GB2024790A

GB2024790A - Crystalline silica

Info

Publication number: GB2024790A
Application number: GB7921622A
Authority: GB
Original assignee: SnamProgetti SpA
Current assignee: SnamProgetti SpA
Priority date: 1978-06-22
Filing date: 1979-06-21
Publication date: 1980-01-16
Also published as: AT381483B; NL7904909A; AU531123B2; HU181955B; PL216527A1; US4656016A; DK165173B; DK593084A; DE2924915C2; YU148479A; DK593084D0; DK240379A; LU81415A1; CA1155824A; DK3592D0; IE48198B1; RO78795B; IL57582A; JPH0230612A; AU4787479A

Description

1 GB 2 024 790 A 1

SPECIFICATION

Synthetic silica-based materials This invention relates to synthetic silica-based materials. More particularly, it relates to synthetic materials comprising modified crystalline silicas which have a high specific surface area.

According to the present invention, there is pro- vided a silica-based material comprising crystalline silica which has been modified with one or more elements which have entered the crystalline lattice of the silica in place of silicon atoms of the silica or in 75 the form of salts of bisilicic or polysilicic acids.

As elements which can be used for obtaining the modified silicas, all those which form metallic cations can be used but preference is given, if only to simplify the procedure fortheir preparation, to elements having, at least partially, an amphoteric character such as chromium, beryllium, titanium, vanadium, manganese, iron, cobalt, zinc, zirconium, rhodium, silver, tin, antimony and boron.

Modified silicas of this kind are characterised by the presence of a single crystalline phase, and may have the following formula:

(0-0001 to 1) MnOm-SiO2 wherein M,Orn is an oxide of the modifying element.

The silica may contain small amounts of water, the quantity being greater or smaller depending upon the calcination temperature. The silicas according to the invention have a high thermal stability and usually have high specific surface areas as well as an acidity due to Lewis'systems and an acidity due to Br(bnsted systems, these acidities depending upon the nature of the cation which has been introduced as the modifying element.

There are known many amorphous silicas having a high or a low specific surface area, such as those obtained by the well known procedure of gelling a silica sol or by precipitation and gelling of various silicates (see U.S. Patent Specifications Nos. 2,715,060; 3,210,273; 3,236,594 and 3,709,833).

More recently U.S. Patent Specification No. 3,983,055 has described a synthetic amorphous silica having a preselected pore distribution. The silica is prepared by the hydrolysis of an organic derivative of silicon, by the condensation by polymerisation, and by calcination. A number of crystalline silicas are known, such as quartz, crys- tobalite, tridymite, keatite and many others, prepared according to procedures which have widely been described in the technical literature. For exam- ple, Heidemann in Beitre. Min. Petrog. 10, 242 (1964) 115 describes the reaction, at 1800C, of an amorphous silica with 0.55% KOH over a period of 21 days to obtain a crystalline silica, called silica-X, which has a specific surface area of about 10 m2P and has a poor stability since, within five days, it is converted into cristobalite and then into quartz. Recently, Flanigen et aL, Nature, 271, 512 (1978) have obtained a crystalline silica, namely silicalite, having a high specific surface area and, on account of its hydrophobic nature, have suggested its use for the purification of water polluted by organic substances.

In the case of the material of the present invention, the nature of crystalline silica is modified, leaving its stability unaltered to enable it to be used as a catal yst or for the preparation of catalysts. Catalytic prop erties can be imparted, for example, by endowing the crystalline silica with acidic properties.

Whereas the modifying element has a predominant bearing on the catalytic properties of the silica, the presence of the element originates the formation of crystalline materials the spectra of which can either be closely similar to that of silicalite or sharply different therefrom, as can be seen from Figures 1 and 2 of the accompanying drawings to be described in more detail below.

The invention also provides a process for prepar- ing a silica-based synthetic material, which cornprises reacting a derivative of silicon and a derivative of at least one modifying element having an at least partially amphoteric nature with a substance having a clathrating effect, the reaction being carried out in an aqueous medium, an alcoholic medium oran aqueous alcoholic medium; crystallising the reaction mixture at a temperature of from 100 to 220'C; cooling the reaction mixture, separating the precipitate formed in the reaction mixture; and firing the precipitate in air at a temperature of from 300 to 7000C.

Preferably, the following procedure is used. A derivative of silicon is reacted, in an aqueous, alcoholic or aqueouslalcoholic solution, with a derivative of a modifying element and a substance having an archivolt or clathrate-forming effect, possibly in the pressence of one or more mineralising agents to encourage crystallisation and possibly in the presence of an inorganic base. Crystallisation of the mixture is allowed to take place in a closed environment fora period ranging from a few hours to several days, preferably for about a week, at a temperature of from 1 00'C to 220'C, preferably from 1500C to 2000C. Thereafter, cooling, washing and col- lection on a filter are carried out. Calcination in air at a temperature of from 300OCto7000C, preferably at 550'C, is carried outfor a time of from 2to 24 hours. Washing is performed to remove any exchangeable cationic impurities, preferably with boiling distilled water containing an ammonium salt, preferably a nitrate or an acetate, dissolved therein. Firing as above is then repeated.

The derivative of silicon is preferably a silica gel (irrespective of how it has been obtained) or a tetraalkyl orthosilicate such as tetraethyl orthosilicate ortetramethyl orthosilicate.

The derivative of the modifying element is preferably an oxide, hydroxide or a salt of an alkoxy derivative. The preferred salts are the nitrates and the acetates.

The substance which displays an archivolt or clathrate-forming effect is preferably a tertiary amine, an aminoalcohol, an aminoacid, a polyalcohol or a quaternary ammonium base such as a The drawing(s) originally filed was/were informal and the print here reproduced is taken from a later filed formal copy.

2 GB 2 024 790 A 2 tetraalkViammonium base (e.g. NR,OH wherein R is a C, to C, alkyl group) or a tetrarylammonium base (e.g. NAOH wherein A is a phenyl or an alkylphenyl group).

The clathrating substances result in the formation of a crystalline structure having pores of well deter mined size. Thus such substances are comparatively big molecules.

The preferred mineralising agents are alkali metal and alkaline earth metal hydroxides and halides, for 75 example UOH, NaOH, KOH, Ca(OHI., KBr, NaBr, Nal, Cal, and CaBr,.

