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Disclosed herein is an improved method for making and obtaining para-xylene from a mixture of xylene isomers, and various embodiments of the method. The method generally includes contacting a mixture comprising xylene isomers and ethylbenzene with a para-xylene selective adsorbent to obtain a para-x

Disclosed herein is an improved method for making and obtaining para-xylene from a mixture of xylene isomers, and various embodiments of the method. The method generally includes contacting a mixture comprising xylene isomers and ethylbenzene with a para-xylene selective adsorbent to obtain a para-xylene depleted raffinate, and a desorption effluent comprising a para-xylene enriched product. The method also includes isomerizing the para-xylene depleted raffinate. The contacting step is carried out in a manner such that the raffinate need not be pressurized prior to isomerization, thus advantageously obviating expensive compression steps.

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What is claimed is: 1. A method comprising the steps of: (a) contacting at a substantially non-decreasing total pressure (i) a gaseous mixture comprising xylene isomers, ethylbenzene, and a non-adsorbable gas, with (ii) a para-xylene selective adsorbent comprising a medium pore zeolite to obtain a

What is claimed is: 1. A method comprising the steps of: (a) contacting at a substantially non-decreasing total pressure (i) a gaseous mixture comprising xylene isomers, ethylbenzene, and a non-adsorbable gas, with (ii) a para-xylene selective adsorbent comprising a medium pore zeolite to obtain a para-xylene depleted raffinate and a desorption effluent comprising a para-xylene enriched product, wherein the non-adsorbable gas comprises hydrogen and is non-reactive with the xylene isomers and ethylbenzene during the contacting step; and, (b) isomerizing at least a portion of the para-xylene depleted raffinate. 2. The method of claim 1, wherein step (b) further comprises isomerizing the para-xylene depleted raffinate at a pressure that is equal to or less than the substantially non-decreasing total pressure. 3. The method of claim 2, wherein step (b) further comprises isomerizing the para-xylene depleted raffinate at a pressure that is less than the substantially non-decreasing total pressure. 4. The method of claim 1, wherein the sum of the partial pressures of the xylene isomers and ethylbenzene is less than the substantially non-decreasing total pressure. 5. The method of claim 4, wherein the sum is about 15% to about 99.5% of the substantially non-decreasing total pressure. 6. The method of claim 1, wherein the para-xylene depleted raffinate comprises hydrocarbons substantially free of para-xylene, and the gas is present in an amount sufficient to provide a gas-to-hydrocarbon mole ratio in the para-xylene depleted raffinate of about 0.1:1 to about 10:1. 7. The method of claim 1, wherein the gas is present in an amount sufficient to ensure that the substantially non-decreasing total pressure is equal to or greater than an isomerization step pressure, while maintaining the partial pressure of the xylene isomers and ethylbenzene at or below the respective condensation pressures of the xylene isomers and ethylbenzene. 8. The method of claim 7, wherein the gas is present in an amount sufficient to avoid condensation of the xylene isomers. 9. The method of claim 1, wherein the gas further comprises one or more materials selected from the group consisting of argon, carbon dioxide, helium, nitrogen, methane, ethane, propane, and butane. 10. The method of claim 1, wherein the para-xylene depleted raffinate comprises meta-xylene, ortho-xylene, and hydrogen. 11. The method of claim 1, wherein step (b) further comprises isomerizing the para-xylene depleted raffinate to obtain a hydrocarbon mixture comprising equilibrated xylene isomers. 12. The method of claim 11, further comprising combining at least a portion of the xylene isomers obtained in step (b) with the mixture in step (a). 13. The method of claim 1, further comprising separating substantially pure para-xylene from the desorption effluent. 14. The method of claim 13, further comprising separating substantially pure para-xylene from the desorption effluent at a pressure that is equal to or less than the substantially non-decreasing total pressure. 15. The method of claim 14, further comprising separating substantially pure para-xylene from the desorption effluent at a pressure that is less than the substantially non-decreasing total pressure. 16. A method comprising the steps or: (a) contacting at a first pressure (i) a mixture comprising xylene isomers, ethylbenzene, and a non-adsorbable gas, with (ii) a para-xylene selective adsorbent comprising a medium pore zeolite to obtain a para-xylene depleted raffinate and a desorption effluent comprising a para-xylene enriched product, wherein the non-adsorbable gas comprises hydrogen and is non-reactive with the xylene isomers and ethylbenzene during the contacting step; and, (b) isomerizing at a second pressure at least a portion of the para-xylene depleted raffinate, wherein the gas is present in an amount sufficient to ensure the first pressure is equal to or greater than the second pressure. 