CA1209119A - Activation of ultra high silica zeolites - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method for enhancing the activity of high silica crystalline material, e.g. a zeolite having a silica-to-alumina mole ratio greater than 500, is disclosed which involves the sequential steps of calcining the material and treating same with a volatile iron compound.

Description

9~9 ACTIVATION OF ULTRA HIOEI SILICA ZEOLITES

BACKEROUND OF THE INVENTION
Field of the Invention This invention relates to a method for enhancing the catalytic activity of certain high silica-containing crystalline matarials which lnvolves the sequential steps of calcining the material and contacting the calcined material with a volatile iron~containing compound having a minimum vapor pressure of 50 mm at 500C. The iron-containing compound contacted material may then be subjected to heating, hydrolyzing the heated material and calcining the resulting hydrolyzed material. The silica-containing crystall;ne material having enhanced activity prepared by the present method exhibits valuable shape selectivity catalytic properties.
Cescription of Prior Art High silica-containing zeolites are well known in the art and it is generally acceoted that the ion exchange capacity of the crystalline aluminosilicate is directly dependent on its aluminum content. Thus, for example, the more aluminum there is in a crystalline structure, the more cations are required to balance the electronegativity thereof, and when such cations are of the acidic type such as hydrogen7 they impart catalytic activity to the crystalline material. On the other hand, high silica-containing zeolites having little or substantially no aluminum, have many important properties and characteristics and a high degree of structural stabil;ty such that they have become candidates for use in f various processes inclu~ins catalytic processes. Materials of this type are known in the art and include high silica-containing aluminosilicates such as ZSM-5 (U.S. Patent 3,702,886), ZSM-ll (U.S.
Patent 3,709,979), and zeolite ZSM-17 (U.S. Patent 3,832,449) to ; mention a few.
The silica-to-aluMina ratio of a given zeolite is often variable; for example, zeolite X can be synthesized with a silica-to-alumina ratio of from 2 to 3; zeolite Y from 3 to about 6.
In some zeolites, the upper limit of silica-to-alumina ratio is lo virtually unbounded. Zeolite ZSM-5 is one such material wherein the silica-~o-alunina ratio ls at least 5. U.S. Patent 3,941,871 discloses a crystalline metal organosilicate essentially free of aluminum and exhibiting an x-ray diffraction pattern characteristic of ZSM-5 type aluminosilicate. U.S. Patents 4,061,724; 4,073,865 and 4tlO4,294 describe microporous crystalline silicas or silicates wherein the aluminum content present is at impurity levels.
ecause o, the extremely low aluminum content of these high silica-containing zeolites, their ion exchange capacity is not as great as materials with a higher aluminum content. Therefore, when these materials are cont æ ted with an acidic solution or otherwise converted to their acidic forms and thereafter are processed in a conventional manner, they are not as catalytically active as their higher aluminum-containing counterparts.
The novel process of this invention permits the preparation of certain ultra high silica-containing materials which have all the desirable properties inherently possessed by such high silica materials and, yet, have an enhanced activity for shape selective catalytic applications which heretofore has only been possible to be achieved by materials having a higher aluminum content in their "as synthesized" form. There is evidence to indicate that the zeolites activated by the present method contain iron as a structural component. Such a zeolite is shown to be different than a mere mixture of i m n and the zeolite. Also, the amount of iron incorporated in the high-silica containing material by the present 3s method is much greater than would be expected by ion exchange relative the aluminum content of the material. - - -~3- ~2~
It is noted that U.S. Patents 3,354,078 and ~,644,220 relate to treating crystalline aluminosilicates with volaiile metal halides.
Neither of these latter patents is, however, concerned with treatment of crystallir,e materials having an ultra high silica-to-alumina mole ratio of at least 500. Also, U.S. Patent 41350~835~ issued September 21, 1982 teaches a process for converting gaseous paraffinic feedstock to aromatics over a catalyst ccmprising gallium and a zeolite characterized by a constraint index of 1 to 12 and a sil;ca-to-alumina mole ratio of at least 12. U.S. Patent 4,180,689 teaches use of gallium-containing aluminosilicate zeolite catalysts to provide improved yields of aromatic hydrocarbons from a feedstock of C3-C12 hydrocarbons. The zeolite therein has a silica`to-alumina mole ratio of from 20 to 70 and the gallium is either deposited on or ion-exchanged into the zeolite. U.S. Patent 4,120,910 teaches use of a ZSM-5 type al~minosilicate zeolite having incorporated therein a minor amount of metal from Group VIII, IIB or I8 of the Periodic Table for catalyzing the conversion of paraffinic hydrocarbons to aromatics.
SUMMARY OF THE INVENTION
The present invention relates to a novel process for improving catalytic activity for shape selective catalytic applications of certain ultra high sil;ca-containing crystalline zeolites which comprises the essential steps of calcining the ultra high silica-containing material and cont æ ting the calcined material at an elevated temperature with a volatile i m n~containing compound having a minimum vapor pressure of 5Q mm at 50QC, e.g. ferric chloride. The iron-containing compound contacted zeolite may then, iF
desired, be subjected to heating, hydIolyzing the heateo material and calcining the hydrolyzed material. The resulting zeolite material exhibits énhanced activity toward catalysis of numerous chemical reactions, such as, for example, dehydrogenation and reforming. They exhibit high selectivites for aromatics production from various feedstocks, e.g. in dehydrogenation of ethylcyclohexane to aromatic compourds with preferential formation of the para-xylene isomer and preferential dehydrogenation of l,'l-dimethyl cyelohexane relative the 1,2-isomer. Evidence suggests that the zeolites treated in accordance he~e~ith contain iron as a structural component.

