JP2002540178A - Separation of para-xylene using ether as desorbent - Google Patents

Abstract

(57) How Abstract: Simulated moving bed countercurrent adsorption method, ether desorbent, and preferably used in combination with BaX zeolite adsorbent, producing paraxylene from a stream of C ₈ aromatic hydrocarbons . This adsorbent / ether desorbent system has been found to be particularly good when the water content of the system is carefully controlled. Preferred ether desorbants are diisopropyl ether and methyl tert-butyl ether.

Description

DETAILED DESCRIPTION OF THE INVENTION

 (Field of the Invention)

The present invention relates to the separation of xylene isomers and ethylbenzene by adsorption to produce high-purity para-xylene.

BACKGROUND OF THE INVENTION Para-xylene is a valuable petrochemical precursor for the production of terephthalate-based polymers such as polyethylene terephthalate. Polyethylene terephthalate is
It is a polymer in several large end uses, including polyester fibers and PET bottle resins. The large market for para-xylene for fibers and PET resins has created a need for large-scale production and purification facilities for para-xylene. Para-xylene
Typically, it is isolated from the reformate produced by a contact reformer at a refinery, although it can be taken from other sources such as pygas. Catalytic reformers produce xylene molecules by dehydrocyclization of linear and branched paraffins, dehydrogenation of naphthenes, and, to a lesser extent, polyalkylaromatics. C ₈ aromatic moiety of reformate contains more than just a paraxylene. Other aromatic isomers present in reformate of C ₈ boiling range ortho-xylene (OX), a meta-xylene (MX) and ethylbenzene (EB). Because these isomers have close boiling points, it is difficult or impossible to separate them from para-xylene by distillation.

[0003] Two methods developed for isolating para-xylene (PX) from other C ₈ isomers are crystallization and adsorption. Continuous simulated moving bed adsorption method (co
ntinuous simulated moving bed adsorption is currently used in most basic PX separation plants. An example of such a PX adsorption method is the Parex method (Pa
rex) (UOP) and Eluxyl (IFP). In these methods, an X or Y zeolite adsorbent is used in combination with either toluene or para-diethylbenzene as a desorbent. The choice of desorbent is one important consideration that has a significant effect on the design and economics of the process. The desorbent will generally be adsorbed not only around the selected adsorbent, but also around the feed components on that adsorbent. If the desorbent is too strongly adsorbed on the adsorbent, an excessively large portion of the total capacity of the adsorbent will be occupied by the desorbent. This adsorbs C ₈ aromatic isomers, effectively reducing the portion of the adsorbent can be utilized to separate, must therefore be used to increase the amount of adsorbent.
If the desorbent is not tightly adsorbed, a large amount of desorbent must be used, leading to a high desorbent-to-feed ratio. High desorbent-to-feed ratios result in the need for larger extract and raffinate distillation columns. The extractive distillation column separates the PX product from the desorbent. In the PX method,
The raffinate distillation column separates the desorbent from the other C ₈ aromatic isomers. These distillation columns are a major part of the cost of the PX separation process. Both distillation columns account for a large portion of the capital cost of the process and are a major factor in the operating cost of the PX separation process. Thus, it is generally best to minimize the amount of desorbent used in this method. Another important parameter of a desorbent is its boiling point. Since the desorbent is separated from the raffinate and the extract by distillation, it is desirable to select a desorbent having a boiling point substantially different from the boiling range of the extract and the raffinate. Higher boiling point of the desorbent closer the boiling range of PX extract or C ₈ aromatic raffinate distillation column is increased to be required and also increases utility costs of operating the distillation column. It is also important to select a desorbent that does not form an azeotrope with any of the feed components in order to undergo clean separation.

[0004] One patent discussing the use of diisopropyl ether as a desorbent in paraxylene adsorption is US Pat. No. 4,255,607, which is incorporated herein by reference. No. 4,255,607 does not describe the water content or control in these methods.

