Title of Invention	AN IMPROVED PROCESS FOR THE PREPARATION OF POROUS CRYSTALLINE SILICOALUMINOPHOSPHATE MOLECULAR SIEVE
Abstract	The present invention provides an improved process for the preparation of a porous crystalline silicoaluminophsphate molecular sieve. The present invention provides an improved process for the preparation of silicoaluminophosphate molecular sieve SAPO-11, wherein the reaction gel formed by combining the reactive aluminium and phosphorous sources followed by the organic template and the silicon source was subjected to programmed heating schedule under hydrothermal conditions in an autoclave at the rate of 1.5°C per minute from room temperature to 160°C, then at the rate of 0.5°C per minute up to 200°C and holding the gel at 200°C for 30 min. to 3 hours prior to cooling rapidly by immersing in cold water. The contents are filtered to separate the crystalline solid which is subsequently washed thoroughly and dried at 120°C and finally calcined in air at 550°C. The SAPO II synthesized by the above improved process is made up of smaller and more uniform particles besides incorporating more silicon ions in the framework.

Title of Invention

AN IMPROVED PROCESS FOR THE PREPARATION OF POROUS CRYSTALLINE SILICOALUMINOPHOSPHATE MOLECULAR SIEVE

Abstract

The present invention provides an improved process for the preparation of a porous crystalline silicoaluminophsphate molecular sieve. The present invention provides an improved process for the preparation of silicoaluminophosphate molecular sieve SAPO-11, wherein the reaction gel formed by combining the reactive aluminium and phosphorous sources followed by the organic template and the silicon source was subjected to programmed heating schedule under hydrothermal conditions in an autoclave at the rate of 1.5°C per minute from room temperature to 160°C, then at the rate of 0.5°C per minute up to 200°C and holding the gel at 200°C for 30 min. to 3 hours prior to cooling rapidly by immersing in cold water. The contents are filtered to separate the crystalline solid which is subsequently washed thoroughly and dried at 120°C and finally calcined in air at 550°C. The SAPO II synthesized by the above improved process is made up of smaller and more uniform particles besides incorporating more silicon ions in the framework.

