Yields in xylene isomerization using layer MFI zeolites

Abstract

A process for the production of para-xylene is presented. The process includes the isomerization of C8 aromatics to para-xylene utilizing a new catalyst. The new catalyst is a layer MFI zeolite and is represented by the empirical composition in the as synthesized and anhydrous basis expressed by the empirical formula of:
M.sub.m.sup.n+R.sub.r.sup.p+AlSi.sub.yO.sub.z
where M is at least one exchangeable cation selected from the group consisting of alkali and alkaline earth metals and R is at least one organoammonium cation.

Claims

1. A process for the production of para-xylene, comprising: passing a mixture of hydrocarbons comprising xylenes to an isomerization reactor, operated at isomerization reaction conditions, to form a reaction mixture over an isomerization catalyst and to generate an effluent stream comprising para-xylene; wherein the isomerization catalyst is characterized by a catalyst having a 2-D layered MFI structure which is stable to calcination, wherein the catalyst is a zeolite having a microporous crystalline structure comprising a framework of AlO.sub.2 and SiO.sub.2 tetrahedral units, and an empirical composition in the as synthesized and anhydrous basis expressed by the empirical formula of:
M.sub.m.sup.n+R.sub.r.sup.p+AlSi.sub.yO.sub.z where M is at least one exchangeable cation selected from the group consisting of alkali and alkaline earth metals, m is the mole ratio of M to Al and varies from about 0 to about 3, R is at least one organoammonium cation selected from the group consisting of quaternary ammonium cations, diquaternary ammonium cations, r is the mole ratio of R to Al and has a value of about 0.1 to about 30.0 n is the weight average valence of M and has a value of about 1 to about 2, p is the weighted average valence of R and has a value of about 1 to about 2, y is the mole ratio of Si to Al and varies from greater than 32 to about 200, a BET surface area is greater than 450 m.sup.2/g and a mesopore area is greater than 250 m.sup.2/g, and z is the mole ratio of O to Al and has a value determined by the equation:
z=(m.Math.n+r.Math.p+3+4.Math.y)/2 and it is characterized in that it has the x-ray diffraction pattern having at least the d spacing and intensities set forth in the following Table wherein relative intensity of 100 is considered to be very strong (vs), relative intensity of 18.8-58.2 is considered to be medium (m), and relative intensity of 5.7-13.3 is considered to be weak (w) TABLE-US-00008 TABLE A 2 d() I/Io 7.92-7.99 11.04-11.31 m 8.79-8.88 9.94-11.09 m 20.28-20.56 4.31-4.35 w 23.10-23.18 3.83-3.84 vs 23.86-24.05 3.69-3.72 m 29.90-30.05 2.97-2.98 w 45.02-45.17 2.00-2.01 w.

2. The process of claim 1 wherein the isomerization reaction conditions include a temperature between 250 C. and 350 C.

3. The process of claim 2 wherein the isomerization reaction conditions include a temperature between 280 C. and 310 C.

4. The process of claim 1 wherein the isomerization reaction conditions include a pressure sufficient to maintain the reaction mixture in the liquid phase.

5. The process of claim 1 wherein a pressure is at least 1025 kPa.

6. The process of claim 1 wherein the mixture of hydrocarbons further includes ethylbenzene.

7. The process of claim 1 where M in the zeolite is selected from the group consisting of sodium, potassium and mixtures thereof.

8. The process of claim 1 where M in the zeolite is a mixture of an alkali metal and an alkaline earth metal.

9. The process of claim 1 where R in the zeolite is selected from the group consisting of tetrabutylammonium hydroxide, tetrabutylphosphonium hydroxide, hexamethonium dihydroxide and mixture thereof.

10. The process of claim 1 where R is a halide or hydroxide compound of an organoammonium cation.

11. The process of claim 1 wherein the catalyst is characterized by the catalyst having the 2-D layered MFI structure which is stable to calcination, wherein the catalyst is a zeolite having a microporous crystalline structure comprising a framework of AlO.sub.2 and SiO.sub.2 tetrahedral units, further including the element E and having the empirical composition in the as synthesized and anhydrous basis expressed by the empirical formula of:
M.sub.m.sup.n+R.sub.r.sup.p+Al.sub.1-xE.sub.xsi.sub.yO.sub.z where M is at least one exchangeable cation selected from the group consisting of alkali and alkaline earth metals, m is the mole ratio of M to (Al+E) and varies from about 0 to about 3, R is at least one organoammonium cation selected from the group consisting of quaternary ammonium cations, diquaternary ammonium cations, r is the mole ratio of R to (Al+E) and has a value of about 0.1 to about 30.0 n is the weight average valence of M and has a value of about 1 to about 2, p is the weighted average valence of R and has a value of about 1 to about 2, E is an element selected from the group consisting of gallium, iron, boron, indium and mixtures thereof, x is the mole fraction of E and has a value from 0 to about 1.0, y is the mole ratio of Si to (Al+E) and varies from greater than 32 to about 200 and z is the mole ratio of 0 to (Al+E) and has a value determined by the equation:
z=(m.Math.n+r.Math.p+3+4.Math.y)/2.

