HK1046898B - Fluorination - Google Patents

Description

Fluorination

The present application relates to fluorination of hydrocarbon substrates. And more particularly to a process and apparatus for the perfluorinated of a hydrocarbon substrate suitable for selective substitution.

The closest prior art known to the applicant is the european patent application 94115454.4, applied in the name of the Minnesota Mining and manufacturing Company, and disclosed in publication No EP O646557 a 1. This prior reference teaches a method of fluorinating a hydrocarbon substrate which comprises diluting the hydrocarbon substrate with an inert diluent liquid and mixing the diluted hydrocarbon substrate with a gaseous fluorinating agent. The resulting reaction mixture is reacted to produce a fluorinated product. The product is then separated into a gaseous component and a liquid component in a separation step. The fluorinated product is extracted from the liquid component by distillation and the inert dilution liquid is recovered from the fraction, the recovered liquid being returned to the dilution step via the separation step. The gaseous components of the separation step are removed from the process.

EP O646557 a1 also discloses an apparatus comprising a dilution column, a mixing column in liquid communication with the dilution column for receiving a liquid feed and a gaseous feed, a reaction column in liquid communication with the mixing column, and a separation column in liquid communication with the reaction column. The separation column is provided with a liquid passage communicating with the dilution column and with a liquid reflux apparatus for refluxing the liquid component from the separation column to the dilution column and flowing the liquid component in a liquid circuit including the dilution column, the mixing column, the reaction column 1 and the separation column. The apparatus also has a liquid feed to the circuit and a gas feed to the mixing column.

EP O646557A 1 also discloses, as background material, US4,523,039(Lagow et al) and Kirk-Othmer "encyclopedia of chemical technology" 3 rd edition, Vol.10, 636, 840-855, John Wiley & Sons, Inc., New York (1980). These background materials also include the articles in "Inorganic Chemistry development (Progress in Inorganic Chemistry) 26", 161-210(1979) and also US4,859,747 (Bierschenk et al), US4,973,716 (Calini et al), US 5,076,949(Kalota et al), US 5,177,275(Baucom et al) and PCT/US89/05413(Costello et al) published in accordance with the patent Cooperation treaty at 6.1990, 14.d. as WO 90/06296.

According to one aspect of the present invention there is provided a method of fluorinating a selectively substituted hydrocarbon substrate, the method comprising the steps of:

diluting a hydrocarbon substrate feedstock with an inert diluent to form a diluted substrate;

mixing the diluted substrate with a gaseous fluorinating agent to form a reaction mixture;

reacting a fluorinating agent with a substrate in a reaction mixture, fluorinating the substrate to obtain a fluorinated product;

separating the reaction mixture containing the fluorinated products into a gaseous component and a liquid component, the liquid component containing the fluorinated products; and

extracting the fluorination product from the liquid component and recovering the fluorination product-extracted liquid component as a dilution to a dilution step, the mixing step forming a foamy reaction mixture and the process further comprising the steps of:

supplementing a fluorinating agent raw material to the gas component; and

the gaseous component comprising the fluorinating agent feedstock is recycled to the mixing step where the gaseous component provides the fluorinating agent in the reaction mixture.

Dilution of the substrate starting material with a diluent in which the diluent forms a continuous phase and acts as a carrier for the substrate may allow the substrate to form a solution, emulsion or suspension in the diluent. The inertness of the diluent in the present invention means that the diluent does not undergo unacceptable chemical reactions and preferably does not undergo any chemical reactions during the operation of the process. The substrate feed is preferably injected into the dilute liquid stream under turbulent flow, requiring an upward flow of the mixing step and not exceeding the mixing step to provide a sufficiently uniform liquid feed to the mixing step. In particular, the hydrocarbon substrate may be injected into the liquid component under turbulent flow, with the feed position of the hydrocarbon substrate between the separation step and the mixing step.

The recovery of the liquid component into the dilution step is conveniently effected by pumping the liquid component from the separation step to the dilution step at a rate sufficient to create turbulence in the pumped liquid component. The hydrocarbon substrate feedstock is injected in liquid form into the turbulent flow of pumped liquid components, but may in principle also be in gaseous form or in the form of a fine solid powder, provided that the substrate is sufficiently dissolved or otherwise dispersed in the diluent as the mixing step is carried out.

Preferably, the mixing is rapid mixing, conveniently by passing the diluted substrate and fluorinating agent together through an in-line continuous mixer, for example a static mixing device, which may conveniently take the form of a jet, eductor or jet pump of an extractor and may be provided with a venturi. Rapid mixing means that the mixing step is substantially completed in a time of at most 1 second.

