PRODUCTION OF CHLORO-2,2,2-TRIFLUOROETHANE

Abstract: A process for producing chloro-2,2,2-trifluoroethane as a co-product of the production of 1,1,1,2-tetrafluoroethane by hydrofluorination of trichloroethylene which comprises (i) treating the 1,1,1,2-tetrafluoroethane product stream containing chloro-2,2,2-trifluoroethane and hydrogen fluoride to form a mixture of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane and (ii) distilling said mixture to separate essentially pure chloro-2,2,2-trifluoroethane from the mixture. A preferred distillation in step (ii) comprises (iia) distilling the mixture to separate essentially pure 1,1,1,2-tetrafluoroethane and form a second mixture of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane and (iib) distilling said second mixture to separate essentially pure chloro-2,2,2-trifluoroethane from the second mixture.

Description: PRODUCTION OF CHLORO-2,2,2-TRTFLUOROETHANE This invention relates to the production of chloro-2,2,2-trifluoroethane, HCFC 133a, from trichloroethylene and particularly to a process for the co-production of 1,1,1, 2-tetrafluoro- ethane and chloro-2,2,2-trifluoroethane from trichloroethylene. A particular embodiment of the invention relates to accessing chloro-2,2,2-trifluoroethane as a co-product from the production of 1,1,1,2-tetrafluoroethane by the two-step reaction of (i) trichloroethylene with hydrogen fluoride to form chloro-2,2,2-trifluoroethane and (ii) chloro-2,2,2-trifluoro- ethane with hydrogen fluoride to produce 1,1,1,2-tetrafluoroethane with recycle of chioro-2,2,2-trifluoroethane to step (i). The two-step reaction of trichloroethylene with hydrogen fluoride in the vapour phase in the presence of a fluorination catalyst such as chromia or based on chromia to produce chloro-2,2,2-trifluoroethane and 1,1,1,2-tetrafluoroethane is well known and is the basis of a number of commercial plants for the production of 1,1,1,2-tetrafluoroethane. The reaction may be carried out in a single reaction zone or the two steps ofthe reaction may be carried out in separate reaction zones. The reaction produces a number of by-products, notably hydrogen chloride and various saturated and unsaturated chlorofluoro(hydro)carbons and the reaction of chloro-2,2,2-trifluoroethane to 1, 1,1,2-tetrafluoroethane is equilibrium limited so that the resulting 1, 1,1,2-tetrafluoroethane product stream usually comprises less than 20% by weight of 1, 1,1,2-tetrafluoroethane and contains major proportions of hydrogen chloride, unreacted chloro-2,2,2-trifluoroethane and hydrogen fluoride (which is commonly used in a large excess). The 1,1,1,2-tetrafluoroethane product stream is normally subjected to several treatments, including distillations, to recover hydrogen chloride and essentially pure 1,1,1,2-tetrafluoroethane and provide a crude recycle stream comprising mainly chloro-2,2,2-trifluoroethane and hydrogen fluoride but including various chlorofluoro(hydro)carbon by-products. Hitherto no attempt has been made to recover essentially pure chloro-2,2,2-trifluoroethane from the 1,1,1,2-tetrafluoroethane product stream as a co-product ofthe 1,1,1,2-tetrafluoroethane production process The present invention resides in a process for the production of chloro-2,2,2-trifluoroethane wherein the 1,1,1 ,2-tetrafluoroethane product stream containing chloro-2,2,2-trifluoroethane and hydrogen fluoride obtained by hydrofluorination of trichloroethylene is treated to recover essentially pure chloro-2,2,2-trifluoroethane as well as essentially pure 1,1,1,2-tetrafluoroethane. According to the present invention there is provided a process for the production of chloro-2,2,2-trifluoroethane as a co-product ofthe production of 1,1,1, 2-tetrafluoroethane by hydrofluorination of trichloroethylene which comprises (i) treating the 1,1,1,2-tetrafluoroethane product stream containing chloro-2,2,2-trifluoroethane and hydrogen fluoride to form a mixture of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane and (ii) distilling said mixture to separate essentially pure chloro-2,2,2-trifluoroethane from the mixture. The distillation carried out in step (ii) may be a single-stage distillation to separate chloro-2,2,2-trifluoroethane directly from the mixture or it may be a two-stage or multi- stage distillation to separate the chloro-2,2,2-trifluoroethane. In the single stage distillation, the mixture of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane formed in step (i) is fed into a distillation column and chloro-2,2,2-trifluoroethane is withdrawn directly from the column as a bottom fraction. It is to be understood that whilst this stage is described as a single-stage distillation, it may be carried out in more than one distillation