CZ471489A3 - P-xylene separation process - Google Patents

Abstract

Process comprises (a) contacting the mixt. with an adsorbent consisting of a crystalline aluminosilicate contg. a Group IA or IIA metal ion at exchangeable cationic sites, to adsorb seletively p-xylene, and obtain a raffinate comprising the C9 (and other C8) hydrocarbons; and then (b) contacting the adsorbent with a desorbent comprising diethyltoluene to remove p-xyleen as an extract stream. The aluminosilicate is esp. a type X or type Y zeolite.

Description

The invention is in the field of hydrocarbon separation by adsorption. In particular, the invention relates to a process for separating para-xylene from a sealable feed containing at least two xylene isomers, including the β-isooer, using a zoolite adsorbent and a dese-desorbent. The invention has considerable advantages, especially in a process in which the coating set also contains arooatic hydrocarbons which are known to have acted in prior art adsorption separation processes of this type.

In the numerous processes described in the patent literature, such as in US Pat.

626 020 (Neuzil), 3 663 638 (Neuzil), 3 665 046 (de Bosset), 3 668 266 (Chen and others), 3 686 342 (Neuzil and others),

700,744 (Berger et al.), 3,734,974 (Meuzil), 3,694,109 (Rosback), 3,997,620 (Neuzil), and B426274 (Hedge) disclose the use of certain zeolite adsorbents to separate para isoaers of dialkylsubstituted aonocyclic aroaatic hydrocarbons from others. In particular, it is proposed to use benzene, toluene or p-diethylbenzene as a desorbent. P-Diethylbenzene (p-DBB) has become an industry standard »for this separation, p- However, diethylbensene is a "heavy" desorbent (which has ^a higher boiling point than p-xylene), which causes the process to separate p-xylene by adsorption when the feedstocks also contain Cg aromatics. This is because the boiling point of p-diethylbenzene is too close to the boiling point Cg of the aromatic hydrocarbons contained in the feed, so that separation by simple fractionation is difficult. Since the C 8 aromatics are difficult to separate from p-diethylbenzene by simple fractionation, if a separation step is allowed in the adsorption feedstock, the sequential ee accumulates in the desorbent, which has to be recirculated for 2 economic reasons. PH of the known method for isolating p-xylene from mixed feeds containing its isomers using p-DEB as desorbent, it was therefore necessary to reduce the Cg content in the feed to below about 0.1% by volume prior to adsorption separation of p-xylene. in the so-called xylene splitting column. Is evident,

While it was not necessary to remove Cg aromatics in advance, the high costs associated with this practice could be avoided or at least substantially reduced by the investment cost of the xylene column and the equipment needed to achieve substantially complete Cg aromatics removal. Although U.S. Pat. No. 3,368,342 mentions 1 additional substituted benzenes as possible heavy dosorbents for separation processes, where p-xylene is obtained, it is clearly stated that p-DEB is the best desorbent for this separation. In addition, this patent does not address the problem that preferred desorbents may encounter when separating feeds containing C < * > from ⁴ aromatics, since it has been sought for a long time and a higher boiling point has not yet been available, that you * hovovela demands on selectivity imposed no desorbents • _f sf and that could be-separated from the aromatics. '> As well known that in adsorption separations of various mixtures used ^{in the} crystalline aluminosilicate, n * · ·. . · Agglomerates or zeolites in the form of agloaerates having high physical strength and abrasion resistance · High purity crystalline zeolite powders are formulated into such agglomerates by mixing and wetting with inorganic binders, usually siliceous and alumina-containing clays. The blended mixture of clay and zeolite is then extruded and pelletized to pellet or pelletize, and then the sludge formations are eaten to convert the clay to a substantially mechanically strong amorphous binder, typically the kaolinite-type clays, organic polymers permeable to water or silica.

The reparation process of the invention may be carried out in a fixed or coated adBorbent bed system, however, the preferred system for such separation is the anti-skid simulated moving bed system such as that described in US Patent No. 2,965,569 (Broughton). The cyclic flow of the feed and discharge streams can be achieved by means of a distribution system also known, for example, by means of rotary disc valves (U.S. Pat.

