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NOV- 29, 1945. H. M. SINGL’ETON . 2,389,215 PROCESS FOR DEHYDROGENATING HYDROCARBONS Filed Feb. 15, 1943' . ' . WM’. INVENTOR. BY Mm ATTORNEY Patented Nov.,20, 1945 _ * 2,389,215 UNITEDVSTATES PATENT OFFICE. I -j , 2,389,215 . / PROCESS FOR DEHYDBOGENATING A HYDROCABBON Henry M. Singleton, Goose Creek, Tex., assignor to Standard Oil Development Company,-a cor poration of Delaware Application February 15, 1943, Serial No. ‘475,866 12 Claims. (Cl. 260-669) The present invention is directed- to the de hydrogenation of hydrocarbons. , In recent years dehydrogenation has become an extremely important tool to the re?ner of petroleum oil. It is one treatment to which gaso-v line is subjected in order to improve its octane number. Most of the important syntheses start with unsaturated hydrocarbons which do not occur naturally and must be otbained primarily by dehydrogenation of naturally occurring sat urated hydrocarbons.’ which are contemplated for use in accordance with the present invention. These various com pounds will be referred to hereinafter as hydrogen acceptors. - . ' ' These organic compounds are characterized, in addition to their property of combining readily with hydrogen, by their susceptibility to decom position into free radicals at elevated tempera tures. The formation of these free radicals en 10 hances the power of these organic compounds Ole?ns'for use in poly- ‘ to consume hydrogen, particularly the nascent merization and ‘alkylation are obtained by de type, which results from the dehydrogenation of hydrocarbons. Under certain conditions these hydrogenation of the corresponding paramns. Diole?ns ‘for the production of rubber are ob free radicals combine either with themselves or tained by further dehydrogenation of the ole?ns. 15 with the dehydrogenatedhydrocarbons to yield Diole?ns, such as butadiene, are also obtained useful by-products. The generation of these free‘ from hydroaromatic hydrocarbons by a reaction radicals can be controlled by the use of suitable which involves dehydrogenation. For example, , addition agents. For example, small percentages cyclohexane is ?rst dehydrogenated to cyclo of acid-reacting substances, such as strong min-‘ hexene, which then breaks down into butadiene 20 eral acids, tend to acceleratethe production of and ethylene. Polymerizable aromatic hydrocar free radicals from these compounds, while the bons, such'as styrene, are obtained from alkylated compounds‘are stabilized and the formation of aromatics by‘aiehydrogenation. _free radicals suppressed by the presence of basic From the foregoing discussion it will be evi substances such as ammonia or amino compounds. dent that the process of dehydrogenation of hy 25 Thus, if, in a given reaction, the operating tem drocarbons is one which has been intensively perature is such as to promote the decomposition studied with a, view of increasing its economy and of the hydrogen acceptor and such decomposi efficiency. Various catalysts have been suggested tion is not desired, a certain percentage of am as promoters of dehydrogenation. The condi monia, aniline, pyridine, or the like is included tions best suited for dehydrogenation of various 30 in the feed stock. On theother hand, if, under- _ hydrocarbons in the presence of and in the ab the operating conditions, the hydrogen acceptor sence of catalysts have been fairly well estab is relatively stable and decomposition thereof is lished after careful investigation. The e?ect of desired, either for the purpose of increasing the pressure, including the partial pressure of hy hydrogen consumption or of producing additional drogen, on the reaction has been fully disclosed 35 amounts of desired end product, a small amount in the literature. of an acidic substance, such as nitric acid, h-y- I According to the present invention, the ef drochloric acid, sulfuric acid, sulfur dioxide, or ?ciency and economy of processes involving the the like is included in the feed. ' dehydrogenation of hydrocarbons are favorably The various dehydrogenation reactions con in?uenced by carrying out the dehydrogenation 40 templated by the present invention are well es in the presence of certain organic compounds tablished in the art, and the operating conditions which possess the property of rapidly consuming therefor are well known. The modi?cation of large quantities of hydrogen, and in some cases these well known processes by the‘ present inven cf undergoing conversion themselves to yield fur tion does not necessarily alter these operating 53-1181‘ quantities of the desired reaction product. 