Energy conservation in heavy-hydrocarbon distillation

• US 8,609,922 B2
• Filed: 08/25/2010
• Issued: 12/17/2013
• Est. Priority Date: 08/25/2010
• Status: Active Grant

• Current Assignee: UOP Llc (Honeywell International Inc.)
• Original Assignee: UOP Llc (Honeywell International Inc.)
• Inventors: Werba, Gregory R., Zhu, Xin X., Daly, Phillip F., Ulas Acikgoz, Saadet, Corradi, Jason T., Ablin, David W.
• Primary Examiner(s): Manoharan, Virginia
• Application Number:
  US12/868,286
• Publication Number:
  US 20120048720A1
• Time in Patent Office: 1,210 Days
• Field of Search: 203/25, 203/27, 203/75, 203/77, 203/78, 203/80, 203/82, 203/84, 203/DIG.8, 585/478, 585/805, 585/910, 585/822, 585/828
• US Class Current: 585/478
• CPC Class Codes: B01D 3/007 Energy recuperation; Heat pumps
• CPC Class Codes: B01D 3/148 in combination with at least one evaporator
• CPC Class Codes: C07C 15/073 Ethylbenzene
• CPC Class Codes: C07C 15/08 Xylenes
• CPC Class Codes: C07C 7/04 by distillation
• CPC Class Codes: C07C 7/12 by adsorption, i.e. purification or separation of hydrocarbons with the aid of solids, e.g. with ion-exchangers
• CPC Class Codes: Y02P 20/10 Process efficiency

Abstract

An aromatics complex producing one or more xylene isomers offers a large number of opportunities to conserve energy by heat exchange within the complex. One previously unrecognized opportunity is through providing two parallel distillation columns operating at different pressures to separate C₈ aromatics from C₉+ aromatics. The parallel columns offer additional opportunities to conserve energy within the complex through heat exchange in associated xylene recovery facilities.

Claims

1. A process for producing para-xylene from feed streams containing C8 aromatics and C9-and-heavier aromatics, comprising:

(a) a distillation process comprising two xylene columns separating C8 aromatics from C9-and-heavier aromatics contained in at least one lower-boiling and at least one higher-boiling feed stream, wherein the at least one higher-boiling feed stream has a higher content of C9-and heavier aromatics than the at least one lower-boiling feed stream, comprising distilling the at least one higher-boiling feed stream in a first xylene column having a reboiler at a low pressure to separate a first C8-aromatics stream from a first C9-and-heavier aromatics stream, distilling the at least one lower-boiling feed stream in a second xylene column at an elevated pressure above the low pressure to separate a second C8-aromatics stream from a second C9-and-heavier aromatics stream, wherein an overhead stream from the second column exchanges heat with the reboiler of the first column;

(b) a para-xylene separation process to recover para-xylene from one or both of the first and second C8-aromatics streams by injecting the one or both C8-aromatics streams and a desorbent stream into a moving-bed adsorption process to obtain a first mixture of para-xylene and desorbent and a second mixture of a raffinate and desorbent; and

,

(c) a desorbent-recovery process to separate the second mixture of step (b) by distillation in a prefractionator followed by a pressurized raffinate column into the raffinate and a desorbent stream returned to the separation process, wherein the overhead stream of the second xylene column of step (a) further provides heat to a reboiler of the raffinate column.

2. The process of claim 1 wherein the low pressure is between 100 and 800 kPa and the elevated pressure is at least about 400 kPa higher than the low pressure.

3. The process of claim 1 wherein the reboiler of the second column has an enhanced nucleate boiling surface.

4. The process of claim 1 wherein the at least one lower-boiling feed stream comprises part or all of a bottoms stream from deheptanization of a C8-aromatics isomerization product.

5. The process of claim 1 wherein overhead from the raffinate column exchanges heat with a medium-pressure steam generator to generate steam.

6. A process for producing para-xylene from feed streams containing C8 aromatics and C9-and-heavier aromatics, comprising:

(a) a distillation process comprising two xylene columns separating C8 aromatics from C9-and-heavier aromatics contained in at least one lower-boiling and at least one higher-boiling feed stream, wherein the at least one higher-boiling feed stream has a higher content of C9-and heavier aromatics than the at least one lower-boiling feed stream, comprising distilling the at least one higher-boiling feed stream in a first xylene column having a reboiler at a low pressure to separate a first C8-aromatics stream from a first C9-and-heavier aromatics stream, distilling the at least one lower-boiling feed stream in a second xylene column having a reboiler at an elevated pressure above the low pressure to separate a second C8-aromatics stream from a second C9-and heavier aromatics stream, wherein an overhead stream from the second column exchanges heat with the reboiler of the first column;

(b) a para-xylene separation process to recover para-xylene from one or both of the first and second C8-aromatics streams by injecting the one or both C8-aromatics streams and a desorbent stream into a moving-bed adsorption process to obtain a first mixture of para-xylene and desorbent and a second mixture of a raffinate and desorbent; and

,

(c) a desorbent-recovery process which separates the second mixture of step (b) by distillation in a pressurized raffinate column into the raffinate and a desorbent stream returned to the separation process, wherein a reboiler effluent of the second xylene column is separated into a vapor and a liquid stream and the vapor stream provides heat to a reboiler of the raffinate column.

7. The process of claim 6 wherein the reboiler of the raffinate column of step (c) has an enhanced nucleate boiling surface.

8. The process of claim 6 wherein overhead from the raffinate column exchanges heat with a medium-pressure steam generator to generate steam.

9. A process for producing para-xylene from feed streams containing C8 aromatics and C9-and-heavier aromatics, comprising:

(a) a distillation process comprising two xylene columns separating C8 aromatics from C9-and-heavier aromatics contained in at least one lower-boiling and at least one higher-boiling feed stream, wherein the at least one higher-boiling feed stream has a higher content of C9-and heavier aromatics than the at least one lower-boiling feed stream, comprising distilling the at least one higher-boiling feed stream in a first xylene column having a reboiler at a low pressure to separate a first C8-aromatics stream from a first C9-and-heavier aromatics stream, distilling the at least one lower-boiling feed stream in a second xylene column having a reboiler at an elevated pressure above the low pressure to separate a second C8-aromatics stream from a second C9-and heavier aromatics stream, wherein an overhead stream from the second column exchanges heat with the reboiler of the first column;

(b) a para-xylene separation process to recover para-xylene from one or both of the first and second C8-aromatics streams by injecting the one or both C8-aromatics streams and a desorbent stream into a moving-bed adsorption process to obtain a first mixture of para-xylene and desorbent and a second mixture of a raffinate and desorbent; and

,

(c) a desorbent-recovery process which separates the second mixture of step (b) by distillation in a prefractionator followed by a pressurized raffinate column into the raffinate and a desorbent stream returned to the separation process, wherein an overhead stream from the raffinate column provides heat to a reboiler of the prefractionator.

10. The process of claim 9 wherein the prefractionator reboiler has an enhanced nucleate boiling surface.