Background of the Invention Reactors used for corrosive media are usually glass-lined or made from corrosion resistant alloys such as INCONEL@, MONEL@, or HASTELLOY@.

These materials are suitable for use for most reactions performed in chemical manufacturing. However, glass-lined equipment may not be suitable for use in certain reactions, for example fluorination reactions using hydrogen fluoride, because the reactants may attack the glass lining. Additionally, a number of industrially important reactions create extremely corrosive reaction media capable of destroying the corrosion resistant alloys.

In the case of halogen exchange reactions, the reactions'corrosivity results from the use of antimony halide catalysts and hydrogen fluoride. Specifically, antimony halide catalysts and hydrogen fluoride form corrosive super-acids. At high catalyst concentrations, or concentrations greater than about 35 weight percent of the antimony halide catalyst, and temperatures above 90° C, the corrosion resistant alloys are corroded quickly in the presence of the super acids One proposed solution to the corrosion problem is the use of polyterafluoroethylene polymer ("PTFE") lining in the reactor. However, PTFE- lined reactors are difficult to manufacture because the PFTE liner has a thermal expansion coefficient much larger than metal. This difference in thermal expansion

coefficients has only a small effect at low reactor diameters because small deformations of PFTE are reversible. However, the effect becomes significant at diameters greater than 3 to 4 feet because the thermal deformations are so large that the PFTE liner may partially collapse. Additionally, PFTE-lined equipment with a diameter greater than 12 inches is generally not suitable for vacuum service because the liner stability decreases markedly with an increase in the diameter.

Therefore, a need exists for a reactor that may be used for corrosive reactions, but that overcomes the problems associated with currently available reactors.

Brief Description of the Drawings Fig. 1 is a schematic diagram of one embodiment of the apparatus of the invention.

Fig. 2 is a schematic diagram of another embodiment of the apparatus of the invention.

Description of the Invention and Preferred Embodiments The present invention provides a pipe reactor for carrying out corrosive reactions, including fluorination reactions, which reactor overcomes some of the disadvantages of the currently available reactors. Additionally, the reactor of the invention provides a heat exchange surface that is larger than standard reactors.

The reactor of the invention comprises a polymer-lined pipe reactor having disposed therein or external thereto at least one circulating tube. The reactor of the invention permits a large reactor volume at diameters of 3 ft or less because the length of the reactor may be made sufficiently long to obtain a large volume.

Additionally, the polymer lining permits the use of the reactor with corrosive reaction materials. Further, the reactor of the invention is more easily constructed

than standard polymer-lined reactors because the diameter of the reactor of the invention may be smaller than that of the standard reactor.

The reactor of the invention generally has a length to inside diameter ratio of about 4: 1 to about 100: 1, preferably about 4: 1 to about 50: 1, more preferably about 8: 1 to about 20: 1. This ratio allows for a heat exchange surface and reactor volume larger than that found on the standard polymer-lined reactor.

The residence time of the fluid in the reactor is a function of the volumetric flow rate through the reactor as well as the reactor length and diameter, which may be varied to achieve an optimum yield or selectivity for the desired product.

Preferably, the inside diameter of the reactor is about 3 feet or less. The reactor may be horizontally, vertically, or inclinedly disposed.

Referring to Fig. 1, one embodiment of the invention, vertically disposed tubular reactor 10 is shown, which reactor is made of reactor shell 11 having a thickness of about 1/8 to about 2 inches, preferably about 1/8 to about 1.5 inches, which reactor shell 11 has an outer surface 12 and inner surface 13. Reactor shell 11 may be constructed of any suitable material such as carbon steel, stainless steel, INCOLOY INCONEL@, HASTELLOY (D, or the like. Reactor 10 is polymer- lined meaning that inner surface 13 is coated, or lined, by any conventional means with polymer lining 14. Polymer lining 14 may be any suitable corrosion resistant, fluorinated polymer, including without limitation, polytetrafluoroethylene ("PTFE"), perfluoroalkoxy polymer, ethylene tetrafluoroethylene polymer, vinylidene fluoride polymer, ethylene hexafluoropropylene polymer, and the like.

Preferably, PTFE polymer is used. Polymer lining 14 may be of any desired thickness, but generally will be from about 1/8 to about 1/2 inch thick, preferably from about 1/4 to about 1/2 inch thick. Most preferably, polymer lining 14 is about 1/4 inch thick.

