Propylene production
View Patent ↗A process for producing propylene from ethylene and a feed stream comprising 1-butene, 2-butene, n-butane, and isobutane is disclosed. A butenes stream (1-butene and 2-butene) is produced from the feed stream by removing the paraffins. The butenes stream is reacted in the presence of an isomerization catalyst to produce an isomerized stream with increased concentration of 2-butene. The isomerized stream is reacted with ethylene in the presence of a metathesis catalyst to produce a reaction mixture comprising propylene; the propylene may be isolated from the reaction mixture by distillation. The removal of paraffins from the feed stream improves the catalyst productivity and the plant throughput.
1. A process for producing propylene comprising:
(a) separating a feed stream comprising 1-butene, 2-butene, n-butane, and isobutane into a paraffins stream and a butenes stream;
(b) reacting the butenes stream in the presence of an isomerization catalyst to produce an isomerized stream with increased concentration of 2-butene and having less than 5 wt. % butanes;
(c) reacting the isomerized stream having less than 5 wt. % butanes and ethylene in the presence of a metathesis catalyst to produce a reaction mixture comprising propylene,
(d) distilling the reaction mixture to separate an ethylene stream, a propylene stream, and a bottoms stream comprising 1-butene, 2-butenes, and C5 and higher olefins;
(e) distilling the bottoms stream to produce a light stream comprising 1-butene and 2-butenes and a heavy stream comprising C5 and higher olefins; and
(f) recycling at least a portion of the light stream to step (b),
wherein the butenes stream comprises butanes in an amount of less than 5 wt. %.
2. The process of claim 1 wherein step (a) is carried out by extractive distillation with a solvent.
3. The process of claim 2 wherein the solvent is selected from the group consisting of acetonitrile, methyl formamide, dimethyl formamide, N-methyl pyrrolidone, N-formyl morpholine, and mixtures thereof.
4. The process of claim 1 wherein 1-butene and 2-butene constitute at least 95 wt. % of the butenes stream.
5. The process of claim 1 wherein 1-butene and 2-butene constitute at least 99 wt. % of the butenes stream.
6. The process of claim 1 wherein the isomerization catalyst is an acidic ion-exchange resin.
7. The process of claim 1 wherein the isomerization catalyst is a basic catalyst.
8. The process of claim 1 wherein the isomerization catalyst comprises magnesium oxide.
9. The process of claim 1 wherein the isomerization catalyst is a hydroisomerization catalyst.
10. The process of claim 9 wherein the hydroisomerization catalyst comprises Pd and alumina.
11. The process of claim 1 wherein the metathesis catalyst comprises a transition metal oxide comprising an element selected from the group consisting of cobalt, molybdenum, rhenium, tungsten, and mixtures thereof.
12. The process of claim 1 wherein the metathesis catalyst comprises tungsten oxide and silica.
13. The process of claim 1 wherein steps (b) and (c) are conducted in the same reactor.
14. The process of claim 13 wherein the reactor contains a mixture of a tungsten oxide-on-silica and magnesium oxide.
15. The process of claim 14 wherein steps (b) and (c) are conducted at a temperature in the range of 500 to 850° F.
16. The process of claim 14 wherein steps (b) and (c) are conducted at a pressure in the range of 300 to 800 psig.
17. The process of claim 14 wherein steps (b) and (c) are conducted in a down-flow fixed-bed reactor.
18. The process of claim 1 wherein the isomerized stream and ethylene are treated in an adsorption bed prior to step (c).
19. The process of claim 18 wherein the adsorption bed is an alumina bed.
20. The process of claim 1 wherein the amount of butanes in the butenes stream is less than 1 wt. %.