"ne preferred inorganic bases are alkali metal and alkaline earth metal hydroxides (for example NaOH, KOH and Ca(OH)2) and ammonia.

As regards the amounts of inorganic base and/or of clathrating substance to be used, these are, as a rule, lowerthan the stoichiometric amount relative to silica and are preferably from 0.05 to 0.50 mol% per mol of silica.

The products are characterized by a protonic-type acidity which can be varied by varying the cation which is introduced. Pure silica contains 101 millie quivalents of hydrogen ions per gram. This acidity can be increased by introducing the substituting element in an amount such that the number of mil liequivalents of hydrogen ions per gram of product is roughly 5 x 10- 1.

For effecting particular catalytic reactions, it may prove appropriate to reduce the acidity by introduc ing an alkali until the product is neutral or even basic.

The materials of the present invention usually have a well defined crystalline structure such as can be seen in the X-ray diffraction spectra given in Fig- 100 ures 1 and 2 of the accompanying drawings and usually posses a high specific surface area which exceeds 150 g/M2 and, as a rule, is from 200 to 500 m2/g. In addition, the materials according to the pre sent invention are characterized by a porous struc- 105 ture having pores which are usually from 4 to 7 Angstrom units in diameter.

To the crystalline silica, which contains a cation which is either a replacement for silicon or is capable of forming with silicon a salt of polysilicic acids, 110 there can be added other metals which are capable of imparting special catalytic properties. Examples of such metals are platinum, palladium, nickel, cobalt, tungsten, copper and zinc. This addition can be effected by impregnation or any other method known to those skilled in the art, using solutions of salts of the metals, preferably nitrates, acetates, or oxides.

Depending Upon the nature of the added metal or metals, catalytic properties can be imparted to silica 120 or alternatively, the catalytic properties thereof can be improved so as to obtain catalysts which can be used in, for example, hydrogenations, hydrations, hydrosulphurisations, crackings, reformings, oxida tions, isomerisations, disproportionations and 125 polymerisations.

The silica-based materials can be used for catalytic reactions or absorptions either as such or when dis persed on a supporting body having a high or low specific surface area porosity and being inert to a lesser or greater extent. The supporting body improves the physical stability and the mechanical resistance and, possibly, the catalytic properties of the material, if any. Procedures of obtaining the sup- ported active material are known to those skilled in the art. The quantity of modified silica is usually between 1 and 900/o but amounts of from 5 to 60% are preferred. The preferred supporting bodies are clays, silica, alumina, diatomaceous earths, and silicaalumina.

The silica-based synthetic materials according to the present invention can be employed as a catalyst for a large number of reactions, e.g. the alkylation of benzene, especially the alkylation of benzene with ethylene and the alkylation of benzene with ethanol. Examples of other possible users are:

(1). Alkylation of toluene with methanol to produce xylene, predominantly para-xylene; (2). Disproportionation of toluene to produce para-xylene; (3) ' Conversion of dimethyl ether and/or methanol or other lower alcohols into hydrocarbons such as olefins and aromatic hydrocarbons; (4). Cracking and hydrocracking; (5). Isomerisation of normal paraffins and naphthenes; (6). Polymerisation of compounds which contain olefin or acetylene bonds; (7). Reforming; (8). Isomerisation of polyalkyl-substituted aromatic hydrocarbons such as ortho-xylene; (9). Disproportionation of aromatic hydrocarbons, especially toluene; (10). Conversion of aliphatic carbonyl compounds into at least partially aromatic hydrocarbons; (11). Separation of ethylbenzene from other C8 aromatic hydrocarbons; (12). Hydrogenation and clehydrogenation of hydrocarbons; (13). Methanisation; (14). Oxidation, more particularly of internal combustion engine exhausts; (15). Dehydration of oxygen-containing aliphatic compounds; and (16). Conversion of olefins into high-octane fuel products.

In a preferred embodiment, the present invention relates to synthetic materials comprising oxides of silicon and boron, and having a porous crystalline structure.

There are known from the literature natural compact borosilicates, that is non-porous materials, in which the boron has a planar or tetrahedral. coordination. Also known are porous glasses, which are obtained by chemically attacking vitreous materials. These materials may contain silica, alkalies, alumina and B203. The literature teaches thatthe incorporation of boron into zeolite-like structures (i.e. crystalline structures having a regular porosity) has not been achieved heretofore (Breck, Zeolite Molecular Sieves, J. Wiley and Sons, New York, 1974, page 322).

It is known to use boric acid to impregnate zeolites which consist of oxides of aluminium and silicon (see U.S. Patent Specification No. 4,049,573). In this

4 3 case the boron does not become an integral part of the crystalline lattice.

In the foregoing description of the present invention, there are disclosed crystalline silicas which have been modified by elements which enter into the crystalline lattice to replace the silicon. One of the replacement elements is boron, and in Example 5 below, the preparation of silica modified with boron is described.

It has been found that boron, in addition to being a replacing element for silicon, is capable of forming novel materials having a crystalline structure which is porous and is well defined and is akin to the zeolite structure.

These latter materials, which will be called "boralites" in the following portion of this specification for convenience and brevity, can be represented, in their anhydrous state, by the following empirical formula:

(0-1) R,.O. (0-1K2/11 0.13203. X Si02 wherein R is the product originated by the organic base used for the formation of the boral ites, C is a cation (such as H', NW4 or a metallic cation having the valency n), and x is equal to or greater than 4 (and preferably tends to higher values of up to 1,000, these values being different for each type of boralite, and improved thermal stability being obtained with high ratios of SiO, to B203).

It should be observed that R20 may be absent after the boralite has been subjected to calcination (fir- ing).

Of the boralites of the general formula above, there have been synthesised, in particular, four differenttypes, which will be called Boralite A, Boralite B, Boralite C and Boralite D for reference purposes, which possess a definite crystalline structure and whose X-ray diffraction spectra, in the H+ forms calcined at high temperatures (4500C to 750'C), contain the significant lines reported in Tables 1 to IV below.

The presence of other cations instead of H+ causes minor variations in the spectra, in a manner which is akin to that of conventional zeolites.

The infrared (M) spectra exhibit a characteristic band which is a function of the quantity of boron which has been introduced and which is between 910 and 925 cm-1.

The method for the preparation of the boralites is based on the reaction, under hydrothermal conditions, of a derivative of silicon, a derivative of boron and an appropriate chelating agent (preferably an alkylonium compound) at a pH between 9 and 14, at a temperature between 1OWC and 22WC and for a time between 1 and 30 days.

