CHLORINE

Field of the Invention The present invention relates to mixtures of difluoromethane CΗFC-32") and chloπne More pamcularly, the invention provides azeotrope-like compositions of HFC-32 and chlorine

Background of the Invention Chloπne is used by industry tn a number of processes including in the production of chloπnated organic and inorganic chemicals For example, methane may be chloπnated to produce methylene chloπde, chloroform, or carbon tetrachloπde As another example, hydrogen and chloπne may be reacted to produce hydrochloric acid

However, these chloπnation reactions are highly exothermic reactions which require close temperature control Additionally, in the manufacture of chloπne itself, cooling of the reactant and product vessels are required

Therefore, a need exists for a reactant that will permit these reactants to be earned out under less exothermic conditions

Description of the Invention and Preferred Embodiments This invention provides azeotrope-like compositions of HFC-32 and chloπne comprising an effective amount of HFC-32 and chloπne By ^" effective amount" is meant an amount of each component that, when the components are combined, formation of an azeotrope or an azeotrope-like mixture results Preferably, the azeotrope-like compositions of the invention compπse about 1 to about 60 weight percent chloπne and from about 99 to about 40 weight percent

HFC-32 and have a boiling point of about 20° = about 4° C, preferably about 20° n I ³ C. at about 234 psia The preferred, more preferred, and most preferred compositions of the invention are set foπh in Table 1 The numeπcal ranges in Table 1 are to be understood to be prefaced by the term "about"

Table 1

In a paπicularly preferred embodiment, the composition of the invention compπses an effective amount of HFC-32 and chloπne wherein the composition boils at about -55' r about 1° C at about atmospheπc pressure (745 mm Hg)

In a still more particularly preferred embodiment, the composition of the invention compπses about 65 ± about 5 weight percent HFC-32 and about 35 r about 5 weight percent chloπne which composition boils at about -55 ³ z about I 0° C

For purposes of this invention, azeotrope-like compositions are compositions that behave like azeotropic mixtures From fundamental pπnciples, the thermodynamic state of a fluid is defined by pressure, temperature, liquid composition, and vapor composition An azeotropic mixture is a system of two or more components in which the liquid composition and vapor composition are equal at the state pressure and temperature In practice, this means that the components of an azeotropic mixture are constant boiling and cannot be separated during a phase change

Azeotrope-like compositions behave like azeotropic mixtures. L_L, or are constant boiling or essentially constant boiling In other words, for azeotrope-like compositions, the composition of the vapor formed duπng boiling or evaporation

IS identical, or substantially identical, to the oπgmal liquid composition Thus, with boiling or evaporation, the liquid composition changes, if at all, only to a minimal or negligible extent This is to be contrasted with non-azeotrope-like compositions in which, duπng boiling or evaporation, the liquid composition changes to a substantial degree All compositions of the invention within the indicated ranges as well as certain compositions outside these ranges are azeotrope-like

The azeotrope-like compositions of the invention may include additional components that do not form new azeotropic or azeotrope-like systems, or additional components that are not tn the first distillation cut The first distillation cut is the first cut taken after the distillation column displays steady state operation under total reflux conditions One way to determine whether the addition of a component forms a new azeotropic or azeotrope-like system so as to be outside of this invention is to distill a sample of the composition with the component under conditions that would be expected to separate a nonazeotropic mixture into its separate components If the mixture containing the additional component is nonazeotropic or nonazeotrope-like, the additional component will fractionate from the azeotropic or azeotrope-like components If the mixture is azeotrope- Itke, some finite amount of a first distillation cut will be obtained that contains all of the mixture components that is constant boiling or behaves as a single substance

It follows from this that another characteπstic of azeotrope-like compositions is that there is a range of compositions containing the same components in varying proportions that are azeotrope-like, or constant boiling .All such compositions are intended to be covered by the terms "azeotrope-like and "constant boiling" As an example, it is well known that at diffeπng pressures, the composition of a given azeotrope will vary at least slightly as does the boiimg point of the composition Thus, an azeotrope of A and B represents a unique type of

relatioπship, but with a variable composition depending on temperature and/or pressure It follows that, for azeotrope-like compositions, there is a range of compositions containing the same components in varying propoπions that are azeotrope-like All such compositions are intended to be covered by the term 5 azeotrope-like as used herein

