JPH035429A - Separation of p-isomer of dialkyl-substituted aromatic hydrocarbon - Google Patents

Abstract

PURPOSE: To efficiently separate the p-isomer by bringing an isomer mixture of the subject compound into adsorptive separation using a specific zeolite-based adsorbent and a fluoro-substituted aromatic hydrocarbon desorbent.

CONSTITUTION: A raw material flow containing a mixture of p-isomer and other isomers of a dialkyl-substituted aromatic hydrocarbon is brought in contact with an adsorbent containing a crystalline aluminosilicate (e.g. zeolite X or Y) possessing Ba and K at a mol ratio of BaO/K₂O=0.6:1 to 1.2:1, especially 0.9:1 to 1.1:1 at the exchangeable cation site within the crystal structure of the adsorbent. The p-isomer is adsorbed by this adsorbent and then brought into contact with a desorbent selected from mono- or difluoro-substituted aromatic hydrocarbon or a mixture of these two to obtain the product richer in p-isomer than the raw material flow. The adsorption and desorption process is conducted at 20 to 250°C, preferably 100 to 200°C under a pressure adequate for maintaining the vapor phase.

COPYRIGHT: (C)1991,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The technical field to which this invention pertains is the adsorptive separation of hydrocarbons. More specifically, the present invention provides the use of certain zeolite-based adsorbents and desorbents to extract certain fluoro-substituted aromatic hydrocarbons from feedstock mixtures containing the p-isomer and at least one other isomer of dialkyl-substituted aromatic hydrocarbons. The present invention relates to a method for separating the p-isomer using group hydrocarbons, and particularly to a method for separating p-xylene from a raw material mixture containing the at least two aromatic isomers (including the p-isomer).

[Background of the invention]

In the field of separation technology, certain types of crystal lines (c
It is well known that rystal-1ine) aluminosilicates can be used.

For example, the separation of n-paraffin and side chain paraffin is
This can be done by using a type A zeolite having about 5 pores. Such a separation process is called Bro
U.S. Patent No. 2,985,589 and 5t of Ughton et al.
Ine No. 3,201,491. Using these adsorbents, it is possible to separate based on the physical size of one molecule, and the smaller n-paraffin molecules can enter the voids of this zeolite adsorbent.
Side chain paraffins with larger molecular weights cannot enter. Type X or Y type adsorbents are used to separate different types of hydrocarbons, but also to separate hydrocarbon isomers. For example, Neuzil U.S. Pat. No. 3,626,020, Nauzil U.S. Pat. No. 3,663
, 638. Rosset's 3,665,046, C
3,668,266 by Hen et al., 3,686,342 by Neuzil et al., 3,700 by Berger et al.
, 744, Neuzil, 3,734,974. R
Osback's 3,894,109, Neuzil's 3,997,620 and Hedge's B426,2
The method described in No. 74 involves the separation of p-isomers of dialkyl-substituted monocyclic aromatics from other isomers, in particular
Certain zeolitic adsorbents have been used to separate xylene from other xylene isomers. 5tine
patents (as one possibility among a very large group) exchanged with Ag or Ag/ It is said that only 0-xylene could be separated during the process (which appears to be distillation).

Many of the above patents use benzene as a desorption agent.

Toluene or p-diethylbenzene is used. It is already known that the use of benzene as a low-boiling desorbent in contact with an adsorbent results in disadvantages (Neuzil
No. 3,686,342).

In the case of toluene, it is difficult to recover the desorbent from the extract and raffinate by separating the xylene isomers. This is because the boiling point of toluene is very close to the isomers being separated.

For this reason, materials with even lower boiling points are preferred to meet the selectivity requirements for the adsorbent described below. Other patents also refer to the separation of p-xylene from other xylene isomers by zeolite exchanged with constant weight ratios of Ba and K (eg, U.S. Pat. No. 3,663,638.
3,878,127, 3,878,129, 3,
686,342, 3,558,732).

Further, JP-A No. 62-5155, filed on March 3, 1960, separates aromatic isomers by adsorption on X-type zeolite exchanged with metals such as Ba, Ca, Na, etc. As the exchange liquid, benzene, toluene, chlorobenzene, 1-fluoroalkane, α,ω-dihaloalkane, halogen-substituted benzene, and halogen-substituted toluene can be used depending on the raw material mixture. For example, benzene is used for xylene and/or ethylbenzene, toluene for trimethylbenzene or ethyltoluene, and chlorobenzene for mixtures of halogenated aromatic isomers.

Barthomenf U.S. Patent No. 4,584,424
discloses the separation of ethylbenzene and xylene by selective adsorption on β-zeolite. p-diethylbenzene is the preferred desorbent for this separation, but monohalobenzenes, especially iodobenzenes, have also been described.

(Summary of the Invention) One embodiment of the present invention, in summary, obtains the dialkyl-substituted aromatic p-isomer from a feed mixture containing the dialkyl-substituted aromatic p-isomer and at least one other isomer. In a preferred embodiment, p-xylene is separated from a feed mixture containing p-xylene and at least one other xylene isomer or ethylbenzene. The ratio of barium oxide to potassium oxide is approximately 0.6:1 to 1.
．． It is characterized by contacting an adsorbent comprising a crystalline aluminosilicate, such as a zeolite of type X or Y, in a molar ratio corresponding to 2:1, preferably 0.9:1.1. This raw material was then converted into the obtained adsorbent-containing p-
After removal from the isomers, a concentrated stream of p-isomers is recovered by desorption under desorption conditions with a desorbent containing a monofluoro- or difluoro-fractionated aromatic hydrocarbon or mixtures thereof.

