METHOD FOR SEPARATING MIXED XYLENE

Abstract

A method for separating mixed xylene includes steps that the mixed xylene is subjected to adsorption separation by means of an adsorbent having a metal organic framework material, so that one or more of xylene isomers are separated out. An organic ligand in the metal organic framework material is 2,5-dihydroxy-1,4-benzoquinone. Xylene isomers can be effectively separated using this method.

Claims

1-10. (canceled)

11. A method for separating mixed xylenes, comprising subjecting the mixed xylenes to adsorptive separation by an adsorbent containing a metal-organic framework material to separate out xylene isomers; wherein the metal-organic framework material comprises metal ions and an organic ligand, wherein the organic ligand comprises 2,5-dihydroxy-1,4-benzoquinone.

12. The method according to claim 11, wherein the metal ions are selected from transition metal ions and alkaline earth metal ions; the mixed xylenes are in gaseous state or liquid state, and comprise two or more of ethylbenzene, ortho-xylene, meta-xylene, and para-xylene; and the xylene isomers are one or more selected from ortho-xylene, meta-xylene, and para-xylene.

13. The method according to claim 11, wherein the metal ions comprise one or more selected from the group consisting of zinc ions, manganese ions, cobalt ions, magnesium ions, vanadium ions, zirconium ions, calcium ions, molybdenum ions, chromium ions, iron ions, nickel ions, copper ions, tin ions, niobium ions, titanium ions, and scandium ions.

14. The method according to claim 11, wherein the metal-organic framework material has a pore size of 4 Å or more, and has a specific surface area of 300 m.sup.2/g-2000 m.sup.2/g.

15. The method according to claim 14, wherein the metal-organic framework material has a pore size of 4 Å-15 Å.

16. The method according to claim 14, wherein the metal-organic framework material has a pore size of 4 Å-10 Å.

17. The method according to claim 11, wherein the adsorptive separation is performed at a temperature of -5° C.-300° C.

18. The method according to claim 11, wherein the adsorptive separation is performed at a temperature of 25° C.-250° C.

19. The method according to claim 11, wherein the adsorptive separation is performed at a temperature of 30° C.-150° C.

20. The method according to claim 11, wherein the adsorptive separation is performed at a pressure of 0.01 MPa-10 MPa.

21. The method according to claim 11, wherein the adsorptive separation is performed at a pressure of 0.1 MPa-6 MPa.

22. The method according to claim 11, wherein the adsorptive separation is performed using a fixed bed, the adsorbent being packed in an adsorption column of the fixed bed.

23. The method according to claim 22, wherein the adsorptive separation comprises the following steps: (1) passing a mixed xylenes vapor formed by the mixed xylenes and a carrier gas through the adsorption column of the fixed bed, so that a strongly adsorbed xylene isomer in the mixed xylenes is adsorbed on the adsorbent and a weakly adsorbed xylene isomer in the mixed xylenes passes through the adsorption column, thereby obtaining the weakly adsorbed xylene isomer; and (2) desorbing the strongly adsorbed xylene isomer from the adsorbent to obtain the strongly adsorbed xylene isomer.

24. The method according to claim 11, wherein the adsorptive separation is performed using a simulated moving bed, the adsorbent being packed in adsorption zone beds of the simulated moving bed.

25. The method according to claim 24, wherein the adsorptive separation comprises the following step: (3) passing the mixed xylenes in liquid state through the liquid phase simulated moving bed for adsorptive separation, so as to withdraw para-xylene, ortho-xylene, and/or meta-xylene from different beds.

26. The method according to claim 23, wherein the mixed xylenes vapor is passed through the adsorption column of the fixed bed at a flow rate of 40-200 mL/min/g adsorbent; and the simulated moving bed has 4-32 adsorbent beds and the ratio of the adsorption zone beds to the desorption zone beds is 1.0-1.5.

27. The method according to claim 11, further comprising regenerating the adsorbent after the adsorptive separation is completed, wherein the regenerating comprises heating the adsorbent to a temperature of 50° C.-300° C. under vacuum or inert atmosphere and keeping the adsorbent at the temperature for 20-120 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] FIG. 1 is an XRD pattern of a metal-organic framework material prepared in Example 1.

[0054] FIG. 2 is a schematic view of a simulated moving bed used in Example 2.

[0055] FIG. 3 is an XRD pattern of a metal-organic framework material prepared in Example 2.

[0056] FIG. 4 is an XRD pattern of a metal-organic framework material prepared in Example 3.

[0057] FIG. 5 is an XRD pattern of a metal-organic framework material prepared in Example 4.

