NOVEL STANNOSILICATES AND PREPARATION AND USE THEREOF

Abstract: Highly crystalline stannosilicates are formed by reacting a tin salt with a source of silica and an hydroxide of a Group 1A or Group 11A metal or an amine. The resulting stannosilicates, preferably after drying, are useful for (inter alia) removing H₂S from gas streams.

Description: Field of the Invention This invention relates to novel class of highly crystalline stannosilicate materials and the preparation thereof. These novel materials are useful as catalysts, catalyst supports, sorbents, e.g., for the separation of hydrogen sulfide from gas streams containing hydrogen sulfides and hydrogen and/or hydrocarbons. Background of the Invention The extensive research and development into alumino-silicates has been highly successful and studies have turned to other materials that might lead to similar types of structures. While frame works containing both octahedral and tetrahedral sites are unknown for zeolites there is some literature suggesting that tin occupies an octahedral position in a mixed oxide structure. See, for example, (Semenov, E.I.; Gerassimovsky, V.I.; Maksimova, N.V.; Andersen, S.; Petersen, O.V. Meddelelser Om Gronland 1965, 181, 1), eakerite (Leavens, P.B.; White, J.S., Jr. Miner, rec. 1970, Fall, 92 and Kossiakoff, A.A.; Leavens, P.B. Amer. Miner. 1976, 61, 956), tin sphene (Hund, F. US Pat. 3,753,754 (1973) and Eppler, R.A. J. Am. Cer. Soc. 1976, 59, 455), and a discussion of tin containing ores (Nekrasov, I.Y. Zakonomer. Razmeshcheniya Polez. Iskop. 1973, 10, 183). Higgins, J.B.; Ross, F.K. Cryst. Struct. Comm. 1977, 6, 179. Higgins, J.B.; Ribbe, P.H. Amer. Miner. 1977, 62, 801. Takenouchi, S. Mineral. Deposita (Berl.) 1971, 6, 335. White, J.S., Jr.; Arem, J.E.; Nelen, J.A.; Leavens, P.B.; Thomssen, R.W. Miner. Rec. 1973, March-April, 73. Rudenko, V.N.; Rozhdestvenskaya, I.V.; Nekrasov, I.Y.; Dadze, T.P. Mineral. Zh. 1983, 5, 70. Larsen, F.K.; Christensen, A.N.; Rasmussen, S.E. Acta Chem. Scand. 1967, 21, 1281. Zayakina, N.V.; Rozhdestvenskaya, I.V.; Nekrasov, I.Y.; Dadze, T.P. Dokl. Akad. Nauk SSSR 1980, 254, 353. Safronov, A.N.; Nevskii, N.N.; Ilyukhin, V.V.; Belov, N.V. Dokl, Akad. Nauk SSSR 1980, 255, 1114. Safronov, A.N.; Nevskii, N.N.; Ilyukhin, V.V.; Belov, N.V. Dokl. Akad. Nauk SSSR 1983, 269, 850. Rozhdestvenskaya, I.V.; Zayakina, N.V.; Nekrasov, I.Y. Mineral. Zh. 1985, 7, 78. Gorokhovskii, V.V.; Krogius, E.A.; Vlasov, V.V.; Dashkevich, T.V. Izv. Akad. Nauk SSSR, Neorg. Mater. 1971, 7, 2033. Nekrasov, I.Y. Dokl, Akad. Nauk SSSR 1973, 212, 705. Nekrasov, I.Y.; Dadze, T.P.; Boronikhin, V.A.; Rudnitskaya, E.S. Dokl. Akad. Nauk SSSR 1977, 232, 909. Nekrasov, I.A.; Dadze, T.P. Ocherki Fiz.-Khim. Petrol. 1978, 8, 193. Nekrasov, I.Y.; Dadze, T.P. Dokl. Akad. Nauk SSSR 1978, 243, 1286. Nekrasov, I.Y.; Dadze, T.P.; Zayakina, N.V. Dokl. Akad. Nauk SSSR 1981, 261, 479. McAnespie, P.; Dyer, A.; Mehta, B.J. US Pat 4,329,328 (1982). Desai, G.T.; Baxi, D.R. Indian J. Tech. 1978, 16, 201. EP-B-0027736 and its United States' counterpart, US-A-4329328 describes and claims: (a) a method of synthesising a sodium zincosilicate, which optionally thereafter is ion-exchanged to replace sodium cations by hydrogen, or inorganic or organic cations, characterized in that the method comprises mixing an aqueous sodium zincate solution of concentration at least 0.5 M (in ZnO) with a source of silica in the molar ratio silica (as SiO₂):sodium zincate (as ZnO) of 3.3:1 to 1:5.5 and maintaining the mixture at a reaction temperature of from 15°C to 100°C for at least 15 minutes, allowing a precipitate to form and removing supernatant liquid therefrom and drying the sodium zincosilicate residue; and also (b) a method of synthesising a sodium stannosilicate which optionally thereafter is ion-exchanged to replace sodium cations by hydrogen or inorganic or organic cations, characterised in that the method comprises mixing an aqueous sodium stannate solution of concentration at least 0.5 M (in SnO₂) with a source of silica in the molar ratio silica (as SiO₂): sodium stannate (as SnO₂) of 3.3:1 to 1:5.5 and maintaining the mixture at a reaction temperature of from 15°C to 100°C for at least 15 minutes, allowing a precipitate to form and removing supernatant liquid therefrom and drying the sodium stannosilicate residue. The molar ratio SiO₂:ZnO or SiO₂:SnO₂ may be from 1:3.5 to 1:5.5, and the mixture may be maintained at the reaction temperature for up to 24 hours. EP-B-0027736 also describes and claims sodium zincosilicate or stannosilicate which is capable of preferentially taking up magnesium in the presence of calcium and which has been synthesised by the said methods. The present invention provides novel, highly crystalline stannosilicates having the generic formula: xM₂0·Sn0₂·4±0.5Si0₂·yH₂0·zR wherein M may be NH₄ or any Group IA or, where M₂O becomes MO, Group IIA metal, or a quaternary amine, e.g., tetraethylamine. x is 1.5 to 4, y is 4 to 15, R is an amine, and z is 0 to 4 are prepared by reacting a base, that is, ammonia or a Group IA or Group IIA metal (e.g., sodium, potassium, cesium, rubidium, magnesium, calcium, strontium) hydroxide or quaternary amine with a water soluble tin salt, e.g., chlorides, nitrates, sulfates or salts derived from dissolving tin oxide in an acid or base, and silica or a source of silica in an aqueous medium at conditions leading to the formation of these novel crystalline materials. Description of the Drawings Figure 1 depicts the X-ray diffraction pattern for phases A, B, L, G and K. Of the metal salts reacted with silica and the tin salt, the alkali metals: lithium, sodium, potassium, rubidium and cesium are preferred. Particularly preferred are sodium and potassium or mixtures thereof. The reaction generally occurs under autogenous pressure at temperatures above about 100°C and below about 250°C, preferably 150-225°C. The reactants generally combine to form a gel-like substance and crystallization occurs at reaction temperatures for a period of a few days to several weeks. e.g., seven days to eight weeks. After the appropriate time period, the reaction is quenched, the crystalline powder is recovered by, for example, filtration, and thoroughly washed and dried. Drying can be accomplished by an overnight heating at about 100°C. Impurities can be removed by an acid treatment, e.g., 1N HCl. Thermal dehydration at, for example, 300°C will drive off water and the x-ray diffraction pattern will change slightly to show a contraction of the lattice, or movement of cations, or both. In adsorbent or catalytic processes the stannosilicate is usually dried or calcined to remove pore filling water cations or amine and in the generic formula shown above, y or z or both may then be zero. The following examples will further illustrate this invention. Reactant grade stannous chloride pentahydrate