Separation of mixed xylenes

Patent metadata

Field	Value
Publication number	US-10150083-B2
Application number	US-201615348010-A
Country	US
Kind code	B2
Filing date	Nov 10, 2016
Priority date	Nov 13, 2015
Publication date	Dec 11, 2018
Grant date	Dec 11, 2018

Abstract

Asymmetric membrane structures are provided that are suitable for hydrocarbon reverse osmosis of small hydrocarbons. Separation of para-xylene from ortho- and meta-xylene is an example of a separation that can be performed using hydrocarbon reverse osmosis. Hydrocarbon reverse osmosis separations can be incorporated into a para-xylene isomerization and recovery system in a variety of manners.

First claim

The invention claimed is:

1. A system for xylene isomerization and separation, comprising:
a separation stage based on boiling point separation configured to generate at least a para-xylene enriched fraction;
a xylene recovery unit in fluid communication with the separation stage for receiving the para-xylene enriched fraction from the separation stage, the xylene recovery unit comprising a product outlet and a residual outlet;
a membrane structure in fluid communication with the residual outlet for receiving at least a portion of residual stream; and

a liquid phase isomerization reactor in fluid communication with the membrane structure for receiving a retentate from the membrane structure,
wherein the membrane structure comprises a plurality of membrane layers, a first membrane layer of the membrane structure comprising a pore volume of at least 0.2 cm 3 /g of pores with a median pore size of at least 20 nm, a second membrane layer of the membrane structure comprising a porous carbon layer having a BET surface area of at least about 100 m 2 /g, the second membrane layer having a pore size distribution comprising a smallest substantial pore size peak having a median pore size of about 5.8 Angstroms to about 6.8 Angstroms.

2. The system of claim 1 , wherein the separation stage is further configured to generate a lower boiling fraction, a bottoms fraction, or a combination thereof.

3. The system of claim 1 , wherein the xylene recovery unit comprises a para-xylene crystallizer, a simulated moving bed separator, or a combination thereof.

4. The system of claim 1 , wherein the first membrane layer comprises a porous carbon layer or wherein the first membrane layer comprises a porous metal structure.

5. A system for xylene isomerization and separation, comprising:
a separation stage based on boiling point separation configured to generate at least a para-xylene enriched fraction;
at least one membrane structure for forming a permeate comprising para-xylene and a retentate; and

an isomerization reactor in fluid communication with the membrane structure for receiving the retentate from the membrane structure,
wherein the at least one membrane structure comprises a plurality of membrane layers, a first membrane layer of the membrane structure comprising a pore volume of at least 0.2 cm 3 /g of pores with a median pore size of at least 20 nm, a second membrane layer of the membrane structure comprising a porous carbon layer having a BET surface area of at least about 100 m 2 /g, the second membrane layer having a pore size distribution comprising a smallest substantial pore size peak having a median pore size of about 5.8 Angstroms to about 6.8 Angstroms.

6. The system of claim 5 , wherein the isomerization reactor comprises a liquid phase isomerization reactor.

7. The system of claim 5 , wherein the at least one membrane structure is in fluid communication with the separation stage for receiving the para-xylene enriched stream, the isomerization reactor being in fluid communication with the separation stage for recycle of at least a portion of an isomerized retentate to the separation stage.

8. The system of claim 5 , wherein the at least one membrane structure comprises a first membrane structure and a second membrane structure,
the isomerization reactor being in fluid communication with the separation stage for receiving the para-xylene enriched stream,
the first membrane structure being in fluid communication with the isomerization reactor for receiving at least a portion of an isomerized para-xylene enriched stream to form a first permeate and a first retentate, the first membrane structure being in fluid communication with the separation stage for recycle of at least a portion of the first retentate to the separation stage, and
the second membrane structure being in fluid communication with the first membrane structure for receiving the first permeate to form a second permeate and a second retentate, the second membrane structure being in fluid communication with the isomerization reactor to recycle at least a portion of the second retentate to the isomerization reactor.

9. The system of claim 5 , the system further comprising a xylene recovery unit, the isomerization reactor being in fluid communication with the separation stage for receiving the para-xylene enriched stream,
the at least one membrane structure being in fluid communication with the isomerization reactor for receiving at least a portion of an isomerized para-xylene enriched stream to form a permeate and a retentate, the at least one membrane structure being in fluid communication with the separation stage for recycle of at least a portion of the retentate to the separation stage, and
the xylene recovery unit being in fluid communication with the at least one membrane structure for receiving at least a portion of the permeate, the xylene recovery unit comprising a product outlet and a residual outlet, the isomerization reactor being in fluid communication with the residual outlet.

10. The system of claim 5 , wherein the first membrane layer comprises a porous carbon layer or wherein the first membrane layer comprises a porous metal structure.

Assignees

• Exxonmobil Res & Eng Co

Inventors

• Weiss Brian
• Mccool Benjamin A

Classifications

• B01D61/007

  Separation by stereostructure, steric separation · CPC title

• C02F2103/08

  Seawater, e.g. for desalination · CPC title

• B01D69/08

  Hollow fibre membranes (manufacture of hollow fibres D01D5/24, D01F1/08) · CPC title

• C07C7/144

  using membranes, e.g. selective permeation · CPC title

• C07C7/14

  by crystallisation; Purification or separation of the crystals · CPC title