RU2817355C1 - Filter element for making highly pure anhydrous aluminium chloride - Google Patents

Abstract

FIELD: filters.

SUBSTANCE: filter element can be used to purify aluminium chloride from organic and metal impurities in order to obtain a material of special purity in a single process of sublimation followed by sublimation. A filter element based on an aluminium-zinc alloy comprises layers of nozzle made in the form of spiral rings made of aluminium-zinc alloy foil and pyrocarbon wool located above the nozzle layer in a ratio of 1:1 to 1: 4 in height. The total height of the filter module (H) is (1-2)D, where D is the diameter of the sublimate-conducting tube. The filter layers are packaged in a quartz fabric cover to prevent filter components from getting into the finished product.

EFFECT: eliminating the multi-stage purification process of aluminium chloride with the achievement of a level of purity that meets the requirements for a particularly pure product, namely, it provides the possibility of obtaining product with a main substance content of at least 99.999 wt.% in one stage.

1 cl, 2 tbl, 3 ex

Description

The invention relates to new filter elements based on aluminum alloy and pyrolytic carbon wool, intended for obtaining especially pure anhydrous aluminum chloride in the process of purifying a technical product from organic impurities and metal impurities.

Aluminum chloride of technical purity is obtained by chlorinating aluminosilicates (kaolin, bauxite) or aluminum metal when heated. It is mainly used in the chemical industry, being the most common catalyst in organic chemistry for refining oil into fractions. This process is based on the property of oil, when heated with aluminum chloride, to decompose to produce gaseous and light hydrocarbons of the gasoline type. It is also used in the production of detergents, dyes and many other products.

The finished technical product is stored and transported in plastic bags packed in metal barrels. Anhydrous aluminum chloride hydrolyzes very easily, gradually turning into oxychloride and releasing hydrochloric acid vapors, which destroys plastic bags. The product acquires organic impurities and an uncharacteristic color. Thus, technical aluminum chloride has a purity of 99-99.9% by weight, contains a significant (up to 20% depending on the duration and method of storage of the material) amount of hydrolyzed forms (aluminum oxide and oxychlorides of various compositions), as well as a significant amount of organic impurities. The main metal impurities contained in the technical product are: calcium (up to 0.003%), magnesium (up to 0.002%), silicon (up to 0.0015%), iron (up to 0.002%), copper (up to 0.001%), in addition , a technical product almost always has color.

There are a number of processes that require especially pure aluminum chloride.

The following requirements are imposed on high-purity aluminum chloride: (TU 20.13.31-001/0-11640530-2020):

Table 1 No. Indicator name Meaning 1 Appearance White powder without foreign inclusions. 2 Main substance content, %
Mass fraction of impurities, %, no more
Li
Na
Mg
Ca
K
Si
Ti
Cr
Fe
Ni
Cu
Zn 99,999
0.00001
0.00002
0.0002
0.0003
0.0002
0.0003
0.00002
0.00005
0.00005
0.00005
0.00001
0.00001 3 Mass fraction of water, %, no more 0.02

Methods for producing high-purity and especially pure aluminum chloride are based on its ability to sublimate (sublimation temperature 183°C) at normal pressure and melt (melting point 192.6°C) at elevated pressure. Methods for its production based on this are chlorination of the metal followed by distillation of chloride vapors and their condensation on cooled surfaces and rectification of aluminum chloride under pressure.

The distillation unit is a steel column filled with Raschig rings for purifying aluminum chloride. It showed the practical possibility of quite effectively separating aluminum and iron chlorides in a batch process at an operating pressure of 2.5 kg/cm ² ; the iron content in the resulting product was 0.015%, which does not at all satisfy the requirement for a particularly pure substance (patent SU199128).

To obtain high-purity aluminum chloride, an installation has been proposed that allows burning metallic aluminum in a flow of chlorine high-frequency plasma at a temperature of 5800°K, followed by multi-stage condensation and separation of chlorine and aluminum chloride vapors (patent RU 2259946 C1).

In addition to the need to use high-purity starting materials, aluminum and specially purified chlorine, the method requires high energy consumption and special equipment (plasma oven and high-frequency generator).

Aluminum chloride easily sublimes when heated (sublimates) and then desublimates, forming crystals of various sizes. To carry out sublimation, an apparatus is known, which is a simple or plate-shaped column equipped with a heated fiberglass filter located at the outlet of the vapor of the sublimated substance (Vacuum apparatus and chemical engineering devices, Shumsky K.P. ed. 2, Moscow, Mechanical Engineering, 1974, p. 160).

However, with a single purification of the material, a sufficient degree of purification from metal impurities and the organic phase is not achieved; multiple or multi-stage purification is required.

The technical result to which the claimed invention is aimed is the possibility of obtaining a product with a main substance content of at least 99.999 wt.% in one stage.

To achieve this result, a filter element is proposed, consisting of a fabric cover, a layer of metal nozzle and a layer of pyrocarbon wool, in which the metal nozzle is made in the form of spiral rings made of an aluminum-zinc alloy, rolled into foil 0.1-0.15 mm thick, and a layer of pyrolytic carbon wool is located above the layer of nozzle and the ratio between the layers of nozzle and pyrolytic carbon wool is from 1:1 to 1:4 in height with a total height of the filter element equal to (1÷2)D, where D is the diameter of the sublimate-conducting tube.

In fig. Figure 1 shows a filter element with a height H in a tube with an internal diameter D, which contains a cover (1) made of quartz fabric, a layer (2) of a metal nozzle, a layer (3) of pyrolytic carbon wool located above the nozzle layer.

A filter element designed to capture vapors of organic impurities and metal impurities (chromium, iron, nickel, copper, zinc) is inserted into a tube for transporting sublimated aluminum chloride, and the height of the filter element depends on the diameter of this tube.

Numerous experiments on the influence of layer height on the content of the listed impurities in the finished product have shown that the required result is achieved with a layer ratio nozzle and pyrocarbon wool, which ranges from 1: 4 to 1:1 in height, and the height of the filter element H = (1÷2) D, where D is the diameter of the sublimate-conducting tube.

As a metal nozzle, foil 0.1-0.15 mm thick rolled into spiral (concentric) rings 8-10 mm wide, rolled from an aluminum alloy with zinc, is used.

When the layer of pyrolytic carbon wool is reduced (the ratio of the spiral nozzle to pyrolytic carbon wool is less than 1:1), a breakthrough of colored particles is observed, i.e. insufficient cleaning.

When the layer of metal nozzle is reduced (the ratio of the spiral nozzle to pyrolytic carbon wool is more than 1:4), the removal of chromium, iron, and nickel impurities is carried out insufficiently.

Exceeding the total height of the filter element by more than 2 times the diameter of the tube (H > 2D) leads to significant resistance to the flow of aluminum chloride vapor, and the process slows down.

Reducing the total height of the filter element relative to the diameter of the tube (H < D) leads to a significant decrease in the degree of purification from both metal impurities and organic impurities (the appearance of a colored product).

Example 1

Technical yellow aluminum chloride is loaded into the cleaning reactor. A quartz tube with an internal diameter of 35 mm is connected to the reactor, into which a filter element with a total height of 70 mm (H = 2D) is inserted. The filter element consists of a 14 mm thick layer of metal nozzle made of an aluminum-zinc alloy, rolled into foil, and a 56 mm thick layer of pyrolytic carbon wool (layer ratio 1:4), packed in a quartz fabric cover. As a result of a single sublimation process followed by desublimation, a white product with an impurity content that meets the requirements for high-purity aluminum chloride is obtained.

Example 2

Technical yellow aluminum chloride is loaded into the cleaning reactor. A quartz tube with an internal diameter of 50 mm is connected to the reactor, into which a filter element with a total height of 50 mm (H=D) is inserted. The filter element consists of a layer of metal nozzle 25 mm thick, made of an aluminum-zinc alloy rolled into foil, and a layer of pyrocarbon wool 25 mm thick (layer ratio 1:1), packed in a quartz fabric cover. As a result of a single sublimation process followed by desublimation, a white product with an impurity content that meets the requirements for high-purity aluminum chloride is obtained.

Example 3

Technical yellow aluminum chloride is loaded into the cleaning reactor. A quartz tube with an internal diameter of 56 mm is connected to the reactor, into which a filter element with a total height of 84 mm (H = 1.5D) is inserted. The filter element consists of a layer of metal nozzle 20 mm thick, made of an aluminum-zinc alloy rolled into foil, and a layer of pyrocarbon wool 64 mm thick (layer ratio 1: 3.2), packed in a quartz fabric cover. As a result of a single sublimation process followed by desublimation, a white product with an impurity content that meets the requirements for high-purity aluminum chloride is obtained.

The results of the experiments carried out in examples 1-3 on the use of the filter element are shown in table 2.

table 2 Determined impurity elements in aluminum chloride Content, % Original product Final product
Example 1 Final product
Example 2 Final product
Example 3 Li
Na
Mg
Ca
K
Si
Ti
Cr
Fe
Ni
Cu
Zn -
0.0001
0.002
0.0008
0.0008
0.0005
0.0016
0.0004
0.0014
0.0002
0.0002
0.0006 <0.00001
0.00002
0.0002
0.0003
0.0002
0.0003
<0.00002
<0.00005
<0.00005
<0.00005
<0.00001
0.00001 <0.00001
0.00001
0.0002
0.0002
0.0002
0.0003
<0.00002
<0.00005
<0.00005
<0.00005
<0.00001
<0.00001 <0.00001
0.00001
0.0001
0.0002
0.0002
0.0002
<0.00002
<0.00005
<0.00005
<0.00005
<0.00001
<0.00001

The results presented show that the proposed filter design provides a one-time purification of aluminum chloride to the required purity.

Claims (1)

A filter element for the process of producing aluminum chloride by sublimation and subsequent desublimation, consisting of a fabric cover, a layer of metal nozzle and a layer of pyrolytic carbon wool, in which the metal nozzle is made in the form of spiral rings made of an aluminum:zinc alloy rolled into foil, and the layer of pyrolytic carbon wool is located above the layer of nozzle and the ratio between the layers of nozzle and pyrocarbon wool is from 1:1 to 1:4 in height with a total height of the filter element equal to (1-2)D, where D is the diameter of the sublimate-conducting tube.