column. The remainder ofthe 1,1,1,2-tetrafluoroethane product stream, depleted in chloro-2,2,2-trifluoroethane, may be withdrawn as a top stream from the column and passed to further processing to recover the 1, 1,1,2-tetrafluoroethane, for example by feeding the stream back into the 1,1,1,2-tetrafluoroethane purification train ofthe production plant. If desired, the top stream from the distillation column may be recycled to the distillation column to separate a further amount of chloro-2,2,2-trifluoroethane before the stream is passed to further processing to separate the 1,1,1,2-tetrafluoroethane. The mixture of 1,1,1, 2-tetrafluoroethane and chloro-2,2,2-trifluoroethane formed in step (i) is essentially free from hydrogen fluoride and hydrogen chloride but will usually contain minor amounts of chlorofluorocaron by-products. In the single-stage distillation in step (ii), these by-products remain in the column and are withdrawn with the 1,1, 1,2-tetrafluoroethane stream. However in an embodiment ofthe single-stage distillation, the by-products of boiling point intermediate those of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane may be withdrawn as a side stream from the column. The distillation in step (ii) may be a two-stage or a multi-stage operation and a preferred distillation is a two-stage distillation in which the first stage (iia) comprises distilling the mixture of 1, 1, 1, 2-tetrafluoroethane and chloro-2,2,2-trifluoroethane formed in step (i) to separate essentially pure 1,1,1,2-tetrafluoroethane as a top fraction from the column and form a second mixture of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane and the second stage (iib) comprises distilling said second mixture to separate essentially pure chloro-2,2,2-trifluoroethane as a bottom fraction and form a third mixture of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane. This preferred embodiment thus provides a process for the production of chloro-2,2,2-trifluoroethane as a co-product ofthe production of 1,1,1,2-tetrafluoroethane by hydrofluorination of trichloroethylene which comprises (i) treating the 1,1,1,2-tetrafluoroethane product sream containing chloro-2,2,2-trifluoroethane and hydrogen fluoride to form a first mixture of 1,1, 1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane, (iia) distilling said first mixture to separate essentially pure 1,1,1 ,2-tetrafluoroethane and form a second mixture of 1 , 1 , 1 ,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane and (iib) distilling said second mixture to separate essentially pure chloro-2,2,2-trifluoroethane and form a third mixture of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane. The third mixture of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane, obtained in step (iia), can be recycled to any step ofthe 1,1,1,2-tetrafluoroethane production process or to the crude 1,1,1,2-tetrafluoroethane product stream prior to step (i) ofthe process according to the invention. - A - The crude 1,1,1,2-tetrafluoroethane product stream fed to step (i) ofthe process preferably is essentially free from hydrogen chloride The process ofthe invention thus preferably includes an additional step of treating the crude product stream, for example by distillation, to separate hydrogen chloride prior to treatment according to step (i) In a typical 1,1,1,2-tetrafluoroethane production process, a mixture of 1,1,1,2-tetrafluoroethane, chloro-2,2,2-trifluoroethane and hydrogen fluoride may be crudely separated from the 1,1,1,2-tetrafluoroethane product stream, for instance as the top stream from a distillation column, from a mixture comprising mainly chloro-2,2,2-trifluoroethane and hydrogen fluoride, for example a liquid bottom stream and/or a gaseous side stream from the distillation cloumn The chloro-2,2,2-trifluoroethane/hydrogen fluoride mixture is preferably recycled to the 1,1,1,2-tetrafluoroethane production process, in the case of a two step process either to the chloro-2,2,2-trifluoroethane conversion step or to the trichloroethylene conversion step Distillation ofthe 1,1,1,2-tetrafluoroethane product stream, after removal of hydrogen chloride, to separate a mixture of 1,1,1, 2-tetrafluoroethane and hydrogen fluoride from a recycle stream comprising mainly chloro-2,2,2-trifluoroethane and hydrogen fluoride is a conventional step in the production of 1 , 1 , 1 ,2-tetrafluoroethane The distillation is fairly crude so that in the conventional distillation the separated mixture of 1,1,1,2-tetrafluoroethane and hydrogen fluoride may contain chloro-2,2,2-trifluoroethane which is removed at a later stage and recycled to the 1,1,1,2-tetrafluoroethane production process. However, the conventional distillation