and anhydrous stannic chloride were used without further purification. Colloidal silica (Ludox HS-40) was obtained from DuPont and fumed silica (Cabosil) was obtained from Cabot Corp. All reactions were carried out hydrothermally in 75ml stainless steel autoclaves under autogenous pressures. Powder x-ray diffraction measurements were conducted on a Siemens D500 powder diffractometer using a Siemens DIFFRAC-5 data system. Reactants were thoroughly mixed at room temperature according to the ratio 2-8 M₂O:SnO₂: 4-20 SiO₂:80-180 H₂O where M = NH₄, Na, K, Cs, Li, Rb, or a quarternary amine such as alkyl (C₁-C₄) quaternary ammonium mixtures of two or more cations. The resulting gel was then reacted at a temperature between 150°C and 250°C for period lasting between one week and two months. At the end of this time the autoclave was cooled to room temperature and the solid product separated by filtration. The crystalline powder was then washed repeatedly with water and dried at 100°C. The following are representatives of typical syntheses in the sodium stannosilicate system. EXAMPLE 1 Sodium stannosilicate (phase A). A 14.9g quantity of sodium hydroxide was dissolved in 20.0g distilled water and added slowly, with mixing, to 27.4g HS-40 (40% colloidal silica in water). A second solution was prepared by dissolving 16.0g of stannous chloride pentahydrate in 20.0g distilled water. The two solutions were combined slowly, thoroughly mixed, and distilled water added to make a total weight of 100g. This corresponded to a reaction ratio of 2Na₂O:SnO₂:4SiO₂:80H₂O. The gel was divided between four 75ml autoclaves which were sealed and kept at 200°C for 24 days. At the end of this period the rection vessels were quenched, the white solid removed by filtration, washed repeatedly with water, and dried at 100°C overnight. Powder x-ray diffraction indicated that a single, highly crystalline phase was produced as shown in Table 1A. Thermal dehydration of this compound at 300°C resulted in a phase which exhibited a different powder pattern by x-ray analysis (Table 1). Minor impurities which sometimes occurred in this material were removed by stirring in 1N HCl for two hours at room temperature followed by filtration and repeated washing with water. This resulted in slightly sharper lines in the x-ray powder pattern with little or no loss of crystallinity. Phase A 2 theta dobsv I/Io 13.97 6.33 29 15.17 5.83 100 15.94 5.56 42 17.08 5.19 12 18.73 4.73 8 20.73 4.28 18 26.97 3.30 23 29.30 3.05 73 30.72 2.91 69 32.25 2.77 27 33.92 2.64 11 36.68 2.45 15 38.31 2.35 9 EXAMPLE 2 Sodium Stannosilicate (phase B). Sodium hydroxide (14.9g) was dissolved in 25.0g distilled water and 11.0g of fumed silica was added. Separately, 16.0g stannous chloride pentahydrate was dissolved in 25.0g distilled water. The two solutions were combined, water added to make 100g total weight, and the gel mixed thoroughly. This corresponded to the reaction ratio in the preceding examples, 2Na₂O:SnO₂:4SiO₂:80H₂O. Crystallization at 200°C for 17 days followed by workup as previously described yielded a crystalline structurally unique phase, as shown by the x-ray diffraction pattern in Table 2. Phase B 2 theta dobsv I/Io 14.17 6.25 74 15.86 5.59 70 20.11 4.41 22 23.65 3.76 13 24.71 3.60 8 26.74 3.33 26 28.66 3.11 6 29.52 3.02 100 32.91 2.72 40 35.25 2.54 10 36.74 2.44 19 37.48 2.40 5 39.58 2.28 6 41.61 2.17 8 44.17 2.05 21 46.64 1.95 19 47.24 1.92 