Full Text	The present invention relates to an improved process for the preparation of porous crystalline silicoaluminophosphate molecular sieves. These molecular sieves are useful as catalysts in the transformation of hydrocarbons, especially in the isomerization of long chain paraffins. The crystalline aluminosilicate zeolite type molecular sieves are well known in the art and are formed by corner sharing Si02 and A102 tetrahedra and have pore openings of uniform dimensions, have a significant ion exchange capacity and are capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without displacing any atoms which make up the permanent crystal structure. The most recently synthesized molecular sieves without silica are the crystalline aluminophosphate compositions disclosed in the U.S. Pat. No. 4, 310, 440 (1982). These materials are formed from AI02 and P02 tetrahedra and have electroneutral frameworks as in the case of silica polymorphs. Unlike the silica molecular sieve, silicalite, which is hydrophobic due to the absence of extraframework cations, aluminophosphate molecular sieves are moderately hydrophilic, apparently due to the difference in the electronegativities of aluminium and phosphorous. Their intracrystalline pore volumes and pore diameters are comparable to those known for zeolites and silica molecular sieves. A novel class of silicon - substituted aluminophosphate molecular sieve was invented by B.M. Lok et al (U.S. Pat. 4, 440, 871) in 1984 which are both crystalline and microporous and exhibit properties which are characteristic of both aluminosilicate zeolite and the aluminophosphates. Members of this novel class of silicoaluminophosphate materials have a three dimensional microporous crystal framework structure of PO2, AI02" and Si02 tetrahedral units, and whose essential empirical chemical composition on an anhydrous basis is (Formula Removed)wherein 'R' represents at least one organic templating agent present in the intracrystalline pore system; 'm' represents the moles of 'R' present per mole of (SixAlyPz)02 and has a value of from 0.1 to 0.3 and x, y and z have a value from 0.01 to 0.20, 0.4 to 0.59 and 0.40 to 0.59 respectively. Aluminophosphates are neutral in that they do not possess any acidity as the (AI02)" and (PO2) tetrahedra alternate in a regular fashion in the structure leading to a neutral framework. However, when (Si02) tetrahedra are introduced in the lattice, they can replace a (P02)* tetrahedra leading to an anionic (negative) charge on the framework which when neutralized by a H* (proton) leads to an acid site just as the replacement of Si4* ions by Al3* ions in zeolites leads to acidity. On the other hand, when both an Al3* and an P5* ion are simultaneously replaced by two Si4* ions, no acidity is generated due to exact charge balancing. It has been found that the method of preparation of the SAPO molecular sieve can influence the manner of incorporation of Si4* ions and the acidity of the material. For example, it has been reported that the synthesis of SAPO-35 in a non-aqueous medium produces a more acidic material through preferential replacement of P5* ions by Si4* ions than when synthesis is carried out in an aqueous medium (Venkatathri and others in J.C.S. Faraday Transactions, volume 93, page 3411, year 1997). In order to obtain catalytically more useful and efficient materials, it is necessary therefore to develop synthesis methods to ensure preferential replacement of P5* ions by Si4* in the lattice (or framework). Synthesis in non-aqueous medium though leads to preferential replacement of P5* ions by Si4* ions is not a suitable method as the crystallization is slow taking more than 2 weeks to obtain good crystalline samples. It is therefore important to develope methods of synthesis which can achieve the preferential Si4* incorporation in a much shorter period. Another important consideration in the use of crystalline microporous materials as catalyst for the transformation of large molecules is their crystallite size. Smaller crystallites essentially are less prone to diffusion effects and will as a result be more catalytically active for the same number of acid sites than larger crystallites as these sites are more accessible in the former due to shorter diffusion path lengths. The prior art procedure for the synthesis of SAPO-11 as disclosed in the U.S. Pat. 4, 440, 87ijinvolves the reaction of aluminium isopropoxide or hydrated aluminium oxide with phosphoric acid and silica sol or fumed silica in the presence of organic templating compounds such as dipropylamine by autoclaving the reaction mixture directly at an elevated temperature of 150°C to 200°C for 24h to 168h. The major disadvantages of the above prior art method for the synthesis of SAPO-11 is lower Bronsted acidity due to lower incorporation of Si in the framework besides producing large crystallites of non-uniform size. While carrying out research on the optimization of process conditions for the synthesis of silicoaluminophosphate molecular sieves, we discovered that heating the reaction gel containing the necessary ingradients in a cotrolled manner reduced the crystallization time besides decreasing the crystallite size and enhancing the incorporation of Si in the aluminophosphate framework. Based on the above studies, we have now developed a heating program to enable the synthesis of SAPO-11 possessing superior catalytic activities than samples synthesized by prior art methods. The object of the present invention is to provide an improved process for the preparation of silicoaluminophosphate molecular sieve. Another object is to provide a process for rapid preparation of silicoaluminophosphate molecular sieve SAPO-11 in 30 min. to 3 hours. Yet another object is to, get_smaller and more uniform particles which are more acidic and catalytically more active than the conventionally prepared samples. Accordingly the present invention provides an improved process for the preparation of a porous crystalline silicoaluminophosphate molecular sieve characterized by the x-ray diffraction pattern as here in described and a chemical composition in terms of the mole ratio of oxides given by the formula (Formula Removed)wherein R represent organic templating agent selected from dialkylamine such as herein described, present in the intracrystalline pore system; 'm' represents moles of 'R' present and has a value between 0.02 to 0.3m 'n1 has a value of from 0.96 to 1.1 and 'q' has a value of from 0.1 to 1.0, which comprises mixing source of an aluminium oxide and oxide of phosphorous , adding organic template as defined above to the above mixture, followed by mixing a silicon oxide, wherein the ratio of the components varies in the range as described herein: heating the said mixture under atmospheric conditions at the rate of * 1.5°C/minute up to 160°C , then at the rate of 0.5C/minute from 160°C to 200°C, holding at this temperature for 30 minutes to 2 hours, cooling the reaction mixture \apidly and separating the crystalline material by filtration, then washingwith wete, and * drying the said crystalline material at120°C . followed by calcinations at 500°C to remove the organic template material occluded in its pore to get porous crystalline silicoaluminophosphate molecular sieve. - - In an embodiment of the present invention the source of silicon oxide may be silica sol, fumed silica, tetramethylorthoslicate, silicic acid or mixtures thereof. In an another embodiment of the present invention the source of aluminium oxide may be pseudoboehmite, aluminium alkoxide preferably aluminium isopropoxide and the source of oxide of phosphorous may be orthophosphoric acid. In yet an another embodiment of the present invention the organic template may be a dialkylamine such as dipropyl amine, diisopropylamine and dibutylamine. Accordingly, the present invention provides an improved process for the preparation of a porous