CA1047944A - Aromatic hydrocarbon isomer separation process - Google Patents
Aromatic hydrocarbon isomer separation processInfo
- Publication number
- CA1047944A CA1047944A CA247,116A CA247116A CA1047944A CA 1047944 A CA1047944 A CA 1047944A CA 247116 A CA247116 A CA 247116A CA 1047944 A CA1047944 A CA 1047944A
- Authority
- CA
- Canada
- Prior art keywords
- para
- isomer
- adsorbent
- char
- acterised
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
- B01J20/10—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising silica or silicate
- B01J20/16—Alumino-silicates
- B01J20/18—Synthetic zeolitic molecular sieves
- B01J20/186—Chemical treatments in view of modifying the properties of the sieve, e.g. increasing the stability or the activity, also decreasing the activity
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- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Analytical Chemistry (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Solid-Sorbent Or Filter-Aiding Compositions (AREA)
- Treatment Of Liquids With Adsorbents In General (AREA)
- Silicates, Zeolites, And Molecular Sieves (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A process for the separation of the para-isomer from a hydrocarbon feed mixture comprising at least two bi-alkyl substituted monocyclic aromatic isomers, including the para-isomer, said isomers having from 8 to about 18 carbon atoms per molecule using a specially prepared adsorbent com-prising a Y zeolite containing at the exchangeable cationic sites one or more selected cations. The feed mixture is passed through a bed of the adsorbent wherein the para-isomer is preferentially adsorbed within the adsorbent and thereafter recovered from the adsorbent. Novel feature of the process is the use of the specially prepared adsorbents which have faster adsorption-desorption rates for the de-sired para-isomer.
A process for the separation of the para-isomer from a hydrocarbon feed mixture comprising at least two bi-alkyl substituted monocyclic aromatic isomers, including the para-isomer, said isomers having from 8 to about 18 carbon atoms per molecule using a specially prepared adsorbent com-prising a Y zeolite containing at the exchangeable cationic sites one or more selected cations. The feed mixture is passed through a bed of the adsorbent wherein the para-isomer is preferentially adsorbed within the adsorbent and thereafter recovered from the adsorbent. Novel feature of the process is the use of the specially prepared adsorbents which have faster adsorption-desorption rates for the de-sired para-isomer.
Description
i~4'~44 The Eield o~ art to whic~l the c]aimed inven-tion pertains is hydrocarbon separat~on. More sl~ecifi- ;
~ally, the inv~ntion relates to a process for separclting ~ ;
a para-isomer from a feed mixture comprisincJ a-t least two bi-al~yl substituted monocyclic aromatic isomers, including the para-isomer, the i~omers having from 8 to about 18 carbon a~oms per molecule which process employs specially prepared zeolitic adsorbent which selectively ~ ~
xemoves the para--isomer from ~he feed. `
It is known in the separation art that certain adsorbents comprising crystalline aluminosilicates and con-taining selected cations can be used in processes to sep-arate hydrocarbon isomers from feed mixtures containing such isomers. For example, U.S. Patent Nos 3,558,730; ;
. -: . :- ~
3,558,732; 3,626,020, 3,663,638i and 3,734,974 teach the ; use of adsorbents comprising X or Y zeolites and selected cations in a process or the separating a specific para-isomer, para-xylene, from a mixture of C8 aromatic hydro-carbons. ;
The prior art has also recognised that the cer-tain properties or characteristics of various zeolites can be modified by treating the zeolites with various substances.
Typically, zeolites are treated to eliminate or suppress an undesirable characteristic such as acidity which may bring -`
2S about such acid-catalyzed reactions as isomerization and polymerization~ Various zeolites may also be treated to enhance a par~icularly desired characteristic when employed in specific processes.
~ally, the inv~ntion relates to a process for separclting ~ ;
a para-isomer from a feed mixture comprisincJ a-t least two bi-al~yl substituted monocyclic aromatic isomers, including the para-isomer, the i~omers having from 8 to about 18 carbon a~oms per molecule which process employs specially prepared zeolitic adsorbent which selectively ~ ~
xemoves the para--isomer from ~he feed. `
It is known in the separation art that certain adsorbents comprising crystalline aluminosilicates and con-taining selected cations can be used in processes to sep-arate hydrocarbon isomers from feed mixtures containing such isomers. For example, U.S. Patent Nos 3,558,730; ;
. -: . :- ~
3,558,732; 3,626,020, 3,663,638i and 3,734,974 teach the ; use of adsorbents comprising X or Y zeolites and selected cations in a process or the separating a specific para-isomer, para-xylene, from a mixture of C8 aromatic hydro-carbons. ;
The prior art has also recognised that the cer-tain properties or characteristics of various zeolites can be modified by treating the zeolites with various substances.
Typically, zeolites are treated to eliminate or suppress an undesirable characteristic such as acidity which may bring -`
2S about such acid-catalyzed reactions as isomerization and polymerization~ Various zeolites may also be treated to enhance a par~icularly desired characteristic when employed in specific processes.
-2 ~i',''`.;'~,;
~ ., ., ~ , . . . .
~:)479~
- U.S. }'aten-t 3,382,039, for exaraple, rel~ltes to a process ~or increasing tl~e e~chan~Je capacity of silver ~ -. .
7eolites ov~r that of known silver zeo]ites And their use ~ -~
in providin~ potable water from saline waters. U.S.
- . .:~ . .
S Patent No. 3,326,797, for example, discloses a process for aqueous caustic treating of high silica zeolites having silica over alumina ratios between about 6 and 12, at ~ -treating conditions, for the sole purpose OL removing a ;~
certain pereentage of s~ructural silica from the zeolite.
The caustic treatment, at conditions to preferably retain a final SiO2/A1203 ratio greater than about 5.5, is found to increase the adsorptive capacity of the zeolite and to increase its catalytic activity when used in hydrocatalytic ; ;~
conversion processes such as olefin hydrogenation, hydro~
; 15 ~ cracking, and desulphurisation. The caustic treating pro~
~ cess of that re~erence patent is concerned only with etch- ;;
, ing or leaching of silica from the zeolite structure to achieve these characteristics.
The prior art references either alone or in com~
bination, however, do not disclose or suggest the adsorbent - preparation method of this invention or the aromatic isomer separation process of this inventlon which process employs the adsorbent so produced.
In brief summary, our invention is, in one em-25 bodiment, a process for separating the para-isomer from a ;~
feed mixture comprising at least two bi-alkyl substituted `
~monocyclic aromatic isomers, including the para-isomer, said isomers having from 8 to 18 carbon atoms per molecule, ;~
which process comprises: (i) contacting at adsorption con~
ditions said mixture with an adsorbent prepared by the
~ ., ., ~ , . . . .
~:)479~
- U.S. }'aten-t 3,382,039, for exaraple, rel~ltes to a process ~or increasing tl~e e~chan~Je capacity of silver ~ -. .
7eolites ov~r that of known silver zeo]ites And their use ~ -~
in providin~ potable water from saline waters. U.S.
- . .:~ . .
S Patent No. 3,326,797, for example, discloses a process for aqueous caustic treating of high silica zeolites having silica over alumina ratios between about 6 and 12, at ~ -treating conditions, for the sole purpose OL removing a ;~
certain pereentage of s~ructural silica from the zeolite.
The caustic treatment, at conditions to preferably retain a final SiO2/A1203 ratio greater than about 5.5, is found to increase the adsorptive capacity of the zeolite and to increase its catalytic activity when used in hydrocatalytic ; ;~
conversion processes such as olefin hydrogenation, hydro~
; 15 ~ cracking, and desulphurisation. The caustic treating pro~
~ cess of that re~erence patent is concerned only with etch- ;;
, ing or leaching of silica from the zeolite structure to achieve these characteristics.
The prior art references either alone or in com~
bination, however, do not disclose or suggest the adsorbent - preparation method of this invention or the aromatic isomer separation process of this inventlon which process employs the adsorbent so produced.
In brief summary, our invention is, in one em-25 bodiment, a process for separating the para-isomer from a ;~
feed mixture comprising at least two bi-alkyl substituted `
~monocyclic aromatic isomers, including the para-isomer, said isomers having from 8 to 18 carbon atoms per molecule, ;~
which process comprises: (i) contacting at adsorption con~
ditions said mixture with an adsorbent prepared by the
-3-:
9a~4 steps o~ ) con~actiny a b~;e materia] conlp~isin~ Y
zeolite wi~h an aqueous sodillm hyclro~ide solu~i~n at first lon eY~chancJe conclitions to effect the additioll o~ sodium cations to s~id basc materi~ b) treating the sodium- ~:
S exchanc~ed base material a-t second ion exchanc3e conditions ~ -to effect the essentially complete exchange (as defined herein) of sodium cations with one or more cations selected from potassium, cesium, and rubidium; and, (c) dryin~ the material at conditions to reduce the LOI (loss on igni~ion) ~ -at 900C. to less than 10 wt. ~, thereby selectively ad~
sorbing said para-isomer; and (ii) contacting the adsorbent ;
with a desorbent material at desorption conditions to ef-fect desorption of said para-isomer from the adsorbent.
The type Y crystalline aluminosilicates or zeo-lS lites herein contemplated are described as a three-dimen-sional network of fundamental structural units consisting o~ silicon-centred Si04 and aluminium-centred A104 tetra-hedra interconnec-ted by a mutual sharing of apical oxygen atoms. The space between the tetrahèdra is occupied by water molecules and subsequent dehydration or partial de-hydration results in a crystal structure interlaced with channels of molecular dimension.
