GB1592809A - Crystalline silica polymorph method for preparing same and its use - Google Patents

Description

(54) CRYSTALLINE SILICA POLYMORPH, METHOD FOR PREPARING SAME AND ITS USE (71) We, UNION CARBIDE CORPORATION, a corporation organised and existing under the laws of the State of New York, whose registered office is 270 Park Avenue, New York, State of New York, 10017, United States of America, (Assignees: ROBERT WILLIAM GROSE and EDITH MARIE FLANIGEN) do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates in general to a novel crystalline silica polymorph and to the method for preparing same. More particularly it relates to a novel crystalline silica polymorph which exhibits molecular sieve properties characteristic of a number of crystalline aluminosilicate compositions but which exhibits none of the ion-exchange properties which are essential to the latter class of compositions commonly referred to as zeolitic molecular sieves.

Crystalline forms of silica are found in nature and also exist as synthetic forms which apparently have no natural counterpart. Among those found in nature are quartz, tridymite and cristobalite, each having polymorphic forms stable in different ranges of temperature. At ordinary temperatures the stable form is alphaquartz which inverts at 573"C. to beta-quartz, which is stable up to 867"C. At this temperature level, tridymite becomes the stable phase and remains so up to 14700C. At temperatures in excess of 1470"C. cristobalite is the stable phase and remains so up to about 1713"C.

What is alleged to be the first true silica polymorph synthesized by man is coesite silica. This crystalline composition is defined and its method of manufacture described in detail in United States Patent Specification No. 2,876,072 issued to L. Coes, Jr. on March 3, 1959. It has also been proposed to prepare crystalline polysilicate by extracting aluminum from the tetrahedral framework of crystalline aluminosilicates of the molecular sieve type by means of treatment with steam, strong acids or organic chelating agents. The products are pseudomorphic after the precursor composition. A specific procedure of this kind is to be found in United States Patent Specification No. 3,506,400 issued to P. E. Eberly, Jr. et al. on April 14, 1970. While the latter class of compositions presumably are composed only of silica, they appear to remain as defect structures having the same quantity of silica per unit cell as their aluminosilicate precursors. In at least some instances in which aluminium is extracted from zeolitic frameworks, the extraction is reversible, and similar elements such as germanium can be inserted into the tetrahedral structure. In this regard see United States Patent Specification No.

3,640,681 issued February 8, 1972 to P. E. Pickert.

In accordance with one aspect of the present invention there is provided a crystalline silica polymorph, said silica polymorph, after calcination in air at 600"C for 1 hour, having as the six strongest d-values of its x-ray powder diffraction pattern those set forth in Table A.

In accordance with a further aspect of the present invention there is provided a process for preparing a crystalline silica polymorph according to the present invention, which comprises providing a reaction mixture having a pH of from 10 to 14, and which in terms of moles of oxides comprises from 150 to 700 moles water, from 13 to 50 moles non-crystalline SiO2, from 0 to 6.5 moles M2O, wherein M is an alkali metal, each of the aforesaid reactants being present per mole of Q2 present wherein Q is an alkylonium cation having the formula (R4X)+ in which each R represents an alkyl group containing from 2 to 6 carbon atoms and X is phosphorus or nitrogen, heating the reaction mixture thus provided at a temperature of from 100 to 2500C. until said crystalline silica polymorph is formed, and isolating said crystalline silica polymorph. Optionally, the process comprises the added step of calcining the crystalline silica polymorph at a temperature of from 480"C to 1000 C.

The crystalline silica polymorph of the present invention will often be referred to hereinafter as "silicalite". Further, when referring to silicalite in the assynthesized form, this is intended to refer to the silicalite before any calcination step.

The X-ray powder diffraction pattern of silicalite (600"C. calcination in air for one hour) has as its six strongest lines (i.e. interplanar spacings) those set forth in Table A below, wherein "S"=strong and "VS"=very strong.

