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Dec. 17, 1946. 2,412,936 H. J, HEPP PRODUCTION OF CYCLOPENTENE Filed June 13, 1944 INVENTéR H. J. H EPP BY ATTORN EY Patented Dec. 17, 1946 . 2,412,936 ‘ UNITED STATES - PATENT orrlcs 2,412,936; PRODUCTION OF CYCLOPENTENE' Harold J. Hepp, Bartlelvllle, 0kla., asslgnor to Phillips Petroleum Company, a corporation of Delaware Application June 13, 1044, Serial No. 540.010 6 Claims. (Cl. 260-668) 1 This invention relates to a process for the pro dehydrogenation in which the production of cyclo duction of cyclopentene by catalytic dehydrogena pentadiene is suppressed. , tion of cyclopentane in the presence of hydrogen. In one of its more speci?c aspects, the invention Other-objects and advantages of the invention, some of which are referred to hereinafter, will be relates to a process in’ which cyclopentane to obvious to those skilled in the art to which the 1 gether with hydrogen is ‘catalytically dehydro genated in the vapor phase to produce cyclo pentene. invention pertains. I have discovered that cyclopentane may be catalytically dehydrogenated in a single step or cyclopentene is useful as an intermediate mate- ' stage to produce greatly increased yields of cyclo rial for the synthesis of a. wide variety of organic 10 pentene when the dehydrogenation is carried ‘out chemicals, such as cyclopentanol and cyclopente in the presence of hydrogen. While the hydrogen none, which are useful as industrial solvents, and that is added to the cyclopentane that is charged ‘ which may be converted to other valuable com suppresses somewhat the extent of dehydrogena ' pounds. Cyclopentane, but not cyclopentene, oc tion of the cyclopentane, the yield of cyclopentene curs naturally in many petroleum fractions. 15 from the cyclopentane that is dehydrogenated is vIt has been found that cyclopentene may be greatly increased. In addition to this favorable readily dehydrogenated catalytically to cyclo pentadiene. Such processes are described, for effect on cyclopentene production, the presence of . hydrogen greatly reduces the amount of carbo example, in the following U. S. patents: Grosse, naceous deposit formed on the catalyst. Loss of No. 2,157,202; Grosse and Mavity, No. 2,157,203; 20 valuable products is also substantially reduced and catalyst regeneration is greatly facilitated. and Morrell, No. 2,157,939. I have found that cyclopentane may be readily dehydrogenated in The dehydrogenation process of my invention is ‘ the presence of a, number of dehydrogenation cat practiced by passing cyclopentane mixed with hy alysts, such as chromic oxide-alumina and mag nesia-alumina, to produce cyclopentadiene. How ever, the unsaturated hydrocarbon product of such processes generally comprises a mixture of cyclo pentadiene and cyclopentene in at least a, 1 to 1 ratio. (Cf. Frey, Industrial and Engineering - drogen, which may be fresh added hydrogen or > 25 recycle hydrogen containing cyclopentadiene, in vapor phase at a total pressure within the-range of approximately 1 to approximately 10 atmos pheres over an active dehydrogenation catalyst at a dehydrogenation temperature and a suitable Chemistry, 1934, vol. 26, page 198.) Attempts to 30 space velocity to produce the desired extent of conduct the dehydrogenation of cyclopentene to conversion. The conversion should be between yield cyclopentene without the production of sub-f approximately 20 and approximately 50 per cent, stantial amounts of cyclo-pentadiene have hereto preferably about 30 per cent, per pass. Conver fore not been successful. sion temperatures in the dehydrogenation range of approximately 1000° to approximately 1300° F., depending upon the catalyst and the other pre vailing reaction conditions, are contemplated. In ' A catalytic process for the production of cyclo pentene from cyclopentane by ?rst dehydrogenat ing cyclopentane to cyclopentadiene, then hydro genating the cyclopentadiene to cyclopentene, is’ general, the more active the catalyst, the lower the required conversion temperature. It is desir C. Ray, Serial No. 493,688, ?led July 6, 1943. This 40 able to employ a highly active dehydrogenation catalyst in order to avoid cracking and other un method, while satisfactory in many respects, has desirable side reactions. I the disadvantage that two separate stages, op Hydrogen should be added or be present in the erated under different reaction conditions, are re cyclopentane charge stock in such quantity that quired. the feed to‘ the catalyst bed comprises not more It is an object of the present invention to pro than approximately 90, and not less than ap vide a process for the production of cyclopentene proximately 10 mol per centof cyclopentene, and ' disclosed in the copending application of Gardner from’cyclopentane by dehydrogenation in which the yield of cyclopentene is greater than has here tofore been obtained. It is a further object of the invention to provide a one-stage process for the ‘production of cyclo pentene by the catalytic dehydrogenation of cy clopentane without the formation of large pro portions of cyclopentadiene, that is, by catalytic preferably not more than 80 nor less than 25 mol per cent, respectively. When such conditions are maintained, a greatly increased yield of cyclo pentene is obtained in the dehydrogenation and the proportion of cyclopentadiene in the result ing product is substantially lower than that ob tefined without the presence of hydrogen. The effect of the hydrogen appears to be more than a 2,412,986 simple mass-action effect of hydrogen in sup pressing the conversion of cyclopentane to cyclo pentadiene since greater proportions of cyclo pentene are produced than can be accounted for on the basis of the hydrogen that is added. The hydrogen that is added to the cyclopentane charge 4 is dehydrogenated. The e?luent mixture is then ‘ cooled to about 200° F. or lower, and passes into ?ash tank 3 under a pressure of about 25 pounds per square inch or higher. From ?ash tank 3 a portion of the hydrogen is removed from the system through conduit I, and the remainder of the hydrogen is recycied through conduit 5 to in the practice of my invention is preferably that the charge conduit l of the reaction zone 2. The produced in the dehydrogenation process itself. amount of hydrogen which is removed is ap The effluent mixture from the catalyst bed is that formed in the dehydrogenation separated by suitable conventional means, as by 10 proximately reaction or that amount which it is necessary‘ condensation and fractionation, into hydrogen, to remove from the cycle at this point to main cyclopentadiene, cyclopentene and cyclopentane tain the hydrogen content of the charge _to the catalytic reaction zone constant. The hydrogen through conduit 4 is preferably passed and part but not all of the hydrogen, is recycled 15 removed to a recovery means, not shown, where any cyclic with fresh charge to the catalyst. hydrocarbons containing five carbons in the ring A very convenient means of facilitating the are recovered, as by liquid extraction or by other separation of cyclopentadiene and cyclopentene, suitable means, and are subsequently returned the boiling points of which differ by only a few the process. Dlcyclopentadiene from the degrees, is first to dimerize the cyclopentadiene to 20. to process may be employed as a liquid for absorb dicyclopentadiene, the boiling point of which is ing such cyclic hydrocarbons, if desired. much higher than that of any of the other ma The liquid kettle product from ?ash tank 3, terials involved‘ in the process. A preferred comprising principally cyclopentene, cyclopenta method of operation according to this modi?ca diene and unconverted cyclopentene, is passed to tion of the invention comprises ?ashing the hy fractionator 6 wherein it is separated into a light drogen from the cooled ei?uent mixture leaving overhead fraction and a heavier kettle product. the catalyst in a ?ash tank, then separating the The kettle product, comprising chie?y unreacted fractions. The unchanged cyclopentane, along with part or, preferably, all of the cyclopentadiene remaining hydrocarbon mixture by fractionation cyclopentane and some dicyclopentadiene, is re cycled through conduit 1 to the reaction zone. prising chie?y cyclopentene and cyclopentadiene 30 into light and heavy fractions, the former com The overhead product from fractionator 6, comprising chie?y cyclopentene. and cyclopenta and the latter comprising chie?y unconverted cyclopentane. The light fraction is then passed diene, is conducted through conduit 8 to dimeriz ing zone 9 in which the cyclopentadiene is poly to a dimerizing zone wherein the cyclopentadiene is polymerized to dicyclopentadiene by maintain ing suitable conditions of temperature, pressure, merized to dicyclopentadiene. The polymeriza tion is effected thermally, merely by maintain and contact time. Suitable temperatures are within the range of 200° to 350° F. at super atmospheric pressures and a time of contact with ing the material at a temperature within the range of approximately 200° to approximately in the range of approximately 1/2 to approx‘ mately \15 hours. The mixture is then passed 350° F. at a superatmospheric pressure for a to a second fractionation means for the separa through conduit‘ l0 into fractionator II, where in it is separated into a cyclopentene fraction period of approximately 1/2 to 15 hours or longer. From