Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Patent
1999-02-08
2000-08-29
Siegel, Alan
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
570142, 570165, C07C 1738, C07C 1908, C07C 1708
Patent
active
061111511
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for the removal of water from process streams and in particular to a process for the removal of water from process steams which are generated during vapour phase catalytic hydrofluorination reactions which employ hydrogen fluoride as the hydrofluorinating reactant.
Recently much attention has been directed at the conception and development of process routes for the production of hydrofluoroalkanes (HF As) which have been proposed as replacements and indeed are now produced and sold as replacements for chlorofluorocarbons.
Amongst the many processes which have been proposed for the production of hydrofluoroalkanes, for example pentafluoroethane (HF A 125), 1,1,1,2-tetrafluoroethane (HFA 134a), difluoromethane (HFA 32) and 1,1,1-trifluoroethane (HFA 143a), vapour phase catalytic hydrofluorination of halogenated, particularly chlorinated alkanes and/or alkenes have received much attention. However a problem with these processes is that during the process, water may be generated as a by-product from reaction of hydrogen fluoride with the catalyst or as a product of catalyst regeneration processes, or indeed, the hydrogen fluoride starting material may contain small amounts of water. If steps are not taken to remove this water, then the concentration of water will increase. Hydrogen fluoride/water mixtures are especially corrosive, and are both difficult and expensive to handle. Moreover water, even at low levels, may act as a catalyst poison.
In the past it has been proposed to remove the water by providing a distillation column which is dedicated to separating substantially anhydrous hydrogen fluoride from a water/hydrogen fluoride mixture. However, such a column must be made of exotic corrosion resistant materials and is expensive.
We have now devised a process by which water may be removed from a process stream and which is cheaper and simpler to operate and eliminates or at least substantially reduces the need for a distillation column which is dedicated to separating substantially anhydrous hydrogen fluoride from water/hydrogen fluoride mixtures.
According to a first aspect of the invention there is provided a process for the removal of water from a process stream which comprises hydrogen fluoride, water, organic products and by-products and unreacted organic starting materials which comprises (i) separating the process stream into a lighter tops stream comprising hydrogen fluoride and lighter boiling organic components from a heavy bottoms stream comprising hydrogen fluoride, water and heavier organic components characterised in that (ii) the heavy bottoms stream is fed to a phase separator under conditions of temperature and pressure such that the heavy stream is in the liquid phase and an organic fraction is separated from a hydrogen fluoride fraction containing water and (iii) disposing of at least a part of the hydrogen fluoride fraction.
We have realised that by performing step (i), which typically comprises separation of a tops vapour from a bottoms liquid, usually by distillation, a degree of separation of hydrogen fluoride from water is achieved there by concentrating up the water in the hydrogen fluoride bottoms phase such that when this bottoms phase undergoes phase separation, the hydrogen fluoride phase contains significantly higher concentration of water than the original process stream, there by allowing the removal of less hydrogen fluoride with the water to be disposed of.
Typically the hydrogen fluoride/water fraction from the phase separator will be divided into a recycle stream, which can be vaporised, to which further hydrogen fluoride is added, and a smaller hydrogen fluoride/water stream which may be further treated or disposed of, for example by being sent to aqueous scrubbers.
The relative proportions of the fraction which is recycled and the fraction which is sent to further treatment will depend particularly upon the rate at which water is produced in the process, but usually the amount of the hydrogen fluoride fraction disposed of will be suc
REFERENCES:
patent: 5334784 (1994-08-01), Blake et al.
Bonniface David William
Bujac Paul David Bernard
Ewing Paul Nicholas
Imperial Chemical Industries plc
Siegel Alan
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