solution of this example contained no undissolved particles / cm ² . The cellulose solution is well suited for direct processing into fibers, filament yarns and foils using the dry-wet spinning process.

The invention is not restricted to the embodiment shown in FIG. 1. The aqueous amine oxide can not only be injected vertically or obliquely up or down to the direction of fall from the circumference (jacket) of the fall zone, but also parallel and / or obliquely to the direction of fall at the inlet 7 of the downpipe. When inserting the circumference, this is expediently carried out in the upper half of the downpipe 9. The feed speed of the downpipe is preferably matched to the conveying speed of the multi-shaft apparatus in such a way that a bed is present in the lowermost part of the downpipe 7 before it enters the multi-shaft apparatus 11 that as little air as possible is drawn into the multi-shaft apparatus,

Claims

claims

1. A process for the continuous production of a suspension of cellulose in an aqueous tertiary ammoxide for use in the Lyocell process, in which

(a) forms a cellulose suspension from cellulose and an amine oxide-free aqueous phase in a mass ratio in the range from 1: 3 to 1:40,

(b) the pulp suspension is dewatered to a material with a cellulose content in the range of 20 to 80% by mass, and

(c) the moist cellulose material is mixed with as much water-containing amine oxide and demands through a horizontal shear zone that after the mixture a suspension with an amine oxide content in the liquid phase in the range of 70 to 80 mass% results, the suspension being the Available cross-section of the shear zone is essentially completely filled, characterized in that in stage (c) finely divided aqueous amine oxide is added to the moist cellulose material in a drop zone only partially filled by the cellulose material, and the cellulose material mixed with the ammoxide is added to the cellulose material Shear zone is introduced.

2. The method according to claim 1, characterized in that the water-containing amine oxide is injected into the drop zone.

3. The method according to claim 1 or 2, characterized in that N-methylmorphol-N-oxide monohydrate is injected into the fall zone.

4. The method according to any one of claims 1 to 3, characterized in that one works in the shear zone with a residence time in the range of 5 to 30 mm.

5. Device for performing the method according to one of claims 1 to 4 with

(a) a mixing apparatus (1) with mixing elements, feed nozzle (2, 3) for cellulose and aqueous suspending agent and a discharge nozzle for the suspension,

(b) a separator (5) connected to the mixer (1) for the partial separation of the suspending agent from the pulp and

(c) a shaving apparatus (11) with horizontal shafts (12) equipped with shearing tools with a feeding device for the cellulose material from the separating apparatus (5) at one end of the shaving apparatus and a discharge pipe (13) for the suspension at the other end of the shaving apparatus , characterized in that the loading device is set up as a downpipe (7) for the formation of a drop zone and is provided with devices directed into the interior of the downpipe for the introduction of water-containing amine oxide into the pulp material.

6. The device according to claim 5, characterized in that the downpipe (7) at least one with nozzles (9) equipped line (8), preferably a ring line is arranged.

7. Apparatus according to claim 5 or 6, characterized in that the at least one ring line (8) is connected to a heated feed line (10).