DE1115017B - Process for the aftertreatment of pourable, solid substances with gaseous agents - Google Patents

Description

Process for the aftertreatment of loose, solid materials with gaseous active agents The invention relates to a process for post-condensation of polyamides in a circumferential countercurrent moving layer of the material to be treated.

The process consists in a pneumatic circulation of the solid bed with the help of a directed partial flow of the gaseous treatment medium.

Most of the reactions between gaseous substances and solids are carried out on a stationary solid layer on an industrial scale.

Such processes are very simple in terms of apparatus, show but shortcomings, especially with regard to space-time yield and evenness of the process. Especially when the solid is itself a reaction product, it is The course of the reaction depends on the respective position of the particles, so that considerable Differences between grains located at the gas inlet and outlet and, if through the wall absorb or dissipate amounts of heat, also between the wall and Occur in the middle of the layer.

Because of these disadvantages, more and more reactions become solid Substances carried out in moving layers, the process being particularly technical Have gained importance in which the solid material movement is achieved pneumatically will. This includes the fluidized bed process.

Fluidized bed processes are particularly characterized by favorable heat transfer conditions between the gaseous substance serving as a heat transfer medium and the solid. They are preferably suitable for gas reactions with fine-grained catalysts uniform grain size. If, on the other hand, the grain size is not uniform, the Fluidized bed segregation. Where such segregation or sifting of the solid bed is undesirable, one works with moving layers. The heat transfer conditions are no longer equally cheap, but a precisely defined one is achieved Solid body movement with homogeneous distribution. The present invention relates to a particular embodiment of a continuous process with a migratory solid layer.

In the previously known moving layer processes, one of which is the "thermophore" process The best known is the solid layer outside of the reaction vessel again returned to the top of the reaction vessel. The solids are promoted in this case continuously by mechanical means with the help of elevators or else pneumatic. In the »Thermophor« process, the pneumatic conveying is next to a number of advantages still have some disadvantages, e.g. B. the long and at least two right-angled bends gen having transport routes. In the Umlenkunaen a considerable part of the kinetic energy is destroyed, resulting in noticeable erosion the pipe wall and considerable abrasion on the material being circulated in the solid layer may result.

From the Swiss patent specification 265206 it is now known solid polyamide particles in one equipped with a drum or a screw conveyor Dryer while the material is circulated in a circulating inert gas stream, to be heated with removal of the water and low molecular weight components.

Apart from the fact that this process also has deficiencies in the space-time yield has, there is considerable wear on the material being circulated.

The dust that occurs here can practically no longer be removed from the material to be treated be separated.

It has now been found that these disadvantages are practically eliminated can when the flow of the solid layer into the interior of the reaction vessel is laid, with a directed partial flow of the gaseous for pneumatic conveyance Treatment agent is used. The invention is illustrated by the drawings.

Fig. 1 shows the scheme of an entire treatment apparatus; Fig. 2 and FIG. 3 illustrate specific embodiments of the reaction vessel.

The reaction vessel 2 (Fig. 1) is conical in the lower part, wherein the cone angle is expediently chosen so that the solid granules are emptied can drain completely. The upward movement takes place in this reaction vessel 2 by one or more tubes, which are preferably arranged centrally in the reaction vessel 2 1. These central tubes 1 are covered with a baffle plate 4.

The reaction vessel is in operation up to about height h (Fig. 1) with filled with the item to be treated.

Already during the filling from the storage vessel 10 through the valve 13, the treatment gas is introduced through the bottom nozzle in the reaction vessel. Part of the gas flow now rises through the central pipe 1 and increases at the same time granular material continuously from the lower part of the treatment vessel with, which is then evenly distributed after leaving the upper end of the central tube distributed on the bulk surface.

If the material to be treated has an uneven grain size, no segregation occurs in the present process, provided that also the finest particles of the migrating layer are not carried by the material being removed. In the upper cone of the reaction vessel there is a gas outlet at a suitable point attached, through the possibly a gas filter 8 and a cutter 9 (for condensable treatment gases) the gas reaches the circulation compressor 7, from where it is returned to the reaction vessel.

If necessary, the treatment gas can be heated via heat exchanger 6 will. Liquid vapors can also be supplied to the gas from the vessel 12 or be introduced as mist or aerosols.

The grains conveyed up through the tube 1, spreading evenly Distribute on the bulk material surface, essentially lay one in the migrating layer vertical way back, d. i.e., those grains that lie against the vessel wall come, remain in contact with the vessel wall during a cycle of the migrating layer. The probability that a grain will hit the wall with several passes promoted is practically zero. The circulation can be regulated within wide limits and is generally between 5 and 50 passes per hour.