All of the components of the reactor of the invention are constructed of suitable corrosion resistant materials. Preferably, the wetted components are made of fluorinated polymer, more preferably PTFE Disposed within reactor shell 11 is at least one circulating tube 17 located in the bottom two-thirds of tubular reactor 10. The walls of circulating tube 17 are sufficiently thick to prevent a buckling of the tube. The wall of circulating tube 17 may be up to about 1 inch thick and the tube may be of any convenient diameter, but preferably is of a diameter that is about 1/3 the diameter of the inside diameter of the reactor. Circulating tube 17 is held in position within reactor shell 11 by a means for holding circular tube 17 vertically within reactor shell 11. Preferably, the holding means 19 is a plurality of spacers located between polymer lining 14 and circulating tube wall outer inner surface 21. Polymer lining 14 and circulating tube outer surface 21 define inner space 22. Inner space 22 below liquid level line 16 provides an area within which the reaction materials may react.

Base 23 of circulating tube 17 rests on at least one supporting means 24 so that base 23 does not rest on polymer lining 14. Circulating tube 17 is open meaning that circulating tube bottom 25 contains one or more openings that permit liquid from space 22 to flow into circulating tube 17.

In one embodiment, flow through circulating tube 17 is in the upward direction. In another embodiment, the flow is reversed and liquid flows out of circulating tube bottom 25. Circulating tube 17 achieves mixing without the use of a mechanical agitator or external circulating pump. The reaction materials mix and circulate within pipe reactor 21 as a result of the hydrostatic pressures inside and outside of circulating tube 17.

Reaction materials are charged to tubular reactor 10 through a means for feeding 26, which means may be any convenient means for feeding reaction materials, such as a sparger or a feeding line. Feeding tube 27, fully or partially disposed within circulating tube 17, is connected to feeding means 26 at its lower end 29. Feeding means 26 may be situated inside or outside of circulating tube 17.

If feeding means 26 is within circulating tube 17, the flow inside of feeding tube 27 will be upward and if outside, the flow will be in the downward direction. The use of a circulating tube permits mixing of the reaction materials without the use of an agitator because the reaction mixture continuously circulates in the reactor due to the flow in the circulating tube, which flow results from differences in the hydrostatic pressure inside and outside of the tube. Such mixing results in an increase in productivity per unit volume.

A product stream containing product, unreacted starting materials, reaction intermediates, and byproducts exits reactor 10 via outlet 31 for further processing.

Reactor shell feed inlet 15, connected to upper end 32 of feeding tube 27, receives recycle from such processing, which recycle contains unreacted starting materials and reaction intermediates.

Referring now to Fig. 2, another embodiment, horizontally disposed reactor 20 is shown having reactor shell 39 and polymer lining 41. Reactor 20 is suitable for use in two phase reactions, including those in which the formation of a suspension is difficult. Reactor 20 may have an circulating tube that is internally or externally disposed to reactor shell 39. Preferably, the horizontally disposed reactor circulating tube is externally disposed. The external circulating tube is disposed to reactor shell 39 at an angle of about y = atan (D/sqrt (L2 + D2) where L is the reactor length and D is reactor diameter. Feeding tube 36 and circulating tube 33 are connected to reactor shell 39 by any convenient, means known in the art. Reaction materials are fed via feeding inlet 37 and feeding means 35, which

may be any known feeding means such as a sparger, into circulating tube 33 and feeding tube 36. Following reaction, a product stream exits via outlet 42.

The reactor of the invention is beneficial because it requires only small diameter polymer-lined pipes to manufacture. Preferably, the reactor is constructed as a segmented reactor to accommodate differences in thermal expansion between the polymer-lining and the reactor outer shell.

Although the reactor of the invention will be useful in any number of highly corrosive reactions, it may find its greatest utility in carrying out liquid phase, halogen exchange reactions in which the starting materials are an organic feed and hydrogen fluoride and which use a halogenated antimony catalyst. Thus, in yet another embodiment, the invention provides a liquid phase, halogen exchange reaction comprising providing the reactor of the invention and carrying out the halogen exchange reaction within the reactor. Such reactions typically are carried out at greater than about 90° C and pressures below about 300 psig.

Suitable organic feed materials for such reactions are any hydrocarbon, chlorofluorocarbon, hydrochlorofluorocarbon, or hydrofluorocarbon that can be fluorinated; that is, the organic feed may be any such material containing a carbon- bonded chlorine or other atom replaceable by fluorine and/or that may contain carbon-carbon bond unsaturation saturatable with fluorine. Representative examples of suitable organic materials include, without limitation, halogenopropanes, chloroethanes, chloromethanes, and chlorobutanes.

Any suitable fluorination catalyst may be used including, without limitation, titanium, tin, niobium, and tantalum halide catalyst. Preferably, antimony halide catalysts, such antimony pentachloride will be used. The concentration of organic feed to hydrogen fluoride used may be determined by one ordinarily skilled in the

art based on a number of considerations including, without limitation, stoichiometric amounts needed to replace the desired number of atoms in the organic feed, amounts needed to fluorinate the catalyst, and amounts needed to provide an excess of hydrofluoric acid.