The compositions of the invention have a lower boiling point than either of the compositions ^' components One ordmaπly skilled in the an will recognize that the compositions of the invention may offer supeπor refrigeration capacity when 0 compared to either chlorine or HFC-32 alone Thus, in one embodiment of the invention, the azeotrope-like compositions of the invention may be used tn a method for cooling In a prefeπed embodiment, the compositions are used in method for cooling the reactant and product vessels in a process for producing chloπne 5

In yet another embodiment of the invention, the compositions may find utility in chloπnation reactions of organic and inorganic starting matenals The chloπnation of these matenals is highly exothermic and, by using the azeotrope- Iike compositions of the invention in place of chloπne in the chloπnation reactions, the heat generated by the reactions may be lowered by a factor of from about 3 to about 6 depending on the HFC-32/chlonne ratio Any organic or inorganic matenals that may be chlonnated may be chloπnated using the compositions of the invention Because the chloπnation reactions of such matenals are well known in the an. the reaction conditions and amounts of starting matenals and of the

-> < azeotrope-like composition of the invention to be used will be readily asceπainable by one ordinanly skilled in the art

In still another embodiment, the compositions of the invention may find utility in fluoπnation reactions Liquid phase processes for the production ot HFC-

32 using antimony catalysts and chloπne feeds are well known tn the an In one liquid phase process for prepanng HFC-32, methylene chlonde ("HCC-30") is fluoπnated with hydrogen fluoπde in the presence of a fluoπnation catalyst, such as an antimony halide catalyst Chloπne is typically added to the reactor to reactivate the catalyst It is known that combinations of hvdrofluorocarbons and chloπne pose a potential flammability risk Thus, the use of a chlonne feed in the production of HFC-32 provides the potential for formation of a flammable mixture of HFC -32 and chloπne if chlorine is permitted to build up to a high enough concentration

Duπng the HFC-32 production process, at least one distillation column separates HFC-32 from unreacted starting matenals. such as HCC-30 and hydrogen fluroide, and the reaction intermediate, monochloromonofluoromethane ("HCFC-31") Because the boiling point of chlonne, -30° F, is between that of HFC-32, -61° F, and HCFC-31, -15 6° F, chloπne may build up to a high concentration in the middle of the distillation column even tf chlorine is fed at a very low rate It has been discovered that the HFC-32/chloπne azeotrope-like composition may be used for purging chlonne. along with HFC-32, from the distillation column By controlling the chloπne feed, the formation of a flammable HFC-32/chlorine mixture in the column may be minimized if not avoided Therefore, in still another embodiment of the invention, a process for producing HFC-32 is provided in which the azeotrope-like composition of the invention is used to control the rate of feed of chlorine in order to minimize, or avoid, the formation of a flammable HFC-32/chloπne mixture

The components of the compositions of the invention are commercially available or may be produced by known methods Preferably, the components are of sufficiently high puπty so as to avoid the introduction of adverse influences on the properties, such as constant boiling, of the compositions

The following non-limiting examples serve to illustrate the invention

Examples Example 1

An ebulhometer which consisted of a vacuum jacketed tube with a condenser on top was used About 20 8 grams of difluoromethane was charged into the ebulhometer and chloπne was added in measured small increments The temperature was measured using a platinum resistance thermometer From about 0 to about 32 weight percent chlorine, the boiling point of the composition changed by only about 4° C Therefore the composition behaves as a constant-boiling over this range

Example 2 Table 2 shows the vapor pressure measurement of HFC-32 and chloπne as a function of composition of chloπne (weight percent chloπne) at constant temperature of about 20° C From this Table it may be observed that at this temperature, the compositions at which the vapor pressure maximum is approximately 31 7 weight percent chlonne and between approximately 26 2 to 36 7 weight percent chloπne The data also show that the vapor pressure of mixtures of HFC-32 and chloπne is higher, at all indicated blend proportions than HFC-32 and chlonne alone, j_fi as indicated in the first and last rows when chloπne is 0 0 weight percent and HFC-32 is at 100 0 weight percent as well as when HFC- 32 is at 0 0 weight percent and chloπne is at 100 0 weight percent