crystalline silicoaluminophsphate molecular sieve. The present invention provides an improved process for the preparation of silicoaluminophosphate molecular sievet SAPO-11 , wherein, the reaction gel formed by combining the reactive aluminium and phosphorous sources followed by the organic template and the silicon source was subjected to programmed heating under hydrothermal conditions in an autoclave at the rate of 1 .5°C per minute from room temperature to 160°C, at the rate of 0.5°C per minute up to (Formula Removed)200°C and holding the gel at 200°C for 30 min. to 3 hours prior to cooling rapidly by immersing in cold water. The contents are filtered to separate the crystalline solid which is subsequently washed thoroughly and dried at 120°C and finally calcined in air at 550°C. The SAPO synthesized by the above improved process^ is made up of smaller and more uniform particles besides incorporating more silicon ions in the framework. As a result of larger incorporation of silica, the _-• material is also more acidic and catalytically more active. The silicoaluminophosphate of the present invention exhibits a larger acidity and greater catalytic activity. The acidity of the catalyst is usually determined by comparing the amount of an adsorbed basic compound such as pyridine retained by it even after heating to an elevated temperature. The silicoaluminophosphate of type 11 (SAPO-11) synthesized by the process of the present invention possessed a larger acidity than the material synthesized by the prior art method of U.S. Pat. 4, 440, 871. For example the SAPO-11 material synthesized by the process of the present invention retained 76 micromoles of pyridine per gram while the SAPO-11 synthesized by the prior art method retained only 59 micromole per gram beyond 300°C for a normalized silica content of 0.05 moles in the two samples. This also suggests that there is a greater substitution of P5* ions by Si4* ions in the SAPO-11 and SAPO-31 prepared by the process of the present invention than that synthesized by the prior art method. The SAPO-11 silicoaluminophosphate synthesized by the process of the present invention possesses a crystalline structure, the X-ray powder diffraction pattern of the as-synthesized form showing the characteristic peaks listed in Table 1. Table 1: X-ray diffraction pattern of the silicoaluminophosphate (SAPO-11) (Table Removed)VS = Very strong; S = Strong; MS = Medium Strong; W = Weak; VW = Very Weak; Sh = Shoulder After calcination in air at 550°C for 8 hours, the SAPO-11 silicoaluminophosphate shows the following characteristic lines in the X-ray diffraction pattern. Table 2 : X-ray diffraction pattern of calcined silicoaluminophosphate (SAPO-11) (Table Removed)VS = Very strong; S = Strong; MS = Medium Strong; W = Weak; VW = Very Weak; Sh = Shoulder The SAPO-11 silicoaluminophosphates in the as synthesized form has a composition in terms of molar oxide ratio on an anhydrous basis expressed by the formula: mR : AI203 : nP2O5 : qSi02 wherein R represents at least one organic templating agent present in the intracrystalline pore system; 'm' represents the moles of 'R' present and has a value such that there are 0.02 to 0.3 moles of 'R1 per mole of alumina; 'n' has a value of from 0.9 to 1.2 and 'q1 has a value of from 0.1 to 1.0. The organic templating agent R is generally an organic secondary amine such as R1(R2)NH, wherein R1 and R2 may be same or different and are alkyl groups with carbon numbers between 2 and 4, the sum of carbon numbers in R1 and R2 being between 5 to 8. In synthesizing the silicoaluminophosphate composition of the present invention, it is preferred that the reaction mixture be essentially free of alkali metal cations, and accordingly the preferred reaction mixture composition expressed in terms of mole ratio of oxides is as follows: aR : AI203 : 0.9-1.2 P2O5 : 0.1-1.0 SiO2 : b H2O where in R is an organic templating agent; 'a' has preferably a value of from 0.20 to 2.0 and more preferably about 0.8 to 1.2; 'b' has a value between 10 to 40. In the synthesis method of the present invention, an aqueous reaction mixture is formed by combining the reactive aluminium and phosphorous sources and thereafter combining the mixture with the template followed by silicon source. More specifically the synthesis methodncomprises;• " a) preparing an aqueous reaction containing aluminium isopropoxide and phosphoric acid, and thereafter combining the resulting mixture with an organic templating agent followed by a silicon oxide source to form the complete reaction mixture. b) adjusting the pH of the reaction mixture at the start of the reaction to about 6.5 to 8.0. c) heating the reaction mixture to a temperature in the range of from 160°C to 240 °C and (preferably from! 17t)°C to 220°C (until crystals are formed usually _- ^- .. from 30 minutes to 10 hours and preferably 45 minutes to 5 h. d) recovering the crystalline silicoaluminophosphate by the known methods of filtration and washing. The crystallization is conducted under hydrothermal conditions in an autoclave at autogenous pressure with or without stirring. Following the crystallization of the SAPO-11 material, the reaction mixture containing the same is filtered and the recovered crystals are washed for example with water and then dried such as by heating at from 25°C to 150°C at atmospheric pressure.. The SAPO-11 synthesized by the present method is subjected to thermal treatment to remove the organic templating agent. This thermal treatment is generally performed by heating at a temperature of 300°C to 1000°C for at least 1 minute and generally no longer than 20h. The thermally treated product is particularly useful in the catalysis of certain hydrocarbon conversion reactions. The improved process of this invention will now be illustrated by examples which are not to be construed as limiting the invention as described in this specification including the attached claims. Example 1 The prior art (U.S. Pat. 4, 440, 871) method of preparation of the crystalline SAPO-11 is described in this example. A reaction mixture was prepared by combining 23.1 g of aluminium isopropoxide and 41.2 gram of water to which was added 12.8 g of 85 wt% orthophosphoric acid (H3PO4) and the mixture stirred well . To this was added 2.2 g of silica sol (30 wt% Si02; 70 wt% H20) and then, after stirring , 5.7g of di-n-propylamine (Pr2NH) was added to the above mixture. The final mixture was stirred until homogeneous. The composition of the final reaction mixture in the molar oxide ratio was: (Formula Removed)The reaction mixture was sealed in a stainless steel autoclave and heated in an oven at 200°C at autogenous pressure for 24h. The solid reaction product was recovered by centrifugation, washed with water and dried in air at room temperature. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be: (Formula Removed)The as-synthesized composition had an X-ray powder diffraction pattern similar to that reported in U.S. Pat. 4, 440,871. Example 2 The prior art (U.S. Pat. 4, 440, 871) method for preparation of the crystalline SAPO-11 but with a larger silica content is described in this example. A reaction mixture was prepared by combining 23.1 g of aluminium isopropoxide and 41.2 g of water to which was added 12.8 g of 85 wt% orthophosphoric acid (H3PO4) and the mixture stirred well. To this was added 3.3 g of silica sol (30 wt% Si02; 70 wt% H20) and then, after stirring , 5.7g of di-n-propylamine (Pr2NH) was added to the above mixture. The final mixture was stirred until homogeneous. The composition of the final reaction mixture in the molar oxide ratio was: (Formula Removed)The reaction mixture was sealed in a stainless steel autoclave and heated in an oven at 200°C at autogenous pressure for 24h. The solid reaction product was recovered by centrifugation, washed with water and dried in air at room temperature. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be : (Formula Removed)The as-synthesized composition had an X-ray powder diffraction pattern similar to that reported in U.S. Pat. 4, 440,871. Example 3 This example illustrates the improved process of the present invention for preparing SAPO-11 rapidly by controlling the heating rate of the reaction mixture. 23.1g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.5 g of dipropylamine followed by 2.2 g of silica sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was: (Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. up_to_200°C. The temperature was maitained at 200°C for 1 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be: (Formula Removed)Example 4 This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 3 but with a higher silica content. 23.1g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.5 g of dipropylamine followed by 3.3 g of silica sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was: 1.5 Pr2NH : 0.3 Si02: 1.0 AI2O3 : 1.1 P205: 40 H20 The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 1 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be: (Formula Removed)Example 5 This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 3 but with a longer crystallization time. 23.1g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.5 g of dipropylamine followed by 3.3 g of silica sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was: (Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be: (Formula Removed)Example 6 This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 5 but with a higher silica input ratio. 23.1g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.5 g of dipropylamine followed by 2.2 g of silica sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was: (Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be: (Formula Removed)Example 7 This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 5 but with catapal B (hydrated alumina) instead of aluminium isopropoxide as the aluminium source. 7.16 g of catapal B was mixed with 32.0 g of water to which was added 12.0 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.0 g of dipropylamine followed by 2.1 g of silica sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was: (Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be: (Formula Removed)Example 8 This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 7 but taking fumed silica instead of silica sol as the source of silicon. 7.16 g of catapal B was mixed with 32.0 g of water to which was added 12.0 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.0 g of dipropylamine followed by 0.63 g of fumed silica and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was: 1.5 (Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be: AI2O3 : (Formula Removed) Example 9 This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 5 but taking fumed silica instead of silica sol as the silica source. 23.1 g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.6 g of dipropylamine followed by 0.68 g of fumed silica and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was: (Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be: (Formula Removed)Example 10 This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 3 but with diisopropylamine as the template instead of dipropylamine. 23.1g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.5 g of diisopropylamine (iPr2NH) followed by 3.3 g of silica sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was: (Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be: (Formula Removed)Example 11 This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 3 but with dibutyiamine as the template instead of dipropylamine. 23.1g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 10.98 g of dibutyiamine (Bu2NH) followed by 3.3 g of silica sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was: (Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be: (Formula Removed)Example 13 This example compares the properties of the samples prepared by the process described in the prior art with the samples prepared according to the process of the present invention. Calcined samples of the SAPO-11 material made according to the examples (1-6) were impregnated with an aqueous solution of Pt(NH3)4CI6 by wet impregnation method to get 0.5% Pt loading on dry basis. The impregnation was carried out by adding 4.35 ml of a solution containing 0.0303 g of Pt(NH3)4CI6 to 5.0 g of the calcined SAPO-11, mixing well and evaporating to dryness slowly at 60° C. The dried sample was further dried at 110°C for 6 h. The samples were further calcined at 400°C in air for 8 h followed by reduction in hydrogen at 380QC for 3 h. The catalytic tests were carried out by passing 1g of n-hexane or n-heptane per hour per gram of the Pt-SAPO-11 samples held in a vertical glass tube of 12mm i.d. maintained at a temperature of 300°C in the presence of H2 as the carrier gas (H2/hydrocarbon mole ratio = 5). At the end of 1h of the passing of the feed, the products were analyzed by a gas chromatogrph using a capillary column (HP1, 50m long) and a FID detector. Table 3: (Table Removed)*I/C = ratio of moles of n-hexane isomerized/ moles of n-hexane cracked. The above table reveals that the samples prepared following the process of the present invention result in SAPO-11 with 1) improved crystallinity 2) higher adsorption capacity as revealed by larger surface area 3) smaller and more uniform particle size distribution and 5) improved catalytic activity. We Claim: 1. An improved process for the preparation of a porous crystalline silicoaluminophosphate molecular sieve characterized by the x-ray diffraction pattern as here in described and a chemical composition in terms of the mole ratio of oxides given by the formula (Formula Removed), wherein R represent organic templating agent, selected from dialkylamine such as herein described, present in the intracrystaline pore system; 'm1 represents moles of 'R' present and has a value between 0.02 to 0.3m , 'n' has a value of from 0.96 to 1.1 and 'q' has a value of from 0.1 to 1.0, which comprises mixing source of an aluminium oxide and oxide of phosphorous an organic template as defined above to the above mixture, followed by mixing a silicon oxide, wherein the ratio of the components varies in the range as described herein, at a pH ranging 6.5 to 8 , heating the said mixture under autogeneous conditions at the rate of 1.5°C/minute up to 160°C. then at the rate of 0.5°C/minute from 160°C to 200°C, holding at this temperature for 30 minutes to 2 hours, cooling the reaction mixture rapidly and separating the crystalline material by filtration, then washing with water and drying the said crystalline material at 120° C followed by calcinations at 500°C to remove the organic template material occluded in its pore to get porous crystalline silicoaluminophosphate molecular sieve , the said process characterized in that heating mixture of aluminum , phosphorus .silicon and organic template at the rate of 1.5°C/minute up to 160°C. then at the rate of 0.5°C/minute from 160°C to 200°C, holding at this temperature for 30 minutes to 2 hours. 2. An improved process as claimed in claim 1 and 2, wherein the source of silicon oxide is selected from silica sol, fumed silica, tetramethylorthosilica, silicic acid or mixtures thereof. 3. An improved process as claimed in the claims 1 and 2, wherein the source of aluminium oxide is selected from pseudoboehmite, aluminium alkoxide preferably aluminium isopropoxide and the source of oxide of phosphorous is orthophosphoric acid. 4. An improved process as claimed in the claims 1,2 and 3, wherein the organic template dialkylamine is selected from dipropyl amine, diisopropylamine and dibutylamine. 5. An improved process for the preparation of porous crystalline silicoaluminophosphate molecular sieve substantially as herein described with reference to the examples.