17 47.82 1.90 7 49.58 1.84 12 This phase can also be synthesized in a higher purity form using a mixture of two cations with the reaction ratio of Na₂O:Li₂O:SnO₂:4SiO₂:80H₂O. The reactants were mixed, as above, and the gel reacted at 200°C for 16 days yielding phase B. EXAMPLE 3 Sodium stannosilicate (phase L). A 21.1g sample of sodium hydroxide was dissolved in 10.0g distilled water; 12.8g stannous chloride pentahydrate was added. This solution was combined with 54.9g HS-40, water added to make 100g total weight, and the resulted gel thoroughly mixed. This mixture corresponded to a reaction ratio of 5Na₂O:SnO₂:10SiO₂:80H₂O. Crystallization at 200°C for 6 weeks followed by workup as above produced a layered phase as indicated by powder x-ray diffraction shown in Table 3. Phase L 2 theta dobsv I/Io 7.95 11.12 96 16.11 5.50 15 17.21 5.15 21 19.10 4.64 39 21.14 4.20 18 23.95 3.71 83 29.44 3.03 18 31.83 2.81 27 32.36 2.76 100 34.45 2.60 27 42.91 2.11 27 44.28 2.04 14 EXAMPLE 4 Potassium Stannosilicate (phase G). A 22.5g quantity of potassium hydroxide was dissolved in 10.0g of distilled water and added slowly to 25.9g HS-40 (40% colloidal silica). A second solution was prepared from 20.0g water and 15.1g stannous chloride. The two solutions were combined to make a gel which was thoroughly mixed; water was added to make 100g total weight. This corresponded to a reaction ratio of 2K₂O:SnO₂:4SiO₂:80H₂O. The mixture was reacted at 175°C for 7 days followed by workup as described above to give a crystalline phase with a distinctive diffraction pattern, as shown in Table 4. Phase G 2 theta dobsv I/Io 10.98 8.05 17 13.44 6.58 59 15.11 5.86 76 16.56 5.35 8 17.51 5.06 18 18.32 4.84 7 20.30 4.37 40 22.10 4.02 13 24.81 3.59 18 25.38 3.51 16 27.28 3.27 17 28.57 3.12 8 29.24 3.05 19 29.92 2.98 100 30.54 2.93 38 31.28 2.86 53 32.49 2.75 12 33.51 2.67 14 34.89 2.57 10 35.87 2.50 12 37.22 2.41 9 42.23 2.14 14 44.37 2.04 12 47.09 1.93 19 49.60 1.84 10 EXAMPLE 5 Cesium Stannosilicate (phase K). A 71.6g sample of 50% aqueous cesium hydroxide was added to 17.9g HS-40 (40% colloidal Silica); 10.5g of stannous chloride was slowly added to this mixture and dissolved completely (no gel formed). This mixture corresponded to a reaction ratio of 2Cs₂O:SnO₂:4SiO₂:95H₂O. Crystallization at 200°C for 3 weeks followed by workup as described above yielded a biphasic material as observed by powder x-ray diffraction, as shown in Table 5. Phase K 2 theta dobsv I/Io 15.87 5.58 14 17.04 5.20 20 18.28 4.85 21 19.99 4.44 67 24.28 3.66 39 25.01 3.56 99 26.51 3.36 56 28.41 3.14 12 29.11 3.07 66 29.78 3.00 100 30.57 2.92 51 31.53 2.84 9 34.42 2.60 23 35.09 2.56 39 36.27 2.48 23 37.21 2.41 23 40.29 2.24 17 43.11 2.10 19 46.35 1.96 14 49.74 1.83 22 49.94 1.83 18 The alkali-metal:tin:silica reaction system was found to yield a new class of crystalline, microporous materials containing only tin, silicon, and oxygen as framework species. The phases generated in this system appear to be new structure types, display reversible water loss, and are capable of ion exchange. The novel stannosilicates of this invention have a variety of uses, e.g., because the alkali metal can be exchanged as in a zeolite material, nuclear waste clean up can be effected when M in the generic formula is radioactive cesium or strontium. A particular utility for the material is as a hydrogen sulfide sorbent. Catalytic reforming reactions, for example, processes