17. The method of claim 16, wherein the mixture in the contacting step (a) is a gaseous mixture. 18. The method of claim 16, wherein the first pressure is greater than the second pressure. 19. The method of claim 16, wherein the sum of the partial pressures of the xylene isomers and ethylbenzene is less than the first pressure. 20. The method of claim 19, wherein the sum is about 15% to about 99.5% of the first pressure. 21. The method of claim 16, wherein the para-xylene depleted raffinate comprises hydrocarbons substantially free of para-xylene, and the gas is present in an amount sufficient to provide a gas-to-hydrocarbon mole ratio in the para-xylene depleted raffinate of about 0.1:1 to about 10:1. 22. The method of claim 16, wherein the gas is present in an amount sufficient to maintain the partial pressure of the xylene isomers and ethylbenzene at or below the respective condensation pressures of the xylene isomers and ethylbenzene. 23. The method of claim 16, wherein the gas is present in an amount sufficient to avoid condensation of the xylene isomers. 24. The method of claim 16, wherein the gas further comprises one or more materials selected from the group consisting of argon, carbon dioxide, helium, nitrogen, methane, ethane, propane, and butane. 25. The method of claim 16, wherein the para-xylene depleted raffinate comprises meta-xylene, ortho-xylene, and hydrogen. 26. The method of claim 16, wherein step (b) further comprises isomerizing the para-xylene depleted raffinate to obtain a hydrocarbon mixture comprising equilibrated xylene isomers. 27. The method of claim 26, further comprising combining at least a portion of the xylene isomers obtained in step (b) with the mixture in step (a). 28. The method of claim 16, wherein the first pressure is a substantially non-decreasing pressure. 29. The method of claim 28, further comprising separating substantially pure para-xylene from the desorption effluent. 30. The method of claim 28, further comprising separating substantially pure para-xylene from the desorption effluent at a pressure that is equal to or less than the first pressure. 31. The method of claim 30, further comprising separating substantially pure para-xylene from the desorption effluent at a pressure that is less than the first pressure. 32. A method comprising the steps of: (a) contacting a mixture comprising xylene isomers, ethylbenzene, and a non-adsorbable, non-reactive gas with a para-xylene selective adsorbent to obtain a para-xylene depleted raffinate and a desorption effluent comprising a para-xylene enriched product; and, (b) isomerizing at least an unfractionated portion of the para-xylene depleted raffinate, wherein the gas is present in an amount sufficient to ensure a raffinate pressure equal to or greater than an isomerization step pressure, while maintaining the partial pressure of the xylene isomers and ethylbenzene at or below the respective condensation pressures of the xylene isomers and ethylbenzene. 33. The method of claim 32, wherein the mixture in the contacting step (a) is a gaseous mixture. 34. The method of claim 32, wherein the gas is present in an amount sufficient to ensure a raffinate pressure greater than the isomerization step pressure. 35. The method of claim 32, wherein the gas is present in an amount sufficient to avoid condensation of the xylene isomers. 36. The method of claim 32, wherein the gas comprises one or more materials selected from the group consisting of hydrogen, nitrogen, and light paraffins. 37. The method of claim 36, wherein the gas comprises hydrogen. 38. The method of claim 37, wherein the para-xylene depleted raffinate comprises meta-xylene, ortho-xylene, and hydrogen. 39. The method of claim 32, wherein step (b) further comprises isomerizing the para-xylene depleted raffinate to obtain a hydrocarbon mixture comprising equilibrated xylene isomers. 40. The method of claim 39, further comprising combining at least a portion of the xylene isomers obtained in step (b) with the mixture in step (a). 41. The method of claim 32, wherein the contacting step (a) is carried out at a substantially non-decreasing total pressure. 42. The method of claim 41, further comprising separating substantially pure para-xylene from the desorption effluent. 43. The method of claim 42, further comprising separating substantially pure para-xylene from the desorption effluent at a pressure that is equal to or less than the substantially non-decreasing total pressure. 44. The method of claim 43, further comprising separating substantially pure para-xylene from the desorption effluent at a pressure that is less than the substantially non-decreasing total pressure. 