Other embodiments of the invention, including details about feedstock mixtures, flow outlines, and operating conditions, are described below.

[Description of the invention]

To first clarify the operation, objects, and advantages of the present invention, it is helpful to define various terms used in this specification.

A "feed mixture" is a mixture containing one or more extractive components and one or more raffinate components that is fed to the adsorbent of the process. The term "feed stream" refers to the flow of the feed mixture through the adsorbent used in the process.

"Extractive components" are single compounds or groups of compounds such as aromatic isomers that are selectively adsorbed in relatively large quantities by the adsorbent, while "raffinate components" are relatively few and selectively adsorbed. A compound or compounds of that type. In this process, the p-isomer of xylene is the sole extractive component and one or more other C1 aromatics are the raffinate components. The term "raffinate stream" or "raffinate output stream" refers to the stream in which raffinate components are removed from the adsorbent.

The composition of the raffinate stream can vary from essentially 100% desorbent (defined below) to essentially 100% raffinate component. The term "extraction stream" or "extraction output stream" means the stream in which the extractant desorbed by the desorbent is removed from the adsorbent. Similarly, the composition of the extract stream can vary from essentially 100% desorbent to essentially 100% extractant. Although it is possible to obtain high purity extract products (defined below) or raffinate products (defined below) with high recoveries by the method of the present invention,
It is recognized that the extract components are never completely adsorbed by the adsorbent or the raffinate components are never completely adsorbed by the adsorbent. Thus, small amounts of raffinate components may be present in the extract stream, and likewise small amounts of extract components may be present in the raffinate stream.

The extract stream and the raffinate stream are then further differentiated from each other and from the feed mixture by the concentration ratio of extract components to specific raffinate components present in a particular stream. For example, the ratio of the concentration of the relatively selectively adsorbed p-isomer to the concentration of the less selectively adsorbed o-, m-isomer or ethylbenzene is highest in the extract stream, followed by the feedstock. It is highest in the mixture and lowest in the raffinate stream.

Similarly, the concentration ratio of the less selectively adsorbed m- or 0-isomer or ethylbenzene to the more selectively adsorbed p-isomer is highest in the raffinate stream;
It is then highest in the feed mixture and lowest in the extract stream.

The term "desorbent" generally refers to a material capable of desorbing extracted components. The term "desorbent stream" or "desorbent input stream" refers to the flow of the desorbent through the adsorbent. When the extract stream and the raffinate stream contain a desorbent, at least a portion of the extract stream, preferably at least a portion of the raffinate stream from the adsorbent, is passed through a separation means, such as a fractionator, which
At least a portion of the desorption material is separated under separation conditions to produce an extracted product and a raffinate product. "Extract product" and "raffinate product" mean a product made by a process that contains higher concentrations of extract and raffinate components than in the extract and raffinate streams, respectively. "Selective pore volume" of the adsorbent The term is defined as the capacity of an adsorbent to selectively adsorb extracted components from a feed mixture.
The term "non-selective void capacity" is the capacity of an adsorbent that does not selectively retain extracted components from the feed mixture.

This volume includes the adsorbent void space, which does not include adsorption sites or void spaces between adsorbent particles. This selective pore volume and non-selective void volume are generally expressed in volumetric quantities and are important in determining the proper flow rate of liquid required to drive an effective operating process for a given amount of adsorbent. .

The raw material mixture that can be used in the method of the present invention is C.

C, , C1a, C11 or C12 dialkyl-substituted aromatic hydrocarbons, and other dialkyl-substituted aromatic hydrocarbons within this range are ethyltoluene (C,),
Diethylbenzene (C), cymene (isopropyltoluene) (C), ethylisopropylbenzene (C)
), diisopropylbenzene (Ciz), etc.
It is a substituted dialkylbenzene.

Said p-substituted dialkylbenzenes can be obtained in large quantities by alkylation processes; for example, cymene isomer mixtures are obtained by alkylation of toluene, and other raw materials are also present. The above raw materials mean the raw materials used in the method of the present invention. Mixtures containing significant amounts of p-xylene and other C6 aromatic isomers are generally produced by modification and isomerization processes. Note that these processes are well known in the refining and petrochemical fields. In addition, methods for preparing isomer compositions that require separation include alkylation and dehydrocyclo-dimerization.
n).

In the reforming process, the naphtha feedstock is converted to pt-1 with selected severity to obtain an eluent stream containing the C1 aromatic isomer.
The sixth reformate contacted with the halogen-containing catalyst is generally C
, fraction (including C8 non-aromatics along with aromatic isomers)
Fractional distillation is performed to concentrate the C1 aromatic isomer therein.

The xylene isomerization process is a method of isomerizing a xylene mixture deficient in one or more isomers under isomerization conditions to obtain an eluent stream containing C1 non-aromatics along with an equilibrium amount of O8 aromatic isomers. The equilibrium compositions of xylene isomers and ethylbenzene at each temperature are shown in Table 1 below.

Table-1 Equilibrium composition temperature of C8 aromatics "C327427527 Mol% of C6 aromatic isomers Ethylbenzene 6811 p-xylene 22 22 21
m-xylene 50 48 45
0-xylene 22 22 23
Too too io.

The raw material mixture contains a small amount of straight or side chain paraffins.

