Title of Invention

"A PROCESS FOR THE PREPARATION OF A NOVEL CHROMIUM CONTAINING MOLECULAR SIEVES"

Abstract

A process for the preparation of chromium containing molecular sieves. A novel catalyst having compositions of the chromium and silica has been developed wherein the molar compositions of the chromium and silica in terms of ratios of oxides may be as H2O/SiO2 = 5-100,, H2O/Cr2O3 = 1000-2000, H2O/(Ri)2O= 125-550, H2O/R2)2O = 40-550. Where R, may be surfactant such as cetyl teimethyl ammonium chloride / hydroxide (CTMACI/OH) and R2 may be tetramethyl ammonium hydroxide (TMAOH). The novel chromosilicate catalyst composite material prepared by the process of this invention has molecular sieve preparation analogous to other known molecular sieve stannosilicate is characterized by its adsorption capacity for molecules of various sizes

Full Text

This invention relates to a process for the preparation of a. chromium-containing molecular sieve. More particularly, the invention relates to the preparation of crystalline, mesoporous chromium silicate molecular sieve having chromium as a part of the mesoporous structure belonging to M-41S family, used as a sorbent or a catalyst component. An amorphous and paracrystalline materials (porous inorganic solids) have been used for many years in industrial applications. Typical examples of these materials are the amorphous silicas commonly used in the catalysts formulations and the paracrystalline transitional aluminas used as solid acid catalysts and petroleum reforming catalyst supports. The size of the pores in amorphous and paracrystalline materials fall into a regime called the mesoporous range (1.3 to 20 nm). Recently, it was observed that the most regular preparations of the preferred material (silicate analogs of MCM-41) of the invention gives a hexagonal array uniform pores, the x-ray diffraction pattern of which shows a few distinct maxima in the extreme low angle region. The x-ray diffraction pattern, however, is not always a sufficient indicator of the presence of these materials, as the degree of regularity in the microstructure and the extent of repetition of the structure within individual particles affect the number of peaks observed. Indeed, preparations with only one distinct peak in the low angle region of the x-ray diffraction pattern have been found to contain substantial amounts of the material of the invention. In this preferred arrangement, the porosity of the crystalline material of the invention is provided by a hexagonal arrangement of pore channels, a property that can be readily observed by electron diffraction and transmission electron microscopy. In the prior art, chromium substituted zeolites have been prepared. For example, US Patent Appl. No. 133, 372 (Dec. 1987) and European Patent application no. 321,177 (Dec. 1988) (both to UOP, Inc) teach treatment of a parent aluminosilicate zeolite with ammonium fluoride salt of tin or chromium. Extraction of aluminum from the framework and insertion of Cr or Sn by secondary synthesis process are described in these patents. Various attempts have been made to substitute chromium into a zeolite framework via primary synthesis methods but none have been truly successful so far. Attempts to synthesize zeolites particularly of the pentasil family (ZSM-5 like) with a number of ions other than aluminum have been made. Dwyer et al. in US Patent No. 3,941,871 describe the presence of Sn in place of or as a part of the organic template in a ZSM-5 type of a structure but not as a part of the ZSM-5 framework structure itself. In US Patent No. 4, 329, 328 (McAnespic et al.) the synthesis of stannosilicate is suggested but no example of such a synthesis is given nor any properties of such materials are suggested. It was presumed that tin is not a part of the zeolite