CN217663078U - Apparatus for preparing a solution of cellulose in an aqueous tertiary amine-oxide - Google Patents

Abstract

The utility model relates to an equipment for preparing solution of cellulose in aqueous tertiary amine oxide, equipment includes the household utensils that are heated indirectly, can be evacuated, the household utensils are equipped with agitating unit, wherein, the household utensils are cylindrical container, the container has the (mixing) shaft, the (mixing) shaft is installed in central authorities, the (mixing) shaft has the agitator rather than the joint, the agitator with the radial interval of the inner wall of container is maximum 20mm the upper portion of container has the import that is used for the cellulose suspension have the export that is used for even cellulose solution in the lower extreme of container, wherein, the circularity of the inner wall of container is between 0.01% and 0.9%, the surface roughness of the internal surface of the inner wall of container is between 0.4 mu m and 3.2 mu m.

Description

Apparatus for preparing a solution of cellulose in an aqueous tertiary amine-oxide

Technical Field

The invention relates to a device for producing a solution of cellulose in an aqueous tertiary amine oxide from a suspension of cellulose in an aqueous tertiary amine oxide solution by heating under reduced pressure, and to a module for carrying out said method.

Background

Initially a stirred vessel was used to attempt to dissolve the cellulose in the aqueous tertiary amine oxide solution. However, this device has not gained widespread acceptance and still includes a number of disadvantages. Therefore, due to the unfavorable ratio of liquid surface to liquid volume, it is difficult to drain water from the stirring vessel, which results in a long residence time within the stirring vessel, which is between 2 and 4 hours. During this time, the polymer cellulose chains are partially degraded, which is further promoted by the increased temperature. This partial degradation, in turn, adversely affects certain properties of the final product after the spinning process, such as strength, elongation and hook strength. It is also known that heating, in particular to temperatures above 130 ℃, can lead to strong discoloration due to decomposition of the amine oxides used. With some compounds, for example with N-methylmorpholine N-oxide, this degradation can even occur as an explosion in the case of rapid gas generation, so that the solution currently present in the stirring vessel constitutes a safety risk in terms of its amount. Therefore, when carrying out the process in large batches, if stirred vessels are used, they must be operated under sufficiently safe conditions by means of autoclaves which, for economic reasons, cannot be used for continuous operation. On the other hand, without safety devices, only discontinuous operation can be performed in the stirred vessel, which makes the process rather inflexible, since it is difficult to change parameters such as temperature and evaporation rate. In addition to this, the agitated vessels retain a large amount of spinning material due to the high viscosity of the cellulose solution, which hampers the washing of the vessels and further reduces the economics of the process.

EP 356 419 B1 discloses a method for producing a cellulose solution in an aqueous tertiary amine-oxide, which method can be operated continuously, wherein the heat treatment of the suspension will be carried out in a significantly shorter time in order to minimize the heat load on the cellulose and the tertiary amine-oxide. According to EP 356 419 B1, the suspension is transported onto a heated surface, distributed in layers or coatings, until a homogeneous solution of fibers is formed, having a viscosity of between 50 and 15000pas, the supply of suspension and the discharge of the homogeneous solution being carried out continuously.

The layered or coated distribution of the cellulose suspension on the heated surface results in a large liquid surface, which helps to remove the water. At the same time, the suspension can be heated rapidly to the temperature required for the preparation of the solution. By transport onto the heating surface, continuous mixing of the suspension is ensured, which further promotes heat and mass exchange. Particularly good mixing is ensured if the thickness of the layer distributed over the heating surface is at most 20mm, preferably 1.5mm to 5 mm. A preferred embodiment of the method according to EP 356 419 B1 is characterized in that the suspension is brought to a temperature between 50 ℃ and 150 ℃, preferably between 60 ℃ and 100 ℃, and the suspension is subjected to a pressure of 0.5mbar to 1000mbar, preferably 50mbar to 150mbar. This means that the apparatus of EP 356 419 B1 must be constructed in a manner to withstand sub-atmospheric pressures. According to EP 356 419 B1 it has proven to be particularly advantageous if the suspension is brought into contact with the heated surface for a period of time of from 1min to 60min. This time is sufficient for producing a homogeneous solution, on the one hand, and is so short, on the other hand, that decomposition of the tertiary amine oxide and degradation of the cellulose are largely prevented. A suitable assembly for carrying out the method of EP 356 419 B1 comprises an indirectly heated vessel which can be evacuated, said vessel being provided with stirring means, which assembly is characterized in that the vessel is designed as a cylindrical container having a stirring shaft which is centrally mounted, which stirring shaft has a stirrer engaging therewith, said stirrer being at a radial distance of maximally 20mm from the inner wall of the container, an inlet for the cellulose suspension being provided in the upper part of the container, and an outlet for the homogeneous cellulose solution being provided in the lower end of the container. An advantageous embodiment of the assembly according to EP 356 419 B1 comprises a distribution ring arranged on the stirring shaft for distributing the cellulose suspension in the form of a layer or coating onto the inner wall of the vessel. In order to control the transport of the cellulose suspension along the inner wall of the vessel, it has proven advantageous if the stirrer has an angle of inclination with respect to the axis of the stirring shaft, the magnitude of which angle of inclination can be adjusted. The device according to EP 356 419 B1 operated with the aid of the assembly according to the invention is more flexible in terms of changing operating parameters than stirring vessels and involves a significantly lower safety risk than the prior art, since a large amount of solvent is not heated simultaneously, but only a relatively small amount of solvent is heated continuously, since the solvent is distributed in layers over the heating surface.

