JPH1111905A - Method for purification of methane-containing hydrogen chloride of gas and use of this hydrogen chloride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to decrease the methane component in methane- contg. hydrogen chloride of gas to the extent of satisfying the purity requirement of the chlorine of an electron level by partially condensing this hydrogen chloride under and at a specific pressure and temp. and separating a gaseous component, then isolating the liquefied hydrogen chloride after evaporation. SOLUTION: Condensation conditions are an overpressure of 8 to 13 bare and -22 to -36 deg.C. The degree of liquefaction of the partial condensation is 0.1 to 0.3. The hydrogen chloride component existing in liquid after the partial condensation is evaporated under the absolute pressure of 5 to 20 bar and is heated to 120 to 220 deg.C and is then brought into reaction in the adiabatically operating reactor with the gaseous chlorine of the amt. at which 100 to 2000 vol.ppm chlorine is still contained in the hydrogen chloride at the time of releasing from the reactor in the presence of an active carbon catalyst impregnated with a transition metal chloride. The reaction product is then brought into reaction with 100 to 1500 vol.ppm olefin or chloroolefin at 80 to 180 deg.C by the same catalyst in the second adiabatically operating reactor. Finally, the pure hydrogen chloride is separated by low-temp. compression rectification.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing high purity hydrogen chloride and to the use of said hydrogen chloride in producing semiconductor materials.

[0002]

BACKGROUND OF THE INVENTION Wafer plates, such as those used to produce computer chips, are manufactured in multiple steps.
At that time, first, trichlorosilane is thermally decomposed, and the resulting polycrystalline silicon is further processed into a rod-shaped single crystal by a zone melting method or a crucible melting method, and finally, a single crystal rod is sawn to produce a wafer. I do. It is important to prevent contamination of the silicon single crystal by foreign atoms as much as possible. This is especially true for carbon contamination (silicon 1
less than 10 ¹⁵ C atoms per cm ³ ).

However, in producing trichlorosilane, the starting product obtained by reacting ferrosilicon with hydrogen chloride, hydrogen chloride from various sources is used, and the hydrogen chloride is often an alkane, an alkene or an alkene. And is contaminated with hydrocarbon compounds such as alkynes. Hydrogen chloride resulting from 1,2-dichloroethane pyrolysis is particularly contaminated with ethylene and acetylene. The hydrogen chloride resulting from the allyl chloride synthesis contains higher olefins, such as propylene. Hydrogen chloride generated during methane chlorination and methyl chloride chlorination is alkane,
Especially contaminated with methane.

A method for purifying hydrogen chloride resulting from 1,2-dichloroethane pyrolysis is disclosed in German Patent No. 3,817,938.
From this specification, it is possible to remove acetylene and ethylene from hydrogen chloride. In the first step, acetylene and ethylene are chlorinated with excess chlorine to give the corresponding saturated or unsaturated chlorohydrocarbons. In the second step, the excess chlorine from the first step is
It is removed by reacting with an olefin that is gaseous at atmospheric pressure and boils at -50 to + 10 ° C. at atmospheric pressure, followed by separation of the hydrogen chloride by cold compression rectification.

[0005] German Patent No. 3817938 discloses
According to the indicated three-step method for purifying hydrogen chloride,
From hydrogen to ethylene and acetylene;
Ken and alkyne can be separated. But
The alkane is removed by distillation during chlorination with this catalyst.
It is converted to a high-boiling substance that cannot be separated. However C _Three
Alkanes and higher homologues are the last step in the process
Which can be separated from hydrogen chloride by rectification
Because they boil at a higher temperature than hydrogen chloride
It is. Methane and ethane boil easily with hydrogen chloride
It is spotted and therefore can be separated from hydrogen chloride by distillation.
And remains in hydrogen chloride.