040 777 and 3 422 848). Devices based on these principles are known in sizes ranging from pilot scale (US Patent No. 3,706,613, de Rosset) to process scale β dispense flow rates from a few ml per hour to many thousands of liters per hour.

The invention may also be applied in a co-current halving batch process such as that described in U.S. Patent No. 4,159,284.

In some cases illustrated in this specification, it is also necessary to remove three streams from the adsorption eeperation stage to collect the desired product whose adsorption strength lies between the adsorption strengths of the extract stream and the raffinate stream. This intermediate stream may be referred to as a second rofinate stream, such as in U.S. Patent No. 4,313,015, or as a second extractor stream, such as in U.S. Patent No. 3,723,302. when the impurity contained in the feed, such as p-ethyltoluene) is more adsorbed than the desired product, p-xylene. p-Ethyltoluene does not always need to be separated from p-xylene, for example when p-xylene is used for oxidation to terephthalic acid, which is the end product, since torophthalic acid also penetrates by oxidation of p-ethyltoluene. However, if it is desired that the concentration of the pollutant in the product be kept as low as possible, a first extract is taken in which the concentration of the desired component and the lower impurities are lower and

then a second desorbent is withdrawn at the point between the desorbent feed and the first extract discharge, the second extract with a higher concentration, impurities and lower concentration of the desired product. However, it is not necessary to use a second desorbent if the 7: 4tst.r6cv3.4desorbent is and more solidly bound impurities remain, as disclosed in the above-cited U.S. Patent No. 3,723,302. If the labeling component is to be obtained in high concentration and purity, this can be accomplished by withdrawing the second tibia extract. pfrs4uj> tur as mentioned above ·. ^f 'í

Functions and properties of adsorbents and desorbents in the chromatographic separation of liquid components in. . 7.,. · Are dbreznáa "1" nieaánd 3 · and refer to Ú8 paa daJ.Í «.-" - '7 ·· $ /?''' * *; ·. · "4ι · ' ^ζ '

A method using · was discovered by hen. 7 77 '. Seolithic adsorbent and desorbent for separating p-xylsine from its lso, which represents a significant improvement in the separation of xylene isomers in those cases where the blend also contains aromatic hydrocarbons as impurities.

.. ^r ý.

In short, it is mpshao to include y-ee7

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process for separating p-xylene from α Mixed feeds containing p-xylene and at least one other xylene isomer, wherein the mixed feed is contacted with an adsorbent containing a crystalline aluminosilicate which, at the exchangeable cation sites, contains a Group I or IIA metal ion of the periodic table under adsorption conditions, adsorbing p-xylene on said adsorbent to form a raffinate stream containing less strongly adsorbed other xylene isomers and then contacting the resulting p-xylene containing adsorbent with desorbent under desorption conditions to remove p-xylene from the desorbent as an extract stream, according to the invention, wherein the desorbent comprises diethyltoluene.

The term diethyltoluene is used in this specification to refer to any of the isomers and any mixture thereof. Accordingly, the invention relates specifically to the use of 2,3-DET, 2,4-DET, 2,5-DET, 2,6-DET, 3,4-DET and 3,5-DET (where DET stands for diethyltoluene) and mixtures of two or more of these isomers. The desorbent is higher boiling point (e.g., boiling point of 3,5-diethyltoluene is from 198 to 200 * C) than the _Cg aromatics, which allows separation of _Cg aromatics from the desorbent by simple fractionation so that the desorbent can be reused in the process without the would accumulate in the recycle desorbent _Cg aromatics. In another aspect the invention also provides a method for separating _Cg aromatics from a feed mixture comprising _Cg aromatics in addition to para-xylene and at least one other xylene isomer.

'? - - 8 ’’

- A brief explanation of the drawings follows.

*, · Γ. FIG. 1 is a chronatogram *>

The separation of p-xylene from a mixture of xylene isoaers and i is illustrated. - b.

and ions of potassium and desorbent, which is 30/70 diethyltoluene and n-heptane. Giant. .2 resembles • ^r,?

