KR100486681B1 - Azeotrope-like compositions of difluoromethane and chlorine - Google Patents

Abstract

The present invention relates to a mixture of difluoromethane ("HFC-32") and chlorine. More specifically, the present invention provides an azeotrope-like composition composed of HFC-32 and chlorine.

Description

Azeotrope-like compositions of difluoromethane and chlorine {AZEOTROPE-LIKE COMPOSITIONS OF DIFLUOROMETHANE AND CHLORINE}

The present invention relates to a mixture of difluoromethane ("HFC-32") and chlorine. More specifically, the present invention provides an azeotrope-like composition of HFC-32 and chlorine.

Chlorine is used in many industrial processes, including the manufacture of chlorinated organic and inorganic chemicals. For example, methane can be chlorinated to produce methylene chloride, chloroform or carbon tetrachloride. As another example, hydrogen and chlorine can be reacted to produce hydrochloric acid.

However, these chlorination reactions are very exothermic, requiring close temperature control. Thus, in the manufacture of chlorine itself, cooling of the reactants and product vessels is required. Therefore, there is a need for reactants that allow these reactions to be run under conditions that are less exothermic.

The present invention provides an azeotrope-like composition of HFC-32 and chlorine comprising an effective amount of HFC-32 and chlorine. By "effective amount" is meant the amount of each component that, when combined, results in the formation of an azeotrope or an azeotrope-like composition. Preferably, the azeotrope-like composition of the present invention comprises about 1 to about 60 weight percent chlorine and about 99 to about 40 weight percent HFC-32, at about 234 psia at about 20 ° C. to about 4 ° C., preferably Has a boiling point of about 20 ° C. ± 1 ° C. Preferred, more preferred, and most preferred compositions of the invention are listed in Table 1. It is understood that the number ranges in Table 1 begin with the term "about."

TABLE 1

In a particularly preferred embodiment, the composition of the present invention comprises an effective amount of HFC-32 and chlorine and the composition is boiled at about -55 ° C ± about 1 ° C at approximately atmospheric pressure (745 mmHg). In even more particularly preferred embodiments, the composition of the present invention comprises about 65 ± about 5% by weight of HFC-32 and about 35 ± about 5% by weight of chlorine, and the composition is at about −55 ° C. to about 10 ° C. Is boiled.

For the purposes of the present invention, azeotrope-like compositions are compositions that act similarly to azeotrope. From the basic principle, the thermodynamic state of a fluid is defined by pressure, temperature, liquid composition and vapor composition. An azeotrope is a two or more component system and the liquid composition and the vapor composition are the same at the state pressure and temperature. In practice, this means that the components of the azeotrope are constant boiling and cannot be separated during phase change.

An azeotrope-like composition acts similarly to an azeotrope, or is constant boiling or essentially boiling. In other words, for an azeotrope-like composition, the vapor composition formed during boiling or evaporation is the same or substantially the same as the original liquid composition. Thus, by boiling or evaporating, the liquid composition changes only to a minimum or negligible degree, if any. This contrasts with an azeotrope-like composition in which the liquid composition changes to a substantial extent during boiling or evaporation. All compositions of the invention within the indicated ranges, as well as any compositions outside these ranges, are azeotrope analogs.

The azeotrope-like compositions of the present invention may include additional components that do not form a new azeotrope or azeotrope-like system or additional components that are not in the first distillation portion. The first distillation part is the first part taken after the distillation column shows stable operation under full reflux conditions. One method for determining whether component addition forms a new azeotrope or azeotrope-like system intended to deviate from the present invention is to prepare a sample of a composition having the component under conditions where the azeotrope is expected to separate into its separate components. To distill. If the mixture containing additional components is an azeotrope or an azeotrope analog, the additional components will be classified from an azeotrope or an azeotrope analogous component. If the mixture is an azeotrope analog, some limited amount of the first distillation portion containing all mixture components that are constant boiling or acting as a single substance will be obtained.

Another characteristic of an azeotrope-like composition from this is that it is in a composition range containing the same components in the azeotrope-like analog or invariant boiling portions. All such compositions are intended to be covered by the terms "azeotrope analogs" and "constant boiling". By way of example, at other pressures, the composition of a given azeotrope will change at least slightly because it provides the boiling point of the composition. Thus, the azeotrope of A and B exhibits a unique type of relationship, but will have various compositions depending on temperature and / or pressure. For azeotrope-like compositions, there is a composition range that contains the same components in the variation, which is an azeotrope-like analog. All such compositions are intended to be covered by the term azeotrope analogs as used herein.