is operated under conditions (temperature and pressure) designed to miriirnise the carry over of chloro-2,2,2-trifluoroethane with the 1,1,1,2-tetrafluoroethane and hydrogen fluoride so as to reduce the burden on the subsequent separation step In contrast the treatment according to step (i) ofthe invention is operated under conditions, for example distillation under higher temperature and/or lower pressure, wherby an appreciable amount of chloro-2,2,2-trifluoroethane is present in the separated mixture so as to provide a source of chloro-2,2,2-trifluoroethane for recovery as a co-product ofthe 1, 1,1,2-tetrafluoroethane production process The amount of chloro-2,2,2-trifluoroethane in the mixture separated in step (i) and hence the amount of chloro-2,2,2-trifluoroethane accessable as a co-product is dependent upon and therefor controlled by the operating conditions ofthe distillation column. It is a simple matter for the operator to select operating conditions appropriate to any particular requirement for chloro-2,2,2-trifluoroethane as a co-product. As a guide, the column will usually be operated at a pressure in the range of about 10 barg to 20 barg The mixture of 1,1,1,2-tetrafluoroethane, chloro-2,2,2-trifluoroethane and hydrogen fluoride separated from the product stream is then treated to remove the hydrogen fluoride and form a mixture of 1 , 1 , 1 ,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane. The removal of hydrogen fluoride may be effected by any suitable technique, for example by scrubbing the mixture with water or an alkaline solution. The process will usually include an additional treatment between hydrogen fluoride removal in step (i) and distillation in step (ii) to recover essentially pure chloro-2,2,2-trifluoroethane. As discussed herinbefore, step (i) usually comprises crude distillation ofthe 1,1,1,2-tetrafluoroethane product stream to separate a mixture of 1,1,1,2-tetrafluoroethane, chloro-2,2,2-trifluoroethane and hydrogen fluoride. However, the 1,1,1,2-tetrafluoroethane product stream usually contains several other chlorofluoro(hydro)carbon components and these will divide on the basis of "lights" and "heavies" between the mixtures separated in step (i) The mixture obtained in step (i) may contain one or more of these "lights" components and is usually treated, for example by distillation, to remove these components prior to feeding to step (ii). The "lights" components removed in this treatment are generally unsuitable for recycle to the 1,1,1,2-tetrafluoroethane production process and so may be vented and disposed of for example in a thermal oxidiser. The operating conditions for "lights"components separation are known and/or readily determined but as a guide the conditions will usually be a column pressure of from about 10 barg to 20 barg Essentially pure chloro-2,2,2-trtifluoroethane is separated in step (ii) ofthe process. In the preferred two-stage distillation, 1,1,1,2-tetrafluoroethane is separated by distillation in step (iia) from a second mixture of chloro-2,2,2-trifluoroethane and a small amount of 1,1, 1,2-tetrafluoroethane, the latter mixture then being distilled in step (iib) to separate essentially pure chloro-2,2,2-trifluoroethane for recovery. The operating conditions for the distillation columns are readily determined by the operator but as a guide the conditions will usually be a column pressure of from about 1 barg to 15 barg, say 5 to 12 barg in step (iia) and a column pressure of about 1 barg to 10 barg in step (iib). As described hereinbefore, any residual (third) mixture of 1,1, 1,2 -tetrafluoroethane and chloro-2,2,2-trifluoroethane from step (iib) may be recycled for further treatment to recover the product values, for example by recycle to the 1,1,1,2-tetrafluoroethane product stream from the 1,1,1,2-tetrafluoroethane production process or to any step ofthe product separation treatment or to any step ofthe 1,1,1,2-production process. The 1,1,1,2-tetrafluoroethane product stream may be the product stream from any process for the production of 1,1,1,2-tetrafluoroethane by hydrofluorination of trichloroethylene and the invention is not restricted to any particular process for producing 1,1,1,2-tetrafluoroethane from trichloroethylene. The process according to the invention may be operated as a batch process although we prefer continuous operation. In the two-sage distillation procedure we prefer continuous operation at least up to and including step (iia). Step (iib) may be included in the continuous operation but if desired the second mixture of chloro-2,2,2-trifluoroethane and 1,1,1,2- tetrafluoroethane from step (iia) may be stockpiled and treated separately as a batchwise operation in step (iib).