Any suitable gaseous fluorinating agent may be used, for example, a compound containing a fluorine oxide. Thus, the gaseous fluorinating agent may be selected from the group consisting of F₂，UF₆，XeF₂，ClF₃And BrF₃Of the group consisting of isofluorinated gases, F is particularly preferred for reasons of yield, cost and availability₂Fluorine component of formAnd (4) adding the active ingredients. To facilitate control of the exothermic reaction step, the fluorinated gas may be diluted with an inert diluent gas, which may be a noble inert gas such as argon, but is still preferred to be nitrogen for cost and availability reasons. In other words, the gaseous fluorinating agent can also be in a diluted form when mixed with a diluted substrate, the gaseous fluorinating agent being diluted with an inert diluent gas. Thus, the recycled gas component is usually F₂/N₂Mixture of F₂From 10 to 80% by volume, preferably from 30 to 60% by volume, for example 50%, suitable or optimum values being determined by routine experimentation. In the mixing step, the volume ratio of gas to liquid mixed together may be from 2: 1 to 1: 50, preferably from 1: 2 to 1: 10, for example 1: 4, the consistency of the foam being determined by this ratio. In a particular embodiment of the invention, the gaseous fluorinating agent may be F₂When the gaseous fluorinating agent is mixed with the diluted substrate, the gaseous fluorinating agent is substantially F₂/N₂In the form of a gas mixture, wherein N₂Is an inert diluent gas, the gas mixture containing 10-80 vol% of F₂And 20-90 vol% N₂The volume ratio of the gas mixture to the diluted substrate during mixing is 2: 1 to 1: 50.

The fluorinating agent is reacted with the substrate in the foam, preferably maintaining the reaction mixture in the form of a foam that does not unacceptably separate into liquid and gaseous components until the reaction has proceeded to an acceptably complete extent. Applicants have found that extending the reaction mixture downwardly, or preferably upwardly, from the mixing step, rather than horizontally into a fluid passageway, such as a conduit in the form of a tube, facilitates retention of foam that resists separation of the mixture into liquid and gaseous components. Thus, reacting the fluorinating agent with the substrate in the foam can comprise passing the reaction mixture 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 horizontal and the fluorinating agent reacting with the substrate in the foam as the foam flows along the flow path. Length of vertical conduit when foam is discharged from the mixing step vertically up a conduit of circular cross-sectionA degree of 1: 15 to 1: 40 is particularly suitable. Routine experimentation may be used to determine the ideal or acceptable values for conduits having different cross-sectional shapes or angles different from horizontal. In a particular embodiment and for a catheter having any cross-sectional profile, the angle of the fluid path to the horizontal should be at least 45 °, preferably at least 80 °, with the fluid path being in mm²The numerical ratio of the cross-sectional flow area expressed to the passage length expressed in mm is pi/4: 15-pi/4: 40.

The separation step may be a deposition step of separating the froth and depositing a liquid layer in the lower part of the gas header space or the separation space. The fluorinated product and recovered liquid component can be separated from the liquid layer while the recycled gaseous component can be separated from the header space or separation space into which the gaseous fluorinating agent feed can be injected. Thus, in detail, the separation step may be a deposition step in which the foam is allowed to deposit as a layer of liquid component below a header space containing the gaseous component, the fluorinated product and recovered liquid component are separated from the liquid layer, the recycled gaseous component is separated from the header space, and the gaseous fluorinating agent raw material is fed into the header space. The fluorinated product is isolated as part of a mixture of the diluent, the fluorinated product, and the partially reacted substrate in the form of an intermediate product. The fluorinated product can be separated from the mixture and the residue formed by the diluent and the partially reacted substrate/intermediate is reintroduced into the liquid component. Thus, that is, the fluorinated product and the recovered liquid component can be separated as a mixture from the liquid layer, the process comprising separating the fluorinated product from the liquid component after separation of the liquid component from the liquid layer and before the dilution step of the liquid component into its diluted substrate feedstock.

In the liquid component, there is a possibility that substrate molecules or partially reacted substrate molecules react with each other and polymerize or oligomerize, which is undesirable. Such polymerization or oligomerization reactions are inhibited by separating the substrate molecules and partially reacted substrate molecules from each other using a diluent and by uniform mixing, preferably foam formation, of the liquid component and the gaseous component. Thus, the time for separating the liquid component from the gaseous component in the foam should be as short as possible, and the residence time of the liquid component in the separation step should be as short as possible, and should be the time required for feeding the liquid component from the separation step to the mixing step, and also the time from the reaction step in the foam to the separation step, since the separation can take place before the separation step. In detail, the sum of the residence time of the liquid component in the separation step and the residence time of the liquid component in the recovery step of the liquid component after leaving the separation step and entering the mixing step may generally be at most 10 seconds. However, the upper limit of the total residence time can generally be determined by the nature of the substrate and the diluent used. Thus, the appropriate residence time for each fluorinated product should be determined by routine experimentation, taking into account commercial and practical considerations, particularly avoiding or limiting the irreversible production of undesirable by-products.