Adsorbents comprising the type Y structured zeo-lites are described and defined in U.S. Patent 3,120,007. -The type Y structured zeolite in the hydrated or - partially hydrated form can be represented in terms of mole oxides as in formula 1 below~
Formula 1 -2)~2/n Al2o3 wsio2 y~l2o
9a~4 steps o~ ) con~actiny a b~;e materia] conlp~isin~ Y
zeolite wi~h an aqueous sodillm hyclro~ide solu~i~n at first lon eY~chancJe conclitions to effect the additioll o~ sodium cations to s~id basc materi~ b) treating the sodium- ~:
S exchanc~ed base material a-t second ion exchanc3e conditions ~ -to effect the essentially complete exchange (as defined herein) of sodium cations with one or more cations selected from potassium, cesium, and rubidium; and, (c) dryin~ the material at conditions to reduce the LOI (loss on igni~ion) ~ -at 900C. to less than 10 wt. ~, thereby selectively ad~
sorbing said para-isomer; and (ii) contacting the adsorbent ;
with a desorbent material at desorption conditions to ef-fect desorption of said para-isomer from the adsorbent.
The type Y crystalline aluminosilicates or zeo-lS lites herein contemplated are described as a three-dimen-sional network of fundamental structural units consisting o~ silicon-centred Si04 and aluminium-centred A104 tetra-hedra interconnec-ted by a mutual sharing of apical oxygen atoms. The space between the tetrahèdra is occupied by water molecules and subsequent dehydration or partial de-hydration results in a crystal structure interlaced with channels of molecular dimension.
Adsorbents comprising the type Y structured zeo-lites are described and defined in U.S. Patent 3,120,007. -The type Y structured zeolite in the hydrated or - partially hydrated form can be represented in terms of mole oxides as in formula 1 below~
Formula 1 -2)~2/n Al2o3 wsio2 y~l2o
-4 ~' ~., ' 1047~44 where "M" i~ at lea~t one ca~ion haVi~lCJ a vcllent~e no-t rnore than 3, "1~" re[~resents the v.llence o "M", "w" is a va~ue ~reater than abou~ 3 up to 9, nncl "y" is a value ~Ip to about 9 depending upon tl~e identity of "M" anct tile deyree of hydration of the crystal. ~;
The term "type Y zeolite" as employed herein shall re~r not only to type Y structured zeolites con-taining sodium cations as the cation"M" indicated in the formulas above but also shall refer to those containing 10 other additional cations such as hydrogen cations, the -~-alkali metal cations, or the alkaline earth cations. Ty~
pLcally type Y structured zeolites as initially prepared ~ ;
and as used as a base material for the special adsorbent described herein are predominantly in the sodium form but 15 they usually contain any or all of the cations mentioned ~ `
. ~
above as impurities. The term "exchanged ca-tionic site" ;~
generally refers to the site in the zeolite occupied by the cation "M". This cation, usually sodium, can be re~
..: .
placed or exchanged w1th other specific cations, depend~
ing an the type of the zeolite to modify characteristics of the zeolite.
The term "base material" as used herein shall refer to a type Y zeolite containing starting material used to make the special adsorbent described below. The ~
25 type Y zeolite can be present in the base material in ~`
~ ~ concentrations generally ran~ing from 75 wt. ~ to 98 wt.
;~ of the base material based on a volatile free composition.
~he remaining material in the base material generally comprises amorphous silica or alumina or both which is
The term "type Y zeolite" as employed herein shall re~r not only to type Y structured zeolites con-taining sodium cations as the cation"M" indicated in the formulas above but also shall refer to those containing 10 other additional cations such as hydrogen cations, the -~-alkali metal cations, or the alkaline earth cations. Ty~
pLcally type Y structured zeolites as initially prepared ~ ;
and as used as a base material for the special adsorbent described herein are predominantly in the sodium form but 15 they usually contain any or all of the cations mentioned ~ `
. ~
above as impurities. The term "exchanged ca-tionic site" ;~
generally refers to the site in the zeolite occupied by the cation "M". This cation, usually sodium, can be re~
..: .
placed or exchanged w1th other specific cations, depend~
ing an the type of the zeolite to modify characteristics of the zeolite.
The term "base material" as used herein shall refer to a type Y zeolite containing starting material used to make the special adsorbent described below. The ~
25 type Y zeolite can be present in the base material in ~`
~ ~ concentrations generally ran~ing from 75 wt. ~ to 98 wt.
;~ of the base material based on a volatile free composition.
~he remaining material in the base material generally comprises amorphous silica or alumina or both which is
-5~
, . :
,~ ;.. , . . : ~ . , ~47944 p.r~`sent .i.n illtimate mlxt~lr~ l th~ zeo:l.it~ In~terial.
This ~morphous m~terial may be an ~1 junct t~ the man~factur-~ncJ process of the type ~ ~eolite (for ex~mple, interl-tionally .incomplete purification oE thc zeol.ite d~ring its ~ .
manufacture) or it may be added to the relatively pure ze-olite to aid in Eorming or agglomerating particles o~ the . .:
zeolite.
We have found that trea-ting a type Y base ma-terial with a dilute acqueous sodium hydroxide solution 10 prior to a subsequent ion exchange of the treated base ma- ~ .
terial to effect the replacement of sodium cations at the - ~ .
exchangeable cationic sites with one or more other selec- .~
ted cations produces a superior adsorbent when used in a ~ ~:
, .
process for the separation of the para-isomer from.a hy~
15 drocarbon feed mixture comprising at least two bi-alkyl ;~
substituted aromatic.isomers including the para-isomer, . ;.
.... .. .
the isomers having from 8 to 18 carbon atoms per molecule.
This treatment step is in the nature of an ion exchange ~- -step (and will hereinafter be referred to as the first ion exchange) since the NaOE~ solution replaces non-sodium im~
purities in the type Y zeolite contained in the base ma- .~
terial thereby converting the zeolite essentially complete~
ly to the sodium form. More specifically, to produce an .. ;:
~,:,~ ' :' acceptable adsorbent it is preferred that the sodium con-~ent of the startin~ material, as characterised by the weight ratio Na20~Al203, be increased to a ratio greater -~
: than 0.70 and more preferably from 0.75 to l.O. First ion -:
exchange conditions should be so regulated to achieve this degree of ion exchange.
_fi_ ~:
Thc soclium hy(lr.oxide used to pr~pa~e the aqu~ouc.
sodium hydro~idc solution should be oE hicJh purity having ~ery low levels of both other Group IA impuritic~s and Group IIA impurities. Sui-table concellt~cl-tions to obtain the de-sired ion exchange can be from 0.5 to 10 wt. ~ of the sod~
ium hydroxide with the preferred concentration beiny from ~-0.5 to 5 wt. ~. By using solutions containing sodium hy~
droxide within these ranges of concentration, the desired first ion exchange can be obtained at temperatures from 10 ..
to 121C with temperatures from 66 to 121 C be~ng especial- ;
ly preEerred. Operating pressure is not critical and need only be sufficient to insure a liquid phase. Operating pressures can range from 1 to 7.8 atmospheres. The length o~ tlme required for the ion exchange will vary, depending ~-upon the solution concentration and tempera~ure, from 0.5 to 5 hours. Within the above preferred concentrations and temperature ranges, a contact time which has been shown to be especially preferred is 2 to 3 hours. Continuous or batch-type operations can be employed. The ion exchange 20 step should be controlled and so that the zeolite structure ~
will not be destroyed so that the final product wil~l have ; .
~ , a Na20/A1203 ratio greater than 0.7 and~more preferably - - from 0.75 to 1Ø
Ater the first ion-exchange step, the sodium exchanged particles are treated at second ion-exchange con~
ditions to ~ffect the essentially complete exchange of the . ~
sodium cations at the exchangeable cationic sites in the zeolite with onè or more other selected cations.
- , ' ~ ;:
.
~ 479~4 q~he c~tiolls which may be placed u~on th~ ze~
olit~ are sclected from pot~ssium, cesium, and rubidiurn.
, C~tiollic or base exehanc~e methods are cJen~rally known to those f~iniliar ~7ith the ield of crystalline aluminosilicate production. They are generally performed ~-~
by contactingi the zeolite with an aqueous solu~ion of the soluble salts of the cation or cations desired to be placed ~
upon the zeolite. The desired degree of exchange takes ~ ~`
place and then the sieves are removed from the aqueous solution, washed and dried to a desired water content. It is contemplated that cation exchange operations may take place using individual solutions of desired cations to be placed on the zeolite or using an exchange solution con- ;
taining a mixture of cations9 where two or more desired cations are to be placed on the zeolite.
When singular cations are based exchanged upon ' a zeolite the singular cations can comprise anywhere from `;~
5 up to 75 wt. % on a relative volatile free basis o the ~- zeolite depending upon the molecular weight of the material exchanged upon the zeolite. It is contemplated that when single ions are placed upon the zeolite that they may be on the zeolite in concentrations of from 1% to 100% of the original cations present ~generally sodium) upon the zeolite prior to its being ion-exchanged.
.
~ When two or more cations are placed upon the ze~
olite there is an additional parametre in which one can operate in order to effectively produce a zeolite having the desired pro~erties. Beside9 the extent of the zeolite -.
ion exchange, which is determined by variables such as the : , ' ~ ' ' ' :''''`; " ~ ' ,,, ~;
~ 79~4 lcngth o~ ion-cxchAncJe times, ion-exchang~ temp~r~ture, and cation conc~ntrations, on~ can also vary the ratio of individu~l cations placed on the zeolite.
Secolld ion-exchange conditions will include a temperature of fxom 10 to 121 C and a pH suffici2nt to preclude the formation of the hydrogen orm of the zeolite.