High-purity boralites can be obtained by the use of organic derivatives of boron and silicon (such as trialkyl borates and tetraalkyl orthosilicates) and by carrying out the hydrothermal process in polytetrafluoroethylene vessels, in polypropylene vessels, in platinum vessels or in other vessels in order to ensure that the alkaline solution does not extract impurities from the vessel. The absence of impurities gives the boralites special properties such as a hydrophobic character and a resulting lack of dehydrating power.

If a very high purity is not essential, there can be used cheaper sources for the components, such as, GB 2 024 790 A 3 for boron, boric acid, sodium borate and borax, and, for silicon, colloidal silica, silica gel, sodium silicate and aerosil, and, for the vessel, glass vessels and stainless steel vessels. In such cases, the boralites may contain impurities from the reactants or the vessels. Thus, for example, commercial silicas contain up to 2,000 ppm of Al,O, but is has been ascertained that amounts as high as 10,000 ppm of A1,03 do not alter their structural and crystallographic properties, even though, obviously, other properties such as the hydrophobic character and the dehydrating power are modified.

Examples of chelating agents are compounds having amine, ketone, alcoholic, acidic functions. How- ever, more preferred are alkylonium bases such as tetraalkylammonium hydroxides. The selection of such compounds, together with the selection of the reactants, has an affect upon the properties of the resulting boralites.

Mineralising agents such as alkali metal or alkaline earth metal hydroxides or halides can be used.

Boralite A is characterised, in terms of molar ratios of the oxides when in the anhydrous condition, by theformula:

(0. Iffi,?O: (o-1) CjnO: 13,03: (8-30)SiO, wherein R is the tetramethylammonium cation and C is H', NW4 or a metallic cation having the valencyn.

The material obtained by calcination of boralite A has an X-ray diffraction spectrum the most signific- ant line of which, when the material is in the H+ form, are as given in Table 1 below.

Boralite B is characterised, in terms of molar ration of the oxides when in the anhydrous state, by the formula:

(0-1)R,,0: (0-1)C240: B20: (5-50002 wherein R is the tetraethylammonium cation (TEA) and C is H', NW,, or a metallic cation having the valencyn.

The material obtained by calcination of boralite B has an X-ray diffraction spectrum the most significant lines of which, when the material is in the H' form, are as given in Table 11 below.

Boralite C is characterised, in terms of molar ratio of the oxides when in the anhydrous state, by the formula:

(0-1)R,0: (0-1)C2lnO: B20: (4-1,000)Si02 wherein R is a tetraethylammonium cation, a tetrapropylammonium cation or a nitrogen- containing cation derived from an amine such as ethylene diamine, and C is H', NW4 or a metallic cation havingthevalencyn.

The boron-modified silica of Example 5 below is a boralite C. The material obtained by calcination of boralite C has an X-ray diffraction spectrum the most significant lines of which, when the material is in the H+ form, are as given in Table lit below.

Boralite D is characterised, in terms of the molar ratios of the oxides when in the anhydrous condi tion, by the formula:

(0-1)1R20: (0-1)C240: B203: (4-20)SiO2 wherein R is a tetrabutylammonium cation, and C is H', NW4 or a metallic cation having the valencyn.

The material obtained by calcination of boralite D has an X-ray diffraction spectrum the most signific- ant lines of which, when the material is in the H' 4 GB 2 024 790 A 4 form, are as given in Table W below.

The boralites are very stable both in thermal treatment at high temperatures and in thermal treatment in the presence of water vapour.

The boralites, more particularly boralites A, B, C and D exemplified above, can be used for catalytic reactions or for absorption processes, either as such or when disposed on supports which are inert to a lesser or greater extent. Examples of such supports are silicas, aluminas and clay-like materials. The boralites can also be used in a large number of other reactions such as those exemplified above.

The invention will now be illustrated by the following Examples, in Examples 1, 2,9 and 10 of which reference is made to Figures 1 to 4 of the accompanying drawings. The words "Pyrex" and "TefloC used in the Examples are registered Trade Marks. EXAIMPLE 1 This example illustrates the preparation of a por- ous crystalline silica which we have designated "TRS-27", in the crystalline lattice of which beryllium has been introduced as a replacement for silicon.

In a Pyrex glass vessel constantly maintained in a nitrogen atmosphere, there were introduced 40 g of tetraethyl orthosilicate. The silicate was heated with stirring to a temperature of 800C. Subsequently, there were added 100 mi of a 20% by weight aqueous solution of tetra propylammonium hydroxide.

The mixture was continued to be stirred, and was heated until it became homogeneous and clear. This took roughly one hour. Atthis stage, there were added 4 g of Be(N0J2.41-1,,0 dissolved in 80 m I of ethanol. A white precipitate quicklyformed, and was heated, still with stirring, to boiling so as to dispel all 100 of the ethanol, i.e. both the ethanol added and the ethanol formed by the hydrolysis.

The mixture was made up to 150 mi with distilled water, whereafter the Pyrex glass vessel was kept in an autoclave at 1WC for 17 days. Upon cooling, the solid which had formed was centrifuged at 10,000 rpm, and the cake obtained was slurried in distilled water and centrifugation was effected once more. This washing operation was repeated four times.

The product was oven-dried at 1200C. It was X-ray crystalline.

In orderto completely remove the alkaline impurities contained in the product, calcination for 16 hours at 5500C in an airstream was effected, whereafter the solid was repeatedly washed with boiling distilled water containing ammonium acetate in solution. Finally, calcination at 5500C for 6 hours was carried out.

The product thus obtained contained 92.7% by wt of Si02,12% by wt of BeO, and 0.02% by wt of Na,.O.

Its weight loss on calcination at 11 OOOC was 4.1% by wt, and its molar ratio Of Si02:BeO was 12: 1. The X-ray diffraction spectrum of the product is given in Figure 1 of the accompanying drawings. The content of W ions of the product was 1.5 x 10-3 meq per 125 gram and its specific surface area was 400 m21g.

E,PLE2 This Example illustrates the preparation of a crys talline silica which we have designated "TRS-28", in the crystalline lattice of which chromium has been 130 introduced as a modifying agent.

In a Pyrex glass vessel kept in a nitrogen atmosphere, there were placed 40 g of tetraethyl orthosilicate. The silicate was heated with stirring to a temp- erature of 8WC.

There were added 20 9 of a 20% aqueous solution of tetrapropylammonium hydroxide, and the mixture was kept, with stirring, at 800C until the mixture became clear. This took roughly one hour. There were added 4 g of Cr(N0j,,3.91-1,0 dissolved in 50 mi of anhydrous methanol. A compact, pale green gel formed nearly immediately.To the gel 0.25 g of KOH dissolved in 20 m] of water were added, and, still with stirring, the mixture was brought to boiling in orderto complete the hydrolysis and in orderto drive off by evaporation both the ethanol which had been added and the ethanol which had been formed by the hydrolysis. The time taken forthe fatter step wasfrom 2 to 3 hours and the gel was slowly and gradually converted into a pale green powder which is the precursor of the chromium-modified crystalI ine silica.

The mixture was made up to 150 m] with distilled water, and the vessel was kept in an autoclave at 1550C for 13 days.

Upon cooling of the autoclave, the solid which had formed was centrifuged at 5,000 rpm for 15 minutes. The formed was washed four times by reslurrying it in distilled water, and was then dried at 1200C. The product obtained was X-ray crystalline.

In order that the alkaline impurities retained in the product may be completely removed the product was fired at 5500C for 16 hours in an air stream, whereafter the solid was repeatedly washed by reslurrying it in boiling distilled water which contained ammonium acetate in solution. Firing (i.e. calcination) at 5500C for 6 hours was carried out.

The productthus obtained contained 90.5% by wt of SiO, and 6.0% by wt of Cr2Q,. Its loss on firing at 11000C was 3.50/6 by wt, and its molar ratio of SiO, to Cr03 was 38A. The material was X-ray crystalline, and its X-ray diffraction spectrum is as given in Figure 2. Its proton content per gram was 5.8 x 10-3 meq of W-, and its specific surface area was 380 m21g.

EXAMPLE3

This Example illustrates the preparation of a porous crystalline silica which we have designed "TRS-66", in the crystalline lattice of which zinc has been introduced as a replacing element.

In a Pyrex glass vessel kept in an atmosphere which was C02-4ree, there were introduced 40 g of tetraethyl orthosilicate. There was added a solution of 4 g of Zn(NO3LI-120 in 40 mi of ethanol (950/6), with stirring. There was then added a solution of 20 g of tetrapropyl-ammonium hydroxide, still with stirring. The solution was heated until a homogeneous and compact gel formed.

The gel was crushed, and water in which 2 g of KBr had been dissolved was added to obtain a slurry. The slurry was heated with stirring until all of the ethanol present (i.e. that introduced and that formed by the hydrolysis) had been evaporated off. The product was made up to 150 m] with distilled water and transferred to a Pyrex glass vessel which was then kept in an autoclave at atemperature of 197'C for 6 GB 2 024 790 A 5 days.

Upon cooling, the solid which had formed was col lected on a filter, washed until a basic reaction was no longer detected, and dried at 12WC. The product was X-ray crystalline.

In order that the residual alkaline impurities in the compound may be completely removed, the product was fired at 5500C for 16 hours in an air stream and subsequently washed repeatedly with boiling dis tilled water in which ammonium acetate had been dissolved. Thereafter, the solid was fired at 5500C for 6 hours.

The product obtained contained 88.30/6 by wt of SiO,, 8.00%, by wt of ZnO and 0.02% of K20. Its loss on firing at 1 1000C was 3.7% bywt, its molar ratio of 80 Si02 tOZnO was 15.0A, its content of H' ions was 2.2 x 10-5 meq per gram, and its specific surface area, determined by the BET method, was 380 m21g.

EXAMPLE4

This Example illustrates the preparation of a crys- talline sillica which we have designated "TRS-42", in the crystalline lattice of which beryllium has been introduced as a modifying element.

The procedure of Example 1 was carried out, using 83 g of tetraethyl orthosilicate, 59.6 9 of triethanolamine, 1.1 g of Be(N0J2.41-120 and 2 g of NaOH.

The product was made up to 200 mi with distilled water, and kept in an autoclave at 20WC for 6 days.

The product, dried at 1200C, was X-ray crystalline.

The product fired at 5500C contained 96.0% by wt Of Si02,0.4% by wt of BeO and o.031% by wt of Na20.

Its loss on firing at 11 OWC was 3.5 % by wt, its molar ratioOf SW2:13eO was 1001, its content of H+ ions was 1.2 x 1 Q-3 meqlg and its specific surface area, determined by the BET method, was 380 mlg.

EXAMPLE 5

This Example illustrates the preparation of a por ous crystalline silica which we have designated "TRS-45", in the crystalline lattice of which boron has been introduced as the modifying agent.

The procedure of Example 1 was carried out, using 30.5 g of tetramethyl orthosilicate, 14.6 g of triethyl borate and 60 m] of water, the mixture being boiled for one hour. There were added 6 g of tetrap ropylammonium hydroxide. A gel formed at once, and was crushed and slurried in waterto form a slurry to which 2 g of KOH were added.

After having stirred the boiling slurry for 20 hours, it was introduced into an autoclave and held at 1750C for six days. The product, dried at 1200C, was X-ray crystalline. The product, fired at 55WC contained 74.9% by wt of Si02,21.3% by wt of B203 and 0.07Yo by wt of K20. Its loss on firing at 11 OOOC was 3.8% by wt, its molar ratio OfSi02:13203 was 4A, and its 120 specific surface area, determined by the BET method, was 410 m21g.

EXAMPLE6

This Example illustrates the preparation of a por ous crystalline silica which we have designated 125 "TRS-64", in the crystalline lattice of which titanium has been introduced as a modifier.

The procedure of Example 1 was carried out, using 9 of tetraethyl orthosilicate, 10 g of tetraethyl orthotitanate (separately hydrolysed with water and 130 digested in 100 mi of 30% H202 solution until a clear yellow-orange solution had formed), 20 g of a 10% aqueous tetrapropylammonium hydroxide solution and 2 g of KBr. The mixture was kept in an autoclave at 1450C for 10 days. The product, dried at 12WC, was X-ray crystalline. The product, fired at 5500C contained 66.5% by wt Of Si02,29.5% by wt of Ti02 and O.OZYo by wt of K20. Its loss on firing at 1 1OWC was 3.9% by wt, its molar ratio Of Si02:W2was3A,and its specific su rface area, determined by the BET method, was 430 m21g. EXAMPLE 7 This Example illustrates the preparation of a porous crystalline silica which we have designated "TRS-48", in the crystalline lattice of which vanadium has been introduced as the modifying element.

The procedure of Example 1 was carried out, by reacting 8 g of NH4V03 with 200 mi of water contain- ing 20 g of tetrapropylammonium hydroxide, heating being effected until complete dissolution had been achieved. Therewere added 88 g of tetramethyl orthosilicate, the gel thus obtained was slurried in water and the slurry was boiled for seve- ral hours. After addition of 0.25 g of KOH, the mixture was placed in autoclave and kept therein at 1750C for six days. The product, dried at 120Q was X-ray crystalline. The product, fired at 5500C contained 81.7% by M Of Si02,14.6% by wt of V205 and 0.01% bywtof K20. Its loss on firing at 11000Cwas 3.7% by wt, its molar ratio Of Si02M05 was 17: 1, and its specific surface area, determined by the BET method, was 410 m'lg. EXAMPLE8 This Example illustrates the preparation of a porous crystalline silica which we have designated '7RS-41 % in the crystalline lattice of which beryllium has been introduced as a modifier.

The procedure of Example 1 was carried out, using 38 g of 30% silica sol instead of tetraethyl orthosilicate, the other reactants and the reaction conditions, being the same as in Example 1.

The product obtained, fired at 1200C, was X-ray crystalline. The product fired at 55WC contained 93.1% bywt OfSi02,12% bywt of BeO and 0.02% by wt of K20. Its loss on firing at 11 OWC was 3.7% by wt, its molar ratio of SiO2/BeO was 12: 1. The other properties of the product were identical to those of the product of Example 1.

EX4MPLE9 Catalyst "TRS-28" (see Example 2) was used in the alkylation of benzene with ethylene, 1 m] of the catalyst in a fixed-bed reactor being used. In a first reaction (reaction A), the LHSV was 14, the molar ratio of benzene to ethylene was 7.5: 1, the temperature was 4400C and the pressure was 20 kg/cM2. Ina second reaction (reaction B), the LHSV was 2, the molar ratio of benzene to ethylene was 7.5: 1, the temperature was 40WC and the pressure was 40 kg/crn2.

The effluents were gaschromatographically analysed and the results are given in Figure 3 in which the mol % of ethylbenzene is plotted as a function of the reaction time in hours. The dash-and-dot line corresponds to 100% of ethylene.

6 GB 2 024 790 A 6 EXAMPLE 10

Catalyst "TRS-28" (see Example 2) was used in the alkylation of benzene with ethanol, 1 ml of the catalyst being employed in a fixed-bed reactor. The LHSV was 10, the molar ratio of benzene to ethanol was 5: 1, the temperature was 4400C and the pressure was 20 kg/cM2.

The effluents were analyzed gaschromatographically, and the results are given in Figure 4, in which the mol % of ethylbenzene present in the reaction product is plotted as a function of the reaction time in hours. The dash-and-dot line corresponds to 1000/6 conversion of ethanol. EXAMPLE 11 This Example illustrates the preparation of boralite 80, A.

A pyrex glass vessel maintained in a COz--free atmosphere was charged with 132 g of a 25% by wt aqueous solution of tetramethylammonium hydrox- ide, to which 18.6 g of boric acid were added with stirring. On completion of the dissolution, there were added, still with stirring, 187. 5 of tetraethylorthosilicate. The reaction mixture was heated, still with stirring, to 60'C, and a white lactescent precipitate gradually formed, the ethanol produced by the hydrolysis being simultaneously driven off. After 12 hours, the alcohol had been entirely eliminated. There were added 0.18 g of KOH and distilled water to make up an overall volume of about 300 ml. At this stage, the reaction mixture was transferred to a Teflon lined static autoclave, and kept at 1450C for a time of twelve days. The product was then allowed to cool to room temperature, collected on a filter, carefully washed with distilled water and dried as 1200C. The product consisted of crystals with a grit size between 0.1 and 0.5 micron approximately.

A portion of the product was calcined at 7500C. The calcined product has a molar ratio of SiO2 to B203 Of 11:1. The X-ray diffraction spectrum of the H+ form is given in Table I below.

The IR spectrum exhibited a characteristic band of boron at 921 cm-1. This band is not present in the spectra of zeolites. EXAMPLE 12 This Example illustrates the preparation of boralite A using colloidal silica.

The procedure of Example 11, including the order of addition of the reactants was employed, using 210 g of a 25% by wt solution of tetramethylammonium hydroxide, 27 g of H31303 and 240 g of 40% Ludox colloidal silica. After keeping the reaction mixture at 800C for one hour, with stirring, the mixture is placed in a one-litre titanium autoclave fitted with a stirring mechanism, and kept at 1500C for 10 days at the pressure which was spontaneously generated.

The crystalline product of the reaction was collected on a filter, washed and dried, and fired at 7500C for 6 hours. It had, in the HI form, the Xray diffraction spectrum given in Table I below. Its IR spectrum has a band at 917 cm-1. In addition, the product has an actual density (helium method) of 2.19 g/CM3, an acidity (CsCl method) of pH 2.4, and a Si02: B203 molar ratio of 12.3: 1. EXAMPLE 13 This Example illustrates the preparation of porous 130 synthetic crystalline boralite B. Under the conditions of Example 12, there were reacted 110 g of a 25% by wt solution of tetraethylammonium hydroxide, 12 g of boric acid and 100 g of 40% LudoxA.S. colloidal silica. The reaction mixture was keptforg days at 1500C in a 300-mi Teflon lined static autoclave.

The crystalline product obtained upon filtration, washing, drying and firing consisted of spherulitic particles having an average diameter of 1.3 microns. It had a molar ratio Of W2:B203 of 6.86. The X-ray spectrum of the H+ form, calcinated at 5500C, is given in Table 11 below. Its IR spectrum had a characteristic band at 921 cm-1. Its specific surface area, determined with nitrogen according to the BET method, was 421 m21g, the volume of its pores was 0. 18 cmllg, its actual density (helium method) was 2.32 g/cm, and its acidity, as measured by the CsCI method, was pH 1.8.

EXAMPLE 14

This example illustrates the preparation of boralite C.

The procedure of Example 11 was employed, using 90 9 of a 25% by wt solution of tetrap- ropylammonium hydroxide, 37.5 g of boric acid, 125 mi of distilled water and 62.4 g of tetraethyl orthosilicate. After keeping the reaction mixture in the autoclave used in Example 13 at 1600C for 11 days and after the usual treatment for obtaining the H+ form, there was obtained a product which had an olive-like shape with dimensions of 10-15 microns. The X-ray diffraction spectrum of the product is given in Table Ill below. Its IR spectrum had a band at 920 cm- 1, and its Si02:13203 molar ratio was 41.

EXAMPLE 15

The procedure of Example 14 was employed, using, in the order given, 37. 5g of orthoboric acid, 250 m 1 of water, 3g of KOH, 180 9 of a 25% by wt solution of tetrapropylammonium hydroxide, 5 g of KBr, and 124.8 g of tetraethyl orthosilicate. The reaction mixture was kept in the autoclave used in Example 12 at 1750C for 6 days, and, after the usual treatmentfor obtaining the H+ form, there was obtained a spheroidal product which has an X-ray diffraction spectrum corresponding to that of boralite C, as given in Table Ill below. The product had an IR band at 915 cm-1 and an Si02:13203 molar ratio of 11.2A. Its actual density (helium method) was 2.36 g/cm3, its specific surface area (BET method with nit- rogen) was 377 m21g, the volume of its pores was 0.18 cm31g, and its pore diameter was between 5 and 30 Angstrom units. EXAMPLE 16 The procedure of Example 14 was employed, using, in the order given, 30 g of tetramethyl orthosilicate, 14.6 g of triethyl borate, 1,100 g of water, 80 g of 25% by wt tetrapropylammonium hydroxide and 2 g of KOH. The reaction mixture was kept at 1 900C for 6 days, and washing and subse- quent operations were carried out as in Example 14.

The X-ray spectrum of the H' form, calcined at 5500C, corresponds to that of Boralite C, as reported in Table Ill. Its molar ratio Of Si02:13203 was 17:1 and its specific surface area, determined with the BET method, was 380 m21g.

7 GB 2 024 790 A 7 EXAMPLE 17

This Example illustrates the preparation of boralite C.

The procedure of Example 14 was employed, using in the order given, 130 g of tetraethyl orthosili- 70 cate, 15 g of boric acid, 250 m] of water, 70 g of tetrapentylammonium hydroxide in 250 mi water and 5 g of KOH in 50 m] of water. Stirring was carried out for 24 hours at 60OC-800C. The mixture was introduced into a 1 -litre titanium autoclave equipped with a stirrer and was maintained for 12 days at 1650C. The product, calcined at 5500C, exhibited the X-ray diffraction spectrum as reported in Table Ill for boralite C. Its molar ratio of SiO2to B203was 13.9: 1.

EXAMPLE 18

This Example illustrates the preparation of boralite C.

The procedure of Example 14 was employed, using 88.7 9 of 201%, by wt tetraethylammonium hyd- roxide solution, 4.15 g of H3B03 and 62.5 g of tetraethyl orthosilicate. From the clear solution obtained, ethanol was driven off at 60'C-80'C. A gel did not form. The mixture was introduced into a 250 m] stainless steel autoclave and was maintained at 1500C for 10 days. Under these conditions, a compact gel formed. This gel was slurried in 100 mi of distilled water containing 2.5 g of KOH, and the mixture was heated with stirring to WC, water being evaporated off until a volume of 250 mi in total ha!d been attained. The operation may be repeated until the gel had a lactescent appearance.

The gel was put in the autoclave again for 15 days at 1750C, whereafter the operations described in Example 14 were carried out.

The X-ray diffraction spectrum of the product, in the form H' after calcination at 55WC, was as reported in Table Ill for boralite C. Its SiO, to B203 molar ration was 12.11: 1. EXAMPLE 19 This Example illustrates the preparation of boralite 105 C from ethylene diamine.

The procedure of Example 12 was employed, using 4.25 g of NaOH, 120 m I of water, 6 g of H3B03, 85 g of ethylene diamine, and 50 9 of 40% Ludox A. S.

Colloidal silica. The reaction mixture was kept in a 300-mi Teflon lined autoclave for 9 days at 1750C.

The X-ray diffraction spectrum of the product, in the form H+ and after calcination at 55WC was as given in Table Ill for boralite C. Its SiO2 to B203 molar ratiowas11.3A. EX4MPLE20 This Example illustrates the preparation of boralite D. The procedure of Example 11 was employed, using 225 9 of a 40% by wt solution of tetrabutylam- monium hydroxide, 20 9 of boric acid, 200 g of tet- raethyl orthosilicate, and 0.2 g of KOH. After driving off the ethanol, distilled water was added to make up to one litre. The reaction mixture was kept in a titanium autoclave, equipped with a stirring device, at 1650C for 12 days.

The crystalline product, in the H' form and after calcination at 550'C, has the X-ray diffraction spec trum of boralite D, as reported in Table IV. Its IR spectrum shows a band at 919 cm-1, which is charac teristic of boron. Its specific surface area (BET 130 method with nitrogen) was 415 m2/g, the volume of its pores was 0.18 cml/g, and its Si% to 13,03 molar ratio was 4.8: 1. EXAMPLE21 The procedure of Example 20 was employed, using 113 g of a 4(YY6 by wt solution of tetrabutylammonium hydroxide, 10 g of boric acid, and 75 g of 40% Ludox A.S. colloidal silica. The reaction mixture was kept for 12 days in a Teflon lined autoclave.

The crystalline product obtained had a molar ratio Of Si02 to B203 of 10. 4:1 and, in the H+ form after calcination at 550'C, has the X-ray diffraction spectrum reported in Table IV below. Its IR spectrum displayed the characteristic 918 cm-1 band. Its specific surface area (BET method with nitrogen) was 335 m2/g, and the volume of its pores was 0.155 CM3/g. EXAMPLE22 An electrically heated tubular reactor having an inside diameter of 8 mm was charged with 3 mi of the boralite A catalyst prepared according to Example 11 and having a grit size between 14 and 30 mesh (ASTM series). Through a metering pump, there was introduced into the reactor methyl-t-butyl ether which had been preheated by causing it to flow through a preheating tube.

Downstream of the reactor, there was a pressurechecking valve calibrated to 6 bar and a heated sampling appliance which, upon reduction of the pressure, permitted the introduction of the reactor effluent into a gas chromatograph. Using the temperatures given in Table V below, methyl-t-butyl ether was fed in at rates of flow of 6 CM3 an hour i.e. at an LHSV (Liquid Hourly Space Velocity) of 2, the results obtained being given in Table V.

E)(AMPLE23 The reactor of Example 22 was charged with 3 ml of the boralite B catalyst prepared according to Example 13 and having a grit size between 30 and 50 mesh (ASTM series). A pressure of 6 bar was used. The results obtained are given in Table VI below. EXAMPLE24 The reactor of Example 22 was charged with 2 ml of the boralite C catalyst prepared according to Example 14, and having a grit size of from 7 to 14 mesh (ASTM series). Using the procedure of Example 22, methyl-t-butyl ether was fed in, and the reaction was continued for a few hours in order to test the constancy of the catalytic activity with the lapse of time.

The reactions were carried out in an oven at 150'C, at a pressure of 6 bar, and at an LHSV of 2. The results obtained are given in Table VII below. EXAMPLE25 The reactor described in Example 22 was charged with 3 ml (1.35 g) of boralite D prepared according to Example 20 and having a grit size of from 30 to 50 mesh (ASTM series). Methyl-t-butyl ether was fed in under the conditions given in Table Vill below. The results obtained are given in Table Vill.

TABLES

In Tables I to IV of the following Tables, the abbreviations have the following meanings:

VS = very strong S = strong MW = medium weak 8 GB 2 024 790 A 8 W = weak Slight variations of the results given in Tables I to 5 the cation.

IV may occur, depending upon the molar ratio of TABLE I

SiO2 to B203, the firing temperature and the nature of Interplanar distances Relative intensity d (;) 8.8z m 8.25 6.52 6.1z 5.61 MW 5.32 W 4.42 MW 4.27 24W 4.09 MW 4,02 MW 3.92 MW 3.83 m 3.47 W 3.42 W 3.27 MW 2.88 W 2.74 W 2.'47 W IABLE 11 Interplanar distances Relative intensity d (1) 11.23 S 6.52 W 5.98 W 4.0 MW 3.90 5 3.46 - MW 3.26 14W 3.05 W 2.98 MW 2.65 W 2AS W TABLE III

Interplanar distances Relative intensity d 11.09 vs 9.94 5 9.67 EW 6.66 W 6.33 - MW 5.96 XW 5.67 Hq 5.55 EW 5.33 W 5.00 W 7 c A 9 1 GB 2 024 790 A 9 XABLE III (continued Interplanar distances Relative intensity d (1) 4.95 W 4.58 W 4.34 W 4.24 MW 3.98 W 3.83 S 3.80 3.73 3.70 m 3.63 MW 3.46 W .42 W 3.33 W 3.29 W 3.23 W 3.03 MW 2.97 MW - 2.93 W 2.72 W 2.59 W 2.48 W 2.41 W 2A8 W 2.00 MW 1.98 MW TAUB IV Interplanar distances Relative Intensity d (1) 11.12 vs 10.00 S 6.67 W.

6.36 W 5.97 m.

5.56 MW 4.99 MW 4.59 W 4.34 W 3.83 S 3.70 m 3.62 W 3.46 W 3.33 W 3.04 W 2.9i MW 2.50 W 2.48 W 1 2.00 MW GB 2 024 790 A 10 T A B L E v 1 Test Oven temperature Conversion of the Recovery of methanoil Recovery of 1 (-c methyl-l-butyi etet- isobutene (%) 1 ( %) 1 200 14.5 99.9 99.8 2 225 22.7 99.9 99.8 3 275 71.7 99.8 99.8 4 305 99.1 99.7 99.7 315 99.9 99.7 99.7 T A B L i V2:

Test Oven temperature LH6V Conversion Recovery of Recovery of 0C of methyl-j- methanol isobutene V/0) % % 1 16o 2 93.7 99.8 99-3 2 170 2 99-3 99.1 99.0 3 170 4 98.2 99.6 99.1 ISO 4 96.1 99.9 99.6 1 T A B L E _ V11 Test Time (_hours) Conversion of methyl 1 Recovery og 1 Recovery of -t-b4AL:YI. ether. methanol isobutene M W ( %) - 1 1 97.6 99.7 99.4 2 2 95.9 99.9 99.5 3 5 96.9 99.9 99.6 4 24 94.5 99.9 99.6 25 96.8 99.9 99.7 6 26 95.8 99.9 - 99.7 i i.

1 11 GB 2 024 790 A 11 T A B L E VIII 11 Test Oven temperature MSV Conversion of Recovery of Recovery of (--c) methyl-t-bu31 methanol isobutene - gther 1 136 2 96.3 99.9 99.. 9 2 136 4 75.3 99.9 99.9 3 150 4 96.s 99.9 99.8 Attention is drawn to an application (No. 7921623) (Serial No. 2023562) filed by us on the same day as the present application for an invention entitled "Process for the preparation of tertiary olefins". The materials of the present invention may be used as catalysts in the process described and claimed in that application. Attention is also drawn to another application (No. 7921621) filed by us on the same day as the present application for an invention entitled "Modified silica and germania and their use as catalysts".

Claims

1. Asilica-based synthetic material comprising crystalline silica which has been modified with one or more elements which have entered the crystalline lattice of the silica in place of silicon atoms of the silica or in the form of salts of bisilicic or polysilicic acids.

2. A material as claimed in claim 1, having the general formula:

(0.0001-1)MnOrn.SiO2 wherein M,,0 is the oxide of the one or more mod ifying elements.

3. A material as claimed in claim 1 or2, wherein the or each modifying element has an at least par- 75 tially amphoteric nature.

4. A material as claimed in claim 3, wherein the or each modifying element is selected from Cr, Be, Ti, V, Mn, Fe, Co, Zn, Zr, Rh, Ag, Sn, Sb and B.

5. A material according to any of claims 1 to 4, having a specific surface area greater than 150 m21g.

6. A material according to claim 5, having a specific surface area of from 200 to 500 m2/g.

7. A material according to any of claims 1 to 6, having, in its anhydrous state, the general formula:

(0-1)R20. WAW2/n 0. 13203. XSi02 wherein R is the product derived from an organic base used for the formation of the material, C is a cation, and x is a number greater than or equal to 4, the material having a porous structure similar to that of the zeolites.

8. A material according to claim 7, wherein C is W, NW4 or an ion of a metal having a valency n.

9. A material according to claim 7 or8, wherein x is from 4 to 1000.

10. A material according to claim 7 or8, wherein R is the tetramethylammonium cation and x is from 8 to 30, and wherein the material has an X-ray diffra ction spectrum, in the H+ form, as tabulated in Table 1 hereinbefore.

11. A material according to claim 7 or8, wherein R is the tetraethyl ammonium cation and x is from 5 to 50, and wherein the material has the Xray diffraction spectrum, in the H+ form, as tabulated in Table 11 hereinbefore.

12. A material according to claim 7 orS, wherein R is the tetraethylammonium cation, the tetrapropylammonium cation, the tetrapentylammonium cation or a nitrogen-containing cation derived from an amine and x isfrom 4to 1000, and wherein the material has the X-ray diffraction spectrum, in the H+ form, as tabulated in Table Ill hereinbefore.

13. A material according to claim 12, wherein R is a cation derived from ethylene diamine.

14. A material according to claim 7 or8, wherein R is the tetrabutylammonium cation and x is from 4 to 20, and wherein the material has the X-ray diffrac tion spectrum, in the H+ form, as tabulated in Table IV hereinbefore.

15. A material according to claim 1, substantially as described in any of the foregoing Examples.

16. A process for preparing a silica-based synth etic material, which comprises reacting a derivative of silicon and a derivative of at least one modifying element having an at least partially amphoteric nature with a substance having a clathrating effect, the reaction being carried out in an aqueous medium, an alcoholic medium or an aqueous alcoholic medium; crystallising the reaction mixture at a temperature of from 100 to 22WC; cooling the reaction mixture; separating the precipitate formed in the reaction mixture; and firing the precipitate in air at a temperature of from 300 to 70OoC.

17. A process according to claim 16, wherein the reaction mixture is crystallised fora time from a few hours to a number of days.

18. A process according to claim 16 or 17, wherein the precipitate is fired for a time of from 2 to 24 hours.

lb. A process according to any of claims 16 to 18, wherein the fired product is washed with boiling dis tilled water having an ammonium salt dissolved therein, and wherein the washed product is fired in air at a temperature of irom 300 to 7000C.

20. A process according to claim 19, wherein the washed product is fired for a time of from 2 to 24 hours.

21. A process according to any of claims 16to 20, wherein the derivative of silicon is a silica gel or a tetraalkyl orthosilicate.

12

22. A process according to claim 21, wherein the tetraalkyl orthosilicate is tetraethyl orthosilicate or tetramethyl orthosilicate.

23. A process according to any of claims 16 to 22, wherein the or each derivative of the modifying element is an hydroxide or alkoxy derivative of chromium, beryllium, titanium, vanadium, manganese, iron, cobalt, zinc, zirconium, rhodium, silver, tin, antimony or boron.

24. A process according to claim 23, wherein the or each derivative of the modifying element is a nitrate or acetate.

25. A process according to any of the claims 16 to 24, wherein the or each clathrating substance is a tertiary amine, an amincialcohol, an. aminoacid, a polyhydric alcohol or a quaternary ammonium base.

26. A process according to claim 25, wherein the quaternary ammonium base is a tetraalkylammonium base of the formula NR40H wherein R is a C, to C5 alkyl group or a tetraarylammonium base of the formula NA40H wherein A is a phenyl or alkylphenylgroup.

27. A process according to any of claims 16 to 26, wherein the amount of the clathrating substance(s) used is below the stoichiometric amount with respect to silica.

28. A process according to claim 27, wherein the amount of clathrating substance(s) used is from 0.05 and 0.50 mol per mol of silica. 30

29. A process according to any of claims 16 to 27, wherein the reaction is carried out in the presence of (a) at least one mineralising agent for encouraging crystallisation andlor (b) at least one inorganic base.

30. A process according to claim 29, wherein the or each mineralising agent is an alkali metal or alkaline earth metal hydroxide or halide.

31. A process according to claim 30, wherein the alkali metal or alkaline earth metal hydroxide or halide is selected from LiOH, KOH, Na011, Ca(OH)2, KBr, NaBr, Nal, Ca12 and CaBr2.

32. A process according to claim 29, wherein the or each inorganic base is an alkali metal or alkaline earth metal. hydroxide or ammonia.

33. A process according to claim 32, wherein the alkali metal orthe alkaline earth metal hydroxide is KOH, Na01-1 or Ca(01- 1)2.

34. A process according to any of claims 29 to 33, wherein the amount of inorganic base(s) used in below the stoichiometric amount with respect to silica.

34. A process according to claim 33, wherein the amount of inorganic base(s) used in from 0.05 and 0.50 mol per mol of silica.

35. A process for preparing a silica-based synth- etic material, which comprises reacting a derivative of silicon, a derivative of boron and a chelation agent under hydrothermal conditions at a pH of from 9 to 14, at a temperature of from 11 OOC to 2200C and for a. time of from 1 to 30 days.

36. A process according to claim 35, wherein the derivative of silicon is an organic derivative of silicon.

37. A process according to claim 36, wherein the organic derivative of silicon is a tetraalkyl orthosili- cate.

GB 2 024 790 A 12

38. A process according to any of claims 35 to 37, wherein the derivative of boron is an organic derivative of boron.

39. A process according to claim 38, wherein the organic derivative of boron is a trialkyl borate.

40. A process according to any of claims 35 to 39, wherein the chelation agent is an alkylonium com- pound.

41. A process according to claim 40, wherein the alkylonium compound is a compound of tetramethylammonium, tetraethylammonium,tetrap- ropylammonium, tetrabutylammonlum or tetrapentylammonium.

42. A process according to any of claims 35to 39, 80. wherein the chelating agent is a compound having an amine function.

43. A process, according to claim 42, wherein the chelating agent is ethylene diamine.

44. A process according to claim 16 or35, sub- stantially as described in any of the foregoing Examples.

45. Asilica-based synthetic material prepared by a process according to any of claims 16 to 44.

Printed for Her Majesty's Stationery Office by The Tweeddale Press Ltd., Berwick-upon-Tweed, 1979.

Published atthe Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.

iL 4 A