Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2001-09-24
2002-06-04
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S177000, C570S164000, C570S165000
Reexamination Certificate
active
06399841
ABSTRACT:
This application is a 371 of PCT/EP00/02282 filed Mar. 15, 2000.
The present invention relates to a process for the separation of hydrogen fluoride from its mixtures with 1,1,1,3,3-pentafluorobutane.
1,1,1,3,3-Pentafluorobutane (HFC-365mfc) may be prepared by the reaction of an appropriate chlorinated precursor with hydrogen fluoride, as described for example in Patent Application EP-A1-0699649 in the name of SOLVAY. In such a process, at the outlet of a hydrofluorination reactor, the mixture of reaction products contains, in addition to the desired 1,1,1,3,3-pentafluorobutane, hydrogen chloride resulting from the elimination of the chlorine atom(s) from the starting chlorinated precursor, hydrogen fluoride and, optionally, inert diluents and various intermediates or by-products in small quantities. Given that an excess of hydrogen fluoride relative to the chlorinated precursor is normally used, unconverted hydrogen fluoride often remains in the mixture of reaction products. While most of the constituents of the mixture of reaction products can be easily completely separated by distillation, complete separation between hydrogen fluoride and 1,1,1,3,3-pentafluorobutane is very difficult to carry out by distillation. It has indeed been observed that these compounds form an azeotropic mixture.
The object of the present invention is to provide an efficient process for the separation of hydrogen fluoride from its mixtures with 1,1,1,3,3-pentafluorobutane.
To this effect, the invention relates to a process for the separation of hydrogen fluoride from its mixtures with 1,1,1,3,3-pentafluorobutane, according to which the separation is carried out by extraction using at least one organic solvent containing at least one chloro(fluoro)butane of general formula
CCl
a
F
3−a
CH
2
CCl
b
F
2−b
CH
3
(I)
with a an integer from 0 to 3, b an integer from 0 to 2, the sum of a and b being at least equal to 1.
Preferably, the organic solvent contains 1,1,1,3,3-pentachlorobutane CCl
3
—CH
2
—CCl
2
—CH
3
, a chlorofluorobutane of formula CCl
2
F—CH
2
—CCl
2
—CH
3
, CClF
2
—CH
2
—CCl
2
—CH
3
, CF
3
—CH
2
—CCl
2
—CH
3
, CF
3
—CH
2
—CClF—CH
3
, CCl
2
F—CH
2
—CClF—CH
3
, CClF
2
—CH
2
—CClF—CH
3
and CClF
2
—CH
2
—CF
2
—CH
3
, CCl
3
—CH
2
—CClF—CH
3
, CCl
3
—CH
2
—CF
2
—CH
3
, CCl
2
F—CH
2
—CF
2
—CH
3
, or a mixture of these compounds. In a particularly preferred manner, the organic solvent contains 1,1,1,3,3-pentachlorobutane.
The organic solvent may contain other halogenated or nonhalogenated compounds.
By way of example of a nonhalogenated compound which may be possibly present in the organic solvent, there may be mentioned hydrocarbons containing from 5 to 10 carbon atoms, in particular n-pentane, n-hexane, n-heptane and n-octane.
Examples of halogenated compounds which may be possibly present in the organic solvent are chloroform, trichloroethylene, tetrachloroethylene, tetrachloro-methane, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,-dichloro-1-fluoroethane (HCFC-141b), 1,1,1- or 1,1,2-trifluorotrichloroethane, 1,2,3-trichloropropane, perfluorinated hydrocarbons, bromobenzene, o-dichlorobenzene, p-chlorotoluene, p-chlorotrifluorobenzene and 1,2-dichloro-4-trifluoro-benzene, as well as mixtures of these compounds.
The organic solvent however preferably consists essentially of one or more chloro(fluoro)butanes of general formula (I), 1,1,1,3,3-pentachlorobutane constituting the most preferred organic solvent.