Claims: CLAIMS 1. A process for the production of chloro-2,2,2-trifluoroethane which comprises (i) treating the 1,1,1,2-tetrafluoroethane product stream obtained by hydrofluorination of trichloroethylene and containing chloro-2,2,2-trifluoroethane and hydrogen fluoride to form a mixture of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane and (ii) distilling said mixture to separate essentially pure chloro-2,2,2-trifluoroethane from the mixture. 2. A process as claimed in claim 1 wherein step (ii) comprises a two-stage distillation to separate 1,1, 1 ,2-tetrafluoroethane in a first stage and to separate chloro-2,2,2-trifluoroethane in a second stage 3 A process as claimed in claim 1 or claim 2 which comprises (i) treating the 1,1,1,2-tetrafluoroethane product stream obtained by hydrofluorination of tricloroethylene and containing chIoro-2,2,2-trifluoroethane and hydrogen fluoride to form a first mixture of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane (iia) distilling said first mixture to separtate esentially pure 1,1,1,2-tetrafluoroethane and form a second mixture of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane and (iib) distilling said second mixture to separate essentially pure chloro-2,2,2-trifluoroethane and form a third mixture of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane 4. A process as claimed in claim 1 wherein step (ii) comprises a single-stage distillation to separate essentially pure chloro-2,2,2-trifluoroethane from the mixture of 1,1,1,2-tetrafluoroethane and chloro-2,2,2-trifluoroethane formed in step (i) 5. A process as claimed in claim 4 wherein the chloro-2,2,2-trifluoroethane is witdrawn as a bottom fraction from the distillation column and the 1,1,1,2-tetrafluoroethane product stream is withdrawn from the top ofthe column and wherein by-products of intermediate boiling point are withdrawn as a side stream from the column ό. A process as claimed in any one of claims 1 to 5 in which the crude 1,1,1,2-tetrafluoroethane product stream is treated prior to step (i) to remove hydrogen chloride. 7. A process as claimed in claim 6 wherein the treatment to remove hydroge chloride comprises distillation. 8. A process as claimed in any one ofthe preceding claims wherein the product stream remaming after separation of chloro-2,2,2-trifluoroethane is recycled to step (i) or to step (ii). 9. A process as claimed in any one ofthe preceding claims wherein the product stream after separation of chloro-2,2,2-trifluoroethane is fed back to the 1,1, 1,2-tetrafluoroethane production process. 10. A process as claimed in any one ofthe preceding claims which is carried out as a continuous process.

Inventors: ANNELLS DAVID HUGH, TAYLOR ANDREW MARK, ANNELLS, DAVID, HUGH, TAYLOR, ANDREW, MARK
Applicants: ANNELLS DAVID HUGH, ICI PLC, TAYLOR ANDREW MARK, ANNELLS, DAVID, HUGH, IMPERIAL CHEMICAL INDUSTRIES PLC, TAYLOR, ANDREW, MARK
Application year: 1996
Main classification: C07C19
IPC codes: C07C17, C07C19