The p~ will therefore be greater than 7 and preferably ;~
within the range of 7 to 10. Operating pressure is not critical and need only be sufficient to insure a liquid :,: .,:
phase. Operating pressures can range from 1 to 11.2 atmospheres. The length of time for the essentially com~
plete exchange of the sodium cations will be from 0.5 to ~ 5 hours depending upon the concentration of the cation in the ion exchange medium and the temperature. The term "essentially complete exchange" as used herein shall mean that the sodium cation content of the base material has been reduced to about 2.0 wt. % or less and more preferably to about 1 wt. % or less When the adsorbent is to contain postassium, the sodium exchanged particles, produced by the first ion exchange, may be ion exchanged with an aqueous SOlUtiOTI of ;~
a potassium salt, preferably an aqueous solution o~ potas-sium chloride, for a time sufficient to reduce the sodium - ;~ `
.
cations to less than about 2 wt. % of the zeolite and yield the potassium form of the zeolite. The exchange can be - either a continuous or a batch type operation. The ion~
~ ~ ~ exchange is suitably accomplished on passing a 7 wt. %
: ~
aqueous potassium chloride solution through a bed of the _g~
~ , ~(~47944 sodium-exch.~ Jed particles at about ~2C at a li~uid hourly space v~locity oE about one until a total o~ ap-proximately 13 yrams of solution per cJL~am of s~id parti-cl~s has b~n passed in contact therewith. Small amounts of potassium hydroxide will be added to the ion exchange solution to maintain the pl-I of the solution within the ~ ;
range of from 7 to about 10. Since the primary purpose of the sodium cation ion exchange was -to remove hydrogen cation (and metal cation~ contaminant:s, this p~I ranye is `~
necessary to avoid redepositing hydrogen cation on the ad~
sorbent mass. - ;~
The potassium-exchanged particles can then be - -washed with water to remove excess ion-exchange solu~ion.
The washing medium will be water to which has been added small amounts of potassium hydroxide to adjust and main-tain the pH within the range of 7 to about 10. Washing temperatures can include temperatures within the range of 38 to 93C. Although the washing step can be done in a ` ;
batch manner with one aliquot of wash water at a time, the washing step is generally and preferably done on a con-.
tinuous flow type basis with water passed through a bed of the adsorbent at a given liquid hourly space velocity and `~
a temperature for a period of time in order that from 1 to 5 gallons of water per pound of starting material is used to wash the material. Preferred washing conditions include using liquid hourly space velocities from about 0.5 to 5, ~
with 1.5 being preferred, to pass from about 1 to about 3 `- ~ !
:
gallons of wash water per pound of starting material over the ion exchanged adsorbent.
' -10- , , 1~47944 ,:
Wh~n ~he wash step is comp].eted, tile we~ ad-sorbellt pclrticles will usua]ly contain from about 30 to about 50 wt. ~ volatile matter (wate~) as Measured by loss on i~nition to 900C. In t~is specification, ~he volatile ~ ~
-.:
matter cont~nt of the zeolitic adsorbent is determined by the ~' wei~h-t difference obtaincd beEore and aftex dryiny a sample of adsorbent in a high temperature urnace at 900C under ~
an inert purge gas stream such as nitrogen for a period of --time sufficient to achieve a constant weiyht. The dif-ference in weight, calculated as a percentage of the sampleis initial weight, is reported as loss on ignition ~ , ;' (LOI) at 900C and represents the volatile matter present ~ , within the adsorbent. ' The remaining step in the method of,manufacture 15 then is the drying step to reduce the LOI at 900C to less- '~
, than 10 wt. % with the preferred LOI being 3 to 7 wt. ~
After the washing has been completed, the particles can be ',~ :
unloaded and dried in a forced air,oven at temperatures a-, bove the boiling point of water but less than 500 C and preferably about 150C, for a period of time sufficient to remove enough water so that the volatile matter conten-t of the zeolite is below about 10 wt. %. Other methods of dry~
ing ~ay be used which can include drying in the presence of an inert gas or under a vacuum, or ~oth.
.
Feed stocks which can be used in the adsorption ,~
separation process of this invention which employs the ad~
sorbent prepared by the method of this invention are characterised by the formula shown in formula 2 below~
..
. .
iL04~
Formula ~
~ . . .~ : ,.
S
4 ~
''' "'` . -wherein Rl, R2, R3, and R4 are selected from the yroup of ;~alkyl chains in a manner to allow an essentially bi-alkyl substitution at either ortho-, meta-, or para-isomer posi-tions. The R substitutional groups can includ~ alkyl groups ranging from methyl substitution groups up to and inoluding chains havlng 11 or less carbon atoms per mole-cule. The alkyl side chains can be both normal and branch~
ed in nature and are preferably saturated chains.
Specific representative compounds which can be utilised as feedstocks in the process include those feed-. ~
stocks containing the xylene isomers and ethylbenzene andthe various isomers of methylethylbenzene, diethylbenzene, ~ ~`
isopropyltoluene(cymen~)~ the methylpropylbenzeneS, ethyl~
propylbenzenes, methylbutylbenzenes, ethylbutylbenzene, ;
dipropylbenzenes, methylpentylbenzene, etc., and combi~
nations thereof. The above lis-t only represents a small ` fraction of compounds whose isomers can be separated by the adsorptive-separation process of this invention which :. .
employs tlle specially prepared adsorbent produced ~y th~
method o~ this invention. Thus the process of this in~
vention will b~ typically used to separate para-xylene from a feed mixture comprising para-xylene and at least ~'' . ` ,1 ~, i.~)47944 ~
one o~her ('~ arom~ltic isome].; p~rc~-di~thylbcnzene ~rom a ~ :
feed mixture com~rising para-~i.ethyl~enzene and at least one other diethylbenzene isomer; and para-cymene from a feed mixture compri.sing para-cymene and at least one other cymene isomer to name a few. . ~:
. The isomers of such compounds are separated by ~ ~
this adsorbent according to their conEiyuration depending ^ .-whether they are of a para-, meta-, or ortho-isomer con-struction. Specifically, the para-isomer is selectively adsorbed relative to the other isomers. It is contem~
.. plated that with feedstocks containing mixtures of more .:
than one class of isomers (for example, C8 isomers in mix~
ture with Cg or C10 isomers) molecular weight differences ;.: :~
will unduly interfere with selective adsorption based up-. 15 on isomer configuration differences. It is therefore preferred that the process utilising the adsorbent pro~
duced by the method of this invention to employ feed-stocks comprisin~ only a single class of aromatic isomers, ~ that is, aromatic isomers having an equal number of carbon atoms per molecule. It is more pre~erable to use isomers having as their only differences the location of the alkyl substituted groups in a para-, meta-, or ortho-position.
The alkyl structures should preferably be the same for : each isomer o~ a classO In some instances an isomer may have alkyl chains which are both normal or branched or one branched and one normal.
: To separate the para-isomer from a feed mixture :: :
containing para-.isomer and at least one other aromatic isomer the mixture is contacted with an adsorbent comprising : ` ~' , -13- ~:
, ~:
, ~:
~04~34~ ~
a crysl:alline alunl;no~i]lcate alld the para~isomer is mor~
selectively adsorbed and r~tained by the adsorbent whil~ ~ -the other isomers are r~latively unadsorbed al-d are re-moved from the interstitial void spaces betwcen the p~rti~
. .
cles of adsorbent and the sur~ace of the adsorbent. The adsorbent containing the more selectively adsorbed para~
isomer is referred as a "rich" adsorbent--rich in the more '- : ~' selectively adsorbed para-isomer.
The more selectively adsorbed feed component is -~ ~ ~
10 commonly referred to as the extract component of the feed ~ ~ -mixture, while the less selectively adsorbed component is -referred to as the raffinate component. Fluid streams .leaving the adsorbent comprising an extract component and comprising a raffinate component are referred to, respec-15 tively, as the extract stream and the raffinate stream.
Thus, the raffinate stream will contain as raffinate co~-ponents all of the feed mixture isomers except the para-- isomer and the extract stream will contain the para-isomer ?
::
as the extract component. ;
The adsorbent can be contained in one or more .: -:
chambers where through programmed flow into and out of the chambers separation of para-isomer is effected. The ad~
sorbent will preferably be contacted with a desorbent ma-~ terial which is capa~le of displacing the adsorbed para~
isomer from the adsorbent. An extract stream comprising .~, .
- the para-isomer and desorbent material separated there~
by leaving high purity para-isomer. Alternatively, the para-isomer could be removed from the adsorbent by purging or by increasing the temperature of the adsorbent or by ;
' . `:
-14- - ~
.:' ~'~ ',:
104~
d~creasincJ the prcssurc! o~ t.he ch~rn~)er or v~ss~l Cont~irl-incj t}l~ adsorbent or by ~ combina~ion of these meanC,.
; The a~lsorbent m~y be ~Inp].oyed in thc form of a dense compact fixed bed which is alterna~ive].y contacted with the feed mixture and a desorhent material (hexein-after described in more d~tail). In the simplest embodi~
ment of the invention th~ adsorbent is employed in the . :
form of a single static bed in which case the process is only semi-continuous. A set of two or more static beds may be employed in fixed-bed contacting with appropria-te valving so that the feed mixture is passed through one or more adsorbent beds while the desorbent material is passed through one or more of the other beds in the set. ;
:.
The flow of feed mixture and desorbent material may be 15 either up or down through the desorbentO Any of the `
, conventional apparatus employed in static bed fluid-solid contacting may be used. Countercurrent moving-bed or simulated countercurrent movlng-bed liquid flow systems, however, have a much greater separation efficiency than ~ixed adsorbent bed systems and are therefore preferred.
In the mov1ng-bed or simulated moving-bed processes the adsorption and desorption operations are continuously taking place which allows both continuous production of an ``
extract and a raffinate stream and the continual use of ~5 feed and desorben streams. One preferred processing flow .
scheme which can be utilised to effect the process of this invention includes what is known in the art as the simulated moving-bed countercurrent system~ The general operating . ~
sequence of such a flow system is described in U.5. Patent , lV47~44 ~ ~
2,985,58~ ~ncllnore specif;c~lly in U.~. PateltS 3,558, 730; 3,55~,732; 3,626,0~0; 3,663,638; and 3,6~6,342.