[0058] FIG. 6 shows isotherms of adsorption of xylenes on the metal-organic framework material prepared in Example 1 at 30° C.

[0059] FIG. 7 shows isotherms of adsorption of xylenes on the metal-organic framework material prepared in Example 2 at 60° C.

[0060] FIG. 8 shows isotherms of adsorption of xylenes on the metal-organic framework material prepared in Example 2 at 120° C.

[0061] FIG. 9 shows breakthrough curves of ortho-xylene/meta-xylene through the metal-organic framework material prepared in Example 2 at 30° C.

[0062] FIG. 10 shows breakthrough curves of meta-xylene/para-xylene through the metal-organic framework material prepared in Example 2 at 90° C.

[0063] FIG. 11 shows isotherms of adsorption of CO.sub.2 on metal-organic framework materials prepared in Examples 1-4 and Comparative Examples 1-2 at 0° C.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0064] The present invention is further described by way of the following embodiments. The present invention however is not limited to these embodiments.

Example 1

[0065] 300 mmol of zinc acetate dihydrate, 300 mmol of 2,5-dihydroxy-1,4-benzoquinone, and 1000 mL of deionized water were mixed and then reacted under stirring at room temperature for 12-48 hours. After the reaction was completed, the resulting solid product was centrifugally washed multiple times with deionized water until the supernatant was clear to obtain a purified metal-organic framework material. Measurement and analysis of isotherms of N.sub.2 adsorption-desorption on the purified metal-organic framework material at 77 K resulted in a specific surface area of 441.7 m.sup.2/g and an average pore size of 5.47-5.51 Å. The purified metal-organic framework material was vacuum activated at 150° C. for 12 hours to give a solvent-removed adsorbent. Vapor-phase adsorption of xylene isomers was then tested.

[0066] In order to test the adsorptive separation performance of the metal-organic framework material synthesized above, isotherms of adsorption of single-component para-xylene, single-component ortho-xylene, and single-component meta-xylene on the above adsorbent were measured. The adsorption was conducted with an appropriate amount of the adsorbent at temperatures of 30° C., 60° C., 90° C., and 120° C., respectively. The test showed that at 30° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of up to 200 mg/g, ortho-xylene was adsorbed by an amount of only 78 mg/g, and meta-xylene was adsorbed by an amount of only 51 mg/g. Isotherms of adsorption are shown in FIG. 5. At 60° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of 165 mg/g, ortho-xylene was adsorbed by an amount of 25 mg/g, and meta-xylene was adsorbed by an amount of 30 mg/g. At 90° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of 66 mg/g, ortho-xylene was adsorbed by an amount of 17 mg/g, and meta-xylene was adsorbed by an amount of 18 mg/g. At 120° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of 19 mg/g, ortho-xylene was adsorbed by an amount of 22 mg/g, and meta-xylene was adsorbed by an amount of 25 mg/g.

[0067] A specific method of separating mixed xylenes with the above synthesized metal-organic framework material is as follows.

[0068] The synthesized adsorbent was first molded. An amount of a binder needed in the molding accounted for 3%-10% of a mass of the adsorbent. Breakthrough experiments on a mixed xylenes vapor were conducted using the molded adsorbent. The mixed vapor for adsorptive separation in this example was a mixed vapor of three or two of para-xylene, meta-xylene, and ortho-xylene, with a ratio of saturation vapor pressures of the single-component xylenes being 1: 1: 1 or 1: 1, and a total pressure of the mixed vapor being 0.1 MPa. A packed column had a size of 10 mm I.D. × 50 mm, and was packed with about 2.2 g of the molded adsorbent. The test showed that, when the adsorbent was at a temperature of 30° C. and with a saturation vapor pressure ratio of ortho-xylene to meta-xylene to para-xylene was 1: 1: 1, ortho-xylene and meta-xylene began to pass through the column at 8 minutes, while para-xylene was retained in the packed column for about 120 minutes before beginning to pass through the column. Such a large difference in retention time indicates that the mixed xylenes were effectively separated. After five cycles of adsorption-regeneration, the metal-organic framework material was still stable in its adsorption performance. Conditions for the regeneration were to heat the adsorbent to 150° C. under vacuum or inert atmosphere and keep the adsorbent at the temperature for 72 hours.

Example 2

[0069] 600 mmol of manganese acetate tetrahydrate, 600 mmol of 2,5-dihydroxy-1,4-benzoquinone, and 2000 mL of deionized water were mixed and then reacted under stirring at room temperature for 24-48 hours. After the reaction was completed, the resulting solid was centrifugally washed multiple times with deionized water to obtain a purified metal-organic framework material. Measurement and analysis of isotherms of N.sub.2 adsorption-desorption on the purified metal-organic framework material at 77 K resulted in a specific surface area of 428.9 m.sup.2/g and an average pore size of 5.48-5.63 Å. The purified metal-organic framework material was vacuum degassed at 150° C. for 12 hours to give a solvent-removed adsorbent. Vapor-phase adsorption test was then conducted.