These amounts are preferably kept to a minimum to prevent contamination of the process product with materials that are not selectively adsorbed or separated by the adsorbent, which may include cycloparaffins or olefinic materials. The amount of contaminants (or impurities) is determined by the amount of raw material mixture introduced into the process (
When this mixture is contacted with an adsorbent to separate p-xylene, preferably less than about 20% of the p-xylene (by volume), a relatively large amount of p-xylene is selectively adsorbed and retained by the adsorbent. In contrast, other components are relatively unadsorbed and are removed from the void space between the adsorbent particles and the adsorbent surface. An adsorbent containing a relatively large amount of selectively adsorbed p-xylene has a relatively large amount of selectively adsorbed p-xylene.
Primary p-xylene, referred to as a "rich" xylene-enriched adsorbent, is removed from the rich adsorbent by contacting the rich adsorbent with a desorbent.

In order to separate the P-isomer in the other raw materials mentioned above, the same process as above can be carried out to obtain an extracted fraction containing the P-isomer as the main component. The same method can be used to obtain similar results.

The desorbent may be a liquid material capable of selectively removing adsorbed feedstock components from the adsorbent. - Generally speaking, in swing bed systems where selectively adsorbed feedstock components are removed from the adsorbent by a purge flow, the choice of desorbent is less important, and methane, ethane, etc. are used to expel the adsorbed feedstock components from the adsorbent. Gaseous hydrocarbons such as N z + H2 and other types of gases can be used at high temperature or at reduced pressure or both. However, in adsorptive separation processes that use zeolitic adsorbents and generally operate at constant pressure and temperature to maintain a liquid phase, the l&fl materials used must be clearly defined to meet several criteria. You have to choose.

First, the desorbent must displace extractable components from the adsorbent at a reasonable mass flow rate without being adsorbed so strongly as to unduly prevent the replacement of extracted components with desorbent in subsequent adsorption cycles. Expressed in terms of selectivity (discussed in more detail below), it is preferred that the adsorbent be more selective for the raffinate component to the extracted component than the desorbent is for the raffinate component.

Second, the desorbent must be compatible with the particular adsorbent and the particular raw material mixture. More specifically, the desorbent must not reduce or eliminate the critical selectivity of the raffinate component of the adsorbent to the extract component. Furthermore, the desorbent used in the process of the present invention must be a substance that can be easily separated from the raw material introduced into the process; after desorbing the extracted components in the raw material, the desorbent and extracted components are generally separated from the adsorbent. removed in a mixed state. Similarly 1
Although more than one raffinate component is typically removed from the adsorbent in admixture with the desorbent, the purity of the extracted components may vary from raffinate product unless a separation method such as distillation is used to separate at least a portion of the desorbent. The purity is not very high either. Therefore, in order to separate the desorbent from the feed components in the extract and raffinate streams by simple fractional distillation and reuse the desorbent in the process, the desorbent used in the process has an average boiling point different from that of the feed mixture. be construed as being materially different. As used herein, the term "substantially different" means that the average boiling point difference between the desorbent and the raw material mixture is at least about 5°C, preferably 40°C. The boiling point range of the desorbent may be higher or lower than that of the raw material mixture;
A lower value is preferable from the advantage of economical operation.

As will be described later, Ba and cation exchange X- or Y- where Ba and cations are present in an amount corresponding to a ratio of barium oxide to potassium oxide of 0.6:1 to 1.2:1.
When using type zeolites as adsorbents, effective desorbents have been found to be monofluoro- or difluoro-substituted aromatic hydrocarbons such as monofluorobenzene, 0- or m-difluorobenzene, or mixtures thereof.

The 0- or m-difluorobenzene of the present invention is a known compound, as described in the literature, for example Kirk-Othmer, vol.
10.1980. pp. 909-14. Also, methods for preparing fluorobenzene are well known; for example, Kirk-Othmer, vol. 9 (19
66)pp.

781-3.

It has been known in the prior art that certain properties of adsorbents are highly desirable, if not absolutely necessary, for successful selective separation processes. Among these properties are the adsorption capacity of the extracted components per volume of the adsorbent, the selective adsorption of the extracted components with respect to the raffinate components and the desorbent, and the sufficient adsorption and desorption rate of the extracted components on the adsorbent. There are things like being fast. Of course, the ability of the adsorbent to adsorb a specific volume of one or more extract components is a prerequisite; without such ability, the adsorbent is useless for adsorptive separation. Furthermore, the higher the ability of the adsorbent to handle extracted components, the better the adsorbent. Increasing the capacity of a particular adsorbent makes it possible to reduce the amount of adsorbent required to separate extractive components at a particular loading rate of the feed mixture. The cost of the separation process is also reduced by reducing the amount of adsorbent required for a particular adsorptive separation. Good initial capacity of the adsorbent is preferably maintained during service in the separation process for an economically favorable lifetime.

The second necessary property of the adsorbent is the ability to separate the components of the raw material. In other words, the adsorbent has a certain adsorptive selectivity (B) for one component over other components. Specific selectivity can be expressed not only for one component relative to other components, but also for any raw material mixture component and desorbent. As used herein, selectivity (8) is defined as the ratio of the same two components in the adsorbed phase to the ratio of the two components in the non-adsorbed phase at equilibrium conditions.

The specific selectivity is as shown in Equation 1 below.

Equation 1 (However, C and D represent the two components in the raw material in vol and %, respectively, and the appended ^ and U represent the adsorbed phase and non-adsorbed layer, respectively.) The equilibrium condition is that the raw material passing over the adsorbent bed Measured when the composition does not change after contact with the adsorbent bed.

In other words, under these conditions, there is no movement of material that occurs between the non-adsorbed layer and the adsorbed layer.

