Perfluorocarbons have a number of industrial uses such as refrigerants, gaseous dielectrics, propellants, and the etching of silicon chips. In addition, perfluorocarbons have a number of important medical applications, including the use of perfluorocarbon liquids in eye surgery or as contrast agents in ultrasonic diagnosis, etc. While sources of many perfluorocarbon liquids are readily available for industrial uses, these are not pure enough for use in medical fields, particularly for use in humans.

A medically important perfluorocarbon for whose production the present invention is particularly suitable is perfluoropropane (C3F8 also known as PFP). Typically, PFP is produced by the catalytic perfluorination of hexafluoropropene (C3F6 or HFP) with cobalt trifluoride (CoF3) as a transfer agent.

Another important contrast agent in medical applications is sulfur hexafluoride (SF6).

Processes for fluorination generally include in situ reaction with electrolysis of hydrogen fluoride, catalytic reaction with metal fluorides such as cobalt fluoride, and direct fluorination. Electrolysis and metal fluoride reactions are expensive both in terms of equipment and material costs. Direct fluorination does not appear to be practiced in industry. However, in the 1950's L. A. Bigelow and others at Duke University experimented with direct fluorination of organic

compounds. They developed a reactor and jet fluorination system for achieving relatively high conversion of carbon and sulfur compounds to various fluorinated products, including about 85% conversion of propane to perfluoropropane (PFP).

This work was published in a series of articles entitled"The Action of Elementary Fluorine upon Organic Compounds"in the Journal Of The American Chemical Society. See E. A. Tyczkowski et al.,"XVIII. A New Type of Reactor and the Mild Fluorination Of Carbon Disulfide,"J. Am. Chem. Soc. 75: 3523-3526 (1953); E. A.

Tyczkowski et al.,"XIX. A New Jet Fluorination Reactor,"J. Am. Chem. Soc.

77: 3007-3008 (1955); A. F. Maxwell et al.,"XXIII. The Jet Fluorination of Certain Aliphatic Hydrocarbons as Oriented and Controlled by Operating Conditions"J.

Am. Chem. Soc. 82: 5827-5830 (1960).

However, for commercial applications higher conversion rates are desired, and for the medical uses mentioned above, high purities are necessary. One problem associated with the original method of Bigelow et al. for forming PFP and other compounds is that unreacted reactants accumulate at the top of the reaction chamber, which allows a build-up of the concentration to sufficiently high levels that sudden reactions and mild explosions can result.

Accordingly, improved methods and apparatus are desired for safer, less expensive, more complete, and more efficient fluorination of carbon and sulfur compounds.

BRIEF SUMMARY OF THE INVENTION According to the present invention, methods are provided for the direct fluorination of carbon and/or sulfur compounds, such as hydrocarbons, hydrofluorocarbons, fluorocarbons, sulfur, sulfocarbons and sulfur fluorides. The basic method comprises providing separate reactant streams of fluorine and the compound to be fluorinated, diluting at least one stream with a gas, mixing the diluted streams together in a reaction zone to provide a fluorinated reaction product, recycling a portion of the reaction product as the dilution gas for at least one of the reactant streams, and collecting the remainder of the reaction product.

The reaction product is preferably recycled countercurrently outside and adjacent to the reaction zone to cool the reaction product, and both reactant streams are preferably diluted with the reaction product. The reactant streams may be fed to the reaction zone in the form of gaseous jets with the recycled reaction product sucked or aspirated into the gaseous jets. The diluted fluorine stream may be formed by aspiration of fluorine gas into a gaseous jet of compressed reaction product or the fluorine may be provided in a gaseous jet of inert gas.

A particularly preferred method of the present invention involves the fluorination of HFP to predominately PFP, wherein at least one of the streams of HFP and fluorine is diluted with PFP prior to mixing of the streams in the reaction zone. The HFP and fluorine are reacted with a slight stoichiometric excess of fluorine to ensure essentially complete reaction and a slight excess of fluorine in the reaction product.

The apparatus according to the invention includes an elongated reaction zone having feed ports at one end for supplying separate gaseous streams of fluorine and the compound to be fluorinated and an opening at the opposite end of the reaction zone for removing reaction product. A chamber adjacent to the reaction zone and connected to the opposite end opening allows passage of the reaction product in separate heat exchange flow countercurrent to the reaction zone.

