Abstract:
The invention deals with a microporous crystalline material, with a characteristic X-ray diffractogram, comprised of oxygen tetrahedra and a metal (T +4  and T +3 ) with the possibility of introducing surface acidity produced by the substitution in the lattice of some T +4  cations by T +3  cations, which gives rise to a structural charge deficiency that may be compensated by protons, Brönsted acidity, and/or high ratio radium charge cations, Lewis acidity; and the obtaining method thereof, based on the preparation of a gel, its hydrothermal treatment under controlled conditions and the treatment of the resulting laminar material with a solution of an organic compound, a swollen material being obtained, which is subjected to a treatment for the formation of interlaminar pillars of polymeric oxides, obtaining a pillared material that maintains the separation between the sheets, even after calcination.

Description:
TECHNICAL FIELD 
     The present invention refers to the area of chemistry, in particular to materials of catalytic interest 
     BACKGROUND 
     The present invention deals with a pillared mixed oxide that maintains a separation between sheets, there being individual structural layers, that have microporous channels and cavities. 
     Laminar materials such as clays, phosphates, hydroxycarbonates, silicic acids (kanemite, magadiite, keniaite, etc.), transition metal sulfides, graphite, laminar hydroxides and others, are capable of swelling in the presence of water and/or suitable interlaminar cations. The individual sheets of these materials are kept together by means of weak hydrogen bond type forces and/or electrostatic interactions. These bonds break easily when the intercalation force or the solvation energy of the cations are greater than the interlaminar attraction forces. 
     The interest of swollen materials is to make the interlaminar space accessible to the reacting molecules, and consequently, the inside surface, considerably increasing the active surface accessible to the reagent. When the material intercalated between the sheets of the mixed oxide is eliminated by calcination, the swollen laminar compound collapses, recovering the original interlaminar distance. 
     In order to prevent the interlaminar collapse, intercalation of the “pillars” comprised of thermally stable inorganic oxyhydroxides in the swollen material has been proposed. These “pillars” are comprised of polymeric hydroxides of Al, Si, Cr, Ni, Zr, etc. . . . , which after calcination treatment give rise to columns of the corresponding oxide that are anchored in the surface of the sheets keeping them separated and stabilizing the final pillared product. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide a pillared material consisting of a mixed oxide, which maintains a separation among sheets, appearing isolated structural layers with channels and microporous cavities, and which may be used as catalyst in acid catalyzed reactions. 
     It is an additional object of the present invention a method for preparing the laminar solid and the subsequent treatment thereof, until a highly accessible microporous pillared material with acid characteristics capable of being used as a catalyst is obtained. 
     It is an additional object of the invention the use of the pillared microporous material in acid catalyzed reactions, such as cracking and isomerization of organic compounds, and preferably of hydrocarbons, as well as in hydroisomerization and hydrocracking processes. 
     It is a further object of the invention to provide catalytic compounds which comprise the pillared micro- or mesoporous material and a matrix and their use in processes of dewaxing and isodewaxing. 
     Finally, it is an additional object of the invention catalytic compositions which comprise the pillared micro- or mesoporous material and a hydrogenating function. 
     DESCRIPTION OF THE INVENTION 
     The present invention refers to an oxide which is a pillared material, called ITQ-36, with a micro- and mesoporous structure and a high external surface area, capable of supporting Brönsted and Lewis acid centers and that is characterized by its X-ray diffractogram and its adsorption and catalytic properties. 
     The material ITQ-36 has a chemical composition represented by the formula 
     
       
         (XO 2 ) n (Y 2 O 3 ) m (H 2 O) p   
       
     
     wherein X represents, at least, a tetravalent element and Y represents, at least, a trivalent element, the atomic ratio between X and Y being at least 5. In preferred embodiments the atomic ratio between X and Y is higher than 10, or even higher than 30. In a more preferred embodiment said atomic ratio is higher than 30, or even higher than 40. Suitable limits for said atomic ratio may be between 30 and 500. 
     Preferably, X in XO 2  represents, at least, a tetravalent element selected from among silicon, germanium and, more specifically silicon, in some cases it being able to also be titanium. 
     Preferably, Y in Y 2 O 3  represents, at least, a trivalent, element, selected from among aluminum, iron, chromium and gallium, and more specifically aluminum. 
     The material ITQ-36 has an X-ray diffraction diagram with basal spacings and relative intensities summarized in Table 1. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 d 
                   
               
               
                   
                 (Å) 
                 I/I O  * 100 
               
               
                   
                   
               
             
             
               
                   
                 37.01  
                 Vs 
               
               
                   
                 18.77  
                 W 
               
               
                   
                 7.01 
                 W 
               
               
                   
                 6.51 
                 W 
               
               
                   
                 3.95 
                 W 
               
               
                   
                 3.50 
                 W 
               
               
                   
                 2.62 
                 W 
               
               
                   
                 2.35 
                 W 
               
               
                   
                   
               
             
          
         
       
     
     In this description, and unless it is specified otherwise, the relative intensities of the X-ray diffraction peaks will be represented with the symbols and meaning established hereinafter: 
     
       
         
               
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 w 
                 weak 
                 0-20% 
                 relative intensity 
               
               
                   
                 m 
                 medium 
                 20-40% 
               
               
                   
                 s 
                 strong 
                 40-60% 
               
               
                   
                 vs 
                 very strong 
                 60-100% 
               
               
                   
                   
               
             
          
         
       
     
     The preparation process of the pillared oxide ITQ-36 consists of: 
     a first step comprising the synthesis of a precursor which is a laminar material that can be swollen, 
     a second step wherein the laminar material obtained is swollen by mixing the same with a swelling solution resulting in a swollen laminar material, which is a swollen laminar mixed oxide, 
     a third step wherein the swollen laminar material is washed and dried giving rise to a swollen dried laminar material, and 
     a fourth step wherein the swollen dried laminar material is pillared, washed, dried and calcined, to obtain the pillared mixed oxide, ITQ-36, of the invention. 
     In the first step the synthesis of a solid which is a laminar material, is carried out by mixing in an autoclave a source of a tetravalent element, which in the case of silicon may be for example a silica source such as AEROSIL, LUDOX, CABOSIL, tetraethylorthosilicate (TEOS) or any other known; a source of a trivalent element, which in the case of aluminum may be a source selected among boehmite, pseudoboehmite, Al 2 (SO 4 ) 3 , AlCl 3 , Al(NO 3 ) or any other one; a fluoride salt and a fluoride acid such as for example ammonium fluoride and hydrogen fluoride; an organic compound such as 1,4-diaminobutane, ethylendiamine, 1,4-dimethylpiperazine, 1,4-diaminocyclohexane, hexamethylenimine and pyrrolidine, preferably, 4-amino-2,2,6,6-tetramethylpiperidine; and water in suitable proportions. 
     Synthesis of said solid material takes place at temperatures between 100 and 200° C., with permanent stirring of the gel and a duration between 1 and 30 days and, preferably between 1 and 18 days, and more preferably between 2 and 12 days. After this time the reaction product, a white solid with a pH between 9 and 10 is washed with distilled water, filtered and dried. 
     During the second step swelling of the obtained solid material takes place by preparing a suspension thereof in a solution that we will call the “swelling” solution, formed by an organic compound of a long hydrocarbonated chain that has a proton acceptor group, such as for example a quaternary alkylammonium, an amine, or an alcohol with more than three carbons in the chain, to which a controlled amount of a compound capable of providing OH −  to the reaction medium, such as for example, a quaternary alkylammonium hydroxide is added, until a pH higher than 10 is obtained. The organic compound used as a OH −  source may be any amine or quaternary alkylammonium compound, preferably cetyltrimethylammonium hydroxide (CTMA + OH − ). 
     The swelling solution prepared is mixed with the previously described solid material of the first step in a weight ratio of swelling solution to solid laminar material between 4 and 200. The resulting suspension is kept under reflux and permanent stirring between 20 and 200° C., and preferably between 40 and 120° C., for a time no less than 1 hour until the swollen laminar material is obtained. 
     During the third step the swollen laminar material is thoroughly washed with distilled water and dried at temperatures lower than 300° C. and preferably lower than 150° C. A swollen dried laminar material is thus obtained. 
     Once washed and dried, the swollen dried material has a characteristic X-ray diffraction diagram whose basal spacings and relative intensities are summarized in Table 2. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 d 
                   
               
               
                   
                 (Å) 
                 I/I O  * 100 
               
               
                   
                   
               
             
             
               
                   
                 28.20  
                 Vs 
               
               
                   
                 14.45  
                 S 
               
               
                   
                 9.81 
                 W 
               
               
                   
                 6.46 
                 W 
               
               
                   