The difference is that in this case, a zeolite of zeolite type was used as the exchange of exchange. ··· · _{(- R} "-. · '' .I .. · · ......:. ..., _Λ 'and barium ions introduced as deeorbentu 100% of the mixture • isoaerů; diethyltoluene.

The adsorbents used in the process according to the invention are specific crystalline aluminum oleum or molecular sieves; namely zeolts of type X and Y. Zeolites are characterized by a skuo cage structure in which alternating tetrahedrons of alumina and silica are firmly joined to form an open three-dimensional mesh reminiscent of a kleee structure whose pores are formed by pores. of oxygen atoms and before partial dehydration of the zeolite, the spaces and the tetrahedron are filled with aolecular water. Dehydration of the zeolts produces bound β-cup crystals that find molecular spreads, and therefore crystalline alualosilicates are often referred to as molecular sieves ”when the separaee they perform is essentially dependent on the difference in size of the batch molecules, such as separation smaller normal paraffin molecules from larger iaoparaffin molecules using a particular molecular sieve. In the process of the invention, however, the term molecular sieves, although widely used, is not particularly suitable since the separation of specific aromatic isomers is clearly dependent on the differences in the electrochemical attraction of the different isomers and adsorbent and not on the purely physical difference in molecular size. isomers ·

In hydratobated form, the type X seolite can be described by empirical formula 1, wherein the molar content of the individual oxides is characterized by formula 1 (0, S ♦ 0, 2) _{2 2 /} , _n OlAl ₂ 0jl (2,5 + 0. a cation of not more than 3, which balances the electrical charge of the alumina tetrahedron and is usually referred to as a replaceable cationic site.

X, indicating the number of moles of water, is up to about 9, depending on the identity of the M cations and the degree of hydration of the crystal. As can be seen from formula (jf), the molar ratio of 2.5 / 0.5 to 2.5% and 2.5% ^may be monovalent, bivalent or trivalent, or may be a mixture thereof. ''' ^F Zeolite and with a structure corresponding to> y. .

-type_Y is possible in hydratovandorbehistonly hydrated formally analogously describe molar oxide oxide in relation to (0,9 + 0,2 µM _{2 / n} 0: Al ₂ 0 ₃ iwSiO ₂ γH ₂ 0 where Μ, nay have the same qualities as in formula 1 AW · * · "S". Λ; · • · ''^'1>' is a value in the range of about 3-6 · molar ratio SiO / algo ^ u seolitu a structure corresponding Y-type aůže be therefore rozaesí about 3 to about 6. Both zeolites may be cationic M one or more different cations in the original state and that the train is generally prepared in such a form that the cation M is predominantly sodium. Type Y zeolts containing predominantly sodium cations at exchangeable cationic sites It is therefore intended to be a type Y-type seolite in the sodium-exchanged hydrogen or as a Ba-type seolite, depending on the reaction purity of the components used to produce the seolite. However, the other cations mentioned above may be present as impurities.

In the process according to the invention, the zeolites of the types described above can be used. In order to be able to carry out the separation, the cations of the initially produced zeolite ions of group IA c 'or / IIa must be exchanged, e.g.

The adsorbents used in the separation processes usually contain a crystalline substance dispersed in an amorphous inorganic matrix or binder that contains channels and cavities allowing liquid access to the crystalline substance. Typical inorganic substances suitable for

C.

For example, the formation of a matrix includes silica, alumina, clay or mixtures thereof. The binder aids in the forming and agglomeration of crystalline particles which would otherwise have the form of a fine powder. The adsorbent may thus be in the form of particles such as extrudates jsau, aggregates, tablets, macrospheres or granules having a size, and preferably from about 16 to 60 .sel _r mesh (US standard sieve stack · Standard US Mesh), i.e. from 250 to 119 / µm.

