DE1221196B - Process for the crystallization of a solution - Google Patents

Description

BONDES REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

Number:
File number:
Registration date:
Display day:

BOId

German class: 12c-2

1221196
A 34796 IVc / 12 c
June 1, 1960
July 21, 1966

The invention relates to a crystallization process that is particularly useful for the separation of isomers of certain organic compounds due to crystallization is important. Specifically aimed the invention relates to a process for the crystallization of p-xylene from mixtures of o-, m- and p-xylene in the presence of ethylbenzene.

Divide with the usual crystallization processes the crystals are generally deposited on the walls of the vessel and have to be extracted therefrom be replaced. The detachment of the crystals from the walls is uncomfortable and can lead to that the crystals are contaminated by the material of the scrapers used or the walls. The transport of the crystals also brings difficulties, since the crystals are not sufficient Form a flowable mass that can be passed on through pipelines like a liquid. Even with continuous crystallization, the mixture of crystals and mother liquor generally forms a relatively compact suspension. These disadvantages are even more pronounced in systems where the solutions to be crystallized are artificially cooled in order to accelerate the formation of the crystals. The crystal deposit that forms on the cooling elements also provides an insulating layer which reduces the heat exchange and thus the performance of the device.

It is already known to cause the precipitation of crystals • from a solution by the solution brings into contact with an immiscible, cold liquid and thereby cools. Even it is already known to use tendons for mixing and transporting the crystallization processes To use crystallization material.

In a process for crystallizing a solution by introducing a coolant that is immiscible with the solution and does not react chemically In the stream of solution moving through a screw, however, it is not only the crystal separation that takes place on device walls, but also the viscosity of the mixture regulated from crystals and mother liquor, if according to the invention the cooling liquid at several, one behind the other Places in controllable amounts is added. The inventive method is preferably carried out Method in a device which consists of a horizontal container with a Screw and inlet and outlet openings for the liquids and the crystals consists and the thereby is characterized in that the container by transverse walls containing passages in the lower part Process for the crystallization of a solution

Applicant:

ANTAR Petroles de PAtiantique, Paris

Representative:

Dipl.-Ing. H. Leinweber, patent attorney,
Munich 2, Rosental 7

Named as inventor:

Andre Rudioff, Wintzenheim, Haut-Rhin;
Eugene Iltis,
Donges, Loire, Atiantique (France)

Claimed priority:
France of June 5, 1959 (796 718)

several consecutive chambers and the screw is divided accordingly and all chambers, with the exception of the last and penultimate chamber, each with an inlet for cooling liquid are provided.

Through the achieved suitable viscosity setting, the mixture is given a consistency, the forwarding of the mixture, for example through pipes, without the occurrence of pipe blockages allowed. In addition, the correct setting of the viscosity results in an even further reduction of heat losses.

A particularly advantageous effect of the method according to the invention is that by the addition of the cooling liquid at several successive points of the stream to be crystallized Solution a substantially constant temperature of the mixture of solution and cooling liquid is achieved. Namely the whole Cooling liquid introduced into the solution stream at a single point, this would create a temperature gradient, whereby the course of the crystallization process eludes precise control. This would have the consequence that the crystals obtained have a non-uniform size or fineness exhibit.

When using the method according to the invention, however, a temperature gradient in the solution

609 590/236

3 4

electricity practically avoided. Furthermore, through 19 and 19 the Archimedean screw can convey that

Appropriate dosage of the mixture containing the crystals attached one after the other through the bottom

arranged cooling liquid added to the inlet points on the partition walls 2, 3, 4, 5 and 6 provided

not only the even course of the crystallization passage to the drainage point 20. Also stir

tion process, but also the fine 5 they build up the mixture in each chamber and ensure

The degree of heat recovery of the crystals obtained, as desired, ensures its homogeneity. "

be set, what for many purposes In the chamber 7 is to be crystallized, of

is of great benefit. the pipe 21 supplied solution with a

For the crystallization of not mixed with water first amount of the added through the pipe 23

solutions can be mixed as a coolant in io led coolant, whereby they dissipate

In many cases an aqueous salt solution cools with advantage and the crystallization is initiated. In the

use which, before being brought into contact with subsequent chambers 8, 9 and 10, which are only the

the solutions to be crystallized through suitable ones supplied from the tubes 24, 25 and 26, respectively

Measures is cooled. Such a saline solution, cooling liquid, is obtained from the previous

the mixture coming from an aqueous, about 30% solution at least 15

at least one of the salts ammonium sulphate, sodium ren amounts of coolant stirred. That too crystal

chloride and calcium chloride, if the mixture is cooled in this way gradually

expediently cooled to a temperature between -20 and and at the same time by an increasing

-40 ° C. Amount of coolant diluted. In the penultimate

The speed at which the cooling liquid 20 enters chamber 11, only that from the preceding

is added to the solution to be crystallized, chamber 10 is the coming mixture, consists

controlled so that the formation of agglomerates, the thermal equilibrium between the cooling liquid

the pipelines or other conveying means and the mixture of crystals and mother liquors,

could be avoided. In the last chamber 12 it is done in this way

It is also possible, by decanting, to allow the homogeneous mixture obtained to flow into

Cooling liquid is kept out of this liquid, the suspension.