                 4.31 
                 M 
               
               
                   
                 4.10 
                 M 
               
               
                   
                 3.93 
                 M 
               
               
                   
                 3.65 
                 W 
               
               
                   
                 3.49 
                 M 
               
               
                   
                 2.87 
                 W 
               
               
                   
                 2.62 
                 W 
               
               
                   
                   
               
             
          
         
       
     
     Then the pillaring process is proceeded with during the fourth step. For this purpose, a suspension of swollen dried material in a pillaring agent, preferably tetraethylorthosilicate (TEOS) is prepared, in a variable weight proportion between 2 and 20. This suspension is kept under reflux and constant stirring, at a temperature between 30 and 150° C., and preferably between 50 and 80° C., for a time no less than 1 hour and with permanent nitrogen flow until the pillared material is obtained. 
     During the fourth step the obtained pillared material is washed and dried at temperatures lower than 300° C. Once dry, it is calcined at temperatures between 300 and 800° C. and, preferably between 400 and 600° C. giving rise to the product ITQ-36. 
     Pillaring agents include polymeric oxides of elements of group IVA of the Periodic Table of the elements, such as silicon, germanium or tin, or of group IVB such as titanium, zirconium, etc., although pillars that include polymeric silica are usually chosen. The pillaring oxides could also include an element that provides catalytically active acid sites in the pillars, preferably aluminum, gallium, rare earth or mixtures thereof. 
     ITQ-36 has, together with its laminar nature and X-ray diffractogram, some characteristic textural properties as a result of having a microporous part, and a high external surface area as a result of the cavities formed by the intercalation of pillars between the sheets. Hence, Table 3 summarizes the values obtained for a sample of ITQ-36 by applying the BET equation to the nitrogen adsorption isotherm at the temperature of liquid nitrogen. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 S TOT   
                 S MIC   
                 S EXT   
                 V TOT   
                 V MIC   
               
               
                   
                 (m 2 /g) 
                 (m 2 /g) 
                 (m 2 /g) 
                 (cm 3 /g) 
                 (cm 3 /g) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 ITQ-36 
                 716 
                 68 
                 648 
                 0.7094 
                 0.2734 
               
               
                   
               
             
          
         
       
     
     The material ITQ-36 may undergoes a subsequent hydrothermal calcination step or a post-calcination in the presence of fluorine or a fluorine compound, or treatment with a phosphorous compound. 
     This material ITQ-36 is capable of being used as a catalyst in acid catalysis reactions such as cracking and isomerization of organic compounds, and preferably of hydrocarbons, as well as in hydroisomerization and hydrocracking for which a hydrogenating-dehydrogenating function such as for example platinum, palladium, nickel, rhodium, ruthenium or mixtures thereof is introduced together with the acid function. 
     The invention also refers to a catalytic composition that comprises an oxide material as ITQ-36 and a hydrogenating function such as Pt, Pd, Ru, Ni, Co, Mo, V, W, Rh or any of the combinations thereof, whether they are deposited on the oxide material or on a high surface support such as alumina, silica or silica-alumina. 
     The invention further refers to the use of a catalytic composition as defined in the preceding paragraph in a process for the isodewaxing of paraffins that comprises contacting the hydrocarbon feed together with hydrogen at temperatures between 250 and 400° C., at pressures between 10 and 90 atmospheres, with the catalytic composition, as well as the use of said catalytic composition as a dewaxing catalyst. 
     The invention additionally refers to a catalytic compound formed by an oxide material as ITQ-36 and a matrix, which may be a refractory oxide. 
     The invention also refers to the use of said catalytic compound in a process for the catalytic isomerization of n-butenes in isobutenes that involves contacting the hydrocarbon with the catalytic compound, at temperatures between 300 and 500°, as well as the use of said catalytic compound in a hydrocarbon cracking process that comprises contacting the hydrocarbons with said catalytic compound, at temperatures higher than 400° C. and that may or may not be in the presence of steam. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 represents the characteristic X-ray diffraction diagram of the swollen dried material and 
     FIG. 2 represents a diffractogram of ITQ-36. 
    