These p~tents describ~ the proc~ssinc~ secluenc:e of the 2,985,5~9 p~t~nt employed in particular sim~lated moving-bed coun-tercurrent solid-fluid contacting processes. The processing se~uence disclosed in these patents i5 the pre- ;
ferred mode of operating the separation process disclosed herein.
Adsorption and desorption conditions for ad-sorptive separation processes can generally be either in the liquid or vapour phase or both but for aromatic isomer separation processes employing zeolitic adsorbents all liquid-phase operations are usually preferred because of the lower temperature requirements and the slightly im-15 proved selectivities associated with the lower temper- -atures. Preferred adsorption condltions ~or the process of this invention will include temperatures within the range from 21 to 232C and will include pressures in the range from I to 35 atmospheres. Desorption conditions for ~`
the process of the invention shall generally include the same range of ~emperatures and pressures as described for ' . .
adsorption operations. The desorption of the selectively ; adsorbed isomer could also be effected at subatmospheric pressures or elevated temperatures or both or by vacuum i~
25 - purging of the adsorbent to remove the adsorbed isomer but ~-this process is not directed to these desorption methods.
The desorbent material which can be used in the ~ -..
various processing schemes employing this adsorbent will vary depending on the type of operation employed. The -16~
,:'"" ~'''~': ~"
' . , . "-'',.' "" ' : : :~.:
~479~4 term "clesor~)ent material" as ~lse~l he~eln shal]. mean any ':
fluid substancc capable o~ relnOVin~J a selec~ively ad-sorbed feed componerlt from the adsorbent. In the swing-bed system in wllich the select.i.vel.y adsorbed feed com- ~ , ' po~ent i.s removed from the adsorbent by ,a pur~Je stream, desorbent materials comprisin~ ~aseous hydrocarbons such as methane, ethane, etc., or other types of ~ases such as nitrogen or hydrogen may be used at elevated temperatures '~
or reduced pressures or both to effectively purge the ad- ; : .
10 sorbed feed component from the adsorbent. :'' However, in adsorptive separation processes :
which employ zeolitic adsorben~s and processes which are .: :
generally operated at substantially constant pressures and temperatures to insure liquid phase, the desorbent material relied upon must be judiciously selected to satisfy several criteria. First, the desorbent material must displace the ~ ~' .-.
adsorbed feed component from the adsorbent with reasonable ' :~
- :
mass flow rates without itself being so strongly adsorbed as to unduly prevent the extract component from displacing '~
~, 20 the desorbent material in a following adsorption cycle. ,~
Secondly, desorbent materials must be compatab,le with the ,~
particular adsorbent and the particular feed mixture. More .,~
specifically, they must not reduce or destroy the critical ., :
seIectivity of the adsorbent for the extract component with ... ,~
25 respect to the raffinate components. ~:;~ ',.', . ~esorbent materials to be used in the process of . .,' :this invention should additionally be substances which are ... '~
: . ~: :
easily separa~le from the feed mixture that is passed into" ' the process. In desorbing the preferentially adsorbed ~ '~
-17- , '`''''.
:
, :
10479~4 component of ~he ~ed, bo~h ~esorb~n~, mat~ria~ ~nd ~he extract componen~ are removed irl a~mi.~ture ~ro~ the ad~ ~-sorbent. Wi~.hou~ ~ method o~ scparation such ~s distil~
lation of these t~o materials, the purity of the extr~ct component of the feed stock would not be very high since it would be diluted with desorbent. It i5 therefore con~
templated that any desorhent material used in thi.s pro~ :-cess will have a substantially different average boiling point than that of the feed mixture. The use of a desor~ .~ -bent material having a substantially different average boiling point than that of the feed allows separation of .
desorbent material from feed,components in the extract and reffinate streams by simple fractionation thereby ' .~..~... .
permitting reuse of desorbent material in the process. '' : 15 The term "substantially different" as used herein shall .;.
mean that the dlfference between the average boiling points between the desorbent material and the feed mixture shall be at least 8C. The boiling range of the desorbent.ma~
. terial may be higher or lower than that of the feed,mix~
2 0 ture .
Preferred desorbent materials for use in the :~
process of this invention are those comprising toluene .;``~
~; . and diethylbenzene. Mixture of these compounds with .
; paraffins are also efective as desorbent materials. Such .;
:25 . paraffins must be compatable with the adsorbent and feed mixture as described above and must be easily separable -,.. ,~
; irom the feed mixture. The paraffi.ns can includc straight ; or branched chain paraffins or cycloparaffins which meet ~, : these criteria... Typical concentrations of toluene or .
'~
-'~
' ' ' -, ~: .
~479~4 diethy:lb~ ene in mix.tures oE sc~rne and ~ par~in Call be fron~ a few vo]~lme pe~cent up to near 100 vol. % of l:he total desor~erlt material mixture but suc:h concentrations preferably will be within -the ran~e of frorn 50 vol. ~ to 100 vol. ~ o~ th~ mixture.
The improved adsorl~nt produced by the method of our invention can be better understood by brief re~
ference to certain adsorbent properties which are neces-sary to the successful operation of a selective adsorption process. It will be recognised that improvements in any of these adsorbent characteristics will result in an im-proved separation process. Among such characteristics ~ .
are: adsorptive capacity for some volume of an extract `~
component per volume of adsorbent, the selective adsorp~
tion of an extract component with respect to a raffinate component and the desorbent material; sufficiently fast rates of adsorption and desorption of the extract com-ponent to and from the adsorbent; and, in instances where the components of the feed mixture are very reactive, .... ~
little or no catalytic activity for undesired reactions such as polymerisation and isomerisation.
Capacity of the adsorbent for adsorb1ng a specific volume of an extract component is, of course, a necessity; wLthout such capacity the adsorbent is useless 25 for adsorptive separation. Furthermore, the higher the -~
adsorbent's capacity for an extract component, the better ~ -is the adsorbent. Increased capacity of a particular ad-sorbent makes it possible to reduce the amount of ad-sorbent needed to separate the extract component contained in a particular charge rcate of feed mixture. A reduction in the amoun-t of adsorbent required for a specific ad-sorptive separation reduces the cost of the separation :. . -, -19- . - , :.
. ,-.; ' . ! . . ' .' : ' , - . . , . ' ' . : ~ , ~ .
~47944 - ~
process. It is ;.mpoxtant that the yoocl initial c~paclty of thc adsorbant be maintained du~in~ actua.l use in the separation process over some economically d~sixabl~ life.
. The second necessary adsorbent characteristic, ~ ::
is the ability of ~he aclsorb~n~ to sep~rate compon~nts :~
. of the feed; or, in other words, that the adsorbent ; .~ .
..
possess adsorptive selectivi~y for one component as com~
pared to another component. Some adsorbents demonstrate acceptable capacity but possess li~tle or no selectivity~
10 Relative selectivity can be expressed not only for one ~ .; .
feed mixture component as compared to another but can `~
also be expressed between any feed mixture component and .. ~ the desorbent. The relatlve selectivity, (B), as used throughout this specification is defined as the ratio of ; 15 : two components o~ an adsorbed phase over the ratio of the same two components in an unadsorbed phase at equili~
brium conditions.
'. Relative selectivity i5 shown as Equation 1 be~
,:. ,, low:
Equation 1 Selectivity = (E) = [vol. percent c/vol. percent D3A
[vol. percent c/vol. percent lU
.... ...
where C and D are two components of the feed represented in ; - ~
volume percent and the subscripts A and U represent the ad~
25 sorbed and unadsorbed phases respectively. The equilibrium .. `~
~:: conditions were determined when the feed passing over a bcd -.
of adsorbent did not change composition after contacting :;
the bed o~ adsorbent. In other words, there was no net transfer of matcrial occurring between the unadsorbed and . .
.' ~.
.
.. ,.. ... .. .... , . ~ .. . . .
.. .... , ,.. - .. - . . , .. . ~ .. . .
~;34794ds adsor~e~ ph~c:es.
Wh~le seleekivity o~ t~o componen-ts approaches 1.0 there is no preferential adsorption of one component by the adsorbent with respcct to the other; they are both adsorbed (or non-adsorbed) to about ~he sarne de~ree with respect -to each other. As the (B) becomes less than or ~ ;
greater than 1.0 there is a preferential adsorption by ~
the adsorbent for one component ~ith respect to the other. ~;-When comparing the selectivity by the adsorbent of one component C over component D, a (B) larger than 1.0 indi~
,.,~
cates preferential adsorption of component C within the ~
,, ~
adsorbent. A (B) less than 1.0 would indicate that com- -~
ponent D is preferentially adsorbed leaving an unadsor~
bed phase richer in component C and an adsorbed phase -~
richer in component D. Desorbent materials i~eally would have a selectivity equal to about 1 or slightly less than 1 with respect to an extract component. -~
The third important characteristic is the rate of exchange of the extract component of the feed mixture material or, in other words, the relative rate of de-sorption of the extract component. This characteristic re~
. ~ ..
lates directly to the amount of desorbent material that ~ ~ -must be employed in the process to recover the extract component from the adsorbent; faster rates of exchange reduce the amount of desorbent material needed to remove the extract component and therefore permit a reduction in ,, the operating cost of the process. With faster rates of ~-exchange, less desorbent material has to be pun-ped through the process and separated from the extract stream for reuse - ~: . :
~ -21- ~ ~
,:" ' ' '~ -.
. ~, . ~
~ 7944 in the ~roc~ss.
The adsorbent E)roclucecl by the method of this invention not only has good aromatic capacity and ~ood se]ectivity but has faster transfer rates than does an adsorbent not produced by this method.