Full Text

The present invention relates to an improved process for the preparation of porous crystalline silicoaluminophosphate molecular sieves. These molecular sieves are useful as catalysts in the transformation of hydrocarbons, especially in the isomerization of long chain paraffins.
The crystalline aluminosilicate zeolite type molecular sieves are well known in the art and are formed by corner sharing Si02 and A102 tetrahedra and have pore openings of uniform dimensions, have a significant ion exchange capacity and are capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without displacing any atoms which make up the permanent crystal structure.
The most recently synthesized molecular sieves without silica are the crystalline aluminophosphate compositions disclosed in the U.S. Pat. No. 4, 310, 440 (1982). These materials are formed from AI02 and P02 tetrahedra and have electroneutral frameworks as in the case of silica polymorphs. Unlike the silica molecular sieve, silicalite, which is hydrophobic due to the absence of extraframework cations, aluminophosphate molecular sieves are moderately hydrophilic, apparently due to the difference in the electronegativities of aluminium and phosphorous. Their intracrystalline pore volumes and pore diameters are comparable to those known for zeolites and silica molecular sieves.
A novel class of silicon - substituted aluminophosphate molecular sieve was invented by B.M. Lok et al (U.S. Pat. 4, 440, 871) in 1984 which are both crystalline and microporous and exhibit properties which are characteristic of both aluminosilicate zeolite and the aluminophosphates. Members of this novel

class of silicoaluminophosphate materials have a three dimensional microporous crystal framework structure of PO2*, AI02" and Si02 tetrahedral units, and whose essential empirical chemical composition on an anhydrous basis is
(Formula Removed)wherein 'R' represents at least one organic templating agent present in the intracrystalline pore system; 'm' represents the moles of 'R' present per mole of (SixAlyPz)02 and has a value of from 0.1 to 0.3 and x, y and z have a value from 0.01 to 0.20, 0.4 to 0.59 and 0.40 to 0.59 respectively.
Aluminophosphates are neutral in that they do not possess any acidity as the (AI02)" and (PO2)* tetrahedra alternate in a regular fashion in the structure leading to a neutral framework. However, when (Si02) tetrahedra are introduced in the lattice, they can replace a (P02)* tetrahedra leading to an anionic
(negative) charge on the framework which when neutralized by a H* (proton) leads to an acid site just as the replacement of Si4* ions by Al3* ions in zeolites leads to acidity. On the other hand, when both an Al3* and an P5* ion are simultaneously replaced by two Si4* ions, no acidity is generated due to exact charge balancing. It has been found that the method of preparation of the SAPO molecular sieve can influence the manner of incorporation of Si4* ions and the acidity of the material. For example, it has been reported that the synthesis of SAPO-35 in a non-aqueous medium produces a more acidic material through preferential replacement of P5* ions by Si4* ions than when synthesis is carried out in an aqueous medium (Venkatathri and others in J.C.S. Faraday Transactions, volume 93, page 3411, year 1997).
In order to obtain catalytically more useful and efficient materials, it is

necessary therefore to develop synthesis methods to ensure preferential replacement of P5* ions by Si4* in the lattice (or framework). Synthesis in non-aqueous medium though leads to preferential replacement of P5* ions by Si4* ions is not a suitable method as the crystallization is slow taking more than 2 weeks to obtain good crystalline samples. It is therefore important to develope methods of synthesis which can achieve the preferential Si4* incorporation in a much shorter period.
Another important consideration in the use of crystalline microporous materials as catalyst for the transformation of large molecules is their crystallite size. Smaller crystallites essentially are less prone to diffusion effects and will as a result be more catalytically active for the same number of acid sites than larger crystallites as these sites are more accessible in the former due to shorter diffusion path lengths.
The prior art procedure for the synthesis of SAPO-11 as disclosed in the U.S. Pat. 4, 440, 87ijinvolves the reaction of aluminium isopropoxide or hydrated aluminium oxide with phosphoric acid and silica sol or fumed silica in the presence of organic templating compounds such as dipropylamine by autoclaving the reaction mixture directly at an elevated temperature of 150°C to 200°C for 24h to 168h. The major disadvantages of the above prior art method for the synthesis of SAPO-11 is lower Bronsted acidity due to lower incorporation of Si in the framework besides producing large crystallites of non-uniform size.
While carrying out research on the optimization of process conditions for the synthesis of silicoaluminophosphate molecular sieves, we discovered that heating the reaction gel containing the necessary ingradients in a cotrolled manner

reduced the crystallization time besides decreasing the crystallite size and enhancing the incorporation of Si in the aluminophosphate framework. Based on the above studies, we have now developed a heating program to enable the synthesis of SAPO-11 possessing superior catalytic activities than samples synthesized by prior art methods.
The object of the present invention is to provide an improved process for the preparation of silicoaluminophosphate molecular sieve. Another object is to provide a process for rapid preparation of silicoaluminophosphate molecular sieve SAPO-11 in 30 min. to 3 hours. Yet another object is to, get_smaller and more uniform particles which are more acidic and catalytically more active than the conventionally prepared samples.
Accordingly the present invention provides an improved process for the preparation of a porous crystalline silicoaluminophosphate molecular sieve characterized by the x-ray diffraction pattern as here in described and a chemical composition in terms of the mole ratio of oxides given by the formula
(Formula Removed)wherein R represent organic templating agent selected from dialkylamine such as herein described, present in the intracrystalline pore system; 'm' represents moles of 'R' present and has a value between 0.02 to 0.3m 'n1 has a value of from 0.96 to 1.1 and 'q' has a value of from 0.1 to 1.0, which comprises mixing source of an aluminium oxide and oxide of phosphorous , adding organic template as defined above to the above mixture, followed by mixing a silicon
oxide, wherein the ratio of the components varies in the range as described
herein: heating the said mixture under atmospheric conditions at the rate of *

