CA1077064A - Process for the separation of cresol isomers - Google Patents
Process for the separation of cresol isomersInfo
- Publication number
- CA1077064A CA1077064A CA245,939A CA245939A CA1077064A CA 1077064 A CA1077064 A CA 1077064A CA 245939 A CA245939 A CA 245939A CA 1077064 A CA1077064 A CA 1077064A
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- Prior art keywords
- cresol
- adsorbent
- para
- feed mixture
- alcohol
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C37/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom of a six-membered aromatic ring
- C07C37/68—Purification; separation; Use of additives, e.g. for stabilisation
- C07C37/70—Purification; separation; Use of additives, e.g. for stabilisation by physical treatment
- C07C37/82—Purification; separation; Use of additives, e.g. for stabilisation by physical treatment by solid-liquid treatment; by chemisorption
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Abstract
ABSTRACT OF THE DISCLOSURE
An improved process for the separation of a para-cresol from a feed mixture containing para-cresol and at least one other cresol isomer which process employs a cry-stalline aluminosilicate adsorbent to selectively adsorb para-cresol from the feed mixture. The improvement basic-ally comprises employing a desorbent material comprising an alcohol to increase the selectivity of the adsorbent for para-cresol thereby allowing a more efficient separation with a higher purity extract stream recovered from the pro-cess.
An improved process for the separation of a para-cresol from a feed mixture containing para-cresol and at least one other cresol isomer which process employs a cry-stalline aluminosilicate adsorbent to selectively adsorb para-cresol from the feed mixture. The improvement basic-ally comprises employing a desorbent material comprising an alcohol to increase the selectivity of the adsorbent for para-cresol thereby allowing a more efficient separation with a higher purity extract stream recovered from the pro-cess.
Description
10770f~
The field of art to which the invention pertains is solid-bed adsorptive separation with an adsorbent com-prising a zeolite. More specifically, the claimed inven-tion relates to an improved process for the separation of cresol isomers by employing a solid crystalline alumino-silicate adsorbent which selectively removes para-cresol from the feed mixture. The para-cresol is then recovered from the adsorbent through a desorption step which em-ploys a desorbent material containing an alcohol.
It is known in the separation art that certain crystalline aluminosilicates can be used to separate hy-drocarbon species from mixtures thereof. In particular, the separation of normal paraffins from branched chained paraffins can be acccmplished by using the type A zeolites which have pore openings from 3 to 5 Angstroms. Suc~ a separation process is disclosed for example in U.S. Patents
The field of art to which the invention pertains is solid-bed adsorptive separation with an adsorbent com-prising a zeolite. More specifically, the claimed inven-tion relates to an improved process for the separation of cresol isomers by employing a solid crystalline alumino-silicate adsorbent which selectively removes para-cresol from the feed mixture. The para-cresol is then recovered from the adsorbent through a desorption step which em-ploys a desorbent material containing an alcohol.
It is known in the separation art that certain crystalline aluminosilicates can be used to separate hy-drocarbon species from mixtures thereof. In particular, the separation of normal paraffins from branched chained paraffins can be acccmplished by using the type A zeolites which have pore openings from 3 to 5 Angstroms. Suc~ a separation process is disclosed for example in U.S. Patents
2,986,589 and 3,201,491. These adsorbents allow a sep-aration based on the physical size differences in the molecules by allowing the smaller or normal hydrocarbons to ~e passed into the cavities within the crystalline aluminosilicate adsorbent, while exciuding the larger or branched chain molecules.
U.S. Patents 3,265,750 and 3,510,423 for example disclose processes in which larger pore diameter zeolites such as the type X or type Y structured zeolites can be used to separate olefinic hydrocarbons.
The type X or type ~ zeolites have additionally been employed in processes to separate individual hydro-carbon isomers. In the process described in U.S. Patents
U.S. Patents 3,265,750 and 3,510,423 for example disclose processes in which larger pore diameter zeolites such as the type X or type Y structured zeolites can be used to separate olefinic hydrocarbons.
The type X or type ~ zeolites have additionally been employed in processes to separate individual hydro-carbon isomers. In the process described in U.S. Patents
3,558,730; 3,558,732; 3,626,020; and 3,686,342 for example, they are used to separate desired _ _ 107706~
xylene isomers; in U.S. Patent 3,66B,267 they are used to separate pa-ticular alkyl substituted naphthalenes.
More specifically, U.S. Patent 3,014,078 teaches the separation of cresol isomers by emp~oying an adsor-bent consisting of a crystalline zeolitic metallo alumino-silicate to selectively adsorb a cresol isomer from a feed mixture thereby producing a rich adsorbent. In the preferred mode of operation, the adsorbed isomer is then removed by contacting with a displacement exchange fluid.
A preferred displacement exchange fluid is phenol although other materials which may be employed include ethers, aromatic hydrocarbons, and paraffin hydrocarbons.
The present invention relates to an improved pro-cess for separating for the separtion of cresol isomers.
In particular we have found that employing a desorbent material comprising an alcohol to remove the selectively adsorbed para-cresol isomer from the zeolitic adsorbent in-creases the selectivity of the adsorbent for para-cresol with respect to the other cresol isomers thereby permittins a more efficient separation with a higher purity extract stream recovered from the process.
It i5, accordingly, a broad ob,ective of our inven-tion to provide an improved process for the separation of para-cresol from a feed mixture containing para-cresol and at least one other cresol isomer.
In brief summary, our invention is, in one embodi-ment, an improved process for separating para-cresol from a feed mixture containing para-cresol and at least one 107706~
other cresol isomer which process comprises: (a) con-tacting at adsorption conditions said feed mixture with a crystalline aluminosilicate s~lected from type X struc-tured and type Y structured zeolites containing one or more selected cations at the exchangeable cationic sites there~y selectively adsorbing para-cresol from said feed mixture; and, (b) contacting said adsorbent with a de-sorbent material at desorption conditions to remove the adsorbed para-cresol therefrom; characterised b~ employ-ing a desorbent material comprising an alcohol which issoluble in the feed mixture at adsorption and desorption conditions and which has an average boiling point subs-tantially different than that of the feed mixture.
Other embodiments and objects of the present in-li vention enc~mpass details about feed mixtures, adsorbentsdesorbent materials, and operating conditions all of which are hereinafter disclosed in th- following discus-sion of each of these facets of the present invention.
The process of this invention provides an improved alternative to the separation of para-cresol from mixed cresols than by toluene sulfonation and caustic fusion.
Para-cresol finds specific use, for example, as a star-ting material in a manufacture of butylated hydroxy toluene, a widely-used antioxidant.
Preferred adsorbents which can be used in the ad-sorptive separation of cresols are certain crystalline aluminosilicates or molecular sieves including both the natural and synthetic aluminosilicates. Such crystalline 107706~
aluminosilicates have cage structures in which the alumina and silica tetrahedra are intimately connected in an open three dimensional network. The tetrahedra are cross-linked by the sharing of oxygen atoms with spaces between the tet-rahedra occupied by water molecules prior to partial ortotal dehydration of this zeolite. The dehydration of the zeolite results in crystals interlaced with cells having molecular dimensions. Thus, the crystalline aluminosilicates are often referred to as molecular sieves and separations performed with molecular sieves are generally thought to take place by a physical "sieving" of smaller from larser molecules appearing in the feed mixture. In the separation of cresol isomers, however, the separation of the isomers apparently occurs b~^ause of differences in electro-chemical attraction of the different isomers and the adsorben~ rather than on pure physical size differences in the isomer mole-cules.
In hydrated form, the preferred crystalline alumino-silicates generally encompass those zeolites represenLed by the formula below:
M2/nO :A1203 :WsiO2 YH2 where "M" is a cation which balances the electrovalence of the tetrahedra and is generally referred to as,an exchang-eable cationic site, "n" represents the valence of the cation, "w" represents the moles of SiO2, and "y" represents the moles of water. The cations may be any one of a number of cations which will hereinafter be described in detail.
Adsorbents comprising the type X structured and _5_ ~07706~
type Y structured zeolites are especially preferred for the adsorptive separation of the cresol isomers. These zeolites are described and defined in U.S. Patents 2,882, 244 and ~,120,007 respectively. The preferred type X and type Y structured zeolites contain from 4 to 8 wt.
water on a volatile-free basis.
Adsorbents contemplated herein include not only the common sodium form of the type X and the type Y zeolites but also crystalline materials obtained from such zeolites by partial or complete replacement of the sodium at the exchangeable cationic sites with one or more other speci-fied cations.
The cations which may be placed upon the zeolite include cations selected from, but not limited to, the Group IA, Group IIA, and Group IB metals of the Periodic Table of Elements. Specific cations which show a pre-ferential selectivity for para-cresol with respect to other cre~sol isomers include lithium, sodium, potassium, rubidium, cesium, beryllium, maqnesium, calcium, strontium, barium, silver, manganese, cadmium, and copper. Where the above cations are used, para-cresol would be the preferen-tially adsorbed component of the feed mixture. In the pro-cess of this invention we have found that an adsorbent com-prising a type X or type Y zeolite containing barium or potassium as a selected single cation at the exchangeable cationic sites is particularly preferred.
Type X or Type Y zeolites containing the following combinations of cations have also been shown to be suitable for para-cresol separation. These cations include potassium 10770~;~
and barium, potassium and beryllium, potassium and man-ganese, rubidium and barium, cesium and barium, copper and cadmium, copper and silver, zinc and silver, and cop-per and potassium, with the barium and potassium co~bi-S nation being preferred. A particularly preferred adsor-bent is one comprising type X or type Y zeolite containing barium and potassium at the exchangeable cationic site, in a weight ratio of barium to potassium of from 1 to 100.
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 of 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 about 1~ to abou 100% of the original cations present (generally sodium) up-on the zeolite prior to its being ion-exchanged.