It is also necessary tha~ the adsorbent possess little or no catalytic actlvity toward any reaction such as polymeris~tion or isomerisation of any of the feed ;! ~-components. Such activity might effect adsorbent capacity :-: .
10 or selectivity or product yields or all of these, but in ~;
the adsorptive separation of aromatic hydrocarbon isomers with a zeolite-containing adsorbent this is generally not a problem.
In order to test various adsorbents and desor~
; :: . . . .
bent material with a particular feed mixture to measure the adsorbent characteristics of adsorptive capacity and selectivity and exchange rate a dynamic testing apparatus `~
is employed. The apparatus consists of an adsorbent cham~
ber of approximately 70 cc volume having inlet and outlet portions at OppQSite ends of the chamber. The chamber is contained within a temperature control means and, in addi-tion, pressure control equipment is used to operate the chamber at a constant predetermined pressure. Chroma-tographic analysis equipment can be attached to the out~
let line of the chamber and used to analyse the effluent stream leaving the adsorbent chamber.
A pulse test, performed using this apparatus and the following general procedure, is used to determine selectivities and other data for various adsorbent systems.
, The adsor~slt: was fill~d to c(~uilibL~iuln wi~h a r)a~ti-cular desorl-)e}lt by pas~.incJ the dcsor~n~ throll~JIl ~he adsorbent chambex. At a convenien~ t:ime, a ~ulse o~ -feed containing kno~n concen~rations o a non-adsorbed paraffinic tracer (n-nonane) and of aromatlc isomers all diluted in desorben~ is injectecl for a duration of several minutes. Desorbent flow is restlmed, and the tracer and ;
the aromatic isomers are eluted as in a liquid-solid chromatographic operation. The effluent is analysed by on-stream chromatographic equipment and traces of the envelopes of corresponding component peaks are developed. ~ -From information derived from the chromatographic ~-traces adsorbent performance can be rated in terms of capacity index for the para-isomer, selectivi~y for the para-isomèr with respect to the other isomers and rate of desorption of the para-isomer by the desorbent. The ;~ -capacity index is characterised by the distance between the centre of the para-isomer peak envelope and the Cg ;~;
tracer peak envelope. It is expressed in terms of the voIume in cubic centimetres of desorbent pumped during this time interval. ~ Selectivity, (B), for para-isomer with re-spect to the other isomers (p/m, p/o) is characterised by the ratio of the distance between the centre of the para- ~;
isomer peak envelope and the Cg tracer peak envelope to the corresponding distance for the other isomers.`
EXAMPLE: Two potassium-exchangedtype-Yzeolite were pre-` pared in accordance with the method of the present inven- ~!' I tion. The selectivities for ~hese adsorbents were then evaluated by the pulse test. The feed stock contained '~
~ '~
~ ~7~4~ ~ :
th~ ~ylelle i~om~rs and etllyl~en~elle. Tlle a~sorhent:s were tes~ed or para~xylene/~thylberl~ene selectivi-~y ~) p-x/EB' ancl for p~r~-~;ylene/llteta-~yl~nè s~l~cl:ivit:y ~B) p ~/rn usin~J t~lO type~ oE desorberlts, na~,ely, toluene and par~
dietllyl~enzene (p-D~B~.
The results of the adsorptive testiny for the two adsorbents are shown in Table 1 below. .
Ta~le 1 .
ADSORBENT S E L E C T I V I 1' Y
_ . .. _ _ _.____ _ ___ . :~
p-DEB Toluene p-rJm-y~ - ~ p-x/m-x ( ) p-x/EB
._. .. . . . . .
Type-Y ~eolite ¦ .
SiO2/Al O3 = 3.7 2.14 1.40 2.03 1.27 lS K-Excha~lyed . . . ~.
Type-Y Zeolite . .
Si2/~123 = 4-9 3.60 2.00 3.05 1.77 - :.
: K-~xchanged . L _ __ _ _ . _ ~
, - .
The results clearly demonstrate that the two ad-sorbents which are prepared in accordance with the present invention preferentially adsorb the para-isomer from a feed , . ~ , : .
mixture containing at least two ison7ers.
~ ~ ' : . . ,: .
..
:, ., :~
-24~
, . :
,~ ;.. , . . : ~ . , ~47944 p.r~`sent .i.n illtimate mlxt~lr~ l th~ zeo:l.it~ In~terial.
This ~morphous m~terial may be an ~1 junct t~ the man~factur-~ncJ process of the type ~ ~eolite (for ex~mple, interl-tionally .incomplete purification oE thc zeol.ite d~ring its ~ .
manufacture) or it may be added to the relatively pure ze-olite to aid in Eorming or agglomerating particles o~ the . .:
zeolite.
We have found that trea-ting a type Y base ma-terial with a dilute acqueous sodium hydroxide solution 10 prior to a subsequent ion exchange of the treated base ma- ~ .
terial to effect the replacement of sodium cations at the - ~ .
exchangeable cationic sites with one or more other selec- .~
ted cations produces a superior adsorbent when used in a ~ ~:
, .
process for the separation of the para-isomer from.a hy~
15 drocarbon feed mixture comprising at least two bi-alkyl ;~
substituted aromatic.isomers including the para-isomer, . ;.
.... .. .
the isomers having from 8 to 18 carbon atoms per molecule.
This treatment step is in the nature of an ion exchange ~- -step (and will hereinafter be referred to as the first ion exchange) since the NaOE~ solution replaces non-sodium im~
purities in the type Y zeolite contained in the base ma- .~
terial thereby converting the zeolite essentially complete~
ly to the sodium form. More specifically, to produce an .. ;:
~,:,~ ' :' acceptable adsorbent it is preferred that the sodium con-~ent of the startin~ material, as characterised by the weight ratio Na20~Al203, be increased to a ratio greater -~
: than 0.70 and more preferably from 0.75 to l.O. First ion -:
exchange conditions should be so regulated to achieve this degree of ion exchange.
_fi_ ~:
Thc soclium hy(lr.oxide used to pr~pa~e the aqu~ouc.
sodium hydro~idc solution should be oE hicJh purity having ~ery low levels of both other Group IA impuritic~s and Group IIA impurities. Sui-table concellt~cl-tions to obtain the de-sired ion exchange can be from 0.5 to 10 wt. ~ of the sod~
ium hydroxide with the preferred concentration beiny from ~-0.5 to 5 wt. ~. By using solutions containing sodium hy~
droxide within these ranges of concentration, the desired first ion exchange can be obtained at temperatures from 10 ..
to 121C with temperatures from 66 to 121 C be~ng especial- ;
ly preEerred. Operating pressure is not critical and need only be sufficient to insure a liquid phase. Operating pressures can range from 1 to 7.8 atmospheres. The length o~ tlme required for the ion exchange will vary, depending ~-upon the solution concentration and tempera~ure, from 0.5 to 5 hours. Within the above preferred concentrations and temperature ranges, a contact time which has been shown to be especially preferred is 2 to 3 hours. Continuous or batch-type operations can be employed. The ion exchange 20 step should be controlled and so that the zeolite structure ~
will not be destroyed so that the final product wil~l have ; .
~ , a Na20/A1203 ratio greater than 0.7 and~more preferably - - from 0.75 to 1Ø
Ater the first ion-exchange step, the sodium exchanged particles are treated at second ion-exchange con~
ditions to ~ffect the essentially complete exchange of the . ~
sodium cations at the exchangeable cationic sites in the zeolite with onè or more other selected cations.
- , ' ~ ;:
.
~ 479~4 q~he c~tiolls which may be placed u~on th~ ze~
olit~ are sclected from pot~ssium, cesium, and rubidiurn.
, C~tiollic or base exehanc~e methods are cJen~rally known to those f~iniliar ~7ith the ield of crystalline aluminosilicate production. They are generally performed ~-~
by contactingi the zeolite with an aqueous solu~ion of the soluble salts of the cation or cations desired to be placed ~
upon the zeolite. The desired degree of exchange takes ~ ~`
place and then the sieves are removed from the aqueous solution, washed and dried to a desired water content. It is contemplated that cation exchange operations may take place using individual solutions of desired cations to be placed on the zeolite or using an exchange solution con- ;
taining a mixture of cations9 where two or more desired cations are to be placed on the zeolite.
When singular cations are based exchanged upon ' a zeolite the singular cations can comprise anywhere from `;~
5 up to 75 wt. % on a relative volatile free basis o the ~- zeolite depending upon the molecular weight of the material exchanged upon the zeolite. It is contemplated that when single ions are placed upon the zeolite that they may be on the zeolite in concentrations of from 1% to 100% of the original cations present ~generally sodium) upon the zeolite prior to its being ion-exchanged.
.
~ When two or more cations are placed upon the ze~
olite there is an additional parametre in which one can operate in order to effectively produce a zeolite having the desired pro~erties. Beside9 the extent of the zeolite -.
ion exchange, which is determined by variables such as the : , ' ~ ' ' ' :''''`; " ~ ' ,,, ~;
~ 79~4 lcngth o~ ion-cxchAncJe times, ion-exchang~ temp~r~ture, and cation conc~ntrations, on~ can also vary the ratio of individu~l cations placed on the zeolite.
Secolld ion-exchange conditions will include a temperature of fxom 10 to 121 C and a pH suffici2nt to preclude the formation of the hydrogen orm of the zeolite.