Suction ports allow for aspiration of a portion of the reaction product into at least one of the feed ports, and an outlet is provided in the chamber for collecting reaction product. Preferably, compressed reaction product is supplied to one of the feed ports, and a line is provided for supplying fluorine gas to a suction port of this feed port.

In a particularly preferred apparatus, the reaction zone is formed by a first tube open at one end which is surrounded by a second longer and larger diameter tube which is closed at both ends, so as to form an annular space around the first tube and the suction ports. The open end of the first tube is spaced from one closed end of the second tube to allow passage of the reaction product into the annular space around the first tube, and an outlet for collecting reaction product is located at the opposite end of the second tube. Preferably, the suction ports are

provided in eductors which supply the gaseous reactants to the reaction zone as jet streams.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiment (s) which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: Fig. 1 is a schematic flow diagram of a reactor system illustrating the method and apparatus according to one embodiment of the present invention; Fig. 2 is a schematic flow diagram of a reactor system illustrating the method and apparatus according to another embodiment of the present invention; Fig. 3 is a simplified lateral view, partially in section and partially broken away, of a reactor used in the system of Fig. 2.; and Fig. 4 is a cross-sectional view, taken along section line 4-4, of the simplified reactor of Fig. 3.

Throughout the drawings, the same or similar elements are designated by the same reference numerals.

DETAILED DESCRIPTION OF THE INVENTION As used herein, the term"fluorination"is intended to include both the initial fluorination of non-fluorinated compounds such as hydrocarbons, sulfur and sulfocarbons as well as perfluorination of already fluorinated compounds such as fluorocarbons, hydrofluorocarbons and sulfur fluorides. Further, as used herein, the term"direct fluorination"refers to the reaction of a compound to be fluorinated directly with fluorine gas (F2), as opposed to reaction with a fluorine compound, such as in situ reaction with electrolysis of hydrogen fluoride or catalytic reaction with a metal fluoride.

Compounds to be fluorinated may include any compound which will react directly with fluorine gas, but principally hydrocarbons, hydrofluorocarbons,

fluorocarbons, sulfur, sulfocarbons such as carbon disulfide, and sulfur fluorides, e. g., SF4 + F2 ~ SF6. Compounds which are particularly suitable for direct fluorination include the unsaturated fluorocarbons, hydrofluorocarbons and hydrocarbons.

Since the fluorine reactant is in gaseous form, it is also preferred that the compound to be reacted, as well as the diluents for the reactant streams, be in gaseous or vapor form. If the compound to be fluorinated is normally a liquid at the temperature and pressure conditions of the fluorination reaction, the liquid compound can be converted to vapor form for reaction with the fluorine by any suitable means, such as atomization, spraying or aspiration into the diluent stream.

For example, liquid (molten) sulfur or a liquid hydrocarbon or fluorocarbon could be injected into a stream of diluent gas or sprayed into the reaction zone with a diluent gas for vapor phase reaction with the gaseous fluorine (e. g., S + 3F2-SF6).

Because of the high reactivity of fluorine gas, many of the fluorination reactions contemplated by the present invention will occur spontaneously at ambient temperature and atmospheric pressure, including particularly the preferred reaction of HFP with fluorine to produce PFP product gas.

The fluorination reaction is essentially exothermic, and the temperature of the reaction according to the method and apparatus of the present invention is controlled by a number of factors, including rapid dilution of the reactants with product gas, expansion of the pressurized gas jets in the reaction zone, and passing of the reaction gases from the top of the reaction zone into the adjacent recycle chamber.

In effect, the reactor apparatus according to the invention provides a heat sink to limit or control any temperature increase due to the fluorination reaction. Moreover, the induced flow from the reaction zone into the recycle chamber prevents buildup of reactants within the reactor, thus preventing or impeding sudden reactions and mild explosions which are typical of prior art direct fluorination processes. Nevertheless, if necessary or desired, external heaters or cooling coils can be provided in or outside of the reaction zone or recycle chamber to further control the reaction temperature. However, as demonstrated below, the

reaction temperature can often be adequately controlled, particularly in the case of the fluorination of HFP to PFP, by suitable setting of dilution ratios and recycle rates within the reactor. For example, dilution of the incoming fluorine with about six times the volume of product gas and dilution of the incoming HFP with an equal volume of product gas gives a temperature of about 500 °F in the inner tube of the reactor.