As far as the parameters of the process are concerned, the reaction step can be carried out at a higher pressure ranging from the vapour pressure of the diluent at the reaction temperature to 28MPa, preferably 200kPa to 700kPa, such as 400 kPa. The reaction temperature is from-40 ℃ to 80 ℃ and suitably from-30 ℃ to 50 ℃, e.g. 20 ℃. Typically, the fluorinating agent and the hydrocarbon substrate are reacted in the foam at a reaction pressure of 200 and 700kPa and a reaction temperature of-10 ℃ to 50 ℃. A suitable inert diluent has been found to be hydrofluoric acid (HF) and the substrate may be added to the recycled liquid component in a ratio of dilution of the substrate in the diluent of from 1: 20000 to 1: 300000 or more, suitably from 1: 50000 to 1: 300000, e.g.1: 160000. In other words, the hydrocarbon substrate feedstock is fed to the inert diluent in such a proportion that the substrate obtained is diluted in the diluent in such a proportion that: the volume ratio of the substrate to the diluent is in the range of 1: 50000-1: 300000.

As indicated above, the hydrocarbon substrate is optionally substituted. Thus, suitable substrates that may be fluorinated or perfluorinated (i.e., fully fluorinated) according to the methods of the present invention include unsubstituted saturated and unsaturated hydrocarbons, such as aromatic hydrocarbons containing alkyl and/or aryl groups, as well as substituted hydrocarbons, such as halocarbons, carboxylic acid halides, sulfonyl halides, esters, and ethers, and the like. Typically, any unsaturated bonds in the substrate are converted to saturated bonds by fluorination. In general, the substrate may be selected from the group of unsubstituted hydrocarbons including alkyl compounds and aryl compounds, and from the group of substituted hydrocarbons including halogenated hydrocarbons, carboxylic acid halides, sulfonyl halides, esters and ethers. As noted above, the preferred inert diluent is Hydrogen Fluoride (HF) because it is sufficiently inert for this purpose and compatible with the materials used in the present process and in the apparatus described below.

According to another aspect of the present invention there is provided an apparatus for fluorinating a selectively substituted hydrocarbon substrate, such as by the method described above, which apparatus is a circuit for a liquid stream comprising:

a dilution tower for receiving the hydrocarbon substrate feedstock and a diluent and diluting the substrate with the diluent, respectively;

a mixing column having a flow path in communication with the dilution column for receiving the diluted hydrocarbon substrate feedstock and the gaseous fluorinating agent from the dilution column, respectively, and mixing the diluted hydrocarbon substrate feedstock with the gaseous fluorinating agent to form a reaction mixture;

a reaction column in flow communication with the mixing column for receiving the reaction mixture from the mixing column and reacting the fluorinating agent with the substrate in the reaction mixture to fluorinate the substrate to form a fluorinated product;

a separation column whose flow path is communicated with the reaction column and which has a liquid flow connected to the dilution column and a gas flow connected to the mixing column for receiving the reaction mixture containing the fluorinated product from the reaction column, separating the reaction mixture into a gas component and a liquid component, feeding the separated liquid component as a diluent to the dilution column, and feeding the separated gas component containing the gaseous fluorinating agent to the mixing column;

a liquid recovery apparatus that recovers the separated liquid component from the separation column to the dilution column to circulate the liquid in a liquid stream circulation circuit including the dilution column, the mixing column, the reaction column, and the separation column;

a substrate liquid feed to the circulation loop; and

a fluorinating agent gas feed pipe for introducing a fluorinating agent into a gas flow connector between the reaction column and the mixing column.

The reaction mixture is formed in the mixing column in the form of a foam, and the apparatus further comprises a gas recycling means for recycling the gas separated from the separation column to the mixing column.

The feed line for the substrate liquid can be connected to the dilution column and the feed line for the fluorinating agent gas can be connected to the separation column.