dimerizing zone 9, the- mixture is passed tion of the cyclopentene from the dicyclopenta diene. The cyclopentene overhead fraction is that is discharged through conduit [2 and a di removed as a product of the process and the dicyclopentadiene may, together with the uncon cyclopentadiene fraction, which is the kettle product. The cyclopentene fraction is removed as a product of the process. The dicyclopenta diene fraction is passed through conduit l3 into verted cyclopentane and part of the hydrogen, be recycled to the catalyst bed. In some cases it may be desircbie to subject the dicyclopentacliene to heating at a temmrature within the rangecf approximately 350° to approximately 450° F. and preferably at atmospheric, subatmospheric or a low superatmospheric pressure, for a sufficient period of time to effect depolymerlzaticn, before recycling it to the catalyst. In another method of operation, wherein the depolymerization zone ‘iii. In this zone the di~ cyciemntadiene is thermally depolymerized at a temperature within the range of approximately 350° to approximately 450° F. and a low pressure, preferably about atmospheric or subatmospheric. to cyclopentadiene. The cyclopentadiene is “hen “recycled from zone id through conduit 15 inlet to reaction zone 2. Alternatively, the o cyclopentadiene is not recycled to the catalyst with the unconverted cyclopentene and hydrogen, a further yield of cyclopentene may be produced by half-hydrcgenating the cyclopentadiene in ac cordance with the method disclosed in the co pending application of Gardner C. Ray referred to hereinabove In the accompanying drawing, which is e. di= agrammatic ?ow sheet of a preferred embodiment of the process of the invention, fresh cyclopen tane in the vapor state, together and in admin may be recycled directly to the dehydrogenation step through conduits i6 and i5. Example 60 Cyclopentane vapor together with added L. ~~ drogen was passed under controlled condi of pressure, temperature and ?ow rate thr a bed of 1%; inch pellets of a chromic o alumina catalyst disposed in a catalyst tube. 65 catalyst tube was a vertically supported, 22-inch length of quartz tubing having an internal di ture with vaporized recycle cyclopentene, cyclo ameter of 17 mm. that was provided with a pentadiene and hydrogen, preheated to a suit coaxial internal quartz thermocouple well. The top'and bottom sections of the tube were packet; with 0 to 14-mesh quartz chips; the central section, approximately 3.75 inches in length, was packed with the chromic oxide-alumina catalyst. able temperature, is conducted through charge conduit or line i into reaction zone 2. The mix ture is contacted in the reaction zone with a suitable active conventional dehydrogenation catalyst under such conditions of temperature The catalyst tube was heated in an 18-inch electric tube furnace. The cyclopentane vapors and pressure and period of contact that about 20 to 50 per cent of the cyclopentane entering 75 passed downwardly through the tube. _ 2,412,936 6 At the beginning of the run, the catalyst was heated to the operating temperature in a stream clopentane to unsaturated cyclic hydrocarbons containing a ?ve-carbon-atom ring, the major portion of which-is cyclopentene. 2. A process for the production of cyclopentene by the catalytic dehydrogenation of cyclopen tane which comprises‘ passing a mixture of cy clopentane and hydrogen containing at least approximately 25 and less than approximately 80 of nitrogen and was then ?ushed with hydrogen. During the run the total e?luent mixture was collected for analysis. At the end of the run, the catalyst was revivi?ed by a stream of air. The water and carbon dioxide formed were weighed and were used for computing the amount of hydrocarbon material deposited on the cat alyst. - mol per cent cyclopentane into contact with a 10 chromium oxide dehydrogenation catalyst at a l For comparison, a run was also made under temperature within the range of approximately 1000” to approximately 1300° F. for a suillcient contact period to‘v convert at least 20 per cent of substantially identical conditions in which no hydrogen was charged with the. cyclopentane va pors. the cyclopentane to unsaturated cyclic hydrocar ' The operating conditions that were maintained and the results obtained were as follows: bons containing a ?ve-carbon-atom ring, the ' major portion of which is cyclopentene. 3. A process for the production of cyclopentane Without Hydrogen added, gas vol. percent__.._ .___ hydro- hydro gen gen None 73 _ 1 1 Average temperature, '’ F ______ __ Cycle length, min ______________ .. No. of cycles ___________________ __ _ . _ 1, 048 30 l 963 30 1 Space velocity (voL/vol. eat./hr.).