[0070] In order to test the adsorptive separation performance of the metal-organic framework material synthesized above, isotherms of adsorption of single-component para-xylene, single-component ortho-xylene, and single-component meta-xylene on the metal-organic framework material as an adsorbent were measured. The adsorption was conducted with an appropriate amount of the adsorbent at temperatures of 30° C., 60° C., 90° C., and 120° C., respectively. The test showed that at 30° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of up to 208 mg/g, ortho-xylene was adsorbed by an amount of 170 mg/g, and meta-xylene was adsorbed by an amount of 204 mg/g. At 60° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of up to 185 mg/g, ortho-xylene was adsorbed by an amount of only 23 mg/g, and meta-xylene was adsorbed by an amount of 159 mg/g. At 90° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of up to 160 mg/g, ortho-xylene was adsorbed by an amount of only 22 mg/g, and meta-xylene was adsorbed by an amount of 69 mg/g. At 120° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of up to 141 mg/g, ortho-xylene was adsorbed by an amount of only 23 mg/g, and meta-xylene was adsorbed by an amount of only 17 mg/g. Isotherms of adsorption are shown in FIGS. 6 and 7.

[0071] A specific method of separating mixed xylenes with the above synthesized metal-organic framework material is as follows.

[0072] The synthesized adsorbent was first molded. An amount of a binder needed in the molding accounted for 3%-10% of a mass of the adsorbent. Breakthrough experiments on a mixed xylenes vapor were conducted using the molded adsorbent. The mixed vapor for adsorptive separation in this example was a mixed vapor of three or two of para-xylene, meta-xylene, and ortho-xylene, with a ratio of saturation vapor pressures of the single-component xylenes being 1: 1: 1 or 1: 1, and a total pressure of the mixed vapor being 0.1 MPa. A packed column had a size of 10 mm I.D. × 50 mm, and was packed with about 2.3 g of the molded adsorbent. Breakthrough curves are shown in FIGS. 8 and 9. The test showed that, when the adsorbent was at a temperature of 30° C. and with a saturation vapor pressure ratio of ortho-xylene to meta-xylene being 50: 50, ortho-xylene began to pass through the column at 45 minutes, while meta-xylene began to pass through the column at 275 minutes. Such a large difference in retention time indicates that the two xylene isomers were effectively separated. In addition, when the adsorbent was at a temperature of 90° C. and with a saturation vapor pressure ratio of meta-xylene to para-xylene being 50: 50, meta-xylene began to pass through the column at 25 minutes, while para-xylene began to pass through the column at 315 minutes. Such a large difference in retention time indicates that meta-xylene and para-xylene were effectively separated under such conditions. After five cycles of adsorption-regeneration, the metal-organic framework material was still stable in its adsorption performance. Conditions for the regeneration were to heat the adsorbent to 150° C. under vacuum or inert atmosphere and keep the adsorbent at the temperature for 72 hours.

[0073] Adsorptive separation was performed on a continuous counter-current small-scale simulated moving bed using the adsorbent described above.

[0074] The small-scale simulated moving bed unit comprised twelve adsorption columns connected in series. Each column had a length of 150 mm and an inner diameter of 10 mm. A total of 140 mL of the adsorbent was loaded. A circulation pump was connected between two ends of the twelve serially connected columns so that a closed loop was formed, as shown in FIG. 2. In FIG. 2, four incoming and outgoing materials, namely an adsorption feedstock, a desorbent, an extract, and a raffinate, divide the twelve adsorption columns into four sections. That is, the three adsorption columns between the adsorption feedstock (column 8) and the raffinate (column 10) form an adsorption zone; the four adsorption columns between the extract (column 4) and the adsorption feedstock (column 7) form a purification zone; the three adsorption columns between the desorbent (column 1) and the extract (column 3) form a desorption zone; and the two adsorption columns between the raffinate (column 11) and the desorbent (column 12) form a buffer zone. The entire adsorption system was controlled to have a temperature of 150° C. and a pressure of 0.5 MPa.

