Abstract:
Feedstock at a first temperature is mixed with a heating fluid at a second temperature and the mixture resulting therefrom is immediately contacted with a catalyst in a catalytic conversion zone as the mixture reaches a third temperature, thus producing an effluent which is cooled to a fourth temperature as it is removed from the catalytic zone. Apparatus is provided useful for carrying out the above process.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to apparatus suitable for carrying out a catalytic process. In another aspect the invention relates to an apparatus suitable for carrying out the catalytic dehydrogenation of hydrocarbons. 
     Many processes involve endothermic catalytic reactions whereby additional heat is added to a reaction zone in order to produce a desired product. In many cases, this additional heat can be added to the feed prior to contacting the catalyst; however, in some cases unwanted products are produced by side reactions caused by heating the feed to too high a temperature prior to contacting the catalyst. In addition, other problems can be encountered in catalytic reactions. For example, side reactions sometimes occur as a result of the feed contacting the catalyst for too long a period. Also where the effluent produced by the process is highly reactive at the temperatures experienced in the catalyst bed, side reactions again limit the desired product obtained per unit of feed. 
     It is an object of the invention to minimize side reactions in catalytic processes. 
     Another object of the invention is to provide an apparatus suitable for use in catalytic conversion processes. 
     Other objects, aspects, and advantages will be apparent to one skilled in the art upon consideration of the specification, drawings, and appended claims. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, apparatus is provided comprising a first chamber; a first conduit means for introducing a feedstock into the first chamber; a second conduit means for introducing a heating fluid into the first chamber to form a mixture of the feedstock and the heating fluid; a second chamber positioned adjacent to and circumferentially surrounding the first chamber and in open communication therewith for receiving the mixture and having means to discharge an effluent therefrom; and a cooling means positioned adjacent to and in open communication with the second chamber for cooling the effluent. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The apparatus and process of the invention will be more easily understood when explained in conjunction with the attached drawings in which FIG. 1 is an elevational view partially in section of one embodiment of the apparatus of this invention, and FIG. 2 is an enlarged view of a portion of the apparatus shown by FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, there is shown an apparatus, generally designated by reference numeral 1, which has a flanged inlet conduit 2 through which a feed enters mixing chamber 4. Flanged inlet conduit 6, coaxially aligned with and surrounding inlet conduit 2, provides means for a heating fluid to enter mixing chamber 4. On the outlet end of inlet conduit 2, as shown more clearly in FIG. 2, there is a frustoconical section 8 with apertures 10 through which the feed enters the mixing chamber 4. The end portion of inlet conduit 6 is constructed as a frustoconical section having apertures 14 at the outlet end thereof through which the heating fluid enters the mixing chamber 4. Apertures 10 and 14 are spaced apart and coaxially aligned. FIG. 2 also shows one embodiment a suitable diffuser 16 surrounding chamber 4 which has two sizes of holes 60 and 62 to evenly distribute the mixture. A cylindrical catalyst bed 18, which can be removed from the apparatus 1 after removing member 36b of flange 36, circumferentially surrounds the mixing chamber 4 and diffuser 16. It is pointed out that catalyst bed 18 can be other than cylindrical in shape provided the catalyst bed circumferentially surrounds mixing chamber 4. Further, the term &#34;circumferentially surrounds&#34; as used in the specification and claims is not intended to limit the structure of the particular components of the apparatus of the invention to circular structures. One end of catalyst bed 18 engages the heating fluid inlet conduit 6 at 64 and the other end engages one end of a frustoconical plug 17 at 66 so as to force all fluids entering mixing chamber 4 through catalyst bed 18. The outer surface and shape of plug 17 and the frustoconical section 8 of conduit 2 approximate the outer surface and shape of frustoconical section 12 of conduit 6 so as to encourage even flow of fluids through catalyst bed 18 and into outlet chamber 19. 