45. A method comprising the steps of: (a) contacting (i) a gaseous mixture comprising xylene isomers, ethylbenzene, and a non-adsorbable gas with (II) a para-xylene selective adsorbent comprising a medium pore zeolite to obtain a para-xylene depleted raffinate and a desorption effluent comprising a para-xylene enriched product, wherein the non-adsorbable gas comprises hydrogen and is non-reactive with the xylene isomers and ethylbenzene during the contacting step; and, (b) isomerizing at least a portion of the para-xylene depleted raffinate, wherein the sum of the partial pressures of the xylene isomers and ethylbenzene is less than the total pressure of the mixture and the gas is present in an amount sufficient to ensure that the total pressure is equal to or greater than the pressure of the isomerizing step. 46. The method of claim 45, wherein the sum is about 15% to about 99.5% of the total pressure. 47. The method of claim 45, wherein the total pressure is substantially non-decreasing. 48. The method of claim 45, wherein step (b) further comprises isomerizing the para-xylene depleted raffinate at a pressure that is equal to or less than the total pressure. 49. The method of claim 48, wherein step (b) further comprises isomerizing the para-xylene depleted raffinate at a pressure that is less than the total pressure. 50. The method of claim 45, wherein the gas is present in an amount sufficient to ensure that the total pressure is equal to or greater than an isomerization step pressure, while maintaining the partial pressure of the xylene isomers and ethylbenzene at or below the respective condensation pressures of the xylene isomers and ethylbenzene. 51. The method or claim 50, wherein the gas as present in an amount sufficient to avoid condensation of the xylene isomers. 52. The method of claim 45, wherein the gas further comprises one or more materials selected from the group consisting of argon, carbon dioxide, helium, nitrogen, methane, ethane, propane, and butane. 53. The method of claim 45, wherein the para-xylene depleted raffinate comprises meta-xylene, ortho-xylene, and hydrogen. 54. The method of claim 45, wherein step (b) further comprises isomerizing the para-xylene depleted raffinate to obtain a hydrocarbon mixture comprising equilibrated xylene isomers. 55. The method of claim 54, further comprising combining at least a portion of the xylene isomers obtained in step (b) with the mixture in step (a). 56. The method of claim 45, further comprising separating substantially pure para-xylene from the desorption effluent. 57. The method of claim 56, further comprising separating substantially pure para-xylene from the desorption effluent at a pressure that is equal to or less than the total pressure. 58. The method of claim 57, further comprising separating substantially pure para-xylene from the desorption effluent at a pressure that is less than the total pressure. 59. A method comprising the steps of: (a) contacting a xylene isomers mixture and a non-adsorbable gas with a para-xylene selective adsorbent to obtain a para-xylene depleted raffinate comprising hydrocarbons substantially free of para-xylene and a desorption effluent comprising a para-xylene enriched product; and, (b) isomerizing at least a portion of the para-xylene depleted raffinate, wherein the gas comprises hydrogen and is non-reactive with the mixture during the contacting step (a), and the gas is present in an amount sufficient to provide a gas-to-hydrocarbon mole ratio in the para-xylene depleted raffinate of about 0.1:1 to about 1:1 and sufficient to ensure a raffinate pressure equal to or greater than the pressure of the isomerizing step. 60. The method of claim 59, wherein the mixture in the contacting step (a) is a gaseous mixture. 61. The method of claim 59, wherein the contacting step (a) is carried out at a substantially non-decreasing pressure. 62. The method of claim 61, further comprising separating substantially pure para-xylene from the desorption effluent. 63. The method of claim 62, further comprising separating substantially pure para-xylene from the desorption effluent at a pressure that is equal to or less than the substantially non-decreasing pressure. 64. The method of claim 63, further comprising separating substantially pure para-xylene from the desorption effluent at a pressure that is less than the substantially non-decreasing pressure. 65. The method of claim 59, wherein the gas is present in an amount sufficient to ensure a raffinate pressure equal to or greater than an isomerization step pressure, while maintaining the partial pressure of the xylene isomers and ethylbenzene at or below the respective condensation pressures of the xylene isomers and ethylbenzene. 66. The method of claim 65, wherein the gas is present in an amount sufficient to avoid condensation of the xylene isomers. 67. The method of claim 59, wherein the gas further comprises one or more materials selected from the group consisting of argon, carbon dioxide, helium, nitrogen, methane, ethane, propane, and butane. 68. The method of claim 59, wherein the para-xylene depleted raffinate comprises meta-xylene, ortho-xylene, and hydrogen. 69. The method of claim 59, wherein step (b) further comprises isomerizing the para-xylene depleted raffinate to obtain a hydrocarbon mixture comprising equilibrated xylene isomers. 70. The method of claim 69, further comprising combining at least a portion of the xylene isomers obtained in step (b) with the mixture in step (a).