I- lZ~lg DESCRIPTION _F SPECIFIC EMBODIMENTS
The novel process of this invention is concerned with the treatment of ultra hish silica-containir,g crystalline material. The expression "ultra high silica-containins crystalline material" is intended to define a crystalline structure Hhich has a silica-to-alumina mole ratio greater than 500 up to and including those highly siliceous materials where the silica-to-alumina mole ratio is infinity or as reasonably close Jo infinity as practically possible. Highly sil1ceous materials are exemplified in U.S. patents 3,941,871; 4,061,724; 4,073,aO5 and 4,104,294 wherein the materials are preparea from reæ tion solutions which involve no deliberate addition of aluminum. However, t ace quantities of aluminum art usually present due to the impurity of the reaction solutions. It is to be understood that the expression ultra high silica-containing crystalline material" also specifically includes those materials which have other metals besides silica and/or alumina associated therewith, such as boron or chromium. Thus, a requirement with regard to the starting materials utilized in the novel process of this invention is that they have a silica-to-alumina mole ratio greater tan about 500 (irrespective of what~other materials or metals are present in the crystal structure).
The crystalline starting materials for the present process may be synthesized from reaction mixtures containing varicus cation sources, including as non-limiting examples trial~ylammonium compounds where alkyl is frcm 1 to about 2a carbon atcms, e.s. ~ripropyl-ammonium cation sources; quaternary ammonium compounds, e.g.
tetraprGpylammonium cation sources; and compounds containing multiple cationic centers, e.g. diquaternary ammonium cation sources. The compounds may be, for example, salts such as halides, e.g. chloride or bromide, nitrates, etc.
The novel process of this invention is simple and easy to carry out although the results therefrom are dramatic. The process is carried out by calcining an ultra high silica crystalline zeolite material having a silica-to-alumina mole ratio of at least 500 by heating the same at a temperature within the ra,-se of from about 2C0C
to about 600~C in an atmosphere of air, nitrogen, etc. at atmospheric, 9~
superatmospheric or subatmospheric pressures for between lo minutes and 48 hours. The calcined zeolite is thereafter treated with a volatile im n-containing compound (i.e. having a minimum vapor pressure of 50 mm at 500C) at a temperature of from about 5ûC to about 500C, preferably from about 75C to about 300C. If desired, the iron-containing compound treated zeolite may then be heated to a temperature in the range of from about 300C to about 600C in an inert atmosphere of air, nitrogen, etc. for from about lO minutes to about 48 hours. The heated zeolite may then be hydrolyzed by contact with water at a temperature of from about ambient room temperature (e.g. 20C) to about lOûC. The hydrolyzed zeolite may then be calcined at a temperature of from about 200C to about 600C in an inert atmosphere of air, nitrogen, etc. at subatmospheric, atmospheric or superatomspheric pressures for from about lO minutes to about 48 hours.
The iron-containing compound contacting step may be accomplished by admixture of the i m n-containing compound vapor with an inert gas such as nitrogen or helium at temperatures ranging from about 50C to about 500C, preferably from about 75C to about 300C.
The amount of iron-containing compourd vapor which is utilized is not narrowly critical but usually from about 0.01 to about 2 grams of iron-containing compou,~d are used per gram of ultra high silica crystalline material.
The iron-containing compourd for use herein must have a minimum vapor pressure of about 50 mm at a temperature of 500C. Said compound may be inorganic or organic. 5uitable inorganic iron compounds include, as a non-limiting example, salts such as ferric chloride. A non-limiting example of an organic iron compourd is ferrocene. Iron carbonyl may also be used. Of course, mixtures of any of the above volatile iron compounds may be used.
The high-silica crystalline material prepared by the present method may have its catalytic activity further tailored for specific chemical conversion by various procedures. One such tailoring procedure involves incorporation by ion exchange or impregnation of one or more other metals, such as, for example, Group VI B (e.g. Cr, Mo and W), IB (e.g. Cu) or IIB (e.g. Zn) metals of the Periodic Table --6- 1Z~9119 of the Elements. Combinations of the above metals may also be ( utilized in this fashion as well as metals from Group VIII other than im n (e.g. Co, Ni, Pt and Ir) and their combinations with each other and the above metals. Another such tailoring procedure involves treatment of the crystalline material prepared by the present method by ion exchange or impregnation, or merely effective cont æ t with Group IA cations (e.g. i+, Na+ and K+) of the Periodic Table.
This latter tailoring procedure reduces any available acid activity and makes the crystalline material more suitable as a catalyst for reactions requiring 10~N acid activity, e.g. dehydrogenation.
Compounds which may be used to provide the Group IA cations include, for example, KOH, K2C03, Na2C03 and NaOH. 4nother such tailoring method involves ion exchange with hydrogen or hydrogen precursors by known methods.
The high silica crystalline material product of this invention exhibits a much larger amount of iIon than would be expected oy ion exchange of ore staring crystaliine material based on aluminum content thereof. For example, assuming ion exchange due to presence of tetrahedrally coordinated aluminum in the starting crystalline material structure, exchange of Fe+ff therein would provide about 0.002 weight percent iron in a material having a silica-to-alumina mole ratio of 26,000 and about 0.001 weight percent im n in a 50,000 silica-to-alumina material. Reverence to the specific examples which follow will indicate much larger quantities of im n present by way of ~5 this invention. This is evidence indicating structural location of im n introduced by the present method.
Of the ultra high silica zeolite materials advantageously treated in accordance herewith, zeolites ZSM-5, ZSM- ll and ZSM-5/ZSM-ll intermediate are particularly noted. ZSM-5 is described in u.S. Patents 3,702,886 and Re 29,948. zsM-ll is described in u.S. Patent 3,709,979. ZSM-5/ZSM-ll intermediate is described in U.S. Patent 4,229,424.

