Title of Invention	A PROCESS FOR THE PREPARATION OF CRYSTALLINE ZINC ALUMINO SILICATE CATALYST USEFUL FOR THE PREPARATION OF LPG AND HIGH OCTANE AROMATICS
Abstract	A process for the preparation of crystalline zinc alumino silicate catalyst useful for the preparation of LPG and high octane aromatics which comprises : (a) mixing water, a source selected from silica , an aluminium source selected from aluminium salts, a zinc source selected from zinc salts and tetrahydral alkyl ammonium cation by conventional methods, (b) heating the said reaction mixture to a temperature ranging from 80°C to 230°C, preferably from 140°C to 210°C, at autogeneous phase and (c) heating the solid content mixture to a temperature atleast 400°C, exchanging/impregnating the above solid obtained in step (c) with metals such as Na. Ca. Sn. Pt and Fe by known methods to obtain crystalline zinc alumino silicate.

Title of Invention

A PROCESS FOR THE PREPARATION OF CRYSTALLINE ZINC ALUMINO SILICATE CATALYST USEFUL FOR THE PREPARATION OF LPG AND HIGH OCTANE AROMATICS

Abstract

A process for the preparation of crystalline zinc alumino silicate catalyst useful for the preparation of LPG and high octane aromatics which comprises : (a) mixing water, a source selected from silica , an aluminium source selected from aluminium salts, a zinc source selected from zinc salts and tetrahydral alkyl ammonium cation by conventional methods, (b) heating the said reaction mixture to a temperature ranging from 80°C to 230°C, preferably from 140°C to 210°C, at autogeneous phase and (c) heating the solid content mixture to a temperature atleast 400°C, exchanging/impregnating the above solid obtained in step (c) with metals such as Na. Ca. Sn. Pt and Fe by known methods to obtain crystalline zinc alumino silicate.