The breadth of variation in the process of the invention is surprising. If the dimensions of the reaction vessel are fixed, they can be changed simply by changing them of the four variables, namely diameter d of the delivery pipe 1, distance a of the delivery pipe 1, velocity v of the circulating gas, bed height h, the various solids in an even, constant and the respective demand corresponding circulation offset. The method leaves in terms of grain size, grain shape and specific Weight of the circulating material has a very wide margin.

A particular advantage is that in the case of solid layers with uneven Grain size no segregation occurs.

By the fact that the individual grains in the different passes not in the migrant class come to lie in the same place, one reaches that in processes in which the reaction vessel must be heated from the outside, a uniform thermal treatment of all solid particles is guaranteed. The heat transfer conditions are very good in the method according to the invention - they are roughly in the middle between the bed process and the fluidized bed process - so that in many External heating can be dispensed with in some cases.

In this case, the heat transfer takes place solely with the help of the Circulating gas that is brought to the required temperature by the heat exchangers mentioned is brought.

When the compressor is at a standstill, it is emptied through the slide 14. A rapid and complete emptying of the reaction chamber 2 is achieved, such as they do not even come close with the resting bed process and only rarely with the fluidized bed process is achieved.

Pneumatic conveyance of the solid granular material is essential gentler on the granulate and the material of the conveyor than with the »Thermophor« process, since the conveying distance is shortened by 20 to 50% and any diversion in the Pipeline is omitted. Since the gas flow in the delivery pipe 1 can be adjusted so that the conveyed particles enter the upper tube opening only at low speed left, there is practically no abrasion and no metal wear. The only Place that is subject to wear is the baffle 4, which is light can be exchanged. For particularly gentle treatment of the granulate can the baffle plate 4 can be replaced by a pitot tube 4 (Fig. 2), or it is the A braking flow according to FIG. 3 is sent in the opposite direction to the rising gas flow.

Example 1 In a reaction vessel 2 according to FIG. 1 with a centrally arranged Conveyor pipe of 120 cm length and 3 cm diameter, through which 80 cbm / hour. purer, oxygen-free nitrogen are circulated, 50 kg of a moist Granules of polyhexamethyldiammonium adipate with an average grain size of 4 mm given. The granules become through the partial gas flow passing through the central pipe 1 circulated ten times an hour.

With the help of a heat exchanger 6 and a tip preheater the circulating nitrogen is heated so that it is in the lower part of the reaction vessel enters at 1200 C. The water that evaporates from the granulate is cut off by means of a cutter 9 and cooler condensed and continuously withdrawn from the cycle gas. After 4 to 5 Hours the water content of the granulate is from an initial 2% to less than 0.10 / o sunk.

Example 2 In an apparatus constructed in accordance with Example 1 are used 50 kg of poly-e-caprolactam granules are given. The granulate has an average Grain size of 2 mm and contains 2 to 3% water and 10 to 11% monomeric constituents. 90 cbm of pure, oxygen-free nitrogen are passed through the apparatus every hour with an inlet temperature of 1860 C. The expelled fugitives Components, i.e. water and low molecular weight products, are cut off using a cutter and cooler continuously withdrawn from the cycle. After 8lía hours if the water content of the granulate is less than 0.1%, the content of extractables low molecular weight products dropped to around 1010.

Example 3 In an apparatus according to Example 1, 50 kg a moist, non-extracted granulate of catalyst-containing poly-e-caprolactam circulated in a stream of 80 cbm of pure oxygen-free nitrogen per hour. The inlet temperature of nitrogen is 1860 C. The volatile products, in this case water and low molecular weight fractions are continuously circulating Gas stream withdrawn and condensed. After 12 hours of treatment, the granules are dry (water content 0.05%) and contains only about 1% extractable components.

The molecular weight of the poly-e-caprolactam is original about 12,000 (basic viscosity 0.9) increased to about 40,000 (basic viscosity 3.0).

Claims (2)

PATENT CLAIMS: 1. Process for the aftertreatment of pourable, solid substances with gaseous agents in a countercurrent migration layer that pneumatically with the help of a directed partial flow of the active agent in the treatment room is circulated, characterized in that pourable solid particles made of organic Plastics with an inert gas for drying and / or. or chemical aftertreatment to be treated in the heat. 2. The method according to claim 1, characterized in that particles of a polyamide are treated with inert gas. Publications considered: Swiss patent specification No. 265 206; U.S. Patent Nos. 2581,670, 2597346, 2606097.