More specifically, the mixing column may be provided with a static mixing device, for example a jet pump comprising a venturi through which the diluted substrate in use flows to effect extraction, and through which the recycle gas from the separation column also passes, so that the jet pump acts as a gas recirculation means to recirculate the gas components. That is, the mixing tower may comprise an in-line continuous mixer, such as a static mixer without any moving parts; specifically, the continuous mixer may be a jet pump connected in-line to a circulation circuit between the dilution column and the reaction column so that the diluted substrate flows from the dilution column to the reaction column as a liquid to be pumped thereby, the jet pump having a gas suction port communicating with the separation column and the fluorinating agent gas feed pipe, the jet pump functioning as a gas recirculation apparatus. The connection of the suction chamber inlet to the feed line for the fluorinating agent gas can be direct or indirect via a separation column. The liquid recovery apparatus that causes the liquid component to be recovered may be a pump that pumps the recovered liquid component at a turbulent flow rate through a dilution column along a conduit to a mixing column, where the conduit receives the substrate feedstock and the conduit between the substrate feed and the mixing stage functions as a dilution column.

The reaction column may also be a conduit, for example a pipe having a circular cross-section, extending upwardly, preferably vertically, from the venturi, preferably the pipe having a diameter to length ratio of from 1: 15 to 1: 40, more preferably from 1: 20 to 1: 35, for example 1: 28. In general, the reaction column may be a conduit having an angle of at least 45 °, preferably at least 80 °, to the horizontal, in mm for any cross-sectional profile²The ratio of the cross-sectional flow area expressed to the length of the conduit expressed in mm is in the range pi/4: 15-pi/4: 40, particularly preferred are substantially vertical (i.e. having an angle greater than 80 deg. to the horizontal) conduits having a circular cross-section with a diameter: length of 1: 20 to 1: 35.

The separation column may be a settling tank arranged alongside the venturi and the conduit forming the reaction column, preferably in an arrangement such that the pump is arranged to pump the liquid component from the settling tank to the venturi as short as possible, bearing in mind that the substrate feedstock is sufficiently distant from the venturi to allow the substrate to be sufficiently uniformly diluted or dispersed by the liquid component prior to entering the venturi, but sufficiently close to the venturi to prevent and preferably prevent undesirable side reactions such as polymerisation or oligomerisation, and the flow from the conduit above the reaction column to the separation column is also as short as possible. This is to keep the residence time of the liquid component, which does not foam with the gas component, as short as possible, so that undesired polymerization or oligomerization of the not yet fully fluorinated substrate molecules is prevented. That is, the separation column may be a deposition tank having a lower outlet leading to the dilution column, an upper outlet leading to the mixing column, and an upper fluorinating agent gas feed inlet; the conduit between the separation column and the dilution column is as short as possible, and on the other hand, the dilution column is positioned so that the diluted substrate enters the mixing column as quickly as possible after the dilution is completed, so that the residence time of the diluted substrate in the conduit, except for as a foam component, is preferably at most 10 seconds. A fluorinating gas may be injected into the header space or separation space of the deposition pot and a diluent inert gas, such as nitrogen, may be injected into the gas component. When the sedimentation of the liquid component is slowed down, a cyclonic separating device, such as a cyclone (hydrocyclone), may be included in the separation column to accelerate the separation process. This upper time limit can be determined by routine experimentation as described above in relation to the process of the invention, bearing in mind the nature of the substrate and the diluent used, practical and economic considerations and the need to avoid the production of undesirable by-products. While shorter times are desirable in most cases, longer residence times are also expected when the substrate and diluent can be subjected to deposition for longer times to varying degrees, which also demonstrates the flexibility of the process of the invention.

In this regard, it is contemplated that while the process of the present invention may be operated on a nominally continuous basis, it may still be considered a quasi-batch type process, since in any fluorinated gas, such as molecular fluorine (F)₂) May be present as impurities and may produce volatile decomposition products during the fluorination step. Therefore, the accumulation of these impurities necessitates periodic emptying of the circulation system formed by the device and the start-up of a new process. Of course, if the purity of the fluorinated gas is sufficiently high and the amount of volatile decomposition products formed is acceptably low, periodic purging is not required, or such purging may be a special or occasional case over a long interval. During the start-up phase, nitrogen is often passed through the gas composition of the deposition tank to dilute the fluorine gas, after which, although during the run-up of the process, it is necessary to continually replenish the process with substrate and fluorine as they are consumed, there is no need to pass nitrogen again until the next start-up or after successful evacuation (if required). It is expected that the consumption of nitrogen is acceptably low and that during operation, no nitrogen make-up is required prior to evacuation. If desired, nitrogen can be introduced after evacuation or before the next start-up.

The overall configuration of the apparatus of the invention is capable of withstanding variations in reaction conditions, allowing optimisation for different products and increasing the ease of process control and the desired degree of safety.