Full Text	The present invention relates to a process for the preparation of crystalline zinc alumino silicate catalyst useful for the preparation of LPG and high octane aromatics. The catalyst material prepared by the process of the present invention is given the name zinc-aluminosilicate or Zn-ZSM-5 molecular sieve catalyst. Hence more specifically the present invention relates to a process for the preparation of a catalyst consisting of Zn-ZSM-5 which is useful for the preparation of LPG and high octane aromatic hydrocarbons such as benzene, toluene, ethyl benzene and xylenes(BTX) from low value, low octane petroleum feed slocks. New gasoline specifications and changing markets have led to large and rapid variations of feed stocks and availablity. The key factor to boost the profitability is to take advantage of these variations and produce high demand, high value products such as LPG, hydrogen and aromatics. Hence, there is a need to develop a versatile process for the preparation of a novel catalyst which will be able to process cheaper, sometimes unwanted and variably available feed stocks to produce LPG and high octane aromatics. Therefore the present invention relates to process for the preparation of a novel catalyst con sisting of Zn-ZSM-5 molecular sieve useful for the conversion of petroleum feed stocks into value added products such as LPG and high octane hydrocarbons. Because of its population, India is in peculiar situation with great demand for LPG, which can not be met by conventional resources such as cracking processes employing naphtha, gas oil and the like. The deficit between demand and production of LPG at the end of 8th plan (1996-97) is expected to be 2.8 million metric tones per annum which is likely to increase to 5.8 million metric tones per annum at the end of 9th plan (2001-02). Similarly, deficit between demand and production of motor gasoline at the end of 9th plan is expected to be 1.5 million metric tonnes per annum. Hence, good amount of foreign exchange has to be spent for meeting the demand of LPG as the demand can not be met by indigenous resources. Natural gas condensate (NGC), aromatic extraction raffinate and light naphtha are considered as some of the few non economically viable feed stocks in the petroleum market today. As these feed stocks being non-reformable by conventional catalytic reforming process; they have been considered only as a fuel for long periods. These feed stocks can be converted in to valuable products like LPG and Benzene, Toluene and Xylenes (BTX aromatics), utilising the shape selective features of medium pore zeolite molecular sieve. The aromatic hydrocarbons can be used as high octane blending feed stocks for the production of high octane gasoline. They are also used as feed stocks for thepreparation of chemical and petrochemical products. Aromatic chemicals constitute about one third of the total organic compounds known to day. They are important chemical precursors for the production of detergents and polymers among others. An article published in the literature [ Ind. Eng. Chem. Process Design Dev. , 25, (1986), 151 3 describes a process proposed by Mobil Research and Development for the preparation of aromatics from variety of feed stocks such as pyrolysis gasoline, unsaturated gases from catalytic cracker, paraffinic naphtha and LPG. The process describes use of purely acidic H-ZSM-5 catalyst. Another report (Hydrocarbon processing, Sep 1989, p-72) descreibes of a process developed jointly by UOP INC and British Petroleum Company, based on gallium doped 2eolite catalyst. In this process LPG was converted into BTX aromatics and the process has been demonstrated in a large scle pilot plant of the British Petroleum's Graigemouth Refinery in Scotland. U.S. Patent 5, 124, 417 dated June 1992 describes the use of Pt-Sn-ZSM-5 Catalyst for the production of mono alkyl aromatics from C8 n-paraffins containing feed stocks. U.S. Patent 5, 026, 938 dated 25 June 1991 describes a process for converting a gaseous feed stocks containing C3-C5 paraffins into aromatic hydrocarbons by contacting the feed with galliosilicate molecular sieve catalyst. Zeolite ZSM-5 is a crystalline alurainosilicate whose preparation was first claimed in 1972 and is described in a U.S. patent 3, 702, 386. The frame work structure is well established and the catalyst is reported to have many catalytic applications. "Silicalite" having a similar zeolite structure constituted by pure crystalline S102, has been descirbed by E,M, Flanigen [Nature 271 (1978), 512]. The highly ordered rigid structure with three dimensional rigid lattice can accomodate MeC-4 in addition to Si04 tetrahedra. Me being for example Al, Fe, Ga, Ti or B. Conventionally, Bensene, Toluene and Xylenes (BTX) aromatics are obtained by catalytic reforming process of naphtha. The catalyst used for this process is Pt/Al2 0s monometallic or Pt-Re/Al2 03 bimetallic catalyst. Although these processes are used all over the world, there are number of limitations in the use of these catalyst for the above mentioned process. These limitations are : i) These catalysts are not effective in promoting aromatlsation of Cs hydrocarbons. Hence, it can not be used for the aromatisation of feed stocks like natural gas condensate (NGC), light naphtha or aromatic extraction raffinate, which contains appreciable amount of n-pentane and iso pentane. ii) These catalysts are also not very effective in promotion of the aromatisation of straight chain paraffins such as n- hexane and n-heptane. Hence, large amount of straight chain paraffins such as n-hexane and n-heptane present in the feed remain unconverted. iii) All catalytic reforming units employing these catalysts require an Organic Chloride additive to provide the proper balance between acid and metal function. The Organic Chloride is broken down during reforming process in to hydrochloric acid, a waste product targeted for stricter regulations. iv) These processes result in the formation of gasoline in the range of 75-95 research octane number and hence require use of tetra ethyl lead to boost the octane number. The use of tetra ethyl lead in gasoline has toxic effects of lead emitted from exhausts and is being banned all over the world including India. The main objective of present invention is to provide a process for the preparation of crystalline zinc alumino silicate catalyst useful for the preparation of LPG and high octane aromatics. The catalyst prepared by the process of present invention can be used for the production of Benzene, Toluene, Xylenes (BTX) aromatics using feed stocks like naturl gas condensate (NGC) and light naphtha, production of LPG carries significance from the Indian point of view as demand for LPG in India is much higher. Zn-ZSM-5 catalyst prepared by the process of the present invention contains Zn, in addition to Al and Si, and possesses MFI structure. Accordingly the present invention provides a process for the preparation of crystalline zinc alumino silicate catalyst useful for the preparation of LPG and high octane aromatics which comprises: (a) mixing water, a source selected from silica / an aluminium source selected from aluminium a salts, a zinc source selected from zinc salts and tetrahydral alkyl ammonium cation by conventional methods, (b) heating the said reaction mixture to a temperature ranging from 80o C to 230 o C, preferably from 140o C to 210 oC, at autogeneous phase and (c) heating the solid content obtained in step (b) to a temperature atleast 4 00 o