88special handles ee uses ♦

the process of the present invention include p-xylene, Alei ^J clips one other aromatic & Isomers C and may also contain one or more Cg aromatics as impurities. Mixtures containing significant amounts of p-xylene and other Οθ isomers and C 8 aromatics and are usually prepared by reforming and laomariation procedures, well known in the art of petroleum refining. Many of the Cy aromatic hydrocarbons boil in the range of 160 to 170 ° C and cannot be separated by distillation from the standard desorbent, p-thylethylbenzene. Therefore, in the procedures carried out so far, C? the aromatics usually removed by distillation and deprotection prior to the pre-adsorption separation step and here before contacting the normal desorbent. Desorbent has been discovered by mane, which can be easily separated by aromatic fractionation by * QW <

adsorption separation step. According to the invention, the use of a deorbent according to the invention does not require a large column process and a number of other devices for pre-treatment of the feedstock, which results in considerable savings in investment costs?

Mixed feedstocks for the process according to the invention can be obtained by reforming. In reforming processes, the naphtha is contacted with a platinum and halogen containing catalyst under conditions whose sharpness is selected to obtain a product containing Cgdeejwy. < ¹ '

Usually ee then reformate fractioned to Sec _Q lsoaery concentrated aromatic Cg fraction containing Cg aromatics le cMet, as well as his nearomatleká Cg hydrocarbons and aromatics · feed stream for the process of vynálesu may also obtain isomerlzačnlmi and transalkylation processes. Mixtures of oxylenes that are poor in one or more isomers can be isomerised under laomerization conditions,

13 to produce a pd product containing C8 aromatic isomers, for example a product enriched in na-p-xylene and C8 non-ornates and aromatics. The aromatics content of the isoaerizing xylene mixture may be as high as 1 to 2% by volume, depending on the conditions of the erection. Similar to trensalkylecl mixtures of C? and aromatics, xylene isomers are formed which contain aromatics.

In these catalytic processes, xylene splitter columns need to be used to remove C sp aromatics with C odstran aromatics before being used for the separation of xylenes by conventional adsorption eoperation methods. Thus, the mixed feedstocks for the process of the present invention may contain certain amounts of C? aromatics and may also contain 1 certain amounts of straight or branched paraffins, cycloparines or olefins. Preferably these amounts are as low as possible in order to prevent contamination of the products obtained in the process according to the invention with substances which are not selectively adsorbed on the adsorbent and which are not selectively separated by means of the adsorbent. Preferably, the content of the above impurities should be less than 20% by volume based on the mixed feed introduced into the process.

When separating p-xylene from the mixed feed containing p-xylene, at least one other C8 aroma and aroma, the mixture is contacted with the adsorbent under adsorption conditions. In doing so, p-xylene (if such p-ethyltoluene is present) adsorbs more selectively on the adsorbent and

- 14 remains on it while the other components remain 'K. ··. '*>·' * ^{'J to} be relatively needsorbovány e are removed from intersticiól •> * thereof (vaezeřených) the voids between the particles of adsorbent and Mon. and the top of the adsorbent, the adsorbent containing the more selective is' ⁴ '>, /'*.; · adsorbing para-xylene rich adsorbent as jeoznečován ·. . '. . . γ .. - · r ie an adsorbent rich in more selectively adsorbing p-xylene. The p-xylene is then removed from the rich adsorbent by switching the rich adsorbent from diethyltoluene to the desorber; * * '·· _T -. . · ..... - · .... · bente · for desorption conditions. \ ''. ' ^í ' ·

Přitoeto process in ASCs with pol t used zeolitickáho adsorbent and which is generally carried • ^r ' »continuously at substantially constant temperature and pressure to ensure the existence of a liquid phase is eusí desorbent, the AA used judiciously chosen so to meet someone _in {· lik criteria. First, the desorbent should displace the extract. . . The adsorbent component and the adsorbent at a sufficiently high mass flow rate and at the same time can be adsorbed to undesirably prevent the extraneous component from displacing the desorbent from the adsorbent during the next adsorption cycle. Of the latter, the desorbent pounds are coepatable with the designated adsorbent and the designated snow shaft. More specifically, the desorbent is not capable of reducing or destroying the important selectivity of the adsorbent for the extract component relative to the raffinate component, nor does it react chemically with the batch components. In addition, the desorbent should be readily communicable from the mixed batch introduced into the process. Both the raffinate component and the extract component are typically removed from the adsorbent in the form of a mixture with the desorbent, and if at least a portion of the desorbent does not separate from these mixed streams, the purity of the extract product and the raffinate product will not be too high. new use in the procedure. It is therefore advantageous