An important factor in controlling the fluorination reaction is the dilution of the reactant stream (s), namely the fluorine gas stream and/or the stream or streams of compound to be fluorinated. Preferably, the diluent consists of the fluorinated compound reaction product which is recycled after leaving the reaction zone. Additionally, or alternatively, the diluent gas may comprise an inert gas, such as argon, nitrogen or helium, which may also be used as a purge gas to remove undesired chemicals from the reactor prior to the fluorination reaction. However, the use of an inert gas as a diluent has the disadvantage of requiring later separation of the inert gas from the PFP or other fluorinated product.

In order to ensure complete mixing of the diluted reactant streams in the reaction zone to produce a fluorinated compound reaction product, it is preferred that the gas stream be fed to the reaction zone in the form of gaseous jets.

Such a high velocity introduction of the reactants is also believed to induce a flow of the product gases along the inside wall of the reaction zone. The product gases are also caused to rapidly pass from the top of the reaction zone into the recycle chamber where the product gases are thus induced to pass in countercurrent, heat exchange flow adjacent to the reaction zone, thereby aiding in the cooling of the reaction product before internal recycling into the reactant feed stream or streams.

Preferably, both fluorine and compound reactant streams are diluted with internally recycled reaction product.

A preferred device for injecting the diluted gas streams into the reaction zone is an eductor. Eductors are well known and commercially available devices in various forms for injecting gas streams. Various types of eductors include venturi tubes, jet pumps, ejectors, syphons, injectors and aspirators.

Suitable eductors for use in the present invention are available, for example, from

Fox Valve Development Corporation of Dover, New Jersey, under the name Fox Mini-Eductors. A typical eductor for use in the present invention has a high pressure input port or motive jet for coupling to the supply line for the reactant and/or diluent gas, at least one suction port for drawing or aspirating recycled reaction product into the high pressure reactant and/or diluent gas stream, and a discharge port or nozzle for injecting the reactant and/or diluent gas into the reaction zone. Since the suction port (s) of the eductors are preferably located within or in direct fluid communication with the recycle chamber, this provides a so-called internal recycle of the reaction product, which is controlled in part by the inlet velocity of the reactant and/or diluent gases through the eductors.

While internal recycle of the reaction product through the suction ports of the eductors may be sufficient in some cases, particularly at lower flow rates, to effectively control the reaction, it has been found according to a preferred embodiment of the present invention that external recycle or recirculation of a portion of the reaction product can more effectively control the reaction, particularly at higher flow rates. According to this preferred embodiment, a portion of the reaction product is removed from the reactor, compressed and cooled to condense out most of the heavy byproduct components, and returned for reintroduction into the reaction zone as a feed stream through at least one of the feed eductors.

In a particularly preferred embodiment, described more fully below, the externally recycled reaction product is recycled through the high pressure jet of one of the eductors, and the fluorine reactant gas is fed directly into one of the suction ports of this recycle eductor, so that the fluorine gas is entrained in and mixed with the externally recycled reaction product for feeding into the reaction zone. This arrangement has the advantage that the fluorine mixes with the recycled reaction product after cooling by expansion through the motive jet of the eductor and is then introduced into the reaction zone at relatively low pressure. As a result, it is less likely that the fluorine will react with the compound to be fluorinated to form lighter byproducts, which can happen when both the fluorine and the compound to be fluorinated are introduced through the eductor jets. Thus, it is

preferred that the major byproducts of the fluorination reaction be heavier compounds which can be easily removed by condensation, as opposed to lighter byproducts which require distillation or other complicated processing for removal.