framework in primary synthesis products because at high pH conditions required for such synthesis, it is probably that tin or such metals precipitate as oxides and/or hydrous oxides much before their crystallization linking with Si-O species to form microporous material wherein tin or such metals become a part of the zeolite framework. The precipitation of metals such as tin, iron, chromium, etc., in alkaline solution can be prevented by complexing it with oxo-anions like the oxalates, citrates, EDTA and tartarates. It is feasible to prevent the polymerization and precipitation of these ions (as hydroxides, oxo-hydroxides or oxides) in basic media, provided these ions are suitably complexed with appropriate ligands. This factor is important in the primary synthesis procedure which is carried out in aqueous, alkaline medium under hydrothermal conditions. It is crucial to prevent the precipitation of the oxo/hydroxide complexed under such conditions and facilitate the incorporation of ions such as Cr possibly in the framework of the zeolite/molecular sieve. Mesoporous molecular sieves (MCM-41) reported in the prior-art were prepared using aluminium (R.B. Borade and A. Clearfield, Catal. Lett., 1995, 31, 267), iron (Zhong Yuan et al., J. Chem. Commun., 1995, 973), titanium (A. Corma et al., j. Chem. Soc. Chem.. Commun., 1994, 147.) and vanadium (K.M. Redy et al, J. Chem. Soc. Chem. Commun., 1994, 1059) and tin (Japan Kr. Das et al., J. Chem. Soc. Chem. Commun., 1995, 2495) ions. The object of the present invention therefore is to provide a process for the preparation of chromium containing mesoporous molecular sieve which prevents the precipitation of the oxo/hydroxide complexes under such conditions and facilitate the incorporation of ions such as Cr possibly in the framework of the zeolite. Accordingly, the present invention provides a process for the preparation of a process for the preparation of a novel chromium containing molecular sieve having a chemical composition in terms of mole ratios of oxides by the formula: (Formula Removed) wherein x and y are between 0.01 to 0.3, w is between 0.003 to 0.04, z is between 0.003 to 0.4 ,v is between 5 to 80, R! is an organic surfactant selected from a group consisting cetyl trimethyl ammonium hydroxide/chloride, cetyl trimethyl ammonium bromide, dodecyl trimethyl ammonium hydroxide/chloride, cetyl trimetyl ammonium bromide, dodecyl trimethyl ammonium hydroxide, meristyl ammonium hydroxide, preferably cetyl trimethyl ammonium chloride/hydroxide and R2 is quaternary ammonium compound selected from tetramethyl ammonium hydroxide, tetrabutyl ammonium hydroxide, tetraethyl ammonium hydroxide, preferably tetramethyl ammonium hydroxide, said process comprises (i) mixing aqueous solutions of sources of chromium, silicon such as herein described, and a mixture of R, and R2 to form a gel at pH ranging between 10.8 to 11.6, wherein mole ratio of chromium, silicon, R1 and R2 in gel composition is 1.0 SiO2: 0.089 R^O : 0.155 R2O : XCr2O3: 40 H2O where x is in the range of 0.003 - 0.04, (ii) heating the obtained gel of step (i) at atmospheric pressure, at temperature in the range 80°-140°C, for a period ranging between 5-12 days, (iii) separating the composite material formed at step (ii) by conventional methods, (iv) washing and drying the composite material followed by calcining the crystalline composite material at 500°-600°C for 2-8 hours in inert atmosphere for 3-10 hours in air, (v) cooling to room temperature and extracting the calcined material with dilute alkali acetate solution such as herein described, followed by calcining at a temperature ranging between 450° to 550°C in air for 4 to 6 hours to obtain chromium containing molecular sieve characterized by the x-ray diffraction pattern shown in Table 1. Table 1: X-ray diffraction