     Actually, a more even distribution of fluids flowing through the catalyst bed 18 is obtained employing outer surfaces of plug 17, section 8 of conduit 2 and section 12 of conduit 6 which are frustrums of a paraboloid of revolution rather than frustrums of a cone. Normally frustoconical structures are used for ease of fabrication, and such structures are shown in the attached drawings; however, it is understood that the present invention is not limited to the use of such frustoconical structures. 
     Heat exchanger outlet tubes 22 positioned in outlet chamber 19 of heat exchanger 20 positioned in the upper portion of apparatus 1 essentially surround the circumference of the outer surface of catalyst bed 18. The heat exchanger 20 is composed of several sections, including heat exchanger inlet plenum 24 with flanged inlet 26 and inlet tubes 28, and heat exchanger outlet plenum 27 with outlet tubes 22 and flanged outlets 30. The heat exchanger outlet plenum 27 is flanged to but isolated from inlet plenum 24 and outlet chamber 19 by flanges 34 and 36, respectively. In addition, flanged outlets 32 are provided in the lower end of chamber 19 near inlets 2 and 6 for removal of effluent. 
     In the operation of the invention, again referring to the apparatus of FIG. 1, a feedstock is passed through inlet conduit 2, frustoconical section 8, apertures 10, and into mixing chamber 4. The temperature of the feedstock should be high enough to minimize the amount of heating required to heat the feedstock to the reaction temperature in the mixing chamber but low enough to limit side reactions of the feedstock. A suitable heating fluid is passed through inlet conduit 6, frustoconical section 12, apertures 14, and into mixing chamber 4. In mixing chamber 4 heating fluid instantaneously and vigorously mixes with the feedstock and heats the feedstock to the desired reaction temperature. The temperature and flow rate of the heating fluid in inlet 6 can be varied to produce the desired reaction temperature of the mixture. As the mixture reaches the reaction temperature, it immediately contacts the catalyst bed 18 after passing through diffuser 16 which evenly distributes the mixture along the inner surface of catalyst bed 18. The effluent produced as the mixture passes through the catalyst bed 18 immediately contacts outlet tubes 22 of heat exchanger 20 in order to lower the temperature of the effluent before side reactions substantially reduce the amount of the desired product in the effluent. The cooled effluent then passes out flanged outlets 32. 
     It is generally desirable to insulate various portions of the apparatus 1 to prevent heat transfer between adjacent sections. For example, as shown in FIG. 2, insulation 38 is provided on inlet conduit 2 to prevent heating the feedstock with heating fluid passing through inlet conduit 6. Inlet conduit 6 is insulated, indicated by reference numeral 40, to prevent additional heating of the mixture passing through the catalyst bed 18. Similarly, the outer surface of frustoconical section 8 is insulated, indicated by the reference numeral 42, to prevent cooling the mixture passing through catalyst bed 18. 
     The apparatus as described above is particularly suitable for such catalytic processes as dehydrogenation of alkanes, alkenes, cycloalkenes, alkylpyridines, and alkylaromatics employing a wide variety of suitable catalysts. As an example, a preferred catalyst for the dehydrogenation of alkenes such as isoamylenes and butenes is one containing iron oxide, potassium oxide, and chromium oxide as known in the art. A number of heating fluids can be used, depending, of course, on the particular process involved. Where alkenes are dehydrogenated, superheated steam can be used as the heating fluid. Frequently superheated steam is mixed with the feedstock to raise it to a suitable temperature prior to passing the feedstock to inlet conduit 2. 
     It is important that apertures 10 and 14 be sized to provide approximately equal momentum of the feedstock and heating fluid entering the mixing chamber 4 to provide proper mixing. 
     The catalytic conversion processes herein described are endothermic within the catalyst bed, and the apparatus of the invention lends itself to rapid heating of the feedstock, minimal catalyst contact time, and rapid cooling of the effluent resulting in a very effective apparatus for carrying out dehydrogenation processes.