TABLE A d-A Relative Intensity 11.1 +0.2 VS 10.0 +0.2 VS 3.85+0.07 VS 3.82+0.07 S 3.76+0.05 S 3.72+0.05 S The following Table B lists the data representing the X-ray powder diffraction pattern of a typical silicalite composition containing 51.9 moles of SiO2 per mole of (TPA)2O, prepared according to the method of the invention (calcined in air at 600"C. for I hour, TPA=tetrapropylammonium).

TABLE B d-A Relative Intensity d-A Relative Intensity 11.1 100 4.35 5 10.02 64 4.25 7 9.73 16 4.08 3 8.99 1 4.00 3 8.04 0.5 3.85 59 7.42 1 3.82 32 7.06 0.5 3.74 24 6.68 5 3.71 27 6.35 9 3.64 12 5.98 14 3.59 0.5 5.70 7 3.48 3 5.57 8 3.44 5 5.36 2 3.34 11 5.11 2 3.30 7 5.01 4 3.25 3 4.98 5 3.17 0.5 4.86 0.5 3.13 0.5 4.60 3 3.05 5 4.44 0.5 2.98 10 Although X-ray powder diffraction pattern data is the most reliable means for characterizing the crystalline silica polymorph of the present invention, the silica polymorph may be characterized by other means, for example, by refractive index and specific gravity.

Crystals of silicalite in both the as-synthesized and calcined form are orthorhombic and have the following unit cell parameters: a=20.05 A. h=20.0 A.

c=13.4 A, with an accuracy of +0.1 A on each of the above values.

The pore diameter of silicalite is about 6 Angstrom units and its pore volume is 0.18 cc./gram as determined by adsorption. Silicalite adsorbs neopentane (6.2 A kinetic diameter) slowly at ambient room temperature. The uniform pore structure imparts size-selective molecular sieve properties to the composition, and the pore size permits the separation of p-xylene from o-xylene, m-xylene and ethylbenzene.

Separations of compounds having quaternary carbon atoms from those having carbon-to-carbon linkages of lower value are also possible using silicalite as a sizeselective adsorbent. The adsorbent also has a very useful hydrophobic/organophilic characteristic which permits its use in selectively adsorbing organic materials from water, either liquid or vapor phase. Neither the as-synthesized silicalite nor the silicalite in its calcined form exhibits ion exchange properties.

The above-mentioned lack of ion-exchange capability in the crystalline silica poiymorph of this invention is highly advantageous. Some aluminosilicate zeolites can be treated in a manner which promotes a hydrophobic character and makes them possible candidates for selective removal of organics from waste water; however, if the hydrophobic aluminosilicate adsorbent contains residual cationexchange capacity, this is detrimental to the adsorbent when in contact with waste water streams containing a source of cations. The fixation of these cations in such alum inosilicate adsorbent drastically changes its hydrophobic character and/or pore size. Silicalite, however, is not affected by the presence of cations in a waste water stream.

The separation process contemplated here comprises, in general terms, contacting an aqueous solution such as a waste water influent containing an organic compound with silicalite, adsorbing at least a portion of the organic compound in the inner adsorption surfaces of the silicalite and thereafter recovering, optionally as an effluent stream, the treated aqueous solution.

The preparation of silicalite involves the hydrothermal crystallization of a reaction mixture comprising water, a source of silica and an alkylonium compound at a pH of 10 to 14 to form a hydrous crystalline silica polymorph and optionally subsequently calcining that crystalline silica polymorph to decompose alkylonium moieties present therein. The exact structural nature of the as-synthesized silicalite is not known. The as-synthesized silicalite exhibits no ion exchange properties and since it does not contain Al O4-tetrahedra as essential framework constituents, the alkylonium compound is not required to provide cations, such as are found in aluminosilicate zeolites, to balance the negative electrovalence thereof.

It can be theorized, however, that the principal function of the alkylonium compound is to provide a template like material which predisposes . the arrangement of SiO4 tetrahedra into the particular lattice form which characterizes the silicalite of the present invention. Although we do not wish to be bound by this theory, the observable properties of the as-synthesized silicalite indicate that the alkylonium moiety is more properly considered as being merely occluded in the SiO4 framework than as a structural constituent thereof.