The invention will now be described, by way of non-limiting example, with reference to the accompanying drawings, which illustrate a method according to the invention and which, at the same time, will be described with reference to the examples which have been described hereinafter, and which show a schematic flow chart of an apparatus according to the invention.

In the drawings, reference numeral 10 generally indicates an apparatus for carrying out the process of the invention in accordance with the invention. In apparatus 10, the substrate feed line is a circular conduit indicated by the numeral 12 and represents the feed to the upstream end of the dilution column in flow line form, wherein the flow line is a circular conduit indicated by 14.

Flow line 14 feeds a mixing column in the form of a jet pump 16 comprising a venturi which in turn feeds a reaction column in the form of flow line 18, flow line 18 being a vertically upwardly extending pipe of circular cross section having a diameter to length ratio of 1: 28. The top end of the conduit 18 feeds a horizontally extending flow line 20, the downstream end of the flow line 20 feeding down a separation column in the form of a settling tank 22.

A fluorinated product outlet flow line 24 begins at the bottom of tank 22 and a fluorine gas feed line 26 and a nitrogen gas feed line 28 feed into the upper portion of tank 22, respectively, and a fluorine feed line feeds tank 22 at an elevated feed inlet 27. A pump 30 is used, the pump 30 having an inlet fed from a flow line 32, the flow line 32 communicating with a low level outlet 33 at the bottom of the tank 22, the pump 30 also having an outlet feeding a flow line 34, the flow line 34 in turn feeding the upstream end of the flow line 14. Although not explicitly shown in the drawings, the arrangement of the various components of the apparatus 10 is such that the flow lines 14, 20, 32 and 34 are as short as possible, and in particular the flow line 14 is not more than required to sufficiently mix and dilute the dilution of the substrate feed from the flow line 12 with the liquid in the flow line 34 before it enters the jet pump 16. A gas flow line 36 extends from a high level outlet 37 at the top of the tank 22 to a gas inlet 38 of the jet pump 16.

In use, at start-up, the tank 22 is filled with a suitable volume of diluent, for example hydrogen fluoride as hereinafter described, and the header or separation space above the diluent in the tank is filled with a suitable fluorine/nitrogen mixture, for example a 50: 50 mixture by volume, with fluorine from flow line 26 and nitrogen from flow line 28.

The process of the invention is operated by use of a pump 30 which pumps liquid from tank 22 along flow lines 32, 34 and 14 to jet pump 16 while supplying substrate along flow line 12 from an external supply source to tank 14 and fluorine along flow line 26 from an external supply source to tank 22 and liquid is withdrawn from tank 22 along line 24. During operation, nitrogen gas need not be passed along flow line 28, but instead the jet pump 16 draws gas from the separation space of the tank 22 via flow line 36 and recirculates it into the gas inlet 38 of the jet pump 16 and thence into the flow line/reaction column 18.

The diluent and substrate feed are rapidly mixed in the flow line 14 to maintain the turbulent flow of the liquid in the flow line 14 by operating the pump 30 at an output rate sufficient to cause turbulent flow in the flow line 14. The mixed substrate and diluent mix in the jet pump 16 with the gaseous components from the flow line 36 and form a continuous foam that completely occupies and fills the flow line 18 and rises up the line 18. The foam passes from flow line 18 along flow line 20 to tank 22 where gas-liquid separation occurs in tank 22.

Fluorination of the substrate takes place in flow line 18 and is as near to completion as possible in flow line 20 and tank 22. The liquid layer (not shown) formed in the lower part of the tank 22 contains the diluent, the partially reacted substrate (partially fluorinated product), the fully fluorinated product, i.e. perfluorinated product, and the dissolved (saturated) reaction gas (F)₂And N₂)。

The substrate is fed along line 12 and fluorine gas along line 26 at the rate at which fluorination occurs in flow lines 18 and 20 and tank 22, while the fluorinated product is withdrawn from tank 22 along line 24 at the rate at which fluorinated product, e.g., perfluorinated product, is produced by fluorination. The extracted fluorinated product is sent to a separation column (not shown), such as a distillation column, where the fluorinated product is separated from the diluent and partially fluorinated product and the diluent and partially fluorinated product are reintroduced into the tank 22. Liquid is withdrawn from tank 22 by pump 30 through lines 32 and 34 to the dilution step in line 14.

