Ethylene separation

The use of silver fluoroborate as a catalyst or reagent often depends on the precipitation of a silver haUde. Thus the silver ion abstracts a CU from a rhodium chloride complex, ((CgH )2As)2(CO)RhCl, yielding the cationic rhodium fluoroborate [30935-54-7] hydrogenation catalyst (99). The complexing tendency of olefins for AgBF has led to the development of chemisorption methods for ethylene separation (100,101). Copper(I) fluoroborate [14708-11-3] also forms complexes with olefins hydrocarbon separations are effected by similar means (102). 

The reactor effluent is cooled and fed to the ethylene separator for recovery of unreacted gaseous ethylene. The liquid phase is filtered to remove small amounts of polymer and then treated with aqueous caustic to remove the catalyst. The dissolved light ends (C2 and C4 olefins) are separated by suitable fractionating towers in series. A portion of the ethylene is purged to remove methane and ethane, and the remaining ethylene is recycled to the compressor. The butene-1 is removed to storage. 

The material balance from Problem 3-6 and either ASPEN PLUS or CHEMCAD-III computer software is used to develop the energy balance around each piece of equipment in the ethylene separation section. For example, around distillation column, C-601, the computer program establishes the heat content 6f streams 533, 602, and 603 above a selected datum plane. The distillation calculation indicates the flow rates of the oveiiiead and bottoms streams. The reflux and reboil then indicate the flow rates of the streams that are returned to the column and permits evaluation of the condenser and reboiler duties. In kW " this pan be expressed as... 

Figure P3-10 Membrane cascade for ethane/ethylene separation...

Once the desired ethylene conversion is obtained, the reaction stream passes to a high-pressure separator where the bulk of the unreacted ethylene is removed from the product and recycled (Fig. 23.1 [4]). High-pressure separation of most of the unreacted ethylene conserves compression costs in much the same way as high-pressure hydrogen recovery does during ammonia production. After high-pressure ethylene separation the hot product moves to a low-pressure separator where the rest of the unreacted ethylene is removed. The polyethylene product is then extruded into cold water and pelletized, dried, and then either bagged or shipped in bulk containers for delivery to fabricators. 

TABLE 30.6 Mixed-Matrix Membrane for Ethylene Separation ... 

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