Among the organic solvents containing chloro(fluoro)-butanes of general formula (I), those which contain at least one chlorofluorobutane containing 3 or 4 fluorine atoms are preferred. Examples of chlorofluorobutanes of general formula (I), containing 3 or 4 fluorine atoms, which can be used in the organic solvent, are 1,1-dichloro-1,3,3-trifluorobutane (HCFC-363kfc), 3-chloro-1,1,1,3-tetrafluorobutane (HCFC-364mfb) and 1-chloro-1,1,3,3-tetrafluorobutane (HCFC-3641fc). These compounds may be obtained when 1,1,1,3,3-pentachlorobutane is subjected to a hydrofluorination reaction.
In one variant, the organic solvent containing at least one chloro(fluoro)butane of general formula (I) containing 3 or 4 fluorine atoms contains in addition 1,1,1,3,3-pentachlorobutane. It may be advantageous to use mixtures containing 1,1,1,3,3-pentachlorobutane in order to improve the decantation properties during extraction.
Another variant of the process according to the invention relates to a process in which
(a) 1,1,1,3,3-pentachlorobutane is subjected to a hydrofluorination reaction
(b) a quantity of reaction mixture is drawn off and subjected to a separation operation in order to recover at least one organic solvent comprising chlorofluorobutanes of general formula (I)
(c) the organic solvent is used in the separation process according to the invention.
The separation operation is, for example, a distillation or a demixing at low temperature. The fractions other than the organic solvent may be recycled to the 1,1,1,3,3-pentachlorobutane hydro-fluorination reaction or may be subjected to subsequent separation stages in order to recover 1,1,1,3,3-pentafluorobutane.
In a preferred manner, the extraction is carried out on a mixture comprising HF and HFC-365mfc in proportions close to those in which they form an azeotropic composition. The mixture may in addition comprise variable quantities of a chlorofluorobutane of general formula (I). Often the chlorofluorobutane is a chlorofluorobutane of general formula (I) in which the sum of a and b is equal to 1 or 2.
If the initial mixture of hydrogen fluoride and HFC-365mfc departs from the azeotropic composition, it may be advantageous to carry out beforehand a distillation in order to separate the azeotrope from the compound in excess. The azeotropic composition is then subjected to extraction.
In the separation process according to the invention, the weight ratio between the organic solvent and the mixture of hydrogen fluoride and 1,1,1,3,3-pentafluorobutane is generally at least 0.1. Preferably, a weight ratio of at least 0.2 is used. Generally, the weight ratio between the organic solvent and the mixture of hydrogen fluoride and 1,1,1,3,3-pentafluorobutane does not exceed 10. Preferably, it does not exceed 5.
The temperature at which the extraction is carried out is generally at least −25° C. Preferably, it is about −10° C. The temperature in general does not exceed 40° C. Preferably it does not exceed 30° C.
The process according to the invention is carried out at a sufficient pressure to maintain the mixture in the liquid state. It may be carried out at the autogenous pressure of the mixture; in this case, the pressure is generally less than 3 bar. Alternatively, it may be carried out at a pressure greater than the autogenous pressure. In this case, the total pressure will be generally less than 10 bar; preferably, the pressure used will be less than 3 bar but greater than 1 bar.
The bringing of the mixture of hydrogen fluoride and 1,1,1,3,3-pentafluorobutane into contact with the organic solvent for extraction is carried out in one or more stages, by means of any conventional liquid—liquid extraction device, for example by bringing into intimate contact by means of a static mixer, a stirred reactor, a rotating disc extractor, a centrifugal extractor or a perforated plate column, operating either countercurrentwise or cocurrentwise. Preferably, the bringing into contact is carried out in a stirred reactor. The extraction may be performed continuously or batchwise. Preferably, it is performed continuously.
After extraction, an organic phase enriched in 1,1,1,3,3-pentafluorobutane is separated from a phase enriched in hydrogen fluoride (called hereinafter HF phase). This separation may be simply carried out by decantation, but it can also use any other conventional phase separation device, such as centrifugation or a separation by hydrocyclone. Separation by decantation is preferred.
The organic phase mainly comprises the extraction solvent enriched in 1,1,1,3,3-pentafluorobutane, but it may also contain a ce
Lambert Alain
Wilmet Vincent
Siegel Alan
Solvay ( Societe Anonyme)
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