SYNTHETIC MODIFIED CRYSTALLINE SILICA

Abstract: A crystalline silica modified by replacement of a prop­ ortion of the silicon atoms in the crystal lattice by nickel, a process for its preparation and its use as a catalyst, particu­ larly in the decomposition of methanol to synthesis gas and the conversion of synthesis gas to hydrocarbons and oxygenated hydrocarbons.

Description: SYNTHETIC MODIFIED CRYSTALLINE SILICA. The present invention relates to a synthetic modified crystalline silica, a process for its production and its use as a catalyst. In US Re. 29948 there is described a crystalline metal organosilicate having a composition, in its anhydrous state, in terms of mole ratios of oxides as follows: 0.9 t0.2 [xR2O+(lx)M2/n0J: 0.005 A1203: 1 SiO2 wherein M is a metal other than a metal of Group IIIA, n is the valence of said metal, R is an alkylammonium radical and x is greater than 0 but not exceeding 1. The crystalline metal organosilicate may be synthesised by preparing a solution containing (R4N)20, sodium oxide, an oxide of a metal other than a metal of Group IIIA and water in defined proportions and thereafter crystallising the mixture. The crystalline metal organosilicates as synthesised can have the original components thereof replaced by a wide variety of others according to techniques well known in the art. Typical replacing components would include hydrogen, ammonium, alkyl ammonium and aryl ammonium and metals other than metals of Group IIIA, including mixtures of the same. The hydrogen form may be prepared, for example, by substitution of original sodium with ammonium followed by calcination. With regard to the structure of the materials it is stated that regardless of the synthesised form of the organosilicate the spatial arrangement of atoms which forn the basic crystal lattices remain essentially unchanged by the described replacement of sodium or other alkali metal or by the presence in the initial reaction mixture of metals in addition to sodium, as determined by an X-ray powder diffraction pattern of the resulting organosilicate. The aforesaid statements imply that the sodium or sodium in combination with other metal does not form an integral part of the structure of the crystalline organosilicate otherwise it would not be possible to exchange them with other components. Moreover the alkylammonium radical is an essential component of the crystalline material as synthesised and this also can be exchanged with other components. UK Patent Application No. 2024790 describes 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 the silica or in the form of salts of bisilicic or polysilicic acids. All those elements which form metallic cations are said to be useable for obtaining the modified silicas but preference is given 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. The modified silicas of this kind are reported to be characterised by the presence of a single crystalline phase and to have the formula: (0.0001 to 1) MnOm.SiO2 wherein MnOm is an oxide of the modifying element. The materials usually have a well defined crystalline structure as demonstrated by the X-ray diffraction spectra appearing in the specification. The silica-based synthetic materials are said to be useful as catalysts for a large number of reactions, including the conversion of dimethyl ether and/or methanol or other lower alcohols into hydrocarbons such as olefins and aromatic hydrocarbons. UK Patent Application No. 2023562 describes a crystalline silica or germania modified with aluminium or gallium, a process for its preparation and its use as a catalyst in a variety of reactions including the conversion of dimethyl ether and/or methanol or other lower alcohols to hydrocarbons (olefins and aromatics). Furthermore European Patent Publication No. 10-572 discloses iron silicate having a zeolitic structure, a process for its production by crystallisation from a mixture of water glass and an aqueous solution of an amine at 100 - 2000C