KR950006513B1 - Water scavengers for hydrochloric acid streams - Google Patents

Abstract

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Description

How to reduce the water content in the HC1 gas stream

The present invention relates to a method for removing trace amounts of water from gaseous hydrochloric acid.

In particular, the present invention relates to a process for calcining the water content of the HC1 gas stream to 1 ppm or less by using certain chlorides as scavenger.

The method of the present invention for reducing the content of water in the HC1 gas stream to 1 ppm or less comprises contacting the HC1 gas stream with silicon chloride or metal chlorides having valences of at least tetravalent. The chloride is preferably floating on a solid support.

Typically, HC1 is more reactive than water and hygroscopic, so it is difficult to remove traces of water from HC1. However, silicon and certain high valence metals react more easily with oxide ligands than with chloride ligands. Such metals include, for example, Ti, Zr and W. Typical reactions are as follows:

WCl ₆ + 3H ₂ O... … WO ₃ + 6HCl (1)

SiCl ₄ + 2H ₂ 0... … SiO ₂ + 4HCl (2)

Other suitable chlorides include, but are not limited to TiCl ₄ and ZrCl ₄ .

In some applications, it may be advantageous to use the scavenger of the present invention at low temperatures above the boiling point of HC1. At lower temperatures, the equilibrium constants for water removal will be greater. This effect is very important for scavengers with low equilibrium constants at room temperature (eg WCl ₆ ). Another effect due to low temperatures is that it can lower the vapor pressure of liquid scavengers such as SiCl ₄ and TiCl ₄ , which have high vapor pressure at room temperature. Under high vapor pressures, metals or silicon compounds may be discharged into the purified HC1 stream.

Solid scavengers such as WCl ₆ and ZrCl ₄ can increase the surface area of the scavenger by adsorbing on solid supports such as macroreticular styrene-divinylbenzene polymers.

The vapor pressure of the liquid chloride scavenger is reduced without immobilizing the chloride on a solid support with free-OH groups or OM 'groups (M' is an alkali or alkaline earth metal) on the surface without the temperature falling below room temperature. Can be. Such supports include wide area inorganic supports such as alumina and silica. Polymers containing functional groups that react with chlorides, such as polyvinyl alcohols, can also be used as supports. As an example, the passivation reaction generated when using SiCl ₄ is as follows.

SiCl ₄ + HOMO ₃ ... … Cl ₃ SiOMO ₃ + HCl (3)

Here, HOMO ₃ represents a metal oxide or hydroxide surface. SiCl ₄ immobilized on alumina is the preferred scavenger. The liquid chloride scavenger can either react directly with the solid support or evaporate by heating prior to contacting the support. When the support is treated with gaseous chloride, loosely bound chloride must be removed by treating the support with immobilized chloride on the surface with hot HC1 gas.

당 2

의 수증기이다. 이어서 정제된 가스 스트림을 활성화된 알루미나를 함유한 포스트-트랩에 통과시킴으로서 잔재된 미량의 실리콘 또는 금속 화합물을 제거할 수 있다. 예를 들면, 열-처리된 SiCl₄/Al₃O₃스캐빈저 및 활성화된 알루미나 포스트-트랩이 통과된 후, 정제된 HC1 스트림내 실리콘의 수치는 통상적으로 0.05ppm 이하이다(HC1 스트림을 100ml의 물에 통과시킨 후 원소 흡착도로서 측정). 포스트-트랩에 사용된 알루미나는 17시간 동안 약 190℃의 질소스트림하에서 가열하고 사용전에 냉각시킨다.Because of the detrimental use of discharging the metal or silicon compound into the purified HC1 stream, it is desirable to heat the alumina with immobilized chlorides on the surface to a temperature of about 190 ° C. for 17 hours before nitrogen contact with the HC1 stream. . The heat treatment will remove the weakly bound metal or silicon chloride. The dose of chloride-alumina scavenger is typically about bed 1

2 per

Water vapor. The purified gas stream can then be passed through a post-trap containing activated alumina to remove residual traces of silicon or metal compounds. For example, after passing through the heat-treated SiCl ₄ / Al ₃ O ₃ scavenger and activated alumina post-trap, the level of silicon in the purified HC1 stream is typically 0.05 ppm or less (100 ml of HC1 stream). Measured as elemental adsorption after passing through water). The alumina used in the post-trap is heated under a nitrogen stream of about 190 ° C. for 17 hours and cooled before use.

The content of water in the purified gas stream is 1 ppm or less, preferably 0.5 ppm or less.

The removal of moisture from the HC1 gas stream to minimize oxidation is a very important task in the semiconductor industry. For example, anhydrous HC1 is needed to prevent contamination of the wafer by cleaning the oven used in the manufacture of semiconductor wafers and to prevent oxides from forming on the wafer surface by etching the silicon wafer. Anhydrous gaseous phase HC1 is used to convert ferrosilicon (FeSi) to HSiCl ₃ and is also used in the manufacture of silicon wafers. It is also important to prevent corrosion of the tubes used to carry HC1.

Example 1

Acidic Al ₂ O ₃ (Woelm ^R A, Akt. 1, manufactured by Woelm Pharma Gmbh & Co) was charged into a 150 ml sample cylinder of stainless steel. The alumina was dried under a stream of nitrogen at 200 ° C. for 10 hours.