The alkylonium cation is supplied to the reaction system by a compound preferably soluble in the reaction mixture and which contains an alkylonium cation generally expressed by the formula

wherein R is an alkyl radical containing from 2 to 6 carbon atoms and X represents either phosphorus or nitrogen. Preferably R is ethyl, propyl or n-butyl, especially propyl, and X is nitrogen. Illustrative compounds include tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrabutylphosphonium hydroxide and the salts corresponding to the aforesaid hydroxides, particularly the chloride, iodide and bromide salts, for example, tetrapropylammonium bromide. The quaternary compounds can be supplied to the reaction mixture per se or can be generated in situ, such as by the reaction of tertiary amines with alkyl halides or sulfates.

When the alkylonium cation is provided to the system in the form of the hydroxide in sufficient quantity to establish a basicity equivalent to the pH of 10 to 14, the reaction mixture need contain only water and a reactive form of silica as additional ingredients. In those cases in which the pH is required to be increased to above 10, ammonium hydroxide or alkali metal hydroxides can be suitably employed for that purpose, particularly the hydroxides of lithium, sodium or potassium. It has been found that not more than 6.5 moles of alkali metal oxide per mole-ion of alkylonium cation is required for this purpose even if none of the alkylonium cation is provided in the form of its hydroxide.

The source of silica in the reaction mixture can be wholly or in part alkali metal silicate but should not be employed in amounts greater than that which would chanee the molar ratio of alkali metal to alkylonium cations set forth above.

Other silica sources include solid reactive amorphous silica such as fume silica, silica sols and silica gel. Since the nature of the reaction system is favorable for the incorporation of alumina as an impurity into the crystalline silica product, care should be exercised in the selection of the silica source from the standpoint of its content of alumina as an impurity. Commercially available silica sols can typically contain from 500 to 700 ppm Al2OI whereas fume silicas can contain from 80 to 2000 ppm of Al2O3 impurity. Small quantities of Al2O3 present in the silicalite product in no way significantly alter its essential properties, and in no sense is silicalite containing alumina or other oxide impurities properly considered to be a metallosilicate. The quantity of silica in the reaction system should be from 13 to 50 moles SiO2 per mole-ion of the alkylonium cation. Water should be present in an amount of from 150 to 700 moles per mole-ion of the alkylonium cation.

Accordingly, in preparing the crystalline silicalite, there is formed a reaction mixture having a pH of 10 to 14 which in terms of moles of oxides contains from 150 to 700 moles H2O, from 13 to 50 moles non-crystalline SiO2 and from 0 to 6.5 moles M2O, wherein M is an alkali metal, for each mole of Q2O present, wherein Q is an alkylonium cation having the formula R4X+ in which each R represents an alkyl group containing from 2 to 6 carbon atoms and X is phosphorus or nitrogen.

The order in which the reagents are admixed is not a critical factor. The reaction mixture is maintained at a temperature of from 100 to 2500C. under autogenous pressure until crystals of the silicalite are formed, ordinarily from about 50 to 150 hours. The crystalline product is recovered by any convenient means such as filtration. Advantageously the product is washed with water and can be dried in air at about 100"C.

When alkali metal hydroxide has been employed in the reaction mixture, alkali metal moieties appear as impurities in the crystalline product. Although the form in which these impurities exist in the crystalline mass has not yet been determined, they are not present as cations which undergo reversible exchange. The alkylonium cation moiety is quite readily thermally decomposed and removed by calcination in an oxidizing atmosphere (air) or inert atmosphere at temperatures of from 480"C.

to 10000C. The residual alkali metal in the product can be removed by washing with alkali metal halide solution or an aqueous acid solution of sufficient strength such as hydrochloric acid. The crystal structure is not otherwise affected by contact with strong mineral acids even at elevated temperatures due to the lack of acid-soluble constituents in its crystal structure.

The method for preparing silicalite and the nature of its chemical and nhvsical properties are illustrated by the following examples.

