Chemistry of inorganic compounds – Halogen or compound thereof – Hydrogen halide
Patent
1995-07-26
1998-10-27
Lewis, Michael
Chemistry of inorganic compounds
Halogen or compound thereof
Hydrogen halide
95901, C01B 707, B01D 5300
Patent
active
058274928
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This application is a national filing under 35 USC 371 of International Application No. PCT/US93/00455 filed Jan. 28, 1993.
This invention relates to purifying hydrochloric acid and more particularly, to the purification of impure hydrochloric acid containing halogenated hydrocarbon impurities.
BACKGROUND
Hydrogen chloride, anhydrous or in aqueous solution as hydrochloric acid, is commercially valuable product which has a wide variety of uses.
Hydrogen chloride is a by-product in the preparation of fluorinated aliphatic hydrocarbons. These include fluorocarbons produced by the reaction of hydrogen fluoride with chlorinated derivatives and also fluorocarbons produced by the hydrogenolysis of chlorinated derivatives. For example, Japanese Kokai No. 3-99026 discloses the catalytic reaction of CClF.sub.2 CF.sub.3 (CFC-115) with hydrogen to produce CHF.sub.2 CF.sub.3 (HFC-125). For each mole of HFC-125 produced, one mole of HCl is also formed. U.S. Pat. No. 4,766,260 discloses the preparation of CHCl.sub.2 CF.sub.3 (HCFC-123) and CHClFCF.sub.3 (HCFC-124) by the reaction of HF and a tetrahaloethylene containing at least one chlorine atom. In addition to HCl which is produced as one mole of HCl per atom of chlorine replaced by fluorine, CHF.sub.2 CF.sub.3 (HFC-125) is formed in amounts varying from 0.5% to 10% depending on the catalyst used. U.S. Pat. No. 5,036,036 discloses the preparation of CFC-115 and CF.sub.3 CF.sub.3 (FC-116) by the reaction of HF and CCl.sub.3 CF.sub.3 (CFC-113) over a chromium oxide catalyst. Typically, product mixtures from these processes are distilled to provide a number of fractions. Normally, HCl containing halogenated hydrocarbon impurities may be obtained as a result of such distilling.
Various methods have been used to remove organic impurities from anhydrous HCl, including absorption with a solvent; liquefaction and distillation; oxidation or combustion; and chemical reaction of the impurities followed by either sorption or distillation. The most common method of purification is by distillation. However, some of the halogenated hydrocarbon impurities occasionally exhibit vapor-liquid equilibrium (i.e., VLE) pinch points and are near azeotropes with HCl; and distillation is not practical for separating trace amounts of halogenated hydrocarbons from the hydrogen chloride.
Both carbon based and zeolite based sorbents have been proposed for various separations. The effectiveness of separation with either sorbent varies with the chemical components and the sorbents involved. The successful design of sorbent based systems is considered highly dependent upon experimental determination of whether the relative sorbencies of the particular compounds are suitable for such systems. U.S. Pat. No. 4,902,312 discloses a method for removing HF and HCl from chlorofluorocarbons using certain carbon molecular sieves to remove these acids from the chlorofluorocarbons.
SUMMARY OF THE INVENTION
We have found that saturated and olefinic halogen substituted organic impurities of the formula C.sub.a H.sub.b Cl.sub.c F.sub.d, wherein a is an integer from 1 to 4, b is an integer from 0 to 9, c is an integer from 0 to 9 and d is an integer from 1 to 10, provided that b+c+d equals 2a+2 for acyclic compounds and equals 2a for cyclic compounds and for olefinic compounds, can be substantially removed from impure hydrogen chloride containing said organic impurities by using a sorbent for said impurities selected from the group consisting of activated carbons and inorganic molecular sieves (e.g., silicalites and zeolites). The present invention provides a process for purifying impure hydrogen chloride containing at least one impurity of said formula which comprises the step of contacting the impure hydrogen chloride containing said halogen substituted organic impurities with said sorbent at a temperature within the range of -20.degree. C. to 300.degree. C. and a pressure within the range of 10 kPa to 3000 kPa for a period of time sufficient to remove a substantial amount of said halo
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Corbin David R.
Mahler Barry Asher
E. I. Du Pont de Nemours and Company
Hendrickson Stuart L.
Lewis Michael
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