1.5°C/minute up to 160°C , then at the rate of 0.5C/minute from 160°C to 200°C, holding at this temperature for 30 minutes to 2 hours, cooling the reaction mixture
\apidly and separating the crystalline material by filtration, then washingwith wete, and
*
drying the said crystalline material at120°C . followed by calcinations at 500°C to remove
the organic template material occluded in its pore to get porous crystalline
silicoaluminophosphate molecular sieve.
- -
In an embodiment of the present invention the source of silicon oxide may be silica sol, fumed silica, tetramethylorthoslicate, silicic acid or mixtures thereof.
In an another embodiment of the present invention the source of aluminium oxide may be pseudoboehmite, aluminium alkoxide preferably aluminium isopropoxide and the source of oxide of phosphorous may be orthophosphoric acid.
In yet an another embodiment of the present invention the organic template may be a dialkylamine such as dipropyl amine, diisopropylamine and dibutylamine.
Accordingly, the present invention provides an improved process for the preparation of a porous crystalline silicoaluminophsphate molecular sieve. The present invention provides an improved process for the preparation of silicoaluminophosphate molecular sievet SAPO-11 , wherein, the reaction gel formed by combining the reactive aluminium and phosphorous sources followed by the organic template and the silicon source was subjected to programmed heating under hydrothermal conditions in an autoclave at the rate of 1 .5°C per minute from room temperature to 160°C, at the rate of 0.5°C per minute up to
(Formula Removed)200°C and holding the gel at 200°C for 30 min. to 3 hours prior to cooling rapidly by immersing in cold water. The contents are filtered to separate the crystalline solid which is subsequently washed thoroughly and dried at 120°C and finally calcined in air at 550°C. The SAPO synthesized by the above improved process^ is made up of smaller and more uniform particles besides incorporating more
silicon ions in the framework. As a result of larger incorporation of silica, the
_-•
material is also more acidic and catalytically more active.
The silicoaluminophosphate of the present invention exhibits a larger acidity and greater catalytic activity. The acidity of the catalyst is usually determined by comparing the amount of an adsorbed basic compound such as pyridine retained by it even after heating to an elevated temperature. The silicoaluminophosphate of type 11 (SAPO-11) synthesized by the process of the present invention possessed a larger acidity than the material synthesized by the prior art method of U.S. Pat. 4, 440, 871. For example the SAPO-11 material synthesized by the process of the present invention retained 76 micromoles of pyridine per gram while the SAPO-11 synthesized by the prior art method retained only 59 micromole per gram beyond 300°C for a normalized silica content of 0.05 moles in the two samples. This also suggests that there is a greater substitution of P5* ions by Si4* ions in the SAPO-11 and SAPO-31 prepared by the process of the present invention than that synthesized by the prior art method.
The SAPO-11 silicoaluminophosphate synthesized by the process of the present invention possesses a crystalline structure, the X-ray powder diffraction pattern of the as-synthesized form showing the characteristic peaks listed in Table 1.
Table 1: X-ray diffraction pattern of the silicoaluminophosphate (SAPO-11)

(Table Removed)VS = Very strong; S = Strong; MS = Medium Strong; W = Weak; VW = Very Weak; Sh = Shoulder
After calcination in air at 550°C for 8 hours, the SAPO-11 silicoaluminophosphate shows the following characteristic lines in the X-ray diffraction pattern.
Table 2 : X-ray diffraction pattern of calcined silicoaluminophosphate (SAPO-11)