C, exchanging/impregnating the above solid obtained in step (c) with metals such as Na, Ca, Sn, Pt and Fe by known methods to obtain crystalline zinc alumino silicates. Silica in the form of hydrogels, aerogels, Colloidal suspension or solution of soluble silicate such as sodium silicate can be used as sources of silica. The alumina sources which can be used include aluminium salts (Sulphates, nitrates, chlorides, fluorides and acetate for example), aluminium hydroxide andoxide, aluminates, esters such as tripropyl ester of mono-ortho aluminic acid [Al (OC3H7)3]. As zinc source, zinc salts which are capable of being converted into zinc oxide upon calcination, especially in the presence of oxygen can be used. As an example of such salt zinc nitrate is mentioned. Instead of starting with separate sources of aluminia and silica, sources in which the two oxides are combined can also be used; for example amorphous alumina, silica gel, crystalline alumino silicate, including clays and zeolites. The source of structuring agent used to provide organic cations are preferably tetra alkyl ammonium cations, the alkyl advantageously being Propyl and the like. The acids or acid salts, bases or basic salts possibly added in the reaction mixture in compliment to adjust the PH of the reaction medium to the desired value can be choosen from commonly used acids such as hydrochloric acid (HC1) , nitric acid (HN03), Sulphuric acid (H2SO4), acetic acid (CH3COOH) or acid salts such as sodium hydrogen sulphate (NaHSO4); commonly used bases are such as ammonium hydroxide (NH4OH), Soda (NaOH), Potash (KOH) or commonly used basic salts such as sodium hydrogen carbonate (NaHCO3), or neutral sodium carbonate (Na2C03) sodium acetate (CH3COONa), neutral sodium sulfide (Na2S) or sodium hydrogen sulphide (NaHS). Buffer mixtures such as acetic acid (CH3COOH) sodium acetate (CH3COONa), ammonium hydroxide (NH4OH), ammonium chloride can be used for the purpose. The catalyst prepared by the process of the present invention may contain by weight (a) 0.01 to 10% zinc. (b) 0.5 to 99.99% of a zeolites with an S102/A1203 molar ratio ranging from 15 to 1000; said zeolite molecular sieve having X-ray diffraction pattern shown in Table - 2. (c) 0.01 to 5.0% by weight of metals from the group Na, K, Ca, Pt, Sn and Re. (d) 0.1 to 99.49% of a matrix choosen from the group consisting of alumina, silica, clay, metal oxides and a combination of the compounds mentioned here in above. The catalyst preferably containing 0.05 to 5.0 % by weight of Zinc, zeolites content varies between 40 to 90 % weight, the total metal content of metals from the group Na, K, Ca, Pt, Sn and Re varying between 0.05 to 1.0% by weight, the solid matrix may be alumina. The catalyst retains the catalytic activity even after multiple regenerations. The diffraction pattern of the catalyst have characteristics corresponding to the sepcifications as presented in Table - 2. Table- 2. Characterisation of the X-Ray Diffraction spectrum of the zeolite having a MFI structur according to the invention. (Table Removed) VS = Very strong S=Strong MS=Medium to strong M=Medium MW = Medium to weak W = Weak VW = Very weak These zeolites molecular sieves of MFI structure have the following appropriate chemical formula after calcination, expressed in the form of oxides. M 2/n 0.x AI2O3. Y Si02 , Z ZnO where in, M represent a proton and/or a metallic cation. n is the valency of the said cation, y/x is a number ranging from 5 to 1000 (Si02/Alz03 molar ratio). Z/Y is a number ranging from 5 to 1000 (Zn0/Si02 molar ratio) The solid was three times exchanged with 3N NH4NO3 solution to get the ammonium form of the catalyst. To get the desired protonic form, decomposition was carried out at 450oC for four hours. In another embodiment of the present invention, the zinc alunino silicate molecular sieve in the protonated form thus obtained is incorporated in another material (matrix) more resistant to the temperature and other conditions employed in the process. Such matrix material includes synthetic or naturally occuring substances, as well as clays, silica, alumina or metal oxides. The relative portion of the molecular sieve and matrix material on anhydrous basis may vary with molecular sieve content ranging between 10 to 90% by weight. In another embodiment of the present invention metals like sodium, potassium, gallium, platinum, tin, iron, rhenium are advantageously incorporated in to Zinc-alumlnosilicate molecular sieve either during synthesis or subsequently by impregnation and/or ion exchange. Incorporation of one or more of these metals in the molecular sieve is expected to enhance activity, selectivity and life of the catalyst. The total amount of such added metals may vary between 0.1 to 0.5% by weight. In another embodiment of the present invention, the catalyst obtained by the process of the present invention is used for the aromatisation reaction of non economically viable petroleum feed stocks which mainly contain paraffins. Such feed stocks include light naphtha, aromatic extraction raffinate, natural gas condensate (NGC) straight run naphtha, etc. This reaction is of particular interest as it produces the products of greater value e.g benzene, toluene, xylenes and LPG from Low value feed stocks. Detailed process conditions and possible application of the catalyst prepared by the process of the present invention are beyond the scope of the present invention and has been made the subject matter of our patent application: &JjLli>E'-l34- , In another embodiment of the present invention, the catalyst prepared by the process of the present invention shows similar catalytic activity even after seventeen regenerations. As reported in the literature (Catalysis Today, vol. 6, 1989-90, p-35) Zinc exchanged zeolites are active for conversion of methanol Into aromatics. But the activity of the catalyst slowly decreases due to elution of zinc from the catalyst under the reducing atmosphere. This phenomenon is well known and is one of the major hurdles in the use of zinc promoted catalyst for practical purposes. But the catalyst used in the present invention does not show such a phenomenon and can be advantageously used even in the reducing atmosphere. The following examples will serve to illustrate the process of this invention which should not be construed to limit the scope of the present invention. Example 1. This example describes a process for the preparation of zeolite molecular sieve zinc silicalite entering in to the composition of the catalyst according to the invention. Silicagel (200-300 mesh) was used as the silica source while zinc nitrate (Zn (NO3)2. H2O) was used as the zinc source. In a typical procedure a mixture of NaOH (0.36 moles), N(CsH7) Br (0.06 moles), Zn(N03)2 (0.007 moles) and water (22.5 moles) were added to the silica gel under stirring. The PH of the reaction gel was controlled by adding 3.5 ml of 1:1 H2SO4 solution. The crystallisation of reaction mixture was carried out at 150oC for 3.5 days. The solid is filtered, washed with hot water and then dried at 80oC, crystallographic analysis shows that the product is a zeolite having a MFI structure where X ray diffraction pattern corresponds to the specification given in Table - 2. The chemical analysis of the product reveals that it contains 1.75 wt% Zn as ZnO. The solid prepared as above is exchanged and/or imprignated with metals from the group Na, Fe, Ca and Pt. The total amount of such metals added is 0.5% by weight. The solid prepared as above is shaped