In each of Examples I to 9 the silicalites produced will, after calcination in air at 600"C for one hour, exhibit x-ray powder diffraction patterns in accordance with Table A. In a number of the Examples, x-ray powder diffraction pattern data is given for the as-synthesized silicalite. However, since the crystal lattice of the assynthesized silicalite has the same unit cell dimensions as the crystal lattice of the silicalite after calcination, the x-ray powder diffraction patterns of the assynthesized and calcined silicalites are substantially the same.

Example 1 (a) A reaction mixture was prepared by dissolving 1.4 grams sodium hydroxide in 10 Prams of water and adding the solution thus formed to 44 grams of an aqueous colloidal silica sol containing 30% by weight SiO2. Thereafter a solution of 2.4 grams tetrapropylammonium bromide dissolved in 15 grams of water was added to form an overall reaction mixture containing 4.1 moles Na2O, 50.0 moles SiO2, 691 moles H2O per mole of tetrapropylammonium oxide. The synthesis mix was placed in a pressure vessel lined with an inert plastic material (polytetrafluoroethylene) and heated at 2000C. for 72 hours. The solid reaction product was recovered by filtration, washed with water and dried at 1 100C. in air. The x-ray powder diffraction pattern of the as-synthesized silicalite was quite similar to that which is exhibited by a class of aluminosilicate zeolite compositions commonly referred to as the "ZSM-5 family" even though they are distinctly different compositions. The significant lines of the latter materials are set forth in United States Patent Specification No. 3,728,408. Chemical analysis of the crystalline silica composition indicated the presence of 0.016 moles tetrapropylammonium (TPA) ion as (TPA)2O; 0.011 moles Na2O and 0.8 moles H2O per mole of silica. Alumina impurity in the amount of about 650 ppm was also present.

(b) A portion of the solid crystalline silica product obtained in part (a) supra was calcined in air at about 600"C. for one hour. After cooling to room temperature in the ambient atmosphere, the adsorption properties of the resulting silicalite were determined using a McBain-Bakr gravimetric adsorption system. In the system the sample was activated by heating to 3500 C. under vacuum for 16 hours.

Adsorption measurements made subsequently on a variety of adsorbates at various temperatures and a pressure of 750 torr produced the following data: Adsorption Adsorbate Kinetic Diam., A Temp., "C. Wt.- /n Adsorbed Oxygen 3.46 -183 13.7 n-butane 4.3 23 7.5 SF6 5.5 23 18.7 Neopentane 6.2 23 0.4 Example 2 Using essentially the same procedure as in Example 1, 3 grams of tetrapropylammonium bromide, 25 grams of water, 44 grams of an aqueous colloidal silica sol (30 wt.-% SiO2) and 2.3 grams of KOH were admixed to form a reaction mixture having a molar oxide ratio of: (TPA)2O 3.25 K2O 40.0 SiO2 560 H2O.

The mixture was maintained at 200"C. for 72 hours, after which the crystalline product was isolated by filtration, washed with water and dried at 110 C. Portions of the product were submitted for X-ray and chemical analyses, which identified the product as silicalite. The chemical composition was, in terms of moles of oxides, 1.0 (TPA)zO 0.63 K2O.55.7 SiO2.9.5 H2O.

Alumina impurity in the amount of 591 ppm was also present.

Example 3 Silicalate was prepared by dissolving 10.8 g. of (CII7)4NBr in 20 g. of H2O and adding the solution to 158.4 g. of silica sol (30% SiO2) with stirring. A solution of 10.2 g. of NaOH dissolved in 20 g. of H2O was then added to the synthesis mix with stirring. The synthesis molar oxide composition was: (TPA)2O 6.2 Na2O 38.4 Six2 .413 H2O.

The synthesis mix was placed in two plastic-lined glass jars. One portion of the mix was heated at 1000C. for 72 hours and the other portion was heated at 1000C. for 144 hours. The solid reaction products were recovered by filtration, washed with H2O, and dried at 1100C. Both products were identified as silicalite by X-ray and chemical analysis. The product crystallized for 72 hours had the following composition: 1.5 wt-% Na2O, 7.7 wt-% C, 0.96 wt- /n N, 82.5 wt-% SiO2; 15.5 wt-% loss on ignition, 769 ppm Al203 impurity.