When the selectivity of the two components approaches 1.0, the adsorbent no longer preferentially adsorbs one component over the other. That is, in this case, the two components are adsorbed to the same extent (or not adsorbed) to each other, and as (B) becomes smaller or larger than 1.0, one component of the adsorbent becomes preferential to the other. Adsorption occurs. If the selectivity of component C by the adsorbent is greater than that of component C, then 1.0
A larger (B) would indicate preferential adsorption of component C in the adsorbent. (B) smaller than 1.0 indicates that the component is preferentially adsorbed away from the component C-rich non-adsorbed layer and the component-rich adsorbed phase. Separation of the extract component and the raffinate component is theoretically possible when the selectivity of the adsorbent for the extract component with respect to the raffinate component exceeds a value of just 1.0, but the selectivity of 1 approaches 2 or It is preferable that the value exceeds 2. Similar to the specific volatility, the higher the 2 selectivity, the easier it is to perform layer separation. ,
The higher the selectivity, the lower the amount of adsorbent used in the process.

Ideally, the desorption material has a selectivity equal to about 1 or less for all extractable components so that all extractable components can be extracted as a class and all raffinate components are clearly discharged into the raffinate stream.

The third important property is the rate of exchange of extractive components in the feed mixture, or in other words the relative rate of desorption of extractive components. This property is directly related to the amount of desorption material required to be used in the process of recovering extracted components from the adsorbent. If the exchange speed is fast,
The amount of desorption material required to remove extractable components is reduced, thus reducing the operating costs of this process. As exchange rates increase, less desorption material must be pumped into the process and separated from the extraction stream for reuse.

Dynamic test equipment is used to test various adsorbents and desorbents with specific feedstock mixtures to determine the adsorption capacity and exchange rate characteristics of the adsorbent. The apparatus consists of an adsorption chamber with a volume of approximately 70 cc having an inlet and an outlet at opposite ends of the adsorption chamber. This chamber is within the temperature control means and a pressure controller is used to operate the chamber at a predetermined constant pressure. The outlet line of this chamber can be equipped with a chromatographic analyzer and used to analyze the "on -5 trea+i", ie, eluent stream leaving the adsorbent chamber.

Pulse tests performed using this apparatus and the following general method are used to determine data such as selectivity for various adsorption systems. By passing the desorbent material through the adsorbent chamber, the adsorbent is filled until it is in equilibrium with the particular desorbent material.

At desired times, pulses of feedstock containing known concentrations of unadsorbed paraffinic tracer (e.g., n-nonane) and specific aromatic isomers diluted with desorbent are injected over several minutes. The desorbent flow is resumed and the tracer and aromatic isomer are eluted as in liquid-isomer chromatographic operation. The eluate can be analyzed by on-current chromatography and tracing the envelope of the developed corresponding component peaks. Alternatively, collect elution samples periodically and then
It can be analyzed separately by gas chromatography.

The performance of the adsorbent, such as the capacity index for the extracted component, the selectivity for one isomer relative to other isomers, and the rate of desorption of the extracted component by the desorbent, is evaluated from the information obtained by the chromatographic trace. The performance index is characterized by the distance between the center of the peak envelope of the selectively adsorbed isomer and the peak envelope of the tracer component or other known point of reference. The index is expressed as the volume of desorbent (aJ) pumped during this time interval. Selectivity (B) is the center of the peak envelope of the extractant and the peak envelope of the tracer (or other reference point) for the raffinate component versus the extractant.
and the corresponding distance between the center of the peak envelope of the raffinate component and the peak envelope of the tracer.

The exchange rate of extracted components by the desorption material is generally 172 strength (
It can be characterized by the difference between the width of the peak envelope of C9 (tracer) and the width of the peak envelope of p-xylene (adsorbed species) at (sometimes written as W). The narrower the width of this peak, the faster the desorption rate. The desorption rate is also characterized by the distance between the center of the tracer's peak envelope and the vanishing point of the just-desorbed extracted component. This distance is also expressed as the volume of desorption material pumped during the time interval.

The adsorbent used in the method of the invention has a B
It is a crystalline aluminosilicate containing a and K in a specific ratio. Crystalline aluminosilicate as in the scope of the present invention has a crystalline aluminosilicate cage structure in which regular tetrahedrons of alumina and silica are strongly bonded in a three-dimensionally open network structure. These regular tetrahedra are bridged by the sharing of oxygen atoms and spaces between the regular tetrahedra occupied by water molecules before dehydration of some or all of the zeolite. Dehydration of zeolites produces interlaced crystals of molecular-scale cells. For this reason, if the separation that occurs with crystalline aluminosilicates is essentially due to differences in the size of the raw material molecules, for example when relatively small n-paraffin molecules are separated from relatively large isoparaffin molecules by using specific molecular sieves. , crystalline aluminosilicates are often referred to as "molecular sieves." Although the term "molecular sieve" is widely used in the method of the present invention, the separation of specific aromatic isomers is apparently due to adsorption with the various isomers rather than due to the pure physical size of the isomer molecules. Strictly speaking, this is not appropriate because this is due to the difference in electrochemical attraction between the two and the agent.

Crystalline aluminosilicates generally include zeolites represented by the following formula in their hydrated state.

People M2/, 10: An, O,: wsio,:
yH20 However, 11 M IT is a cation that balances the ion valence of the regular tetrahedron, and is generally called an exchangeable cation site. 'n' represents the valence of this cation, 'w' represents the number of moles of SiO□, and 'yIT represents the number of moles of water. - The filmed cation "M" may be a monovalent, divalent or trivalent cation, or a mixture thereof.