by extrusion with a binder material or matrix, prefereably alumina in a proportion of 65% by weight of zeolite and 35% by weight of binding agent, A paste is obtained by adding water in these two components. This paste is passed through a die having a diameter of 1.4 mm, then dried under stream of air at 120C and calcined at 550"C for one hour. The yield of the catalyst is 92%. Example - 2. This example illustrates a process for the preparation of a zeolite molecular sieve, zinc alumino silicate entering into the composition of the catalyst according to the invention. In this example, aluminium sulphate [Al2(S04)3H20] is used as a source of alumina, silica gel (200-330 mesh) was used as the silica source while zinc nitrate [Zn(N03)2 H2O] was used as the zinc source. In a typical procedure a mixture of N(C3H7) Br (0.06 moles), Zn (N03)2 (0.007 moles), Al2(S04)3. H2O (0.003 moles) and water (22.5 moles) were added to the silica gel (0.6 moles) under stirring. The PH of the reaction gel was controlled by adding 3.5 ml of H2SO4 (H2SO4; water, 1:1), The crystallisation of reaction mixture was carried out in autoclave at 1500C for 3.5 days. After crystallisation, the solid is filtered, washed with hot water and then dried at 800C. Crystallographic analysis shows that these zeolites have MFI Structure whose X-ray dlfferaction pattern corresponds to the specification given in Table-2, chemical analysis of the product after calcination in air at 5500C shows Al (as AI2O3), 0.8% and Zn (as ZnO) , 1.7%. Protonation of zeolites samples was caried out by submitting the sample to 3 cycles of ion exchange with 0,2 N NH4NO3 at 80C for four hours, followed by filtration and washing with hot water. The solid obtained as above was exchanged/or Impregnated with metals such as Na, Ca, Sn, Pt and Fe to obtain catalyst sample. The total amount of such metals added is 0.5% by weight. The yield of the catalyst is 95% . The solid prepared as above is shaped by extrusion with a binder material or matrix, preferably alumina in a proportion of 65% by weight of zeolite and 35% by weight of binding agent. A paste is obtained by adding water to the above mixture. This paste is passed through a die having a diameter of 1.4mm, then dried under a stream of air at 120C and calcined at 550"C for one hour. Example 3. This example illustrates a process for the preparation of a zeolite molecular sieve zinc aluminosilicate entering into composition of the catalyst according to the invention. In this example, silica gel (200-300 mesh) was used as the silica source, aluminium sulfate [Al2(S04)s H2O] as a source of alumina while [Zn(N03)2.H2O] was used as the zinc source. In a typical procedure, a mixture of N(C3H7)4 Br (0.06 moles), [Al2(S04)3. H2O] (0.003 moles), [Zn (N03)2 H2O] (.015 moles) and water (24 moles) were added to the silica gel (0.6 moles) under stirring. The PH of the reaction gel was controlled by adding 3.5 ml of H2SO4 (H2SO4 : water, 1:1). The crystallisation of reaction mixture was carried out in autoclave at 1500C for 3.5 days. After crystallisation, the solid is filtered, washed with hot water and then dired at 800C. Crystallographic analysis shows that the product is a zeolite having a MFI structure. The chemical analysis of the product after calcination in air at 550C shows Al (as AI2O3), 0.8% and Zn (as ZnO) 3.3%. Protonation of zeolite samples was carried out by submitting the sample to 3 cycles of ion exchange with 0.2N NH4NO3 at 800C for four hours, followed by filtration and washing with hot water. The solid obtained as above was exchanged or impregnated with metals such as Na, Ca, Sn, Pt and Fe to obtain the catalyst Sample. The total amount of such metals added Is 0.5% by weight. The yield of the catalyst is 95%. The solid prepared as above is shaped by extrusion with a binder material or matrix, preferably alumina in a proportion of 65% by weight of zeolite and 35% by weight of binding agent. A paste is obtained by adding water to above mixture. This paste is passed through a die having a diameter of 1.4 mm, then dried under a stream of air at 120*C. Example-4. This example shows the catalytic activity of Zinc alumino silicate molecular sieve [Al as (A1203), 0.8% and Zn (as ZnO), 1.7%] catalyst (Zn ZSM-5) prepared in example -2, in fresh form, after six regenerations (after regeneration of the coked catalyst to regain its catalytic activity) and after 17 regenerations for aromatisation reaction. Pure n-heptane was used as a feed for the study and reaction was carried out in a pressure micro reactor unit. The reaction conditions, conversion of n-heptane and selectivity to products are described in Table - 3. table-3 Aromat.isation of. n-heptane in presence of Zn-ZSM - 5. Reactlon conditions : Temperature : 400"C Pressure : 10Kg/Cm2 LHSV : 2 hr-i N2/n-heptane : 2 (Table Removed) The main advantages of the present invention are as follows: i) The catalyst prepared by the process of present invention is most versatile when used for the conversion of economically non viable petroleum feed stocks in to value added products. ii) Metal, zinc which is quite cheap has been used in the catalyst formulation instead of the costly gallium, or platinum which is used in the hitherto known catalysts. iii) Irrespective of presence of zinc in the catalyst formulation (which has low m. p and b. P) , the catalyst does not show any loss of activity even after multiple for example seventeen regenerations. iv) The catalyst prepared by the process of the present invention is not very sensitive to sulfur. v) The catalyst prepared by the process of the present invention does not require use of corrosive organic chloride additive. We claim : 1. A process for the preparation of crystalline zinc alumino silicate catalyst useful for the preparation of LPG and high octane aromatics which comprises: (a) mixing water, a source selected from silica- , an aluminium source selected from aluminium salts, a zinc source selected from zinc salts and tetrahydral alkyl ammonium cation by conventional methods, (b) heating the said reaction mixture to a temperature ranging from 800 C to 230 0 C, preferably from 1400 C to 210 0 C, at aucogeneous phase and (c) heating the solid content obtained in step (b) to a temperature atleast 400 0 C, exchanging/impregnating the above solid obtained in step (c) with metals such as Na, Ca, Sn, Pt and Fe by known methods to obtain crystalline zinc alumino silicates. 2. A process as claimed in claim 1, where the source of silica used is selected from silica in the form of hydrogels, aerogels, colloidal suspension or solution of soluble silicate such as sodium silicate. 3. A process as claimed in claims 1&2 where the source of alumina used is selected from aluminium salts (such as sulphates, nitrates, chlorides, fluorides and acetates for example), aluminium hydroxide and oxide, aluminates, esters such as tripropyl ester of mono- orthoaluminic acid Al(OC H ) . 4. A process as claimed in claims 1-3 wherein the zinc salts used is zinc nitrate. 5. A process as claimed in claims 1-4 where the oxide of alumina and silica are combined and used, is amorphous alumina, silicagel, crystalline aluminosili-cate, including clays and zeolites. 6. A process as claimed in claim 1-5 wherein the tetrahydral alkyl ammonium cation used is tetrahydral propyl ammonium cation. 7. A process for the preparation of crystalline zinc alumino silicate catalyst useful for the preparation of LPG and high octane aromatics subdyanyially as herein described with reference to the examples.

