GB578085A - Improved process for the isomerization of paraffins - Google Patents

Abstract

<PICT:0578085/IV/1> Normal paraffins of at least 4 carbon atoms are isomerized using a Friedel-Crafts' type catalyst and a gaseous halogen-containing promoter, the reacted mixture being passed through a stripping zone to remove the promoter and gaseous degradation products which are subjected to selective absorption with liquefied hydrocarbon feed under controlled conditions of temperature, pressure and throughput, so that the feed to the isomerization zone contains a desired constant quantity of the promoter. The reacted mixture is stripped and the overhead comprising, for example, hydrogen halide and degradation products such as methane, ethane and propane, passed direct to an absorber where the promoter is absorbed and the inert gases removed as overhead. The absorber may be of a bubble plate or packed tower type, the liquid hydrocarbon flowing down against the stream of promoter. A reboiler or steam jacket may be used to keep a constant temperature, the pressure being controlled by a condenser at the top of the column which normally operates under total reflux conditions. Part only of the feed may pass through the tower so that after admixture with the remainder the desired concentration of promoter is obtained. When isomerizing butane using aluminium chloride and hydrogen chloride, the absorption column is operated between about 100-200 lbs./sq. in. and at a temperature varying between about 50 DEG and 110 DEG F. to give a concentration of promoter varying between about 12 and 2 per cent. The solution of promoter in butane is then brought to a temperature of about 125-220 DEG F. for liquid phase, or 200-450 DEG F. for vapour phase operation. Liquefied butane is fed to absorber 7 by lines 2, 5 and absorbs hydrogen chloride fed by line 43 from an outside source or from the stripping tower 39. Both the solution leaving by line 8, and the overhead may be recycled to ensure equilibrium under the absorption conditions. Inert gases may be withdrawn through line 12, and the butane solution led by pipes 15, 21 to reactor 24 containing "Porocel" (Registered Trade Mark) with absorbed aluminium chloride. The reaction products pass, if desired, partly or wholly by way of cooler 30, to a surge drum 32 which also removes any catalyst, and thence to stripper 39 wherein the pressure is maintained slightly above that of the absorber and the top temperature about the same, while the bottom temperature is generally about 150-300 DEG F. and is controlled by reboiler 47. The overhead comprising hydrogen chloride and part or substantially all the propane returns to the absorber. The bottoms are treated with caustic soda in mixer 50, the butane layer being separated in settler 52 and fed to fractionator 60 giving isobutane with any propane as overhead and normal butane with some pentane which may be returned to the isomerizer through lines 68, 70 and drier 69.