It is generally recognized in the prior art that type X and type Y zeolitic adsorbents can be used in certain adsorptive separation processes. These zeolites are well known in the art.

Zeolite having an X-type structure in a hydrated state or a partially hydrated state can be expressed in terms of molar oxides as shown in the following formula 2.

Person (0,9ゝ0.2)M,, nO: A Q zO,:
(2,5ゝ0.5)SiO2: yt120 but 11
M fir is at least 1811 with a valence of 3 or less
The cation of tl nII is the valency of l(M
The molar ratio of in2/A Q 20□ is 2.5ゝ0.2. The cation "M" may be one or more hydrogen cations, alkali metal cations, or alkaline earth cations, or other selected cations, and is commonly referred to as an exchangeable cation site. Since type X zeolites were first made, the cation “M” is usually mostly Na.
Therefore, this zeolite is called Na-X type zeolite. However, depending on the purity of the reactants used to produce the zeolite, other cations such as those mentioned above may be present as impurities.

A zeolite having a Y-type structure in a hydrated or partially hydrated state can be similarly expressed by a molar oxide as shown in the following formula 3.

Formula' - (0,910,2)M2. no: ^U, O, :suSin
, : yl120 However, 11 M" is at least one cation having a valence of 3 or less. 11 nty is "M
Valence of Tt.

"w" is a value larger than about 3 to 6, and "yu is gi M
The value is about 9 or less depending on the type of jj and the degree of hydration of the crystal. Therefore, 5i02 for zeolites with Y-type structure
The molar ratio of /AQ,O□ may be from about 3 to about 6. Similar to the X-structured zeolite, the cation "M" can be one or more of a variety of cations, but the Y-type zeolite is initially As created, the cation “M” is also mostly Na.

Therefore, Y-type zeolite containing mainly Na in exchangeable cation sites is called Na-Y-type zeolite.

Representative zeolites useful in the present invention are as described above.

However, exchange of cations in the olide is necessary as it is produced by a specific range of mixtures of Ba and Ba ions. Ba and K are Ba O/K in the zeolite formula
The final molar ratio of zO is 0.6: 1 to 1.2: 1,
Preferably, they are exchanged in relative amounts of 0.921 to 1.1:1. This exchange may be carried out in one step using a mixture of Ba and K in such a ratio that the final zeolite obtained falls within the range mentioned above, or alternatively, it may be carried out in one step using a mixture of Ba and K in proportions such that the final zeolite obtained falls within the above range, or alternatively, each step may be carried out in such a way that the correct desired range of zeolite is obtained. It may be carried out continuously by ion exchange of a suitable amount.

It has been found that it is necessary to use a zeolite with O in the above range for BaO/. If this ratio is too large, the p-xylene retention capacity will become very large. Such a large retention capacity indicates a long desorption time. If this ratio is lower than the specified range, the selectivity of the adsorbent to the desorbent becomes too great and p-xylene will not effectively replace the desorbent in the next cycle.

Typical adsorbents used in separation processes are a dispersion of crystalline zeolite material in an amorphous or inorganic matrix with channels and cavities that allow the liquid to access the zeolite and also serve as a binder for the zeolite powder. It is. Such inorganic matrices include, for example, silica, alumina or certain clays and mixtures thereof. This binder helps shape or solidify the fine powdery crystalline particles.

Therefore, the adsorbent can be used in a desired particle size range, preferably from about 16 to about 60 mesh (standard U, S mesh) (250
~1190 microns) extrudates, aggregates, tablets 1
Lower water content in the adsorbent, which may be in the form of spheres or powder, is advantageous as it also reduces water impurities in the product.

The adsorbent can be used in the form of a dense fixed bed in alternating contact with the feed mixture and the desorbent. The process in this case is limited to semi-continuous operation. In other embodiments, the feed mixture passes through one or more adsorbent beds of a set of two or more static adsorbent beds, while the desorbent material passes through one or more other adsorbent beds of the set of two or more static adsorbent beds. A set of adsorbent beds may be used, suitably valved to allow passage through the adsorbent beds. The feed mixture and desorbent can flow either upwardly or downwardly into the adsorbent in such a bed.

However, moving bed or simulated moving bed flow systems are preferred because of their much greater separation efficiency than fixed beds; in moving bed or simulated moving bed processes, retention and displacement operations occur continuously, resulting in continuous production of extract and raffinate streams. Continuous use of feedstock and displacement liquid streams can be performed. One preferred embodiment of the invention is the use of what is known in the art as a simulated moving bed countercurrent flow system.

In such systems, it is the forward movement of multiple liquid access points on the chamber that simulates the upward movement of the molecular sieve within the chamber. D. B. Broug
U.S. Pat.
At the annual general meeting of the Society of Chemical Engineers, Hari, B., and Broughton presented “
They are published under the title ``Continuous Adsorption Processing...A New Separation Technology,'' so you can also refer to them.

Both documents are incorporated herein as reference in order to further explain the outline of the simulated moving bed countercurrent process flow.

Other embodiments of simulated moving flow systems suitable for use in the method of the present invention include Gerhold U.S. Pat.
02,832 (The entire text is included here for reference.

) is a co-current high-efficiency simulated moving bed process.