utilizing a supported platinum catalyst to upgrade the octane level of naphtha, produce hydrogen which can be recycled to the reaction zone. Because naphtha feeds generally contain low sulfur levels which can build up during recycle processes and cause catalyst deterioration, the recycle hydrogen stream containing some hydrogen sulfide is passed through a sorbent to reduce the sulfide level of the recycle hydrogen. The sorbent process can be conducted at reforming pressures, e.g., 125 psig to about 600 psig (0.862 to 4.137 MPa gauge), to avoid recompression of the hydrogen and at temperatures ranging from about 50°C to 500°C. Hydrogen flow rates or space velocities, that is, volume of feed per hour per volume of sorbent, are easily determined based on the desired level of hydrogen sulfide removal, usually in excess of about 80%, preferably in excess of about 90%. Similar sorption processes are used to remove H₂S from hydrocarbon streams containing H₂S such as sour natural gas streams, and streams resulting from petrochemical refining operations. The following example shows the ability of a form of the stannosilicate material to remove hydrogen sulfide from hydrogen streams and, more importantly, the regenerability of the stannosilicate so that it can be used and reused in multicycle fashion. In catalytic reforming operations, it is normal to have two or more beds of hydrogen sulfide sorbent so that the sulfide can be continuously adsorbed in one bed or another while the bed that is off stream is being regenerated. Such processes will be rather obvious to those skilled in the art. Regeneration of the stannosilicate is readily effected by passing a small amount of hydrogen through the sorbent stannosilicate for several hours, e.g., one hour to 24 hours, while maintaining a positive pressure and at higher temperature than the adsorbing cycle but within the same general temperature range. EXAMPLE 6 A stannosilicate prepared in accordance with example 1 above was then exchanged with NH₄+ and loaded into a thermogravimetric analyzer and heated overnight at 650°F (343.3°C) in flowing hydrogen. 10.5% volatile matter, corresponding to 9.45mg of the original 90.01mg charge was lost. The results of several adsorption/desorption cycles are shown in Table 6 and demonstrate the ability of these novel, highly crystalline materials to separate H₂S from H₂S-containing streams. Table 10, below, shows a variety of stannosilicate compositions, most of which are in accordance with this invention, items noted with an asterisk resulted either in an amorphous structure or a quartz structure and are not part of this invention. In Table 10, sl is slight, TEA is triethanolamine and examples 1-5 are noted. While the preparations shown in Table 10 are similar to the previous examples, in some instances the mixture was cold aged for a short period to promote nucleation and then held at reaction temperature for the requisite time period. In another instance a small amount of Al₂O₃ was added for the same purpose.

Claims: A highly crystalline stannosilicate of the formula xM₂O.SnO₂.4±0.5SiO₂.yH₂O.zR wherein M is NH₄, a Group 1A metal, a Group 11A metal( whereupon M₂O becomes MO), or a quaternary amine; x is 1.5 to 4; y is 4 to 15; R is an amine; and z is 0 to 4. The composition of claim 1 having the X-ray diffraction pattern one of phases A, B, L, G or K of Tables 1, 2, 3, 4 and 5, respectively, which follow : Phase A 2 theta dobsv I/Io 13.97 6.33 29 15.17 5.83 100 15.94 5.56 42 17.08 5.19 12 18.73 4.73 8 20.73 4.28 18 26.97 3.30 23 29.30 3.05 73 30.72 2.91 69 32.25 2.77 27 33.92 2.64 11 36.68 2.45 15 38.31 2.35 9 Phase B 2 theta dobsv I/Io 14.17 6.25 74 15.86 5.59 70 20.11 4.41 22 23.65 3.76 13 24.71 3.60 8 26.74 3.33 26 28.66 3.11 6 29.52 3.02 100 32.91 2.72 40 35.25 2.54 10 36.74 2.44 19 37.48 2.40 5 39.58 2.28 6 41.61 2.17 8 44.17 2.05 21 46.64 1.95 19 47.24 1.92 17 47.82 1.90 7 49.58 1.84 12 Phase L 2 theta dobsv I/Io 7.95 11.12 96 16.11 5.50 15 17.21 5.15 21 19.10 4.64 39 21.14 4.20 18 23.95 3.71 83 29.44 3.03 18 31.83 2.81 27 32.36 2.76 100 34.45 2.60 27 42.91 2.11 27 44.28 2.04 14 Phase G 2 theta dobsv I/Io 10.98 8.05 17 13.44 6.58 59 15.11 5.86 76 16.56 5.35 8 17.51 5.06 18 18.32 4.84 7 20.30 4.37 40 22.10 4.02 13 24.81 3.59 18 25.38 3.51 16 27.28 3.27 17 28.57 3.12 8 29.24 3.05 19 29.92 2.98 100 30.54 2.93 38 31.28 2.86 53 32.49 2.75 12 33.51 2.67 14 34.89 2.57 10 35.87 2.50 12 37.22 2.41 9 42.23 2.14 14 44.37 2.04 12 47.09 1.93 19 49.60 1.84 10 Phase K 2 theta dobsv I/Io 15.87 5.58 14 17.04 5.20 20 18.28 4.85 21 19.99 4.44 67 24.28 3.66 39 25.01 3.56 99 26.51 3.36 56 28.41 3.14 12 29.11 3.07 66 29.78 3.00 100 30.57 2.92 51 31.53 2.84 9 34.42 2.60 23 35.09 2.56 39 36.27 2.48 23 37.21 2.41 23 40.29 2.24 17 43.11 2.10 19 46.35 1.96 14 49.74 1.83 22 49.94 1.83 18 A process for preparing crystalline stannosilicates according to claim 1 or claim 2 which comprises reacting a water-soluble tin salt, a source of silica, and ammonia or a Group IA or Group IIA metal hydroxide or quaternary amine in an aqueous medium to form a reaction mixture having a composition : 2-8 M₂O:SnO₂:4-20 SiO₂:8-180 H₂O wherein M is selected from NH₄, Group IA or IIA metals, or quaternary ammonium cations, ageing the reaction mixture at reacting temperatures until crystallization occurs, and recovering the said crystalline stannosilicate. The process of claim 3 wherein the reaction temperature is in the range of from 100° to 250°C. The process of claim 3 or claim 4 wherein the crystalline stannosilicate is treated with an acid. The process of any one of claims 3 to 5 wherein the crystalline stannosilicate is dried to remove water contained therein. A process for removing H₂S from a feed stream containing H₂S and hydrocarbons and/or H₂S and hydrogen, or from a stream resulting from petrochemical refining operations, which comprises contacting the stream with a crystalline stannosilicate of the general formula xM₂O.SnO₂.4±O.5SiO₂.yH₂O.zR x is 1.5 to 4; y is 4 to 15; R is an amine; and z is O to 4, and which crystalline stannosilicate is either in accordance with claim 1 or claim 2 or is made by the process of any one of claims 3 to 6, and recovering a stream depleted in H₂S. The process of claim 7 conducted at temperatures in the range of from about 50° to about 500°C. The process of claim 7 or claim 8 wherein the stannosilicate is dried prior to contact with the feed stream. The process of claim 9 wherein the stannosilicate is dried in situ. The process of any one of claims 7 to 10 wherein the stannosilicate containing H₂S is regenerated by purging with hydrogen.

Inventors: CORCORAN, EDWARD WILLIAM, JR., EBERLY, PAUL EARL, JR., VAUGHAN, DAVID EVAN WILLIAM
Applicants: EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1988
Main classification: C01G19
IPC codes: B01J20, B01J38, C01B3, B01J29, C07F7, C01B39, C10K1, C01B33, C01G19