(Table Removed)VS = Very strong; S = Strong; MS = Medium Strong; W = Weak; VW = Very Weak; Sh = Shoulder
The SAPO-11 silicoaluminophosphates in the as synthesized form has a composition in terms of molar oxide ratio on an anhydrous basis expressed by the formula:
mR : AI203 : nP2O5 : qSi02
wherein R represents at least one organic templating agent present in the intracrystalline pore system; 'm' represents the moles of 'R' present and has a value such that there are 0.02 to 0.3 moles of 'R1 per mole of alumina; 'n' has a value of from 0.9 to 1.2 and 'q1 has a value of from 0.1 to 1.0. The organic templating agent R is generally an organic secondary amine such as R1(R2)NH, wherein R1 and R2 may be same or different and are alkyl groups with carbon numbers between 2 and 4, the sum of carbon numbers in R1 and R2 being between 5 to 8.
In synthesizing the silicoaluminophosphate composition of the present invention, it is preferred that the reaction mixture be essentially free of alkali metal cations, and accordingly the preferred reaction mixture composition expressed in terms of mole ratio of oxides is as follows:
aR : AI203 : 0.9-1.2 P2O5 : 0.1-1.0 SiO2 : b H2O
where in R is an organic templating agent; 'a' has preferably a value of from 0.20 to 2.0 and more preferably about 0.8 to 1.2; 'b' has a value between 10 to 40.
In the synthesis method of the present invention, an aqueous reaction mixture is formed by combining the reactive aluminium and phosphorous sources and thereafter combining the mixture with the template followed by silicon source. More specifically the synthesis methodncomprises;• "
a) preparing an aqueous reaction containing aluminium
isopropoxide and phosphoric acid, and thereafter combining the resulting mixture
with an organic templating agent followed by a silicon oxide source to form the
complete reaction mixture.
b) adjusting the pH of the reaction mixture at the start of the reaction to
about 6.5 to 8.0.
c) heating the reaction mixture to a temperature in the range of from 160°C
to 240 °C and (preferably from! 17t)°C to 220°C (until crystals are formed usually
_- ^- ..
from 30 minutes to 10 hours and preferably 45 minutes to 5 h.
d) recovering the crystalline silicoaluminophosphate by the known methods of filtration and washing.
The crystallization is conducted under hydrothermal conditions in an autoclave at autogenous pressure with or without stirring. Following the crystallization of the SAPO-11 material, the reaction mixture containing the same is filtered and the recovered crystals are washed for example with water and then dried such as by heating at from 25°C to 150°C at atmospheric pressure..
The SAPO-11 synthesized by the present method is subjected to thermal treatment to remove the organic templating agent. This thermal treatment is generally performed by heating at a temperature of 300°C to 1000°C for at least 1 minute and generally no longer than 20h. The thermally treated product is particularly useful in the catalysis of certain hydrocarbon conversion reactions.
The improved process of this invention will now be illustrated by examples which are not to be construed as limiting the invention as described in this specification including the attached claims.
Example 1
The prior art (U.S. Pat. 4, 440, 871) method of preparation of the crystalline SAPO-11 is described in this example. A reaction mixture was prepared by combining 23.1 g of aluminium isopropoxide and 41.2 gram of water to which was added 12.8 g of 85 wt% orthophosphoric acid (H3PO4) and the mixture stirred well . To this was added 2.2 g of silica sol (30 wt% Si02; 70 wt% H20) and then, after stirring , 5.7g of di-n-propylamine (Pr2NH) was added to the above mixture. The final mixture was stirred until homogeneous. The composition of the final reaction mixture in the molar oxide ratio was:
(Formula Removed)The reaction mixture was sealed in a stainless steel autoclave and heated in
an oven at 200°C at autogenous pressure for 24h. The solid reaction product was recovered by centrifugation, washed with water and dried in air at room temperature. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be:
(Formula Removed)The as-synthesized composition had an X-ray powder diffraction pattern similar to that reported in U.S. Pat. 4, 440,871.
Example 2
The prior art (U.S. Pat. 4, 440, 871) method for preparation of the crystalline SAPO-11 but with a larger silica content is described in this example. A reaction mixture was prepared by combining 23.1 g of aluminium isopropoxide and 41.2 g of water to which was added 12.8 g of 85 wt% orthophosphoric acid (H3PO4) and the mixture stirred well. To this was added 3.3 g of silica sol (30 wt% Si02; 70 wt% H20) and then, after stirring , 5.7g of di-n-propylamine (Pr2NH) was added to the above mixture. The final mixture was stirred until homogeneous. The composition of the final reaction mixture in the molar oxide ratio was:
(Formula Removed)The reaction mixture was sealed in a stainless steel autoclave and heated in an oven at 200°C at autogenous pressure for 24h. The solid reaction product was recovered by centrifugation, washed with water and dried in air at room temperature. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be :
(Formula Removed)The as-synthesized composition had an X-ray powder diffraction pattern
similar to that reported in U.S. Pat. 4, 440,871.
Example 3
This example illustrates the improved process of the present invention for preparing SAPO-11 rapidly by controlling the heating rate of the reaction mixture. 23.1g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.5 g of dipropylamine followed by 2.2 g of silica sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was:
(Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. up_to_200°C. The temperature was maitained at 200°C for 1 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be:
(Formula Removed)Example 4
This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 3 but with a higher silica content. 23.1g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.5 g of dipropylamine followed by 3.3 g of silica
sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was:
1.5 Pr2NH : 0.3 Si02: 1.0 AI2O3 : 1.1 P205: 40 H20 The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 1 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be:
(Formula Removed)Example 5
This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 3 but with a longer crystallization time. 23.1g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.5 g of dipropylamine followed by 3.3 g of silica sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was:
(Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition
of the solid material in terms of the mole ratio of oxides was found to be:
(Formula Removed)Example 6
This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 5 but with a higher silica input ratio. 23.1g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.5 g of dipropylamine followed by 2.2 g of silica sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was:
(Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be:
(Formula Removed)Example 7
This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 5 but with catapal B (hydrated alumina) instead of aluminium isopropoxide as the aluminium source. 7.16 g of catapal B was mixed with 32.0 g of water to which was added 12.0 g of