A portion of the 72-hour product was calcined at 600"C. for 2 hours in an air purge. One gram of the calcined product was added to 10 ml of 1.0 vol.% n-butanol in H20 solution and shaken. The absorbent selectively removed 98.8 /" of the nbutanol from the solution as indicated by gas chromatographic analysis of the treated solution. In another test demonstrating the selectivity of silicalite for organics over H2O, a one-gram sample of the above calcined product was added to 10 ml of 0.1 wt- /n phenol in H2O solution and shaken. The gas chromatographic analysis of the solution after contact with calcined silicalite revealed that the adsorbent removed 81% of the phenol from the solution.

In another test, this time demonstrating aromatic separation, a one-gram sample of the above calcined product was contacted with 10 ml. of 1.0 wt- /" benzene in cyclohexane and shaken. The adsorbent removed 16.1 wt-% benzene from the solution as analyzed by gas chromatography.

Example 4 A (C2H7)4NOH solution was prepared by dissolving 9.9 g of (CH7)4NBr in 25 g of H2O and adding 5.0 g of Ag2O. After heating to about 80 C. the (C3H7)4NOH solution was separated from precipitated AgBr by filtration and added to 44 g ol aqueous silica sol (300/" SiO2) with manual stirring. The synthesis molar oxide composition was: (TPA)20. 13.3 SiO2 184 1120.

The synthesis mix was placed in a polytetrafluoroethylene-lined pressure vessel and heated at about 200 C. and autogenous pressure for about 72 hours. The solid reaction product was recovered by filtration, washed with H2O, and dried at 1 l00C.

A portion of the solids was submitted for X-ray analysis and chemical analysis. The silicalite of the analyzed solids exhibited the characteristic physical properties hereinbefore described. The overall solids analyzed as 0.19 wt-% Na2O, 8.1 wt-% carbon, 0.91 wt-% nitrogen, 87.4 wt-% SiO2 and 1.5 wt-% H2O. The trace amount of Na2O is attributable to the silica sol reagent.

Example 5 Silicalite was prepared by dissolving 9.0 g of (C3H7)4NBr in 30 g of H2O and adding the solution to 39.6 grams of fume silica slurried in 100 g of H2O. A solution of 4.2 g of NaOH dissolved in 37 g of H2O was then added to the synthesis mix with stirring. The synthesis molar oxide composition ratio was: (TPA)2O. 3.25 Na2O 40 SiO2 .552 1120.

The silicalite product obtained by crystallizing the synthesis mixture at 2000C. for 70 hours was found to contain only 155 ppm alumina as an occluded impurity.

Example 6 Silicalite was prepared by dissolving 10.0 g of (C4Hg)4PCl in 50 g of H2O and adding the solution to 44 g of aqueous colloidal silica sol (30 wt-% SiO2) with stirring. A solution of 1.4 g of NaOH dissolved in 50 g of H2O was then added with stirring to the synthesis mix. The synthesis molar oxide composition was: (TBP)O 1.08 Na2O 13.3 SiO2#441 H2O.

The synthesis mix was placed in a polytetrafluoroethylene-lined pressure vessel and heated at about 200"C. and autogenous pressure for 72 hours. The solid reaction product was recovered by filtration washed, with H2O, and dried at 1100C.

The crystalline product was identified as silicalite by its characteristic X-ray powder diffraction pattern and by chemical analysis, which gave the following composition: 0.6 wt.-% Na2O, 6.5 wt.- /n C, 1.1 wt.- /n P, 88.0 wt.- /n SiO2, 2.4 wt.- /" 1120.

The product molar oxide composition was: (TBP)20 0.58 Na2O .87.3 SiO2 7.9 H20.

A sample of the product was calcined in air at about 600 C for one hour. The calcined sample was then placed in a McBain-Bakr gravimetric adsorption system and activated at 3500C under vacuum for about 16 hours. The activated sample adsorbed 14.1 wt.% 02 -1830C and 750 torr, 7.7 wt.-% n-butane, 21.1 wt.-% SF8, and 0.5 wt.-% neopentane at 23 C and 750 torr.