and in the presence of Fe(III) oxide and/or Fe(III) hydroxide and its use as a catalyst in cracking, hydrocracking and isomerisation processes. We have previously found that contrary to the teaching of UK 2024790 synthetic cobalt-modified crystalline silica decomposes methanol to synthesis gas. This finding forms the subject of our copending UK Application No. 8013361 (BP Case No. 4964). We have now synthesised a nickel-modified crystalline silica and have found that this also catalyses, inter alia, the decomposition of methanol to synthesis gas. Accordingly, the present invention provides a synthetic modified crystalline silica comprising crystalline silica in which a proportion of the silicon atoms in the crystal lattice have been replaced by nickel, which modified crystalline silica has an X-ray powder diffraction pattern characterised by the lines substantially as set forth in Table 1. The synthetic nickel-modified crystalline silica of the present invention has a characteristic X-ray powder diffraction pattern as shown in Table 1. The values in Table 1 were determined using standard techniques. The radiation was the K-alpha doublet of copper and a scintillation counter spectrometer with a strip chart pen recorder was used. The peak heights, I, and the positions as a function of 2 theta, where theta is the Bragg angle, were read from the spectrometer chart. From these the relative intensities 100 x I/Io, where Io is the intensity of the strongest line or peak, and d, the interplanar spacing in X corresponding to the recorded lines or peaks, were calculated. In Table 1, the relative intensities of the peaks are given in terms of symbols S = strong, M = medium, W = weak and VW = very weak. TABLE 1 EMI4.1 <tb> D <SEP> (Angstrom) <SEP> I/I0 <tb> 11.0 <SEP> i <SEP> 0.2 <SEP> S <tb> 10.0 <SEP> + <SEP> 0.2 <SEP> S <tb> <SEP> 9.8 <SEP> i <SEP> 0.2 <SEP> S <tb> <SEP> 9.2 <SEP> # <SEP> <SEP> 0.2 <SEP> W <tb> <SEP> 6.3 <SEP> i <SEP> 0.1 <SEP> VW <SEP> <tb> <SEP> 5.9 <SEP> + <SEP> 0.1 <SEP> W <tb> <SEP> 5.85 <SEP> i <SEP> 0.1 <SEP> VW <tb> <SEP> 5.64 <SEP> + <SEP> 0.1 <SEP> VW <tb> <SEP> 5.50 <SEP> i <SEP> 0.1 <SEP> VW <SEP> <tb> <SEP> 5.00 <SEP> i <SEP> 0.08 <SEP> VW <SEP> <tb> <SEP> 4.90 <SEP> f <SEP> 0.08 <SEP> VW <tb> <SEP> 4.22 <SEP> f <SEP> 0.08 <SEP> VW <tb> <SEP> 3.83 <SEP> i <SEP> 0.07 <SEP> M <tb> <SEP> 3.80 <SEP> i <SEP> 0.07 <SEP> M <tb> <SEP> 3.79 <SEP> i <SEP> 0.07 <SEP> M <tb> <SEP> 3.73 <SEP> + <SEP> 0.05 <SEP> W <tb> <SEP> 3.69 <SEP> t <SEP> 0.05 <SEP> W <tb> <SEP> 3.64 <SEP> + <SEP> 0.05 <SEP> VW <tb> <SEP> 3.60 <SEP> # <SEP> 0.05 <SEP> VW <tb> <SEP> 3.42 <SEP> + <SEP> 0.05 <SEP> VW <SEP> <tb> <SEP> 3.33 <SEP> # <SEP> 0.04 <SEP> VW <tb> <SEP> 3.30 <SEP> + <SEP> 0.04 <SEP> VW <SEP> <tb> <SEP> 2.89 <SEP> # <SEP> 0.02 <SEP> VW <tb> <SEP> 2.95 <SEP> + <SEP> 0.02 <SEP> VW <SEP> <tb> In another aspect the present invention also provides a process for the production of a synthetic modified crystalline silica which process comprises mixing, in a liquid medium comprising either water, an alcohol, or a mixture thereof, a source of silica, a source of nickel and an organic base in the absence of an alkali or alkaline earth metal compound and maintaining the mixture at elevated temperature for a time sufficient to effect crystallisation of the modified crystalline silica and recovering the modified crystalline silica so-formed. Suitable sources of silica include, for example, sodium silicate, silica hydrosol, silica gel, silica sol and silicic acid. The preferred source of silica is an aqueous colloidal dispersion of silica particles. A suitable commercially available source of silica is LUDOX Colloidal Silica marketed by Du Pont (Ludox is a Registered Trade Mark). Suitable sources of nickel include the oxide, hydroxide, salts such as the nitrate and alkoxy derivatives such as the acetate. Suitable organic bases include nitrogenous bases such as amines and substituted amines, e.g. alkanolamines. Preferably the nitrogenous base is a