IE41447B1

IE41447B1 - Process for the separation of distillation sump products

Info

Publication number: IE41447B1
Application number: IE1770/75A
Authority: IE
Original assignee: Bayer Ag
Priority date: 1974-08-09
Filing date: 1975-08-08
Publication date: 1980-01-02
Also published as: BE832214A; BR7505052A; FR2281147A1; LU73174A1; GB1511315A; NL7509436A; DE2438290B2; ZA755112B; DK361975A; IE41447L; IN141301B; DE2438290C3; JPS5142077A; ES440101A1; DE2438290A1

Abstract

1511315 Thin layer evaporator BAYER AG 7 Aug 1975 [9 Aug 1974] 33011/75 Heading BIB A thin-layer evaporator comprises a spray ring 6 for the introduction of solvent to dissolve sump product, and, above this, a further spray ring. 4 for the introduction of vapour, e.g. steam, to form a vapour lock to isolate the distillate vapour from the solvent.

Description

This invention relates to a process for the separation of a distillate-free sump product in thin layer evaporators, which sump product is obtained by the concentration of solutions comprising water, organic substances and nonvolatile constituents to form a solid which is then dissolved in a solvent.

In thin layer evaporators it is frequently necessary to solve the problem of concentrating aqueous solutions of organic substances and non-volatile constituents. If the organic substances have a higher boiling point than water or > if they form an azeotropic mixture with water, then the water must be evaporated together With the organic substance in order that the organic substance may be recovered. The water is then removed from the organic substance in a subsequent operation. The non-volatile constituents are obtained as solids in the lower part of the thin layer evaporator.

These solids oan be removed semicontinuously from the thin layer evaporator by means of alternate receivers or continuously by means of rotary air lock extractor or screw conveyors. If the solids are removed continuously, the apparatus used for removing them oan cnly be effectively sealed off from the thin layer evaporator with great difficulty. To ensure complete removal of the solid material from the sump of the thin layer evaporator, it is therefore often dissolved in a suitable solvent before it is continuously removed by known methods. Since the solvent used for this purpose is at a lower temperature than the walls of the thin layer evaporator, vapours of distillate which are normally removed at the head of the apparatus condense in the solvent. Consequently, the sump product of a thin layer evaporator cannot be obtained in a pure form and always contains some distillate. This not only reduces the efficiency of thin - 2 41447 layer evaporators but also in many cases necessitates considerable effort to purify the sump products.

It is an object of this invention to provide a procoss by which sump products dissolved in solvent can be obtained completely free from distillate in thin layer evaporators.

According to the invention, this problem is solved by providing a vapour lock above the solvent inlet.

The particular advantages achieved by the process according to the invention lie in the fact that the vapour lock, which is produced by injecting a gas, produces a stre'am against the direction of the solids descending through the apparatus, so that the vapours of distillate are prevented from descending as far as the solvent and condensing there.

The gas used for producing the vapour lock, which must not enter into any undesirable reactions with the distillate, is removed at the head of the thin layer evaporator together with the distillate and subsequently separated.

According to a further embodiment of the process of the invention, steam is used to form the vapour lock.

The particular advantages thereby achieved lie in the fact that no foreign substance is introduced into the distillate of the thin layer evaporator. Since, in the problem which is required to be solved here, water must in any case be evaporated together with the organic substance, no additional problem arises in the subsequent course of the process when steam is used as the vapour lock.

A practical example of the process according to the invention is illustrated in the drawing and described below.

Figure 1 Is a schematic representation of a thin layer evaporator having a vapour lock.

The non-volatile constituents of the solution accumulate as solid below the bottom wiper blade 1 of the thin layer evaporator. The vapour look Is situated just below a hearing 2 of the shaft for the wiper blades. Steam is introduced into a spray ring 4 from a pipe 3. The spray ring directs the steam obliquely upwards. About 10 to 100 cm below the spray ring 4 is a second spray ring 6 through which the solvent required for dissolving the solid is introduced into the lower part of the thin layer evaporator from a pipe 5.

The dissolved solid is continuously removed through a pipe 7 by way of a siphon 8. A heating jacket 9 which extends down the evaporator as far as the vapour look keeps the thin layer evaporator at a sufficiently high temperature to prevent the condensation of distillate vapour.

Two examples of prooesses according to the invention are described below.

Example 1 A solution of 7OJ6 of morpholine, 12% of water and 18% of sodium chloride is evaporated at normal pressure in a thin layer evaporator. The boiling point of morpholine at normal pressure is 128eC. The distillate from the thin layer evaporator is a mixture of morpholine and water, and the sump product is sodium chloride in the form of a powder. The solvent used to dissolve the sodium chloride is water.

When the solution was introduced at the rate of 1000, kg/hour the quantity of steam required for the vapour lock was 100 kg/hour and the quantity of solvent required so as to recover a 20% sodium chloride solution was 720 kg of water per hour. The water is introduced at a temperature of 80eC so that condensation of the steam used as vapour look is prevented as far as possible. No distillate oould be deteoted in the dissolved sump produot in a test carried out with a lower limit of detectability of 0.1%. - 4 41447 Example 2 A solution of 25/ of water, 55/ of cyclohexylamine and 20/ of organic residues is evaporated in a thin layer evaporator at normal pressure. Cyclohexylamine and water form a homo5 geneous azeotropic mixture at 96.4°C and 55.3/ water at normal pressure. The distillate from the thin layer evaporator is a mixture of cyclohexylamine and water while the nonvolatile constituents accumulate as a granulate in the sump.

The solvent used to dissolve the granulate is o-dichlorobenzene.

When 1000 kg/hour of solution were used, the quantity of steam required for the vapour lock was 80 kg/hour and the quantity of solvent required for producing a 50/ solution was 470 kg/hour of o-dichlorobenzene. No distillate could be detected in the sump product.

Claims

1. A process for the separation of a sump product substantially free from distillate during distillation in thin layer evaporators, which sump product is obtained by the 5 concentration of solutions comprising water, organic substances and non-volatile constituents to form a solid, by dissolving said solid in a solvent, and removing the solution so formed from the evaporator wherein a vapour lock is provided above the inlet for the solvent. 10

2. A process as claimed in claim 1, wherein steam is used as the vapour lock.

3. . A process for the separation of a sump product substantially free from distillate in. thin layer evaporators, substantially as herein described in either of the Examples.