Crystals and the mixture formed by the mother liquors.

to begin with and then the crystals from the parent leading crystallization a smaller or larger one

to deposit caustic solutions. Number of chambers (but at least three)

In general, it is convenient to have the mixture 30.

from cooling liquid and solution to be crystallized As a cooling liquid one can besides cooled

all the while, while the cooling liquid- aqueous salt solutions also liquefied gases like

The ability to stir vigorously in order to avoid halogenated hydrocarbons or the general

uniform temperature in the crystallization gases used for cooling purposes (e.g. sulfur

to ensure resources. 35 dioxide and ammonia), but the

Continuous crystallization can have the disadvantage of using such gases

simple device, e.g. B. an Archimedean leads to the formation of microcrystals, their later

Screw (see attached drawing) carried out filtration can cause difficulties,

will. The device described above can for example

The 40 shown in the drawing in longitudinal section for the crystallization of p-xylene from a Device consists of an elongated mixture used, which is about 70 to holder 1, surrounded by a series of partitions, 80 percent by weight p-xylene, 5 to 7 percent by weight z. B. 2, 3, 4, 5 and 6, in several chambers, z. B. o-xylene, 12 to 15 percent by weight m-xylene and 7, 8, 9, 10, 11 and 12, which in turn contains 4 to 6 percent by weight ethylbenzene. as by means of cooling liquid provided in the lower part of the partition walls, an aqueous salt passages can be created are connected to each other. A wave solution with a density of about 1.2, which is about 13 penetrates the container 1 along its entire length and contains 30 percent by weight calcium chloride and carries a number of sections of a den. The saline solution is placed in a cooling system Archimedean screw with a double part, a temperature between 0 and -40 ° C (preferred in the opposite direction, e.g. B. 14, 15, 16, 17, 50 wise between -20 and -25 ° C) cooled and then 18 and 19, each section within a gradually, with vigorous stirring, the xylene mixture Chamber is arranged. A motor 18 effects the addition of the device described in FIG. Circulation of the shaft 13 and the drain attached to it. The flow time of the mixture through the crystal sections the Archimedean screw. sation device can be easily adjusted by regulating the

An overflow drain pipe 20 opens into the wall 55. Flow in the various pipes are controlled

of the container 1 at the end that corresponds to the. The contact time depends on the concentration of the

Return flow of the Archimedean screw sections to the crystallizing solution and from the temperature

is equivalent to. The liquid to be crystallized depends on the cooling liquid. To ensure easy transport

The supply pipe 21 leads into the camouflaged mixture of crystals, cooling liquid and

mer 7 to receive the farthest 60 mother liquors from the discharge point 20, the content of Kri-

away. Suitable branches 23, 24, 25 expediently occur at about 20 percent by weight

and 26 of a cooling liquid supply pipe 22 held centrally. After pouring off the saline solution and

open into all chambers with the exception of the Kam separation from the mother liquors by filtration

mern 11 and 12, which follow the drainage point 20 on- one obtains p-xylene crystals of a purity between

most lie. By suitable (not shown) advantages 65 92 and 96%. After liquefying the crystals

directions, such as normal taps or the like, can keep this less than 0.1 part per million parts

Flow of coolant through these various pipelines. The crystal yield can be 60 ° / »des

being controlled. Sections 14, 15, 16, 17, 18 exceed starting material.

Claims (2)

Patent claims: 1. Method of crystallizing a solution by introducing a solution immiscible with it and chemically non-reactive cooling liquid in the moved by a screw Solution stream, characterized in that the cooling liquid is supplied to several, one behind the other Places in controllable amounts is added. 2. Apparatus for performing the method according to claim 1, consisting of a horizontal Container with a screw and a and outlet openings for the liquids and crystals, characterized in that the Container through transverse walls containing passages in the lower part into several one behind the other Chambers and the snail is divided accordingly and all chambers, except the last and penultimate chambers are each provided with an inlet for cooling liquid. Considered publications:
German Patent Nos. 552584, 817138;
Austrian patent specification No. 49 486. For this purpose, 1 sheet of drawings