SUMMARY OF THE INVENTION The present invention is an adsorptive separation process for separating para-xylene from a hydrocarbon feedstock containing a mixture of C ₈ aromatic hydrocarbons, comprising:

A) contacting the feed at adsorption conditions with an adsorbent bed comprising a crystalline aluminosilicate selected from the group consisting of type X and type Y zeolites, whereby para-xylene is removed from the feed; Adsorbs;

B) contacting said adsorbent bed at desorption conditions with a desorbent material comprising diisopropyl ether;

[0008] c) removing from the adsorbent bed a stream comprising a desorbent and less selectively adsorbed components of the feed;

D) removing a stream containing the desorbent and the para-xylene from the adsorbent bed

The process as above, wherein the water content is maintained at 1 to 8% by weight based on the weight of the adsorbent.

The above method further comprises the following:

E) a stream containing the desorbent and less selectively adsorbed components, a second stream containing the desorbent and less selectively adsorbed components. Separated from the stream; and

F) separating the second stream containing the desorbent and para-xylene into a third stream containing the desorbent and a stream containing para-xylene. Can be.

The present invention is particularly useful when the X or Y zeolite molecular sieve adsorbent is used in combination with a diisopropyl ether desorbent or an MTBE desorbent. Based on knowledge of impact. Also, surprisingly, when the water content of the system is maintained at 1 to 8% by weight based on the weight of the X or Y zeolite adsorbent, diisopropyl ether is a particularly good desorbent for adsorptive separation of PX. Has been found to be. It has been found that both the selectivity and the capacity of the adsorption system vary substantially depending on the water content of the system. 1) PX, in order to maintain both the proper selectivity and 2) the proper capacity of the system for other C ₈ aromatic hydrocarbons and desorbent, unless carefully controlled water content of the process No.

The present invention is based on the surprising finding that ethers can be a particularly good desorbent in the PX adsorption separation method for separating para-xylene (PX) from mixed xylene. Since oxygenates may have too high an affinity for the adsorbent, they have generally been considered poor candidate compounds for desorbents. Good desorbent dont is adsorbed less strongly, it must be able to replace the C ₈ isomers from the adsorbent nevertheless. Paraxylene adsorption methods include simulated moving bed countercurrent adsorption separation methods such as the Parex method and the Elxyl method. A particularly preferred desorbent of the present invention is diisopropyl ether (IPE). Another preferred desorbent of the present invention is methyl tertiary butyl ether (MTBE)
It is.

DETAILED DESCRIPTION OF THE INVENTION In particular, diisopropyl ether (IPE) has been found to be an effective desorbent for adsorption separation systems using an adsorbent consisting of barium exchanged X or Y zeolite. Also, surprisingly, the selectivity of the adsorbent / IPE system depends on this adsorbent / I
It has also been found that when the water content of the PE system is controlled, it can be better than the adsorbent / toluene system. In particular, in the IPE system, the selectivity of PX to EB is better. PX
The selectivity to EB is 2.8 in the IPE system as compared to 1.7 in the toluene system. PX vs. EB
Selectivity was, EB, except PX, it is important because it is the most strongly adsorbed among the C ₈ aromatic isomers. Thus, separation of EB / PX is the most difficult.

[0017] The selectivity of PX versus desorbent is also a very important parameter. A selectivity greater than 1 means that PX is adsorbed more strongly than the desorbent. A selectivity of less than 1 means that the PX is less adsorbed than the desorbent. Desorption agent is C ₈
Preferably, it is adsorbed almost as strongly as the aromatic isomer. Strength desorbent is adsorbed is smaller than PX isomers are desired, it then greater than the strongest C ₈ aromatic isomers adsorbed is most preferred. If the desorbent is adsorbed too strongly, an excessively large part of the total capacity of the adsorbent will be occupied by the desorbent. This adsorbs C ₈ aromatic isomers, effectively reduces the adsorbent portion available to separate, thus increasing the amount of adsorbent should be used. If the desorbent is not strongly adsorbed sufficiently, a large amount of desorbent must be used, which will increase the desorbent-to-feed ratio and reduce the capital and operating costs of the method. increase.