[0075] During operation, p-diethyl benzene as the desorbent as well as the adsorption feedstock were continuously injected into the simulated moving bed unit at flow rates of 130 mL/h and 100 mL/h, respectively; the extract was withdrawn from the unit at a flow rate of 80 mL/h; and the raffinate was withdrawn from the unit at a flow rate of 150 mL/h. The adsorbent feedstock comprised 10 wt% of ethylbenzene, 20 wt% of para-xylene, 50 wt% of meta-xylene, and 20 wt% of ortho-xylene. The circulation pump was set to have a flow rate of 270 mL/h. According to the principle of simulated counter-current chromatography, a position of each of the four materials was shifted forward by one adsorption column every 70 seconds following a liquid flow direction. In the case of a stable operating state, the resulting para-xylene had a purity of 99.75-99.9 wt%, and a recovery rate of para-xylene was 98.0-99.0 wt%.

Example 3

[0076] 30 mmol of cobalt chloride hexahydrate, 30 mmol of 2,5-dihydroxy-1,4-benzoquinone, and 200 mL of deionized water were mixed and then reacted under stirring at room temperature for 12-24 hours. After the reaction was completed, the resulting solid was centrifugally washed multiple times with deionized water to obtain a purified metal-organic framework material. Measurement and analysis of isotherms of N.sub.2 adsorption-desorption on the purified metal-organic framework material at 77 K resulted in a specific surface area of 412.5 m.sup.2/g and an average pore size of 5.47-5.54 Å. The purified metal-organic framework material was vacuum degassed at 150° C. for 12 hours to give a solvent-removed adsorbent. Vapor-phase adsorption test was then conducted.

[0077] In order to test the adsorptive separation performance of the metal-organic framework material synthesized above, isotherms of adsorption of single-component para-xylene, single-component ortho-xylene, and single-component meta-xylene on the metal-organic framework material as an adsorbent were measured. The adsorption was conducted with an appropriate amount of the adsorbent at temperatures of 30° C., 60° C., 90° C., and 120° C., respectively. At 30° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of up to 43 mg/g, meta-xylene was adsorbed by an amount of 35 mg/g, and ortho-xylene was adsorbed by an amount of 22 mg/g. At 60° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of 23 mg/g, meta-xylene was adsorbed by an amount of 23 mg/g, and ortho-xylene was adsorbed by an amount of 11 mg/g. At 90° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of 14 mg/g, ortho-xylene was adsorbed by an amount of 5 mg/g, and meta-xylene was adsorbed by an amount of 14 mg/g. At 120° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of 8 mg/g, ortho-xylene was adsorbed by an amount of 1 mg/g, and meta-xylene was adsorbed by an amount of 8 mg/g.

[0078] A specific method of separating mixed xylenes with the above synthesized metal-organic framework material is as follows.

[0079] The synthesized adsorbent was first molded. An amount of a binder needed in the molding accounted for 3%-10% of a mass of the adsorbent. Breakthrough experiments on a mixed xylenes vapor were conducted using the molded adsorbent. The mixed vapor for adsorptive separation in this example was a mixed vapor of three or two of para-xylene, meta-xylene, and ortho-xylene, with a ratio of saturation vapor pressures of the single-component xylenes being 1: 1: 1 or 1: 1, and a total pressure of the mixed vapor being 0.1 MPa. A packed column had a size of 10 mm I.D. × 50 mm, and was packed with about 3.1 g of the molded adsorbent. The test showed that, when the adsorbent was at a temperature of 60° C. and with a saturation vapor pressure ratio of ortho-xylene to meta-xylene to para-xylene being 1: 1: 1, ortho-xylene and meta-xylene began to pass through the column at 15 minutes, while para-xylene was retained in the packed column for about 100 minutes before beginning to pass through the column. Such a large difference in retention time indicates that the mixed xylenes were effectively separated. After five cycles of adsorption-regeneration, the metal-organic framework material was still stable in its adsorption performance. Conditions for the regeneration were to heat the adsorbent to 150° C. under vacuum or inert atmosphere and keep the adsorbent at the temperature for 72 hours.

Example 4

[0080] 30 mmol of magnesium acetate hydrate, 30 mmol of 2,5-dihydroxy-1,4-benzoquinone, and 300 mL of deionized water were mixed and then reacted under stirring at room temperature for 24-72 hours. After the reaction was completed, the resulting solid was centrifugally washed multiple times with deionized water to obtain a purified metal-organic framework material. Measurement and analysis of isotherms of N.sub.2 adsorption-desorption on the purified metal-organic framework material at 77 K resulted in a specific surface area of 577.2 m.sup.2/g and an average pore size of 5.38-5.53 Å. The purified metal-organic framework material was vacuum degassed at 150° C. for 12 hours to give a solvent-removed adsorbent. Vapor-phase adsorption test was then conducted.

