Oxidative dehydrogenation of organic compounds
United States Patent [191 Haag et al. 51 Apr. 1, 1975 1 OXIDATIVE DEHYDROGENATION OF ORGANIC COMPOUNDS [56] References Cited {75] Inventors: Werner O. llaag; Joseph N. Miale, UNITED STATES PATENTS both of Trenton, Ni I 3,652,698 3/1972 Benslay 6t 3| 260/669 R [73] Assignee: Mobil Oil Corporation, New York,  
  NY. Primary ExaminerC. Davis Filed: J 1974 Attorney, Agent, or Firm-C. A. Huggett [21] Appl. No.: 429,994 [57] ABSTRACT Related Application Data Alkyl aromatic compounds, such as ethylbenzene, are [63] Continuation-impart of Ser. No. 10,023, Feb. 7, dehydrogenated by reaction with carbonyl sulfide in 1970, Pat. No. 3,787,517. the vapor phase in the presence of either silica or a supported heavy metal catalyst, e.g., iron on an oxide [52] US. Cl. 260/669 R, 260/465 K, 260/650 R carrier. [51] Int. Cl. C07c 5/20, C070 15/10 0 Cl N D 58 Field of Search 260/669 R &#39;awmgs ()XIDATIVE DEHYDROGENATION OF ORGANIC COMPOUNDS RELATED APPLICATION This application is a continuation-in-part of applica tion Ser. No. 10.023. filed Feb. 7. 1970. now U.S. Pat. No. 3.787.517.  
 BACKGROUND OF THE INVENTION This invention relates to a process for the dehydrogenation of alkyl aromatics. More specifically. this invention is directed to the catalytic vapor phase oxidative dehydrogenation of alkyl aromatic compounds by reaction with carbonyl sulfide in the presence of either silica or a supported heavy metal catalyst. e.g.. iron on an oxide carrier.  
  The dehydrogenation of organic compounds for the production of compounds having a higher degree ofunsaturation by oxidative dehydrogenation is generally well known. The process may be illustrated in connection with the stoichiometric reaction of a compound containing a paraffinic group with a hydrogen acceptor or oxidant in accordance with the general equation:  
 l =C H2X H I wherein X is the hydrogen acceptor or oxidant. to produee an olelinic group and a compound H. ,X.  
  As the oxidant X. oxygen has been commonly employed. but in general. with resulting low selectivity.  
 This also applies to the halogens. with the exception of iodine. which produces olefins in high yields. However. the corrosion problems and high cost of iodine have prevented commercialization so far.  
  The use of sulfur as a relatively available and cheap oxidant is well known. reacting at moderate temperatures of 4()()-47()F. with paraffins to yield mostly sulfides and disulfides. At high temperatures paraffins with four or more carbon atoms yield thiophenes and the conversion of cylcohexane to aromatics with sulfur is an old. well-established laboratory procedure. The use of sulfur in the formation of styrene from ethyl benzene has been claimed in the recent patent to Schuman. U.S. Pat. No. 3.344.201. Sept. 26. 1967.  
  The use ofsulfur dioxide as the oxidant in the conversion of paraffins (C -C to aromatics has been reported by V. J. Frilette in (/it&#39;mit&#39; e! lmluxrric. 88. 487 1962). with good yields over C110 and MgO as catalysts. The use of sulfur dioxide as the oxidant in the conversion of paraffins (C wl to olefins and aromatics has also been reported by C. R. ADAMS. l &amp; E C Ol 30 (1969) with good yields over bismuth phosphotungstate, bismuth molybdatc and calcium nickel phosphate as catalysts with selectivities for unsaturated hydrocarbons of -757. thiophenes being a major product for paraffins having carbon chain-lengths greater than three. Adams obtained high selectivity with cthylbenzene but not with other alkyl-aromatics.  
  In a patent issued to Boswell. U.S. Pat. No. 3.399.243 Aug. 27. 1968. carbonyl sulfide. COS. is disclosed as an oxidant for the conversion of ethylbenzene to styrene. The reaction proceeds at acceptable rates of conversion per pass and in satisfactory yields over magnesia as a catalyst.  
  The U.S. Pat. No. 3.429.943 issued to Trevillyan et al. discloses conversion of paraffins to olefins by reacting them with carbonyl sulfide in the absence of catalyst. They used excess hydrocarbon and very long contact times. Conversion drops rapidly with contact time while adverse selectivity effects are incurred by increasing temperature to achieve higher conversion.  
 SUMMARY OF THE INVENTION In accordance with the present invention. alkylaromatic compounds are dehydrogenated by reaction with carbonyl sulfide. COS. in the presence of either silica or a supported heavy metal catalyst. e.g.. iron on an oxide carrier. to produce compounds having a higher degree of unsaturation than the starting material.  
  The process is applicable to a wide variety of alkylaromatic reactants wherein the aromatic compound has the formula:  
 where Ar is an aryl or substituted aryl group (e.g.. phe nyl. naphthyl. thienyl C H S. pyridyl); R R R are selected from H or lower alkyl (C -C R is selected from the group consisting of lower alkyl (C C alkoxy. halogen. cyano. aromatic and mixtures thereof. and where n is 0-5.  
  Preferred are alkyl benzenes such as ethylbenxene and substituted ethylbenzenes of the generic formula:  
 thylethylbenzcne; 2-ethylthiophene; l-methyl-4-isopropylthiophene; Z-propylpyridine; 4- isopentylpyridine&#39;. 2.7-diethylnapthalene; and lethylnaphthalene. The ethylbenzenes. which can have a substituent or substituents R as aforedefined. are preferred alkyl aromatic compound reactants.  
  The carbonyl sulfide employed in the present process as the oxidant may be charged as such with the feed. or may be formed in situ. as by the addition of a mixture of carbon monoxide and sulfur. hydrogen sulfide and carbon monoxide. or of carbon dioxide and carbon disulfide. Throughout the present specification and claims. the term carbonyl sulfide&#34; is accordingly intended to be inclusive of carbonyl sulfide whether formed in situ in the reactor or formed as such prior to introduction into the reaction.  
  The catalysts employed in the present invention are of special importance and constitute a point of particular novelty. These catalysts are. in general. the (heavy) metals. Groups 18. Group &#34;B. and Groups [II to Group Vlll. e.g.. the elements scandium. titanium, vanadium. chromium. molybdenum. manganese, iron. cobalt. nickel. cadmium. tin. antimony. and bismuth (including compounds thereof). Especially preferred catalysts are molybdenum, iron. cobalt. nickel and vanadium.  
 The catalysts are deposited on support or carrier material which is selected from a large class of known catalyst supports which are generally difficultly reducible oxides such as alumina. silica. boria. magnesia and silica-alumina. The metal catalyst may be deposited on the catalyst support material by any of the well known methods employed in this art. e.g.. by impregnation. evaporation from a solution. etc. The preferred carrier is silica.  
  Although the preferred catalyst is a heavy metal. deposited on a silica carrier. it has been unexpectedly found that silica. alone. may be used as a catalyst. As shown hereinafter. pure silica. substantially free of impurities. is about l /1 more selective and productive than a commercial silica containing trace amounts of alumina. Addition of a heavy metal such as iron to silica improves substantially the rate of reaction which leads to increased productivity.  
  The catalysts are most commonly prepared from compounds of heavy metals. including their oxides. sulfides. hydroxides. silicates. citrates. sulfates. as well as mixtures thereof.  
  An especially preferred catalyst system has been found to be iron. prepared from ferric ammonium citrate deposited on a pure form of silica. such as silica gel prepared from ethyl-orthosilicate. which has been activated by treatment with hydrogen sulfide before use.  
  While as pointed out above. the oxidative dehydrogenation reaction using carbonyl sulfide as oxidant is in stoiehiometric proportions. the molar ratios of the oxidant to the organic feed material may vary from 0.2 to 10. However. the preferred range of ratios has been found to be from I to 5. The reaction may be carried out under pressures of l to 5 atmospheres although one atmosphere is usually preferred.  
  It is contemplated that the process of the invention can be carried out batchwise. but it is more feasible to use a continuous operation.  
  The liquid hourly space velocity (LHSV-liquid volume compound charged per volume of catalyst per hour) may be between 0.05 to 40. preferably 1 to l0 and is correlative with the temperature. The temperature employed can be between 300C. and about 700C. although a preferred range is between about 500C. and 600C.  
  The invention will be further understood by reference to the following examples which illustrate the best mode now contemplated for carrying out the invention.  
 EXAMPLE I The conversion of ethylbenzene to styrene was carried out using carbonyl sulfide as oxidant over a silica supported iron catalyst prepared from ferric ammonium citrate deposited by impregnation on pure silica gel and activated by treatment with hydrogen sulfide. At atmospheric pressure and with a feed stock molar ratio of COS to cthylbenzene of 4.45. the results obtained at temperatures of 538C. and 593C. and at varying sp&#39;ace velocities are tabulated below:  
  The conversion of ethylbenzene to styrene was carried out as in Example 1. but substituting for the catalyst system cobalt as the catalyst deposited on silica. At a temperature of 538C. and molar proportions of COS ethylbenzene of 4.5. the following results were obtained:  
 TABLE II LHSV 4 Conversion &#39;7! Selectivity EXAMPLE 3 The conversion of ethylbenzene to styrene was carried out as in Example I. but substituting nickel as the catalyst deposited on silica. At a temperature of 538C. and LHSV of 3.0. the percent conversion was 73% and selectivity of 9871.  
 EXAMPLE 4 The reaction as carried out in Example 3 was repeated but with vanadium as the catalyst supported on silica. This resulted in conversion of 84% and percent selectivity of 99% EXAMPLES 5-] 1 Conversion of ethylbenzene was carried out as in Example l. but substituting the following catalysts: copper on silica. cadmium on silica. molybdenum on silica, iron on magnesia. cerium on silica. bismuth on silica. all prepared from deposition of concentrated salt solutions by the basic method used in Example 1 and antimony on magnesia prepared by ballmilling equal amounts of antimony sulfide (Sb S and magnesia followed by calcination and hydrogen sulfide treatment prior to use.  
 EXAMPLES l3 14 Ex CATALYST c LHSV gl&#39; A series of experiments were carried for the conversion of t-butylethylbenzene to t-butylstyrene using the 5 UPPWSWC i v ii The silica SLI&#39;) orted iron cat- 6 Cadmiuiii/silica 38 3.0 51 99+ 5 1 m UH l l p 7 Molvhdenum/ 538 3.0 91 99+ alyst was prepared according to Example l whereas f x 32 molybdenum on silica was prepared according to Ex- 8 t v t) 533 m 96+ ample 7. The experimental conditions and results oh- 54 tained are set forth below in Table IV. l0 Bismuth/silica 538 3.0 00 )8 0.75 75 10 l l Antimonyl- 538 3.0 45  
 magnesia [:XAMPLE 0.75 79 99+ 3.0 82 Conversion of ethylbenzene to styrene was carried 593 36 99+ out using carbonyl sulfide as the oxidant on an aliquot TABLE IV Mol Ratio Con- Yields, Wt.&#34;/1  
  COS/ tact Run Cata- Temp t-butylethyl- Time Time t-Butyl- Selec- Productiv lyst&#34; F. LHSV benzene (sec) Hrs. styrene Other tivity ity MO/SiO 1000 3.0 1.5 .067 1 42.5 5.5 88.5 1.07 1.5 3.0 .083 2 52.9 10.2 83.8 .67 3 55.1 6.8 89.0 .70 4 35.1 1.9 94.9 .44 1055 6 15.9 1.0 94.1 .20 7 14.9 0.4 97.4 .19  
 Fe/Si0 1000 3.0 1.5 .067 1 5 t .0 3.3 93.9 1.29 2 30.l 3.6 89.3 .76 1.5 3.0 .083 3 29.8 0.8 97.4 .38 4.5 .061 4 33.5 0.5 98.5 .42  
 Regen.&#34;&#34; t000 1.0 4.5 .091 I 68.2 4.9 93.2 .58 2.0 4.5 .045 i 5 42.2 1.3 97.0 .71  
 &#34;&#34;$eleetivity=t-Rutylstyrenc/Total Converted Products &#34;Productivity -Hutylstyrcnc. grams per hour per gram catalyst &#34;Regeneration 3 hrsll000F in air (not complete) 50 min. H- -S treat EXAMPLE 12 metal such as iron to magnesia improves the rate of reaction (productivity of the catalyst) as shown in the following table:  
 TABLE III Conversion of Ethylbenzene to Styrene of pure silica gel prepared from ethyl orthosilicate which had a surface area of 436 in /g( B.E.T. The catalyst was calcined at 538C prior to use. At atmospheric pressure. 0.5 LHSV. and with a feedstock molar ratio ofCOS to ethylhenzcne of 4.45. the following results were obtained:  
 &#39;l&#39;empci&#39;aturc Conversion Selectivity 538C 50% 9 W, 593 X: )0  
 EXAM PLE l 6 In Table V below the addition of a heavy metal such Catalyst MgO Fe/MgO MgO P&#39;s/ as iron to silica increases the efficiency by a factor of mm) [m0 about 2. without loss of selectivity. for converting eth- LHSV 0.5 3.0 0.5 3.0 ylbenzene to styrene at high conversion (about 92% Contact Time. Sec. 0.7 l.l (1.7 1.] r t Yield Styrene 77. SR7 7x: 70] As also shown. pure silica is ahoutl tl /r more selective W1. /1 Conversion 78.5 54.6 80.8 73.7 and productive than commercial silica which is mildly K-I g-l i l &#34;8&amp; $2 acidic due to traces of alumina. The reaction condia e&#34; t tions include a mole ratio oi COS to ethylbenzene of g styrene produced per hour per catalyst IO 1 at atmospheric pressure.  
 TABLE V Contact Yield Wt.&#39;7 Con- CATALYSTS F LHSV Time,Sec. of Styrene version 7( Selectivity Rate&#34; Si0 (commercial) vs sulfided Fe/SiO (commercial) SiO 1000 0.5 6.7 35.9 39.0 91 .28 Fe/SiO 88.4 9.18 96.3 .56 Commercial vs Organically derived pure SiO [commsio- 1000 0.5 6.7 35.9 39.0 91 .28 Pure SiO 39.0 39.4 99+ .31  
 &#34;&#39;g styrene produced per hour per g catalyst EXAMPLE 17 Relative Rates of (unver- Feed Product sion Ethylhenzene Styrene l1) n-Pl&#39;opylbenzene B-Methylstyrcne l1) lsopropylbenzene u-Melh \&#39;|sl \t&#39;el\e 4.8 lsobutylbcnzene tifi-Diniethylstyrene 1.! l Methy|-3-etliylhenzene iii-Melliylstyrene 1.2 l-Methyl-4-ethylbenzene p-Methy &#39;tyrene 1.5 l-Methoxy-J-etliylhenzene p-Metho yrenc l.l l-(&#39;liloro -l-ethylhenzene p-(hlorostyrene 1.05 l-Bnnno-4-ethylbenzcne p-Bromostyrcne 0.71  
 The data indicate that ethylbenzenes having substituents on the side chain or on the aromatic nucleus can be converted to the corresponding styrene derivatives under conditions similar to those for ethylbenzene itself. The substituents can be alkyl groups or other functional groups such as methoxy. or halogens such as ehloro or bromo groups.  
 What is claimed is:  
  l. A process for the catalytic oxidative dehydrogenation of an alkyl aromatic hydrocarbon to produce compounds having a higher degree of unsaturation which comprises contacting said aromatic hydrocarbon and carbonyl sulfide with a catalyst consisting of a heavy metal deposited on an oxide carrier. said aromatic having the formula:  
  t t (R&#39;ln Ar-cl: R3  
 wherein R R and R are hydrogen or lower alkyl: and R is selected from the group consisting of hydrogen. lower alkyl. alkoxy. halogen. cyano. and mixtures thereof.  
  3. The process of claim 2 wherein the alkyl benzene is ethylbenzene.  
  4. The process of claim 2 wherein the alkyl benzene is t-butylethylbenzene.  
  5. The process of claim 3 wherein the catalyst is a silica supported iron compound.  
  6. The process of claim 4 wherein the catalyst is a silica supported iron compound.  
  7. A process for the catalytic oxidative dehydrogenation of an alkyl aromatic hydrocarbon to produce compounds having a higher degree of unsaturation which comprises contacting said aromatic hydrocarbon and carbonyl sulfide with a catalyst consisting of silica.  
 said aromatic having the formula:  
  f1 Y2 (R&#39;h&#39;t Ar-fi T- R3 H H where Ar is an aryl or substituted aryl group; R R R are selected from H or lower alkyl (C C R is selected from the group consisting of lower alkyl (C.C.,). alkoxy. halogen. cyano. aromatic and mixtures thereof. and where I1 is 0-5.  
  8. The process of claim 7 wherein the aromatic hydrocarbon is an alkyl benzene having the formula:  
 wherein R,. R and R are hydrogen or lower alkyl; and R is selected from the group consisting of hydrogen. lower alkyl. alkoxy. halogen. eyano. and mixtures thereof.  
  9. The process of claim 8 wherein the alkyl benzene is ethylbenzene.  
  10. The process ofclaim 8 wherein the alkyl benzene is t-butylethylbenzene.