Process for enhanced olefin production
The present invention relates to a process for the production of light weight olefins comprising olefins having from 2 to 3 carbon atoms per molecule from an oxygenate feedstock. The process comprises passing the oxygenate feedstock to an oxygenate conversion zone containing a metal alumino phosphate catalyst to produce a light weight olefin stream. A propylene stream and/or mixed butylene is fractionated from said light weight olefin stream and a medium weight C 4 to C 7 stream is cracked in a separate olefin cracking reactor to enhance the yield of ethylene and propylene products.
1. A process for the production of light weight olefins comprising:
a) producing an olefin-rich feedstock by contacting an oxygenate-containing feedstock with a catalyst comprising a non-zeolitic molecular sieve;
b) passing the olefin-rich feedstock comprising C 2 to C 8 olefins to a first stage separation zone to provide a light weight olefin stream comprising C 2 to C 3 olefins and a heavy weight olefin stream comprising C 4 + olefins;
c) passing the heavy weight olefin stream to a second stage separation zone to provide a second light weight olefin stream, a medium weight olefin stream comprising C 4 to C 7 olefins, and a C 7 + olefin stream;
d) passing the medium weight olefin stream to an olefin cracking reactor operated at an inlet temperature of about 450° to 600° C. to convert at least a portion of the medium weight olefin stream into a cracked olefin stream comprising C 2 to C 3 olefins wherein said medium weight olefin stream contacts a catalyst comprising a crystalline silicate of the MFI family or the MEL family;
e) returning at least a portion of the cracked olefin stream to the second stage separation zone, withdrawing a drag stream comprising the remaining portion of the cracked olefin stream; and
f) returning at least a portion of the second light weight olefin stream to the first separation zone.
2. The process of claim 1 wherein said medium weight olefin stream comprises C 4 to C 6 olefins.
3. The process of claim 1 wherein said medium weight olefin stream comprises C 5 to C 6 olefins.
4. The process of claim 1 wherein said cracking catalyst is selected from the group consisting of ZSM-5, silicalite, ZSM-11 and Boralite D.
5. The process of claim 1 wherein said olefin cracking reactor is operated at an inlet temperature of about 540° to 580° C.
6. The process of claim 1 wherein said olefin cracking reactor increases ethylene and propylene yield by about 5 to 15% relative to the carbon content of the oxygenate feed to said first stage separation zone.