When two or more cations are placed upon the zeolite there are two parameters in which one can operate in order to effectively produce a zeolite having the maximum selec-tive properties. One of the parameters is the extent of the zeolite ion exchange which is aetermined by variables such as the length or ion-exchange times, ion-exchange temperature, and cation concentration. The other paramater is the ratio of individual cations placed on the zeolite.
In instances in which the cation pairs comprise a Group IIA
metal and a Group IA metal the weight ratio of these two components upon the zeolite can vary anywhere from about 1~7706~ .
less than one up to about one hundred dcpending upon the molecular weight of the Group I IA or Group IA metal.
In the process of this invention we have additionally found that a small amount of water on the adsorbent is bene-ficial to promote relatively sharp isomer separation and toprevent "tailing" of one cresol isomer into another. The preferred range of water on the adsorbent is from 3 to 8 wt.
% LOI (loss on ignition) at 600C. This desired range can be maintained by intermittent or preferably continuous water addition to the process.
The ortho-, meta-, and para-cresols are commonly obtained by the distillation of coal tar. ,An unpurified mixture of tle three isomeric cresols is known as "tri-cresol" or"cresylic acid". Since the amounts obtainable by this source may not equal the demand, they can also be produced from the toluidines by the diazo reaction or more frequently by toluene sulphation and caustic fusion.
Proper selection of reaction conditions favours the pro-duction of para-cresol. Since the boiling points for ortho-, meta-, and para-cresol are respectively 191.5C., 202.8C., and 202.5C., it can be seen that ortho-cresol can be re-covered by fractionation but because of their close boil-ing points meta- and para-cresols cannot. The separation of meta- and para-cresol thus is ideally suited to separation by selective adsorption with a solid adsorbent.
We have found that the selectivity of adsorbents comprising type X and type Y zeolites for para-cresol with respect to the other cresol isomers is strongest when the 10770~;~
feed mixture to be separated contains concentrations of para-cresol and one or more other cresol isomers of up to 15 vol. % each. Apparently because of the relatively high acidity of cresols, selectivity of the adsorbent for any cresol isomer diminishes as the cresol concentration in the feed mixture increases. Separation of a desired isomer by selective adsorption takes place, it is theorized, because of a rather delicate acidity~basicity difference between the desired isomer and the adsorbent. At cresol isomer concentrations higher than 15 vol. % each of para-cresol-and at least one other cresol isomer this difference diminishes. The feed mixtures may contain as diluents materials which are generally less selectively adsorbed ~if at all) in this adsorption system than ary of the cresol isomers and in which the cresols are soluble. As one example, hereinafter described liquid desorbent ma-terials can be employed as diluents to achieve the proper concentrations of cresol isomers in the feed mixture.
To separate para~cresol from a feed mixture con-taining para-cresol and at least one other cresol isomer the mixture is contacted with an adsorbent comprising a crystalline aluminosilicate and the para-cresol is more selectively adsorbed and retained by the adsorbent while the other cresol isomers are relatively unadsorbed and are removed from the interstitial void spaces between the particles of adsorbent and the surface of the adsorbent.
The adsorbent containing the more selectively adsorbed para-cresol is referred as a "rich" adsorbent--rich in the 1077Q6~
more selctively adsorbed para-cresol.
The more selectively adsorbed feed component is 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-tively, as the extract stream and the raffinate stream.
Thus, the raffinate stream will contain as raffinate com-ponents all of the feed mixture isomers except para-cresol and the extract stream will contain para-cresol as the ex-tract component.
Although it is possible by the process of this in-vention to produce high purity (98% or greater) para-cresol at high recoveries, it will be appreciated that an extract c~mponent is never completely adsorbed by the adsorbent, nor is a raffinate component completely non-adsorbed by the ad-sorbent. Therefore, small amounts of a raffinate component can appear in the extract stream, and, likewise, small a-mounts of an extract component can appear in the raffinatestream. The extract and raffinate streams then are further distinguished from each other and from the feed mixture by the ratio of the concentrations of an extract component and a specific raffinate component, both appearing in the par-ticular stream. For example, the ratio of concentration ofthe more select~vely adsorbed para-cresol to the concentration of less selectively adsorbed meta-cresol will be highest in the extract stream, next highest in the feed mixture, and lowest in the raffinate stream. Likcwise, the ratio of the less selectively adsorbed meta-cresol to the more selec-tively adsorbed para-cresol will be highest in the raf-finate stream, next highest in the feed mixture and the lowest in the extract stream.
The adsorbent can be contained in one or more cham-bers where through programmed flow into and out of the cham-bers separation of para-cresol is ef~ected. The adsorbent will preferably be contacted with a desorbent material which is capable of displacing the adsorbed para-cresol from the adsorbent. An extract stream comprising para-cresol and de-sorbent material will tllen be withdrawn from the adsorbent and the desorbent material separated thereby leaving high purity para-cresol. Alternatively, the para-cresol could be removed from the adsorbent by purging or by increasing the temperature of the adsorbent or by decreasing the pressure of the chamber or vessel containing the adsorbent or by a com-bination of these means.
~he adsorbent may be employed in the form of a dense compact fixed bed which is alternatively contacted with the feed mixture and a desorbent material (herinafter described in more detail). In the simplest embodiment of the inven-tion the adsorbent is employed in the form of a single static bed in which rase the process is only semi-continuous.
A set of two or more static beds may be employed in fixed-bed contacting with appropriate 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 mix-ture and desorbent material may be either up or down through 10770~
the desorbent. Any of the conventional apparatus employedin static bed fluid-solid contacting may be used. Counter~
current moving-bed or simulated countercurrent moving-bed liquid flow systems, however, have a much greater sep-aration efficiency than fixed adsorbent bed systems and aretherefore preferred. In the moving-bed or simulated moving-bed processes the adsorption and desorption operations are continuously taking place which allows both continuous pro-duction of an extract and a raffinate stream and the continual use of feed and desorbent streams. One preferred process-ing 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 op-erating sequence of such a flow system is described in U.S.
Patent 2,985,589. This patent generally described the pro-cessing sequence involved in a particular simulated mo~ing-bed countercurrent solid-fluid contacting process. The processing sequence generally described in that patent is the preferred mode of operating the separation process dis-closed herein.
One broad embodiment of this process is a process for separating para-cresol from a feed mixture comprising para-cresol and at least one other cresol isomer which process generally employs the operatin~ sequence descrlbed in U.S. Patent 2,985,589 and which comprises the steps of:
contacting the feed at adsorption conditions with a par-ticular zeolitic adsorbent thereby selectively adsorbing para-cresol; withdrawing from the adsorbent bed a stream comprising less selectively adsorbed components in the feed;
10770~4 contacting the adsorbent at desorption conditions with a desorbent material to effect the removal of para-cresol from the adsorbent; and, withdrawing from the adsorbent a stream comprising desorbent material and para-cresol.
S Adsorption and desorption conditions for adsor~-tive separation processes can generally be either in the liquid or vapour phase or both but for cresol separation processes employing zeolitic adsorbents all liquid-phase operations are preferred because of the lower temperature requirements and the slightly improved selectivities associated with the lower temperatures. Adsorption con-ditions will include temperature within the range of from 38C to 260C and will include pressures in the range from 1 to 35 atmospheres. Pressures higher than 35 atm~spheres do not appear to affect the selectivity to a measureable amount and additionally would increase the cost of the pro-cess. Desorption conditions for the process of the inven-tion shall generally include the same range of temperatures 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 purging of the adsorbent to remove the adsorbed isomer but this process is not directed to these desorption methods.
The desorbent materials which can be used in the various processing schemes employing this adsorbent will vary depending on the type of operation employed. The term "desorbent material" as used herein shall mean any fluid substance capable of removing a selectively adsorbed feed component from thc adsorbent. In the swing-bed system in 1C~77064 which the selectively adsorbed feed component is removed from the adsorbent by a purge stream, desorbent materials comprising gaseous hydrocarbons such as methane, ethane, etc., or other types of gases such as nitrogen or hydrogen may be used at elevated temp~ratures or reduced pressure or both to effectively purge tlle adsorbed feed component from the adsorbent.
However, in processes which are generally operated at substantially constant pressures and temperatures to insure liquid phase, the desorbent material relied upon must be judiciously selected in order that it may dis-place the adsorbed feed component from the adsorbent with reasonable mass flow rates without itself being so strong-ly adsorbed as to unduly prevent the extract component from displacing the desorbent material in a following adsorption cycle.
Desorbent materials which can be used in the pro-cess of this invention should additionally be substances which are easily separable from the feed mixture that is passed into the process. Indesorbing the preferentially adsorbed component of the feed, both desorbent material and the extract component are removed in admixture from the adsorbent. Without a method of separation such as distillation of these two materials, the purity of the extract component of the feed stock would not be very high since it would be diluted with desorbent. It is therefore contemplated that any desorbent material used in this process will have a substantially different average boiling point than that of the feed mixture. T'ne use of 10770~;~
a desorbent mat~rial having a substantially different average boiling point than that of the feed allows sep-aration of desorbent material from feed components in the extract and raffinate streams by simple fractionation thereby permitting reuse of desorbent material in the pro-cess. The term "substantially different" as used herein shall mean that the difference between the average boil-ing points between the desorbent material and the feed mixture shall be at least 8C. The boiling range of the desorbent material may be higher or lower than that of the feed mixture, although for the process of tnis invention it is preferred that desired desorbent material have a boiling range less than that of the feed material.
The prior art has generally chosen phenol as the preferred "displacement exchange fluid" or de,orbent ma-terial for separation processes employing an adsorbent comprising cyrstalline aluminosilicate to separate the cresol isomers. Other materials which have been recognised by the prior art are ethers, aromatic hydrocarbons, and paraffin hydrocarbons. Such desorbent materials are best suited to adsorptive separation processes generally char-acterised as equilibrium adsorptive type operations. How-ever, in processes characterised by less ~han equilibrium adsorption, we have discovered that there is a distinct advantage in employing a desorbent material comprising an alcohol and that this advantage results in an improved pro-cess for the separation of cresol isomers by selective adsorption on a zeolite-containing adsorbent.