    
     EXAMPLES 
     Example 1 
     (i) Preparation of the Swollen Laminar Mixed Oxide: 
     This example describes the preparation of a laminar mixed oxide with a molar Si/Al ratio, in the starting gel, of 5. The laminar oxide was prepared by mixing in an autoclave 10 grams of SiO 2 (Aerosil 200, Degussa), 2.3 grams of Al 2 O 3  (boehmite, Catapal B, Vista Corp., with 73.7% Al 2 O 3 ), 9.2 grams of ammonium fluoride NH 4 F, Aldrich of 98% purity), 3.1 grams of hydrofluoric acid (HF, Aldrich at a concentration of 49.8%), 26 grams of 4-amino-2,2,6,6-tetramethylpiperidine (Fluka of 98% purity) and 27.9 grams of MiliQ deionized water. The synthesis gel, with a pH between 8 and 9, was kept with vigorous stirring for an hour at room temperature. The resulting mixture was introduced in autoclaves and kept at 175° C. for five days after which the resulting product was filtered and washed with 3 liters of deionized water up to a pH ≦9, then drying in an oven at 60° C. 
     One gram (1 gr.) of the laminar material obtained is exchanged with a solution prepared with 20 grams of CTMA + OH −  (29% solution), 6 grams of tetrapropylammonium hydroxide (TPA + OH −  40% solution) and 4 grams of deionized water. The solution obtained is kept, under reflux and vigorous stirring, for 16 hours at 95° C. The suspension is finally washed thoroughly with water before the liquid phase separates from the obtained solid. The swollen material (1.8 grams) has a diffraction diagram summarized in Table 2. 
     (ii) Preparation of the Pillared Laminar Material Described in the Invention: 
     A suspension comprised of 1.5 gr. of the swollen laminar material together with 3 gr. of tetraethylorthosilicate, TEOS, (Merck) is formed. This mixture is treated under reflux with constant stirring at a temperature of 60° C. for 16 hours, always under an inert nitrogen atmosphere. Then the solid is recovered by centrifugation (12000 rpm for 25 minutes). The obtained material is dried at 60° C. overnight, and it is finally calcined at 580° C. for 7 hours in the presence of air, in order to produce a material, in accordance with the present invention (1 gram), with a diffraction diagram like the one in FIG. 2 with the relative intensities summarized in Table 1. 
     Example 2 
     The process followed in example 1 was repeated except the fact that the amounts of reagents in step (i) were varied in order to obtain a gel with a molar Si/Al ratio of 30. 
     The oxide obtained at the end of step (ii) has a diffraction diagram like the one in FIG.  2  and intensities like those of Table 1. 
     Example 3 
     The process followed in example 1 was repeated, except that in step (ii) a suspension comprised of 1.5 gr. of the swollen material and 15 gr. of tetraethylorthosilicate (TEOS) was formed, keeping the mixture under reflux for 24 hours at 80° C. with a nitrogen atmosphere. Once calcined, a product that has a diffraction diagram like the one in FIG. 2 was obtained. 
     Example 4 
     The process followed in example 1 was repeated except the fact that in step (i) N,N-tetradecylammonium (29% solution) was used instead of cetyltrimethylammonium hydroxide (CTMA + OH − ). The swollen material, that has a diffractogram like the one of FIG.  1  and relative intensitites comparable to those of Table 2, is obtained. 
     Example 5 
     Catalytic Experiments: 
     0.05% by weight of platinum was added by impregation with PtCl 6  to a sample of ITQ-36 with a Si/Al ratio of 30. The final material, after being calcined at 500° C. for 3 h, was reduced in a fixed bed reactor passing H 2  (300 ml.min −1 ), the molar H 2 /n- hexadecane ratio being 50. The reaction conditions were: 40 atmospheres of total pressure and reaction temperatures between 290° C. and 350° C. 
     The results obtained, that are given in table 4, show that the catalyst based on ITQ-36 is suitable to carry dewaxing of hydrocarbons. 
     
       
         
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Temperature 
                 % 
                 % 
                 % 
                 % Mono- 
                 % Di- 
                 % Tri- 
               
               
                 ° C. 
                 Conversion 
                 Isomerization 
                 Cracking 
                 branched 
                 branched 
                 branched 
               
               
                   
               
             
             
               
                 294 
                 20.72 
                 2.67 
                 18.05 
                 2.67 
                 0.19 
                 0   
               
               
                 310 
                 72.53 
                 3.51 
                 69.02 
                 3.51 
                 0   
                 0   
               
               
                 322 
                 88.91 
                 3.26 
                 85.65 
                 3.26 
                 0.67 
                  0.07 
               
               
                 335 
                 96.64 
                 2.36 
                 94.29 
                 2.36 
                 0.67 
                  0-17