quaternary ammonium compound, which may be a tetraalkylammonium compound in which the alkyl group contains from 1 to 5 carbon atoms or a tetraarylammonium compound in which the aryl group is phenyl or an alkylphenyl group. A particularly suitable tetraalkylammonium compound is tetrapropylammonium hydroxide. The amount of organic base employed may suitably be lower than the stoichiometric amount relative to silica and is preferably from 0.05 to 0.50 mole x per mole of silica. The amounts of the source of silica and the source of alumina in the mixture may suitably be such that they provide a silicon to nickel atomic ratio greater than 5:1, preferably greater than 10:1. The mixture may suitably be maintained at a temperature in the range from 100 to 220, preferably from 150 to 2000C for a period of from a few hours to several days, preferably for about 7 days. The mixture is preferably maintained at the requisite temperature in a closed vessel such as an autoclave under autogenous pressure. The modified crystalline silica may suitably be recovered from the liquid medium, after cooling, by filtration. After recovery it is preferred to wash the crystalline material, suitably with boiling distilled water having dissolved therein an ammonium salt such as the nitrate or acetate. Finally it is preferred to calcine the modified crystalline silica. Calcination may suitably be effected by heating in air at a temperature in the range from 300 to 7000C, preferably at about 5500 C, for a period of from 2 to 24 hours. The nickel-modified crystalline silica so produced may be used without any further modification as a catalyst in a variety of chemical reactions or there can be added other metals which are capable of imparting specific catalytic properties. Examples of such metals are platinum, palladium, nickel, cobalt, tungsten, rhodium, copper and zinc. The addition may suitably be effected by impregnation, using solutions of salts of the metals, e.g. nitrates, acetates, oxides or halides. As mentioned hereinbefore the nickel-modified crystalline silica catalyses the decomposition of methanol to synthesis gas. In another aspect therefore the invention provides a process for the production of synthesis gas from methanol which comprises contacting at elevated temperature methanol in the vapour phase with a catalyst comprising a nickel-modified crystalline silica as described hereinbefore. Methanol is available commercially on a very large scale. It may be anhydrous or it may contain water up to, for example, 90% w/w. Alternatively water may be introduced as a separate feed in the form of steam. Furthermore the methanol may be diluted with carbon monoxide or carbon dioxide. Since the decomposition of methanol is endothermic the use of diluents offers a convenient method for introducing heat into the reaction. The catalytic activity of the modified crystalline silica catalyst for methanol decomposition may be further enhanced by the addition of a metal of Group VIII of the Periodic Table either alone or in combination with one or more other metals of Groups I to VIII of the Periodic Table. The Periodic Table referred to is that contained in the Handbook of Chemistry and Physics, 44th Edition, published by the Chemical Rubber Publishing Company. Group VIII metals which are particularly effective include, for example, rhodium and cobalt, both alone and in combination with other metals. The Group VIII metal may be admixed with one or more other Group VIII metals and/or with metals of Groups I to VII of the Periodic Table, such as iron, copper, chromium, gold and zinc. A particularly preferred combination is a mixture of rhodium and copper. The metal or metals may be added by any of the known-techniques. Preferably the metal or metals are added by impregnating the modified crystalline silica with a solution of a compound of the metal or metals in a suitable solvent, such as water, and thereafter removing the solvent. The catalyst may suitably contain from 0.1 to 20%, preferably from 0.2 to 10%, by weight of the metal or metals. It will be appreciated that although the metal may be added in the form of a compound of the metal, under the conditions pertaining during the methanol decomposition process such compounds may well be chemically reduced. Alternatively or in addition the modified crystalline silica may be mixed with other materials such as the amorphous aluminosilicate described in our copending European application No. 79302108.0 (Case 4663) or dispersed on a supporting body such as clays, silica, alumina and silica/alumina. The methanol may suitably be contacted with the modified crystalline silica catalyst at a temperature in the range from 200 to 600, preferably from 300 to 4500C, and at a pressure up to 100, preferably from 1 to 50 atmospheres. Since the decomposition of methanol is equilibrium limited it is preferred to employ high temperatures in combination with high pressures. The process may be operated batchwise or continuously, continuous operation being preferred. The contact time, as hereinafter defined, for continuous operation may be up to 30, preferably from 1 to 5 seconds. For the purpose of this specification the contact time is defined as follows: Volume of catalyst in millilitres Total volume of gas (in millilitres/second at NTP) The catalyst may be used either as a fixed bed or as a fluidised bed. The decomposition of methanol produces 2 volumes of hydrogen for every volume of carbon monoxide. This ratio can be altered if so desired by treating the hydrogen/carbon monoxide mixture in a manner well-known to those skilled in the art i.e. by the so-called shift reaction". The mixtures of hydrogen and carbon monoxide produced by the process of the present invention may be used in a variety of chemical reactions, including carbonylation, hydrocarbonylation and chemical reduction. Alternatively the nickel-modified crystalline silica may be used as a catalyst for the conversion of synthesis gas at elevated temperature and pressure to hydrocarbons and/or oxygenated hydrocarbons. Typically elevated temperatures in the range from 150 to 450 C, preferably from 200 to 400 C and elevated pressures in the range from 1 to 700 bars, preferably from 10 to 300 bars, may suitably be employed. The contact time for continuous operation may be up to 30 seconds and is preferably in the range from 0.01 to 5 seconds. The catalytic activity of the modified crystalline silica may be enhanced by the addition of one or more metals in amounts suitably in the range from 0.1 to 20%, preferably from 0.2 to 10% by weight. Suitable metals include cobalt, iron, manganese, nickel, ruthenium, rhodium, palladium, zinc, chromium and copper. The invention will now be particularly described by reference to the following Examples. In the Examples reference will be made to the molar yield of a particular product, to the CO conversion and to the selectivity. These terms are defined as follows: The molar yield of a particular product Moles of methanol converted to a particular product Moles of methanol fed x 100 CO Conversion = ################################# x 100 Moles of carbon monoxide converted to Selectivity = ########################### Moles of carbon monoxide consumed x 100 Preparation of the modified crystalline silica Example 1 Nickel nitrate hexahydrate (2.9g) was dissolved in deionised water (22.8g). Tetrapropyl ammonium hydroxide (22.9g, 20% w/w) was mixed with Ludox silica (21.8g containing 40% silica) and the above nickel nitrate solution was added with stirring. The gel was allowed to stand for one hour, transferred to a pressure vessel and heated at 1700C for 50 hours with rotation. The vessel was cooled to room temperature, the contents filtered and the filter cake washed three times by heating with 1 molar ammonium chloride solution (3 x 150 ml). Finally the solid was washed with deionised water (150 ml), dried at 1200C and calcined at 5000C for 16 hours. The material was shown to be crystalline and the X-ray diffraction data are given in Table 2. Analysis of the crystalline solid showed 41.4% wt/wt silicon and 5.3% wt/wt nickel. Example 2 The procedure of Example 1 was repeated using nickel nitrate hexahydrate (0.9 g), tetrapropylammonium hydroxide (22.9 g), 20% wt/wt), Ludox silica (21.8 g, containing 40% silica) and deionised water (22.8 g). The material was shown to be X-ray crystalline and the X-ray diffraction data are given in Table 3. Analysis of the solid showed 41.9% wt/wt silicon and 1.39% wt/wt nickel. Use of the modified crystalline silicas as catalysts. Example 3 The decomposition of methanol into carbon monoxide and hydrogen (synthesis gas). A gaseous feed of methanol was passed over the modified crystalline silica product of Example 1 contained in a glass reactor at 400 C and 2.8 seconds contact time. The molar yield of carbon monoxide based on the total methanol feed was 88%. The remaining products were methane and dimethyl ether. The hydrogen to carbon monoxide ratio of the synthesis gas obtained was approximately 2:1. Example 4 The conversion of synthesis gas into hydrocarbons and oxygenated hydrocarbons. With reference to the accompanying Figure a mixture of carbon monoxide and hydrogen in a molar ratio of 1:2 was passed via the inlet manifold through the two preheater coils (1) and (2) maintained at 1500C and 200 C respectively in silicone oil baths. The heated gases were then fed via a heat-traced line to the copper-lined reactor (4) containing a fixed bed of the nickel silicate catalyst, prepared in the manner described above, in the form of 1/16 in. extrudate. The reactor was maintained at the desired reaction temperature by immersion in a molten salt bath (5). The product gases were passed via a heat-traced line through a knock-out pot for wax products (6) to a small quench vessel (7) into the top of which water was sprayed. The gases were then passed through a water cooler to the bottom of the water wash tower (9) which was packed with 3/8 inch Raschig rings. In the tower (9) the product gases were washed counter-current with water. The resulting liquid product was fed into the receiver (16) and any dissolved gases were recombined with the product gas stream from the back pressure regulator (15). The separated gas stream from the top of the water wash tower (9) was passed through a water cooler to the knock-out pot (11) and then to the inlet side of the dome-loaded back pressure regulator (15). Recycle gas was recovered from the inlet side of the back pressure regulator (15), passed through a molecular sieve drier (13) and compressed up to 67 bars in the gas ballast vessel (18) using the gas recycle pump (17). The recycle gas was fed back to the inlet manifold. Provision was made to feed spot samples of the inlet gases and the total gas stream to a gas chromatographic analytical unit. The product gas stream leaving the back pressure regulator (15) was measured and samples were withdrawn and analysed by gas chromatography. The liquid product was also sampled and analysed by gas chromatography. When the reactor had reached equilibrium a balanced run was carried out over a one hour period at a temperature of 400"C. The results obtained are given in Table 4. Table 2 X-ray Diffraction Data for Modified Crystalline Silica Product of Example 1. 2-Theta D(AO) I/Io 7.41 11.935 5 8.07 10.960 72 8.64 10.236 20 8.95 9.884 100 9.02 9.799 98 9.23 9.584 14 14.09 6.289 6 14.93 5.932 14 15.11 5.864 7 15.71 5.640 7 16.05 5.521 6 17.80 4.983 5 18.00 4.929 8 21.03 4.224 7 22.32 3.983 4 23.22 3.830 54 23.44 3.795 33 23.49 3.786 33 23.87 3.728 17 24.10 3.693 17 24.49 3.635 6 24.70 3.604 6 26.10 3.415 4 26.76 3.332 4 27.05 3.296 6 29.54 3.024 4 30.04 2.975 7 30.35 2.945 4 Table 3 X-ray Diffraction Data for Modified Crystalline Silica Product of Example 2 2-Theta D(AO) I/Io 7.26 12.180 4 7.55 11.715 9 7.76 11.398 30 8.03 11.012 100 8.36 10.574 6 8.89 9.950 77 8.98 9.845 63 9.18 9.632 16 13.32 6.648 7 