10770ti~ ~
The term "equilibrium adsorption" as used herein shall mean that there is essentially no competitive ad-sorption of the adsorbent of both desorbent material and an extract com~onent of the feed mixture during the pro-cess adsorption step or steps, Equilibrium adsorptionessentially takes place in the sequence of steps in which a feed stream which does not contain any desorbent material is first passed through a zeolitic adsorbent bed until the effluent stream which passes out of the adsorbent after contact therewith is essentially of the same composition as the material fed to the adsorbent bed indicating no,net transfer of material between the adsorbed material within the adsorbent and the feed stock surrounding the adsorbent.
A desorbent material is then passed through the bed of ad-sorbent to displace the selectively adsorbed components OL
the feed. In this type sequential operation there is no desorbent material in contact with the adsorbent when ad-sorption operations are completed (any desorbent initially present on the adsorbent is displaced by feed components).
The term "less than equilibrium adsorption" shall mean that there is this competitive adsorption of desorbent material and an extract component during the process ad-sorption step. In continuous simulated or actual coun-tercurrent liquid flow systems in which an extract com-ponent of the feed is continuously and selectively ad-sorbed from the feed mixture by a solid adsorbent, there are zones in which there is essentially a simultaneous con-tacting of the adsorbent during adsorption with a mixture comprising desorbent material and the feed mixture. The `
10770~i;'l ~
presence of feed and desorbent material in admixture creates a condition where there is a competitive ad-sorption of the adsorbent of both desorbent material and the selectively adsorbed component of the feed mixture.
In most continuous countercurrent solid-fluid sep-aration processes, the solid adsorbent contacts the feed mixture in what is generally referred to as an adsorption zone. The feed and solid adsorbent countercurrently con-tact each other with the adsorbent passing out of the ad-sorption zone containing an extract component of the feed and some desorbent within the solid adsorbent. The solid adsorbent is eventually contacted with desorbent material in a desorption zone. The desorbent material displaces an extract component from the solid adsorbent and allows a l; mixture of desorbent and extract component of the feed to be removed from the process as an extract stream. The extract stream eventually passes to a separation means where-in the desorbent material is separated from the extract com-ponent giving a stream enriched in an extract component of 20 the feed. The solid adsorbent aft~r being contacted with -the desorbent in the desorption zone, continues to flow in a countercurrent direction in relation to the fluid flow in thesystem and eventually is recontacted witn the feed in the adsorption zone for the adsorption of the extract com-ponent of the feed by the solid adsorbent. Between the ad-sorption zone and desorption zone are located the flushing or rectification zones which by carefully controlled pre-ssure drops and liquid flow rates prevent the raffinate or extract streams from contaminating each other. The material 1 r 107706~
contained in the flushing or rectification zones gen-erally contains desorbent material. The desorbent ma-terial in the flushing or rectification zones flushes a raffinate material carried by the solid adsorbent back into the adsorption zone and eventually ends up con-tacting the adsorbent in the adsorption zone substantially the same time the feed mixture contacts the solid adsor-bent in the adsorption zone. The desorbent material which contacts the adsorbent in the adsorption zone causes competi-tive adsorption between it and the extract component offeed. The presence of desorbent material during the ad-sorption step can affect selectivity of tne adsorbent for the extract component.
We have found that improved separation is obtained in an adsorption process for separating cresol isomers in which the desorbent material is present while adsorption of para-cresol takes place by employing a desorbent material comprising an alcohol. Specifically, we have found that employing such a desorbent material increases the selec-tivity of particular adsorbents for para-cresol with re-spect to other cresol isomers and also increases the rate of desorption of para-cresol from the adsorbent. The exact mechanism by which this occurs is not fully under-stood but it is thought that the alcohols modify the acidity/
basicity relationships between the cresol isomers and the adsorbent.
Alcohols which can be used in the process of this invention shall broadly be those which satisfy these two criteria: they shall be soluble in the feed mixture used in 10770f~
th~ process at adsorption and desorption conditions andthey shall have an average boiling point substantially different than that of the feed mixture. Preferably the alcohols will be derivatives of normal paraffins or cy-S cloparaffins. Although secondary and tertiary alcoholsare suitable for use in the process of our invention, primary alcohols are more preferred because they do not readily dehydrate to form olefins. Even more preferred are those primary alcohols which have boiling points less than, rather than higher than, that of the feed mixture.
These particular primary alcohols are preferred because the larger chain higher-boiling primary alcohols tend to behave more like normal paraffins and thus their ability to modify the adsorbent characteristics is diminished.
Thus as indicated in Table No. 1 below primary alcohols having from one to and including seven carbon atoms per molecule will be the preferred primary alcohols. Of these l-hexanol is particularly preferred. Primary al-cohols having greater than seven carbon atoms per molecule which generally have boiling points greater than any of the cresol isomers are not as desirable for use as de-sorbent materials for this process.
Mixtures of alcohols with hydrocarbons such as paraffins or aromatics are also effective as desorbent ma-terials in the process of this invention. Such hydrocarbonsshall be those which are soluble in both the alcohol and the feed mixture at adsorption and desorption conditions and, like the alcohols employed, shall have average boil-ing points substantially different than that of the feed 10770~ .
mixtures. The paraffins can include straight or branched chain paraffins or cycloparaffins which meet these two criteria. Particularly preferred aromatics are benzene, toluene, and the xylenes. Typical concentrations of the alcohol in mixtures of an alcohol and a hydrocarbon can be from a few volume percent up to near 100 vol. % of the total desorbent material mixture but such concentration preferably will be within the range of from 25 vol. % to 75 vol. % of the mixture.
Table No. 1 Normal Boiling Points of Selected Primary Alcohols normal boiling point, C
Methanol 64.7 Ethanol 78.5 l-Propanol 97.2 l-Butanol 117.7 l-Pentanol 138 l-Hexanol 157.2 l-Heptanol 176 - l-Octanol 195 l-Nonanol 213 l-Decanol 231 ortho-cresol 190.8 para-cr~sol 201.1 meta-cresol 202.8 benzene 80.1 toluene 110.6 ortho-xylene 114.4 meta-xylene 139.1 para-xylene 138.3 The improvement that results from employing a de-sorbent material comprisin~ an alcohol can be better under-25 stood by brief reference to certain adsorbent properties I ;
which are necessary to the successful operation of a selec- !
tive adsorption process. It will be recognised that im-provements in any of these adsorbent characteristics will .
` 107706~
result in an improved separation process. ~mong such characteristics are: adsorptive capacity for some volume of an extract component per volume of adsorbent; the selective adsorption of an extract component with respect to a raffinate component and the desorbent material; suf-ficiently fast rates of adsorption and desorption of the extract component to and from the adsorbent; and, in in-~tances where the components of the feed mixture are very reactive, little or no catalytic activity for undesired reactions such as polymerization and isomerization.
Capacity of the adsorbent for adsorbing a specific volume of an extract component is, of course, a necessity;
without such capacity the adsorbent is useless for ad-- sorptive separation. Furthermore, the higher the adsorbent's capacity for an extract component, the better is the adsor-bent. Increased capacity of a particular adsorbent makes it possible to reduce the amount of adsorbent needed to separate the extract component contained in a particular charge rate of feed mixture. A reduction in the amount of adsorbent required for a specific adsorptive separation reduces the cost of the separation process. It is im-portant that the good initial capacity of the adsorbent be maintained durin~ actual use in the separation process over some economically desirable life.
The second necessary adsorbent characteristic is the ability of the adsorbent to separate components of the feed; or, in other words, that the adsorbent ~ossess ad-sorptive selectivity for one component as compared to a-nother component. Some adsorbents demonstrate acceptable 10~7064 capacity but possess little or no selectivity. Silver ni-trate on silica gel for instance possesses a large capacity for cresols but little selectivity for one isomer with re-spect to another. 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 relative selectivity, (B), as used throughout this specification is defined as the ratio of two components of an adsorbed phase over the ratio of the same two components in an unadsorbed phase at equilibrium conditions.
Relative selectivity is shown as Equation 1 below: {
Selectivity = (B) = ~ol. percent C/vol. percent ~ol. percent C/vol. percent ~ UA
where C and D are two components of the feed represented in volume percent and the subscripts A and U represent the adsorbed and unadsorbed phases respectively. The equili-brium conditions were determined when the feed passing over a bed of adsorbent did not change composition after contact-ing the bed of adsorbent. In other words, there was no nettransfer of material occurring between the unadsorbed ar.d adsorbed phases. ¦
Where selectivity of two components approaches 1.0 there is no preferential adsorption of one component by the adsorbent with respect to the other;they are both adsorbed ~or non-adsorbed) to about the same degree with respect to the other. As the (B) becomes less than or greater than 1.0 there is a preferential adsorption by the adsorbent for one component with respect to the other. When comparing the 1077~
selectivity by the adsorbent of one component C over com-ponent D, a (B) larger than 1.0 indicates preferential ad-sorption of component C within the adsorbent. A (B) less than 1.0 would indicate that component D is preferentially adsorbed leaving an unadsorbed phase richer in camponent :
C and an adsorbed phase richer in component D. Desorbent materials ideally would have a selectivity equal to about 1 or slightly less than 1 with respect to an extract component.
Employing a desorbent material comprising an alco-~0 hol increases the selectivity of the adsorbent for a para-cresol with respect to the other cresol isomers thereby permitting sharper separation of the isomers and improving the process.
The third important characteristic is the rate of exchange of the extract component of the feed mixture ma-terial or, in other words; the relative rate of desorption of the extract component. This characteristic relates 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 a-mount 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 pumped through the process and separated from the extract stream for reuse in the process.
We have found that the use of a desorbent material comprising an alcohol also increases the transfer rates besides im-proving the selectivity for para-cresol.
It is also necessary that the adsorbent possess 1()770~
little or no catalytic activity toward any reaction such as polymerization or isomerization of any of the feed com-ponents. Such activity might effect adsorbent capacity or selectivity or product yields or all of these, but in the adsorptive separation of cresol isomers with a zeolite-containing adsorbent this is generally not a problem.