85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.0 g of dipropylamine followed by 2.1 g of silica sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was:
(Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be:
(Formula Removed)Example 8
This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 7 but taking fumed silica instead of silica sol as the source of silicon. 7.16 g of catapal B was mixed with 32.0 g of water to which was added 12.0 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.0 g of dipropylamine followed by 0.63 g of fumed silica and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was: 1.5 (Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was
immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be: AI2O3 : (Formula Removed)
Example 9
This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 5 but taking fumed silica instead of silica sol as the silica source. 23.1 g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.6 g of dipropylamine followed by 0.68 g of fumed silica and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was:
(Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be:
(Formula Removed)Example 10
This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 3 but with
diisopropylamine as the template instead of dipropylamine. 23.1g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 8.5 g of diisopropylamine (iPr2NH) followed by 3.3 g of silica sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was:
(Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be:
(Formula Removed)Example 11
This example illustrates the improved process of the present invention for preparing SAPO-11 similar to that described in Example 3 but with dibutyiamine as the template instead of dipropylamine. 23.1g of aluminium isopropoxide was mixed with 33.0 g of water to which was added 14.1 g of 85 wt% orthophosphoric acid and the mixture was stirred well. To this was added 10.98 g of dibutyiamine (Bu2NH) followed by 3.3 g of silica sol and the final mixture was stirred until homogeneous. The composition of the final reaction mixture in terms of the molar oxide ratio was:
(Formula Removed)The mixture was sealed in an autoclave and heated at the rate of 1.5 °C/min. upto 160°C and then at the rate of 0.5°C/min. upto 200°C. The temperature was maitained at 200°C for 2 h. Then the autoclave was immediately cooled and the product was filtered washed with water, dried overnight at 120°C and calcined in air for 8h at 550°C. The chemical composition of the solid material in terms of the mole ratio of oxides was found to be:
(Formula Removed)Example 13
This example compares the properties of the samples prepared by the process described in the prior art with the samples prepared according to the process of the present invention. Calcined samples of the SAPO-11 material made according to the examples (1-6) were impregnated with an aqueous solution of Pt(NH3)4CI6 by wet impregnation method to get 0.5% Pt loading on dry basis. The impregnation was carried out by adding 4.35 ml of a solution containing 0.0303 g of Pt(NH3)4CI6 to 5.0 g of the calcined SAPO-11, mixing well and evaporating to dryness slowly at 60° C. The dried sample was further dried at 110°C for 6 h. The samples were further calcined at 400°C in air for 8 h followed by reduction in hydrogen at 380QC for 3 h. The catalytic tests were carried out by passing 1g of n-hexane or n-heptane per hour per gram of the Pt-SAPO-11 samples held in a vertical glass tube of 12mm i.d. maintained at a temperature of 300°C in the presence of H2 as the carrier gas (H2/hydrocarbon mole ratio = 5). At the end of 1h of the passing of the feed, the products were analyzed by a gas chromatogrph using a capillary column (HP1, 50m long) and a FID detector.
Table 3:

(Table Removed)*I/C = ratio of moles of n-hexane isomerized/ moles of n-hexane cracked.
The above table reveals that the samples prepared following the process of the present invention result in SAPO-11 with 1) improved crystallinity 2) higher adsorption capacity as revealed by larger surface area 3) smaller and more uniform particle size distribution and 5) improved catalytic activity.

We Claim:
1. An improved process for the preparation of a porous crystalline silicoaluminophosphate molecular sieve characterized by the x-ray diffraction pattern as here in described and a chemical composition in terms of the mole ratio of oxides given by the formula
(Formula Removed),
wherein R represent organic templating agent, selected from dialkylamine such as herein described, present in the intracrystaline pore system; 'm1 represents moles of 'R' present and has a value between 0.02 to 0.3m , 'n' has a value of from 0.96 to 1.1 and 'q' has a value of from 0.1 to 1.0, which comprises mixing source of an aluminium oxide and oxide of phosphorous an organic template as defined above to the above mixture, followed by mixing a silicon oxide, wherein the ratio of the components varies in the range as described herein, at a pH ranging 6.5 to 8 , heating the said mixture under autogeneous conditions at the rate of 1.5°C/minute up to 160°C. then at the rate of 0.5°C/minute from 160°C to 200°C, holding at this temperature for 30 minutes to 2 hours, cooling the reaction mixture rapidly and separating the crystalline material by filtration, then washing with water and drying the said crystalline material at 120° C followed by calcinations at 500°C to remove the organic template material occluded in its pore to get porous crystalline silicoaluminophosphate molecular sieve , the said process characterized in that heating mixture of aluminum , phosphorus .silicon and organic template at the rate of 1.5°C/minute up to 160°C.
then at the rate of 0.5°C/minute from 160°C to 200°C, holding at this temperature for 30 minutes to 2 hours.
2. An improved process as claimed in claim 1 and 2, wherein the
source of silicon oxide is selected from silica sol, fumed silica,
tetramethylorthosilica, silicic acid or mixtures thereof.
3. An improved process as claimed in the claims 1 and 2, wherein the
source of aluminium oxide is selected from pseudoboehmite,
aluminium alkoxide preferably aluminium isopropoxide and the
source of oxide of phosphorous is orthophosphoric acid.
4. An improved process as claimed in the claims 1,2 and 3, wherein the
organic template dialkylamine is selected from dipropyl amine,
diisopropylamine and dibutylamine.
5. An improved process for the preparation of porous crystalline
silicoaluminophosphate molecular sieve substantially as herein
described with reference to the examples.

Documents:

574-del-1999-abstract.pdf

574-del-1999-claims.pdf

574-del-1999-correspondence-others.pdf

574-del-1999-correspondence-po.pdf

574-del-1999-description (complete).pdf

574-del-1999-form-1.pdf

574-del-1999-form-19.pdf

574-del-1999-form-2.pdf

574-del-1999-form-3.pdf

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Patent Number

215579

Indian Patent Application Number

574/DEL/1999

PG Journal Number

11/2008

Publication Date

14-Mar-2008

Grant Date

27-Feb-2008

Date of Filing

15-Apr-1999

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	ANIL KUMAR SINHA	NATIONAL CHEMICAL LABORATORY, PUNE 411 008, INDIA.
2	SUBRAMANIAN SIVASANKER	NATIONAL CHEMICAL LABORATORY, PUNE 411 008, INDIA.

PCT International Classification Number

B01J 27/182

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA