Patent GB-796048-A (GB)
Title: Conversion of hydrocarbons
IPC: C07C5/44
Filed: 1956-08-14
Abstract: Hydrocarbons containing at least two carbon atoms and containing non-aromatic carbonhydrogen bonds are converted to hydrocarbons containing a new carbon-carbon linkage and having a higher carbon to hydrogen ratio by contacting a mixture of the first hydrocarbon and hydrogen iodide in the vapour phase at 300-800 DEG  C. with a catalyst capable of converting hydrogen iodide to hydrogen and iodine; the iodine dehydrogenates the first hydrocarbon to the second and is itself converted to hydrogen iodide which may be recontacted with the catalyst to regenerate iodine for further conversion. Conversions include dehydrogenation, e.g. alkanes to alkenes and alkadienes, and aralkanes to aralkenes; dehydrocoupling through acyclic carbon atoms, e.g. propylene to diallyl, isobutylene to dimethallyl, and toluene to dibenzyl and stilbene; aromatization, e.g. n-hexane to benzene, n-heptane to toluene, n-octane to o-xylene and ethylbenzene, 2,5-dimethylhexane to p-xylene, hexadiene-1,3 to benzene, o-diethylbenzene to naphthalene, o-methylpropylbenzene to naphthalene, n-butylbenzene to naphthalene (and 4 - phenylbutadiene - 1,3), 2,3 - diethyl - naphthalene to anthracene and butylcyclopentane to indene.  Acyclic hydrocarbons of at least six carbon atoms at least one of which is quaternary may be dealkylated and/or dehydroisomerized, e.g. 2,2,5-trimethylhexane gives p-and m-xylenes. Generally the starting hydrocarbon is heated with iodine or a compound, e.g. an alkyl iodide, which yields iodine under the reaction conditions and the resulting mixture containing hydrogen iodide is contacted with the catalyst.  Pressures of 1-10 atmospheres are preferred. Reaction times of 0.01 seconds to 5 minutes may be used.  The total amount of iodine should be at least 0.05 mol. per mol. of hydrocarbon, and is preferably 0.025 to 4 times to theoretical equivalent for the conversion, amounts above 1 equivalent being added to suppress the reaction between hydrogen iodide and unsaturated hydrocarbon products.  Suitable catalysts are high surface area solids such as alumina or active carbon or metals and metal iodides stable under the reaction conditions, supported, if desired, on silica or alumina.  Specified are platinum, palladium, rhodium, "Hastelloy" C (Registered Trade Mark), an alloy of nickel, molybdenum, iron and chromium; ferrous iodide, cuprous iodide, lead iodide, vanadous iodide, chromous iodide and manganous iodide. Carbonaceous deposits can be burned off conventionally.  Fixed or fluidized beds can be used with hydrogen iodide injected at intervals, wire gauze catalysts can be stretched at intervals across the reactor or the catalyst may be the walls of the reactor, baffles being inserted to give better contact.  An example illustrates the use of platinum alone and supported on silica gel in the aromatization of n-hexane in the presence of iodine.  Specifications 793,214 and 796,049, [Group III], are referred to.ALSO:<PICT:0796048/III/1> Hydrogen iodide is formed in the reaction between iodine and a hydrocarbon (see Group IV (b)) and the hydrogen iodide so formed is catalytically decomposed to give hydrogen and more iodine.  The hydrocarbon is fed by line 101 to the reactor 104, and iodine is fed by line 102 from an outside source and/or by recycle line 111. The catalyst 105 may be a metal or a metal iodide stable under the reaction conditions and may be supported or is a solid of high surface area and no acidic cracking activity.  Hydrogen iodide may be introduced at intervals by lines 117-120, and the reaction mixture is cooled and fed into the distillation column 107. Hydrogen and hydrogen iodide are removed overhead or recycled by line 115.  They may be separated by distillation, by dissolving the hydrogen iodide in water or adsorbing it on a solid such as calcium oxide.  Hydrocarbon and iodine leave by line 108 and are separated by distillation, iodine being recycled. Reaction conditions may be 300-800 DEG  C. and 1-10 atmospheres for 0.01 seconds to 5 minutes.  Catalysts specified are active carbon, alumina of high surface area, platinum, palladium, rhodium, "Hastelloy C" (Registered Trade Mark; anl alloy of nickel, molybdenum, iron and chromium) ferrous iodide, cuprous iodide, lead iodide, vanadous iodide, chromous iodide and manganous iodide.  A comparison is given of the catalytic activities of various catalysts under varying conditions for the decomposition of hydrogen iodide. Specifications 793,214, [Group IV (b))], and 796,049 are referred to.