In order to test various adsorbents and desorbent materials with a particular feed mixture to measure the adsorbent characteristics of adsorptive capacity and selec-tivity and exchange rate a dynamic testing apparatus isemployed. The apparatus consists of an adsorbent chamber of approximately 70 cc. volume having inlet and outlet portions at opposite 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 outlet llne of the chamber and used to analyse the effluent stream r 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.
Theadsorbent is filled to equilibrium with a particular desorbent material by passing the desorbent material through the adsorbent chamber. At a convenient time, a pulse test of feed containing known concentrations of cresol isomers all diluted in desorbent material is injected for a dur-ation of several minutes. For convenience a known con~
centration of a non-adsorbcd tracer compound may be -2~-1~7706~ ~
included in ~he feed. Flow of desorbent material is re-sumed, and the tracer (if one is employed) and the cresols are eluted as in liquid-solid chromatographic operation.
The effluent can be analysed by on-stream chromato~raphic S equipment and traces of the envelopes of corresponding component peaks developed. Alternativeli~, effluent samples can be collected periodically and later analysed separately by gas chromatography.
From information derived from the chromatographic -~
10 traces adsorbent performance can be rated in terms of ca- ¦
pacity index for para-cresol, selectivity for para-cresol with respect to the other cresols and rate of desorption of para cresolby the desorbent. The capacity index is char- I ;
acterised by the distance between the centre of the para-15 cresol peak envelope and the tracer peak envelope or some other known reference point such as volume of desorbent pumped. It is expressed in terms of the volume in cubic centimetres of desorbent pumped during this time interval.
Relative selectivity, (B), for para-cresol with respect to f 20 the other cresols is characterised by the ratio of the distance between the centre of the para-cresol peak envel-ope and the tracer peak envelope (or other reference point) to the corresponding distances for the other cresol isomers.
The rate of exchange of para-cresol with the desorbent can 25 be characterised by the width of tile para-cresol peak envelope at half intensity. The narrower the peak width, the faster the desorption rate.
To further evaluate promising adsorbent systems and to translate this type of data into a practical cresol separation process requires actual testing of the best sys-tem in a continuous countercurrent liquid-solid contacting d'evice.
The general operating principles of such a device S have been previously described and are found in U.S. Patent 2,985,589. A specific laboratory-size fluid-solid contact-ing apparatus utilising these principles is described in U.S. Patent 3,706,812.
The improved process of this invention for sep-arating para-cresol from a feed mixture containing para-cresol and at least one other cresol isomer, which was demonstrated by pulse tests, was confirmed by actual con-tinuous testing in the continuous device.
The examples below illustrate first the selectivity characteristic of adsorbents comprising zeolites which makes possible a process for the adsorptive separation of cresol isomers and second the improvement in that characteristic, as well as in the rate of desorption, which results in the improved process of our invention. The examples are pre-sented to further illustrate the process of the present in-vention and are not intended to limit the scope and spirit of the invention.
The examples present pluse test results obtained with an adsorbent comprising type X crystalline alumino-silicate which contained barium and potassium cations atthe exchangeable cationic sites within the aluminosilicate.
Results for one pulse test which employed an adsorbent com-prising a type X crystallinc aluminosilicate containing calcium cations at the exchan~eable cationic sites are 10770~4 .
also include~ for comparison. The first-mentioned ad-sorbent was essentially totally ion-exchanged, con-tained a weight ratio of barium oxide to potassium oxide of about 3.3, and was approximately 20-40 mesh particle t 5size. Analyses of this adsorbent are shown in Table No.
2 below.
Table No. 2 ADSORBENT ANALYSES
Volatile Matter (LOI @ 900 C.) 6.43 Si0 (volatile free) wt. ~ 42.1 A12~ (volatile free) wt. % 28.3 Na 03(volatile free) wt. % 2.0 K2~ (volatile free) wt. % 6.1 BaO (volatile free) wt. % 20.3 Si02/A1203 2.53 The latter adsorbent was commercially-available Linde 10X
Molecular Sieves of approximately 20-40 mesh particle size.
EXAMPLE I
In this example the adsorbent comprising the type X
zeolite containing barium and potassium cations described above was placed in the testing unit and a pulse test was conducted in the following manner.
The desorbent material employed was 15 vol. ~ phe-nol in toluene. The feed mixture utilised contained 5 vol.
~ each of para-cresol and meta-cresol in desorbent material.
Ortho-cresol was omitted from the feed mixture in order to simplify the test and focus on the para/meta selectivity which is the most critical selectivity because of their close boiling points. Additionally from previous experi-ments it had been determined that the meta- and orth-isomers behave in substantially the same manner. Since desorbent material was a part of the feed mixture, adsorption of 107701 i~ j para-cresol took place in the presence of, and in compe-tition with, desorbent material, and; therefore, selec-tïvities were obtained at less than equilibrium condi-tions. The desorbent was placed in a 70 cc adsorbent column which was maintained at a constant temperature of about 150C. with constant moderate pressure during the entire operation. A Waters Automatic Fraction Collector was connected to the effluent end of the chamber to sample the effluent every 2.1 minutes.
Desorbent was first pumped through the adsorbent r chamber at approximately 1 cc~min at about 150C. A 4.7 cc feed pulse was then cut into the system via an injection loop and the effluent was periodically sampled in the man- ¦
ner indicated above. A measured void volume of 43.0 cc was used for the 70 cc adsorbent column and sampling was started after 40 cc of desorbent was p~mped beginning at feed injection. The individual effluent samples were stop-pered after collection and analysed separately by Gas Chromatography (GC). A digital integrator was used to ob-tain peak areas and the count produced (x 10 ) was plot-ted versus cc of desorbent from time of feed injection, for both para- and meta-cresol. This plot produced an envelope for para- and meta-cresols similar to those ob-tained when using on-stream GC analysis. The cresol samples take 50 minutes to elute from the analytical GC column.
The selectivities were calculated by measuring the cc of the desorbent pumped from the measured 43 cc void ~ volume to the midpoints of the individual para- and meta-cresol envelopes at one-half the peak heights. The ratio 1~)770~
of these volumes represent the relative selectivity of para-cresol with respect to meta-cresol.
Reproducible data from this test gave a relative para-cresol to meta-cresol selectivity of 1.53 which -demonstrates the characteristic of the adsorbent which makes the adsorptive separation process possible.
EXAMPLE II .
In this example three pulse tests A, B, and C
were performed; tests A and B with the adsorbent des-cribed above and used for Example I and test C with anadsorbent comprising a type X zeolite having calcium at the exchangeable cationic sites. The results are shown in Table No. 3 below.
~ . ~
r 107706~ 1 ~, W
-W W ~
U~
I I U~
3 o ~5 X ~D~D ~
X X r~
.
. C
~D ' 3 W ~3 O o O o O o ~D
Ln C ~ C ~ C
r~ u~ C~
X tD X ~D ~ ~D O ~
~s ~ ~ ~3 Y o "-O O 1- ~ ~D ~
_ ~ ~h t-r U~ f3 ~D ~
O 1- 1_ It fD ~S
ID n ~D CO W Ul ~ r~
~I o ~- 1~-~' ~
~`
ID--U~ ~
~o ~ .
o ~ ~t tD
, ,_ ~P~ o ~I ~
Ul o o O O
ID ~h ~ D ~
~ ~ C
rt ~ I~
~a -- P~
1077~)t;4 The test procedure and cquipment used was the same as that described in Example I.
For test A the desorbent material was 30 vol. ~ phe-nol in toluene and the feed mixture contained 5 vol. % each of para-cresol and meta-cresol in desorbent material. The relative selectivity of the adsorbent for para-cresol with respect to meta-cresol in the presence of this desorbent material was 1.37 and the para-cresol peak envelope width at half height was 17Ø
The same adsorbent was employed for test B but the desorbent material was 50 vol. % hexanol in toluene. Now the relative selectivity of the same adsorbent for para-cresol with respect to meta-cresol in the presence of this desorbent material was 1.8 or an increase of 31% over that of test A. The para-cresol peak envelope width at half height had decreased from 17.0 obtained for test A to 11.0 for test B indicating a faster rate of desorption of para-cresol for test B. The comparison of the results of test A and B, therefore indicates the improvements in the ad-sorbent characteristics of selectivity and transfer rateand hence in the separation process itself when a desorb-ent material comprisin~ an alcohol is employed.
Test C was conducted with the same desorbent ma-terial as was used for test B but a different adsorbent was ~mployed. l'he adsorbent used comprised a type X zeolite containing calcium cations at the exchan~eable cationic sites. With the same desorbent material, hexanol-l in toluene, this adsorbent exhibited essentially no selec-tivity for either cresol isomers thus indicatin~ that this adsorbent, while suitable for use in the prior art cresol separation process, is not suitable for use in the cresol isomer separation process of this invention.
xylene isomers; in U.S. Patent 3,66B,267 they are used to separate pa-ticular alkyl substituted naphthalenes.
More specifically, U.S. Patent 3,014,078 teaches the separation of cresol isomers by emp~oying an adsor-bent consisting of a crystalline zeolitic metallo alumino-silicate to selectively adsorb a cresol isomer from a feed mixture thereby producing a rich adsorbent. In the preferred mode of operation, the adsorbed isomer is then removed by contacting with a displacement exchange fluid.
A preferred displacement exchange fluid is phenol although other materials which may be employed include ethers, aromatic hydrocarbons, and paraffin hydrocarbons.
The present invention relates to an improved pro-cess for separating for the separtion of cresol isomers.
In particular we have found that employing a desorbent material comprising an alcohol to remove the selectively adsorbed para-cresol isomer from the zeolitic adsorbent in-creases the selectivity of the adsorbent for para-cresol with respect to the other cresol isomers thereby permittins a more efficient separation with a higher purity extract stream recovered from the process.
It i5, accordingly, a broad ob,ective of our inven-tion to provide an improved process for the separation of para-cresol from a feed mixture containing para-cresol and at least one other cresol isomer.
In brief summary, our invention is, in one embodi-ment, an improved process for separating para-cresol from a feed mixture containing para-cresol and at least one 107706~
other cresol isomer which process comprises: (a) con-tacting at adsorption conditions said feed mixture with a crystalline aluminosilicate s~lected from type X struc-tured and type Y structured zeolites containing one or more selected cations at the exchangeable cationic sites there~y selectively adsorbing para-cresol from said feed mixture; and, (b) contacting said adsorbent with a de-sorbent material at desorption conditions to remove the adsorbed para-cresol therefrom; characterised b~ employ-ing a desorbent material comprising an alcohol which issoluble in the feed mixture at adsorption and desorption conditions and which has an average boiling point subs-tantially different than that of the feed mixture.
Other embodiments and objects of the present in-li vention enc~mpass details about feed mixtures, adsorbentsdesorbent materials, and operating conditions all of which are hereinafter disclosed in th- following discus-sion of each of these facets of the present invention.
The process of this invention provides an improved alternative to the separation of para-cresol from mixed cresols than by toluene sulfonation and caustic fusion.
Para-cresol finds specific use, for example, as a star-ting material in a manufacture of butylated hydroxy toluene, a widely-used antioxidant.
Preferred adsorbents which can be used in the ad-sorptive separation of cresols are certain crystalline aluminosilicates or molecular sieves including both the natural and synthetic aluminosilicates. Such crystalline 107706~
aluminosilicates have cage structures in which the alumina and silica tetrahedra are intimately connected in an open three dimensional network. The tetrahedra are cross-linked by the sharing of oxygen atoms with spaces between the tet-rahedra occupied by water molecules prior to partial ortotal dehydration of this zeolite. The dehydration of the zeolite results in crystals interlaced with cells having molecular dimensions. Thus, the crystalline aluminosilicates are often referred to as molecular sieves and separations performed with molecular sieves are generally thought to take place by a physical "sieving" of smaller from larser molecules appearing in the feed mixture. In the separation of cresol isomers, however, the separation of the isomers apparently occurs b~^ause of differences in electro-chemical attraction of the different isomers and the adsorben~ rather than on pure physical size differences in the isomer mole-cules.
In hydrated form, the preferred crystalline alumino-silicates generally encompass those zeolites represenLed by the formula below:
M2/nO :A1203 :WsiO2 YH2 where "M" is a cation which balances the electrovalence of the tetrahedra and is generally referred to as,an exchang-eable cationic site, "n" represents the valence of the cation, "w" represents the moles of SiO2, and "y" represents the moles of water. The cations may be any one of a number of cations which will hereinafter be described in detail.
Adsorbents comprising the type X structured and _5_ ~07706~
type Y structured zeolites are especially preferred for the adsorptive separation of the cresol isomers. These zeolites are described and defined in U.S. Patents 2,882, 244 and ~,120,007 respectively. The preferred type X and type Y structured zeolites contain from 4 to 8 wt.
water on a volatile-free basis.
Adsorbents contemplated herein include not only the common sodium form of the type X and the type Y zeolites but also crystalline materials obtained from such zeolites by partial or complete replacement of the sodium at the exchangeable cationic sites with one or more other speci-fied cations.
The cations which may be placed upon the zeolite include cations selected from, but not limited to, the Group IA, Group IIA, and Group IB metals of the Periodic Table of Elements. Specific cations which show a pre-ferential selectivity for para-cresol with respect to other cre~sol isomers include lithium, sodium, potassium, rubidium, cesium, beryllium, maqnesium, calcium, strontium, barium, silver, manganese, cadmium, and copper. Where the above cations are used, para-cresol would be the preferen-tially adsorbed component of the feed mixture. In the pro-cess of this invention we have found that an adsorbent com-prising a type X or type Y zeolite containing barium or potassium as a selected single cation at the exchangeable cationic sites is particularly preferred.
Type X or Type Y zeolites containing the following combinations of cations have also been shown to be suitable for para-cresol separation. These cations include potassium 10770~;~
and barium, potassium and beryllium, potassium and man-ganese, rubidium and barium, cesium and barium, copper and cadmium, copper and silver, zinc and silver, and cop-per and potassium, with the barium and potassium co~bi-S nation being preferred. A particularly preferred adsor-bent is one comprising type X or type Y zeolite containing barium and potassium at the exchangeable cationic site, in a weight ratio of barium to potassium of from 1 to 100.
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 of 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 about 1~ to abou 100% of the original cations present (generally sodium) up-on the zeolite prior to its being ion-exchanged.
When two or more cations are placed upon the zeolite there are two parameters in which one can operate in order to effectively produce a zeolite having the maximum selec-tive properties. One of the parameters is the extent of the zeolite ion exchange which is aetermined by variables such as the length or ion-exchange times, ion-exchange temperature, and cation concentration. The other paramater is the ratio of individual cations placed on the zeolite.
In instances in which the cation pairs comprise a Group IIA
metal and a Group IA metal the weight ratio of these two components upon the zeolite can vary anywhere from about 1~7706~ .
less than one up to about one hundred dcpending upon the molecular weight of the Group I IA or Group IA metal.
In the process of this invention we have additionally found that a small amount of water on the adsorbent is bene-ficial to promote relatively sharp isomer separation and toprevent "tailing" of one cresol isomer into another. The preferred range of water on the adsorbent is from 3 to 8 wt.
% LOI (loss on ignition) at 600C. This desired range can be maintained by intermittent or preferably continuous water addition to the process.
The ortho-, meta-, and para-cresols are commonly obtained by the distillation of coal tar. ,An unpurified mixture of tle three isomeric cresols is known as "tri-cresol" or"cresylic acid". Since the amounts obtainable by this source may not equal the demand, they can also be produced from the toluidines by the diazo reaction or more frequently by toluene sulphation and caustic fusion.
Proper selection of reaction conditions favours the pro-duction of para-cresol. Since the boiling points for ortho-, meta-, and para-cresol are respectively 191.5C., 202.8C., and 202.5C., it can be seen that ortho-cresol can be re-covered by fractionation but because of their close boil-ing points meta- and para-cresols cannot. The separation of meta- and para-cresol thus is ideally suited to separation by selective adsorption with a solid adsorbent.
We have found that the selectivity of adsorbents comprising type X and type Y zeolites for para-cresol with respect to the other cresol isomers is strongest when the 10770~;~
feed mixture to be separated contains concentrations of para-cresol and one or more other cresol isomers of up to 15 vol. % each. Apparently because of the relatively high acidity of cresols, selectivity of the adsorbent for any cresol isomer diminishes as the cresol concentration in the feed mixture increases. Separation of a desired isomer by selective adsorption takes place, it is theorized, because of a rather delicate acidity~basicity difference between the desired isomer and the adsorbent. At cresol isomer concentrations higher than 15 vol. % each of para-cresol-and at least one other cresol isomer this difference diminishes. The feed mixtures may contain as diluents materials which are generally less selectively adsorbed ~if at all) in this adsorption system than ary of the cresol isomers and in which the cresols are soluble. As one example, hereinafter described liquid desorbent ma-terials can be employed as diluents to achieve the proper concentrations of cresol isomers in the feed mixture.
To separate para~cresol from a feed mixture con-taining para-cresol and at least one other cresol isomer the mixture is contacted with an adsorbent comprising a crystalline aluminosilicate and the para-cresol is more selectively adsorbed and retained by the adsorbent while the other cresol isomers are relatively unadsorbed and are removed from the interstitial void spaces between the particles of adsorbent and the surface of the adsorbent.
The adsorbent containing the more selectively adsorbed para-cresol is referred as a "rich" adsorbent--rich in the 1077Q6~
more selctively adsorbed para-cresol.
The more selectively adsorbed feed component is 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-tively, as the extract stream and the raffinate stream.
Thus, the raffinate stream will contain as raffinate com-ponents all of the feed mixture isomers except para-cresol and the extract stream will contain para-cresol as the ex-tract component.
Although it is possible by the process of this in-vention to produce high purity (98% or greater) para-cresol at high recoveries, it will be appreciated that an extract c~mponent is never completely adsorbed by the adsorbent, nor is a raffinate component completely non-adsorbed by the ad-sorbent. Therefore, small amounts of a raffinate component can appear in the extract stream, and, likewise, small a-mounts of an extract component can appear in the raffinatestream. The extract and raffinate streams then are further distinguished from each other and from the feed mixture by the ratio of the concentrations of an extract component and a specific raffinate component, both appearing in the par-ticular stream. For example, the ratio of concentration ofthe more select~vely adsorbed para-cresol to the concentration of less selectively adsorbed meta-cresol will be highest in the extract stream, next highest in the feed mixture, and lowest in the raffinate stream. Likcwise, the ratio of the less selectively adsorbed meta-cresol to the more selec-tively adsorbed para-cresol will be highest in the raf-finate stream, next highest in the feed mixture and the lowest in the extract stream.
The adsorbent can be contained in one or more cham-bers where through programmed flow into and out of the cham-bers separation of para-cresol is ef~ected. The adsorbent will preferably be contacted with a desorbent material which is capable of displacing the adsorbed para-cresol from the adsorbent. An extract stream comprising para-cresol and de-sorbent material will tllen be withdrawn from the adsorbent and the desorbent material separated thereby leaving high purity para-cresol. Alternatively, the para-cresol could be removed from the adsorbent by purging or by increasing the temperature of the adsorbent or by decreasing the pressure of the chamber or vessel containing the adsorbent or by a com-bination of these means.
~he adsorbent may be employed in the form of a dense compact fixed bed which is alternatively contacted with the feed mixture and a desorbent material (herinafter described in more detail). In the simplest embodiment of the inven-tion the adsorbent is employed in the form of a single static bed in which rase the process is only semi-continuous.