Full Text

The present invention relates to a process for the preparation of crystalline zinc alumino silicate catalyst useful for the preparation of LPG and high octane aromatics. The catalyst material prepared by the process of the present invention is given the name zinc-aluminosilicate or Zn-ZSM-5 molecular sieve catalyst. Hence more specifically the present invention relates to a process for the preparation of a catalyst consisting of Zn-ZSM-5 which is useful for the preparation of LPG and high octane aromatic hydrocarbons such as benzene, toluene, ethyl benzene and xylenes(BTX) from low value, low octane petroleum feed slocks.
New gasoline specifications and changing markets have led to large and rapid variations of feed stocks and availablity. The key factor to boost the profitability is to take advantage of these variations and produce high demand, high value products such as LPG, hydrogen and aromatics. Hence, there is a need to develop a versatile process for the preparation of a novel catalyst which will be able to process cheaper, sometimes unwanted and variably available feed stocks to produce LPG and high octane aromatics.
Therefore the present invention relates to
process for the preparation of a novel catalyst con
sisting of Zn-ZSM-5 molecular sieve useful for the
conversion of petroleum feed stocks into
value added products such as LPG and high octane
hydrocarbons.
Because of its population, India is in peculiar situation with great demand for LPG, which can not be met by conventional resources such as cracking processes employing naphtha, gas oil and the like. The deficit between demand and production of LPG at the end of 8th plan (1996-97) is expected to be 2.8 million metric tones per annum which is likely to increase to 5.8 million metric tones per annum at the end of 9th plan (2001-02). Similarly, deficit between demand and production of motor gasoline at the end of 9th plan is expected to be 1.5 million metric tonnes per annum. Hence, good amount of foreign exchange has to be spent for meeting the demand of LPG as the demand can not be met by indigenous resources.
Natural gas condensate (NGC), aromatic extraction raffinate and light naphtha are considered as some of the few non economically viable feed stocks in the petroleum market today. As these feed stocks being non-reformable by conventional catalytic reforming process; they have been considered only as a fuel for long periods. These feed stocks can be converted in to valuable products like LPG and Benzene, Toluene and Xylenes (BTX aromatics), utilising the shape selective features of medium pore zeolite molecular sieve.
The aromatic hydrocarbons can be used as high octane blending feed stocks for the production of high octane gasoline. They are also used as feed stocks for thepreparation of chemical and petrochemical products. Aromatic chemicals constitute about one third of the total organic compounds known to day. They are important chemical precursors for the production of detergents and polymers among others.
An article published in the literature [ Ind. Eng. Chem.
Process Design Dev. , 25, (1986), 151 3 describes a process
proposed by Mobil Research and Development for the
preparation of aromatics from variety of feed stocks such as
pyrolysis gasoline, unsaturated gases from catalytic cracker,
paraffinic naphtha and LPG. The process describes use of
purely acidic H-ZSM-5 catalyst. Another report (Hydrocarbon
processing, Sep 1989, p-72) descreibes of a process developed
jointly by UOP INC and British Petroleum Company, based on
gallium doped 2eolite catalyst. In this process LPG was
converted into BTX aromatics and the process has been demonstrated in a large scle pilot plant of the British Petroleum's Graigemouth Refinery in Scotland. U.S. Patent 5, 124, 417 dated June 1992 describes the use of Pt-Sn-ZSM-5 Catalyst for the production of mono alkyl aromatics from C8 n-paraffins containing feed stocks. U.S. Patent 5, 026, 938 dated 25 June 1991 describes a process for converting a gaseous feed stocks containing C3-C5 paraffins into aromatic hydrocarbons by contacting the feed with galliosilicate molecular sieve catalyst.
Zeolite ZSM-5 is a crystalline alurainosilicate whose preparation was first claimed in 1972 and is described in a
U.S. patent 3, 702, 386. The frame work structure is well
established and the catalyst is reported to have many
catalytic applications. "Silicalite" having a similar
zeolite structure constituted by pure crystalline S102, has been descirbed by E,M, Flanigen [Nature 271 (1978), 512]. The highly ordered rigid structure with three dimensional rigid lattice can accomodate MeC-4 in addition to Si04 tetrahedra. Me being for example Al, Fe, Ga, Ti or B.
Conventionally, Bensene, Toluene and Xylenes (BTX) aromatics are obtained by catalytic reforming process of naphtha. The catalyst used for this process is Pt/Al2 0s monometallic or Pt-Re/Al2 03 bimetallic catalyst. Although these processes are used all over the world, there are number of limitations in the use of these catalyst for the above mentioned process.
These limitations are :
i) These catalysts are not effective in promoting
aromatlsation of Cs hydrocarbons. Hence, it can not be used
for the aromatisation of feed stocks like natural gas
condensate (NGC), light naphtha or aromatic extraction
raffinate, which contains appreciable amount of n-pentane and
iso pentane.
ii) These catalysts are also not very effective in promotion
of the aromatisation of straight chain paraffins such as n-
hexane and n-heptane. Hence, large amount of straight chain
paraffins such as n-hexane and n-heptane present in the feed
remain unconverted.
iii) All catalytic reforming units employing these catalysts require an Organic Chloride additive to provide the proper balance between acid and metal function. The Organic Chloride is broken down during reforming process in to hydrochloric acid, a waste product targeted for stricter regulations.
iv) These processes result in the formation of gasoline in the range of 75-95 research octane number and hence require use of tetra ethyl lead to boost the octane number. The use of tetra ethyl lead in gasoline has toxic effects of lead emitted from exhausts and is being banned all over the world including India.
The main objective of present invention is to provide a process for the preparation of crystalline zinc alumino silicate catalyst useful for the preparation of LPG and high octane aromatics. The catalyst prepared by the process of present invention can be used for the production of Benzene, Toluene, Xylenes (BTX) aromatics using feed stocks like naturl gas condensate (NGC) and light naphtha, production of LPG carries significance from the Indian point of view as demand for LPG in India is much higher. Zn-ZSM-5 catalyst prepared by the process of the present invention contains Zn, in addition to Al and Si, and
