Fluorination

Details Fluorination Fluorination

2000-05-18

2001-09-11

Geist, Gary (Department: 1623)

Organic compounds -- part of the class 532-570 series

Organic compounds

Halogen containing

C560S187000, C562S602000

Reexamination Certificate

active

06288291

ABSTRACT:

This invention relates to the fluorination of a hydrocarbon substrate. More particularly, it relates to a process and installation suitable for the perfluorination of an optionally substituted hydrocarbon substrate.
According to one aspect of the invention there is provided a process for the fluorination of an optionally substituted hydrocarbon substrate, the process including the steps of:
diluting a hydrocarbon substrate feed with an inert diluent liquid to form a diluted substrate;
mixing the diluted substrate with a gaseous fluorinating reagent to form a reaction mixture which is a foam;
allowing the fluorinating reagent to react in the foam with the substrate, to fluorinate the substrate to obtain fluorinated product material;
separating the foam containing the fluorinated product material into a gas component and a liquid component, the liquid component containing the fluorinated product material;
withdrawing the fluorinated product material from the liquid component and returning the liquid component from which the fluorinated product material has been withdrawn to the diluting step where it acts as the diluent liquid;
feeding a feed of the fluorinating reagent into the gas component; and
recirculating the gas component containing the fluorinating reagent feed to the mixing step where it provides the fluorinating reagent in the reaction mixture.
Diluting the substrate feed with the diluent liquid may be such as to form a solution, emulsion or suspension of the substrate in the diluent liquid, which diluent liquid forms a continuous phase and acts as a carrier for the substrate. By inert in the context of the diluent liquid of the present invention is meant that the diluent liquid undergoes no unacceptable chemical reactions and preferably undergoes no chemical reactions whatsoever, during the operation of the process. Preferably the substrate feed is fed into a stream of the diluent liquid which is undergoing turbulent flow, upstream of the mixing step and no further from the mixing step than is necessary to provide a sufficiently homogenous liquid feed into the mixing step. In particular, the feeding of the hydrocarbon substrate may be into a stream of the liquid component which is undergoing turbulent flow, the feeding of the hydrocarbon substrate being at a position between the separating step and the mixing step.
Conveniently returning of the liquid component to the diluting step is by pumping the liquid component, from the separating step to the diluting step, at a rate sufficient to cause turbulent flow in the pumped liquid component, the hydrocarbon substrate feed being fed into the turbulent flow of the pumped liquid component with the hydrocarbon substrate feed in liquid form, although, in principle, the substrate may be in gaseous or finely divided solid form, provided that it is sufficiently dissolved or otherwise dispersed in the diluent liquid by the time the mixing step takes place.
The mixing is preferably flash mixing, conveniently by passing the diluted substrate and the fluorinating reagent together through an in-line continuous mixer such as a static mixing device, which is conveniently in the form of a jet pump of the ejector, eductor or extractor type and may include a venturi. By flash mixing is meant that the mixing should be by a mixing step which progresses substantially to completion in at most 1 second.
Any suitable gaseous fluorinating reagent may be used, such as oxidizing fluorine-containing chemicals. The gaseous fluorinating agent may thus be selected from the group of fluorinating gases selected from F
2
, UF
6
, XeF
2
, CIF
3
and BrF
3
, molecular fluorine as F
2
typically being preferred, for reasons of yield, cost and availability. To facilitate control over the reaction step, which is exothermic, the fluorinating gas may be diluted by means of an inert diluent gas, which may be a noble inert gas such as argon, but which, again for reasons of cost and availability, is preferably nitrogen. In other words, the gaseous fluorinating reagent, when it is mixed with the diluted substrate may also be in dilute form, the gaseous fluorinating reagent being diluted with an inert diluent gas. The gas component which is recirculated is thus usually an F
2
/N
2
mixture in which the F
2
forms 10-80% by volume, preferably 30-60% by volume, eg 50%, a suitable or optimum value being determined by routing experimentation. The ratio of gas:liquid mixed together in the mixing step may be 2:1-1:50 by volume, preferably 1:2-1:10, eg 1:4, the consistency of the foam being determined thereby. In a particular embodiment of the invention, the gaseous fluorinating reagent may be F
2
, being in the form of part of an essentially F
2
/N
2
gas mixture in which N
2
is an inert diluent gas, when the gaseous fluorinating reagent is mixed with the diluted substrate, the gas mixture including 10-80% by volume F
2
and 20-90% by volume N
2
,the volume ratio in the mixing step of the gas mixture:diluted substrate being 2:1-1:50 by volume.
Allowing the fluorinating reagent to react in the foam with the substrate preferably includes keeping the reaction mixture in the form of a foam, without unacceptable separation thereof into liquid and gaseous components, until the reaction has proceeded to an acceptable degree of completion. The Applicant has found that discharging the reaction mixture from the mixing step into a downwardly, or preferably upwardly extending, but no horizontal, flow path, such as a conduit in the form of a pipe, promotes retention of a foam which is resistant to separation into liquid and gaseous components. Thus, allowing the fluorinating reagent to react in the foam with the substrate may include causing the reaction mixture to pass, in the form of a foam, along a flow path leading from the mixing step to the separating step, the flow path being inclined at an angle to the horizontal and the fluorinating agent reacting in the foam with the substrate as the foam moves along the flow path. When the foam is discharged vertically upwardly from the mixing step along a conduit of circular cross-section, a diameter:length ratio in the vertical conduit be of 1:15-1:40 is typlically adequate. Routine experimentation can be used to establish optimum or acceptable values for conduits of different cross-sectional outlines or at different inclinations to the horizontal. In a particular embodiment and for conduits of any cross-sectional outline, the flow path may be inclined by an angle of at least 45°, preferably at least 80°, to the horizontal, the numerical ratio of the cross-sectional flow area in mm
2
of the flow path to its length in mm being in the range &pgr;/4:15-&pgr;/4:40.
The separating step may be a settling step in which the foam separates and settles in to a liquid layer below a gaseous header space or freeboard. Fluorinate product material and returned liquid component may be withdrawn from this liquid layer, while recirculated gaseous component can be withdrawn from the header space or freeboard, into which freeboard the gaseous fluorinating reagent feed may be fed. In particular, thus, the separation step may be a settling step in which the foam is allowed to settle into a layer of liquid component below a header space containing the gas component, fluorinated product material and returned liquid component being withdrawn from the liquid layer, recirculated gas component being withdrawn from the header space, and a feed of the gaseous fluorinating reagent being fed into the header space. Fluorinated product material will be withdrawn as part of a mixture of diluent liquid, fluorinated product material and partially reacted substrate in the form of intermediates. Fluorinated product material can be separated from this mixture, the residue formed from diluent liquid and partially reacted substrate/intermediates being reintroduced into the liquid component. Thus, in other words, the fluorinated product material and returned liquid component may be withdrawn as a mixture from the liquid layer, the process including separating the fluorinated pr

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