| 摘要 |
1,264,502. Destructive pyrolysis gas, hydrocarbons &c. UNION CARBIDE CORP. 28 March, 1969 [29 March, 1968], No. 16370/69. Heading C5E. A xylene mixture containing a non-equilibrium proportion of meta-xylene is isomerized by a process which comprises contacting the xylene mixture, in the vapour phase and under isomerization reaction conditions, for example a temperature of from 500‹ to 800‹ F., a pressure of from atmospheric pressure to 750 pounds per square inch and a xylene mixture weight hourly space velocity of from 1 to 25, with a catalyst which comprises a crystalline zeolitic molecular sieve having a deposit thereon of hydrocarbonaceous "coke" in an amount of from 5 to 20 weight per cent based on the weight of the molecular sieve in its dehydrated state. The molecular sieve, which may be natural or synthetic mordenite, zeolite X, zeolite Y, zeolite L or zeolite TMA-omega, has a pore size large enough to adsorb the benzene molecule, a silica/alumina molar ratio of at least 2À2, an alkali metal cation content not greater than 10 equivalent per cent of the total cation content and a residual volatile content, exclusive of the "coke" deposit, such that when heated at 1000‹ C. for half-an-hour a weight loss of not greater than 2À5 weight per cent is incurred. Alkali metal cations of the molecular sieve may be replaced by ions selected from hydrogen, ammonium, alkylammonium, magnesium, calcium, aluminium, thorium, manganese and rare earth metal cations; as exemplified, the molecular sieve is zeolite Y which has been subjected to successive ion exchange with ammonium and "didymium" cations and in which the equivalent sodium : ammonium : rare earth metal cation ratio is either 4 : 34 : 60 or 5 : 47 : 46. Prior to deposition thereon of "coke", the cation-exchanged molecular sieve may be activated by heating at a temperature of from 400‹ to 750‹ C. for a period of time such as to provide the aforementioned characteristic relating to weight loss. The deposit of "coke" may be provided by the polymerization and subsequent coking of an easily polymerizable unsaturated hydrocarbon, for example styrene, isobutylene, butadiene or methylacetylene; as exemplified, the coke may result from the use of the molecular sieve in a process for the disproportionation of toluene to benzene and xylene at a temperature of 700‹ F. and a pressure of 450 pounds per square inch. The process for isomerization may employ carrier gas for the xylene mixture, for example hydrogen, nitrogen, methane, helium, argon or a mixture thereof. |