[0006] In the synthesis of the above-mentioned trichlorosilane from ferrosilicon and hydrogen chloride, which is the first step in the production of extremely pure silicon, the ethane contained in the purified hydrogen chloride does not cause any problems. This is because, for example, the ethyldichlorosilane (HSiCl ₂
C ₂ H ₅ ) can be easily separated by distillation from silicon tetrachloride (boiling point 56.7 ° C.), a possible by-product of trichlorosilane and the trichlorosilane synthesis, due to its boiling point which is higher by about 35 ° C. Because. However, when synthesizing trichlorosilane from ferrosilicon and hydrogen chloride, methane is already 20 to 1 in hydrogen chloride.
It interferes at about 00 ppm by volume. That is, methane reacts with methyldichlorosilane (HSiCl ₂ CH ₃ ,
Boiling point 40.4 ° C.), which is separated from the desired product, trichlorosilane (SiHCl ₃ , boiling point 31.7 ° C.) by distillation, due to the narrow boiling point difference, even if many yields are lost. Extremely difficult. The methane content in the starting product, trichlorosilane, raises the carbon content in the final product, single crystal silicon, to unacceptable values.

[0007]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method for reducing the methane content of hydrogen chloride from various sources which can reduce the methane content in hydrogen chloride to the extent that it meets the purity requirements of electronic chlorine. Develop an economical method for purifying hydrogen.

[0008]

Surprisingly, when partially condensing methane-containing hydrogen chloride, methane is concentrated in the hydrogen chloride gas phase, and the liquefied component significantly dissolves the dissolved methane. It was found to be contained in concentrated form.

It is an object of the present invention to provide a process for purifying gaseous, methane-containing hydrogen chloride by partially condensing gaseous hydrogen chloride at an overpressure of 8 to 13 bar and a temperature of -22 ° C. to -36 ° C. The gaseous component is separated, and liquefied hydrogen chloride is isolated after evaporation.

The process of the present invention purifies methane-containing hydrogen chloride in gases from various sources, such as 1,2-dichloroethane pyrolysis to produce vinyl chloride, methane chlorination and methyl chloride chlorination. Suitable for. Mixtures of hydrogen chlorides from various methods of producing hydrogen chloride can also be used.

The degree of liquefaction during partial condensation (Verfluessigu
ngsgrad) depends on the proportion of the amount of methane in the hydrogen chloride and on the desired purity of the hydrogen chloride liquefied by the process according to the invention. Along with this, the degree of liquefaction determines the economics of the process according to the invention.

The following relational expression is determined by experience.

The volume p of methane in the condensed hydrogen chloride component
pm = 0.0485 × ppm of methane in gaseous starting hydrogen chloride, preferably operating at a liquefaction degree of 0.1 to 0.3, ie gaseous, methane-containing hydrogen chloride 0.1 to 0.3.
Partially condense parts by weight.

Using the process according to the invention, it is possible to use hydrogen chloride having a methane content of less than 5 ppm by volume, based on 100 ppm by volume of methane in the starting product. Such high-purity hydrogen chloride can be used in a pre-process for producing pure silicon, for example in the synthesis of trichlorosilane. Non-condensed, methane-rich components
For example, it can be used for the production of oxychlorination, methanol esterification, or hydrochloric acid.

In the case of purifying gaseous hydrogen chloride which, in addition to methane, also contains a high proportion of alkenes or alkynes, the process according to the invention further provides German Patent 38,793.
The three-stage purification method described in the specification of Japanese Patent No. 8 can be carried out.

For this purpose, the hydrogen chloride component present in the liquid after the partial condensation is evaporated at a pressure of 5 to 20 bar absolute, heated to a temperature of 120 to 220 ° C. and in an adiabatically operating reactor, In the presence of an activated carbon catalyst impregnated with a transition metal chloride, it reacts on discharge from the reactor with an amount of chlorine gas which still contains 100 to 2000 ppm by volume of chlorine in hydrogen chloride. In a second step, in a second adiabatically operating reactor, in the presence of the same catalyst as the first reactor,
At a temperature of from 80 to 180 ° C., the reaction mixture is reacted with an olefin or chloroolefin which is gaseous at atmospheric pressure and boils at atmospheric pressure in the temperature range from -50 ° C. to + 10 ° C., wherein the olefin or chloroolefin is The amount is such that the olefin or chloroolefin is still contained in the hydrogen chloride discharged from the reactor in an amount of 100 to 1500 ppm by volume. In the last step, the reaction mixture obtained in these steps is separated by cold compression rectification and pure hydrogen chloride is separated off at 9-14 bar absolute pressure and -20
Isolate by condensation at a temperature between -40 and -40C. This variant is described in DE 38 17 938 at column 2, line 34 to 5
Details are described in column 55, line.

[0017]

The present invention will be described in detail with reference to the following examples.

Example 1 5 kph of gaseous hydrogen chloride with 50 ppm by volume of methane
The mol is brought to 8.5 bar overpressure and cooled to -33 DEG C., liquefying 0.5 kmol / h of hydrogen chloride (degree of liquefaction of 0.5).
1), 4.5 kmol of hydrogen chloride per hour remained as a gas. The liquefied hydrogen chloride was separated and subsequently evaporated in a heat exchanger. Separation and subsequent measurement of the methane content of 2.40 ppm by volume in the evaporated liquid hydrogen chloride. The gaseous hydrogen chloride remaining on partial condensation contained 55.3 ppm of methane.

Example 2 The procedure was as in Example 1, but with an overpressure of 8.5 bar and -3.
At a temperature of 3 ° C., 5 kmol / h of hydrogen chloride having 50 ppm by volume of methane to 1.25 kmol / h of hydrogen chloride were liquefied (liquefaction degree 0.25). The subsequently evaporated liquid hydrogen chloride contained only 2.42 ppm by volume of methane and the residual gaseous hydrogen chloride contained 65.9 ppm by volume of methane.

Example 3 The procedure was as in Example 1, except that 5 kmol / h of hydrogen chloride having a methane content of 80 ppm by volume was cooled to -25 ° C. at an overpressure of 11.5 bar. 0.75 kmol / h of components were condensed (liquefaction 0.15). The condensed component was evaporated in the heat exchanger, and 3.9 vol ppm of the methane component was measured. The gaseous hydrogen chloride component remaining on partial condensation contained 93.4 ppm by volume of methane.

EXAMPLE 4 1,2-Dichloroethane pyrolysis yields vinyl chloride at 3 h / h
A cracked gas mixture of 0 t and 482 kmol / h of hydrogen chloride was obtained. Hydrogen chloride was separated from the cracked gas mixture at -33 ° C and 8.5 bar overpressure. The gaseous hydrogen chloride released from the column contains 60 ppm by volume of methane and 2.
It was contaminated with 5 ppm by volume, 362 ppm by volume of ethylene, 2560 ppm by volume of acetylene, 1.2 ppm by volume of vinyl chloride and 2.1 ppm by volume of ethyl chloride.

At the above pressure and temperature levels, 110 kmol of contaminated hydrogen chloride per hour is liquefied (liquefaction of 0.2
3) Subsequently, after increasing the pressure via a liquid HCl pump, the mixture was evaporated at an overpressure of 13 bar. The evaporated liquid hydrogen chloride still has 3.4 vol ppm methane, 0.7 vol pp ethane
m, ethylene 20.9 ppm by volume, acetylene 386
It contained 6.6 ppm by volume, 1.1 ppm by volume of vinyl chloride and 6.2 ppm by volume of ethyl chloride.

[0023] The mixture was preheated to 0.99 ° C., after addition of the corresponding chlorine gas per hour 22.5 m ³ pressure, CuCl ₂ and MnCl ₂ catalyst 0.8 m ³ comprising each 16% by weight doped activated carbon is filled Into the first reactor. In carrying out the adiabatic reaction, ethylene, acetylene and vinyl chloride are reacted with chlorine to form 1,1,2,2-
Tetrachloroethane, 1,2-dichloroethane and 1,
1,2-Trichloroethane was obtained. The reaction mixture is about 1
The first reactor was left with an excess of 000 ppm by volume of chlorine. The concentration of ethylene and acetylene is 1 volume pp
m.

