Plastic pyrolysis
Disclosed are methods of reduction of chlorine in pyrolysis products derived from a mixed plastics stream. Methods may comprise: (a) causing pyrolysis of a plastic feedstock to produce a first stream of C1-C4 gaseous hydrocarbons and light gas olefins and a second stream comprising the remaining pyrolysis components. The second stream and hydrogen gas may be fed into a hydrocracker to produce a third stream of gaseous C1-C4 hydrocarbon gases and a fourth stream comprising the remaining hydrocracker components. The fourth stream may be fed to either (i) a steam cracker to produce a fifth stream comprising C1-C4 gaseous hydrocarbons and light gas olefins, a sixth stream comprising C6-C8 hydrocarbons and a seventh stream comprising hydrocarbons heavier than C8; or (ii) a fluidized catalytic cracker to produce an eighth stream comprising C1-C4 gases and light gas olefins and a ninth stream comprising hydrocarbons that are C5 or greater.
1. A method of producing pyrolysis products from a mixed plastics stream, the method comprising:
(a) conducting pyrolysis of a plastic feedstock to produce a first stream comprising C1-C4 gaseous hydrocarbons and light gas olefins and a second stream comprising hydrocarbons having 5 or more carbon atoms, wherein at least a portion of the plastic feedstock comprises chlorinated plastic;
(b) feeding the second stream and hydrogen gas into a hydrocracker to produce a third stream comprising gaseous C1-C4 hydrocarbon gases and a fourth stream comprising hydrocarbons having 5 or more carbon atoms; and
(c) feeding the fourth stream to:
i. a steam cracker to produce a fifth stream comprising C1-C4 gaseous hydrocarbons and light gas olefins, a sixth stream comprising C5-C8 hydrocarbons and a seventh stream comprising hydrocarbons having 8 or more carbon atoms; and
ii. a fluidized catalytic cracker to produce an eighth stream comprising C1-C4 gases and light gas olefins, and a ninth stream comprising hydrocarbons having 5 or more carbon atoms,
wherein the feeding the fourth stream further comprises feeding the fourth stream to a distillation column, wherein the distillation column supplies a bottom stream comprising hydrocarbons heavier than C8 to the fluidized catalytic cracker, the fluidized catalytic cracker producing a C1-C4 gaseous hydrocarbon stream and light gas olefins and a stream comprising hydrocarbons having 5 or more carbon atoms, the stream comprising hydrocarbons having 5 or more carbon atoms being recycled to the hydrocracker, and wherein the distillation column supplies a top stream comprising hydrocarbons that have 8 or fewer carbon atoms to the steam cracker, the steam cracker producing the fifth stream, the sixth stream, and the seventh stream.
2. The method of claim 1 , wherein the ninth stream is being recycled to the hydrocracker.
3. The method of claim 1 , wherein the ninth stream is being supplied to a hydrogenation reactor to produce a tenth stream comprising hydrogenated product, the hydrogenated product being supplied to an aromatic extraction unit to produce a C6-C8 aromatics stream and a stream comprising hydrocarbons having at least 9 carbon atoms that is recycled to the hydrocracker.
4. The method of claim 1 , wherein the mixed plastic stream comprises at least one of polyolefins, polystyrene, polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyamide, polycarbonate, polyurethane, polyester, natural and synthetic rubber.
5. The method of claim 1 , wherein at least one of the first stream, third stream, fifth stream and eighth stream additionally comprises hydrochloric acid (HCl).
6. The method of claim 5 , wherein the hydrochloric acid (HCl) is scrubbed from at least one of the first stream, third stream, fifth stream and eighth stream.
7. The method of claim 3 , wherein the hydrochloric acid (HCl) is scrubbed via a process of liquid scrubbing and/or reactive adsorption.
8. The method of claim 1 , wherein the pyrolysis is performed in the presence of a catalyst at a temperature of 350° C. to 1000° C.
9. The method of claim 1 , wherein the hydrocracker is a fixed bed reactor in the presence of a catalyst.
10. The method of claim 1 , wherein the fluidized catalytic cracker operates at a temperature of 550° C. or higher, in the presence of a catalyst composition comprising a fluidized catalytic cracking catalyst and a ZSM-5 zeolite catalyst, wherein the ZSM-5 zeolite catalyst makes up at least 10 wt. % of the total weight of the fluidized catalytic cracking catalyst and the ZSM-5 zeolite catalyst, the fourth stream and the catalyst composition being at a catalyst-to-feed stream ratio of from 6 or greater.
11. The method of claim 10 , wherein the fluidized catalytic cracking catalyst is comprised of at least one of an X-zeolite, a Y-zeolite, a USY-zeolite, mordenite, faujasite, nano-crystalline zeolites, MCM mesoporous materials, microporous silica, a silico-alumino phosphate, a gallophosphate, and a titanophosphate.
12. The method of claim 1 , wherein fourth stream contains 10 ppmw or less of chloride when fed to the steam cracker.
13. The method of claim 1 , wherein the mixed plastic stream comprises at least 1000 ppmw of chloride.
14. The method of claim 1 , wherein at least one of the sixth and ninth streams comprises less than 1 ppmw of chloride.