A set of two or more static beds may be employed in fixed-bed contacting with appropriate 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 mix-ture and desorbent material may be either up or down through 10770~
the desorbent. Any of the conventional apparatus employedin static bed fluid-solid contacting may be used. Counter~
current moving-bed or simulated countercurrent moving-bed liquid flow systems, however, have a much greater sep-aration efficiency than fixed adsorbent bed systems and aretherefore preferred. In the moving-bed or simulated moving-bed processes the adsorption and desorption operations are continuously taking place which allows both continuous pro-duction of an extract and a raffinate stream and the continual use of feed and desorbent streams. One preferred process-ing 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 op-erating sequence of such a flow system is described in U.S.
Patent 2,985,589. This patent generally described the pro-cessing sequence involved in a particular simulated mo~ing-bed countercurrent solid-fluid contacting process. The processing sequence generally described in that patent is the preferred mode of operating the separation process dis-closed herein.
One broad embodiment of this process is a process for separating para-cresol from a feed mixture comprising para-cresol and at least one other cresol isomer which process generally employs the operatin~ sequence descrlbed in U.S. Patent 2,985,589 and which comprises the steps of:
contacting the feed at adsorption conditions with a par-ticular zeolitic adsorbent thereby selectively adsorbing para-cresol; withdrawing from the adsorbent bed a stream comprising less selectively adsorbed components in the feed;
10770~4 contacting the adsorbent at desorption conditions with a desorbent material to effect the removal of para-cresol from the adsorbent; and, withdrawing from the adsorbent a stream comprising desorbent material and para-cresol.
S Adsorption and desorption conditions for adsor~-tive separation processes can generally be either in the liquid or vapour phase or both but for cresol separation processes employing zeolitic adsorbents all liquid-phase operations are preferred because of the lower temperature requirements and the slightly improved selectivities associated with the lower temperatures. Adsorption con-ditions will include temperature within the range of from 38C to 260C and will include pressures in the range from 1 to 35 atmospheres. Pressures higher than 35 atm~spheres do not appear to affect the selectivity to a measureable amount and additionally would increase the cost of the pro-cess. Desorption conditions for the process of the inven-tion shall generally include the same range of temperatures 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 purging of the adsorbent to remove the adsorbed isomer but this process is not directed to these desorption methods.
The desorbent materials which can be used in the various processing schemes employing this adsorbent will vary depending on the type of operation employed. The term "desorbent material" as used herein shall mean any fluid substance capable of removing a selectively adsorbed feed component from thc adsorbent. In the swing-bed system in 1C~77064 which the selectively adsorbed feed component is removed from the adsorbent by a purge stream, desorbent materials comprising gaseous hydrocarbons such as methane, ethane, etc., or other types of gases such as nitrogen or hydrogen may be used at elevated temp~ratures or reduced pressure or both to effectively purge tlle adsorbed feed component from the adsorbent.
However, in processes which are generally operated at substantially constant pressures and temperatures to insure liquid phase, the desorbent material relied upon must be judiciously selected in order that it may dis-place the adsorbed feed component from the adsorbent with reasonable mass flow rates without itself being so strong-ly adsorbed as to unduly prevent the extract component from displacing the desorbent material in a following adsorption cycle.
Desorbent materials which can be used in the pro-cess of this invention should additionally be substances which are easily separable from the feed mixture that is passed into the process. Indesorbing the preferentially adsorbed component of the feed, both desorbent material and the extract component are removed in admixture from the adsorbent. Without a method of separation such as distillation of these two materials, the purity of the extract component of the feed stock would not be very high since it would be diluted with desorbent. It is therefore contemplated that any desorbent material used in this process will have a substantially different average boiling point than that of the feed mixture. T'ne use of 10770~;~
a desorbent mat~rial having a substantially different average boiling point than that of the feed allows sep-aration of desorbent material from feed components in the extract and raffinate streams by simple fractionation thereby permitting reuse of desorbent material in the pro-cess. The term "substantially different" as used herein shall mean that the difference between the average boil-ing points between the desorbent material and the feed mixture shall be at least 8C. The boiling range of the desorbent material may be higher or lower than that of the feed mixture, although for the process of tnis invention it is preferred that desired desorbent material have a boiling range less than that of the feed material.
The prior art has generally chosen phenol as the preferred "displacement exchange fluid" or de,orbent ma-terial for separation processes employing an adsorbent comprising cyrstalline aluminosilicate to separate the cresol isomers. Other materials which have been recognised by the prior art are ethers, aromatic hydrocarbons, and paraffin hydrocarbons. Such desorbent materials are best suited to adsorptive separation processes generally char-acterised as equilibrium adsorptive type operations. How-ever, in processes characterised by less ~han equilibrium adsorption, we have discovered that there is a distinct advantage in employing a desorbent material comprising an alcohol and that this advantage results in an improved pro-cess for the separation of cresol isomers by selective adsorption on a zeolite-containing adsorbent.
10770ti~ ~
The term "equilibrium adsorption" as used herein shall mean that there is essentially no competitive ad-sorption of the adsorbent of both desorbent material and an extract com~onent of the feed mixture during the pro-cess adsorption step or steps, Equilibrium adsorptionessentially takes place in the sequence of steps in which a feed stream which does not contain any desorbent material is first passed through a zeolitic adsorbent bed until the effluent stream which passes out of the adsorbent after contact therewith is essentially of the same composition as the material fed to the adsorbent bed indicating no,net transfer of material between the adsorbed material within the adsorbent and the feed stock surrounding the adsorbent.
A desorbent material is then passed through the bed of ad-sorbent to displace the selectively adsorbed components OL
the feed. In this type sequential operation there is no desorbent material in contact with the adsorbent when ad-sorption operations are completed (any desorbent initially present on the adsorbent is displaced by feed components).
The term "less than equilibrium adsorption" shall mean that there is this competitive adsorption of desorbent material and an extract component during the process ad-sorption step. In continuous simulated or actual coun-tercurrent liquid flow systems in which an extract com-ponent of the feed is continuously and selectively ad-sorbed from the feed mixture by a solid adsorbent, there are zones in which there is essentially a simultaneous con-tacting of the adsorbent during adsorption with a mixture comprising desorbent material and the feed mixture. The `
10770~i;'l ~
presence of feed and desorbent material in admixture creates a condition where there is a competitive ad-sorption of the adsorbent of both desorbent material and the selectively adsorbed component of the feed mixture.
In most continuous countercurrent solid-fluid sep-aration processes, the solid adsorbent contacts the feed mixture in what is generally referred to as an adsorption zone. The feed and solid adsorbent countercurrently con-tact each other with the adsorbent passing out of the ad-sorption zone containing an extract component of the feed and some desorbent within the solid adsorbent. The solid adsorbent is eventually contacted with desorbent material in a desorption zone. The desorbent material displaces an extract component from the solid adsorbent and allows a l; mixture of desorbent and extract component of the feed to be removed from the process as an extract stream. The extract stream eventually passes to a separation means where-in the desorbent material is separated from the extract com-ponent giving a stream enriched in an extract component of 20 the feed. The solid adsorbent aft~r being contacted with -the desorbent in the desorption zone, continues to flow in a countercurrent direction in relation to the fluid flow in thesystem and eventually is recontacted witn the feed in the adsorption zone for the adsorption of the extract com-ponent of the feed by the solid adsorbent. Between the ad-sorption zone and desorption zone are located the flushing or rectification zones which by carefully controlled pre-ssure drops and liquid flow rates prevent the raffinate or extract streams from contaminating each other. The material 1 r 107706~
contained in the flushing or rectification zones gen-erally contains desorbent material. The desorbent ma-terial in the flushing or rectification zones flushes a raffinate material carried by the solid adsorbent back into the adsorption zone and eventually ends up con-tacting the adsorbent in the adsorption zone substantially the same time the feed mixture contacts the solid adsor-bent in the adsorption zone. The desorbent material which contacts the adsorbent in the adsorption zone causes competi-tive adsorption between it and the extract component offeed. The presence of desorbent material during the ad-sorption step can affect selectivity of tne adsorbent for the extract component.
We have found that improved separation is obtained in an adsorption process for separating cresol isomers in which the desorbent material is present while adsorption of para-cresol takes place by employing a desorbent material comprising an alcohol. Specifically, we have found that employing such a desorbent material increases the selec-tivity of particular adsorbents for para-cresol with re-spect to other cresol isomers and also increases the rate of desorption of para-cresol from the adsorbent. The exact mechanism by which this occurs is not fully under-stood but it is thought that the alcohols modify the acidity/
basicity relationships between the cresol isomers and the adsorbent.
Alcohols which can be used in the process of this invention shall broadly be those which satisfy these two criteria: they shall be soluble in the feed mixture used in 10770f~
th~ process at adsorption and desorption conditions andthey shall have an average boiling point substantially different than that of the feed mixture. Preferably the alcohols will be derivatives of normal paraffins or cy-S cloparaffins. Although secondary and tertiary alcoholsare suitable for use in the process of our invention, primary alcohols are more preferred because they do not readily dehydrate to form olefins. Even more preferred are those primary alcohols which have boiling points less than, rather than higher than, that of the feed mixture.
These particular primary alcohols are preferred because the larger chain higher-boiling primary alcohols tend to behave more like normal paraffins and thus their ability to modify the adsorbent characteristics is diminished.
Thus as indicated in Table No. 1 below primary alcohols having from one to and including seven carbon atoms per molecule will be the preferred primary alcohols. Of these l-hexanol is particularly preferred. Primary al-cohols having greater than seven carbon atoms per molecule which generally have boiling points greater than any of the cresol isomers are not as desirable for use as de-sorbent materials for this process.
Mixtures of alcohols with hydrocarbons such as paraffins or aromatics are also effective as desorbent ma-terials in the process of this invention. Such hydrocarbonsshall be those which are soluble in both the alcohol and the feed mixture at adsorption and desorption conditions and, like the alcohols employed, shall have average boil-ing points substantially different than that of the feed 10770~ .
mixtures. The paraffins can include straight or branched chain paraffins or cycloparaffins which meet these two criteria. Particularly preferred aromatics are benzene, toluene, and the xylenes. Typical concentrations of the alcohol in mixtures of an alcohol and a hydrocarbon can be from a few volume percent up to near 100 vol. % of the total desorbent material mixture but such concentration preferably will be within the range of from 25 vol. % to 75 vol. % of the mixture.