5 m / hr of gaseous vinyl chloride at a corresponding pressure
³ were mixed, the mixture was intermediate cooled to about 125 ° C., the free chlorine is reacted with vinyl chloride, 1,1,2-trichloroethane to produce the reaction mixture, the same catalyst 0.5m in the first reactor ³ was introduced into a second reactor packed. The reaction mixture is chlorine-free and contains approximately 1000 volumes
Leave the second reactor with a content of pm.

After cooling and partial condensation of the chlorinated product formed, the liquid hydrogen chloride is refluxed in the distillation column at 12.5 bar overpressure and at an overhead temperature of -23 ° C. as reflux to the column. The gas stream was fractionated by refluxing 1.5 t / h.
In order to maintain a constant distillation state and a constant distillation temperature of about 75 ° C., the distiller was fed with liquid at about 20 kg per hour of vinyl chloride. The products formed at the bottom of the column are, in addition to vinyl chloride and ethyl chloride, chlorinated products, 1,2-dichloroethane, 1,1,2-trichloroethane and 1,1,1,2
It contained 2,2-tetrachloroethane. Hydrogen chloride generated at the top of the column was used to produce trichlorosilane with the following purity. Methane 3.4 vol ppm ppm Ethane 0.7 vol ppm Ethylene 0.1 vol ppm Acetylene 0.4 vol ppm ppm Vinyl chloride 0.3 vol ppm Ethyl chloride 9.1 vol ppm

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Klaus Haselwalter Germany, Emerging Day Bulstraße 3 (72) Inventor Hermann Klaus, Germany Marktur Ada Luber-Stifter-Strasse 1a (72) Inventor Albin Frank Germany Burghausen Spitalgasse 208

Claims (5)

[Claims] 1. A process for purifying gaseous, methane-containing hydrogen chloride, comprising the steps of: overpressure of 8 to 13 bar and -22 ° C.
A method for purifying gaseous methane-containing hydrogen chloride, comprising partially condensing gaseous hydrogen chloride at a temperature of -36 ° C, separating gaseous components and isolating liquefied hydrogen chloride after evaporation. . 2. The process as claimed in claim 1, wherein the partial condensation at a liquefaction degree of 0.1 to 0.3 is carried out. 3. The hydrogen chloride component present in the liquid after partial condensation is a) evaporated at a pressure of 5 to 20 bar absolute,
In a reactor heated to a temperature of 20 ° C. and operated adiabatically, in the presence of an activated carbon catalyst impregnated with transition metal chlorides, chlorine is still present in the hydrogen chloride on discharge from the reactor.
B) reacting with an amount of chlorine gas containing from 0 to 2000 ppm by volume; b) in a second adiabatically operating reactor in the presence of the same catalyst as in the first reactor, at a temperature of 80 to 180 ° C. At which the reaction mixture is gaseous at atmospheric pressure and from -50 ° C to +
The olefin or chloroolefin boiling in the temperature range of 10 ° C. is reacted with the olefin or chloroolefin in such a way that the amount of olefin or chloroolefin is still less than 100% in the hydrogen chloride discharged from the reactor.
C) The reaction mixture obtained in these steps is separated by low-temperature compression rectification and pure hydrogen chloride is separated off at a pressure of 9-14 bar absolute and -20 ° C. 3. The process according to claim 1, wherein the isolation is by condensation at a temperature of 40.degree. 4. The method according to claim 1, wherein the semiconductor material is manufactured.
Use of hydrogen chloride obtained by the method according to any one of the above. 5. Use according to claim 4, wherein hydrogen chloride is used for the synthesis of trichlorosilane.