45 conditions, although the invention does afford "l'hese organic compounds may be referred to the possibility of increasing the desired conver generally as heterocyclic compounds,-which.in-' sion at any given set. of conditions.v To put it, clude in their ring structure at least one of’ the _ elements oxygen, nitrogen, and sulfur. Examples of such organic compounds are furan, thiophene, pyrrole and derivatives thereof. Readily avail able compounds ofthis type are furfural and another way, the present invention makes -pos-, sible the realization under milder conditions of ~ 50 yields heretofore requiring more severe condi . tions. As has previously been indicated, the pres ent invention is applicable to dehydrogenation effected both by heat alone, as well as by heat and catalysts. Suitable catalysts for these reac ‘ types speci?ed above are typical of compounds 55 tions are numerous and fully disclosed .in the furf‘uryl alcohol. The alkyl derivatives and the partial reduction compounds of the three general i 2,889,216 2 reactions may occur. After the process is once prior art. Especially effective catalysts are oxides started, all of the fresh feed may be introduced by way of line 6. The mixture of reaction prod uct and fresh feed is conducted by line ‘I to a fractionating tower 8, ahead of which is ar ranged atemperature controlled unit 9 which may be utilized to impart heat to, or cool, the mix— ture in line ‘I, as required. The fractionator 8 and sulfides of metals of group VI of the periodic system, alone or in conjunction with supports such as activated aluminum. Molybdenum sul ?de and chromium oxide may be mentioned as representative examples of group VI dehydro genation catalysts. In general, dehydrogenation reactions contem is so operated as to give off, as an overhead plated by the present invention are carried out stream through line I0, butadiene and lower boil 10 at temperatures ranging from about 600° to ing compounds. Unreacted cyclohexane is with 1400“ F. Reactions which involve the conversion drawn. as bottoms by way of line I I and recycled of ole?ns to diole?ns are ordinarily carried out to line I. in the upper end of this range, while the dehydro genation of the para?ins to ole?ns is ordinarily ' The temperature inside reactor 3 is maintained . preferably between about 1l00° and 1400" F. The pressure should preferably be less than about 100 lbs/sq. in., 30 lbs/sq. in. being satisfactory. At this pressure the partial pressure of the re acting material is reduced by including in the conducted in the lower end of the range. A higher operating pressure than ordinarily em ployed in dehydrogenation is permissible in the practice of the present invention because the re action, when carried out according to the present invention, is not necessarily accompanied by an increase ‘in volume. Pressures as high as 250 lbs/sq. in. may be employed, but lower pressures I are preferred. It is advantageous to dilute the ' reaction mixture with an inert gas, such as nitro gen, steam, molecular hydrogen, or natural gas. A ratio of diluent-to product as high as 50:1 may be employed, but preferably this ratio is main reaction mixture an inert gas. For this purpose, steam may be introduced into line I by way of branch line I2. Nitrogen may be used if desired. Methane is also a useful diluent and in some cases may find its way into the ?nal product, as herein after suggested. In operating according to the present inven tion, a hydrogen acceptor is introduced into line I by branch line I3. In the particular embodi ment shown, the hydrogen‘ acceptor may be as presence of the diluent makes possible the em sumed to be’ furfural. This hydrogen acceptor ployment of higher pressures without giving rise 30 may be used in an amount equal to, and prefer to excessive polymerization, to which there may ably somewhat in excess of, the amount theo be a considerable tendency under the operating retically required to consume the hydrogen lib conditions with certain hydrocarbons. The same ' erated in the conversion of cyclohexane to buta tained below 20:1 when diluent is used. The > effect as that realized with a diluent may be ob diene and ethylene. Of course, for a lesser effect tained by using a su?iciently high feed rate to 35 a smaller amount of the hydrogen acceptor is em provide a large amount of unreacted feed at all ployed. There is no objection to using a con times in the reaction chamber. ‘This type of oper- - siderable‘excess of the hydrogen acceptor, except and ation yields only a low conversion per pass, that it reduces the capacity of the unit for the involves considerable recycling. desired reaction. A slight excess over stoichio- . The nature of the present invention may be 40 metrical requirements will ordinarily be