Light hydrocarbon separation using 8-member ring zeolites

Abstract

A method of selectively adsorbing propylene in mixtures of propylene/propane and propylene/olefins through the use of zeolites having structures with a maximum of 8-member rings of tetraheda controlling the diffusion rate. Suitable zeolite adsorbents are those having the CHA and ITE structure types. Other 8-member ring zeolites, including aluminosilicates, with a Si:Al molar ratio of at least about 200 and having substantially no free acid are also suitable adsorbents.

What is claimed:  
     
         1 . A process for kinetic separation of a light hydrocarbon mixture comprising at least two components, by preferentially adsorbing one of said two components on a zeolite adsorbent, said zeolite phase containing 8-member rings of tetrahedra as the pore opening controlling hydrocarbon diffusion, the other of said two components being non-preferentially adsorbed, said process comprising the steps of: 
 (a) contacting said light hydrocarbon mixture with a zeolite adsorbent, characterized by having a diffusion rate which is at least 50 times greater for the preferentially adsorbed component as compared to said non-preferentially adsorbed component; and    (b) recovering said preferentially adsorbed component.    
     
     
         2 . A process as claimed in  claim 1 , wherein said hydrocarbon mixture includes an olefin as said preferentially adsorbed component and a paraffin as said non-preferentially adsorbed component.  
     
     
         3 . A process as claimed in  claim 2 , wherein said olefin is propylene and said paraffin is propane.  
     
     
         4 . A process as claimed in  claim 3 , wherein said zeolite has a diffusion rate which is at least 200 times greater for propylene than for propane.  
     
     
         5 . A process as claimed in  claim 1 , wherein said zeolite has a silica-to-alumina ratio greater than about 200.  
     
     
         6 . A process as claimed in  claim 1 , wherein said zeolite has a silica-to-alumina ratio greater than about 500.  
     
     
         7 . A process as claimed in  claim 1 , wherein said zeolite has a silica-to-alumina ratio greater than about 1000.  
     
     
         8 . A process as claimed in  claim 1 , wherein said zeolite has a silica-to-alumina ratio greater than about 2000.  
     
     
         9 . A process as claimed in  claim 1 , wherein said zeolite has alkali metal cations as the ions balancing the framework charge.  
     
     
         10 . A process as claimed in  claim 1 , wherein said zeolite has a propylene adsorption capacity greater than 40 mg/g.  
     
     
         11 . A process as claimed in  claim 1 , wherein said zeolite is of CHA structure type.  
     
     
         12 . A process as claimed in  claim 11 , wherein said zeolite has a silica-to-alumina ratio greater than about 200 and contains alkali metal ions as the cations balancing the framework charge.  
     
     
         13 . A process as claimed in  claim 11 , wherein said zeolite has a silica-to-alumina ratio greater than about 500 and contains alkali metal ions as the cations balancing the framework charge.  
     
     
         14 . A process as claimed in  claim 11 , wherein said zeolite has a silica-to-alumina ratio greater than about 1000 and contains alkali metal ions as the cations balancing the framework charge.  
     
     
         15 . A process as claimed in  claim 11 , wherein said zeolite has a silica-to-alumina ratio greater than about 2000 and contains alkali metal ions as the cations balancing the framework charge.  
     
     
         16 . A process as claimed in  claim 11 , wherein said CHA structure type 8-member rings zeolite is selected from the group consisting of Si-CHA, high silica chabazite, AlPO 4 -(CHA), CaAPO-44, CaAPO-47, GaPO 4 -34, LZ-218, Linde D, Linde R, MeAPO-47, MeAPSO-47, Phi, SAPO-34, SAPO-47, Si-CHA, SSZ-13, Wilhendersonite, ZK-14 and ZYT-6 and mixtures thereof.  
     
     
         17 . A process as claimed in  claim 1 , wherein the zeolite has the ITE structure type.  
     
     
         18 . A process as claimed in  claim 17 , wherein the zeolite has the ITE structure type, a silica-to-alumina ratio greater than about 200 and contains alkali metal ions as the cations balancing the framework charge.  
     
     
         19 . A process as claimed in  claim 17 , wherein the zeolite has the ITE structure type, a silica-to-alumina ratio greater than about 500 and contains alkali metal ions as the cations balancing the framework charge.  
     
     
         20 . A process as claimed in  claim 17 , wherein the zeolite has the ITE structure type, a silica-to-alumina ratio greater than about 1000 and contains alkali metal ions as the cations balancing the framework charge.  
     
     
         21 . A process as claimed in  claim 17 , wherein the zeolite has the ITE structure type, a silica-to-alumina ratio greater than about 2000 and contains alkali metal ions as the cations balancing the framework charge.  
     
     
         22 . A process as claimed in  claim 17 , wherein said ITE structure type is ITQ-3.  
     
     
         23 . A process as claimed in  claim 17 , wherein the zeolite has the SAPO-34 structure type, and contains alkali metal ions as the cations balancing the framework charge.  
     
     
         24 . A process for kinetic separation of a light hydrocarbon mixture comprising at least two components, by preferentially adsorbing one of said two components on a zeolite adsorbent, said zeolite phase containing 8-member rings of tetrahedra as the pore opening controlling hydrocarbon diffusion, the other of said two components being non-preferentially adsorbed, said process comprising the steps of: 
 (a) contacting said light hydrocarbon mixture with a zeolite adsorbent, characterized by having a diffusion rate which is at least 50 times greater for the preferentially adsorbed component as compared to said non-preferentially adsorbed component; and    (b) recovering said non-preferentially adsorbed component.