The diethyltoluene desorbent used in the process of the present invention has a much better 3 ° C boiling point than the blend batch or any of its components, i.e. the difference is greater than about 9 ° C. This makes it possible to separate at least a portion of the desorbent from the feed components in the extract and raffinate stream by a simple traction distillation, thereby obtaining a desorbent stream which can be recirculated to the production process.

Finally, the desorbent should be readily available, affordable and reasonably priced. It is not always possible to predict which desorbent or desorbents will be suitable for a particular separation and use of a particular adsorbent. It has been found that in a preferred isothermal liquid phase process of the present invention using a mixed feed for the aeparation process that contains more than about 0.1% by volume of aromatics, a suitable diethyl toluene desorbent (individual isomers or their isomers thereof). mixture), which desorbs.extract from the adsorbent and can be separated from the raffinate containing aromatics by distillation ·

Adsorption ^conditions include a temperature

An interval from about 20 ° C to about 250 ° C, with a temperature in the range of about 60 ° C to about 200 ° C and a pressure that is preferred.

it is sufficient to maintain the liquid phase at a pressure range from atmospheric to positive pressure of 4.1 ° C. The adsorption conditions include the same temperature and pressure range as used in adsorption. / ir · - jj

For testing various adsorbents and in W. '/' i · '' · desorbitants associated with a certain mixed handle are used '4 V5i <

-i * * * - & ^{1 in a} dynamic test facility · This device has a *, f L y- -.

The adsorbent properties, such as adsorption capacity and exchange rate, are comprised of a rack-like adsorbent chamber having a volume of approximately 70 ml. At the opposite ends of this mosquito is a supply; The chamber is located in theiwostat and in addition to this at '/' · '·. . ... '/' <1 /. / · uses a pressure control device to operate at a constant predetermined pressure.

I * output piping and chambers can be connected to quantitative and qualitative analysis devices, such as refractoaeters, polarimeters, chromographs, etc., which can analyze the current leaving the chamber with sdsorbents measurement directly in the stream.

τ

The pulse test performed using this device and the following general procedure

It is used to determine data such as selectivity (In the case of various adsorbent systems. By passing the desorbent through the adsorbent chamber, the adsorbent is saturated with a certain desorbent until equilibrium. concentration of the indicator and the direct concentration of a certain extract component or raffinate component, or both of these components, each of which are desorbed, and then the desorbent stream is restored, and the indicator and extract and raffinate components are lysed as in a liquid-solid ehrometograph. Alternatively, samples of the outgoing stream can be taken periodically and can be gas chromatographed at a later time.

The information obtained in this test can be used to calculate the adsorbent performance expressed as void volume, retention volume for extractor and prorafine component, rate of desorption of extract component with adsorbent e selectivity · Empty volume is a non-inactivated volume of adsorbent expressed as the amount of desorbent pumped over Interval from the start of the flow up to _; correspondingly reaching the center of the peak area of the indicator. the net retention volume of the extract or raffinate component can be characterized by the distances between the center of the peak envelope (gross retention volume) of the extract or raffinate component and the center of the peak envelope (empty volume) of the indicator component or other known reference as the volume in cm ^ of desorbent pumped during this time interval corresponding to the distance between the sheaths of the sheaths. The exchange rate or desorption rate of the extract component by the desorbent can generally be characterized by the sheath thickness of the sheath at half the intensity, the narrower the peak width _and the faster the desorption rate. The rate of sorption can also be characterized by the distance between the center of the indicator peak envelope and the disappearance of the extract component that has just been desorbed. This distance is again expressed as the volume of desorbent pumped during this time interval. The selectivity (0) is determined by the purity ratio above the thinner volume of the more strongly adsorbed component to the net retention volume of each of the remaining components.