However, in the apparatus disclosed in EP 356 419 B1 for commercial scale, the stirring shaft with the stirrer (i.e. rotor) engaged with the stirring shaft will exhibit a diameter of several meters, and the length of the rotor and hence the vessel will exhibit a length of more than ten meters, possibly even more than 20 meters. For a dissolving apparatus of this size, the specification of a constant radial spacing of the stirrer from the inner wall of the vessel of maximum 20mm over the entire extension of the vessel is not sufficient to provide a high quality spinning solution and a safe long-term reliability of the process.

SUMMERY OF THE UTILITY MODEL

Therefore, in view of the above-described prior art, there are problems as follows: an apparatus for preparing a solution of cellulose in an aqueous tertiary amine-oxide from a suspension of cellulose in an aqueous tertiary amine-oxide solution is provided which is capable of providing a high quality solution and which is safe for long term reliability of the process. In addition, such a device should be economical in construction, manufacture and handling.

It was surprisingly found that such an apparatus meets the requirements if it exhibits a roundness of the inner wall of the vessel measured according to the industrial standard AD2000 of between 0.01% and 0.9% and a surface roughness of the inner surface of the inner wall of the vessel measured according to the industrial standard ISO 4287 1997 of between 0.4 μm and 3.2 μm.

In order to solve the above-mentioned technical problem, the invention proposes an apparatus for preparing a solution of cellulose in an aqueous tertiary amine oxide, comprising an indirectly heated vessel which can be evacuated and which is provided with a stirring device, wherein the vessel is a cylindrical container having a stirring shaft which is centrally mounted and has a stirrer which engages with it, the stirrer being at a radial distance of at most 20mm from the inner wall of the container, an inlet for the cellulose suspension being provided in the upper part of the container and an outlet for the homogeneous cellulose solution being provided in the lower end of the container. Wherein the roundness of the inner wall of the container is between 0.01% and 0.9%, and the surface roughness of the inner surface of the inner wall of the container is between 0.4 μm and 3.2 μm.

Preferably, the roundness of the inner wall of the container is between 0.01% and 0.2%. A roundness of between 0.01% and 0.05% is even more preferred. The surface roughness of the inner surface of the inner wall of the container is preferably between 0.5 μm and 1.6 μm.

Higher circularity values will result in variations in the thickness of the cellulose suspension and thus in inhomogeneous solution quality and may additionally result in mechanical vibrations which may ultimately lead to mechanical damage of the entire apparatus. Smaller roundness values require thicker vessel walls, i.e., more material and higher overall plant weight.

A higher surface roughness may result in a portion of the cellulose suspension adhering to the inner wall of the vessel, resulting in a longer and uneven residence time of the cellulose suspension inside the vessel and thus in poor solution quality and the risk of heat evolution inside the vessel. Lower surface roughness may require higher polishing costs, resulting in higher manufacturing costs for the device.

Drawings

Now, the apparatus according to the invention is explained in more detail with reference to fig. 1 and 2, wherein fig. 1 is a partial longitudinal section of the apparatus according to the invention, and fig. 2 shows an enlarged section along the line II-II of fig. 1.

Detailed Description

1 denotes the inner wall of a preferably upright rotor which, as shown in the exemplary embodiment, is designed as a cylindrical container 2 over almost its entire length. The main part of the inner wall 1 is surrounded by a heating jacket 3 with connections 4 and 5 for a heating medium, the connection 4 being used for supplying the heating medium and the connection 5 being used for discharging the heating medium.