At least a portion of the extraction output stream is passed through a separation means in which at least a portion of the desorbent is expected to be separated under separation conditions to yield an extracted product containing a low concentration of desorbent. . Although not necessary for the operation of the process, it is preferred that at least a portion of the raffinate output stream also be passed through separation means. In the saw, at least a portion of the desorbent is separated under separation conditions and the process yields a reusable desorbent stream and a raffinate product containing a low concentration of desorbent. Typically, the concentration of desorbent in the extraction and raffinate products is less than about 5 vol.%, preferably about 1 vol.%. %
less than

The separation means is usually a fractionating column. Its shape and operation are well known in the separation art.

Although liquid- and gas-phase open operations can also be used in many adsorptive separation processes, liquid-phase operation is preferred in the present process because of the lower temperatures required and liquid-phase operation is superior to gas-phase operation. This is due to the higher yield of extracted products compared to other methods. The adsorption conditions are a temperature range of about 20 to 250°C, preferably about 100 to about 200°C, and a pressure sufficient to maintain a liquid phase, specifically from atmospheric pressure to 600p.
sig (4238kPa). Desorption conditions are in the same range of temperature and pressure as for adsorption conditions.

Unit sizes that can be used in the process of the invention include pilot plant scale (e.g., U.S. Pat. No. 3,706,
812) to industrial scale, and flow rates can vary from as low as a few cc/hr to thousands of gallons/hr.

Examples are given below for illustrative purposes and to explain in more detail the selectivity relationships possible in the process of the present invention.

Example I In this experiment, P-xylene (bp 138°C) and other
In order to evaluate the ability of the present invention to separate aromatics (bp, 136-145°C), a pulse test was conducted using the apparatus as described above. The adsorbent used was Ba and cation exchanged Y zeolite in the following proportions.

A small amount of amorphous binder material consisting of clay was used. Zeolites contain K or Ba cations at substantially all exchangeable cation sites. The amounts and ratios are shown in the table. Cation exchange is 1 mole of KCQ
200cc of 1.5Q liquid at 500cc/hr at 50℃
upwards through a bed of adsorbent and then 0.2M
BaC+112 volume solution was circulated at IQ/hr for 4 hours,
Finally, it was washed with IQ water at 500 cc/hr. The adsorbent was calcined at 300°C.

For each pulse test, the column maintains liquid phase operation at a temperature of 150°C and a pressure of 150ρsig (1136k
Pa). A gas chromatographic analyzer was attached to the column effluent stream to measure the eluted material at regular time intervals.

The raw material mixture used for each test contained approximately 5 Vol. each of xylene isomers and ethylbenzene. %, n-nonane 5vol. used as trace. % and desorption material 75vol.
%.

The desorption materials for tests A, B, and C were m-difluorobenzene (m-D F B ) 30 vol, % and n-C,
Consists of paraffin residue. The desorption material for Test D was 100% m-difluorobenzene. The operations performed in each test are as follows. Desorption material is approximately 1.20c
It was run continuously at a speed of c/win. The run of the desorbent was stopped at appropriate time intervals, and the raw material mixture was pumped at 1 cc/min.
It was run for 10 minutes. The desorbent flow was then resumed and continued to flow through the adsorbent base until all of the raw aromatics had eluted from the tower, as measured by WA observation of the chromatograph produced in the elution stream exiting the adsorption tower.

The test results are shown in Table 2. Also, 1A, IB and IC
The chromatograph in the figure illustrates the invention. p
- The elution curve of xylene is clearly separated from other curves that are well separated.

Figure 1D shows a chromatograph for comparison, but the long desorption time would make it impractical.

This figure also shows that the desorption power decreases as the BaO/0 molar ratio increases beyond the range of the present invention. Note that the BaO/K*0 molar ratio used in the run in Figure 1D was 5.17:1. The relevant data calculated from this curve is as follows. ΔW (cc) is the difference in the width of the peak envelope at 1/2 of the peak height between p-xylene and n-C tracer, and is a measure of the exchange rate of the desorption material.

The capacity of p-xylene required to change the concentration by 10 to 90% is a measure of the adsorption rate of p-xylene.

Sd]9+1 is the capacity of the desorption material required to change the concentration of pixylene in the eluate by 90 to 10% of the maximum concentration, and is a measure of the desorption rate of p-xylene.

The capacity required for a 10-90% change in Sa is as follows.
It is called "adsorption breakthrough slope".The larger the value of Sd or Sa, the more
If the rate of desorption or adsorption is slow or rapid, respectively, then the selectivity of the adsorbent to p-xylene for the desorbent is less than 1 and is unfavorable for this adsorption process. The ideal system would have a p-xylene/desorbent selectivity slightly greater than 1 and a peak envelope of p-xylene with a low retention capacity. p-
The xylene/desorbent selectivity CB) can also be expressed as the Sd/Sa ratio.

Therefore, using the data in Table 2, Examples IC1IA and IB
becomes as follows.

Blc = Old = 1.34 BIA = Moth = 0.55 14.6 BIB'' 0.76 Therefore the selectivity of the adsorbent of Example IC for P-xylene is very good, whereas the adsorbents of Examples IA and IB The selectivity tends to be unfavorable.

Another trend shown in this example data is that the desorbent becomes weaker as the barium oxide/potassium oxide ratio increases.