12. The process of claim 1 further comprising: passing the effluent stream to a para-xylene separation unit to generate a para-xylene process stream and a second stream comprising meta-xylene and ortho-xylene.

13. The process of claim 12 wherein the separation unit is an adsorption separation unit and generates an extract stream comprising para-xylene and desorbent and a raffinate stream comprising meta-xylene and ortho-xylene.

14. The process of claim 13 further comprising passing the extract stream to a fractionation unit to generate a bottoms stream comprising para-xylene and an overhead stream comprising desorbent.

15. The process of claim 13 wherein the raffinate stream is passed to the isomerization reactor.

16. A process for the production of para-xylene, comprising: passing a mixture of hydrocarbons comprising xylenes to an isomerization reactor, operated at isomerization reaction conditions, to form a reaction mixture over an isomerization catalyst, and to generate an effluent stream comprising para-xylene; wherein the isomerization catalyst is characterized by a catalyst having a 2-D layered MFI structure which is stable to calcination, wherein the catalyst is a zeolite of claim 1 having a microporous crystalline structure comprising a framework of AlO.sub.2 and SiO.sub.2 tetrahedral units, further including the element E and having the empirical composition in the as synthesized and anhydrous basis expressed by the empirical formula of:
M.sub.m.sup.n+R.sub.r.sup.p+Al.sub.1-xE.sub.xSi.sub.yO.sub.z where M is at least one exchangeable cation selected from the group consisting of alkali and alkaline earth metals, m is the mole ratio of M to (Al+E) and varies from about 0 to about 3, R is at least one organoammonium cation selected from the group consisting of quaternary ammonium cations, diquaternary ammonium cations, r is the mole ratio of R to (Al+E) and has a value of about 0.1 to about 30.0 n is the weight average valence of M and has a value of about 1 to about 2, p is the weighted average valence of R and has a value of about 1 to about 2, E is an element selected from the group consisting of gallium, iron, boron, indium and mixtures thereof, x is the mole fraction of E and has a value from 0 to about 1.0, y is the mole ratio of Si to (Al+E) and varies from greater than 32 to about 200, a BET surface area is greater than 450 m.sup.2/g and a mesopore area is greater than 250 m.sup.2/g, and z is the mole ratio of 0 to (Al+E) and has a value determined by the equation:
z=(m.Math.n+r.Math.p+3+4.Math.y)/2 and it is characterized in that it has the x-ray diffraction pattern having at least the d spacing and intensities set forth in the following Table A wherein relative intensity of 100 is considered to be very strong (vs), relative intensity of 18.8-58.2 is considered to be medium (m), and relative intensity of 5.7-13.3 is considered to be weak (w). TABLE-US-00009 TABLE A 2 d() I/Io 7.92-7.99 11.04-11.31 m 8.79-8.88 9.94-11.09 m 20.28-20.56 4.31-4.35 w 23.10-23.18 3.83-3.84 vs 23.86-24.05 3.69-3.72 m 29.90-30.05 2.97-2.98 w 45.02-45.17 2.00-2.01 w.

17. The process of claim 16 wherein the isomerization reaction conditions include a temperature between 250 C. and 350 C.

18. The process of claim 16 wherein the isomerization reaction conditions include a pressure sufficient to maintain the reaction mixture in the liquid phase.

19. The process of claim 16 wherein the pressure is at least 1025 kPa.

20. The process of claim 16 wherein the mixture of hydrocarbons further includes ethylbenzene.

Description

DETAILED DESCRIPTION

(1) Para-xylene production is a valuable commercial process, wherein the reduction of losses can entail a significant economic advantage. One method of improving para-xylene yields is to increase the conversion from C.sub.8 compounds to para-xylene and to reduce losses during that conversion. The operating of a liquid phase xylene isomerization reactor using a conventional MFI catalyst generates a significant xylene loss per pass. The loss is greater than 1.5%. The invention of a new catalyst allows for a significant reduction in the xylene loss. The new catalyst has a new zeolitic MFI morphology and can achieve comparable para-xylene content with xylene losses of around 0.2% or less.