Example 7 Silicalite was prepared by dissolving 7.2 g of (C2Hs)4NBr in 15 g of H2O and adding the solution to 44 g of aqueous silica sol (30 wt- " SiO2) with stirring. A solution of 1.4 g of NaOH dissolved in 10 g of H2O was then added with stirring to the synthesis mix. The synthesis molar oxide composition was: (TEA)20. 1.08 Na2O. 13.3 SiO2 184 1120.

The synthesis mix was placed in a tetrafluoroethylene-lined pressure vessel and heated at about 200 C, and autogenous pressure for 72 hours. The solid reaction product was recovered by filtration, washed with H2O, and dried at 1100C. The product was found to be silicalite.

Example 8 A (C3H,)4NOH solution was prepared by dissolving 13.5 g of (C3H7)4NBr in 30 g H2O and adding 7.5 g of Ag2O. After heating to about 80"C, the (C3H,)4NOH solution was separated from the precipitated AgBr by filtration and mixed with a slurry of 20.8 g of "Cab-O-Sil" (Cab-O-Sil is a Registered Trade Mark) fume silica in 54 g of 1120. The synthesis molar oxide composition was: (TPA)2O. 13.3 SiO2. 184 H2O The synthesis mix was placed in a tetrafluoroethylene-lined pressure vessel and heated at about 200 C and autogenous pressure for about 72 hours. The solid reaction product was recovered by filtration, washed with H2O, and dried at 1100C.

A portion of the product was submitted for X-ray analysis and contained the dvalues listed in Table A. Chemical analysis of the product gave the following composition: 8.7 wt.-% C, 0.81 wt.- /n N, 87.3 wt.- /n SiO2, 1.0 wt.-O/, H2O, 90 (+30) ppm Al2O3, and less than 50 ppm Na2O. The product structural molar oxide composition was: (TPA)2O.48.2 Six, 48.2 SiO2 1.8 H2O.

Although no Na2O or Al2O3 was deliberately added to the synthesis mix, the silica source does contain trace amounts of Al2O3 and Na2O which was incorporated in the product. A sample of the product was calcined in air at about 600 C for one hour. The activated sample adsorbed 18.2 wt.-% O2 at -1830C and 750 torr, 9.9 wt. . /n n-butane, 26.6 wt.-% SF6, and 0.5 wt.-% neopentane at 230C and 750 torr.

Example 9 10.9 g of (C3H,)4NBr was dissolved in 30 g of H2O and added to a slurry of 49.4 g of "Ucar" (Ucar is a Registered Trade Mark) fume silica in 100 g of H2O and 3 g NH4OH. The synthesis molar oxide composition was: (TPA)2O. 1.3(NH4)2O 40 SiO2 365 1120.

The synthesis mix was placed in a tetrafluoroethylene-lined pressure vesesl and heated at about 200 C for 95 hours. The solid reaction product was recovered by filtration, washed with H2O, and dried at 1100C. A portion of the product was submitted for X-ray analysis; the resulting X-ray pattern was found to contain the d-values listed in Table A.

Example 10 Samples of calcined silicalite prepared by the method of Example 1 (200"C synthesis, 6000C calcination) were stirred with aqueous solutions of HCI or NaCI as outlined below which removed residual alkali metal to the levels shown: Alkali Metal Concentra- Contents tion of Time Temp. wt.% Na2O Sample No. NaCI HCl (hrs.) ("C) before after 1 - IN 1 20 1.12 0.09 2 - IN I 80--100 1.19 < 0.02 3 5M - 1 80100 1.1 < 0.02 The excellent stability of silicalite was illustrated by subsequent treatment of the essentially pure SiO2 product derived from Sample No. 2 with 6000C steam at one atmosphere for 6 hours. The product still exhibited the characteristic unique properties of silicalite.