pattern of cromo-silicate (Cr-MCM-41) (Table Removed) And infra red spectrum as shown in table 2, Table 2 : Framework infra red vibration frequencies of the chromo-silicate (Cr-MCM- 41) (Table Removed) VS = very strong ; S = strong ; MS = medium strong ; W = weak ; VW = Very weak. In an embodiment of the present invention the template RI may be an organic surfactant selected from cetyl trimethyl ammonium chloride/hydroxide, cetyl trimethyl ammonium bromide, dodecyl trimethyl ammonium hydroxide, meristyl ammonium hydroxide. A preferred source is cetyl trimethyl ammonium chloride/hydroxide. In an another embodiment of the present invention the template R2 is selected from tetramethyl ammonium hydroxide, tetrabutyl ammonium hydroxide, tetraethyl ammonium hydroxide. A preferred source is tetramethyl ammonium hydroxide. In still another embodiment of the present invention the source of chromium may be chromium chloride hexahydrate (CrCl3.6 H2O) or chromium nitrate nonahydrate (Cr(NO3)3.9H2O). A preferred source of chromium is chromium chloride hexahydrate (CrCl3.6 H2O). In still another embodiment the molar compositions of the chromium and silica in terms of ratios of oxides may be as H2O/ SiO2 = 5-100, H2O/ Cr2O3 = 1000-2000, H2O/(R,)2O = 125-550, H2O/(R2)2O = 40-550 where R, may be surfactant such as cetyl teimethyl ammonium chloride/hydroxide (CTMAC1/OH)) and R2 may be tetramethyl ammonium hydroxide (TMAOH). According to a preferable feature of the present invention the starting gel has a composition in terms of mole ratios as follows : SiO2 : 0.089 (CTMA)2O : 0.155 (TMA)2O : x Cr2O3 : 40 H2O where 0.003 In yet another embodiment the aqueous solutions of acetates of sodium, potassium or ammonium can be used for extraction of nonframework chromium ions. A preferred source is an aqueous solution of ammonium acetate. The novel chromosilicate catalyst composite material prepared by the process of this invention has molecular sieve preparation analogous to other known molecular sieve stannosilicate may be characterized by its adsorption capacity for molecules of various sizes. Typical results are shown in Table 3. Table 3 : Sorption capacity of Cr-MCM-41 samples (Table Removed) "Gravimetric adsorption (Mcbain Baker Balance) at p/p0 = 0.5 and at 298K. hThe numbers in the parenthesis indicate the Si/Cr molar ratio in the gel. The uptake of water, n-hexane and benzene indicate that the chromosilicate has significantly hydrophilic voids. The process of the present invention is described herein below with examples which are illustrative only and should not be construed to limit the scope of the present invention in any manner. Example 1 This example illustrates the preparation of silicalite MCM-41 using the hydrothermal gel with the following molar composition : SiO2 : 0 086 (NH4)2O : 0.089 (CTMA)2O : 0.155 (TMA)2O : 40 H2O where (CTMA)2O and (TMA)2O are organic templates. 3.6 g ammonium hydroxide (25% solution) diluted with water (25 g) was added to 33.4 g solution of cetyl trimethyl ammonium chloride (25% solution, Aldrich) with stirring. To this mixture, 4.16 g tetramethyl ammonium hydroxide, TMAOH.5H2O (99%, Aldrich) dissolved in 25 g water was added followed by the addition of 27.2 g tetramethyl ammonium silicate (10% SiO2, SACHEM Inc.). This thick gel was allowed to stir for 20 minutes. 6.2 g fumed silica (99% SiO2, Sigma) was added slowly to the above gel under stirring and the mixture was stirred for 1 hour. The pH of the mixture was 11.5. The gel was then transferred to a stainless steel autoclave and heated in an air oven at 383 K for 4 days to complete the crystallization. After the crystallization, the product was filtered, washed with deionized water, dried at 373K for 5 hours. The product was then calcined at 823K for 1 hour in nitrogen, followed by 6 hours in air. The x-ray diffraction pattern of the calcined product of this example is given in Table 1. Example 2 This example illustrates the preparation of aluminium containing MCM-41 using the hydrothermal gel with the following molar composition : SiO2 : x A12O3 : y Na20 : 0.089 (CTMA)2O : 0.155 (TMA)2O : 40 H2O where x and y 0.04 (CTMA)2O and (TMA)2O are organic templates 0.74 g sodium aluminate dissolved in water (20 g) was added to 33.4 g of 24.6% solution of cetyl trimethyl ammonium chloride/hydroxide [prepared by partial exchange of CTMAC1 (Aldrich) over Amberlite IRA-400(OH) (Aldrich) ion-exchange resin] with stirring. 0.08 g NaOH pellet dissolved in 10 g of water and added to the above mixture. To this mixture, 4.16 g tetramethyl ammonium hydroxide, TMAOH.5H2O (99%), Aldrich) dissolved in 20 g water was added followed by the addition of 34.6 g tetramethyl ammonium silicate (10% SiO2, SACHEM Inc.). This thick gel was allowed to stir for 20 minutes. 6.2 g fumed silica (99% SiO2, Sigma) was added slowly to the above gel under stirring and the mixture was stirred for 1 hour. The pH of the mixture was 11.5. The gel was then transferred to a stainless steel autoclave and heated in an air oven at 383K for 5 days to complete the crystallization. After the crystallization, the product was filtered, washed with deionized water, dried at 373K for 5 hours. The product was then calcined at 823K for 1 hour in nitrogen, followed by 6 hours in air. The x-ray diffraction pattern of the calcined product of this example is given in Table 1. Example 3 This example illustrates the preparation of Cr-MCM-41 using the hydrothermal gel with the following molar composition : Si02 : x Cr203 : y Na2O : 0.089 (CTMA)2O : 0.155 (TMA)2O : 26.1 H2O where x and y (CTMA)2O and (TMA)2O are organic templates 4.16 g tetramethyl ammonium hydroxide, TMAOH.5H2O (99%), Aldrich) was added to 33.4 g of 24.6% solution of cetyl trimethyl ammonium chloride/hydroxide [prepared by partial exchange of CTMAC1 (Aldrich) over Amberlite IRA-400(OH) (Aldrich) ion-exchange resin] with stirring. 0.08 g NaOH pellet dissolved in 10 g of water and added to the above mixture of templates. 6.2 g Hi Silica (99% SiO2, Sigma) was added slowly to the above mixture followed by the addition of 27.2 g tetramethyl ammonium silicate (10% SiO2, SACHEM Inc.). Finally, a solution of 1.6 g CrCl3.6H2O (99%, Loba Chemie, India) dissolved in 5 g water was added to the above thick gel. The resultant homogenous mixture was then stirred for 1 hour. The pH of the mixture was 11.5. The gel was then transferred to a stainless steel autoclave and heated in an air oven at 383K for 5 days to complete the crystallization. After the crystallization, the light green product was filtered, washed with deionized water, dried at 373K for 5 hours. The product was then calcined at 823K for 1 hour in nitrogen, followed by 6 hours in air. The x-ray diffraction pattern of the calcined product of this example is given in Table 1. The colour of the sample was greenish after calcination. The yellow colour of the sample was leached out into the filtrate and the colour of the sample remained green. The sample was again calcined at 813K in air for 4 hours. Example 4 This example illustrates the preparation of Cr-MCM-41 using Chromium nitrate nonahydrate (Cr(NO3)3.9H2O) the source of chromium instead of CrCl3.6H2O in the hydrothermal gel with the following molar composition : SiO2 : x Cr2O3 : y Na20 : 0.089 (CTMA)2O : 0.155 (TMA)2O : 26.1 H2O where x and y (CTMA)2O and (TMA)2O are organic templates 4.16 g tetramethyl ammonium hydroxide, TMAOH.5H2O (99%), Aldrich) was added to 33.4 g of 24.6% solution of cetyl trimethyl ammonium chloride/hydroxide [prepared by partial exchange of CTMAC1 (Aldrich) over Amberlite IRA-400(OH) (Aldrich) ion-exchange resin] with stirring. 0.08 g NaOH pellet dissolved in 10 g of water and added to the above mixture of templates. 6.2 g Hi Silica (99% SiO2, Sigma) was added slowly to the above mixture followed by the addition of 27.2 g tetramethyl ammonium silicate (10% SiO2, SACHEM Inc.). Finally, a solution of 2.36 g Cr(NO3)3.9H2O (99%, Loba Chemie) dissolved in 5 g water was added to the above thick gel. The resultant homogeneous mixture was then stirred for 1 hour. The pH of the mixture was 11.5. The gel was then transferred to a stainless steel autoclave and heated in an air oven at 383K for 5 days to complete the crystallization. After the crystallization, the light green product was filtered, washed with deionized water, dried at 373K for 5 hours. The product was then calcined at 823K for 1 hour in nitrogen, followed by 6 hours in air. The x-ray diffraction pattern of the calcined product of this example is given in Table 1. The colour of the sample was greenish after calcination. The yellow colour of the sample was leached out into the filtrate and the colour of the sample remained green. The sample was again calcined at 813K in air for 4 hours. Example 5 This example illustrates the preparation of Cr-Al-MCM-41 using CrCl3.6H2O as the source of Cr and sodium aluminate as the source of aluminium in the hydrothermal gel with the following molar composition : SiO2 : x Cr2O3 : y Na2O : z A12O3 : 0.089 (CTMA)2O : 0.155 (TMA)2O : 26.1 H2O where x y (CTMA)2O and (TMA)2O are organic templates 4.16 g tetramethyl ammonium hydroxide, TMAOH.5H2O (99%), Aldrich) was added to 33.4 g of 24.6% solution of cetyl trimethyl ammonium chloride/hydroxide [prepared by partial exchange of CTMAC1 (Aldrich) over Amberlite IRA-400(OH) (Aldrich) ion-exchange resin] with stirring. 0.44 g NaOH pellet dissolved in 10 g of water and added followed by the addition of 0.246 g sodium aluminate dissolved in 6 g of water to the above mixture of templates. 6.2 g Hi Silica (99% SiO2, Sigma) was added slowly to the above mixture followed by the addition of 27.2 g tetramethyl ammonium silicate (10% SiO2, SACHEM Inc.). Finally, a solution of 1.6 g CrCl3.6H2O (99%, Loba Chemie, India) dissolved in 5 g water was added to the above thick gel. The resultant homogeneous mixture was then stirred for 1 hour. The pH of the mixture was 11.5. The gel was then transferred to a stainless steel autoclave and heated in an air oven at 383K for 5 days to complete the crystallization. After the crystallization, the light green product was filtered, washed with deionized water, dried at 373K for 5 hours. The product was then calcined at 823K for 1 hour in nitrogen, followed by 6 hours in air. The x-ray diffraction pattern of the calcined product of this example is given in Table 1. The colour of the sample was greenish after calcination. The yellow colour of the sample was leached out into the filtrate and the colour of the sample remained green. The sample was again calcined at 813K in air for 4 hours. Example 6 This example illustrates the preparation of Cr--MCM-41 using dodecyl trimethyl ammonium bromide (DTMABr) instead of cetyl trimethyl ammonium chloride/hydroxide in the hydrothermal gel with the following molar composition : SiO2: x Cr2O3 : y Na2O : 0.089 (DTMA)2O : 0.155 (TMA)2O : 26.1 H2O where x 4.16 g tetramethyl ammonium hydroxide, TMAOH.5H2O (99%), Aldrich) was added to 8.06 g of dodecyl trimethyl ammonium bromide(98%, Aldrich) dissolved in 25.0 g water with stirring. 0.32 g NaOH pellet dissolved in 10 g of water and added to the above mixture of templates. 6.2 g Hi Silica (99% SiO2, Sigma) was added slowly to the above mixture followed by the addition of 27.2 g tetramethyl ammonium silicate (10% SiO2, SACHEM Inc.). Finally, a solution of 1.6 g CrCl3.6H2O (99%, Loba Chemie) dissolved in 5 g water was added to the above thick gel. The resultant homogeneous mixture was then stirred for 1 hour. The pH of the mixture was 11.5. The gel was then transferred to a stainless steel autoclave and crystallization was carried out at 383K for 5 days to complete the crystallization. After the crystallization, the light green product was filtered, washed with deionized water, dried at 373K for 5 hours. The product was then calcined at 823K for 1 hour in nitrogen, followed by 6 hours in air. The x-ray diffraction pattern of the calcined product of this example is given in Table 1. The colour of the sample was greenish after calcination. The yellow colour of the sample was leached out into the filtrate and the colour of the sample remained green. The sample was again calcined at 813K in air for 4 hours. We Claim: 1. A process for the preparation of a novel chromium containing molecular sieve having a chemical composition in terms of mole ratios of oxides by the formula: X(Ri)2 O : y(R2)2 O : z Na20 : SiO2: w Cr2O3: v H2O wherein x and y are between 0.01 to 0.3, w is between 0.003 to 0.04, z is between 0.003 to 0.4 ,v is between 5 to 80, R-i is an organic surfactant selected from a group consisting cetyl trimethyl ammonium hydroxide/chloride, cetyl trimethyl ammonium bromide, dodecyl trimethyl ammonium hydroxide/chloride, cetyl trimetyl ammonium bromide, dodecyl trimethyl ammonium hydroxide, meristyl ammonium hydroxide, preferably cetyl trimethyl ammonium chloride/hydroxide and R2 is quaternary ammonium compound selected from tetramethyl ammonium hydroxide, tetrabutyl ammonium hydroxide, tetraethyl ammonium hydroxide, preferably tetramethyl ammonium hydroxide, said process comprises (i) mixing aqueous solutions of sources of chromium, silicon such as herein described, and a mixture of RI and R2 to form a gel at pH ranging between 10.8 to 11.6, wherein mole ratio of chromium, silicon, RI and R2 in gel composition is 1.0 SiO2 : 0.089 RiO : 0.155 R2O : XCr2O3: 40 H2O where x is in the range of 0.003 - 0.04, (ii) heating the obtained gel of step (i) at atmospheric pressure, at temperature in the range 80°-140°C, for a period ranging between 5-12 days, (iii) separating the composite material formed at step (ii) by conventional methods, (iv) washing and drying the composite material followed by calcining the crystalline composite material at 500°-600°C for 2-8 hours in inert atmosphere for 3-10 hours in air, (v) cooling to room temperature and extracting the calcined material with dilute alkali acetate solution such as herein described, followed by calcining at a temperature ranging between 450° to 550°C in air for 4 to 6 hours to obtain chromium containing molecular sieve. 2. A process as claimed in claim 1 wherein the source of silicon is selected from silicon dioxide, silica hydrosol, silica gel, silicic acid, alkoxide of silicon, alkali metal silicate, preferably silicon dioxide and tetramethyl ammonium silicate. 3. A process claimed in claims 1 to 2 wherein the source of chromium is selected from chromium chloride hexahydrate (CrCl3.6H2O) or chromium nitrate nonahydrate (Cr(NO3)3.9H2O), preferably chromium chloride hexahydrate (CrCI3.6H20). 4. A process as claimed in claims 1 to 3 wherein the dilute solutions of alkali acetates used is selected from sodium, potassium or ammonium acetate. 5. A process claimed in claims 1 to 4 wherein the inert gas used is selected from nitrogen, helium and argon. 6. A process for the preparation of a novel chromium containing molecular sieves substantially as herein described with reference to the examples.

Documents:

1194-del-1999-abstract.pdf

1194-del-1999-claims.pdf

1194-del-1999-correspondence-others.pdf

1194-del-1999-correspondence-po.pdf

1194-del-1999-description (complete).pdf

1194-del-1999-form-1.pdf

1194-del-1999-form-19.pdf

1194-del-1999-form-2.pdf

1194-del-1999-form-3.pdf