It has been found that the feed rate of the fluorinated gas to tank 22 can be conveniently adjusted by means of a pressure regulating valve (not shown) at the location of inlet 27 from line 26 to obtain the desired constant pressure in tank 22. This is because the pressure drop in the apparatus forming the closed circuit is caused by the lowering of the partial pressure of fluorine gas due to fluorination of the substrate. Thus, the fluorine gas feed rate is directly dependent on the substrate feed rate and is also self-regulating, provided that the pressure in the cycle is kept constant. The substrate feed rate, in turn, is also adjusted to maintain the temperature within the apparatus within an acceptable range, keeping in mind that fluorination of the substrate will generate heat.

The apparatus and method may be operated in accordance with the following examples.

Example 1

Perfluorination of n-hexane

In an apparatus according to the drawing, with a total volume of 8 liters, except for the flow lines 12, 26, 28 and 24, 6kg of anhydrous hydrofluoric acid (hydrogen fluoride or HF) were fed into the tank 22. The liquid is then pumped at a rate of 60kg/min using pump 30 along a circulation loop constituted by pump 30, venturi pump 16, flow lines 14, 18, 20, 32 and 34, so that hydrofluoric acid circulates 10 times per minute within the loop, thus overall the residence time in the circulation, and the sum of the residence times in the separation step, the circulation step and the dilution step is at most 6 seconds.

Nitrogen gas was introduced into the tank 22 to a pressure of 200kPa, and then fluorine gas was slowly introduced into the tank 22 until a pressure of 400kPa was reached to obtain F in the tank₂∶N₂In a 50: 50 volume ratio. The tank 22 is set to a temperature controlled at 25 ℃.

The dried n-hexane was pumped at a rate of 50 μ l/min to the recycle loop through conduit 12 using a piston pump (not shown) while fluorine gas was passed to tank 22 at a rate sufficient to maintain a pressure of 400kPa within tank 22. Then, a slight increase in temperature within the tank 22 and a change in fluorine feed along the line 26 are noted. Liquid is withdrawn from tank 22 along conduit 24 at a rate sufficient to maintain a constant low liquid level within tank 22 and no foam is withdrawn.

The liquid withdrawn from the tank through line 24 is allowed to settle and separate into two layers, the bottom layer being perfluorinated n-hexane. The partially fluorinated product is recycled back to tank 22 by distillation purification, discarding the heavier oligomerization waste. The deposited supernatant liquid is distilled to obtain purified hydrofluoric acid suitable for recovery in line 14 or elsewhere, and other fractions containing partially fluorinated products obtained by distillation of the supernatant liquid are also recovered in tank 22.

A theoretical yield of 85% of perfluorinated n-hexane was obtained, with fluorine losses of less than 2%.

Example 2

Perfluorination of octanoyl fluoride

Example 1 was repeated except that octanoyl fluoride as a substrate was fed to HF as a diluent through a line 12 at a rate of 300. mu.l/min. Likewise, 50: 50F at a total reaction pressure of 400kPa is used₂∶N₂And (4) the ratio. The reaction temperature is controlled between-10 ℃ and-5 ℃. Liquid is continuously drawn from the conduit 24 to maintain the level of the deposition tank 22 constant. The product mixture is distilled to separate HF from the organic components. The perfluorinated product thus obtained is further purified by removing by-products therefrom by distillation once more. Under non-optimal conditions, a yield of perfluorinated octanoyl fluoride of 62% was obtained.

Example 3

3-methoxy-tetrafluoropropionic acid methyl ester per seFluorination of

Example 1 was repeated with perfluorinated methyl 3-methoxy-tetrafluoropropionate as substrate, which was fed via line 12 to HF as diluent at a rate of 900. mu.l/min. A40: 60F total reaction pressure of 350kPa was used₂∶N₂And (4) the ratio. The reaction temperature is controlled between 4 ℃ and 10 ℃. Liquid is continuously drawn from the conduit 24 to maintain the level of the deposition tank 22 constant. The expected product was found to be very unstable in the undiluted state. It was found that in the presence of a suitable nucleophile, deesterification occurred to yield acyl fluoride and carbonyl difluoride. To analyze the product, methoxy ester was formed. This is achieved by first separating the organic product from the HF. Thus, a sample of the product mixture is added to and reacted with methanol therein. The mixture thus obtained was put into ice and allowed to separate into different layers. The lower organic layer was separated and mixed again with additional methanol and potassium fluoride. The mixture was then stirred for 6 hours. After further washing and subsequent drying over sodium sulfate, and then filtration, the methoxy esters were analyzed. Under non-optimal conditions, a 47% yield of methyl 3-trifluoromethyloxy-tetrafluoropropionate was obtained.