Table No. 1 Normal Boiling Points of Selected Primary Alcohols normal boiling point, C
Methanol 64.7 Ethanol 78.5 l-Propanol 97.2 l-Butanol 117.7 l-Pentanol 138 l-Hexanol 157.2 l-Heptanol 176 - l-Octanol 195 l-Nonanol 213 l-Decanol 231 ortho-cresol 190.8 para-cr~sol 201.1 meta-cresol 202.8 benzene 80.1 toluene 110.6 ortho-xylene 114.4 meta-xylene 139.1 para-xylene 138.3 The improvement that results from employing a de-sorbent material comprisin~ an alcohol can be better under-25 stood by brief reference to certain adsorbent properties I ;
which are necessary to the successful operation of a selec- !
tive adsorption process. It will be recognised that im-provements in any of these adsorbent characteristics will .
` 107706~
result in an improved separation process. ~mong such characteristics are: adsorptive capacity for some volume of an extract component per volume of adsorbent; the selective adsorption of an extract component with respect to a raffinate component and the desorbent material; suf-ficiently fast rates of adsorption and desorption of the extract component to and from the adsorbent; and, in in-~tances where the components of the feed mixture are very reactive, little or no catalytic activity for undesired reactions such as polymerization and isomerization.
Capacity of the adsorbent for adsorbing a specific volume of an extract component is, of course, a necessity;
without such capacity the adsorbent is useless for ad-- sorptive separation. Furthermore, the higher the adsorbent's capacity for an extract component, the better is the adsor-bent. Increased capacity of a particular adsorbent makes it possible to reduce the amount of adsorbent needed to separate the extract component contained in a particular charge rate of feed mixture. A reduction in the amount of adsorbent required for a specific adsorptive separation reduces the cost of the separation process. It is im-portant that the good initial capacity of the adsorbent be maintained durin~ actual use in the separation process over some economically desirable life.
The second necessary adsorbent characteristic is the ability of the adsorbent to separate components of the feed; or, in other words, that the adsorbent ~ossess ad-sorptive selectivity for one component as compared to a-nother component. Some adsorbents demonstrate acceptable 10~7064 capacity but possess little or no selectivity. Silver ni-trate on silica gel for instance possesses a large capacity for cresols but little selectivity for one isomer with re-spect to another. 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 relative selectivity, (B), as used throughout this specification is defined as the ratio of two components of an adsorbed phase over the ratio of the same two components in an unadsorbed phase at equilibrium conditions.
Relative selectivity is shown as Equation 1 below: {
Selectivity = (B) = ~ol. percent C/vol. percent ~ol. percent C/vol. percent ~ UA
where C and D are two components of the feed represented in volume percent and the subscripts A and U represent the adsorbed and unadsorbed phases respectively. The equili-brium conditions were determined when the feed passing over a bed of adsorbent did not change composition after contact-ing the bed of adsorbent. In other words, there was no nettransfer of material occurring between the unadsorbed ar.d adsorbed phases. ¦
Where selectivity of two components approaches 1.0 there is no preferential adsorption of one component by the adsorbent with respect to the other;they are both adsorbed ~or non-adsorbed) to about the same degree with respect to the other. As the (B) becomes less than or greater than 1.0 there is a preferential adsorption by the adsorbent for one component with respect to the other. When comparing the 1077~
selectivity by the adsorbent of one component C over com-ponent D, a (B) larger than 1.0 indicates preferential ad-sorption of component C within the adsorbent. A (B) less than 1.0 would indicate that component D is preferentially adsorbed leaving an unadsorbed phase richer in camponent :
C and an adsorbed phase richer in component D. Desorbent materials ideally would have a selectivity equal to about 1 or slightly less than 1 with respect to an extract component.
Employing a desorbent material comprising an alco-~0 hol increases the selectivity of the adsorbent for a para-cresol with respect to the other cresol isomers thereby permitting sharper separation of the isomers and improving the process.
The third important characteristic is the rate of exchange of the extract component of the feed mixture ma-terial or, in other words; the relative rate of desorption of the extract component. This characteristic relates 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 a-mount 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 pumped through the process and separated from the extract stream for reuse in the process.
We have found that the use of a desorbent material comprising an alcohol also increases the transfer rates besides im-proving the selectivity for para-cresol.
It is also necessary that the adsorbent possess 1()770~
little or no catalytic activity toward any reaction such as polymerization or isomerization of any of the feed com-ponents. Such activity might effect adsorbent capacity or selectivity or product yields or all of these, but in the adsorptive separation of cresol isomers with a zeolite-containing adsorbent this is generally not a problem.
In order to test various adsorbents and desorbent materials with a particular feed mixture to measure the adsorbent characteristics of adsorptive capacity and selec-tivity and exchange rate a dynamic testing apparatus isemployed. The apparatus consists of an adsorbent chamber of approximately 70 cc. volume having inlet and outlet portions at opposite 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 outlet llne of the chamber and used to analyse the effluent stream r 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.
Theadsorbent is filled to equilibrium with a particular desorbent material by passing the desorbent material through the adsorbent chamber. At a convenient time, a pulse test of feed containing known concentrations of cresol isomers all diluted in desorbent material is injected for a dur-ation of several minutes. For convenience a known con~
centration of a non-adsorbcd tracer compound may be -2~-1~7706~ ~
included in ~he feed. Flow of desorbent material is re-sumed, and the tracer (if one is employed) and the cresols are eluted as in liquid-solid chromatographic operation.
The effluent can be analysed by on-stream chromato~raphic S equipment and traces of the envelopes of corresponding component peaks developed. Alternativeli~, effluent samples can be collected periodically and later analysed separately by gas chromatography.
From information derived from the chromatographic -~
10 traces adsorbent performance can be rated in terms of ca- ¦
pacity index for para-cresol, selectivity for para-cresol with respect to the other cresols and rate of desorption of para cresolby the desorbent. The capacity index is char- I ;
acterised by the distance between the centre of the para-15 cresol peak envelope and the tracer peak envelope or some other known reference point such as volume of desorbent pumped. It is expressed in terms of the volume in cubic centimetres of desorbent pumped during this time interval.
Relative selectivity, (B), for para-cresol with respect to f 20 the other cresols is characterised by the ratio of the distance between the centre of the para-cresol peak envel-ope and the tracer peak envelope (or other reference point) to the corresponding distances for the other cresol isomers.
The rate of exchange of para-cresol with the desorbent can 25 be characterised by the width of tile para-cresol peak envelope at half intensity. The narrower the peak width, the faster the desorption rate.
To further evaluate promising adsorbent systems and to translate this type of data into a practical cresol separation process requires actual testing of the best sys-tem in a continuous countercurrent liquid-solid contacting d'evice.
The general operating principles of such a device S have been previously described and are found in U.S. Patent 2,985,589. A specific laboratory-size fluid-solid contact-ing apparatus utilising these principles is described in U.S. Patent 3,706,812.
The improved process of this invention for sep-arating para-cresol from a feed mixture containing para-cresol and at least one other cresol isomer, which was demonstrated by pulse tests, was confirmed by actual con-tinuous testing in the continuous device.
The examples below illustrate first the selectivity characteristic of adsorbents comprising zeolites which makes possible a process for the adsorptive separation of cresol isomers and second the improvement in that characteristic, as well as in the rate of desorption, which results in the improved process of our invention. The examples are pre-sented to further illustrate the process of the present in-vention and are not intended to limit the scope and spirit of the invention.
The examples present pluse test results obtained with an adsorbent comprising type X crystalline alumino-silicate which contained barium and potassium cations atthe exchangeable cationic sites within the aluminosilicate.
Results for one pulse test which employed an adsorbent com-prising a type X crystallinc aluminosilicate containing calcium cations at the exchan~eable cationic sites are 10770~4 .
also include~ for comparison. The first-mentioned ad-sorbent was essentially totally ion-exchanged, con-tained a weight ratio of barium oxide to potassium oxide of about 3.3, and was approximately 20-40 mesh particle t 5size. Analyses of this adsorbent are shown in Table No.
2 below.
Table No. 2 ADSORBENT ANALYSES
Volatile Matter (LOI @ 900 C.) 6.43 Si0 (volatile free) wt. ~ 42.1 A12~ (volatile free) wt. % 28.3 Na 03(volatile free) wt. % 2.0 K2~ (volatile free) wt. % 6.1 BaO (volatile free) wt. % 20.3 Si02/A1203 2.53 The latter adsorbent was commercially-available Linde 10X
Molecular Sieves of approximately 20-40 mesh particle size.
EXAMPLE I
In this example the adsorbent comprising the type X
zeolite containing barium and potassium cations described above was placed in the testing unit and a pulse test was conducted in the following manner.
The desorbent material employed was 15 vol. ~ phe-nol in toluene. The feed mixture utilised contained 5 vol.
~ each of para-cresol and meta-cresol in desorbent material.
Ortho-cresol was omitted from the feed mixture in order to simplify the test and focus on the para/meta selectivity which is the most critical selectivity because of their close boiling points. Additionally from previous experi-ments it had been determined that the meta- and orth-isomers behave in substantially the same manner. Since desorbent material was a part of the feed mixture, adsorption of 107701 i~ j para-cresol took place in the presence of, and in compe-tition with, desorbent material, and; therefore, selec-tïvities were obtained at less than equilibrium condi-tions. The desorbent was placed in a 70 cc adsorbent column which was maintained at a constant temperature of about 150C. with constant moderate pressure during the entire operation. A Waters Automatic Fraction Collector was connected to the effluent end of the chamber to sample the effluent every 2.1 minutes.
Desorbent was first pumped through the adsorbent r chamber at approximately 1 cc~min at about 150C. A 4.7 cc feed pulse was then cut into the system via an injection loop and the effluent was periodically sampled in the man- ¦
ner indicated above. A measured void volume of 43.0 cc was used for the 70 cc adsorbent column and sampling was started after 40 cc of desorbent was p~mped beginning at feed injection. The individual effluent samples were stop-pered after collection and analysed separately by Gas Chromatography (GC). A digital integrator was used to ob-tain peak areas and the count produced (x 10 ) was plot-ted versus cc of desorbent from time of feed injection, for both para- and meta-cresol. This plot produced an envelope for para- and meta-cresols similar to those ob-tained when using on-stream GC analysis. The cresol samples take 50 minutes to elute from the analytical GC column.
The selectivities were calculated by measuring the cc of the desorbent pumped from the measured 43 cc void ~ volume to the midpoints of the individual para- and meta-cresol envelopes at one-half the peak heights. The ratio 1~)770~
of these volumes represent the relative selectivity of para-cresol with respect to meta-cresol.
Reproducible data from this test gave a relative para-cresol to meta-cresol selectivity of 1.53 which -demonstrates the characteristic of the adsorbent which makes the adsorptive separation process possible.
EXAMPLE II .
In this example three pulse tests A, B, and C
were performed; tests A and B with the adsorbent des-cribed above and used for Example I and test C with anadsorbent comprising a type X zeolite having calcium at the exchangeable cationic sites. The results are shown in Table No. 3 below.
~ . ~
r 107706~ 1 ~, W
-W W ~
U~
I I U~
3 o ~5 X ~D~D ~
X X r~
.
. C
~D ' 3 W ~3 O o O o O o ~D
Ln C ~ C ~ C
r~ u~ C~
X tD X ~D ~ ~D O ~
~s ~ ~ ~3 Y o "-O O 1- ~ ~D ~
_ ~ ~h t-r U~ f3 ~D ~
O 1- 1_ It fD ~S
ID n ~D CO W Ul ~ r~
~I o ~- 1~-~' ~
~`
ID--U~ ~
~o ~ .
o ~ ~t tD
, ,_ ~P~ o ~I ~
Ul o o O O
ID ~h ~ D ~
~ ~ C
rt ~ I~
~a -- P~
1077~)t;4 The test procedure and cquipment used was the same as that described in Example I.
For test A the desorbent material was 30 vol. ~ phe-nol in toluene and the feed mixture contained 5 vol. % each of para-cresol and meta-cresol in desorbent material. The relative selectivity of the adsorbent for para-cresol with respect to meta-cresol in the presence of this desorbent material was 1.37 and the para-cresol peak envelope width at half height was 17Ø
The same adsorbent was employed for test B but the desorbent material was 50 vol. % hexanol in toluene. Now the relative selectivity of the same adsorbent for para-cresol with respect to meta-cresol in the presence of this desorbent material was 1.8 or an increase of 31% over that of test A. The para-cresol peak envelope width at half height had decreased from 17.0 obtained for test A to 11.0 for test B indicating a faster rate of desorption of para-cresol for test B. The comparison of the results of test A and B, therefore indicates the improvements in the ad-sorbent characteristics of selectivity and transfer rateand hence in the separation process itself when a desorb-ent material comprisin~ an alcohol is employed.
Test C was conducted with the same desorbent ma-terial as was used for test B but a different adsorbent was ~mployed. l'he adsorbent used comprised a type X zeolite containing calcium cations at the exchan~eable cationic sites. With the same desorbent material, hexanol-l in toluene, this adsorbent exhibited essentially no selec-tivity for either cresol isomers thus indicatin~ that this adsorbent, while suitable for use in the prior art cresol separation process, is not suitable for use in the cresol isomer separation process of this invention.
Claims (19)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for separating para-cresol from a feed mixture containing para-cresol and at least one other cresol isomer which process comprises: (a) contacting at adsorption conditions said feed mixture with a crystalline aluminosilicate selected from type X structured and type Y
structured zeolites containing at the exchangeable cationic sites one or more selected cations thereby selectively adsorbing para-cresol from said feed mixture; and, (b) con-tacting said adsorbent with a desorbent material at desorption conditions to remove the adsorbed para-cresol therefrom;
characterised by employing a desorbent material comprising an alcohol which is soluble in the feed mixture at adsorption and desorption conditions and which has an average boiling point at least 8°C different from that of the feed mixture.
structured zeolites containing at the exchangeable cationic sites one or more selected cations thereby selectively adsorbing para-cresol from said feed mixture; and, (b) con-tacting said adsorbent with a desorbent material at desorption conditions to remove the adsorbed para-cresol therefrom;
characterised by employing a desorbent material comprising an alcohol which is soluble in the feed mixture at adsorption and desorption conditions and which has an average boiling point at least 8°C different from that of the feed mixture.
2. The process of claim 1 characterised in that said crystalline aluminosilicate is an X structured zeolite.
3. The process of claim 1 characterised in that said crystalline aluminosilicate is a Y structured zeolite.
4. The process of any of claims 1 to 3 characterised in that said crystalline aluminosilicate contains from 4 to 8 wt.
% water on a volatile-free basis.
% water on a volatile-free basis.
5. The process of any of claims 1 to 3 characterised in that said cation is selected from Group IA, Group IIA, and Group IB metals of the Periodic Table of Elements.
6. The process of any of claims 1 to 3 characterised in that said alcohol has a boiling point which is at least 8°C
less than that of the feed mixture.
less than that of the feed mixture.
7. The process of claim 1 characterised in that said alcohol is a primary alcohol.
8. The process of claim 7 characterised in that said primary alcohol has from one to and including seven carbon atoms per molecule.
9. The process of claim 8 characterised in that said primary alcohol is 1-hexanol.
10. The process of claim 1 characterised in that said desorbent material comprises a mixture of an alcohol and a hydrocarbon which is soluble in both the feed mixture and the alcohol at both adsorption and desorption conditions and which has an average boiling point which is at least 8°C
different from that of the feed mixture.
different from that of the feed mixture.
11. The process of claim 10 characterised in that said hydrocarbon is a paraffin or a cycloparaffin.
12. The process of claim 10 characterised in that said hydrocarbon is an aromatic.
13. The process of claim 12 characterised in that said aromatic hydrocarbon is selected from benzene, toluene, and xylene.
14. The process of any of claims 10 to 12 characterised in that said mixture contains from 25 to 75 vol.
percent alcohol with said hydrocarbon.
percent alcohol with said hydrocarbon.
15. The process of any of claims 1 to 3 characterised in that said absorption conditions include a temperature from 38° to 260°C and a pressure of from 1 to 35 atmospheres.
16. The process of any of Claims 1 to 3 char-acterised in that said desorption conditions include a tem-perature from 38° to 260°C and a pressure of from 1 to 35 atmospheres.
17. The process of any of Claims 1 to 3 char-acterised in that said X structured zeolite contains barium and potassium at the exchangeable cationic sites.
18. The process of any of Claims 1 to 3 char-acterised in that said X structure zeolite contains barium at the exchangeable cationic sites within said zeolite.
19. The process of any of Claims 1 to 3 char-acterised in that said Y structured zeolite contains potas-sium at the exchangeable cationic sites.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US05/551,456 US3969422A (en) | 1973-06-06 | 1975-02-19 | Process for the separation of cresol isomers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1077064A true CA1077064A (en) | 1980-05-06 |
Family
ID=24201347
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA245,939A Expired CA1077064A (en) | 1975-02-19 | 1976-02-17 | Process for the separation of cresol isomers |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS51108025A (en) |
| CA (1) | CA1077064A (en) |
| DE (1) | DE2606276C2 (en) |
| FR (1) | FR2301504A1 (en) |
| GB (1) | GB1535269A (en) |
| IT (1) | IT1053863B (en) |
| NL (1) | NL164545C (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5813527B2 (en) * | 1976-02-02 | 1983-03-14 | 旭化成株式会社 | Improved xylenol separation method |
| JPS5645429A (en) * | 1979-09-20 | 1981-04-25 | Toray Ind Inc | Separation of cresol isomer |
| US5149887A (en) * | 1989-12-28 | 1992-09-22 | Uop | Separation of alkyl-substituted phenolic isomers with barium-potassium exchanged zeolitic adsorbent |
| DE4201853A1 (en) * | 1992-01-24 | 1993-07-29 | Bayer Ag | METHOD FOR SEPARATING M- AND P-CRESOL |
| CN115970638A (en) * | 2022-07-29 | 2023-04-18 | 正大能源材料(大连)有限公司 | Preparation method and application of molecular sieve type adsorbent |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3014078A (en) * | 1959-02-02 | 1961-12-19 | Union Oil Co | Separation of cresol isomers |
| JPS5126830A (en) * | 1974-08-22 | 1976-03-05 | Mitsubishi Chem Ind | Kurezooruiseitaino bunrihoho |
-
1976
- 1976-02-17 IT IT4814376A patent/IT1053863B/en active
- 1976-02-17 DE DE19762606276 patent/DE2606276C2/en not_active Expired
- 1976-02-17 CA CA245,939A patent/CA1077064A/en not_active Expired
- 1976-02-18 GB GB633376A patent/GB1535269A/en not_active Expired
- 1976-02-19 FR FR7604620A patent/FR2301504A1/en active Granted
- 1976-02-19 JP JP1745076A patent/JPS51108025A/en active Granted
- 1976-02-19 NL NL7601660A patent/NL164545C/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| DE2606276A1 (en) | 1976-09-09 |
| DE2606276C2 (en) | 1981-10-08 |
| GB1535269A (en) | 1978-12-13 |
| NL164545B (en) | 1980-08-15 |
| FR2301504B1 (en) | 1980-04-11 |
| JPS51108025A (en) | 1976-09-25 |
| JPS5754492B2 (en) | 1982-11-18 |
| NL164545C (en) | 1981-01-15 |
| IT1053863B (en) | 1981-10-10 |
| FR2301504A1 (en) | 1976-09-17 |
| NL7601660A (en) | 1976-08-23 |
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