[0081] In order to test the adsorptive separation performance of the metal-organic framework material synthesized above, isotherms of adsorption of single-component para-xylene, single-component ortho-xylene, and single-component meta-xylene on the metal-organic framework material as an adsorbent were measured. The adsorption was conducted with an appropriate amount of the adsorbent at temperatures of 30° C., 60° C., 90° C., and 120° C., respectively. At 30° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of up to 79 mg/g, ortho-xylene was adsorbed by an amount of 22 mg/g, and meta-xylene was adsorbed by an amount of 49 mg/g. At 60° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of 39 mg/g, ortho-xylene was adsorbed by an amount of 12 mg/g, and meta-xylene was adsorbed by an amount of 29 mg/g. At 90° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of 24 mg/g, ortho-xylene was adsorbed by an amount of 6 mg/g, and meta-xylene was adsorbed by an amount of 19 mg/g. At 120° C. and at a single-component saturation vapor pressure of 1000 Pa, para-xylene was adsorbed by an amount of 13 mg/g, ortho-xylene was adsorbed by an amount of 2 mg/g, and meta-xylene was adsorbed by an amount of 12 mg/g.

[0082] A specific method of separating mixed xylenes with the above synthesized metal-organic framework material is as follows.

[0083] The synthesized adsorbent was first molded. An amount of a binder needed in the molding accounted for 3%-10% of a mass of the adsorbent. Breakthrough experiments on a mixed xylenes vapor were conducted using the molded adsorbent. The mixed xylenes vapor for adsorptive separation in this example was a mixed vapor of three or two of para-xylene, meta-xylene, and ortho-xylene, with a ratio of saturation vapor pressures of the single-component xylenes being 1: 1: 1 or 1: 1, and a total pressure of the mixed vapor being 0.1 MPa. A packed column had a size of 10 mm I.D. × 50 mm, and was packed with about 1.8 g of the molded adsorbent. The test showed that, when the adsorbent was at a temperature of 30° C. and with a saturation vapor pressure ratio of ortho-xylene to meta-xylene to para-xylene being 1: 1: 1, ortho-xylene and meta-xylene began to pass through the column at 23 minutes, while para-xylene was retained in the packed column for about 96 minutes before beginning to pass through the column and precipitate. Such a large difference in retention time indicates that the mixed xylenes were effectively separated. Conditions for the regeneration were to heat the adsorbent to 150° C. under vacuum or inert atmosphere and keep the adsorbent at the temperature for 72 hours.

Comparative Example 1

[0084] 15 mmol of nickel acetate hydrate, 15 mmol of 2,5-dihydroxy-1,4-benzoquinone, and 200 mL of deionized water were mixed and then reacted under stirring at room temperature for 24-72 hours. After the reaction was completed, the resulting solid was centrifugally washed multiple times with deionized water to obtain a purified metal-organic framework material. The purified metal-organic framework material was vacuum degassed at 150° C. for 12 hours to give a solvent-removed adsorbent. Vapor-phase adsorption test was then conducted.

[0085] In order to test the adsorptive separation performance of the metal-organic framework material synthesized above, isotherms of CO.sub.2 adsorption-desorption on the material at 273 K were first measured to examine whether voids were present in the material. As shown in FIG. 10, the metal-organic framework material has no adsorption capacity for the small molecular gas CO.sub.2 (3.3 Å in kinetic size), indicating that the material does not have a suitable pore size or that the material has no voids inside for adsorptive separation of xylenes.

Comparative Example 2

[0086] 1.5 mmol of copper chloride hydrate, 1.5 mmol of 2,5-dihydroxy-1,4-benzoquinone, and 30 mL of deionized water was mixed and then reacted under stirring at room temperature for 24-48 hours. After the reaction was completed, the resulting solid was centrifugally washed multiple times with deionized water to obtain a purified metal-organic framework material. The purified metal-organic framework material was vacuum degassed at 150° C. for 12 hours to give a solvent-removed adsorbent. Vapor-phase adsorption test was then conducted.

[0087] In order to test the adsorptive separation performance of the metal-organic framework material synthesized above, isotherms of CO.sub.2 adsorption-desorption on the material at 273 K were first measured to examine whether voids were present in the material. As shown in FIG. 10, the metal-organic framework material, like the nickel metal-organic framework material obtained in Comparative Example 1, has an adsorption capacity for CO.sub.2 that is close to 0, indicating that the material does not have a suitable pore size or that the material has no voids inside for adsorptive separation of xylenes.

[0088] The above described are merely specific embodiments of the present invention, and technical features of the present invention are not limited thereto. Variations or modifications made by any person skilled in relevant arts within the spirit of the present invention shall all fall within the scope of the present invention.