The composition of the present invention has a lower boiling point than the components of the composition. Those skilled in the art will appreciate that the compositions of the present invention can provide excellent cooling capacity when compared to chlorine or HFC-32 alone. Thus, in one embodiment of the present invention, the azeotrope-like compositions of the present invention can be used in cooling methods. In a preferred embodiment, the composition is used in a process for cooling the reactant and product vessels in the process for producing chlorine.

In another embodiment of the present invention, the composition may find utility in the chlorination of organic and inorganic starting materials. The chlorination of these materials is very exothermic and the heat generated by the reaction can be lowered to a factor of about 3 to about 6 depending on the HFC-32 / chlorine ratio by using an azeotrope-like composition of the present invention instead of chlorine in the chlorination reaction. . Any organic or inorganic material that can be chlorinated can be chlorinated using the compositions of the present invention. Since chlorination reactions of such materials are known in the art, the amounts and reaction conditions of the azeotrope-like compositions and starting materials of the invention to be used will be readily ascertained by those skilled in the art.

In another embodiment, the compositions of the present invention may find utility in fluorination reactions. Liquid phase processes for the production of HFC-32 using antimony catalysts and chlorine are known in the art. In one liquid phase process for preparing HFC-32, methylene chloride (“HCC-30”) is fluorinated with water fluorinated in the presence of a fluorinated catalyst such as an antimony halide catalyst. Chlorine is typically added to the reactor to react the catalyst. It is known that hydrofluorocarbons and chlorine present a potential flammable hazard. Thus, the chlorine feed used in the production of HFC-32 provides for the formation of a flammable mixture of potential HFC-32 and chlorine if it is allowed to enhance the chlorine to a sufficiently high concentration.

In the HFC-32 manufacturing method, at least one distillation column separates HFC-32 from unreacted starting material such as HCC-30 and hydrogen fluoride, and the intermediate, monochloromonofluoromethane ("HCFC-31"). . Since the chlorine boiling point, -30 ° F, is between HFC-32, -61 ° F and HCFC-31, -15.6 ° F, chlorine can be enriched in medium distillation columns even if chlorine is supplied at very low rates. It has been found that HFC-32 / chlorine azeotrope-like compositions can be used to purge chlorine with HFC-32 from distillation columns. By controlling the chlorine feed, the formation of combustible HFC-32 / chlorine mixtures in the column can be minimized if it cannot be avoided. Thus, in another embodiment of the present invention, the method for preparing HFC-32 is used in which the azeotrope-like composition of the present invention is used to control the feed rate of chlorine to minimize or avoid formation of flammable HFC-32 / chlorine mixtures.

The composition components of the present invention can be purchased commercially or prepared by known methods. Preferably, the component has a sufficiently high purity to avoid adversely affecting properties such as the constant boiling of the composition.

The invention is illustrated by the following non-limiting examples.

Example 1

A boiling point measuring device consisting of a vacuum jacketed tube with a condenser on top was used. The boiling point was charged with about 20.8 g of difluoromethane and added in small increments of chlorine. The temperature was measured using a platinum resistance thermometer. At about 0-32% by weight of chlorine the boiling point of the filled composition only changed by about 4 ° C. Thus, the composition acts as a constant boiler over this range.

Example 2

Table 2 shows chlorine and HFC-32 vapor pressure measurements as a function of chlorine composition (wt% chlorine) at a constant temperature of about 20 ° C. From this table, it can be seen that the composition at which the vapor pressure becomes maximum at this temperature is about 31.7 wt% chlorine and about 26.2 to 36.7 wt% chlorine. Also from this data, the vapor pressures of the HFC-32 and chlorine mixtures at all the indicated blending ratios are 0.0 wt% chlorine and HFC-32 as shown in the first and last lines than the HFC-32 and chlorine alone. Is higher than 100.0% by weight and HFC-32 is 0.0% by weight and chlorine is 100.0% by weight.

TABLE 2

Claims (7)

An azeotrope composition comprising 40 to 99% by weight of difluoromethane and 1 to 60% by weight of chlorine and boiling at a temperature of 20 ° C. ± 4 ° C. at 161 × 104 Pa (234 psia). The composition of claim 1 which boils at 20 ° C. ± 1.0 ° C. at 161 × 10 4 Pa (234 psia). The composition of claim 1 comprising from 50 to 95% by weight of difluoromethane and from 5 to 50% by weight of chlorine. 4. A composition according to claim 3 comprising 60 to 90% by weight of difluoromethane and 10 to 40% by weight of chlorine. The composition of claim 1 comprising 32 ± 5% by weight of chlorine and 68 ± 5% by weight of difluoromethane. The composition of claim 1 which boils at −55 ° C. ± 1.0 ° C. at 993 × 102 Pa (745 mmHg). The composition of claim 6 comprising 35 ± 5% by weight of chlorine and 65 ± 5% by weight of difluoromethane.