Example 4

Perfluorination of methyl 2-methoxy-tetrafluoropropionate

Example 1 was repeated with a perfluorinated 2-methoxy-tetrafluoropropionic acid methyl ester substrate. The substrate was fed through line 12 to HF as a diluent at a rate of 900. mu.l/min. Using a 40: 60F to give a total reaction pressure of 350kPa₂∶N₂And (4) the ratio. The reaction temperature is controlled between 4 ℃ and 10 ℃. Liquid is continuously drawn from the conduit 24 to maintain the level of the deposition tank 22 constant. A sample of the product mixture was added to methanol and allowed to react therein with methanol. The mixture thus obtained was discharged into ice and allowed to separate into different layers. The lower organic layer was separated and dried over sodium sulfate, and then filtered. The filtered material is distilled at a temperature between 32 ℃ and 34 ℃ to obtain a product fraction. In the non-optimal stateUnder these conditions, a yield of perfluorinated 2-methoxy-propionic acid methyl ester of 35% was obtained.

An advantage of the present invention, particularly as described with reference to the drawings and with reference to examples 1 to 4 described above, is that it provides an efficient process and apparatus for the fluorination or perfluorination of hydrocarbon substrates which provides good yields, particularly under optimised conditions, in a manner which is simple to operate and economically competitive in practice.

Claims (25)

1. A method of fluorinating a hydrocarbon substrate, the method comprising the steps of:

diluting a hydrocarbon substrate feedstock with an inert diluent to form a diluted substrate;

mixing the diluted substrate with a gaseous fluorinating agent to form a reaction mixture;

reacting a fluorinating agent with a substrate in a reaction mixture, fluorinating the substrate to obtain a fluorinated product;

separating the reaction mixture containing the fluorinated products into a gaseous component and a liquid component, the liquid component containing the fluorinated products; and

extracting the fluorination product from the liquid component and recovering the fluorination product-extracted liquid component as a dilution to a dilution step, the method being characterized in that a foamy reaction mixture is formed in the mixing step and the method further comprises the steps of:

supplementing a fluorinating agent raw material to the gas component; and

the gaseous component comprising the fluorinating agent feedstock is recycled to the mixing step, wherein the gaseous component provides the fluorinating agent in the reaction mixture.

2. A process as claimed in claim 1, wherein the hydrocarbon substrate feedstock is introduced into the liquid component stream in a turbulent flow, the hydrocarbon substrate feed being at a location between the separation step and the mixing step.

3. A method as claimed in claim 2, wherein the hydrocarbon substrate feedstock is added in liquid form to the turbulent flow of pumped liquid component and hydrocarbon substrate by pumping the liquid component back to the dilution step at a rate sufficient to cause turbulent flow of the pumped liquid component.

4. A process as claimed in any one of claims 1 to 3, wherein the mixing is effected by a mixing step which is substantially complete in a time of at most 1 second.

5. A process as claimed in any one of the preceding claims wherein the gaseous fluorinating agent is selected from the group consisting of F₂，UF₆，XeF₂，ClF₃And BrF₃Of the group of fluorinated gases.

6. A process as claimed in any one of the preceding claims wherein the gaseous fluorinating agent, when mixed with the diluted substrate, is a gaseous fluorinating agent diluted with an inert diluent gas.

7. A process as claimed in any one of the preceding claims wherein the gaseous fluorinating agent is F₂Mainly of F₂/N₂In the form of a fraction of the gas mixture of (1), wherein N is₂Is an inert diluent gas, the gaseous fluorinating agent, when mixed with the diluted substrate, containing 10-80% by volume of F₂And 20-90 vol% N₂In the mixing step, the volume ratio of the gas mixture to the diluted substrate is 2: 1 to 1: 50.

8. A process as claimed in any one of the preceding claims wherein reacting the fluorinating agent with the substrate in the foam comprises passing the reaction mixture as a foam through a flow from the mixing step to the separation step at an angle to the horizontal, the fluorinating agent reacting with the substrate in the foam as the foam moves within the flow.

9. A process as claimed in claim 8, wherein the angle between the flow path and the horizontal is at least 45 ° in mm²The numerical ratio between the cross-sectional flow area of the flow path represented and the length of the flow path in mm is between pi/4: 15 and pi/4: 40.

10. A process as claimed in any one of the preceding claims wherein the separation step is a deposition step in which the foam is deposited as a layer of liquid component located below a header space containing the gaseous component, the fluorinated product and recovered liquid component being withdrawn from the liquid layer, the recycled gaseous component being withdrawn from the header space and the gaseous fluorinating agent feed being passed into the header space.

11. A process as claimed in claim 10, wherein the fluorination product and recovered liquid component are withdrawn as a mixture from the liquid layer, the process comprising separating the fluorination product from the liquid component after the liquid component has been withdrawn from the liquid layer, before the step of diluting the liquid component into the dilution substrate.