Surprisingly, as the examples will show, when the water content is carefully controlled when using diisopropyl ether desorbent, PX becomes the most strongly adsorbed component, followed by diisopropyl ether desorbent. It has been found that it is possible to achieve a state in which the next is another C ₈ aromatic compound, while maintaining good capacity.

Another aspect of the invention is that the water content of the adsorption / desorption system must be kept between 1 and 8% by weight based on the dry weight of the adsorbent when the desorbent is diisopropyl ether. That's what it means. If the water level is too low, diisopropyl ether will be adsorbed weakly and will not be an effective desorbent. If the water level is too high, the capacity of the adsorbent will be greatly reduced, which will require more adsorbent, making the process of the present invention uneconomical. The water content on the adsorbent can be measured by the loss on ignition method (LOI), in which case the adsorbent is weighed, then heated to a predetermined temperature, heated for a set period of time, and then again It is weighed to determine how much water has been released from the sorbent.

As mentioned above, diisopropyl ether is one preferred desorbent of the present invention. Diisopropyl ether has been found to have surprising advantages over conventional conventional desorbents such as toluene and para-diethylbenzene. One advantage is separated from PX or other C ₈ isomers diisopropyl ether desorbent, due to difference in boiling point wider is that it is easier. One advantage of certain ether desorbents, particularly the preferred diisopropyl ether (IPE) desorbent, is that the desorbent is derived from extracts containing PX (Bp = 138.4 ° C.) and PX depleted xylenes and EB ( (Boiling range 136-145 ° C.). The boiling point of IPE is 69 ° C, compared to 110.6 ° C for toluene, the best light desorbent currently used. This large boiling point difference allows for a smaller extractant and raffinate distillation column so that both capital and operating cost savings can be realized. These savings are due to the economics of hybrid processes where the cost of separating the desorbent from the extract stream and raffinate stream may be as high or greater than the cost of separating xylenes in the adsorption tower. Can be particularly important for The hybrid PX method includes both an adsorption part and a crystallization part. The hybrid adsorption section is typically used as the first step in the process to produce a PX-enriched stream. Then, by using crystallization, the PX
The concentrated stream is purified to produce high purity PX.

When using a diisopropyl ether desorbent, the inventors have found that the water content of the adsorption system should be kept between 1 and 8% by weight, based on the weight of the adsorbent. The water content of the adsorption system is preferably 1 to 8% by weight, and 2 to 6% by weight.
Is more preferable, and 2 to 5% by weight is still more preferable.

When using a methyl tert-butyl ether desorbent, the inventor has found that the water content of the adsorption system should be kept below 4% by weight, based on the weight of the adsorbent. The water content of the adsorption system is preferably less than 3% by weight, more preferably less than 2% by weight, even more preferably less than 1% by weight.

The adsorbent used in the present invention is preferably a type X or type Y molecular sieve zeolite. The zeolite adsorbent is preferably modified to include one or more alkali metal or alkyl earth metal ions at the exchangeable cation sites. The X or Y zeolite is modified such that the exchangeable cation site contains one or more alkali metal or alkyl earth metal ions selected from the group consisting of barium, potassium, calcium, strontium and cesium. More preferably, it is performed. Most preferably, the X or Y zeolite contains barium at the exchangeable cation sites.

The adsorbent to be used in the process according to the invention consists, as mentioned above, of certain crystalline aluminosilicates, in other words molecular sieves, ie X and Y zeolites. The zeolites have a known cage structure in which alumina and silica tetrahedra are tightly bound in an open three-dimensional network to form a cage structure with window-like pores. Prior to the partial or complete dehydration of the zeolite, the tetrahedra are cross-linked by sharing oxygen atoms with the space between the tetrahedra occupied by water molecules. This dehydration of the zeolite results in crystals entangled with a lattice having the size of the molecule, and thus the crystalline aluminosilicates when the separation they effect is essentially dependent on the differences between the sizes of the feed molecules. Often referred to as "molecular sieves", for example, when smaller normal paraffin molecules are separated from larger isoparaffin molecules by using a particular molecular sieve. In the method of the present invention, however, the term "molecular sieve" is not strictly appropriate, though it is widely used. It is clear that the separation of specific aromatic isomers is obviously dependent on the difference in electrochemical attraction between the different isomers and the adsorbent rather than the difference in pure physical size of the isomer molecules Because.

Crystalline aluminosilicates, in hydrated form, include zeolites of type X, which zeolites have the following formula 1: in terms of moles of oxide: (0.9 ± 0.2) M _{2 / n} O: Al ₂ O ₃ : (2.5 ± 0.5) SiO ₂ : yH ₂ O Formula 1

Wherein, in the above formula, “M” is a cation having a valency of 3 or less, which balances with the ion valency of the tetrahedron, and is generally referred to as an exchangeable cation site; "n" represents the valency of the cation and "y" represents the number of water molecules.
Is up to about 9 depending on the identity of "M" and the degree of hydration of the crystals. As can be noticed from equation 1, the SiO ₂ / Al ₂ O ₃ molar ratio is 2.5 ± 0.5. Cation “M”
"Can be a monovalent, divalent or trivalent cation or a mixture thereof.

In the hydrated or partially hydrated form, zeolites of type Y structure likewise have the following formula 2 with respect to the number of moles of oxide: (0.9 ± 0.2) M _{2 / n} O: Al ₂ O ₃ : wSiO ₂ : yH ₂ O Formula 2

Wherein: “M”, “n” and “y” are the same as above, and “w” is a value of about 3 or more and about 6 or less. It is. The molar ratio of SiO ₂ / Al ₂ O ₃ types Y structured zeolite may thus be about 3 to about 6. For both zeolites, the cation "M" can be one or more of a wide variety of cations, but when the zeolite was first produced, the cation "M" Is dominant. Type Y zeolites containing predominantly sodium cations at exchangeable cation sites are therefore referred to as sodium-exchanged type-Y, or NaY zeolites. However, depending on the purity of the reactants used to produce the zeolite, the other cations may be present as impurities.

The zeolites useful in the present invention are typical as described above. However, in order to achieve the separation according to the invention, the exchange of the cations of the as-produced zeolite with ions from Group IA or IIA, such as barium or potassium or mixtures thereof, is necessary. A preferred adsorbent useful in the present invention is barium exchanged X zeolite.

Typically, the sorbents used in the separation method include such channels having channels and holes in an amorphous inorganic matrix or binder that allow liquids to access the crystalline material. Contains crystalline material dispersed. Silica, alumina, clay or mixtures thereof are typical of such inorganic matrix materials. The binder helps to form or agglomerate the particles of the crystalline material, but without the binder, the crystalline material particles would consist of a fine powder. The sorbent thus has a desired particle size range, preferably between about 16 and
It can be in the form of particles such as extrudates, agglomerates, tablets, macrospheres or granules having a particle size of about 60 mesh (US standard mesh) (1.9 mm to 250 microns).

The feed mixture which can be used in the process according to the invention comprises para-xylene and at least one other C ₈ aromatic isomer and one or more C ₈ aromatics as impurities. sometimes it contains ₉ aromatics. Mixtures containing substantial amounts of para-xylene and other C ₈ aromatic isomers, and C ₉ aromatics,
Generally, they are produced by reforming and isomerization methods, which are well known in the refining and petrochemical arts. Many C ₉ aromatics have boiling points in the range of 160-170 ° C. and cannot be easily removed from the standard desorbent p-diethylbenzene by distillation. In the current method, therefore:
C ₉ acids usually prior to contact with the standard desorbent occur as adsorption separation and result are removed from the feedstock by distillation. The present inventors have found that they can be easily separated by fractionation from C ₉ aromatics and do not require large distillation columns and large amounts of utility to pre-treat the feed, resulting in substantial cost savings Found a desorbent that fulfills.

[0032] Patents teaching about substantially faujasite-type, X and Y zeolites are all incorporated by reference herein in US Pat.
No. 82,244, No. 3,130,007, No. 3,789,107, No. 3,949,059, No. 4,007,253, No. 4,340,573, Nos. 4,440,366, 4,436,708 and 4,678
, 651.

A reforming process can provide the feed mixture for the process of the present invention. The reforming process, the naphtha feedstock, strictly selected platinum to generate effluent containing the C ₈ aromatic isomers - is brought into contact with a halogen-containing catalyst. Generally, the reformate is then fractionated, C ₈ aromatic isomers, more C ₈ aromatic isomers of C ₈ fraction in containing the C ₈ non-aromatics and C ₉ aromatics Is concentrated. The feed mixture for the process of the present invention can also be obtained from isomerization and transalkylation processes. Xylene mixture deficient in one or more isomers isomerized under isomerization conditions,
C ₈ aromatic isomers, eg p- xylene C ₈ aromatic isomer enriched, more can be produced effluent containing also C ₈ non-aromatics and C ₉ aromatics. The content of C ₉ aromatics isomerization xylene isomers may be a large amount of about 1-2% depending on isomerization conditions. Similarly, transalkylation of a mixture of C ₇ and C ₉ aromatics produces xylene isomers containing C ₉ aromatics. In all of these contact methods, in order to remove C ₉ aromatics from C ₈ aromatics before they can be used to adsorb xylene separation methods conventional must use xylene splitter column. Thus, the feed mixture for the process of the present invention may contain a certain amount of each of the C ₉ aromatics, and may also contain a certain amount of linear or branched paraffins, cycloparaffins or olefinic materials, respectively. Can be included. Each of the above amounts is preferably a minimal amount in order to prevent contamination of the product from this process by substances that are not selectively adsorbed or separated by the adsorbent. The above contaminants should preferably be less than about 20% based on the volume of the feed mixture introduced into the process.

To separate para-xylene from a feed mixture comprising para-xylene, at least one other C ₈ aromatic compound and C ₉ aromatic compound, the mixture is adsorbed at adsorbing conditions with an adsorbent. Upon contact, the para-xylene (and para-ethyltoluene, if present) is more selectively adsorbed and retained by the adsorbent, while the other components are relatively unadsorbed and the adsorbent It is removed from interstitial void spaces between particles and from the surface of the adsorbent. These more selectively adsorbed adsorbents containing para-xylene are referred to as "rich" adsorbents--adsorbents that are more selectively adsorbed para-xylene. Next, para-xylene is recovered from the rich adsorbent by contacting the rich adsorbent with the desorbent material under desorption conditions.

In this process, which uses a zeolite adsorbent and is generally operated at a substantially constant pressure and temperature to ensure that it is in a liquid state, the reliable desorbent material is: They must be chosen wisely to satisfy some criteria. First, the desorbent material removes the extract component from the desorbent without the extract component itself being adsorbed too strongly to prevent it from displacing the desorbent material in subsequent adsorption cycles. It should be replaced with a reasonable mass flow. Second, the desorbent material must be compatible with the particular adsorbent and the particular feed mixture. More specifically, these desorbent materials reduce or impair the critical selectivity of the adsorbent for the extract component, for the raffinate component, or chemically react with the feed component. Not be. The desorbent material should also be easily separable from the feed mixture that is fed into the process. Both the raffinate component and the extract component are typically removed from the adsorbent that is in a mixed state with the desorbent material, but if not by a method that separates at least some of the desorbent material, the extraction The purity of the liquor and raffinate products will not be too high and the desorbent material will not be effective for reuse in this way. Thus, in the extract and raffinate streams, it is possible to separate at least a portion of the desorbent material from the feed components by simple fractional distillation, thereby regenerating the desorbent material in this manner. To be usable, any desorbent material used in the process must have an average boiling point that is substantially different from the boiling point of the feed mixture or any of its components, i.e., no less than about 20 <0> C. Is intended.

Finally, the desorbent material should be readily available and the cost should be reasonable.

As discussed above, there are several criteria that must be met for the sorbent / desorbent pair. Suitable desorbents or desorbents for a particular separation by a particular adsorbent are generally not predictable. The present inventor further provides the adsorbent of the present invention /
The water content of the desorbent system depends on the above selection criteria and on the adsorbent / desorbent pair,
In particular, it has been found that the effect of using an ether-based desorbent can be significantly affected.

EXAMPLES The present inventor studies the effect of changing the concentration of water on the X-type zeolite adsorbent / ether desorbent system to determine the effectiveness of ethers as desorbents. For this purpose, the following test was conducted.

Example 1Production of Ba-X zeolite by ion exchange The starting material used was Na-X zeolite (Si / Al molar ratio = 1.0, ie SiO 2_Two/ Al _Two O_Three(Molar ratio = 2.0). See here for suitable Na-X zeolites
Nos. 5,370,859 and 3,7, incorporated herein by reference.
It can be synthesized using the methods outlined in 89,107.

The following procedure was used to make barium exchanged X-zeolite: 7.84 g of Ba (NO ₃ ) ₂ was added to water to give a total volume of 100 mL.

Next, 1.0 g of Na-X zeolite was added to 10.0 g of the above Ba (NO ₃ ) ₂ solution.

Next, the Na-X / Ba (NO ₃ ) ₂ suspension was added to 25 mL of Teflon (registered trademark).
) Placed in a lined Parr autoclave and spun at 43 rpm at 80 ° C for 16.5 hours.

The obtained Ba-X zeolite was filtered and then washed with ２００200 mL of water. Next, the Ba-X zeolite was air-dried at 65 ° C. overnight.

The zeolite was used at 122 ° C. for 16 hours prior to use in subsequent adsorption tests.
Dried for 3 hours at 300 ° C for an hour.

Example 2 Adsorbent without added water / IPE desorbent system In this experiment, barium exchanged X zeolite was used as the adsorbent. All reagents and materials used were carefully kept dry using appropriate means, unless otherwise noted.

[0046] About 4 g of the above adsorbent is mixed with about 2 g of the title ether desorbent and a known amount of ethylbenzene, meta-xylene, para-xylene and ortho-xylene containing 2.0 g.
The vial was carefully weighed with g of mixed xylene. 0.1 g of GC tracer (triisopropylbenzene) was also added to the adsorbent / desorbent / xylenes system. This tracer, in this case triisopropylbenzene, is not adsorbed by the adsorbent and therefore measures the composition change of the free liquid in the system,
Thus, it is known that the amount of each component adsorbed by the adsorbent can be used as a standard or reference that is measured by difference.

The above system was equilibrated at 140 ° F. for 3 hours. A sample of the free liquid in the system was removed with a syringe and injected into a gas chromatograph (GC). Using the GC results and the known amounts of components added to the system, the capacity and selectivity of the system were calculated by difference. The calculation results for this example are given in Table 1.

Example 3 Adsorbent / IPE Desorbent System with 4% by Weight of Added Water The procedure used in this experiment was that a controlled amount of water was added to the title system with the tracer triisopropylbenzene. The procedure was the same as that used in Example 2, except that it was added. In this example, 0.16 g of water was added to bring the system to 4% water by weight based on the dry weight of the adsorbent.

The calculation results of this embodiment are given in Table 1.

Example 4 Adsorbent / IPE Desorbent System with 5.9% by Weight Added Water The procedure used in this experiment was that a controlled amount of water was added to the title system along with a triisopropylbenzene tracer. The procedure was the same as that used in Example 2, except that it was added. In this example, 0.236 g of water was added to bring the system to 5.9 wt% water based on the dry weight of the adsorbent.

The calculation results of this embodiment are given in Table 1.

Example 5 Adsorbent / IPE Desorbent System with 9.6% by Weight Water The procedure used in this experiment was to add a controlled amount of water to the title system along with a triisopropylbenzene tracer. Except as noted, the procedure was the same as that used in Example 2. In this example, 0.384 g of water was added to bring the system to 9.6% water by weight based on the dry weight of the adsorbent.

The calculation results of this embodiment are given in Table 1.

[0054]

Example 6 Ba-X zeolite adsorbent / MTBE desorbent system without added water In this experiment, barium exchanged X zeolite was used as the adsorbent. All reagents and materials used were carefully kept dry using appropriate means, unless otherwise noted.

About 4 g of the above adsorbent is mixed with about 2 g of the title ether desorbent and a known amount of ethylbenzene, meta-xylene, para-xylene and ortho-xylene containing 2.0 g.
Weighed into vial with g of mixed xylene. 0.1 g of GC tracer (triisopropylbenzene) was also added to the adsorbent / desorbent / xylenes system. This tracer, in this case triisopropylbenzene, is not adsorbed by the adsorbent and therefore measures the composition change of the free liquid in the system, thus differentiating the amount of each component adsorbed by the adsorbent. It is known that it can be used as a standard or reference measured by

The above system was equilibrated at 140 ° F. for 3 hours. A sample of the free liquid in the system was removed with a syringe and injected into a gas chromatograph (GC). Using the GC results and the known amounts of components added to the system, the capacity and selectivity of the system were calculated by difference. The calculation results for this example are given in Table 2.

Example 7 Ba-X Zeolite Adsorbent / MTBE Desorbent System with 9.6% by Weight of Water The procedure used in this experiment was that a controlled amount of water was added to the title system using triisopropyl The procedure was the same as that used in Example 6, except that it was added with the benzene tracer. In this example, 0.384 g of water was added to bring the system to 9.6% water by weight based on the dry weight of the adsorbent.

The calculation results for this example are given in Table 2.

[0060]

Relatively 8 Ba-X Zeolite Adsorbent / Toluene Desorbent System In this experiment, barium exchanged X zeolite was used as the adsorbent. All reagents and materials used were carefully kept dry using appropriate means, unless otherwise noted.

[0062] About 4 g of the above adsorbent was weighed into a vial with about 2 g of toluene desorbent and 2 g of mixed xylene containing known amounts of ethylbenzene, meta-xylene, para-xylene and ortho-xylene. About 0.1 g of GC tracer (triisopropylbenzene) was also added to the adsorbent / desorbent / xylenes system. This tracer, in this case triisopropylbenzene, is not adsorbed by the adsorbent and therefore measures the composition change of the free liquid in the system, thus differentiating the amount of each component adsorbed by the adsorbent. It is known that it can be used as a standard or reference measured by

The above system was equilibrated at 140 ° F. for 3 hours. A sample of the free liquid in the system was removed with a syringe and injected into a gas chromatograph (GC). Using the GC results and the known amounts of components added to the system, the capacity and selectivity of the system were calculated by difference. The calculation results for this example are given in Table 3.

A relatively 9 Ba-X zeolite adsorbent / para-diethylbenzene desorbent system In this experiment, barium exchanged X zeolite was used as the adsorbent. All reagents and materials used were carefully kept dry using appropriate means, unless otherwise noted.

About 4 g of the above adsorbent was weighed into a vial along with about 2 g of para-diethylbenzene desorbent and about 2 g of mixed xylene containing known amounts of ethylbenzene, meta-xylene, para-xylene and ortho-xylene. About 0.1 g of GC tracer (triisopropylbenzene) was also added to the adsorbent / desorbent / xylenes system. This tracer, in this case triisopropylbenzene, is not adsorbed by the adsorbent and therefore measures the composition change of the free liquid in the system, thus differentiating the amount of each component adsorbed by the adsorbent. It is known that it can be used as a standard or reference measured by

The above system was equilibrated at 140 ° F. for 3 hours. A sample of the free liquid in the system was removed with a syringe and injected into a gas chromatograph (GC). Using the GC results and the known amounts of components added to the system, the capacity and selectivity of the system were calculated by difference. The calculation results for this example are given in Table 3.

[0067]

The results of Comparative Examples 8 and 9 shown in Table 3 are based on the same criteria and conditions as in the previous example using ethers of two commercially available desorbents commonly used in the PX adsorption process. Shown below is the selectivity and capacity. These results indicate that the ethers are
It shows that in terms of selectivity and capacity, it can be the same or better than commercial desorbents. These ether desorbents offer advantages over these commercial desorbents, especially in that they have a significantly lower boiling point than the commercial desorbents described above, and are therefore much easier and cheaper to separate. Diisopropyl ether and MTBE also provide p-DEB because they are less expensive.
Have significant advantages over The cost of the desorbent can be a significant capital and operating cost for the PX complex. Due to the loss of desorbent and contamination of the desorbent in these methods, supplemental desorbent is often required. Thus, inexpensive desorbents can provide significant benefits to the economics of the PX adsorption process.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, TZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CR, CU, CZ, DE, DK, DM, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID , IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG, UZ, VN, YU, ZA, ZW

Claims (11)

[Claims] 1. An adsorption separation method for separating para-xylene from a hydrocarbon feed comprising a mixture of C ₈ aromatic hydrocarbons, comprising the steps of: a) separating said feed under adsorption conditions of type X Contacting with an adsorbent bed comprising a crystalline aluminosilicate selected from the group consisting of and zeolite of type Y, thereby adsorbing para-xylene from its feed; b) dissolving said adsorbent bed in desorption conditions with diisopropyl ether And a desorbent material comprising an ether selected from the group consisting of methyl tert-butyl ether and c) comprising from the adsorbent bed desorbent and less selectively adsorbed components of the feed. Removing a stream; and d) removing a stream comprising a desorbent and said para-xylene from said adsorbent bed. Wherein, if the desorbent material comprises diisopropyl ether, the water content is maintained at 1-8% by weight based on the weight of the adsorbent, and if the desorbent material comprises methyl tert-butyl ether, Such a method, wherein the water content is maintained at less than 4% by weight based on the weight of the adsorbent. 2. The method of claim 1, wherein the adsorbent bed further comprises one or more alkali metal or alkaline earth metal ions at the exchangeable cation sites of the crystalline aluminosilicate. . 3. The water content is maintained at 2 to 6% by weight based on the weight of the adsorbent when the desorbent material comprises diisopropyl ether, and the water content is maintained when the desorbent material comprises methyl tert-butyl ether. The method according to claim 1, wherein the content is kept below 3% by weight based on the weight of the adsorbent. 4. The method of claim 2, wherein the one or more alkali or alkaline earth metals is selected from the group consisting of barium, potassium, calcium, strontium, and cesium. 5. The method of claim 1, wherein the adsorbent bed further comprises barium at the exchangeable cation sites of the crystalline aluminosilicate. 6. The method according to claim 1, wherein when the desorbing substance comprises diisopropyl ether, water in the adsorption separation method is kept at 2 to 5% by weight based on the weight of the adsorbent.
The method described in. 7. The method of claim 1, wherein the adsorption separation method is a simulated moving bed countercurrent adsorption separation method. 8. The following: e) a stream containing the desorbent and less selectively adsorbed components was less selectively adsorbed with a second stream containing the desorbent. F) separating said second stream containing said desorbent and para-xylene into a third stream containing said desorbent and a stream containing para-xylene The method of claim 1, further comprising the step of: 9. The following: g) combining a second stream containing the desorbent with a third stream containing the desorbent; and h) combining at least a portion of the combined desorbent stream described above. From step g) to step b
9. The method of claim 8, further comprising the step of) recirculating to at least a portion of the source of the desorbent material. 10. The method of claim 1, wherein the desorbent material comprises methyl tertiary butyl ether, and wherein water is maintained at less than 2% by weight based on the weight of the sorbent. 11. The method of claim 1, wherein the desorbent material comprises methyl tertiary butyl ether, and wherein water is maintained at less than 1% by weight based on the weight of the adsorbent.