The reactor according to the apparatus of the present invention is similar to a reactor developed by British Gas Corporation for direct hydrogenation of oil-derived hydrocarbon feedstocks and known as a gas recycle hydrogenator. In its simplest form, the reactor consists of an outer pipe with closed ends and a co- axial inner pipe which is slightly shorter than the closed pipe and positioned so that gas can circulate around both open ends of the inner pipe. The apparatus of the invention, as well as the direct fluorination methods according to the invention as carried out by the apparatus, will now be described with particular reference to the accompanying drawings, which illustrate systems developed especially for the direct fluorination of hexafluoropropene (HFP) with fluorine gas (F2) to yield perfluoropropane (PFP) as the predominant reaction product. Of course, as discussed above, it will be understood that other direct fluorination reactions can be carried out in the apparatus in essentially the same manner, with appropriate variations and adjustments which will be readily understood by one of ordinary skill in the art based upon the present disclosure.

Referring first to Fig. 1, there is shown a schematic flow diagram of a reactor system illustrating the method and apparatus according to one embodiment of the present invention. Primary reactor 10 consists of an elongated inner pipe or tube 12, which is open at its upper end, surrounded by a closed outer pipe or tube 14, which is longer and slightly larger in diameter than the inner tube 12. The interior of the inner tube 12 forms a reaction zone, while the annular space formed between the two tubes 12,14 forms a recycle chamber. However, it will be understood that the reaction which begins in the reaction zone may continue in the recycle chamber as the mixture of reaction gases passes over the top edge of the inner tube and down through the annular space 16.

The bottom walls of the inner and outer tubes are separated by at least two eductors 18,18'. Each eductor consists of a motive jet 20, at least one suction port 22 and a discharge nozzle 24, for feeding reactants and diluent gases as

high pressure jets for mixing in the reaction zone. Compound to be fluorinated is fed from compound supply 26 through supply line 28 to eductor 18, while fluorine gas is supplied by fluorine supply 30 through supply line 32 to eductor 18'. Either or both of these reactants are diluted with an inert gas diluent and/or a product gas diluent from inert gas supply 34 or product gas supply 36 through respective supply lines 38,40 and 42,44.

After mixing and reaction of the diluted reactants in the reaction zone, reaction product passes into the recycle chamber and down through the annular space 16 past the eductors 18,18', where a portion of the reaction product is drawn into the suction ports 22 for further dilution of the reactant gas streams. The remainder of the reaction product passes through product outlet 46 to a secondary reactor 48 for completion of the reaction, if necessary. Although product outlet 46 is shown in the bottom wall of outer tube 14, it will be understood that other positions, such as in the side wall, may be suitable. It is only important that the reaction product flow past the suction ports 22 of the eductors 18,18'and that the reactants have sufficient residence time in reactor 10 for substantial reaction to take place.

The secondary reactor 48 may take a number of forms. According to one embodiment, the secondary reactor may simply be a long tube formed into a coil and enclosed in a cylindrical heater with a temperature controller. In another embodiment, the secondary reactor may be in the form of a fluidized bed or packed bed containing cobalt fluoride as a transfer agent. In this type of reactor, cobalt difluoride is converted to cobalt trifluoride by reaction with fluorine, and the cobalt trifluoride then fluorinates any remaining compound to the fluorinated reaction product. In the process, the cobalt trifluoride is converted back to cobalt difluoride.

In this embodiment, the secondary reactor may have various modes of operation, including alternating excess of fluorine and compound reactant in the primary reactor 10, a slight excess of fluorine in the primary reactor 10, or a substantially stoichiometric ratio of fluorine and compound to be reacted in primary reactor 10.

The output from secondary reactor 48 (or from primary reactor 10 if the secondary reactor is bypassed 49) flows to a product collection system 50,

which may include, for example, a fan cooled heat exchanger and pressure control valve, a soda-lime bed to remove excess fluorine and hydrogen fluoride, and a refrigerated bath for condensing the reaction product in a collection vessel. Final purification of the product is preferably performed by distillation in a separate product purification system 52. These collection and purification systems and procedures are conventional, and one of ordinary skill in the art will readily understand that other appropriate collection and purification systems could be used, depending upon the particular reaction products and byproducts obtained from the primary and/or secondary reactors.

Referring now to Fig. 2, a schematic flow diagram is shown of another reactor system further illustrating the method and apparatus according to a preferred embodiment of the present invention. The reactor 10 of Fig. 2 is essentially the same as the primary reactor in Fig. 1, with inner tube 12 forming a reaction zone in its interior, outer closed tube 14 forming an annular space 16 around the inner tube, and eductors 18,18'feeding reactants and diluent gases to the reaction zone.