(Leaving space below) Various types of Ba/Relative to Ba- -Y Pulse test percentage to Hojasite 1M, ... ICLD Loobu desorption material □30% n+-DFB -n+-
DFBn-C, 1/2 width (H, W,) 11.
5 9.94 12.312.9 Selectivity (B) B p/eb 3.27 3.53
3.32 4.64B p/s+
4.04 4.47 4.13 5.22B pl
o 3.40 3.64 3.56
5.16P-xylene holding capacity cc 16.4
17.0 34.7 78.9ΔWe c
0.04 1,3 6,9 32.5sa
]::c c 14.6 10.8 10.8
6.1Sd]:,'cc 8.0 8.3
145 30Sin, 60.6
60.9 607 59.0 AI, 0.
19.6 18.6 187 18.0, 0
8.8 8.6 69 2.
2Ba0 9,1 10.0 11
0 18.5Na, 0 0.72
0.53 068 0.58BaO/, Omore L
+ shape 0.63 0.71 098 5.1
Example 7 ■ Example IC was repeated except that the temperature was lowered to 125°C.

This result was hardly affected, as seen in Clothe 3 below.

Meshi lost B p/e 3.37B
p/m 4.21B ρ1
0 3.70Wcc
7,6n-C,H,W,cc
12.00 p-xylene holding capacity cc
34.0 BaO/20 mol 0.98 adsorbent Ba- to -Y and desorbent 30% m-DF'B (n-C
, mixed) is the same as Example IC.

Example ■ Example ■ except that the B a O / K 2 O molar ratio was 1.2
Another pulse test was conducted using the same conditions and materials. The desorption material was 30% mixed with n-hebutane (n-c7).
%m-DFB (bp, 82°C). The selectivity (B) for xylene isomers is as follows.

B p/eb = 3.028 p/m
= 3.94 8p10 = 3.00 Sa]', := 11.7 cc Sa] ”= 1
The 6.7 cc xylene retention capacity was 22.8, indicating a satisfactory desorption time. The width of the n-(:,g peak at 1/2 height was 11.9 eC. ΔW defined as above
was 1.1cc. The composition of the adsorbent is as follows.

Sin, (Wt,%) 60.6A120. (
19.1BaoOWt, %)
13.1 to 20 (Wt, %) 6.7 Na20 (wt, %) 0.6 BaO/,
O (molar ratio) 1.2 The results are shown in the chromatograph of FIG.

As can be seen from this figure, when the B a O/K z 0 molar ratio is 1°2:1, p-xylene can be separated from other isomers.

Example ■ 100% fluorobenzene (bp, 85℃
) was used, but the pulse test of Example (■) was repeated. The selectivity for xylene was as follows.

B p/eb = 2.728p/a+
= 3.85 8p10 = 3.40 The holding capacity of xylene was 25.7 cc.

The n-C peak width at 1/2 height was 12.3 cc.

ΔWee (defined above) was 18.3 cc.

The Bao/20 molar ratio is 1.2:1. There is a breakthrough slope. The results of the pulse test are shown in the chromatograph of FIG. Although the selectivities obtained here were similar to those obtained using toluene as the desorbent, fluorobenzene has the same advantage as the other fluorobenzenes disclosed here, namely a low boiling point, which makes it difficult to distill. It is possible to recover the desorption material by

Example■ Using 30% m-DFB mixed with n-C as a desorbing material, -Y zeolite is added to Ba-/20/,
The pulse test of Example (2) was repeated, except that a sample having a 1.05:1 ratio and the following composition was used.

068 18.8 11.8 6.9 0.63 Sin, (!+lt, Phantom A1□0. (St0%) BaO (Wt, %) K2O (Wt, %) Na20 (St 1%) Xylene isomer The selectivity (B) for

B p/eb :': 2.72Bp/+
= 3.85 8p10 = 3.40 The retention capacity of P-xylene was 39.6 cc. 1/
n-C at 2 heights, peak width is 10.1cc, and ΔW
was 6.71 cc. The results are shown in the chromatograph of FIG.

Example (2) 30% 0-difluorobenzene mixed with 70% n-C was used as a desorption material. The BaO/K20 molar ratio was 0.05. The selectivity for xylene isomers was as high as for m-difluorobenzene.

B p/eb = 2.4B p/seagull
= 3.23Bp10 = 4
．． The retention capacity of 45 ρ-xylene was 32.2, indicating an appropriate desorption time. The n-C and peak envelope width at 1/2 height were 10.1 cc, and ΔW was 9.7 cc.

Example■ One example with B a O / K z 0 molar ratio of 1.13■
In A, 30vo1.70% m-D F B is flowed, and in Example ■B, 100vo1. Examples other than playing %mDFB ■
The pulse test was repeated. From Figures 5A and 5B and Table 4, at a constant B a OZ K z O ratio, m-D
It can be seen that the selectivity improves when the F B concentration is increased from 30% to 100%.

Red example VIIA V
IIBBad/20 molar ratio 1,13
1.13 theory arrival material 30vo1. % m-DF
B 100vo1. %a+-DFBB p/eb
2.50 3.05B
plo 3.63
4.46B plo 3.21
3.82 p-xylene retention capacity 47.89
cc 17.97 ccΔW
10.84 cc -0.7ccn-
C, HJ, -9,64cc 11.8
ccsa, i', 9.32 cc
7.2 ccSd]:”, 14.5 c
c 7.2 cc Example ■ The pulse test of Example ■ was repeated except that the B a O/K * 0 molar ratio was changed to 0.99:1. The result is 6A
and shown in FIG. 6B and Table 5. m- contained in raw materials
Xylene is recovered before the ethylbenzene fraction is removed as in Figure 6A, but m-xylene is not separated from ethylbenzene and/or O-xylene as in Figure 6B and is recovered separately. Comparing the results of Figure 6A and Figure 5B and the results of Figure 6B and Figure 5B for Example 6, B
As the O ratio increases, the desorption force of m-D FB decreases as shown by the retention capacity of P-xylene.For example, at a ratio of 0.99, the retention capacity is 37.17cc (example
and Figure 6A), and the ratio of 1 and 13 is 47.89cc.
(Example ■ and Figure 5A) (Both are 30% m-D
FB), similarly for a retention capacity of 11.44 cc at 100% m-DFB and a ratio of 0.99, the retention capacity increases to 17.97 cc at a molar ratio of 1.13. Furthermore, as for the desorption material, the selectivity of the adsorbent for ρ-xylene is greater than 1, which is preferable.