~7~ ~Z~ 9 The activity enhanced high silica crystalline materials prepared by the present method are useful as catalyst components for a variety of organic, e.g. hydrocarbon, compound conversion processes.
Such conversion processes include, as non-limiting examples, desulfurization of sulfur-containing feedstocks with reaction corditions including a temperature of from about 120C to about 400C, a hydrogen partial pressure of from about 0.2 atmosphere (bar) to about 20 atmospheres and a liquid hourly space velocity of from about 0.1 to about 15; dehydrogenating hydrocarbon compounds with reaction conditions including a temperature of from about 3~0C tc about ,00C, a pressure of from about 0.1 tmosphere to about 10 atmospheres and a weight hourly space velocity of from about 0.1 to about 20; converting paraffins to aromatics with reaction conaitions including a temuerature of from about lû0C to about 7C0C, a pressure of from about 0.1 atmosphere to about 60 atmospheres, a weight hourly space velocity ox from about 0.5 to about 400 and a hydrogen/hydrocarbon mole ratio of from about 0 to about 20; converting olefins to aromatics, e.g. benzene, toluene and xylenes, with reaction conditions including a temperature of from about 100C to about 700C, a pressure of from about 0.1 atmosphere to about 60 atmospheres, a weight hourly space velccity of from about 0.5 to about 400 and a hydrogen/hydrocarbon mole ratio of from about a to aoout 2û;
converting synthesis gas to organic compounds with reaction conditions including a temperature of from about 230C to about 400C and a pressure of from about 40 atmospheres to about 400 atmospheres.
Specific chemical reactions of interest for the shape-selective catalyst prepared herehy include conversion of n-hexane to benzene; shape-selective conversion of 1,4-di~ethylcyclohexane to p-xylene; conversion of ethylbenzene to styrene; and the selective conversion of p-ethyltoluene in admixture with o-ethyltoluene to p-methylstyrene.
In practicing a particularly desired chemical conversion process, it may be useful to incorporate the above-described activity enhanced crystalline zeolite with a matrix comprising another material resistant to the temperature and other conditions employed in the process. Such matrix material is useful as a blnder and imparts greater resistarce to the catalyst for the severe temperature, pressure and reactant feed stream velocity conditions encountered in many processes.
Useful matrix materials ir~lude both synthetic ard naturally occurring substances, as well as inorganic materials such as clay, silica and/or metal oxides. The latter may be either naturally occurring or in the form ox gelatinous precipitates or gels including mixtures of silica and metal oxides. Naturally occurring clays which oan be composited with the zeolite include tnose of the montmorillonite ano kaolin families, which families include the sub-bentonites and the kaolins commonly known as Dixie, McNamee, Georgia and Florida clays or others in which the main mineral constituent is halloysite, kaolinite, dickite, nacrite or anauxite.
Such clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment or chemical modification.
In addition to the foregoing materials, the zeolites employed herein may be composited with a porous matrix material such as alumina, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, and silica-titania, as well as ternary compositions, such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia and silica-magnesia-zirconia. The matrix may be in the form of a cogel. The relative proportions of activity enhanced zeolite component and inorganic oxide gel matrix, on an anhydrous basis, may vary widely with the zeolite content ranging from between about 1 to about 99 percent by weight and more usually in the range of about 5 to about 80 percent by weight of the dry composite.
The following examples will illustrate the novel process of the present invention.

.
Zeolite ZSM-5 having a silica-to-alumina mole ratio of 50,000 was prepared and then calcined at 538C for 8 hours. After cooling, anhydrous ferric chloride (FeC13) vapors in a nitrogen stTeam were passed over the zeolite, while the temperature was programmed from room temperature to 300C at a rate of 2-3C/minute, where it was held for 1 hour. The temperature was then raised to 500C, where it was g lZ~

maintained for an hour. The iron-containing compound ccntacted material was cooled to about room te~oerature and was then slurried in water at rocm temperature for 15 minutes. The flltered and washed resulting catalyst material was then calcined in air at 538C for 8 hours. The yellow b m wn catalyst material obtained was analyzed, indicating 4.9 weight percent iron.

___ Zeolite ZSM-5 having a silica-to-alumina mole ratio of 26,0~0 was prepared and subjeoted Jo calcination ard cont æ ted with iIon-containing compound, i.e. anhydr~us ferric chloride, as in Example 1. The cooled iron-containing compound cont æ ted material was then slurried in water at room temperature for 17 hours. The filtered and washed resulting catalyst material was then calcined in air at 538C for 8 hours. The fir~l catalyst material contained 2.8 weight percent iron by analysis.

A quantity of the catalyst material prepared in Example 2 was subjected to ammonium exchange by slurring it in 25 ml lM aqueous NH4Cl solution containing 2 ml NH40H for 17 hours at room temperature. The ammonium content of the ion-exchanged material was greater than û.ll meq/gram indicating significant ammonium exdnange.
As a basis for comparison, the ZSM-5 starting material of Example 2 was subjected to the same ammonium exchange procedure as above and no significant ammonium exchange was observed, i.e. the ammonium content was less than 0.01 ,T~q/gram. This is evidence indicating structural location of iron introduced by the present method.

To exemplify shape-selective dehydrogenation of isomeric ethyltoluenes over the catalyst material prepared by way of the present invention, an equimolar mixture of para- and ortho-ethyltoluene was reacted over the catalyst material prepared in Example 2 at 575C and a weight hourly space velocity of û.25 hr 1.
A mixture of isomeric methylstyrenes was obtained including the meta-isomer. The residual ethyltoluenes were predominantly the ortho-isomer, indicating preferential conversion of the para-isomer.

Claims (7)

WHAT IS CLAIMED IS:

1. A method for enhancing the activity of a silica-containing crystalline material having a silica-to-alumina mole ratio greater than about 500 which comprises calcining said crystalline material at a temperature of from about 200°C to about 600°C and contacting said calcined crystalline material at a temperature of from about 50°C to about 500°C with a volatile iron-containing compound having a minimum vapor pressure at 500°C of 50 mm.

2. The method of Claim 1 which comprises heating said iron-containing compound contacted crystalline material at a temperature of from about 300°C to about 600°C, hydrolyzing said heated crystalline material at a temperature of from about ambient to about 100°C and thereafter calcining said hydrolyzed crystalline material at a temperature of from about 200°C to about 600°C.

3. The method which comprises incorporating a metal selected from the group consisting of metals of Groups VIII, IB, IIB, and VIB of the Periodic Table of the Elements and combinations thereof with the iron-containing compound contacted crystalline material of Claim 1.

4. The method which comprises contacting the iron-containing compound contacted crystalline material of Claim 1 with a source of cations selected from the group consisting of elements of Group IA of the Periodic Table of the Elements.

5. The method of Claim 1 wherein said crystalline material is ZSM-5, ZSM-11 or ZSM-5/ZSM-11 intermediate.

6. The method of Claim 2 wherein said crystalline material is ZSM-5, SM-11 or ZSM-5/ZSM-11 intermediate.

7. The method of Claim 1 wherein said iron-containing compound is ferric chloride.