12. A process as claimed in any one of the preceding claims wherein the residence time of the liquid component in the separation step and the residence time of the liquid component in the recovery step after it leaves the separation step until it enters the mixing step add up to 10 seconds.

13. A process as claimed in any one of the preceding claims wherein the fluorinating agent is reacted with the hydrocarbon substrate in the foam at a reaction pressure of 200kPa and a reaction temperature of-30 ℃ to 50 ℃.

14. A process as claimed in any one of the preceding claims wherein the hydrocarbon substrate feedstock is fed to the inert diluent in a ratio such that in the diluted substrate the volume ratio of substrate to diluent is in the range 1: 50000 to 1: 300000.

15. A process as claimed in any one of the preceding claims wherein the substrate is selected from the group of unsubstituted hydrocarbons consisting of alkyl and aryl compounds and substituted hydrocarbons consisting of halogenated hydrocarbons, carboxylic acid halides, sulphonyl halides, esters and ethers.

16. A process as claimed in any one of the preceding claims wherein the inert diluent liquid is hydrogen fluoride.

17. An apparatus for fluorinating a hydrocarbon substrate, the apparatus being a liquid flow recycle loop comprising:

a dilution tower for receiving the hydrocarbon substrate feedstock and a diluent and diluting the substrate with the diluent, respectively;

a mixing column in fluid communication with the dilution column for receiving the diluted hydrocarbon substrate feedstock and the gaseous fluorinating agent from the dilution column, respectively, and mixing the diluted hydrocarbon substrate feedstock with the gaseous fluorinating agent to form a reaction mixture;

a reaction column in fluid communication with the mixing column for receiving the reaction mixture from the mixing column and reacting the fluorinating agent with the substrate in the reaction mixture to fluorinate the substrate to form a fluorinated product;

a separation column in fluid communication with the reaction column and having a liquid stream connected to the dilution column and a gas stream connected to the mixing column for receiving the reaction mixture containing the fluorinated product from the reaction column, separating the reaction mixture into a gaseous component and a liquid component, feeding the separated liquid component as a diluent to the dilution column, feeding the separated gaseous component containing the gaseous fluorinating agent to the mixing column;

a liquid recovery apparatus that recovers the separated liquid component from the separation column to the dilution column to circulate the liquid in a liquid stream circulation circuit including the dilution column, the mixing column, the reaction column, and the separation column;

a substrate liquid feed to the circulation loop; and

a fluorinating agent gas feed pipe for introducing a fluorinating agent into a gas flow connector between the reaction column and the mixing column, the apparatus being characterized in that a foamed reaction mixture is formed in the mixing column, and the apparatus further comprising gas recycling means for recycling the separated gas component from the separation column to the mixing column.

18. An apparatus as claimed in claim 17, wherein the substrate liquid feed feeds the dilution column and the fluorinating agent gas feed feeds the separation column.

19. An apparatus as claimed in claim 17 or 18, wherein the mixing column comprises an in-line continuous mixer without any moving parts.

20. An apparatus as claimed in claim 19, wherein the continuous mixer is a jet pump connected in-line to the circulation circuit between the dilution column and the reaction column to allow the diluted substrate to flow as its pumped liquid from the dilution column to the reaction column, the jet pump having a gas suction port communicating with the separation column and the fluorinating agent gas feed pipe, the jet pump functioning as a gas recirculation device.

21. An apparatus as claimed in any one of claims 17 to 20 wherein the liquid recovery means is a pump for pumping the recovered liquid component through the dilution column at a turbulent flow rate.

22. An apparatus as claimed in any one of claims 17 to 21 wherein the reaction column is a conduit angled at least 45 ° to the horizontal, the conduit being in mm²The ratio of the expressed cross-sectional flow area to the length of the conduit in mm is in the range of pi/4: 15 to pi/4: 40.

23. Apparatus as claimed in any one of claims 17 to 22 wherein the conduit is a substantially vertical tube having a circular cross-section with a diameter to length ratio of from 1: 20 to 1: 35.

24. An apparatus as claimed in any one of claims 17 to 23 wherein the separation column is a deposition tank having a lower liquid outlet to the dilution column, an upper gas outlet to the mixing column and an upper fluorinating agent gas feed inlet.

25. An apparatus as claimed in any one of claims 17 to 24, wherein the portion of the communication line between the separation column and the dilution column is as short as possible, the dilution column being arranged such that the diluted substrate after completion of the dilution enters the mixing column as quickly as possible, so that the residence time of the diluted substrate in the communication line, except for as a foam component, is at most 10 seconds.