satis better understood by reference to the accompany factory. Under the particular conditions em ing drawing, in which is shown, in front eleva ployed furfural, in taking up hydrogen, is con tion in diagrammatic form, an apparatus of the verted ?rst to furfuryl alcohol, which, through type suitable for the practice of the method. further absorption of hydrogen, yields piperylene In referring to the drawing in detail, a spe as an end product. Piperylene is a highly desir cific embodiment of the process of the present able by-product since it may be used as a raw invention will be discussed. This particular em material for the production of synthetic rubber, bodiment is the production of butadiene from either by way of polymerization or copolymeriza cyclohexane, to the treatment of which the appa tion with isobutylene or butadiene or other rub ratus shown is particularly adapted. Itwill be understood, of course, that, with slight modifica tion, the apparatus can be used forthe dehydro genation or conversion of other materials.- ber forming unsaturated hydrocarbons. Pipery_ lene is advantageously recovered from the system \ Numeral one designates a. fresh feed line, in which is arranged a heating coil 2, where the feed stock is supplied with suflicient heat to support the subsequent reaction. The feed is discharged as a side stream from fractionator 8 by way of draw-oi! line I4. Any unconverted furfural or residual furfuryl alcohol or intermediate prod ucts boiling above piperylene and still capable of taking up hydrogen go into the bottoms with un clzlonvfrted cyclohexane and are returned to inlet from line 1 into the bottom of reactor 3, which, in the particular case illustrated, is provided at It is believed to be evident that, instead of its lower end with a bed 4 of catalytic material 60 using furfural as the initial hydrogen acceptor, effective for catalyzing dehydrogenation. Also furfuryl alcohol may be employed with equal suc included in the catalyst bed may be substances cess. It may beobserved that, depending upon ‘which favor the splitting of molecules, such as the specific conditions of working employed, the free iron, nickel, cobalt, copper, and the like. In hydrogen acceptor may exhibit a greater or lesser the upper part of reactor 3 is provided a heating tendency to decompose into free radicals. As has element 5 which may be used to supply any heat 'ne required to complete the conversion of the cyclo . ' previously been suggested, this tendency may be enhanced by adding a small amount of an acid hexane to butadiene and ethylene. I reacting substance to the feed. When an acid Arranged as close to ‘the outlet of reactor 3 as convenient is an inlet line 6 for the introduction 70 reacting substance is employed it may be used in an amount ranging from 0.01% to about 10% of of cold fresh feed. The purpose of introducing cold feed at this point is to quench the reaction ' the hydrogen acceptor. Ordinarily, the concen tration of the acid-reacting substance need not products so as to reduce them, as rapidly as possi substantially .exceed 1% of the hydrogen ac ble, from reaction temperature to a temperature below that at which polymerization and other side ' 75 ceptor. Particularly when methane is employed 2,889,915 as a diluent, it is desirable to promote the fema tion of free radicals in the reactor. In this cue, a substantial excess of the hydrogen acceptor over that normally required to assimilate the hy drogen given up by the cyclohexane is‘advan tageous. With methane and free} radicals pres ent in the reactor, the yield of useful product is increased by including phosphoric acid either in the catalyst bed 4 or by arranging a separate bed 3. molecular weight of the initial hydrocarbon ma terial. . ’ 3. A process for converting a hydrocarbon into a less saturated hydrocarbon which comprises subjecting the hydrocarbon in admixture with an organic heterocyclic compound containing a plurality of double bonds in its ring structure to t a temperature sufiicient to split 0!! hydrogen from said hydrocarbon and favoring formation of phosphoric acid on a suitable support, such as 10 of‘ free radicals from said organic heterocyclic silica gel or activated alumina in the upper part compound, the formation of free radicals being of the reactor. In this case, a more careful promoted by adding to the organic heterocyclic fractionation of the product, or additional frac tionation of the bottoms drawn oil.’ from frac tionator 8 by line I I is advisable. In like manner, if the operating conditions are such that an undesirably high‘ conversion of the compound an acid reacting substance. _ ,4- A process in accordance with claim 3 in which the acid