An agitator shaft 7 is mounted centrally in the vessel 2 and is driven by the motor 6, the agitator shaft including an agitator 6 engaged therewith. The stirrer 8, which is shown flat in the exemplary embodiment, extends radially to the axis, the plane of said stirrer enclosing an inclination angle α with respect to the axial direction 9 of the stirring shaft 7, the magnitude of which is preferably adjustable. Suitable examples of stirrers can be found, for example, in patent publications WO 2008/154666 A1, WO 2008/154668 A1 and WO 2008/154667 A1. A distribution ring 10 is attached to the stirring shaft 7 above the stirrer 8, distributing the cellulose suspension introduced through the inlet 11 in layers onto the inner wall 1. The distribution ring 10 is thus arranged at the level of the inlet 11.

The lower end of the vessel 2 is frusto-conical (frustoconical) and has an outlet 12 for the homogenous cellulose solution. Throughout the extension of the vessel 2, the stirrer 8 has a constant radial spacing 13 from the inner wall 1 of the vessel 2, which spacing is influenced by the roundness according to the invention as defined above.

In the upper part of the container 2, i.e. above the plane of the distribution ring 10, an opening 14 is provided for evacuating the container 2 and for discharging water vapour.

The assembly functions in the following manner:

the cellulose suspension, if necessary in a preheated state, is continuously supplied into the vessel 2 through the inlet 11 under reduced pressure, is captured there by the distribution ring 10, distributed onto the inner wall 1 and transported by the stirrer 8 along the indirectly heated inner wall 1, which serves as a heating surface and is influenced by the surface roughness according to the invention as defined above, to the outlet 13 on the lower end of the vessel 2. Heat transfer media, such as water, oil or steam, are suitable for indirect heating.

The cellulose suspension is heated during transport along the indirectly heated inner wall 1, while the water evaporates due to the reduced pressure, so that the tertiary amine-oxide is concentrated until the cellulose is dissolved.

Figure 2 shows in detail how the apparatus according to the invention operates for processing the cellulose suspension in the vessel 2. Fig. 2 shows the stirring shaft 7 with stirrer 8, inner wall 1 and heating jacket 3, assuming and indicated by arrow 7' the direction of rotation of the stirring shaft 7 in the clockwise direction. The distribution of the layers, i.e. the thickness of the layers of the cellulose suspension in each case, is set by the radial distance 13 of the stirrer 8 from the heated inner wall 1. The bow wave, which is schematically shown in fig. 2, of the cellulose suspension is formed at the stirrer by a rotational movement. As shown in fig. 2, the cellulose particles circulate in these bow waves, which movement propagates to the suspension layer distributed on the inner wall 1. This ensures continuous rearrangement and intensive mixing of the suspension, greatly facilitating heat and mass exchange.

The discharge of the separated water vapour counter-currently to the transport of the suspension is decisive for the continuous control of the apparatus according to the invention. In addition, it is also important to provide a sufficiently large discharge steam space 15 for rapid discharge of water vapour, as is the case if the ratio of the length to the diameter of the cylindrical part of the container 2 is between 4 and 8. By means of the invention, cellulose solutions containing up to 30% by weight of cellulose can be produced.

Claims (6)

1. Apparatus for the preparation of a solution of cellulose in an aqueous tertiary amine-oxide, comprising an indirectly heated vessel which can be evacuated and which is provided with a stirring device, wherein the vessel is a cylindrical vessel having a stirring shaft which is centrally mounted with a stirrer engaging therewith, which stirrer has a radial spacing of maximally 20mm from the inner wall of the vessel, an inlet for the cellulose suspension in the upper part of the vessel and an outlet for the homogeneous cellulose solution in the lower end of the vessel, characterized in that the roundness of the inner wall of the vessel is between 0.01% and 0.9%, and the surface roughness of the inner surface of the inner wall of the vessel is between 0.4 μm and 3.2 μm.

2. The apparatus of claim 1, wherein the roundness of the inner wall of the vessel is between 0.01% and 0.2%.

3. The apparatus of claim 1, wherein the roundness of the inner wall of the vessel is between 0.01% and 0.05%.

4. The apparatus according to claim 1, characterized in that the surface roughness of the inner surface of the inner wall of the vessel is between 0.5 μm and 1.6 μm.

5. The apparatus according to claim 1, characterized in that the stirring shaft has a distribution ring for distributing the cellulose suspension in the form of a layer or coating onto the inner wall of the vessel.

6. The apparatus according to claim 1, characterized in that the stirrer is angled (a) with respect to the axis of the stirring shaft, said angle being adjustable.

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