The invention is described in more detail in the following examples. The examples are illustrative only and do not limit the scope of the invention in any way.

- 19 Example I

In this experiment, a pulse test is performed using the apparatus described above to investigate the ability to use the method of the invention to separate p-xylene (bp 138 ° C) from other xylene and ethylbenzene isomers (bp 136-145 ° C). ) and aromatics. Potassium exchanged faujasite Y dried at 400 to 450 ° C mixed with 15% by weight amorphous clay binder is used as the adsorbent.

In all pulse tests, the column is maintained at a temperature of 150 ° C and a pressure of 1.24 MPa to maintain liquid phase operation. A gas chromatogrof detecting the composition of the effluent at given time intervals is connected to the column effluent stream. Like i

Mixtures were used in all tests using 5 cm mixtures containing 0.45 cm each of the xylene isomers, ethylbenzene and each of the following aromatics / stone, n-propylbensene, p-ethyltoluene, mesltylene, 1,2,4-trimethylbenzene and 1. 2,3-trimethylbenzene. Normal nonane is used as an indicator and 4.95 eq of desorbent is added to each batch. The desorbent takes up 30% by volume of diethyl toluene (DEJ) as an isomeric mixture, the remainder being η-Ογ paraffin. The distribution of the isomers of diethyl 14 toluene in dssorbenu corresponds to mixture A shown in Table 1.

- 20 - ř “i * '- = r_ =', .....-. ..... < ·. T a b at 1 k a ‘1 '· -' '... ·. * •> ·  mixture mixture' AND (B) 3,5-DBT i _{47 (6;} - - 18.6 ...... ~ 3,4-DEf!  tracks tracks 2,4-DET: - 2,5 ' · '·· 1.6 ·' 2,3-DET  . · · ·. '* ..... ^; · / 7.4 - • r. r-. -:. 7.3 - - to- 2,5-BBT 16.6  41.9 2,6-DET: 23.6 30.6 - í ^ · · Test t is performed as follows

Method: The absorbent was continuously fed to the column at a flow rate of 1.2 cm 2. min “ ¹ . At a suitable time, the desorbent feed was cut off and the mixed feed was introduced for 4.2 minutes. Then _t se.obnoví supply deeombentu continues growing and * '··, / >>. i _r - * ', · l ·, * / ·. · ». ' ^S ''syjSl.tS' * * '* .. »··, -J' · \ 'ί · Λ' Sh '' t, '''*' 1 r * '' -. '' ”« · Ί * '' £ ', £ ·! '· I "* · · · ^in" jesévjeho uváděnídbsloupceadsorbentu until it is.

řtÓřW ⁵ '-' ^T '' · '* f ·' iX r. - · ϊ. - '. ΐ; The columns did not elute all aromatics with the feedstocks, which is assured by ehromatographic analysis of the stream of substances coming out of the adsorption column.

The results of this test are shown in Table 2, and a corresponding chromatographic record illustrating the method of the invention is shown in Figure 1. The table shows the gross retention volume (®V) and the net retention volume (NRV) and the selectivity (3) for each component relative to p-xylene for each component.

Lt

Table component reference number k Fig. 1 Gross net selectivity retention temperature (8) boiling (° C) volume volume (ml) (ml)

n-nonsn 1 46.9 0.0 0.00 (Indicator) ethylbenssn 8 73.8 26.9 1.86 136 p-xylene 10 97.0 90.1 1.00 138

(ref.látka)

kumen 9 72.9 29.6 1.96 133 o-xylene 4 99.0 13.1 4.14 144 n-propylbensene 7 86.9 30.0 3.30 159 p-ethyltoluene 11 128.6 61.9 0.61 162

1,3,4-triaethyl- ,. 'X Λ. * ·' · - * »Ίί .- * '* ·'. , ··· ^ '· / · * *' ^r i * ·> - ·. ·. * *, '/ í *, “ ^r '” · ^ Λ A! r. ? »Ό -M .. , y /, TV · '·' e '; OWSOi • ξι ýi Λ * - · Λ '· ¹ ·', '·'ίνΜΜ'ΜΤ'Μ: Μ '.,.' · - ». .'ί '' ·· * - · - - * ^Λ MTMvVdK j · J * v · _t . ' beosen C 6 66.8 19.8 8.53 168 1,3,3-trimethyl- .'- beosen 6 61.4 14.3 3.45 179 Xylene 3 87.3 10.3 4.64 139

- 22 ./ Example II <

. .

