DE3128988A1 - Crystalline inclusion compounds of silicon dioxide, method for their preparation, and use - Google Patents

Abstract

The invention relates to crystalline inclusion compounds, having a structure analogous to the gas hydrates of structural type II, of silicon dioxide with the formula 136 [(Si1-xTx)O2].(24-y)M, where T is an atom coordinated tetrahedrally by oxygen, x represents a numerical value of </= 0.1, y represents a numerical value of 0 </= y </= 24, and M represents atoms, molecules and/or ions having kinetic diameters according to Lennard-Jones of sigma </= 9 ANGSTROM , and to the method for their preparation by heating alkaline SiO2-containing solutions having SiO2 contents >/= 0.01 M and base: SiO2 ratios between 0.4 : 1 and 20 : 1 at superatmospheric pressures to temperatures above 120 DEG C, and to their use as agents for absorbing and storing atoms, molecules and/or ions having kinetic diameters according to Lennard-Jones of sigma </= 9 ANGSTROM .

Description

Crystalline silicon dioxide SiO2 comes in the form of stishovite,

Coesite, quartz, keatite, cristobalite and tridymite have their densities between 4.8 -3 (stishovite) and 2.27 of 3 (tridymite).

In addition to these relatively dense SiO2 modifications, there is also the mineral Melanophlogite, which is mostly referred to as a Si02 modification, but correct as an inclusion compound of the formula 46 SiO2 (8-y) M with M = CH4, N2, CO2 and 0 # y # 8 is to be designated. [H. Gies & F. Liebau, Acta Cryst. A 37 (1981) J.

Melanophlogite is cubic above about 400C with aO = 13.44 Å and the content of the unit cell given by the formula and the space group symmetry Oh³ -Pm3n. The [SiO4] tetrahedra form a framework with 8 cage-shaped cavities (two pentagon dodecahedra and six 14 planes) per unit cell. These hollow cages are more or less completely occupied by the M molecules. Below 400C will the structure is reversibly slightly distorted and thus tetragonal. The structure of melanophlogite is analogous to that of the so-called type I gas hydrates von Stackelberg & H. R. Müller [Z. Electrochem.

58 (1954) 25J. The measured density of melanophlogite is each according to the type and amount of the enclosed molecules M 1.99 to 2.11 gcm; its without Taking into account the enclosed M-molecules is the calculated framework density 1.90 gcm-3.

The by Flanigen et al. [Nature 271, 512 (1978)] and Bibby et al. Nature 280 (1979), 664] synthesized compounds silicalite-1 and silicalite - 2 are the aluminum-free end links of the zeolites ZSM - 5 and ZSM - 11 (to these For definitions see e.g. Donald W. Breck "Zeolite Molecular Sieves: Structure, Chemistry and Usen J. Wiley & Sons, New York 1974). They make a difference It differs from the other compounds mentioned by the fact that its [SiO4] tetrahedra The structure formed has continuous channel-shaped cavities in which molecules and ions of suitable size can be reversibly adsorbed and desorbed. she therefore belong to the molecular sieves.

In contrast, the molecules trapped in melanophlogite M cannot be released and resumed reversibly, since its structure is nonexistent Contains channel-shaped cavities. It is therefore not a molecular sieve.

It has now been found that one can crystalline, the gas hydrates of the structure type II after M. von Stackelberg and H.R. Müller [Zeitschrift Elektrochemie, 58 (1954), 25-39] similarly constructed inclusion compounds of silicon dioxide of the formula 136 [(Si1-xTx) O2] . (24-y) M can be obtained in which atoms, molecules and / or ions depending on their kinetic throughput according to Lennard-Jones [D.W. Breck: Zeolite Molecular Sieves, J. Wiley & tons, New York 1974, pp. 634 ff or can be exchanged, as will be explained in more detail. With these connections can silicon up to about 10 mol% (x <0.1) by other tetrahedrally coordinated Atoms are replaced. The ion radius of the built-in atoms T is within the limits rBor # rT # travel. In particular, T can be B, Al, Ge, Ti and P, but not C.N. Atoms, molecules or ions with kinetic diameters according to Lennard-Jones D.W. Breck, loc, cit.] Smaller than about 9 Å, which are in the framework of r (Si, T) O4] tetrahedra are included. Such species are e.g. H2, N2, O2, CO2, NO, noble gases, SF6, aliphatic and cyclic hydrocarbons and their derivatives, such as CH4, CF4, ethers, ketones, aldehydes, primary, secondary and tertiary amines and Ammonium compounds such as NH3, N (CH) 3, heterocycles such as tetrahydrofuran, pyrrole, Pyrrolidine and pyridine.

The ratio M: (Si, T) is a maximum of 24: 136 or 3:17.

The substance forms optically isotropic, i.e. cubic crystals, which on cooling reversibly into anisotropic crystals with lamellar twinning convert. The transition temperature depends on the type and amount of the trapped Molecules M and can, depending on the type and amount of M, above or below room temperature take place.

The lattice constant of the high-temperature cubic form varies depending on Type and amount of T slightly around the value ao = 19.4 Å.

The cell content is 136 [(Si1-xTx) O2]. (24-y) M.

The following is the crystal structure of the cubic compounds described. For a sample with x = 0 and y = 0, with sixteen of the species M the meaning of CH4 and eight the meaning of dimethylamine and trimethylamine (approximate ratio of 5 trimethylamine to 3 dimethylamine) were under the Assumption of room group symmetry T4 - Fd3 as given in table 1 of the appendix Atomic coordinates determined.

The L (Si, T) 042 tetrahedra form a framework with 24 cage-shaped Cavities (sixteen pentagonal dodecahedra and eight 16-sided) per unit cell. These hollow cages are more or less completely occupied by the N molecules. The pseudo-cubic structure that emerges from the cubic structure when it cools is a slightly distorted variant of the cubic structure shown schematically in FIG is shown.

TABLE I atom point location a) x y z Si 1 8a 0.125 0.125 0.125 Si 2 32e 0.216 0.216 0.216 Si 3 96g 0.068 0.068 0.370 0 1 96g 0.093 0.406 0.000 0 2 48f 0.125 07374 0.125 Q 3 32e 0.171 0.171 0.171 0 4 96g 0.050 0.293 0.050 M 1 16c 0 0 0 M. 2 8b 0.625 0.625 0.625 -Table 1 coordinates (in fractions of the lattice constants) the silicon and oxygen atoms and the. Centers of the cage-shaped cavities, in which the molecules M are incorporated.

a) Point location according to the designation in International Tables for X-Ray Crystallography, Vol. 1, p.313, Kynoch Press, Birmingham 1965.

For the end link with x = 0, the enclosed molecules the framework density to 1.80 gcm-3. The experimental density Depending on the type and degree of Si / T replacement and the cage occupancy, it can be between 1.8 and 2.5 gcm 3 vary. Typical values are 1.90 gcm-3 to 2.2 gcm 3 for x = 0, M = N2, CH4 or noble gas.

Table 2 gives the X-ray diffraction diagram according to Debye-Scherrer pseudocubic variant of using [N (CH3) 4] OH and tetrahydrofuran restored Si02 inclusion compound. The species M were in the present Case di- and trimethylamine, tetrahydrofuran and, since not with exclusion of air was worked, also 02 and N2. Depending on the type and quantity of the embedded molecules M and depending on the type and degree of Si / T replacement, the X-ray diffraction diagrams slightly differ in intensity (I) and grid level spacing (d) from the tabulated.

TABLE II d Å Intensity 12.28 20 6.86 40 5.84 80 5.60 100 4.851 60 4.446 50 3.953 50 3.736 90 3.422 70 3.279 80 3.054 25 2.946 25 2.520 25 2.362 25 2.280 30 1.864 25 Table 2 X-ray diffraction diagram The new Compounds are useful in the acidic, neutral and weakly alkaline range insoluble.

The SiO2 framework is stable up to temperatures of at least 10000C. The guest species remain enclosed in the cage-like cavities when whose kinetic diameter is not less than the maximum opening of the five rings of the pentagon dodecahedron and / or the rings of six of the 16-sided, i.e. larger than 3 Å.

The synthesis of the compounds can be carried out by using basic, preferably aqueous, silicic acid-containing solutions, - their SiO2 content above 0X01M, in particular 0.1 and 3 M and their base to SiO2 ratio is between about 0.4: 1 to 20: 1, in the presence of the guest molecule M in the closed system, e.g.

in melted quartz glass vessels, at temperatures above 1200C, in particular are heated above 1700C. The formation of the connections can occur in 170 ° C several days to weeks and at 2200C about a day. It turned out as appropriate, the SiO2 solutions by basic hydrolysis of orthosilicic acid esters [e.g. Si (OCH3) 4, Si (OC2H5) 4], SiCl4 or other easily hydrolyzable compounds of silicon. The bases are primary, secondary, tertiary amines and Quaternary ammonium compounds [especially NH3, HN (CH3) 2, N (CH3) 3, (CH3) 2N. CH2 . N (CH3) 2, pyrrolidine, urea are suitable, but analogous organic compounds can also be used Chemicals of e.g. phosphorus or sulfur (e.g. thiophene) take on the role of amines.

Suitable guest components are those under the test conditions stable elements or compounds whose atoms or molecules or ions unite have kinetic diameters of less than about 9 2, as already explained became. Of the aliphatic and aromatic hydrocarbons already mentioned are particularly suitable up to approx.

6 carbon atoms and their derivatives.

Depending on the choice of starting materials and test conditions, the Formation of the crystalline inclusion compounds either via an intermediately precipitated Gel or straight from the solution.

For the Si / T replacement, aluminate, borate and phosphate have been used with good success used.

Amines, in particular, are used as basic agents, which are but can also be partially replaced by inorganic bases.

However, amines are clearly preferred because when using, for example NaOH, other phases can arise. The process medium is an aqueous one Medium preferred, but liquid ammonia, lower alcohols, for example, could also be used or the organic bases themselves are used as solvents.

The following examples illustrate the invention and show the preparation compounds according to the invention.

Example 1 2 ml of a 2.7 M solution of silicon prepared by Hydrolysis of tetramethyl orthosilicate in a 2.7 m aqueous solution of tetramethylammonium hydroxide were melted in an oarz glass ampoule under a methane atmosphere.

The methane gas pressure was 100 bar at room temperature.

The reaction vessel was heated to 200 ° C. in the oven, during which it fell 1500C precipitated a gel-like solid.

After 24 hours at 2000C, the crystallization of the was clearly visible phase to be produced. After a further 24 hours, the crystallization had progressed so far that that the intermediate gel phase is consumed and the total conversion is completed was. The crystalline phase was isotropic at room temperature and has the formula 136 SiO2 (24-y) M, where M = trimethylamine, dimethylamine, methane, N2 and CO2; y was not determined.

Example 2 The procedure was as in Example 1, with the exception that a) the solution of base and Si was 1 molar and b) the crystallization from the Solution took place without gel interphase.

Example 3 The procedure was as in Example 1, with the exception that a) a 1 molar solution was used, which consists of base and (silicon + Phosphorus) = 17: 3 composed. Phosphorus was introduced as EN (CH3) 4j2 H PO4.

b) The ampoule was sealed in the presence of tetrahydrofuran and air.

c) The crystallization took place from the solution.

d) The crystals were anisotropic at room temperature.

Example 4 The procedure was as in Example 1 with the exception that a) a 1 molar solution was used, consisting of base and (silicon + Aluminum) = 17: 3 composed.

b) The ampoule was sealed in the presence of tetrahydrofuran and air.

c) The crystals were anisotropic at room temperature.

Example 5 Two solutions were assumed for the Si / B replacement Solution I-: By converting calculated amounts of tetramethyl orthosilicate and aqueous The trimethylamine solution was a 1-molar orthoselic acid / trimethylamine solution with regard to both components manufactured.

Solution II: In an analogous manner, trimethyl borate and aqueous Trimethylamine solution a 1-molar orthoboric acid / trimethylamine solution in relation to both components obtain.

A mixture of IMI solution I and 0.02 ml of solution II was in a Quartz ampoule melted down and heated to 200 ° C.

After 3 days, the phase to be produced began to crystallize.

Example 6 Was also used in the synthesis in the presence of sodium hydroxide solution starting from two solutions: Solution I: As solution I in Example 5 Solution II: 1-molar aqueous NaCl solution.

0.5 ml of solution 1 and 0.2 ml of solution II were combined, in a quartz ampoule melted and heated to 2000C. After 3 days, the phase to be produced and was practically over after 6 days.

The indicated reaction mixture was in the gross composition identical to one from 0.3 ml of solution I, 0.2 ml of 1 molar sodium hydroxide / orthosilicic acid solution and 0.2 ml of 1 molar aqueous trimethylammonium chloride solution.

In the synthesis of the new compounds, the amines and ammonium compounds were used or their thermal decomposition products and / or other additives that are are in the educational phase and beyond the educational phase in the enclosed space, enclosed in the hollow cages of the compounds according to the invention. This at The guest molecules included in the synthesis remain up to very high temperatures included if their kinetic diameters are t> 3 Å, because the 6-rings Have openings of approximately 2.9 Å.

The new compounds can therefore as thermally s bile, acid and Water-resistant stores are used for substances whose molecules or ions are kinetic Have a diameter between 3 and 9 Å. E.g. in the case of nuclear power generation formed radioactive noble gases like Ar, Kr and Xe bound and safe in this way be stored. Because of the compared to zeolite 5 A [K.Körting, Physikal. leaves 36 (1980), 1713 higher thermal stability are those synthesized here for the first time Compounds particularly well suited for nuclear waste disposal.

Another application arises for the small gaseous species He, Ne, H2 and MH3, whose kinetic diameter is <3 Å. These molecules can at medium temperatures under pressure in the previously synthesized and degassed Phase introduced and by further increasing the temperature, especially at lower Gas printing, to be marketed again.

This reversible gas uptake and release results from the fact that the kinetic diameter of this species is so small is that they pass through the rings of the hollow cages above a certain temperature can.

The new inclusion compounds can therefore be used as molecular sieves Separation of gases with very small molecular diameters can be used by the zeolites are not selectively adsorbed.

While Figure 1 is a schematic representation of the overall structure of high-temperature cubic form of the inclusion compounds 136 [(Si1-xTx) O2]. (24 - y) M, FIG. 2 shows the linkage of the [512] cages with [51264] cages. L. e e r e i t e

Claims (6)

Crystalline Inclusion Compounds of Silicon Dioxide, Process for Production and use P A T E N T A N S P R Ü C H E 1.) Crystallines, the gas hydrates Inclusion compounds of silicon dioxide of the formula similarly built of structure type II 136 [(Si1-xTx) O2-]. (24-y) M, where T is a tetrahedrally coordinated by oxygen Atom, x a numerical value of # 0.1, y a numerical value of 0 # y # 24 and M atoms, molecules and / or ions with kinetic diameters according to Lennard-Jones ## 9 A mean. 2.) Crystalline inclusion compounds according to claim 1, wherein T the Means atoms B, Al, Ge, Ti or P. 3.) A method for producing the inclusion compounds according to claim 1, characterized in that basic SiO2 -containing solutions with SiO2 contents # 0.01 m and base: SiO2 ratios between 0.4: 1 and 20: 1 for uranium atmospheres Pressing heated to temperatures above 1200C. 4.) The method according to claim 3, characterized in that the Basicity of the solutions produced by amines. 5.) The method according to claim 3, characterized in that on heated to a temperature above 170 ° C. 6.) Use of the inclusion compounds according to claim 1, as a means for the absorption and storage of atoms, molecules and / or ions with kinetic Lennard-Jones diameters # # 9 Å.