Method of making hydrofluorocarbons

Details Method of making hydrofluorocarbons Method of making hydrofluorocarbons

1999-12-22

2001-05-22

Siegel, Alan (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Halogen containing

Reexamination Certificate

active

06235950

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to new methods for making hydrofluorocarbons (HFCs).
BACKGROUND OF THE INVENTION
HFCs are of particular interest as potential replacements for highly useful, yet environmentally undesirable, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Unlike CFCs and HCFCs, HFCs do not contain chlorine and therefore do not decompose to form chlorine-containing chemical species, which are suspected of causing depletion of the ozone layer. While HFCs thus avoid the main disadvantage of such chlorine-containing compounds, they nevertheless possess many of the beneficial properties of those compounds. For example, HFCs have been used successfully in place of HCFCs and CFCs as heat transfer agents, blowing agents, and propellants. Thus, HFCs are desirable targets of chemical synthesis.
Unfortunately, known methods for forming HFCs generally use as starting materials highly-halogenated alkanes and alkenes, such as, for example, hexafluoropropene, hexafluoropropane and 2-chloroheptafluoropropene. For example, U.S. Pat. No. 5,399,795—Franz et al discloses a method of making 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) in which hexafluoropropene is used as the starting material and is reacted with hydrogen fluoride (HF) to form the desired HFC. U.S. Pat. No. 5,780,6791, Tung et al. discloses a process which uses hexafluoropropane as a starting material to form HFC-227ea.
The present inventors have come to appreciate that such prior processes are disadvantageous for several reasons. One such disadvantage is that highly-halogenated compounds, when used as starting materials, tend to be very expensive. For example, hexafluoropropane at present costs about $6.00 per pound. Another disadvantage is that these prior art processes are not flexible and produce only HFC-227ea as a sole product. No useful intermediates or by-products are co-produced. Thus, the HFC-227ea produced by the prior art processes have relatively high operating costs, as well as relatively high capital costs.
Recognizing these and other drawbacks of the prior art, the present inventors have perceived a need for a new, efficient and more desirable method for producing a wide range of HFCs. These and other objects are achieved by the present invention as described below.
DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
The present invention is directed to a method of producing hydrofluorocarbons (HFCs) and to methods of producing other commercially attractive compounds which are produced as by-products of the inventive process. An important aspect of the invention is the discovery that HFCs can be advantageously produced using ketones as a principal reactant. Although it is contemplated that ketones in general will provide the advantages of the present invention, particularly preferred ketones are illustrated in Formula I below:
wherein, a+b3; x+y=3; and R
b
and R
y
are halogens or other chemical moieties replaceable by chlorine such as, for example, hydroxyl, sulfhydryl, or alkoxy groups.
A large number of ketones in accordance with Formula I are commercially available, including, for example, acetone. Furthermore, many compounds of Formula I are known in the literature and are obtainable by art-recognized procedures.
Applicants have discovered that ketones as a class of compounds can be used with great advantage in a process which comprises converting the ketone, and preferably a ketone in accordance with Formula I, to a hydrofluorocarbon. Applicants have discovered that a process which utilizes such a conversion operation is highly advantageous in at least two respects. First, the cost of producing HFC's according to the present ketone conversion operation is greatly reduced relative to conventional HFC production techniques. Second, the preferred form of the present ketone conversion process can be adapted to also produce valuable by-products that enhance the overall desirability of the process.
According to preferred embodiments of the present invention, the step of converting the ketone to an HFC comprises the steps of: (a) chlorinating the ketone, preferably acetone, to produce a chlorinated ketone; and (b) converting said chlorinated ketone to an HFC. Preferably the chlorinating step produces a highly chlorinated ketone, and even more preferably a fully chlorinated ketone, that is, a perchlorinated ketone. As used herein, the term “highly-chlorinated ketone” refers generally to a ketone in which the carbon chain(s) surrounding the ketone functionality are at least 80% chlorinated, wherein the percentage refers to the relative degree of chlorination, with 100% being per chlorination.
Although applicants do not wish to be bound by or to any particular theory of operation, it is believed that the methods according to the preferred aspects of the present invention involve the reaction steps shown below.
The ketone chlorination step preferably comprises reacting the ketone with a chlorinating agent under conditions effective to achieve chlorination of at least a portion of the ketone in the reactant stream, and preferably a substantial portion of the ketone in the reactant stream. It is contemplated that, in view of the teachings contained herein, those skilled in the art will be able to readily select suitable chlorinating agents for use with any particular ketone or mixture of ketones as well as the conditions effective for obtaining the desired results. In general, a suitable chlorinating agent is any material capable of providing chlorine in the reaction. A preferred chlorinating agent comprises elemental chlorine.
Those skilled in the art will appreciate that the amount of chlorinating agent to be used according to the present process will depend on many variables, including the particular ketone being chlorinated, the degree of chlorination desired and the desired yield from the chlorination reaction. Preferably, the amount of chlorinating agent used is an amount effective to achieve a greater than 90% conversion of the ketone starting material to fully-chlorinated ketone. For preferred processes in which the ketone is acetone, the mole ratio of ketone starting material to elemental chlorine is preferably from about 1:3 to about 1:12, more preferably from about 1:4 to about 1:10, and even more preferably from about 1:6 to about 1:8.
According to preferred embodiments of the present process, the ketone is reacted with a chlorinating agent to produce a stream comprising chlorinated ketones. In such embodiments, one or more reactant streams comprising a ketone and a chlorinating agent are reacted to produce a stream containing chlorinated ketones. The reactants can be fed individually or as a mixture to a chlorination reactor, or diluted with inert material, such as nitrogen or argon, or perchlorinated material. Once the reaction is under way, the reactants may be continuously added under pressure to supply the additional amounts of reactants needed to continue the process.
As desired, one or more of the reactants comprising the chlorination agent and the ketone may be preheated in at least one vaporizer before being feed to the reactor. The term “preheating” refers to vaporizing and optionally superheating the reactants. Suitable temperatures for preheating range from about 30° C. to about 200° C., preferably from about 50° C. to about 100° C. The vaporizer, as well as other vessels used in this process, may be made of any suitable corrosion resistant material.
Those skilled in the art will appreciate that the conditions under which the chlorination reaction occurs, including the pressure, temperature and period of reaction, will depend on numerous factors, including the particular starting materials used and the HFCs which are desired. In view of the teachings contained herein, those skilled in the art will be able to select the appropriate reaction conditions to achieve the particular desired result. For preferred embodiments in which the ketone reactant is acetone, the chlorination reaction is preferably carried out at temper

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