14.05 6.305 10 14.90 5.947 14 15.07 5.878 4 15.61 5.677 6 15.71 5.640 6 16.01 5.535 7 17.77 4.993 5 17.95 4.940 6 20.49 4.334 5 21.00 4.231 6 23.18 3.837 55 23.38 3.806 26 23.47 3.790 25 23.84 3.732 16 24.07 3.698 23 24.44 3.643 8 24.69 3.605 8 25.96 3.433 4 26.09 3.416 4 26.73 3.336 4 27.01 3.301 5 27.13 3.287 6 30.03 2.976 10 30.34 2.946 5 Table 4 Reaction paremeters: GHSV = 4650 hr-1 H2:CO molar ratio = 2:1 Pressure = 50 bar Recycle ratio = nil EMI13.1 <tb> <SEP> SELECTIVITY <SEP> % <tb> <SEP> Reaction <SEP> CO <tb> Temperature <SEP> Conversion <SEP> Carbon <tb> <SEP> C <SEP> % <SEP> Dioxide <SEP> Methane <SEP> Ethane <SEP> Propane <SEP> Methanol <tb> <SEP> 400 <SEP> 5 <SEP> 29 <SEP> 44 <SEP> a <SEP> . <SEP> 12 <tb>

Claims: Claims: 1. A synthetic modified crystalline silica comprising crystalline silica in which a proportion of the silicon atoms in the crystal lattice have been replaced by nickel, which modified crystalline silica has an X-ray diffraction pattern characterised by the lines substantially as set forth in Table 1. 2. A process for the production of the synthetic modified crystalline silica as claimed in claim 1 which process comprises mixing, in a liquid medium comprising either water, an alcohol, or a mixture thereof, a source of silica, a source of nickel and an organic base in the absence of an alkali or alkaline earth metal compound, maintaining the mixture at elevated temperature for a time sufficient to effect crystallisation of the modified crystalline silica and recovering the modified crystalline silica so-formed. 3. A process according to claim 2 wherein the organic base is a tetraalkylammonium compound in which the alkyl group contains from 1 to 5 carbon atoms. 4. A process according to either claim 2 or claim 3 wherein the recovered modified crystalline silica is washed with boiling distilled water having dissolved therein an ammonium salt. 5. A process according to any one of claims 2 to 4 wherein the recovered modified crystalline silica is calcined by heating in air at a temperature in the range from 300 to 700 C for a period of from 2 to 24 hours. 6. A process for the production of synthesis gas from methanol which comprises contacting at elevated temperature methanol in the vapour phase with a catalyst comprising the nickel-modified crystalline silica as claimed in claim 1. 7. A process according to claim 6 wherein there is added to the nickel modified crystalline silica a metal of Group VIII of the Periodic Table either alone or in combination with one or more other metals of Groups I to VIII of the Periodic Table. 8. A process according to claim 7 wherein the Group VIII metal is rhodium and/or cobalt. 9. A process according to claim 7 wherein the Group VIII metal is admixed with one or more of the metals iron, copper, chromium, gold and zinc. 10. A process according to any one of claims 7 to 9 wherein there is added to the nickel-modified crystalline silica a mixture of rhodium and copper. 11. A process according to any one of claims 6 to 10 wherein the temperature is in the range from 300 to 4500C and the pressure is in the range from 1 to 50 atmospheres. 12. A process for the conversion of synthesis gas to hydrocarbons and/or oxygenated hydrocarbons which process comprises contacting synthesis gas at elevated temperature and pressure with a catalyst comprising the nickel-modified crystalline silica as claimed in claim 1. 13. A process according to claim 12 wherein the temperature is in the range from 200 to 4000C and the pressure is in the range from 10 to 300 bars. 14. A process according to either claim 12 or claim 13 wherein there is added to the modified crystalline silica one or more of the metals cobalt, iron, manganese, nickel, ruthenium, rhodium, palladium, zinc chromium and copper.

Inventors: BALL, WILLIAM JOHN, STEWART, DAVID GORDON
Applicants: THE BRITISH PETROLEUM COMPANY P.L.C.
Application year: 1981
Main classification: C01B33
IPC codes: C07C29, B01J29, B01J23, C01B33, C01B3, C07C1