• V

T t t!

Under the same conditions as in Example ¹⁴ '

X using a handpiece As in Example I, a further pulse test was performed. In contrast to Example 1, the deaorbent is 100% diethyltoluene, &quot; N &quot; * • gí '' ·: ·; -.! · ''' _T * V? · *? · · <''''H>I' r, '- ·. ř V. *> _Button. · _{7χ: ρ} -. '- · v; '·. · X · · ..' f · "->'i.' · -» · '- ?. ·>ι''- ^Γ ij ··' ^Λ '''s-:'; * "* 'sAV r. ·' / .j, * ·, · / · ύ '· «Z ¹ , ·''Sj' ^ř : '• ÍaJ. Does he know ^? · Corresponds to B in the tabuloel. As bioreactor, it uses a barium exchangeable type X (BaX),

The results of this test are shown in Table 3 and Figure 2.

• YI Z

i. · t and b 'f · u i k β 3 .. -Li - ^ -. ^ WJiřAťl '··' · '- * γ · ¹ component H * he said grossly re- éietý re- . ^r 'm: “* · ¹ selectivity dlelo k i tenénl X tenénl <é> Fig. 2 volume (ml) volume (ml) .-. / .. At, ·,; · '· * -r ·'<-.'.i<*, ^k - 4. * W * · - * · /.'φΛ'Ι n-aonnn /// <// ethylboenene »- • 1 i * 'λΧΑ- <. n <- ^r *** · Λ 1- ·, * ·· »-t. ·. ·, ·. ***» · £; ·. · '' -fr ¹ _v - * 4 4 ^. _f „8 / , / Have- J -; -. «Ϊ · j. and áůjsgpSjj Sil «Wl »· Ί2 · 7> · ν λ -: <, /., </ '/,' .. · ί-Ζ; Ύ // * ♦ 09 7 p-xylene 10 043 833 1.00 kumeo 9 58.8 17.0 1.37 O-xylene 4 48.8 7.8 3.28 n-propylbenzene f-. ' and. 80.4 8.1 83 « pvethy1toluene 'r 11 68.0 87.7 0.84 mešitylen / 9 44.0 93 8.86 1,2 _e -trimethyl benzen ..... O 47.9 - 03 / 3.83 1,2,3-trimethylbenzene 5 48.8 5-4 4-2 «

Γ r Z r-r r r r f

- 23 - g.

PRINTING.

Claims (3)

PATENT CLAIMS A method for separating p-xylene comprising a mixed feed comprising p-xylene and at least one other xylene isomer, wherein the mixed feed is contacted with an adsorbent containing crystalline. aluminosilicate ,. which, at the sites of exchangeable cations, contains a Group I or HA metal ion of the periodic table under adsorption conditions, selective adsorption of p-xylene on the uvodonium adsorbent to form a raffinate stream containing less strongly adsorbed other xylene isomers and xylene is contacted with the desorbent under desorption conditions to remove p-xylene from the desorbent as an extract stream, wherein the desorbent comprises diethyltoluene. 2,3-diethyltoluene, 2,5-diethyltoluene, 2,6-diethyltoluene, 2. The method of claim 1 wherein the adsorbent is selected from the group consisting of Type X zeolites and Type Y zeolites. 3. The process of claim 1 wherein the mixed feed comprises C8 aromatic hydrocarbons. 4. The process of claim 2 wherein the zeolite at the exchangeable cation site comprises potassium or barium cations or a mixture thereof. 5. The method of claim 1 wherein the desorbent is selected from the group consisting of 3,4-diethyltoluene, 3,5-diethyltoluene and mixtures of two or more thereof.