___ E?luent analysis, percent by weight _ 468 630 0 3 9 ' l. Cyclopen tane ____ ._ __ Deposit on catalyst _____________________ _ _ . tane which comprises passing a mixture of cy 20 clopentane and hydrogen containing at least ap Pressure, atmospheres __________ __ l. 4 by the catalytic‘ dehydrogenation of cyclopen With . . 4. 8 8. 3 8. 3 ll. 9 9. l 70. 4 9. 7 7i. 6 2. 8 100. 0 100. 0 cyclopentane conversion, percent ___________ __ 29. 6 28. 4 Weight ratio, eyclopentene/cyclopentadiene_._ 1.0 _ 1.31 From the above results it will be noted that less material ‘is deposited on the catalyst when hydrogen is charged with the cyclopentane and that, although the conversion of cyclopentane is proximately 25 and less than approximately 80 mol per cent cyclopentane into contact with a dehydrogenation catalyst at a temperature within the range of approximately 1000“ to ap proximately 1300° F. for a sufficient contact pe _ riod to convert at least 20 per cent of the cyclo pentane touns'aturated cyclic hydrocarbons con taining a ?ve-carbon-atom ring comprising cy clopentene, cyclopentadiene, and dicyclopenta diene, the major portion of which is cyclopen tene, removing hydrogen in an amount equiva lent approximately to that formed in the dehy drogenation, separating cyclopentane from .the resulting products, and recycling the unconverti ed. cyclopentane, cyclopentadiene and any dicy clopentadiene and the remaining hydrogen to gether with additional fresh cyclopentane to the dehydrogenation catalyst. , somewhat smaller, the amount of cyclopentene 4. A process as de?ned in claim 3 and flir formed is greater and the formation of cyclopen 40 ther characterized in that the cyclopentene is tadiene is suppressed. separated from the cyclopentadiene in the prod Although a chromium oxide catalyst is speci» uct by subjecting the product to thermal treat fled in the above example, it is to be understood ment to dimerize the eyclopentadiene contained that the. invention is not limited thereto. Chro therein without substantial polymerization of the mium oxide catalysts in general are preferred ,cyclopentene and thereafter separating the cy catalysts but other conventional dehydrogena» clopentene from the dicyclopentadiene by frac- x, tion catalysts, particularly highly active catalysts, may be used. Such alternative dehydrogenation catalysts include bauxite, alumina and other ' metal oxides, alone or supported on catalyst car- . riers, and with or without promoters. The con version temperature which it will be desirable to maintain will be dependent upon the ,nature of the catalyst but will, in general, be within the range of approximately NOW’ to approximately . - 1300° F. Inasmuch as the foregoing description‘ com prises preferred embodiments of the invention it is to be understood that the invention is not lim ited thereto and that modifications and varia 60 tions may be made therein without departing substantially from the invention, the scope of which is to be limited only by the appended claims. I claim: ' - - 1. A process for the production of cyclopentene by the catalytic dehydrogenation'of cyclopen tane which comprises passing a. mixture of cy clopentane and hydrogen containing at least approximately 25 and less than approximately 80 mol per cent of cyclopentane into contact with a dehydrogenation catalyst at a temperature tional distillation. 5. A process as de?ned in claim 3 and fur ther characterized in that the cyclopentene is separated from the cyclopentadiene in the prod _uct by subjecting the product to thermal treat ment to dimerize the cyclopentadiene contained therein without substantial polymerization of the cyclopentene, thereafter separating cyclopentene from the dicyclopentadiene by fractional distil lation, thermally depolymerizing the separated dicyclopentadiene, and recycling the recovered cyclopentadiene together-with the recovered un converted cyclopentane and hydrogen together with additional fresh cyclopentane to the dehy drogenation catalyst. 6. A process for the production of cyclopentene by the catalytic dehydrogenation of cyclopenf ‘tane which comprises passing a. mixture oi.’ cy-' clopentane and hydrogen containing at least ap proximately 25 and less than approximately 80 mol per cent cyclopentane into contact with a dehydrogenation catalyst at conversion condi tions of temperature and‘ pressure for a sufficient contact period to convert at least 20 per cent of the cyclopentane to unsaturated-cyclic hydrocar~ bons containing a ?ve-carbon-atom ring, the. within the range 01’ approximately 1000° to ap major portion or which is’cyclopentene. proximately'1300° F. for a su?icient contact pe; dad to convert at least 20 per cent or the cy-' 75 ' HAROLD J. HEPP.