The p~ will therefore be greater than 7 and preferably ;~
within the range of 7 to 10. Operating pressure is not critical and need only be sufficient to insure a liquid :,: .,:
phase. Operating pressures can range from 1 to 11.2 atmospheres. The length of time for the essentially com~
plete exchange of the sodium cations will be from 0.5 to ~ 5 hours depending upon the concentration of the cation in the ion exchange medium and the temperature. The term "essentially complete exchange" as used herein shall mean that the sodium cation content of the base material has been reduced to about 2.0 wt. % or less and more preferably to about 1 wt. % or less When the adsorbent is to contain postassium, the sodium exchanged particles, produced by the first ion exchange, may be ion exchanged with an aqueous SOlUtiOTI of ;~
a potassium salt, preferably an aqueous solution o~ potas-sium chloride, for a time sufficient to reduce the sodium - ;~ `
.
cations to less than about 2 wt. % of the zeolite and yield the potassium form of the zeolite. The exchange can be - either a continuous or a batch type operation. The ion~
~ ~ ~ exchange is suitably accomplished on passing a 7 wt. %
: ~
aqueous potassium chloride solution through a bed of the _g~
~ , ~(~47944 sodium-exch.~ Jed particles at about ~2C at a li~uid hourly space v~locity oE about one until a total o~ ap-proximately 13 yrams of solution per cJL~am of s~id parti-cl~s has b~n passed in contact therewith. Small amounts of potassium hydroxide will be added to the ion exchange solution to maintain the pl-I of the solution within the ~ ;
range of from 7 to about 10. Since the primary purpose of the sodium cation ion exchange was -to remove hydrogen cation (and metal cation~ contaminant:s, this p~I ranye is `~
necessary to avoid redepositing hydrogen cation on the ad~
sorbent mass. - ;~
The potassium-exchanged particles can then be - -washed with water to remove excess ion-exchange solu~ion.
The washing medium will be water to which has been added small amounts of potassium hydroxide to adjust and main-tain the pH within the range of 7 to about 10. Washing temperatures can include temperatures within the range of 38 to 93C. Although the washing step can be done in a ` ;
batch manner with one aliquot of wash water at a time, the washing step is generally and preferably done on a con-.
tinuous flow type basis with water passed through a bed of the adsorbent at a given liquid hourly space velocity and `~
a temperature for a period of time in order that from 1 to 5 gallons of water per pound of starting material is used to wash the material. Preferred washing conditions include using liquid hourly space velocities from about 0.5 to 5, ~
with 1.5 being preferred, to pass from about 1 to about 3 `- ~ !
:
gallons of wash water per pound of starting material over the ion exchanged adsorbent.
' -10- , , 1~47944 ,:
Wh~n ~he wash step is comp].eted, tile we~ ad-sorbellt pclrticles will usua]ly contain from about 30 to about 50 wt. ~ volatile matter (wate~) as Measured by loss on i~nition to 900C. In t~is specification, ~he volatile ~ ~
-.:
matter cont~nt of the zeolitic adsorbent is determined by the ~' wei~h-t difference obtaincd beEore and aftex dryiny a sample of adsorbent in a high temperature urnace at 900C under ~
an inert purge gas stream such as nitrogen for a period of --time sufficient to achieve a constant weiyht. The dif-ference in weight, calculated as a percentage of the sampleis initial weight, is reported as loss on ignition ~ , ;' (LOI) at 900C and represents the volatile matter present ~ , within the adsorbent. ' The remaining step in the method of,manufacture 15 then is the drying step to reduce the LOI at 900C to less- '~
, than 10 wt. % with the preferred LOI being 3 to 7 wt. ~
After the washing has been completed, the particles can be ',~ :
unloaded and dried in a forced air,oven at temperatures a-, bove the boiling point of water but less than 500 C and preferably about 150C, for a period of time sufficient to remove enough water so that the volatile matter conten-t of the zeolite is below about 10 wt. %. Other methods of dry~
ing ~ay be used which can include drying in the presence of an inert gas or under a vacuum, or ~oth.
.
Feed stocks which can be used in the adsorption ,~
separation process of this invention which employs the ad~
sorbent prepared by the method of this invention are characterised by the formula shown in formula 2 below~
..
. .
iL04~
Formula ~
~ . . .~ : ,.
S
4 ~
''' "'` . -wherein Rl, R2, R3, and R4 are selected from the yroup of ;~alkyl chains in a manner to allow an essentially bi-alkyl substitution at either ortho-, meta-, or para-isomer posi-tions. The R substitutional groups can includ~ alkyl groups ranging from methyl substitution groups up to and inoluding chains havlng 11 or less carbon atoms per mole-cule. The alkyl side chains can be both normal and branch~
ed in nature and are preferably saturated chains.
Specific representative compounds which can be utilised as feedstocks in the process include those feed-. ~
stocks containing the xylene isomers and ethylbenzene andthe various isomers of methylethylbenzene, diethylbenzene, ~ ~`
isopropyltoluene(cymen~)~ the methylpropylbenzeneS, ethyl~
propylbenzenes, methylbutylbenzenes, ethylbutylbenzene, ;
dipropylbenzenes, methylpentylbenzene, etc., and combi~
nations thereof. The above lis-t only represents a small ` fraction of compounds whose isomers can be separated by the adsorptive-separation process of this invention which :. .
employs tlle specially prepared adsorbent produced ~y th~
method o~ this invention. Thus the process of this in~
vention will b~ typically used to separate para-xylene from a feed mixture comprising para-xylene and at least ~'' . ` ,1 ~, i.~)47944 ~
one o~her ('~ arom~ltic isome].; p~rc~-di~thylbcnzene ~rom a ~ :
feed mixture com~rising para-~i.ethyl~enzene and at least one other diethylbenzene isomer; and para-cymene from a feed mixture compri.sing para-cymene and at least one other cymene isomer to name a few. . ~:
. The isomers of such compounds are separated by ~ ~
this adsorbent according to their conEiyuration depending ^ .-whether they are of a para-, meta-, or ortho-isomer con-struction. Specifically, the para-isomer is selectively adsorbed relative to the other isomers. It is contem~
.. plated that with feedstocks containing mixtures of more .:
than one class of isomers (for example, C8 isomers in mix~
ture with Cg or C10 isomers) molecular weight differences ;.: :~
will unduly interfere with selective adsorption based up-. 15 on isomer configuration differences. It is therefore preferred that the process utilising the adsorbent pro~
duced by the method of this invention to employ feed-stocks comprisin~ only a single class of aromatic isomers, ~ that is, aromatic isomers having an equal number of carbon atoms per molecule. It is more pre~erable to use isomers having as their only differences the location of the alkyl substituted groups in a para-, meta-, or ortho-position.
The alkyl structures should preferably be the same for : each isomer o~ a classO In some instances an isomer may have alkyl chains which are both normal or branched or one branched and one normal.
: To separate the para-isomer from a feed mixture :: :
containing para-.isomer and at least one other aromatic isomer the mixture is contacted with an adsorbent comprising : ` ~' , -13- ~:
, ~:
, ~:
~04~34~ ~
a crysl:alline alunl;no~i]lcate alld the para~isomer is mor~
selectively adsorbed and r~tained by the adsorbent whil~ ~ -the other isomers are r~latively unadsorbed al-d are re-moved from the interstitial void spaces betwcen the p~rti~
. .
cles of adsorbent and the sur~ace of the adsorbent. The adsorbent containing the more selectively adsorbed para~
isomer is referred as a "rich" adsorbent--rich in the more '- : ~' selectively adsorbed para-isomer.
The more selectively adsorbed feed component is -~ ~ ~
10 commonly referred to as the extract component of the feed ~ ~ -mixture, while the less selectively adsorbed component is -referred to as the raffinate component. Fluid streams .leaving the adsorbent comprising an extract component and comprising a raffinate component are referred to, respec-15 tively, as the extract stream and the raffinate stream.
Thus, the raffinate stream will contain as raffinate co~-ponents all of the feed mixture isomers except the para-- isomer and the extract stream will contain the para-isomer ?
::
as the extract component. ;
The adsorbent can be contained in one or more .: -:
chambers where through programmed flow into and out of the chambers separation of para-isomer is effected. The ad~
sorbent will preferably be contacted with a desorbent ma-~ terial which is capa~le of displacing the adsorbed para~
isomer from the adsorbent. An extract stream comprising .~, .
- the para-isomer and desorbent material separated there~
by leaving high purity para-isomer. Alternatively, the para-isomer could be removed from the adsorbent by purging or by increasing the temperature of the adsorbent or by ;
' . `:
-14- - ~
.:' ~'~ ',:
104~
d~creasincJ the prcssurc! o~ t.he ch~rn~)er or v~ss~l Cont~irl-incj t}l~ adsorbent or by ~ combina~ion of these meanC,.
; The a~lsorbent m~y be ~Inp].oyed in thc form of a dense compact fixed bed which is alterna~ive].y contacted with the feed mixture and a desorhent material (hexein-after described in more d~tail). In the simplest embodi~
ment of the invention th~ adsorbent is employed in the . :
form of a single static bed in which case the process is only semi-continuous. A set of two or more static beds may be employed in fixed-bed contacting with appropria-te valving so that the feed mixture is passed through one or more adsorbent beds while the desorbent material is passed through one or more of the other beds in the set. ;
:.
The flow of feed mixture and desorbent material may be 15 either up or down through the desorbentO Any of the `
, conventional apparatus employed in static bed fluid-solid contacting may be used. Countercurrent moving-bed or simulated countercurrent movlng-bed liquid flow systems, however, have a much greater separation efficiency than ~ixed adsorbent bed systems and are therefore preferred.
In the mov1ng-bed or simulated moving-bed processes the adsorption and desorption operations are continuously taking place which allows both continuous production of an ``
extract and a raffinate stream and the continual use of ~5 feed and desorben streams. One preferred processing flow .
scheme which can be utilised to effect the process of this invention includes what is known in the art as the simulated moving-bed countercurrent system~ The general operating . ~
sequence of such a flow system is described in U.5. Patent , lV47~44 ~ ~
2,985,58~ ~ncllnore specif;c~lly in U.~. PateltS 3,558, 730; 3,55~,732; 3,626,0~0; 3,663,638; and 3,6~6,342.
These p~tents describ~ the proc~ssinc~ secluenc:e of the 2,985,5~9 p~t~nt employed in particular sim~lated moving-bed coun-tercurrent solid-fluid contacting processes. The processing se~uence disclosed in these patents i5 the pre- ;
ferred mode of operating the separation process disclosed herein.
Adsorption and desorption conditions for ad-sorptive separation processes can generally be either in the liquid or vapour phase or both but for aromatic isomer separation processes employing zeolitic adsorbents all liquid-phase operations are usually preferred because of the lower temperature requirements and the slightly im-15 proved selectivities associated with the lower temper- -atures. Preferred adsorption condltions ~or the process of this invention will include temperatures within the range from 21 to 232C and will include pressures in the range from I to 35 atmospheres. Desorption conditions for ~`
the process of the invention shall generally include the same range of ~emperatures and pressures as described for ' . .
adsorption operations. The desorption of the selectively ; adsorbed isomer could also be effected at subatmospheric pressures or elevated temperatures or both or by vacuum i~
25 - purging of the adsorbent to remove the adsorbed isomer but ~-this process is not directed to these desorption methods.
The desorbent material which can be used in the ~ -..
various processing schemes employing this adsorbent will vary depending on the type of operation employed. The -16~
,:'"" ~'''~': ~"
' . , . "-'',.' "" ' : : :~.:
~479~4 term "clesor~)ent material" as ~lse~l he~eln shal]. mean any ':
fluid substancc capable o~ relnOVin~J a selec~ively ad-sorbed feed componerlt from the adsorbent. In the swing-bed system in wllich the select.i.vel.y adsorbed feed com- ~ , ' po~ent i.s removed from the adsorbent by ,a pur~Je stream, desorbent materials comprisin~ ~aseous hydrocarbons such as methane, ethane, etc., or other types of ~ases such as nitrogen or hydrogen may be used at elevated temperatures '~
or reduced pressures or both to effectively purge the ad- ; : .
10 sorbed feed component from the adsorbent. :'' However, in adsorptive separation processes :
which employ zeolitic adsorben~s and processes which are .: :
generally operated at substantially constant pressures and temperatures to insure liquid phase, the desorbent material relied upon must be judiciously selected to satisfy several criteria. First, the desorbent material must displace the ~ ~' .-.
adsorbed feed component from the adsorbent with reasonable ' :~
- :
mass flow rates without itself being so strongly adsorbed as to unduly prevent the extract component from displacing '~
~, 20 the desorbent material in a following adsorption cycle. ,~
Secondly, desorbent materials must be compatab,le with the ,~
particular adsorbent and the particular feed mixture. More .,~
specifically, they must not reduce or destroy the critical ., :
seIectivity of the adsorbent for the extract component with ... ,~
25 respect to the raffinate components. ~:;~ ',.', . ~esorbent materials to be used in the process of . .,' :this invention should additionally be substances which are ... '~
: . ~: :
easily separa~le from the feed mixture that is passed into" ' the process. In desorbing the preferentially adsorbed ~ '~
-17- , '`''''.
:
, :
10479~4 component of ~he ~ed, bo~h ~esorb~n~, mat~ria~ ~nd ~he extract componen~ are removed irl a~mi.~ture ~ro~ the ad~ ~-sorbent. Wi~.hou~ ~ method o~ scparation such ~s distil~
lation of these t~o materials, the purity of the extr~ct component of the feed stock would not be very high since it would be diluted with desorbent. It i5 therefore con~
templated that any desorhent material used in thi.s pro~ :-cess will have a substantially different average boiling point than that of the feed mixture. The use of a desor~ .~ -bent material having a substantially different average boiling point than that of the feed allows separation of .
desorbent material from feed,components in the extract and reffinate streams by simple fractionation thereby ' .~..~... .
permitting reuse of desorbent material in the process. '' : 15 The term "substantially different" as used herein shall .;.
mean that the dlfference between the average boiling points between the desorbent material and the feed mixture shall be at least 8C. The boiling range of the desorbent.ma~
. terial may be higher or lower than that of the feed,mix~
2 0 ture .
Preferred desorbent materials for use in the :~
process of this invention are those comprising toluene .;``~
~; . and diethylbenzene. Mixture of these compounds with .
; paraffins are also efective as desorbent materials. Such .;
:25 . paraffins must be compatable with the adsorbent and feed mixture as described above and must be easily separable -,.. ,~
; irom the feed mixture. The paraffi.ns can includc straight ; or branched chain paraffins or cycloparaffins which meet ~, : these criteria... Typical concentrations of toluene or .
'~
-'~
' ' ' -, ~: .
~479~4 diethy:lb~ ene in mix.tures oE sc~rne and ~ par~in Call be fron~ a few vo]~lme pe~cent up to near 100 vol. % of l:he total desor~erlt material mixture but suc:h concentrations preferably will be within -the ran~e of frorn 50 vol. ~ to 100 vol. ~ o~ th~ mixture.
The improved adsorl~nt produced by the method of our invention can be better understood by brief re~
ference to certain adsorbent properties which are neces-sary to the successful operation of a selective adsorption process. It will be recognised that improvements in any of these adsorbent characteristics will result in an im-proved separation process. Among such characteristics ~ .
are: adsorptive capacity for some volume of an extract `~
component per volume of adsorbent, the selective adsorp~
tion of an extract component with respect to a raffinate component and the desorbent material; sufficiently fast rates of adsorption and desorption of the extract com-ponent to and from the adsorbent; and, in instances where the components of the feed mixture are very reactive, .... ~
little or no catalytic activity for undesired reactions such as polymerisation and isomerisation.
Capacity of the adsorbent for adsorb1ng a specific volume of an extract component is, of course, a necessity; wLthout such capacity the adsorbent is useless 25 for adsorptive separation. Furthermore, the higher the -~
adsorbent's capacity for an extract component, the better ~ -is the adsorbent. Increased capacity of a particular ad-sorbent makes it possible to reduce the amount of ad-sorbent needed to separate the extract component contained in a particular charge rcate of feed mixture. A reduction in the amoun-t of adsorbent required for a specific ad-sorptive separation reduces the cost of the separation :. . -, -19- . - , :.
. ,-.; ' . ! . . ' .' : ' , - . . , . ' ' . : ~ , ~ .
~47944 - ~
process. It is ;.mpoxtant that the yoocl initial c~paclty of thc adsorbant be maintained du~in~ actua.l use in the separation process over some economically d~sixabl~ life.
. The second necessary adsorbent characteristic, ~ ::
is the ability of ~he aclsorb~n~ to sep~rate compon~nts :~
. of the feed; or, in other words, that the adsorbent ; .~ .
..
possess adsorptive selectivi~y for one component as com~
pared to another component. Some adsorbents demonstrate acceptable capacity but possess li~tle or no selectivity~
10 Relative selectivity can be expressed not only for one ~ .; .
feed mixture component as compared to another but can `~
also be expressed between any feed mixture component and .. ~ the desorbent. The relatlve selectivity, (B), as used throughout this specification is defined as the ratio of ; 15 : two components o~ an adsorbed phase over the ratio of the same two components in an unadsorbed phase at equili~
brium conditions.
'. Relative selectivity i5 shown as Equation 1 be~
,:. ,, low:
Equation 1 Selectivity = (E) = [vol. percent c/vol. percent D3A
[vol. percent c/vol. percent lU
.... ...
where C and D are two components of the feed represented in ; - ~
volume percent and the subscripts A and U represent the ad~
25 sorbed and unadsorbed phases respectively. The equilibrium .. `~
~:: conditions were determined when the feed passing over a bcd -.
of adsorbent did not change composition after contacting :;
the bed o~ adsorbent. In other words, there was no net transfer of matcrial occurring between the unadsorbed and . .
.' ~.
.
.. ,.. ... .. .... , . ~ .. . . .
.. .... , ,.. - .. - . . , .. . ~ .. . .
~;34794ds adsor~e~ ph~c:es.
Wh~le seleekivity o~ t~o componen-ts approaches 1.0 there is no preferential adsorption of one component by the adsorbent with respcct to the other; they are both adsorbed (or non-adsorbed) to about ~he sarne de~ree with respect -to each other. As the (B) becomes less than or ~ ;
greater than 1.0 there is a preferential adsorption by ~
the adsorbent for one component ~ith respect to the other. ~;-When comparing the selectivity by the adsorbent of one component C over component D, a (B) larger than 1.0 indi~
,.,~
cates preferential adsorption of component C within the ~
,, ~
adsorbent. A (B) less than 1.0 would indicate that com- -~
ponent D is preferentially adsorbed leaving an unadsor~
bed phase richer in component C and an adsorbed phase -~
richer in component D. Desorbent materials i~eally would have a selectivity equal to about 1 or slightly less than 1 with respect to an extract component. -~
The third important characteristic is the rate of exchange of the extract component of the feed mixture material or, in other words, the relative rate of de-sorption of the extract component. This characteristic re~
. ~ ..
lates directly to the amount of desorbent material that ~ ~ -must be employed in the process to recover the extract component from the adsorbent; faster rates of exchange reduce the amount of desorbent material needed to remove the extract component and therefore permit a reduction in ,, the operating cost of the process. With faster rates of ~-exchange, less desorbent material has to be pun-ped through the process and separated from the extract stream for reuse - ~: . :
~ -21- ~ ~
,:" ' ' '~ -.
. ~, . ~
~ 7944 in the ~roc~ss.
The adsorbent E)roclucecl by the method of this invention not only has good aromatic capacity and ~ood se]ectivity but has faster transfer rates than does an adsorbent not produced by this method.