4 B=Sd ko', 2 cc/Sa]', ', c
c, = 8.6 = 1.17
Front foot side ■Engineer IA VI
IIBBaO/20 molar ratio 0.99
0.99 theory material 30vo1. %s+-DF
B 100vo1. %m-DFBB plo
2.86 3.84B plo
3,77 4.18B p
lo 3.44 3.94P
-Xylene holding capacity 37.17 cc 11.
44 ccΔW 6.02 cc
-2,39ccn-C,H,V,
9.91 cc 13.05 ccsa]
::9.05 cc 8.6 ccSd]::I
L3 cc 10.1 cc Example■ Replacement of p-diethylbenzene (p-deb) with m-diethylbenzene (m-da) by Y faujasite exchanged with Ba-
b) ~0-Diethylbenzene (o-deb) To determine its separation ability from the mixture, another feedstock was used in a pulse test as described above. This Ba K-Y adsorbent is
aO/K20 molar ratio = 0.99:1. The same clay binder as in Example 1 was also used. Other changes are the same as in Example I. The desorbent is 30% m-difluorobenzene mixed with n-hebutane. The selectivity for this desorption material is 1.09. The results are shown in Table 6 and Figure 7 below.

BaO, 0 molar ratio Desorption material B plo Bp/.

P-DEB holding capacity n-C, Hl S, ]:: s d] I (I First day 0.99 n-C, mixed 30% m-DFB 2.30 3.78 43.27 cc 9.72 cc 11.7cc 12.7 cc 1.09

[Brief explanation of drawings]

Figure 1A shows Y zeolite adsorbent exchanged with Ba- (however, B
The chromatographic diagrams, LB, IC and ID diagrams for the separation of p-xylene from the xylene isomer-ethylbenzene mixture by m-difluorobenzene desorbent and m-difluorobenzene desorbent (AO/Km O molar ratio = 0.63) are shown in FIG. When the conditions and ion concentration in the adsorbent are changed (however, Ba
O/, 0 molar ratio is 0.71.0.98.5.17 respectively
) chromatographic diagram (however, in each case above, 〇- and m
- xylene trace omitted). Figure 2 is a chromatographic diagram when the B a O / K z 0 molar ratio is set to 1°2 in Figure 1A (however, 〇- and m
- including traces for xylene). FIG. 3 is a chromatograph in which the molar ratio of 20 to BaO/ is 1°2 in FIG. 1A and the desorption agent is fluorobenzene. Figure 4 shows Figure 1A with a 30% molar ratio of 1°05 and 20 molar ratio of Ba○/, and n-hebutane mixed as a desorption agent.
- Chromatographic diagram when using difluorobenzene (however, it also includes a trace of m-xylene). Figures 5A and 5B are BaO/K in Figures 1C and ID, respectively.
Figures 6A and 6B are chromatographic diagrams when the zO molar ratio is 1.13.6 Figures 6A and 6B are chromatographic diagrams when the 0 molar ratio is 0.99 for BaO/ in Figures 1C and ID, respectively.
However, m-xylene is used in Figure 6A, and 〇-xylene is used in Figure 6B.
and m-xylene). Figure 7 also shows p from diethylbenzene isomer mixture using Ba-exchanged Y faujasite adsorbent (however, Ba○/K20 molar ratio = 0.99) and n-hebutane mixed 30% m-difluorobenzene desorbent. - Chromatographic diagram for the separation of diethylbenzene. Atsushi 6B side

Claims (1)

[Scope of Claims] 1. A feed stream containing a mixture of the p-isomer and at least one other isomer of a dialkyl-substituted aromatic hydrocarbon is transferred to an exchangeable cation site within the crystal structure of the adsorbent. is contacted with a crystalline aluminosilicate adsorbent containing Ba and K in a molar ratio of BaO/K_2O=approximately 0.6:1 to 1.2:1 under selected adsorption conditions so that the adsorbent absorbs the
- adsorbing the isomer and then combining the p-isomer-containing adsorbent with a desorption material selected from the group consisting of monofluoro-substituted aromatic hydrocarbons, difluoro-substituted aromatic hydrocarbons and mixtures thereof; p-isomerization of dialkyl-substituted aromatic hydrocarbons, characterized in that the p-isomer is removed from the adsorbent by contacting under conditions to obtain a product enriched in the p-isomer compared to the feed stream. A process for the separation of p-isomers of dialkyl-substituted aromatic hydrocarbons from a feed stream comprising a mixture of dialkyl-substituted aromatic hydrocarbons and at least one other isomer. 2. The method of claim 1, wherein the adsorbent is a type X zeolite, a type Y zeolite, or a mixture thereof. 3. Claim 1, wherein the adsorbent is m-difluorobenzene, o-difluorobenzene, or a mixture thereof.
Or method 2. 4. The method of claim 1, 2 or 3, wherein said adsorption and desorption conditions include a temperature in the range of about 20 to about 250C and a pressure sufficient to maintain a liquid phase. 5. BaO/K_2O molar ratio is 0.9:1 to 1.1:1
The method according to any one of claims 1 to 4.