Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
1999-11-29
2001-09-11
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
Reexamination Certificate
active
06288292
ABSTRACT:
The present invention relates to chemical processes involving the vaporisation of a liquid phase organic compound which is to undergo chemical reaction in the course of the process. The invention has particular application to organic compounds which can be vaporised satisfactorily at atmospheric pressure but become prone to degradation when vaporisation is effected at elevated pressure, with consequent elevation of the boiling point (or bubble point) of the compound.
For instance, when trichloroethylene is vaporised at elevated pressures such that the boiling point thereof is in excess of 150° C., degradation products are formed which cause fouling of heat exchange surfaces thereby impairing performance (vaporisation efficiency). Also, such degradation of trichloroethylene leads to the formation of undersirable chemical species which are vaporised and pass into the process utilising the vaporised trichloroethylene.
Trichloroethylene is used in the production of compounds such as 1,1,1,2-tetrafluorethane by reaction thereof with a stoichiometric excess of HF in the presence of a fluorination catalyst. Where this process is carried out at elevated pressure (which is advantageous since the plant for carrying out the process can be made compact), problems arise in achieving satisfactory vaporisation of the trichloroethylene.
According to a first aspect of the invention there is provided a process for carrying out a chemical reaction involving a first organic compound which has been vaporised from the liquid phase under conditions which render the liquid phase form of the pure compound prone to degrade, characterised in that vaporisation of said first compound from the liquid phase is effected using a second compound in such a way as to suppress degradation of said first compound.
The chemical reaction may be one involving both compounds as reactants as in, for example, the fluorination of trichloroethylene using hydrogen fluoride. However, we do not exclude the possibility of the chemical reaction being one which does not involve the second compound as a reactant (primary or otherwise), eg the chemical reaction may be one involving the isomerisation of a vaporised chlorocarbon in the presence of an isomerisation catalyst, eg the isomerisation of HCFC 123
a
to produce HCFC 123.
The invention in all aspects thereof defined herein has particular application to the vaporisation of halocarbons (which term is used herein to include halogenated compounds which incorporate hydrogen) and more specifically chlorocarbons such as chloroethenes, eg trichloroethylene and perchloroethylene, and chloroethanes such as 1,1,1,2-tetrachloroethane and 1,1,2,2-tetrachloroethane.
The term “degradation product” as used herein is to be construed as including within its ambit, derivatives of said organic compound which are not desired in the context of the particular chemical reaction. For instance, in the case of 1,1,2,2-tetrachloroethane, the chemical reaction may be one in which it is to be converted to 1,1,2-trichloro-2-fluoroethane but may be prone to convert to trichloroethylene if subjected to high temperature whilst in the liquid phase (eg as a result of coming into contact with a hot metal surface) and, in this instance, for the purposes of the present invention, trichloroethylene may be regarded as a degradation product of 1,1,2,2-tetrachloroethane.
When used in suppressing degradation of said first compound, the second compound may be in the liquid or gas phase. In the former case, the degradation suppression may be effected by co-vaporising the first compound in admixture with the second compound.
According to a second aspect of the present invention there is provided a process for carrying out a chemical reaction at elevated pressure, comprising vaporising under elevated pressure conditions a liquid phase organic compound which forms one of the reactants and is prone to degrade when vaporised under such conditions, and reacting the vaporised compound with at least one other reactant in the gaseous phase under conditions which permit the reaction to proceed, characterised by modifying the boiling characteristics of the organic compound such that vaporisation can be effected at reduced temperature thereby preventing or substantially reducing the production of degradation products.
Preferably the boiling characteristics of the organic compound are modified by co-vaporising the compound in admixture with another compound which may form one of the reactants. The compound which is added to said organic compound is preferably one which provides a mixture capable of forming a minimum boiling azeotrope. In general, the second compound will have a boiling point lower than that of the first compound.
According to another aspect of the present invention there is provided a process for effecting fluorination of a chlorocarbon compound at elevated pressure, comprising vaporising the compound under elevated pressure conditions at which the boiling point of the compound per se is such that vaporisation of the compound per se is accompanied by degradation of the compound if vaporised at that boiling point, and reacting the vaporised compound with a fluorinating agent in the gaseous phase under conditions with permit the reaction to proceed, characterised by the selection of hydrogen fluoride as the fluorinating agent and effecting vaporisation of the chlorocarbon by co-vaporising a mixture of the chlorocarbon compound with hydrogen fluoride whereby the boiling temperature of the chlorocarbon compound/HF mixture is such that vaporisation thereof is accompanied by substantially less degradation of the chlorocarbon compound.
Preferably the chlorocarbon compound is a chloroethene such as trichloroethylene or perchloroethylene, or a chloroethane such as 1,1,1,2-tetrachloroethane or 1,1,2,2-tetrachloroethane.
In yet another aspect of the invention there is provided a process for carrying out a chemical reaction involving a halocarbon in its vapour phase, in which prior to the reaction the halocarbon is vaporised under elevated pressure conditions at which the boiling point of the compound per se is such that vaporisation of the compound per se is accompanied by degradation of the compound if vaporised at that boiling point, characterised in that the halocarbon is co-vaporised in admixture with hydrogen fluoride whereby the boiling temperature of the halocarbon compound/HF mixture is such that vaporisation is accompanied by substantially less degradation of the halocarbon compound.
Typically the reduction in degradation is at least 50% by weight, ie the amount of degradation products produced is at least 50% by weight less than would occur if the pure halocarbon is vaporised at its boiling point under said elevated pressure conditions.
In one embodiment of the chemical reaction may comprise isomerisation of the halocarbon compound, eg the isomerisation of 1,2-dichloro-1,2,2-trifluoroethane (HCFC
123
a
) in its vapour phase to the more stable 1,1-dichloro-2,2,2-trifluoroethane (HCFC
123
).
In another embodiment of the invention the chemical reaction may comprise the fluorination of a chlorocarbon such as a chloroethane or a chloroethene in which case vaporisation of the chlorocarbon by co-vaporisation with HF and the HF may also constitute the fluorinating agent. For example, the chloroethene may comprise trichloroethylene and the reaction is one involving fluorination of trichloroethylene. We have found that, whilst vaporisation of trichloroethylene at elevated pressure would normally result in the production of degradation products, co-vaporisation of the chloroethylene in admixture with HF has a marked affect on the boiling point to the extent that even small additions of HF allow efficient vaporisation of the chloroethylene under elevated pressure conditions without any significant degradation of the chloroethylene.
Where the chloroethene comprises trichloroethylene, the elevated pressure at which fluorination is carried out is typically in excess of that at which the boiling point of trichloroethylene is 150°
Blake Charles Brian
Ewing Paul Nicholas
Hunns Jeremy Charles Bauser
Scott John David
Cook Alex McFarron Manzo Cummings & Mehler, Ltd.
Imperial Chemical Industries PLC
Siegel Alan
LandOfFree
Process and apparatus for vaporization of halocarbons does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process and apparatus for vaporization of halocarbons, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process and apparatus for vaporization of halocarbons will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2535769