EB/SM splitter heat recovery
View Patent ↗Improved methods and related apparatus are disclosed for efficiently recovering the heat of condensation from overhead vapor produced during separation of various components of dehydrogenation reaction effluent, particularly in ethylbenzene-to-styrene operations, by the use of at least a compressor to facilitate azeotropic vaporization of an ethylbenzene and water mixture within a preferred range of pressure/temperature conditions so as to minimize undesired polymerization reactions.
1. In a method of manufacturing styrene by dehydrogenation of ethylbenzene in the presence of steam at elevated temperatures in a reactor system containing a dehydrogenation catalyst, the improvement comprising the steps of:
(a) separating the unreacted ethylbenzene from the crude styrene by fractionation in an ethylbenzene-styrene fractionator carried out at an overhead pressure below about 200 mmHg in the presence of a polymerization inhibitor;
(b) condensing the ethylbenzene overhead vapor from the fractionator in an azeotropic vaporizer to provide heat for boiling a reactor feed consisting essentially of an azeotropic mixture of ethylbenzene and water; and,
(c) compressing the vaporized reactor feed, the overhead vapor from the fractionator, or both to obtain an azeotropic mixture of ethylbenzene and water at a suitable pressure for feeding to the reactor system.
2. A method according to claim 1 , further wherein the ethylbenzene-styrene fractionator is operated at an overhead pressure of between about 50-170 mmHg.
3. A method according to claim 1 , further wherein the azeotropic mixture is boiled at a pressure of between about 250-390 mmHg.
4. A method according to claim 1 , further wherein the temperature difference between the condensing overhead vapor and the boiling azeotropic mixture of ethylbenzene and water in the azeotropic vaporizer is between about 15-25° C.
5. A method according to claim 1 , further wherein the fraction of overhead ethylbenzene vapor condensed in the azeotropic vaporizer is between 0.30 and 1.0.
6. A method according to claim 1 , further wherein the water in the azeotropic mixture is derived from process condensate.
7. A method according to claim 1 , further wherein the molar ratio of water to ethylbenzene in the reactor feed is between about 4 and 12.
8. A method according to claim 1 , further wherein the pressure at the inlet to the reactor system is between about 400-1100 mmHg.
9. A method according to claim 1 , further wherein said dehydrogenation catalyst consists essentially of an iron oxide based dehydrogenation catalyst.
10. A method according to claim 1 , further wherein said fractionation is carried out under vacuum.
11. A method according to claim 1 wherein step (c) comprises compressing only the vaporized reactor feed.
12. A method according to claim 1 wherein step (c) comprises compressing only the overhead vapor from the fractionator.
13. A method according to claim 1 wherein step (c) comprises compressing both the vaporized reactor feed and the overhead vapor from the fractionator.
14. In a method of dehydrogenation of an alkylaromatic compound in the presence of steam at elevated temperatures in a reactor system containing a dehydrogenation catalyst, the improvement comprising the steps of:
(a) separating unreacted alkylaromatic compound from the crude product by fractionation in a fractionator carried out at an overhead pressure below 200 mmHg in the presence of a polymerization inhibitor;
(b) condensing the overhead vapor from the fractionator to provide heat for boiling a reactor feed consisting essentially of an azeotropic mixture of the alkylaromatic compound and water; and,
(c) compressing the vaporized reactor feed, the overhead vapor from the fractionator, or
both to obtain an azeotropic mixture of the alkylaromatic compound and water at a suitable pressure for feeding to the reactor system.