possesses MFI structure.
Accordingly the present invention provides a process for the preparation of crystalline zinc alumino silicate catalyst useful for the preparation of LPG and high octane aromatics which comprises:
(a) mixing water, a source selected from silica / an
aluminium source selected from aluminium a salts, a
zinc source selected from zinc salts and tetrahydral
alkyl ammonium cation by conventional methods,
(b) heating the said reaction mixture to a temperature
ranging from 80o C to 230 o C, preferably from 140o C to
210 oC, at autogeneous phase and
(c) heating the solid content obtained in step (b)
to a temperature atleast 4 00 o C, exchanging/impregnating
the above solid obtained in step (c) with metals such
as Na, Ca, Sn, Pt and Fe by known methods to obtain
crystalline zinc alumino silicates.
Silica in the form of hydrogels, aerogels, Colloidal suspension or solution of soluble silicate such as sodium silicate can be used as sources of silica.
The alumina sources which can be used include aluminium salts (Sulphates, nitrates, chlorides, fluorides and acetate for example), aluminium hydroxide andoxide, aluminates, esters such as tripropyl ester of mono-ortho aluminic acid [Al (OC3H7)3].
As zinc source, zinc salts which are capable of being converted into zinc oxide upon calcination, especially in the presence of oxygen can be used. As an example of such salt zinc nitrate is mentioned.
Instead of starting with separate sources of aluminia and silica, sources in which the two oxides are combined can also be used; for example amorphous alumina, silica gel, crystalline alumino silicate, including clays and zeolites.
The source of structuring agent used to provide organic cations are preferably tetra alkyl ammonium cations, the alkyl advantageously being Propyl and the like.
The acids or acid salts, bases or basic salts possibly
added in the reaction mixture in compliment to adjust the PH of the reaction medium to the desired value can be choosen from commonly used acids such as hydrochloric acid (HC1) , nitric acid (HN03), Sulphuric acid (H2SO4), acetic acid (CH3COOH) or acid salts such as sodium hydrogen sulphate (NaHSO4); commonly used bases are such as ammonium hydroxide (NH4OH), Soda (NaOH), Potash (KOH) or commonly used basic salts such as sodium hydrogen carbonate (NaHCO3), or neutral sodium carbonate (Na2C03) sodium acetate (CH3COONa), neutral sodium sulfide (Na2S) or sodium hydrogen sulphide (NaHS). Buffer mixtures such as acetic acid (CH3COOH) sodium acetate (CH3COONa), ammonium hydroxide (NH4OH), ammonium chloride can be used for the purpose. The catalyst prepared by the process of the present invention may contain by weight
(a) 0.01 to 10% zinc.
(b) 0.5 to 99.99% of a zeolites with an S102/A1203 molar ratio ranging from 15 to 1000; said zeolite molecular sieve having X-ray diffraction pattern shown in Table - 2.
(c) 0.01 to 5.0% by weight of metals from the group Na, K, Ca, Pt, Sn and Re.
(d) 0.1 to 99.49% of a matrix choosen from the group
consisting of alumina, silica, clay, metal oxides and a
combination of the compounds mentioned here in above.
The catalyst preferably containing 0.05 to 5.0 % by weight of Zinc, zeolites content varies between 40 to 90 % weight, the total metal content of metals from the group Na, K, Ca, Pt, Sn and Re varying between 0.05 to 1.0% by weight,
the solid matrix may be alumina. The catalyst retains the
catalytic activity even after multiple regenerations.
The diffraction pattern of the catalyst have
characteristics corresponding to the sepcifications as
presented in Table - 2.
Table- 2.
Characterisation of the X-Ray Diffraction spectrum of the zeolite having a MFI structur according to the invention.
(Table Removed)
VS = Very strong
S=Strong
MS=Medium to strong
M=Medium
MW = Medium to weak
W = Weak
VW = Very weak
These zeolites molecular sieves of MFI structure have the following appropriate chemical formula after calcination, expressed in the form of oxides. M 2/n 0.x AI2O3. Y Si02 , Z ZnO where in, M represent a proton and/or a metallic cation. n is the valency of the said cation, y/x is a number ranging from 5 to 1000 (Si02/Alz03 molar ratio).
Z/Y is a number ranging from 5 to 1000 (Zn0/Si02 molar ratio) The solid was three times exchanged with 3N NH4NO3 solution to get the ammonium form of the catalyst. To get the desired protonic form, decomposition was carried out at 450oC for four hours.
In another embodiment of the present invention, the zinc
alunino silicate molecular sieve in the protonated form thus
obtained is incorporated in another material (matrix) more
resistant to the temperature and other conditions employed in
the process. Such matrix material includes synthetic or
naturally occuring substances, as well as clays, silica,
alumina or metal oxides. The relative portion of the
molecular sieve and matrix material on anhydrous basis may vary with molecular sieve content ranging between 10 to 90% by weight.
In another embodiment of the present invention metals like sodium, potassium, gallium, platinum, tin, iron, rhenium are advantageously incorporated in to Zinc-alumlnosilicate molecular sieve either during synthesis or subsequently by impregnation and/or ion exchange. Incorporation of one or
more of these metals in the molecular sieve is expected to enhance activity, selectivity and life of the catalyst. The total amount of such added metals may vary between 0.1 to 0.5% by weight.
In another embodiment of the present invention, the catalyst obtained by the process of the present invention is used for the aromatisation reaction of non economically viable petroleum feed stocks which mainly contain paraffins. Such feed stocks include light naphtha, aromatic extraction raffinate, natural gas condensate (NGC) straight run naphtha, etc. This reaction is of particular interest as it produces the products of greater value e.g benzene, toluene, xylenes and LPG from Low value feed stocks. Detailed process conditions and possible application of the catalyst prepared by the process of the present invention are beyond the scope of the present invention and has been made the subject matter of our patent application: &JjLli>E'-l34- ,
In another embodiment of the present invention, the catalyst prepared by the process of the present invention shows similar catalytic activity even after seventeen regenerations. As reported in the literature