As additional illustration of the remarkable selectivity of the silicalite of the invention for organic materials over water, Table C containing Examples 11 to 13 is presented. The procedure employed is similar to that described in Example 3, above. A 1.0-gram sample of calcined (600"C) silicalite and 10.0 grams of the aqueous organic solution are placed in a serum bottle which is capped, shaken and allowed to equilibrate for at least 12 hours. A blank (same aqueous organic solution without adsorbent) is always used for comparison. Analysis of the treated solution is done by gas chromatography.

TABLE C % Concentra tion of O.C.* Example Silicalite Organic tion of 0.C.* /,%O.C.

No. Lot No. Component (O.C.) Start End Removal 11*** 35-1 (a) n-butanol 1.0 bv 0.008 bv 99.2 methyl cellosolve** 1.0 bv 0.282 bv 71.8 methanol 1.0 bv 0.825 bv 17.5 phenol 0.1 bw 0.021 bw 79 12 66-2(b) n-butanol 1.Obv 0.015bv 98.5 phenol 0.1 bw 0.020bw 80.

13 48 (a) n-butanol 1.0 bv 0.008 bv 99.2 phenol 0.1 bw 0.011 bw 89.

* bv= /n by volume; bw= /^ by wt.

** Cellosolve is a Registered Trade Mark.

*** SO2 also removed in this Example (starting concentration0.7% bw, end concentration=0.245 bw, 64.9 removal).

(a) Synthesized at 2000 C.

(b) Synthesized at 100 C.

Example 14 In a procedure similar to that described in the last paragraph of Example 3 above, a one-gram silicalite sample synthesized at 2000C and calcined at 6000 C, was contacted with 10 ml. of a 1.0 wt.- /n solution of benzene in cyclohexane. Gas chromatography analysis indicated that 23.8 /" of the benzene had been removed from the solution. These data indicate that silicalite is able to make separations despite very small differences in the size of adsorbate molecules.

The foregoing information on the separation capabilites of silicalite demonstrates that a variety of useful industrial processes employing this adsorbent are now made possible. As examples of organic components often found in various industrial or municipal waste streams, methanol, butanol, methyl cellosolve and phenol are effectively separated from aqueous solutions containing such components. Sulfur dioxide may also be effectively separated from aqueous solutions.

The foregoing X-ray powder diffraction data were obtained by standard techniques. Thus the radiation was the K-alpha doublet of copper, and a Geigercounter spectrometer with a strip-chart pen recorder was used. The peak or line heights and the positions thereof as a function of 2 times theta, where theta is the Bragg angle, were read from the spectrometer chart. From these the relative intensities of the reflected lines or peaks, and d, the interplanar spacing in Angstrom units corresponding to the recorded lines were determined.

WHAT WE CLAIM IS:- 1. A crystalline silica polymorph, said silica polymorph, after calcination in air at 600"C for one hour, having as the six strongest d-values of its X-ray powder diffraction pattern those set forth in Table A.

2. A process for preparing a crystalline silica polymorph as claimed in claim 1, which comprises providing a reaction mixture having a pH of from 10 to 14, and which in terms of moles of oxides comprises from 150 to 700 moles water, from 13 to '0 moles non-crystalline SiO2, from 0 to 6.5 moles M 20, wherein M is an alkali metal, each of the aforesaid reactants being present per mole of Q2 present wherein Q is an alkylonium cation having the formula (R4X)+ in which each R represents an alkyl group containing from 2 to 6 carbon atoms and X is phosphorus or nitrogen, heating the reaction mixture thus provided at a temperature of from 100 to 2500C. until said crystalline silica polymorph is formed, and isolating said crystalline silica polymorph.

3. A process as claimed in claim 2 wherein M is sodium, R represents the propyl radical and X represents nitrogen.

4. A process as claimed in claim 2 or claim 3, which comprises the added step of calcining the crystalline silica polymorph at a temperature of from 480"C to 1000 C.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   TABLE C % Concentra tion of O.C.* Example Silicalite Organic tion of 0.C.* /,%O.C.

   No. Lot No. Component (O.C.) Start End Removal 11*** 35-1 (a) n-butanol 1.0 bv 0.008 bv 99.2 methyl cellosolve** 1.0 bv 0.282 bv 71.8 methanol 1.0 bv 0.825 bv 17.5 phenol 0.1 bw 0.021 bw 79

   12 66-2(b) n-butanol 1.Obv 0.015bv 98.5 phenol 0.1 bw 0.020bw 80.

   13 48 (a) n-butanol 1.0 bv 0.008 bv 99.2 phenol 0.1 bw 0.011 bw 89.

   * bv= /n by volume; bw= /^ by wt.

   ** Cellosolve is a Registered Trade Mark.

   *** SO2 also removed in this Example (starting concentration0.7% bw, end concentration=0.245 bw, 64.9 removal).

   (a) Synthesized at 2000 C.

   (b) Synthesized at 100 C.

   Example 14 In a procedure similar to that described in the last paragraph of Example 3 above, a one-gram silicalite sample synthesized at 2000C and calcined at 6000 C, was contacted with 10 ml. of a 1.0 wt.- /n solution of benzene in cyclohexane. Gas chromatography analysis indicated that 23.8 /" of the benzene had been removed from the solution. These data indicate that silicalite is able to make separations despite very small differences in the size of adsorbate molecules.

   The foregoing information on the separation capabilites of silicalite demonstrates that a variety of useful industrial processes employing this adsorbent are now made possible. As examples of organic components often found in various industrial or municipal waste streams, methanol, butanol, methyl cellosolve and phenol are effectively separated from aqueous solutions containing such components. Sulfur dioxide may also be effectively separated from aqueous solutions.

   The foregoing X-ray powder diffraction data were obtained by standard techniques. Thus the radiation was the K-alpha doublet of copper, and a Geigercounter spectrometer with a strip-chart pen recorder was used. The peak or line heights and the positions thereof as a function of 2 times theta, where theta is the Bragg angle, were read from the spectrometer chart. From these the relative intensities of the reflected lines or peaks, and d, the interplanar spacing in Angstrom units corresponding to the recorded lines were determined.

   WHAT WE CLAIM IS:- 1. A crystalline silica polymorph, said silica polymorph, after calcination in air at 600"C for one hour, having as the six strongest d-values of its X-ray powder diffraction pattern those set forth in Table A.
2. 2. A process for preparing a crystalline silica polymorph as claimed in claim 1, which comprises providing a reaction mixture having a pH of from 10 to 14, and which in terms of moles of oxides comprises from 150 to 700 moles water, from 13 to '0 moles non-crystalline SiO2, from 0 to 6.5 moles M 20, wherein M is an alkali metal, each of the aforesaid reactants being present per mole of Q2 present wherein Q is an alkylonium cation having the formula (R4X)+ in which each R represents an alkyl group containing from 2 to 6 carbon atoms and X is phosphorus or nitrogen, heating the reaction mixture thus provided at a temperature of from

   100 to 2500C. until said crystalline silica polymorph is formed, and isolating said crystalline silica polymorph.
3. 3. A process as claimed in claim 2 wherein M is sodium, R represents the propyl radical and X represents nitrogen.
4. 4. A process as claimed in claim 2 or claim 3, which comprises the added step of calcining the crystalline silica polymorph at a temperature of from 480"C to 1000 C.
5. 5. A process for separating organic molecules from admixture with water which

   comprises contacting said mixture with the crystalline silica polymorph of claim 1.
6. 6. A silica polymorph as claimed in claim I and substantially as hereinbefore described with reference to any of the foregoing Examples.
7. 7. A process for preparing a silica polymorph as claimed in claim 2 and substantially as hereinbefore described with reference to any of the foregoing Examples 1 to 9.
8. 8. A process for separating organic molecules from admixture with water as claimed in claim 5 and substantially as hereinbefore described with reference to any of Examples 3 or II to 13.
9. 9. A process of separating organic molecules from admixture with other organic molecules which comprises contacting said mixture with the crystalline silica polymorph of claim 1.
10. 10. A process as claimed in claim 9 and substantially as hereinbefore described in Examples 3 or 14.