Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2000-07-17
2001-11-06
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
Reexamination Certificate
active
06313359
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to new methods for making hydrofluorocarbons (HFC's).
BACKGROUND OF THE INVENTION
HFCs are of particular interest as potential replacements for highly useful 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.
Known methods for forming HFC's generally use as starting materials halogenated alkanes and alkenes, such as, for example, vinylidene chloride, carbon tetrachloride and perchloroethylene. For example, U.S. Pat. No. 5,574,192—Van Der Puy et al discloses a method of making 1,1,1,3,3-pentafluoropropane (HFC-245fa) in which vinyl chloride is reacted with carbon tetrachloride and then fluorinated to produce the desired HFC. U.S. Pat. No. 5,728,904—Van Der Puy et al discloses a three-step method of reacting carbon tetrachloride with vinylidene chloride, fluorinating and then reducing to make the desired HFC.
The present inventors have come to appreciate that such prior processes are disadvantageous for several reasons. One such disadvantage is that the availability of many halogenated compounds, such as carbon tetrachloride, is limited and their use as starting materials tends to be very expensive. Another disadvantage is that these prior art processes are not flexible and produce HFC-245fa as the sole product. No useful intermediates or by-products are co-produced. Thus, the HFC-245fa 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 aldehydes as a principal reactant. Although it is contemplated that aldehydes in general will provide the advantages of the present invention, particularly preferred aldehydes are illustrated in Formula I below:
H
a
X
b
C—C(O)—H (I)
wherein, a+b=3 and each X is a halogen or other chemical moiety replaceable by chlorine such as, for example, hydroxyl, alkoxy, acetate, amino, thio or phosphorus groups.
A large number of aldehydes in accordance with Formula I, are commercially available, including, for example, acetaldehyde, diacetate acetaldehyde and the like. In addition, a number of aldehyde derivatives, which can be used to form readily aldehydes for use in the present invention, are commercially available, including, for example, dimethyl acetal, hemiacetal and the like. Furthermore, many compounds of Formula I are known in the literature and are obtainable by art-recognized procedures.
Applicants have discovered that aldehydes as a class of compounds can be used with great advantage in a process which comprises converting the aldehyde, and preferably an aldehyde 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 aldehyde conversion operation is greatly reduced relative to conventional HFC production techniques. Second, the preferred form of the present aldehyde 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 aldehyde to an HFC comprises the steps of: (a) chlorinating the aldehyde, preferably acetaldehyde, to produce a chlorinated aldehyde; and (b) converting said chlorinated aldehyde to an HFC. Preferably, the chlorinating step produces a highly-chlorinated aldehyde, and even more preferably a fully-chlorinated aldehyde, that is, an aldehyde molecule wherein the aldehyde functionality (CHO) remains intact but the carbon chain extending therefrom is perchlorinated. As used herein, the term “highly-chlorinated aldehyde” refers generally to an aldehyde in which the carbon chain extending from the aldehyde functionality is at least 65% chlorinated, wherein the percentage refers to the relative degree of chlorination, with 100% being perchlorination of the extending carbon chain.
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 aldehyde chlorination step preferably comprises reacting the aldehyde with a chlorinating agent under conditions effective to achieve chlorination of at least a portion of the aldehyde in the reactant stream, and preferably a substantial portion of the aldehyde 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 aldehyde or mixture of aldehydes 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, including elemental chlorine, elemental chlorine diluted with inert gases, such as nitrogen or helium, metallic chloride, hydrochloric acid (“HCl”), HCl and oxygen mixtures, HCl and air mixtures, and hypochlorides. 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 aldehyde 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 aldehyde starting material to fully-chlorinated aldehyde. For example, in certain preferred processes in which the aldehyde is acetaldehyde and the fully-chlorinated aldehyde is trichloroacetaldehyde, the mole ratio of aldehyde 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 1:5 to about 1:8.
According to preferred embodiments of the present process, the aldehyde is reacted with a chlorinating agent to produce a stream comprising chlorinated aldehydes. In such embodiments, one or more reactant streams comprising an aldehyde and a chlorinating agent are reacted to produce a stream containing chlorinated aldehydes. 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 aldehyde 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 prehe
Tung Hsueh Sung
Wedinger Robert Scott
Honeywell International , Inc.
Siegel Alan
Szuch Colleen D.
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