reacting substance is a mineral acid. - 5. A process for dehydrogenating a hydrocar hydrogen acceptor into free radicals occurs in bon which comprises subjecting the hydrocarbon the reactor 3, there is added to the reaction mix in admixture with a compound of the furan se ture, by way of line II, a basic substance in addi 20 ries to a temperature between 600° F. and 1400' tion to the hydrogen acceptor. ' A suitable basic‘ substance for this purpose is aniline or pyridine, although ammonia itself may be employed. F., said dehydrogenation being promoted by ad dition of a mineral acid to said compound of the furan series. _ ’ When the apparatus shown in the drawing is ' 6. A process in accordance with claim 5 in utilized for the dehydrogenation of other hydro 25 which the mineral acid added to said compound carbons, such as the dehydrogenation of para?ins to the corresponding ole?ns, it may be advan tageously modi?ed by either ?lling the reactor 3 entirely with catalyst or, if desired, leaving the of the furan series is in an amount ranging be tween 0.01% to 10% of the‘ compound of the furan series in admixture withthe hydrocarbon. 7. A process for converting; hydrocarbon into reactor entirely empty. Likewise, in this case the 30 a hydrocarbon of less saturated nature which comprises subjecting the hydrocarbon in admix tion and may be omitted, the entire fresh feed ture with an organic heterocyclic compound con- ' being introduced by way of line I. When, ‘how taining a plurality of double bonds in its ring ever, the apparatus is used for the conversion of structure to a temperature sufiicient to split oi! quenching operation serves no particular func ole?ns into diole?ns, the quenching step is highly 35 hydrogen from said hydrocarbon and favoring ' desirable. It will be understood that the use of the formation of free radicals, said formation of a catalyst is not necessary in any of these dehy free radicals being inhibited by adding to said drogenation reactions. When the apparatus is organic heterocyclic compound a basic substance. used for the production of styrene from ethyl 8. A process in accordance with claim '7 in benzene it will be understood that the fractiona which the basic substance is a nitrogen com tion step must be suitably modified. Here the degradation products of‘ the hydrogen acceptor _ 9. A process for dehydrogenating a hydrocar boiling below styrene'are taken oi! as an over bon which comprises adding to the hydrocarbon head stream and the styrene taken of! as a side _ an organic heterocyclic compound containing a stream, leaving unconverted ethylbenrene in the plurality of double bonds in its ring structure bottoms together with the hydrogen acceptor and subjecting the mixture to the action of a where the latter is furfural or furfuryl alcohol. dehydrogenation catalyst at a temperature be The nature and objects of the present inven tween about 600" F. and 1400" 1". tion having been thus described and illustrated, 10. A method according to claim 9 in which what is claimed as new and useful and is desired the heterocyclic compound is used in an amount to be secured by Letters Patent is: ' . -_ranging from 0.01% to 10% of the amount of 1. A method for subjecting a hydrocarbon to a hydrocarbon employed. conversion involving dehydrogenation which 11. A method for converting cyclohexane into comprises adding an organic heterocyclic com ' unsaturated compounds which comprises pound containing a plurality of double bonds in cyclohexane in admixture with an organic hetero its ring structure to the hydrocarbon to be con cyclic compound containing a plurality of double verted and subjecting the hydrocarbon in admix bonds in its ring ‘structure into contact with a ture with the organic heterocyclic compound to dehydrogenation catalyst at a temperature be conditions suitable for said conversion. tween about 1100° F'. and 1400° F. fora limited 2. A method for converting a hydrocarbon into period of time, quenching the reaction products a less saturated hydrocarbon which comprises pound. adding an organic heterocyclic compound con taining a plurality of double bonds in its ring structure to the hydrocarbon to be converted and subjecting the hydrocarbon in admixture with the‘ organic heterocyclic-compound to a tem perature su?icient to split o? hydrogen from a said hydrocarbon, said temperature being at least 600° F. and being higher the lower the . _ and recovering unsaturated hydrocarbons there- . from . - 12. A process according to claim 11 in which ‘the reaction products are quenched with fresh cyclohexane feed and the latter is recovered from , the quenched reaction products and ‘fed to the catalyst zone. ' ‘ HENRY H; BINGIIION. '