Silicon tetrachloride functionalized Al ₂ O ₃ scavenger was prepared as follows. After flowing 30 vol% SiCl ₄ solution in nucleic acid into the dried Al ₂ O ₃ layer, SiCl ₄ was kept in contact with the bed for one hour. The layer was then washed with four bed volumes of sparged hexanes. The sample was dried under a stream of N ₂ at 65 ° C. to remove hexane. Volatile components were removed by maintaining the functionalized alumina at 190 ° C. for 17 hours.

The heat-treated scavenger was placed in a polymerization tube of ". N ₂ was passed through the sample. No acidity was detected by the tricolor pH paper. N ₂ was then passed through water in a 4" polymerization tube. And water-containing gas was passed through a scavenger. The vented gas became acidic, which shows that SiCl ₄ can remove moisture from the gas stream in accordance with Scheme 2 above.

Example 2

Silicon tetrachloride-functionalized Al ₂ O ₃ scavenger was prepared and tested as described in Example 1 above, except that pure SiCl ₄ was flowed into the dried alumina rather than a solution of SiCl ₄ in hexane. The volatiles were removed by leaving the reaction mixture for at least one hour before heating.

Example 3

Acid alumina was charged into a 1-gallon stainless steel reactor. The alumina was dried overnight under N ₂ stream at 190 ° C.

Silicon tetrachloride-functionalized alumina scavenger was prepared as follows. Silicon tetrachloride (250 ml) was transferred via cannula into a bubbler heated to a temperature of 57 ° C. SiCl ₄ that was all passed through the evaporation of the heated nitrogen gotta SiCl ₄ when passing through the alumina in the reactor. Any loosely bound SiCl _{4 was} then removed by passing a heated HC1 gas through a preheated coil through a SiCl ₄ -functionalized alumina for 5 hours. The excess HC1 was then removed by maintaining the scavenger under a nitrogen stream at 190 ° C. for at least 8 hours.

Example 4

The capacity of SiCl ₄ -functionalized alumina scavenger to remove water from the gas stream was measured via the following method. N ₂ was bubbled through water maintained at 24 ° C. At this temperature, the vapor pressure of water was 24 mmHg. Wet N ₂ was passed through a 30 ml scavenger sample in a polymerization ash tube at a rate of 200 ml per minute.

The gas exiting the tube containing the scavenger was passed through 200 ml of water. In the case of stainless steel, gas was injected through a Teflon tube because of the problems associated with the pH electrode. The H + concentration of water was measured with a pH meter as a function of time. The wet N ₂ flow rate was 0.302 standard liters per minute. If you know the trap volume of water, the final proton concentration of the water trap, and the bed volume, you can calculate the bed capacity. The capacity of the various types of SiCl ₄ / Al ₂ O ₃ scavenger is as follows.

Example 5

The HC1 gas stream was mixed with nitrogen containing a predetermined amount of water so that the dried HC1 gas stream could contain 5 ppm of water. The HC1 was then passed under 1 atmosphere to a 500 ml column containing heat-treated SiCl ₄ / Al ₂ O ₃ scavenger prepared according to the method described in Example 1. The flow rate of HC1 gas through the column was 160 volumes of gas per bed volume per hour and was run at room temperature. The process was repeated again with a gas stream containing 20 ppm water, except that the water content of the off gas increased 1/2 hour for 2 hours and the flow rate to 760 volumes of HC1 per bed volume per hour. In each case the moisture content of the HC1 stream was less than 0.1 ppm at the end of the two hours. The moisture content of the HC1 stream was analyzed by Anal. Chem. It was measured according to the method described in (Flaherty et al., 1986, 58, 1903-1904).

Example 6

Macroreticular styrene / divinylbenzene (PSDVB) polymer (Amberlite XAD4 manufactured by Rohm and Hass) was washed with water and decanted to remove fine particles. The polymer was washed sequentially with three bed volumes of water, methanol, isopropyl alcohol and hexanes. A large amount of solvent was removed by passing air through the bed for about 2 hours. The air-dried resin was charged into a stainless steel reactor and dried under a stream of nitrogen at 110 ° C. for 10-12 hours.

A supported WCl ₆ scavenger was prepared as follows. The dried PSDVB (25 g) was mixed with WCl ₆ (2.52 g) in 50 ml sparged toluene (50 ml). Toluene was removed by passing nitrogen stream through the mixture at 110 ° C. overnight.

For testing, PSDVB adsorbed on the surface of WCl ₆ was placed in the burette. The dried nitrogen was passed through a PSDVB-WCl ₆ scavenger. No acidity was detected with the tricolor pH paper. Subsequently, N ₂ was bubbled by passing through the 4 "polymerization reaction tube and water-dropping gas was passed through the scavenger. The exhaust-gas became acidic, so that WCl ₆ was reacted according to the above reaction formula (1). It was found that moisture could be removed from the gas stream.

Claims (4)

Contacting the HCl gas stream with silicon chloride or metal chloride having a valence of at least 4, wherein the content of water in the HCI gas stream is less than or equal to 1 ppm. The method of claim 1 wherein the chloride is SiCl ₄ . The method of claim 2, wherein the SiCl ₄ is immobilized by reaction with a solid support. The method of claim 3 wherein the gaseous SiCl ₄ is reacted with an alumina support.