(2) The present invention is a process for the production of para-xylene. The process includes passing a mixture of hydrocarbons including xylenes to an isomerization reactor, operated at isomerization reaction conditions to generate an effluent stream having para-xylene, or p-xylene. The reaction conditions include forming a reaction mixture comprising C.sub.8 hydrocarbons and passing the mixture over an isomerization catalyst. The present invention utilizes a new catalyst that reduces the loss of xylenes during the isomerization process. The catalyst is a zeolite catalyst made by using a charge density mismatch method. The isomerization catalyst is a zeolite having a microporous crystalline structure comprising a framework of AlO.sub.2 and SiO.sub.2 tetrahedral units, and an empirical composition in the as synthesized and anhydrous basis expressed by the empirical formula of:
M.sub.m.sup.n+R.sub.r.sup.p+AlSi.sub.yO.sub.z.

(3) The catalyst comprises M, which is at least one exchangeable cation selected from the group consisting of alkali and alkaline earth metals, R, which is at least one organoammonium cation selected from the group consisting of quaternary ammonium cations, diquaternary ammonium cations, E, which is at least one element from gallium, iron, boron and indium. Aluminum and silicon are supplied from alumina and silica. In the formula, m is the mole ratio of M to Al and varies from about 0 to about 3, r is the mole ratio of R to Al and has a value of about 0.1 to about 30.0, y is the mole ratio of Si to Al and varies from greater than 32 to about 200 and z is the mole ratio of O to Al. The value n is the weight average valence of M and has a value of about 1 to about 2, and p is the weighted average valence of R and has a value of about 1 to about 2. The value of z is determined by the equation:
z=(m.Math.n+r.Math.p+3+4.Math.y)/2.

(4) The catalyst can be further characterized by its unique x-ray diffraction pattern as at least the d spacing and intensities set forth in Table A:

(5) TABLE-US-00003 TABLE A 2 d() I/Io 7.92-7.99 11.04-11.31 m 8.79-8.88 9.94-11.09 m 20.28-20.56 4.31-4.35 w 23.10-23.18 3.83-3.84 vs 23.86-24.05 3.69-3.72 m 29.90-30.05 2.97-2.98 w 45.02-45.17 2.00-2.01 w

(6) The M in the zeolite can be a mixture of alkali metals and alkaline earth metals, with a preferred M including sodium and potassium. The R cation can be selected from one or more of quaternary ammonium cations, quaternary phosphonium cations, and methonium cations. The R cation can come from an halide compound or a hydroxide compound. Preferred R cations for the zeolite are selected from the reactive materials including one or more of tetrabutylammonium hydroxide, tetrabutylphosphonium hydroxide and hexamethonium dihydroxide.

(7) The isomerization reaction conditions include a temperature between 250 C. and 350 C., with a preferred reaction temperature between 280 C. and 310 C. The reaction conditions include a pressure sufficient to maintain the reaction mixture in the liquid phase. In one embodiment, the pressure in the reactor is at least 1025 kPa, with a preferred reactor pressure in the range of 1750 kPa to 2400 kPa.

(8) The feedstream preferably comprises C.sub.8 aromatics, having meta-xylene and ortho-xylene. The feedstream can also include ethylbenzene, wherein the isomerization reactor converts the meta-xylene and ortho-xylene to para-xylene, and the ethylbenzene to benzene.

(9) The effluent stream leaving the isomerization reactor includes para-xylene is passed to a para-xylene separation unit to generate a para-xylene process stream, and a second stream comprising meta-xylene, ortho-xylene and ethylbenzene. The para-xylene separation unit can comprise an adsorption separation unit, wherein the para-xylene process stream is the extract stream and the second stream is the raffinate stream. The extract stream and raffinate streams can include a desorbent. The extract stream is passed to a fractionation unit to generate a bottoms stream comprising para-xylene and an overhead stream comprising desorbent. The process can further include passing the raffinate stream to the isomerization reactor. The raffinate stream can also be passed to a second fractionation column to separate the desorbent from the raffinate stream before passing the raffinate stream to the isomerization reactor.

(10) In another embodiment, the catalyst is characterized by a zeolite having a microporous crystalline structure comprising a framework of AlO.sub.2 and SiO.sub.2 tetrahedral units, further including the element E and having the empirical composition in the as synthesized and anhydrous basis expressed by the empirical formula of:
M.sub.m.sup.n+R.sub.r.sup.p+Al.sub.1-xE.sub.xSi.sub.yO.sub.z

(11) where M is at least one exchangeable cation selected from the group consisting of alkali and alkaline earth metals, m is the mole ratio of M to (Al+E) and varies from about 0 to about 3, R is at least one organoammonium cation selected from the group consisting of quaternary ammonium cations, diquaternary ammonium cations, r is the mole ratio of R to (Al+E) and has a value of about 0.1 to about 30.0 n is the weight average valence of M and has a value of about 1 to about 2, p is the weighted average valence of R and has a value of about 1 to about 2, E is an element selected from the group consisting of gallium, iron, boron, indium and mixtures thereof, x is the mole fraction of E and has a value from 0 to about 1.0, y is the mole ratio of Si to (Al+E) and varies from greater than 32 to about 200 and z is the mole ratio of O to (Al+E) and has a value determined by the equation:
z=(m.Math.n+r.Math.p+3+4.Math.y)/2.

Example 1 (Commercial Reference Example)

(12) Commercial pentasil zeolite from TOSOH (lot:HSZ-900-940NHA) was formulated into a catalyst containing 70% zeolite and 30% silica. In the catalyst preparation, the zeolite was mixed with LUDOX AS-40 and Hi-Sil 250 into a muller mixer. Additional water was added to the Muller mixer, while mixing, until dough with a proper texture for extrusion was formed. The dough was extruded to form 1/16 diameter trilobes, which were dried at 100 C. overnight and then sized to a length to diameter ratio of approximately 3. The dry extrudates was calcined in a box oven with a flowing air at 560 C. for 6 hours to remove the template. This is referred to as catalyst A.

Example 2

(13) An aluminosilicate reaction solution was prepared by first mixing 13.73 g of aluminum tri-sec-butoxide (95.sup.+%), 559.89 g tetrabutylphosphonium hydroxide (40 mass-% solution), and 200 g of ice water mixture while stirring vigorously. After thorough mixing, 574.76 g tetraethyl orthosilicate was added. The reaction mixture was homogenized for an additional hour with a high speed mechanical stirrer. A composite aqueous solution containing 2.70 g of NaOH dissolved in 48.92 g distilled water, was added, drop-wise, to the aluminosilicate solution. After the addition was completed, the resulting reaction mixture was homogenized for 1 hour, transferred to a 2000 ml Parr stainless steel autoclave which was heated to 115 C. and maintained at that temperature for 120 hrs. The solid product was recovered by centrifugation, washed with de-ionized water, and dried at 80 C.

(14) The product was identified as a pentasil zeolite by powder x-ray diffraction. Representative diffraction lines observed for the product are shown in Table 1. A portion of the material was calcined by ramping to 560 C. for 5 hours followed by a 8 hour dwell in air. The BET surface area was 526 m.sup.2/g, the micropore area was 220 m.sup.2/g, the mesopore area was 306 m.sup.2/g, the micropore volume was 0.115 cc/g, and mesopore volume was 0.99 cc/g. Scanning Electron Microscopy (SEM) revealed clusters of nano spheres of less than 20 nm. Chemical analysis was as follows: 1.22% Al, 42.8% Si, and 0.70% Na, Na/Al=0.67, Si/Al.sub.2=49.8.

(15) TABLE-US-00004 TABLE 1 2 d() I/I.sub.0 % 7.99 11.04 m 8.88 9.94 m 20.50 4.32 w 23.16 3.83 vs 24.05 3.69 m 30.05 2.97 w 45.02 2.01 w

Example 3 (Pentasil Layered Extrudates)

(16) The pentasil zeolite of example 2 was formulated into a catalyst containing 70% zeolite and 30% silica. In the catalyst preparation, the zeolite was mixed with LUDOX AS-40 and Hi-Sil 250 into a muller mixer. Additional water was added to the Muller mixer, while mixing, until dough with a proper texture for extrusion was formed. The dough was extruded to form 1/16 diameter trilobes, which were dried at 100 C. overnight and then sized to a length to diameter ratio of approximately 3. The dry extrudates was calcined in a box oven with a flowing air at 560 C. for 6 hours to remove the template. The calcined support was then exchanged using a 10 wt-% NH.sub.4NO.sub.3 solution at 75 C. for one hour. This was followed by water wash using 20 cc of water per cc of extrudates. The NH.sub.4NO.sub.3 exchange and water wash was repeated three more times. The extrudates was then dried at 120 C. for 4 hours and then activated at 550 C. This is labeled catalyst B.

Example 4

(17) An aluminosilicate reaction solution was prepared by first mixing 13.87 g of aluminum tri-sec-butoxide (95.sup.+%), 386.39 g tetrabutylammonium hydroxide (55 mass-% solution), and 300 g of ice water mixture while stirring vigorously. After thorough mixing, 580.35 g tetraethyl orthosilicate was added. The reaction mixture was homogenized for an additional hour with a high speed mechanical stirrer. A composite aqueous solution containing 2.73 g of NaOH dissolved in 116.67 g distilled water was added, drop-wise, to the aluminosilicate solution. After the addition was completed, the resulting reaction mixture was homogenized for 1 hour, transferred to a 2000 ml Parr stainless steel autoclave which was heated to 115 C. and maintained at that temperature for 57 hrs. The solid product was recovered by centrifugation, washed with de-ionized water, and dried at 80 C.

(18) The product was identified as a pentasil zeolite by powder x-ray diffraction. Representative diffraction lines observed for the product are shown in Table 2. The product composition was determined by elemental analysis to consist of the following mole ratios: Si/Al=24.9, Na/Al=0.92. A portion of the material was calcined by ramping to 560 C. for 5 hours followed by a 8 hour dwell in air. The BET surface area was 517 m.sup.2/g, the micropore area was 258 m.sup.2/g, the mesopore area was 259 m.sup.2/g, the micropore volume was 0.135 cc/g, and mesopore volume was 0.94 cc/g. Scanning Electron Microscopy (SEM) revealed clusters of nano spheres of less than 20 nm. Chemical analysis was as follows: 1.73% Al, 44.9% Si, and 1.37% Na, Na/Al=0.93, Si/Al.sub.2=49.8.

(19) TABLE-US-00005 TABLE 2 2 d() I/I.sub.0 % 7.94 11.12 m 8.79 10.04 m 20.38 4.35 w 23.16 3.83 vs 23.86 3.72 m 29.96 2.98 w 45.07 2.00 w

Example 5

(20) The pentasil zeolite of example 4 was formulated into a catalyst containing 70% zeolite and 30% silica. In the catalyst preparation, the zeolite was mixed with LUDOX AS-40 and Hi-Sil 250 into a Muller mixer. Additional water was added to the Muller mixer, while mixing, until dough with a proper texture for extrusion was formed. The dough was extruded to form 1/16 diameter trilobes, which were dried at 100 C. overnight and then sized to a length to diameter ratio of approximately 3. The dry extrudates was calcined in a box oven with a flowing air at 560 C. for 6 hours to remove the template. The calcined support was then exchanged using a 10 wt-% NH.sub.4NO.sub.3 solution at 75 C. for one hour. This was followed by water wash using 20 cc of water per cc of extrudates. The NH.sub.4NO.sub.3 exchange and water wash was repeated three more times. The extrudates was then dried at 120 C. for 4 hours and then activated at 550 C. This is labeled catalyst C.

Example 6

(21) Catalyst A was evaluated for xylene isomerization and ethyl-benzene retention using a pilot plant flow reactor processing a non-equilibrium C.sub.8 aromatic feed having the following approximate composition in wt-%:

(22) TABLE-US-00006 C.sub.8 non-aromatics 0.5 ethylbenzene 4.5 para-xylene 0.9 meta-xylene 64.6 ortho-xylene 29.5

(23) Pilot-plant test conditions and results are as follows. The above feed contacted the Catalyst at a pressure of 3.5 MPa in the liquid phase at a weight hourly space velocity of 10 under a range of temperatures. The resulting performance measures are shown below:

(24) TABLE-US-00007 Catalyst A Catalyst B Catalyst C WHSV, hr 1 10 10 10 Temperature to reach 23 PX/X 348 314 320 Xylene Loss 1.31 0.20 0.30 A11+ selectivity 0.24 0.11 0.06

(25) Note that the Xylene Loss is in mol-% defined as (1(para, meta, ortho xylene in product)/((para, meta, ortho xylene in feed))*100, which represents material that has to be circulated to another unit in an aromatics complex. Such circulation is expensive and a low amount of C.sub.8 ring loss is preferred. A11+ represents material that is heavier than 145 molecular weight. This material represents unrecoverable losses. Ethylbenzene conversion, 2 to 4.5% was low in all cases.

(26) While the invention has been described with what are presently considered the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.