It is also necessary tha~ the adsorbent possess little or no catalytic actlvity toward any reaction such as polymeris~tion or isomerisation of any of the feed ;! ~-components. Such activity might effect adsorbent capacity :-: .
10 or selectivity or product yields or all of these, but in ~;
the adsorptive separation of aromatic hydrocarbon isomers with a zeolite-containing adsorbent this is generally not a problem.
In order to test various adsorbents and desor~
; :: . . . .
bent material with a particular feed mixture to measure the adsorbent characteristics of adsorptive capacity and selectivity and exchange rate a dynamic testing apparatus `~
is employed. The apparatus consists of an adsorbent cham~
ber of approximately 70 cc volume having inlet and outlet portions at OppQSite ends of the chamber. The chamber is contained within a temperature control means and, in addi-tion, pressure control equipment is used to operate the chamber at a constant predetermined pressure. Chroma-tographic analysis equipment can be attached to the out~
let line of the chamber and used to analyse the effluent stream leaving the adsorbent chamber.
A pulse test, performed using this apparatus and the following general procedure, is used to determine selectivities and other data for various adsorbent systems.
, The adsor~slt: was fill~d to c(~uilibL~iuln wi~h a r)a~ti-cular desorl-)e}lt by pas~.incJ the dcsor~n~ throll~JIl ~he adsorbent chambex. At a convenien~ t:ime, a ~ulse o~ -feed containing kno~n concen~rations o a non-adsorbed paraffinic tracer (n-nonane) and of aromatlc isomers all diluted in desorben~ is injectecl for a duration of several minutes. Desorbent flow is restlmed, and the tracer and ;
the aromatic isomers are eluted as in a liquid-solid chromatographic operation. The effluent is analysed by on-stream chromatographic equipment and traces of the envelopes of corresponding component peaks are developed. ~ -From information derived from the chromatographic ~-traces adsorbent performance can be rated in terms of capacity index for the para-isomer, selectivi~y for the para-isomèr with respect to the other isomers and rate of desorption of the para-isomer by the desorbent. The ;~ -capacity index is characterised by the distance between the centre of the para-isomer peak envelope and the Cg ;~;
tracer peak envelope. It is expressed in terms of the voIume in cubic centimetres of desorbent pumped during this time interval. ~ Selectivity, (B), for para-isomer with re-spect to the other isomers (p/m, p/o) is characterised by the ratio of the distance between the centre of the para- ~;
isomer peak envelope and the Cg tracer peak envelope to the corresponding distance for the other isomers.`
EXAMPLE: Two potassium-exchangedtype-Yzeolite were pre-` pared in accordance with the method of the present inven- ~!' I tion. The selectivities for ~hese adsorbents were then evaluated by the pulse test. The feed stock contained '~
~ '~
~ ~7~4~ ~ :
th~ ~ylelle i~om~rs and etllyl~en~elle. Tlle a~sorhent:s were tes~ed or para~xylene/~thylberl~ene selectivi-~y ~) p-x/EB' ancl for p~r~-~;ylene/llteta-~yl~nè s~l~cl:ivit:y ~B) p ~/rn usin~J t~lO type~ oE desorberlts, na~,ely, toluene and par~
dietllyl~enzene (p-D~B~.
The results of the adsorptive testiny for the two adsorbents are shown in Table 1 below. .
Ta~le 1 .
ADSORBENT S E L E C T I V I 1' Y
_ . .. _ _ _.____ _ ___ . :~
p-DEB Toluene p-rJm-y~ - ~ p-x/m-x ( ) p-x/EB
._. .. . . . . .
Type-Y ~eolite ¦ .
SiO2/Al O3 = 3.7 2.14 1.40 2.03 1.27 lS K-Excha~lyed . . . ~.
Type-Y Zeolite . .
Si2/~123 = 4-9 3.60 2.00 3.05 1.77 - :.
: K-~xchanged . L _ __ _ _ . _ ~
, - .
The results clearly demonstrate that the two ad-sorbents which are prepared in accordance with the present invention preferentially adsorb the para-isomer from a feed , . ~ , : .
mixture containing at least two ison7ers.
~ ~ ' : . . ,: .
..
:, ., :~
-24~
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for separating the para-isomer from a feed mixture comprising at least two bi-alkyl substituted monocyclic aromatic isomers, including the para-isomer, said isomers having from 8 to 18 carbon atoms per molecule, which process comprises:
(i) contacting at adsorption conditions said mix-ture with an adsorbent prepared by the steps of: (a) con-tacting a base material comprising Y zeolite with an aqueous sodium hydroxide solution at first ion exchange conditions to effect the addition of sodium cations to said base ma-terial; (b) treating the sodium-exchanged base material at second ion exchange conditions to effect the essentially complete exchange (as defined herein) of sodium cations with one or more cations selected from potassium, cesium, and rubidium; and, (c) drying the material conditions to reduce the LOI (loss on ignition) at 900°C. to less than 10 weight percent; thereby selectively adsorbing said para-isomer; and, (ii) contacting the adsorbent with a desorbent ma-terial at desorption conditions to effect desorption of said para-isomer from the adsorbent.
(i) contacting at adsorption conditions said mix-ture with an adsorbent prepared by the steps of: (a) con-tacting a base material comprising Y zeolite with an aqueous sodium hydroxide solution at first ion exchange conditions to effect the addition of sodium cations to said base ma-terial; (b) treating the sodium-exchanged base material at second ion exchange conditions to effect the essentially complete exchange (as defined herein) of sodium cations with one or more cations selected from potassium, cesium, and rubidium; and, (c) drying the material conditions to reduce the LOI (loss on ignition) at 900°C. to less than 10 weight percent; thereby selectively adsorbing said para-isomer; and, (ii) contacting the adsorbent with a desorbent ma-terial at desorption conditions to effect desorption of said para-isomer from the adsorbent.
2. The process of Claim 1 characterised in that said para-isomer is para-xylene and said feed mixture com-prises para-xylene and at least one other C8 aromatic isomer.
3. The process of Claim 1 characterised in that said para-isomer is para-diethylbenzene and said feed mix-ture comprises para-diethylbenzene and at least one other diethylbenzene isomer.
4. The process of Claim 1 characterised in that said para-isomer is para-cymene and said feed mixture com-prises para-cymene and at least one other cymene isomer.
5. The process of any of Claims 1 to 3 char-acterised in that said cation is potassium.
6. The process of any of Claims 1 to 3 char-acterised in that said adsorption and desorption conditions are selected from a temperature within the range of from 21° to 232 C and a pressure within the range of from 1 to 35 atmospheres to maintain liquid phase.
7. The process of any of Claims 1 to 3 char-actarised in that said base material has a Na2O/Al2O3 ratio of less than 0.7.
8. The process of any of Claims 1 to 3 char-acterised in that said first ion exchange conditions include a temperature within the range of from 10° to 121°C and a sodium hydroxide solution concentration of from 0.5 to 10 weight percent.
9. The process of any of Claims 1 to 3 char-acterised in that said sodium-exchanged base material has a Na2O/Al2O3 ratio greater than 0.7.
10. The process of any of Claims 1 to 3 char-acterised in that said second ion exchange conditions include a pH sufficient to preclude formation of the hydrogen form of the zeolite, and a temperature within the range of from 10° to 121°C.
11. The process of any of Claims 1 to 3 characterised in that said desorbent material has an average boiling point substantially different (as herein defined) than that of the feed mixture.
12. The process of any of Claims 1 to 3 char-acterised in that said desorbent material comprises diethyl-benzene.
13. The process of any of Claims 1 to 3 char-acterised in that said desorbent material comprises toluene.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/562,604 US3943184A (en) | 1974-02-15 | 1975-03-27 | Aromatic hydrocarbon isomer separation process |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1047944A true CA1047944A (en) | 1979-02-06 |
Family
ID=24246959
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA247,116A Expired CA1047944A (en) | 1975-03-27 | 1976-03-04 | Aromatic hydrocarbon isomer separation process |
Country Status (7)
| Country | Link |
|---|---|
| CA (1) | CA1047944A (en) |
| ES (1) | ES446113A1 (en) |
| FR (1) | FR2305414A1 (en) |
| GB (1) | GB1535232A (en) |
| IT (1) | IT1055910B (en) |
| SU (1) | SU674666A3 (en) |
| ZA (1) | ZA76937B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8704031B2 (en) * | 2010-06-30 | 2014-04-22 | Uop Llc | Adsorptive process for separation of C8 aromatic hydrocarbons |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3878127A (en) * | 1973-05-02 | 1975-04-15 | Universal Oil Prod Co | Method of manufacturing a zeolitic absorbent |
| US3943184A (en) * | 1974-02-15 | 1976-03-09 | Universal Oil Products Company | Aromatic hydrocarbon isomer separation process |
-
1976
- 1976-02-17 ZA ZA760937A patent/ZA76937B/en unknown
- 1976-02-19 GB GB6540/76A patent/GB1535232A/en not_active Expired
- 1976-02-26 IT IT20609/76A patent/IT1055910B/en active
- 1976-03-04 CA CA247,116A patent/CA1047944A/en not_active Expired
- 1976-03-16 ES ES446113A patent/ES446113A1/en not_active Expired
- 1976-03-24 FR FR7608532A patent/FR2305414A1/en active Granted
- 1976-03-26 SU SU762338458A patent/SU674666A3/en active
Also Published As
| Publication number | Publication date |
|---|---|
| GB1535232A (en) | 1978-12-13 |
| ZA76937B (en) | 1977-04-27 |
| FR2305414B1 (en) | 1979-10-05 |
| SU674666A3 (en) | 1979-07-15 |
| IT1055910B (en) | 1982-01-11 |
| ES446113A1 (en) | 1977-06-01 |
| FR2305414A1 (en) | 1976-10-22 |
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