(Catalysis Today, vol. 6, 1989-90, p-35) Zinc exchanged zeolites are active for conversion of methanol Into aromatics. But the activity of the catalyst slowly decreases due to elution of zinc from the catalyst under the reducing atmosphere. This phenomenon is well known and is one of the major hurdles in the use of zinc promoted catalyst for
practical purposes. But the catalyst used in the present invention does not show such a phenomenon and can be advantageously used even in the reducing atmosphere.
The following examples will serve to illustrate the process of this invention which should not be construed to limit the scope of the present invention. Example 1.
This example describes a process for the preparation of zeolite molecular sieve zinc silicalite entering in to the composition of the catalyst according to the invention. Silicagel (200-300 mesh) was used as the silica source while zinc nitrate (Zn (NO3)2. H2O) was used as the zinc source.
In a typical procedure a mixture of NaOH (0.36 moles), N(CsH7) Br (0.06 moles), Zn(N03)2 (0.007 moles) and water (22.5 moles) were added to the silica gel under stirring. The PH of the reaction gel was controlled by adding 3.5 ml of 1:1 H2SO4 solution. The crystallisation of reaction mixture was carried out at 150oC for 3.5 days. The solid is filtered, washed with hot water and then dried at 80oC, crystallographic analysis shows that the product is a zeolite having a MFI structure where X ray diffraction pattern corresponds to the specification given in Table - 2. The chemical analysis of the product reveals that it contains 1.75 wt% Zn as ZnO.
The solid prepared as above is exchanged and/or imprignated with metals from the group Na, Fe, Ca and Pt. The
total amount of such metals added is 0.5% by weight.
The solid prepared as above is shaped by extrusion with a binder material or matrix, prefereably alumina in a proportion of 65% by weight of zeolite and 35% by weight of binding agent, A paste is obtained by adding water in these two components. This paste is passed through a die having a diameter of 1.4 mm, then dried under stream of air at 120*C and calcined at 550"C for one hour. The yield of the catalyst is 92%. Example - 2.
This example illustrates a process for the preparation of a zeolite molecular sieve, zinc alumino silicate entering into the composition of the catalyst according to the invention. In this example, aluminium sulphate [Al2(S04)3H20] is used as a source of alumina, silica gel (200-330 mesh) was used as the silica source while zinc nitrate [Zn(N03)2 H2O] was used as the zinc source.
In a typical procedure a mixture of N(C3H7) Br (0.06 moles), Zn (N03)2 (0.007 moles), Al2(S04)3. H2O (0.003 moles) and water (22.5 moles) were added to the silica gel (0.6 moles) under stirring. The PH of the reaction gel was controlled by adding 3.5 ml of H2SO4 (H2SO4; water, 1:1), The crystallisation of reaction mixture was carried out in autoclave at 1500C for 3.5 days.
After crystallisation, the solid is filtered, washed with hot water and then dried at 800C. Crystallographic analysis shows that these zeolites have MFI Structure whose
X-ray dlfferaction pattern corresponds to the specification given in Table-2, chemical analysis of the product after calcination in air at 5500C shows Al (as AI2O3), 0.8% and Zn (as ZnO) , 1.7%.
Protonation of zeolites samples was caried out by submitting the sample to 3 cycles of ion exchange with 0,2 N NH4NO3 at 80*C for four hours, followed by filtration and washing with hot water.
The solid obtained as above was exchanged/or Impregnated with metals such as Na, Ca, Sn, Pt and Fe to obtain catalyst sample. The total amount of such metals added is 0.5% by weight. The yield of the catalyst is 95% . The solid prepared as above is shaped by extrusion with a binder material or matrix, preferably alumina in a proportion of 65% by weight of zeolite and 35% by weight of binding agent. A paste is obtained by adding water to the above mixture. This paste is passed through a die having a diameter of 1.4mm, then dried under a stream of air at 120*C and calcined at 550"C for one hour. Example 3.
This example illustrates a process for the preparation of a zeolite molecular sieve zinc aluminosilicate entering into composition of the catalyst according to the invention. In this example, silica gel (200-300 mesh) was used as the silica source, aluminium sulfate [Al2(S04)s H2O] as a source of alumina while [Zn(N03)2.H2O] was used as the zinc source. In a typical procedure, a mixture of N(C3H7)4 Br (0.06
moles), [Al2(S04)3. H2O] (0.003 moles), [Zn (N03)2 H2O] (.015 moles) and water (24 moles) were added to the silica gel (0.6 moles) under stirring. The PH of the reaction gel was controlled by adding 3.5 ml of H2SO4 (H2SO4 : water, 1:1). The crystallisation of reaction mixture was carried out in autoclave at 1500C for 3.5 days.
After crystallisation, the solid is filtered, washed with hot water and then dired at 800C. Crystallographic analysis shows that the product is a zeolite having a MFI structure. The chemical analysis of the product after calcination in air at 550*C shows Al (as AI2O3), 0.8% and Zn (as ZnO) 3.3%.
Protonation of zeolite samples was carried out by submitting the sample to 3 cycles of ion exchange with 0.2N NH4NO3 at 800C for four hours, followed by filtration and washing with hot water.
The solid obtained as above was exchanged or impregnated with metals such as Na, Ca, Sn, Pt and Fe to obtain the catalyst Sample. The total amount of such metals added Is 0.5% by weight. The yield of the catalyst is 95%.
The solid prepared as above is shaped by extrusion with a binder material or matrix, preferably alumina in a proportion of 65% by weight of zeolite and 35% by weight of binding agent. A paste is obtained by adding water to above mixture. This paste is passed through a die having a diameter of 1.4 mm, then dried under a stream of air at 120*C. Example-4.
This example shows the catalytic activity of Zinc alumino silicate molecular sieve [Al as (A1203), 0.8% and Zn (as ZnO), 1.7%] catalyst (Zn ZSM-5) prepared in example -2, in fresh form, after six regenerations (after regeneration of the coked catalyst to regain its catalytic activity) and after 17 regenerations for aromatisation reaction. Pure n-heptane was used as a feed for the study and reaction was carried out in a pressure micro reactor unit. The reaction conditions, conversion of n-heptane and selectivity to products are described in Table - 3. table-3
Aromat.isation of. n-heptane in presence of Zn-ZSM - 5.
Reactlon conditions :
Temperature : 400"C
Pressure : 10Kg/Cm2
LHSV : 2 hr-i
N2/n-heptane : 2
(Table Removed)