The main difference of reactor 10 of Fig. 2, compared to primary reactor 10 of Fig. 1, is that the fluorine gas is introduced into the reactor through an inlet tube 54 passing through the bottom wall of the outer tube 14 and terminating at one of the suction ports of the eductor 18'. In this case the motive gas fed to eductor 18'is externally recycled product gas, as discussed below. Although not shown in Fig. 2, externally recycled product gas could also be mixed with the compound to be fluorinated before that compound is fed to eductor 18.

As in the primary reactor 10 of Fig. 1, the flow of reactant and diluent gases through eductors 18,18'creates a low pressure at the suction ports, which draws reaction product from annular space 16 into the reactant/diluent streams to further dilute them. The mixed gases are then ejected through the discharge nozzles 24 of the eductors 18,18'for mixing and reaction in the reaction zone. In the reactor of Fig. 2 the low pressure created at the suction ports of eductor 18'also draws fluorine from inlet tube 54 for rapid mixing with the feed of

externally recycled product and the internally recycled reaction product drawn directly from the annular space 16.

Reaction gases which pass over the top of the inner tube 12 are cooled as they flow down through the annular space 16 to the bottom of reactor 10.

The cooling is caused in part by countercurrent heat exchange flow along the wall of the inner tube 12, but may also be assisted by cooling coils (not shown) on the outside of outer closed tube 14. Reaction product which is not internally recycled through the suction ports 22 of the eductors passes out of the reactor through product outlet 46 for further processing.

A portion of the product withdrawn from product outlet 46 is compressed in compressor 56 and cooled in a heat exchanger (byproduct condenser 58) to condense some of the heavy byproducts, which are trapped and drained from the system. The cooled and compressed product is returned to the reactor through eductor 18'as the diluent for the fluorine feed from inlet tube 54.

The remaining product from product outlet 46 flows to a valve 60 operated by a pressure controller 62 that is used to control the pressure within the reactor. The actual pressure in the reactor is not critical to the reaction itself, but does affect the flow of recycled product through the compressor.

A sample of the product is taken continuously through line 64 from the inlet to the pressure control valve 60 and fed to an analyzer 66, such as a mass spectrometer, to measure the concentration of fluorine remaining in the product.

The bulk of the sample is returned to the low pressure side of valve 60.

After the pressure control valve 60, the product flows through a bed of alumina beads 68 to remove any excess fluorine. The product then flows through a tube to a vessel 70 contained in a cooling bath 72 to condense as crude product.

The cooling bath 72 is maintained at a temperature which brings the product vapor pressure to just above atmospheric pressure, so that any non-condensable gases can be vented from the system. The cooled receiving vessel 70 is then removed from the system and allowed to warm to room temperature, so that crude product reaches its normal pressure.

The crude product is then fed to a distillation system 74 with two columns 76,78. The crude product feed enters the larger column 76 where the primary product and the lighter byproducts are separated from the heavier byproducts. The product is condensed and flows down the smaller column 78 for the removal of the lighter byproducts. Some of the purified product is returned to the larger column 76 as reflux, while the remainder is fed as a liquid to weighed receiving cylinders as final product. A vapor sample of the final product from each filled cylinder is analyzed to confirm that it meets the purity specifications.

The reactors 10 and reaction systems generally shown in Figures 1 and 2 may also be provided with various sensors for monitoring such factors as reaction rate, quality and amount of reaction product. These sensors (not shown) may include for example, thermocouples for measuring the reaction temperature, pressure sensors for monitoring the reaction, collection or purification pressures, and gas analyzers such as mass spectrometers for analyzing the product gas at various points in the system as necessary or desired. Moreover, although only one source of compound to be fluorinated has been shown, it will be understood that more than one compound could be provided for reaction with fluorine gas, and other components such as conditioning gases could also be provided to the reaction system.

Specific embodiments of the present invention will now be described in more detail with reference to the following specific, non-limiting examples in which hexafluoropropene (HFP) is reacted with fluorine gas (F2) to produce perfluoropropane (PFP) as the primary desired reaction product.

EXAMPLE 1 This embodiment of a method according to the invention was carried out in accordance with a system according to Fig. 1, wherein outer closed tube 14 is <BR> <BR> a 2"nominal ID, stainless steel pipe about 30"in length, and inner tube 12 is a 1'/4" nominal ID stainless steel pipe about 24"in length.. Prior to operating the system, the reactor and input and output tubing surfaces are passivated using fluorine diluted by an inert gas, for example 1% fluorine in helium. Passivation removes any traces of hydrocarbon in the system and allows a fluoride surface to be formed on any of the exposed metal. Once passivation is complete, the system is purged with an inert gas, such as argon from the inert gas supply 34.

Before introducing any reactants into primary reactor 10, a supply of PFP is provided through either or both of the eductors 18,18', for example from a cylinder of liquid PFP at about 100 psig. By introducing PFP into the reactor prior to the introduction of any reactant gases, the initial reaction rate may be controlled.

Thus, an undesirable reaction rate may occur without providing the PFP diluent prior to build-up of the reaction product in the recycle chamber for recycle through the suction ports of the eductors.

Fluorine reactant is supplied from fluorine supply 30, which is a cylinder containing about 1.6 pounds of fluorine at a maximum pressure of 400 psig. A pressure regulator (not shown) is used between fluorine supply 30 and eductor 18'to regulate the amount of fluorine to 30 psig. A shut-off valve and mass flow controller may also be used prior to eductor 18'. Also, a conventional containment device and a conventional scrubber vessel may be used to enclose the fluorine reactant supply for safety and environmental purposes. The scrubber is filled with 10 pounds of alumina beads, which is more than adequate to react with the 1.6 pounds of fluorine if a leak occurs. The HFP reactant is supplied directly from compound supply 26, which is a cylinder of liquid HFP at about 65 psig. A mass flow controller and check valve may also be used in supply line 28 before eductor 18.

Upon start up, after PFP has been introduced into primary reactor 10, the PFP is continued as diluent for the PFP gas stream supplied to eductor 18, while fluorine gas is introduced to eductor 18'. However, the PFP diluent may be introduced with both reactants. At start up a total flow rate of 600 cm3/min of fluorine, PFP and HFP is used. After start up, the amount of PFP introduced to the motive jets 20 of eductors 18,18'may be gradually reduced to a lower rate or to zero, as the amount of reaction product in annular space 16 builds up for adequate recycle through suction ports 20 for dilution of the reactant streams. The PFP buildup in the recycle chamber may be monitored by a gas analyzer, such as a mass spectrometer, at product outlet 46.

The reaction of fluorine gas with HFP upon mixing in the reaction zone occurs spontaneously and exothermically. From the discharge nozzles 24 of eductors 18,18'to the product outlet 46, the reactants and reaction products have a residence time of about 2l/2 minutes. By the use of a cooling jacket around outer closed tube 14, the operating temperature in the reaction zone is maintained at a maximum of about 200 °F, and the pressure is maintained at about 20 psia with a pressure control valve.

Product passing from product outlet 46 proceeds to a secondary reactor 48 which consists of a 0.5 inch diameter stainless steel tube about 17 feet long formed into a coil of 4 inch diameter and enclosed in a cylindrical heater with a temperature controller. The secondary reactor 48 may be desirable in some commercial applications to allow more conversion of any unreacted reactants, but otherwise where reaction is substantially complete in the primary reactor 10, the reaction products may pass through bypass 49 directly to collection system 50. The product from the primary or secondary reactor is collected in a collection vessel immersed or partially immersed in a chilled bath. During start up and prior to formation of the desired product, the collection vessel can be bypassed to a vent.

The method and apparatus described in this example achieved approximately 90% conversion of HFP to PFP.

EXAMPLE 2 The preferred embodiment of this example will be described with reference to the reactor system shown in Fig. 2, as well as the reactor 10 shown diagrammatically in more detail in Figs. 3 and 4. The reactor 10 has a vertical stainless steel outer pipe 14 closed at both ends by upper and lower flanges 80,82.

The outer pipe 14 is 2"Schedule 10 S (2.375"o. d. x 2.157" i. d.) by 52"long, which is shown partially broken away in Figs. 2 and 3. The outside of tube 14 is wrapped with copper tubing 84 to carry cooling water. A thermocouple 88 and pressure sensor 90 are provided in the upper flange 80 for monitoring temperature and pressure in the upper part of the reaction zone. The inner tube 12 is a second, <BR> <BR> concentric, stainless steel pipe of 11/4"Schedule 40 (1.66" o. d. x 1.38" i. d.), which is open at the top with a l/2"spacing from the upper flange 80. The bottom of the inner pipe is closed by a supporting disk 86 with two holes that allow it to rest on the two eductors 18,18', attached side-by-side to the lower flange 82.

The supporting disk 86 allows the discharge nozzles 24 of the two eductors 18,18'to be inside the inner tube 12 (reaction zone), while the suction ports 22 (three in each eductor) are located below the disk 86 and above the lower flange 82, so as to be in direct fluid communication with the annular space 16 of the outer pipe 14. The motive jets 20 of the two eductors are connected through the lower flange 82; one to a source of HFP and the other to the outlet of a compressor which recycles product PFP as a diluent. Fluorine is introduced into the reactor through supply line 32 and inlet tube 54 which passes through the lower flange 82 and terminates at one of the three suction ports of eductor 18'which is being fed with recycled PFP product as the motive stream. Reaction products are withdrawn from reactor 10 through product outlet 46 which also passes through the lower flange 82.

The method of this embodiment is preceded by passivation, purging and startup operations similar to those in Example 1. In operation, HFP is fed to the motive jet 20 of eductor 18 at a flow rate of about 2 liters per minute. Similarly, recycled product (mostly PFP) is fed to the motive jet 20 of eductor 18'at a flow rate of about 6-8 liters per minute. These high speed gas streams create a low

pressure at the three suction ports of the respective eductors which draws reaction product from the recycle chamber into the three suction ports of each eductor (about 2 liters per minute into 18 and about 5 liters per minute into 18'), and also draws fluorine gas into one of the suction ports of eductor 18'from the inlet tube 54 which is fed with about two liters fluorine per minute. The incoming fluorine is rapidly mixed with incoming recycled product and product drawn directly from the reactor and flows through the discharge nozzle 24 into the reaction zone.

In the reaction zone, the diluted fluorine and HFP are mixed and rapidly react to form mostly PFP but also some heavier fluorocarbons and traces of lighter fluorocarbons. The reaction gases reach a temperature of about 400-500 °F near the top of the reaction zone. At the top of inner tube 12, the product gases and any unreacted reactants flow out into the annular space 16 where they are cooled as they flow down to the bottom of the reactor. At the bottom of the reactor, some of the reaction product (i. e., about 7 liters per minute total, as indicated above) is drawn into the suction ports 22 for dilution of the reactants, and 8-10 liters per minute of reaction product are withdrawn through outlet tube 46.

Of the product withdrawn from the reactor, 6-8 liters per minute are compressed to about 60 psig and cooled in the byproduct condenser 58 to remove some of the heavy byproducts before returning the compressed product to the reactor as the diluent for the fluorine feed. The remaining two liters per minute of product flow to valve 60 to control the pressure within the reactor to a value in the range of 20-40 psia.

It has been found that if the relative feed rates of fluorine and HFP are adjusted so that there is a fluorine excess of about a few hundred parts per million in the reaction product, then HFP is essentially completely reacted. As a result, the concentration of HFP in the product is less than the maximum allowable 10 ppm, and no purification step is required to meet this specification. After the pressure control valve, excess fluorine is removed from the product by passing through bed 68 of alumina beads. The product is then cooled in cooling bath 72 which is maintained at about-42°F, which brings the product vapor pressure to just above atmospheric pressure.

After cooling, the receiving vessel is allowed to warm to room temperature so that the crude product reaches its normal pressure of about 100 psig, and the crude product is then fed to the distillation system 74 for final fractionation.

The method and apparatus described in this example achieved approximately 80-90 % conversion of HFP to PFP. No secondary reactor was required. The major byproducts are heavier fluorocarbons, mostly with six carbon atoms, which can be partially condensed out by cooling and completely removed by distillation.

It will be appreciated by those skilled in the art that changes could be made to the embodiment (s) described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiment (s) disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.