The main advantages of the present invention are as follows:
i) The catalyst prepared by the process of present invention
is most versatile when used for the conversion of
economically non viable petroleum feed stocks in to value
added products.
ii) Metal, zinc which is quite cheap has been used in the
catalyst formulation instead of the costly gallium, or
platinum which is used in the hitherto known catalysts.
iii) Irrespective of presence of zinc in the catalyst
formulation (which has low m. p and b. P) , the catalyst does
not show any loss of activity even after multiple for example
seventeen regenerations.
iv) The catalyst prepared by the process of the present
invention is not very sensitive to sulfur.
v) The catalyst prepared by the process of the present
invention does not require use of corrosive organic chloride
additive.

We claim :
1. A process for the preparation of crystalline zinc
alumino silicate catalyst useful for the preparation of
LPG and high octane aromatics which comprises:
(a) mixing water, a source selected from silica- , an
aluminium source selected from aluminium salts, a
zinc source selected from zinc salts and tetrahydral
alkyl ammonium cation by conventional methods,
(b) heating the said reaction mixture to a temperature
ranging from 800 C to 230 0 C, preferably from 1400 C to 210 0 C, at aucogeneous phase and
(c) heating the solid content obtained in step (b) to a temperature atleast 400 0 C, exchanging/impregnating
the above solid obtained in step (c) with metals such
as Na, Ca, Sn, Pt and Fe by known methods to obtain
crystalline zinc alumino silicates.
2. A process as claimed in claim 1, where the source
of silica used is selected from silica in the form of
hydrogels, aerogels, colloidal suspension or solution
of soluble silicate such as sodium silicate.
3. A process as claimed in claims 1&2 where the
source of alumina used is selected from aluminium salts
(such as sulphates, nitrates, chlorides, fluorides and
acetates for example), aluminium hydroxide and oxide,
aluminates, esters such as tripropyl ester of mono-
orthoaluminic acid Al(OC H ) .
4. A process as claimed in claims 1-3 wherein the

zinc salts used is zinc nitrate.
5. A process as claimed in claims 1-4 where the
oxide of alumina and silica are combined and used, is amorphous alumina, silicagel, crystalline aluminosili-cate, including clays and zeolites.
6. A process as claimed in claim 1-5 wherein the tetrahydral alkyl ammonium cation used is tetrahydral propyl ammonium cation.
7. A process for the preparation of crystalline zinc alumino silicate catalyst useful for the preparation of LPG and high octane aromatics subdyanyially as herein described with reference to the examples.

Documents:

600-del-1995-abstract.pdf

600-del-1995-claims.pdf

600-del-1995-correspondence-others.pdf

600-del-1995-correspondence-po.pdf

600-del-1995-description (complete).pdf

600-del-1995-form-1.pdf

600-del-1995-form-2.pdf

600-del-1995-form-3.pdf

600-del-1995-form-4.pdf

600-del-1995-form-9.pdf

600-del-1995-petition-others.pdf

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Patent Number

191297

Indian Patent Application Number

600/DEL/1995

PG Journal Number

45/2003

Publication Date

08-Nov-2003

Grant Date

07-Jun-2004

Date of Filing

31-Mar-1995

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	AJIT RAMCHANDRA PRADHAN	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005,INDIA
2	NAGABHATLA VISWANADHAM	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005,INDIA
3	SURENDRANATH SURESH	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005,INDIA
4	NIRMALYA RAY	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005,INDIA
5	UMA SHANKER	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005,INDIA
6	TURAGA SUNDARA RAMA PRASADA RAO	INDIAN INSTITUTE OF PETROLEUM, DEHRADUN-248005,INDIA

PCT International Classification Number

C01G 9/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA