Title of Invention	" A PROCESS FOR THE PREPARATION OF ACTIVE ZINC-MAGNESIUM AND NICKEL OXIDE BEARING COMPOSITES USEFUL AS TOXIC GAS ADSORBENT AND DECOMPOSITION CATALYST"
Abstract	This invention is about a process for the preparation of active zinc-, magnesium- and Nickel oxide bearing composites useful as toxic gas adsorbents or decomposition catalyst of toxic gases, which combines reacting oxides and salts of metals in a known manner so as to produce mixed metal layered hydroxides (MMLH) such as Zn-Cr, Mg-Al, Ni-Al type possessing positive layer charge; adding swellable clay such as montmorillonite, laponite, hectorite, nontronite, saponite etc. having a negative charge, in the ratio of MMLH to clay 1:0.25 to 0.25:1 by weight in dry states followed by homogenising in water tilt the completion of hydration; drying at 40 to 2500C, followed by calcination at 350 to 7500C for 15 — 60 minutes to obtain activemetal oxide composites useful as solid adsorbent or catalyst.

Title of Invention

" A PROCESS FOR THE PREPARATION OF ACTIVE ZINC-MAGNESIUM AND NICKEL OXIDE BEARING COMPOSITES USEFUL AS TOXIC GAS ADSORBENT AND DECOMPOSITION CATALYST"

Abstract

This invention is about a process for the preparation of active zinc-, magnesium- and Nickel oxide bearing composites useful as toxic gas adsorbents or decomposition catalyst of toxic gases, which combines reacting oxides and salts of metals in a known manner so as to produce mixed metal layered hydroxides (MMLH) such as Zn-Cr, Mg-Al, Ni-Al type possessing positive layer charge; adding swellable clay such as montmorillonite, laponite, hectorite, nontronite, saponite etc. having a negative charge, in the ratio of MMLH to clay 1:0.25 to 0.25:1 by weight in dry states followed by homogenising in water tilt the completion of hydration; drying at 40 to 2500C, followed by calcination at 350 to 7500C for 15 — 60 minutes to obtain activemetal oxide composites useful as solid adsorbent or catalyst.

Full Text	The present invention relates to a process for the preparation of active metal zinc-, magnesium- and Nickel oxide bearing composites useful as adsorbents or decomposition catalyst for toxic gases. More particularly, the present invention relates to the preparation of active metal zinc-, magnesium- and Nickel oxide bearing composites useful for adsorption of toxic hydrogen sulphide (H2S) gas, from mixed metal layered hydroxides and smectite clay mainly montmorrillonite. Additionally, the present invention also relates to preparation of active metal zinc-, magnesium- and Nickel oxide bearing composites for adsorption of toxic gas like Sulphur-di-Oxide (SO2) and catalytic decomposition of environmentally harmful green-house gas Nitrous Oxide (N20). Different metal oxides like MnO, CoO, BaO, CaO, Fe304, M0O2, W03, V2O3 and ZnO etc. have been studied for their reactivity with H2S at different temperatures. Out of these ZnO is the most extensively studied because of favourable thermodynamic changes from ZnO to ZnS and back (Schrodt et al. Fuel, 54, 269, 1975). Therefore, preparation of microfine ZnO has gained special interest (Gangwal et al. Heat Recovery System & CHP, Vol 15, No 2, 205, 1995 and Baird et al. Recent Advances in Oilfield Chemistry 234, Royal Society of Chemistry, Cambridge 1994). Desulphurisation studies using mixed oxides with ZnO as one of the components e. g. ZnO/Fe203 and ZnO/Ti02 have also been reported (Sasaoka et al. - Ind. Eng. Chem. Res. 35, 2389, 1996). However, these type of adsorbents with a Ferrite like structure is accompanied with a highly exothermic sulphidisation reaction. In desulphurisation by the extruded pellets of pure ZnO powders, a difference of reactivity between the exposed surface and the internal surface is found due to large resistance to diffusion of gas. The large internal resistances arises because of various associated factors like diffusion of gas through a solid product layer in the outer surface of each spherical grain until the reaction occurs at the unreacted core (Harrison & Gibson, Ind. Eng. Chem. Proc. Des. Dev., 19, 231, 1980). Loading of ZnO on ceramic filters for desulphurisation of hot coal gas has also been reported (Steinike et al., 3rd European Powder Diffraction Conference, Vienna, Sept 25-28, 1994). The ceramic matrix consists of mullite, quartz and metakaolinite etc. obtained from thermal degradation of kaolinite clay. The adsorbents are prepared by calcination of ZnO impregnated kaolinite clay. A high porosity of the filters was maintained by mixing polyurethane foams, which on calcination formed cavities. However, since the surface of kaolinite clay is neutral, such a supported system of ZnO would have inherent problem of nonuniform distribution of solids, because the driving force for mixing the solids is only mechanical not chemical or electrostatic in nature. In an another patent, Burgess and Coates (British Patent 1,273, 738 - 1972) reported the preparation of an adsorbent formulation for sulphur bearing gases from a paste consisting of ZnO, bentonite, Fe oxide and H20, which are then extruded, dried and calcined at 350°C. This invention although involves bentonite (a smectite group of clay) the amount of clay used is very low (in amount 4.8% w/w with following ingredients ratios ZnO:Fe203:H20:Clay = 76.7:4.03:4.8 :14.6) and hence the clay acts here as a simple binder only. Formation of active ZnO particles from Zn-AI type mixed metal layered hydroxide (MMLH) has been reported by Baird et al. (J. Chem. Soc. Faraday Trans., 91(18), 3219, 1995), however presence of Aluminium in the precursor structure led to the formation of highly stable Zn-AI spinel rather than active ZnO and consequently there is lowering of the sulphur adsorption ability. From this perspective Zn-Cr type mixed metal layered hydroxide undertaken in the present work is advantageous as oxidic phases formed on thermal decomposition of parent MMLH can react with H2S which is evidenced in XRD pattern by the presence of ZnCr2S4 (Powder Diffraction File, International Center for Diffraction Data, Pennsylvania, USA, No 16 - 507) Like adsorption of H2S at high temperature by different metal oxides, adsorption of SO2 by oxidic adsorbents at high temperature is also highly important. Since, SO2 is mainly produced during gasification of low grade coals, residual oil and coke oven gas etc. (Baruah et al. J. of Sci. & Ind. Res. 59, October, 2000), it is desirable to remove it from hot stage, otherwise if there is lowering of temperature during adsorption there would be loss of thermal efficiency which is highly detrimental to industrial processes like hot gas clean up. But most of the desulphuhsation processes operate at ambient or lower temperatures only. In an Indian patent Abram et al. (No 171664, 1988) have described a method for adsorption of S02 in Mg(OH)2 suspension. As the. process involves bubbling gas stream through aqueous medium there would be cooling down of the gas resulting in loss of thermal efficiency during hot gas clean up stage. SO2 adsorption on MgO-AI203 based mixed oxide adsorbents derived from Hydrotalcites have been reported (Corma et al. Appl. Catal. B Env. 4, 1994, 29 - 43). N2O is another highly toxic gas which is of urgent environmental concern. The lethal Green-House effect of the gas can be understood from the fact that one mole of N20 in the atmosphere is 270 times more harmful than the same amount of CO2 (Hitzler G. and Bargende M. FKFS Sttutgart, Feb 2000 from Web Page). N20 is formed as an undesired product in aged catalytic converters in cars, in nitric acid production, in adipic acid production, in circulating bed fluidised combustion, in non-selective catalytic reduction of NOx with cyanuric acid or urea. In US in 1999 N20 emission from automobile combustion totaled 63.4 Tg C02 eq. or 15% of US N20 emissions. In compliance with Kyoto declaration of 1997, G8 countries of the world is bound to bring down its level at least 5% below 1990 level during the period 2008 to 2012 (Agarwal S B and Partha Sarathy R: Proc. of Seventh NCB Int. Sem. on Cement and Build. Mat., New-Delhi 21-24 Nov. 2000). One of the promising class of material for catalytic decomposition of N20 is mixed metal layered hydroxides. Perez-Ramirez et al. (Appl. Catal B Env, 25, 2000, 191-203) has described a Co-Rh-AI based system capable of decomposing N20 to N2 and 02. Similarly, Swamy et al. (Appl. Catal. B Env., 7, 1996, 397-406) has reported that Co-AI hydrotalcites on thermal decomposition produces a high surface area material which is quite effective for catalytic decomposition of N20 under simulated conditions typical for emissions found in Nylon 6,6 productions. Dandl and Emig (Appl. Catal. A Gen., 168, 1998, 261-268) have reported that Co-La-AI type hydrotalcites form very good catalysts for decomposition of N20 to N2 and 02. They have also reported CoO-MgO impregnated over silica is extremely good for decomposition of N20 to N2 and 02. Main object of the present invention is to provide a process for the preparation of active zinc-, magnesium- and Nickel oxide bearing composites useful as toxic gas adsorbents or decomposition catalyst of toxic gases, which combines reacting oxides and salts of metals in a known manner so as to produce mixed metal layered hydroxides (MMLH) such as Zn-Cr, Mg-AI, Ni-AI type possessing positive layer charge; adding swellable clay such as montmorillonite, laponite, hectorite, nontronite, saponite etc. having a negative charge, in the ratio of MMLH to clay 1:0.25 to 0.25:1 by weight in dry states followed by homogenizing in water till the completion of hydration; drying at 40 to 250°C, followed by calcination at 350 to 750°C for 15 - 60 minutes to obtain active metal oxide composites useful as solid adsorbent or catalyst. In an embodiment of the present invention active zinc-, magnesium-and Nickel oxide bearing composites obtained has actve ZnO, MgO and NiO in the range of 0.25 to 0.75% by wt of clay. In an embodiment of the present invention the amount of water added ranges from 10 to 25 times the weight of total solid in the slurry. In an embodiment of the present invention the drying is effected preferably at a temperature in the range of 50oC - 65 °C for 10 to 1 hour and calcination is carried out at 350 to 750°C for 15 - 60 minutes. Accordingly, the present invention provides a process for the preparation of active metal zinc-, magnesium- and Nickel oxide bearing composites useful as toxic gas adsorbent or decomposition catalyst of toxic gases, which combines reacting oxides or salts of metals in a known manner so as to produce mixed metal layered hydroxides (MMLH) such as Zn-Cr, Mg-AI, Ni-AI type possessing positive layer charge; adding swellable clay such as montmorillonite, laponite, hectorite, nontronite, saponite etc. having a negative charge in ratio of MMLH to clay 1:0.25 to 0.25:1 by weight in dry states followed by homogenising in water till the completion of hydration; drying at 50 to 250°C followed by calcination at 350 to 750°C for 15 - 60 minutes to obtain active metal zinc-, magnesium-and Nickel oxide bearing composites useful as solid adsorbent or decomposition catalyst. In present invention the starting material Zn-Cr MMLH was synthesised by reacting ZnO with an aqueous solution of CrCl3. 6H20 at 60°C. The pink coloured product was filtered and dried. The dried MMLH was then mixed thoroughly in a ratio of clay to MMLH (1:0.25 to 0.25:1 weight/weight). The dry mix was homogenised in water in a Hamilton beach mixture. The homogenised slurry was allowed to hydrate and dry followed by calcination in an electric furnace at 350°C to 750°C. Allowed to cool gradually to obtain active ZnO particles projected up from the surface of clay matrix (as evaluated by XRD & SEM-EDXA). ZnO like particles obtained from Zn-Cr MMLH is due to formation of a solid solution of Zn and Cr giving some ZnO like non-stoichiometric oxide particles. On increasing the calcination temperature the active oxide formed segregates to bivalent oxide (e.g. ZnO) and spinel (e.g. ZnCr204). However, at active oxide stage the trivalent ion (Cr3+) from the MMLH precursor accommodates itself with bivalent oxide structure in the form of a solid solution. The synthesised composite acts as a strong adsorbent at high temperature (about 600°C) for adsorpotion of sulphur from H2S. In invention a Mg-AI MMLH was synthesised by reacting AI(N03)3.9H20 with Mg(N03)2.6H20 at 80°C in presence of NaOH at pH 10. The white product was filtered and dried. The dried MMLH was then mixed thoroughly with montmorillonite clay. The dry mix was homogenised in water in a Hamilton beach mixture. The homogenised slurry was allowed to hydrate and dry followed by calcination in an electric furnace. Cooling was done gradually to obtain some non-stoichiometric oxides of Mg and Al which have structural similarity with MgO. The synthesised composite acts as a strong adsorbent for S02 at 700°C giving MgS04 (as evidenced by XRD). Which can be decomposed at 850°C to give back MgO. In present invention a Ni-AI MMLH was synthesised by reacting AI(N03)3.9H20 with Ni(N03)2.6H20 in presence of NaOH at pH 10 at 80°C. The green coloured product was filtered and dried. The dried MMLH was then mixed thoroughly with montmorillonite clay. The dry mix was homogenised in water in a Hamilton beach mixture. The homogenised slurry was allowed to hydrate and dry, followed by calcination in an electric furnace and cooling was done slowly to obtain active NiO particles projected up from the surface of ceramic matrix (as evaluated by XRD & SEM-EDXA). The synthesised adsorbent acts as a catalyst for decomposition of N20 to N2 and 02 at 500°C. The following examples are given by the way of illustrations of the present invention and should not be construed to the limit of the scope of the present invention, Examples : (1) To a suspension of 40 g (0.49 M) ZnO in 1000 cm3 water, 200 cm3 of 1 M aqueous solution of CrCl3.6H20 was added in drops under stirring condition at 60°C. The slurry was stirred for 2 hours. The decolorised supernatant liquid was decanted off and 200 cm3 of fresh 1 M CrCl3.6H20 solution was added in drops under stirring condition. The process was repeated once. The pink coloured product was filtered, washed with water and dried in an air oven at 40°C for 48 hours. The synthesised MMLH was found to give XRD patterns typical of layered structures with high intensity (001) peaks at regular interval of d-spacings alongwith specific positions for other (hkl) reflections. The dried MMLH (5 g) was then mixed thoroughly with 5 g of montmorillonite clay (M/S LOBA Chemie, India) for more than 1 hour in a mortar. The dry mix was then homogenised in 300 ml water in a Hamilton beach mixture for about fifteen minutes at 14000 rpm. The homogenised slurry was then kept for hydration for about 7 days after which it was dried in an air oven at 110°C; the dried mass was then gradually calcined in an electric furnace at 500°C for 30 minutes. Cooling was done slowly to obtain active ZnO projected surface matrix (as evaluated by XRD & SEM-EDXA). 5.0 g calcined MMLH-clay powder ( two ends of the tube were fixed with outlet and inlet tubes in a leak-proof manner with the help of epoxy resins. The tube was placed inside a cylindrical furnace, and a flow of dry hydrogen sulphide gas was maintained at a flow-rate of 40 cm3/minute. The temperature of the reactive zone of the tube containing the adsorbent plug was maintained at 600°C for a period of 60 minutes. The flow of hydrogen sulphide gas was also maintained during cooling and was continued till the temperature of reactor came down to 200°C. The cooled powders were subjected for different physico-chemical analysis. In order to compare the efficacy of the supported system with a non-supported one, a neat sample of Zn-Cr MMLH was calcined at 500°C in a similar way as that of calcined MMLH-clay system. 5.0 g of the calcined product (particle size Example 2 188.32 g (0.502 M) of AI(NO)3.9H20 and 230.79 g (0.9 M) of Mg(NO)2- 6H20 were dissolved in 700 cm3 water. A mixture of 280 cm3 of 12.5 M NaOH solution and 1000 cm3 of 1 M Na2C03 solution was added in drops over a period of 4 hours under stirring condition maintaining a pH of 9.5. The slurry was rolled in a roller oven for 24 hours at 65°C. The product was filtered, washed to free of sodium ion and dried at 100 ± 5°C for 24 hours in an air oven to obtain dried Mg-AI MMLH. The dried MMLH (5 g) was then mixed thoroughly with 5 g of montmorillonite clay (M/S LOBA Chemie, India) for more than 1 hour in a mortar. The dry mix was then homogenised in 300 ml water, in a Hamilton beach mixture for about fifteen minutes at 14000 rpm. The homogenised slurry was then kept for hydration for about 7 days after which it was dried in an air oven at 110°C; the dried mass was then gradually calcined in an electric furnace at 500°C for 30 minutes. Cooling was done slowly to obtain active MgO particles projected up from the surface of clay matrix (as evaluated by XRD &SEM-EDXA). 1 g of MMLH-clay powder ( 2 hours. The temperature of the composite was decreased under N2 flow from 750 to 700°C. The composite was reacted with a mixture of SO2 and air at 700°C under a flow rate of SO2 25 ml min"1 and air 10 ml min"1 and subsequently the temperature of the substance was decreased to 300°C under S02 flow. Ultimately the composite was cooled down to room temperature under N2 atmosphere. XRD evaluation of the product showed formation of well crystallised MgS04 {Powder Diffraction Data File no 74-13641(c)}. Example 3: 60.02 g (0.16 M) of AI(N03).9H20 and 130.86 g (0.45 M) of Ni(N03)2- 6H20 were dissolved in 320 cm3 water. The solution was heated at 80°C. 400 cm3 of 1.8 M Na2C03 solution was added in drops under stirring condition maintaining the pH between 7 and 8. The process of addition was completed in 6 hours. The slurry was set aside for 12 hours. The pale green product was filtered, washed and dried in an air oven at 40°C for 48 hours. The dried MMLH (5 g) was then mixed thoroughly with 5 g of montmorillonite clay (M/S LOBA Chemie, India) in a mortar for a period of more than one hour. The dry mix was then homogenised in 300 ml water in a Hamilton beach mixture for about fifteen minutes at 14000 rpm. The homogenised slurry was dried in an air oven at 110°C and the dried mass was gradually calcined in an electric furnace at 500°C for 30 minutes. Cooling was done slowly within the furnace to obtain layered NiO particles projected up over ceramic matrix of montmorillonite clay ( as evaluated by XRD & SEM-EDXA). 30 g calcined MMLH-clay powder ( has been observed that there is 98% and 94% conversion after 9 hours and 0.5 hours respectively. The effectiveness of the catalyst was observed even after 13 hours of reaction at 500°C. In the present invention a system of MMLH and montmorillonite clay in an aqueous medium is used, which is a self organising system due to interaction of positive and negative layer charges present in the MMLH and montmorillonite clay respectively. This helps in the exfoliation of MMLH layers to discreet layers by the bridging of two montmorillonite layers. The mechanism of bridging is visualised by remarkable rise of thixotropy in such suspensions (Felixberger J, Recent Advances in Oilfield Chemistry 84 - 98, Royal Society of Chemistry, Cambridge, 1994). Such a fully extended thixotropic suspension on calcination at proper temperature gives metal oxide particles in the form of layers. The main advantages of the present invention are 1. Highly reactive metal oxide particles over a ceramic matrix can be prepared easily. 2. Surface active ZnO particles obtained from Zn-Cr MMLH-montmorillonite show very high adsorption of sulphur from H2S gas. 3. After sulphurisation the adsorbent may be regenerated easily by thermal treatment. We claim 1. A process for the preparation of active zinc-, magnesium- and Nickel oxide bearing composites useful as toxic gas adsorbents or decomposition catalyst of toxic gases, which combines reacting oxides and salts of metals in a known manner so as to produce mixed metal layered hydroxides (MMLH) such as Zn-Cr, Mg-AI, Ni-AI type possessing positive layer charge; adding swellable clay such as montmorillonite, laponite, hectorite, nontronite, saponite etc. having a negative charge, in the ratio of MMLH to clay 1:0.25 to 0.25:1 by weight in dry states followed by homogenizing in water till the completion of hydration; drying at 40 to 250°C, followed by calcination at 350 to 750°C for 15 - 60 minutes to obtain active metal oxide composites useful as solid adsorbent or catalyst. 2. A process as claimed in claim 1, wherein active zinc-, magnesium-and Nickel oxide bearing composites obtained has active ZnO, MgO and NiO in the range of 0.25 to 0.75% by wt of clay. 3. A process as claimed in claims 1 & 2, wherein the amount of water added ranges from 10 to 25 times the weight of total solid in the slurry. 4. A process as claimed in claims 1 to 3, wherein the drying is effected preferably at a temperature in the range of 500C - 65 °C for 10 to 1 hour and calcination is carried out at 350 to 750°C for 15 - 60 minutes. 5. A process for the preparation of active zinc-, magnesium- and Nickel oxide bearing composites useful as toxic gas adsorbent and decomposition catalyst as herein substantially described with reference to examples.

Full Text

The present invention relates to a process for the preparation of active metal zinc-, magnesium- and Nickel oxide bearing composites useful as adsorbents or decomposition catalyst for toxic gases.
More particularly, the present invention relates to the preparation of active metal zinc-, magnesium- and Nickel oxide bearing composites useful for adsorption of toxic hydrogen sulphide (H2S) gas, from mixed metal layered hydroxides and smectite clay mainly montmorrillonite.
Additionally, the present invention also relates to preparation of active metal zinc-, magnesium- and Nickel oxide bearing composites for adsorption of toxic gas like Sulphur-di-Oxide (SO2) and catalytic decomposition of environmentally harmful green-house gas Nitrous Oxide (N20).
Different metal oxides like MnO, CoO, BaO, CaO, Fe304, M0O2, W03, V2O3 and ZnO etc. have been studied for their reactivity with H2S at different temperatures. Out of these ZnO is the most extensively studied because of favourable thermodynamic changes from ZnO to ZnS and back (Schrodt et al. Fuel, 54, 269, 1975). Therefore, preparation of microfine ZnO has gained special interest (Gangwal et al. Heat Recovery System & CHP, Vol 15, No 2, 205, 1995 and Baird et al. Recent Advances in Oilfield Chemistry 234, Royal Society of Chemistry, Cambridge 1994). Desulphurisation studies using mixed oxides with ZnO as one of the components e. g. ZnO/Fe203 and ZnO/Ti02 have also been reported (Sasaoka et al. - Ind. Eng. Chem. Res. 35, 2389, 1996). However, these type of adsorbents with a Ferrite like structure is accompanied with a highly exothermic sulphidisation reaction.
In desulphurisation by the extruded pellets of pure ZnO powders, a difference of reactivity between the exposed surface and the internal
surface is found due to large resistance to diffusion of gas. The large internal resistances arises because of various associated factors like diffusion of gas through a solid product layer in the outer surface of each spherical grain until the reaction occurs at the unreacted core (Harrison & Gibson, Ind. Eng. Chem. Proc. Des. Dev., 19, 231, 1980).
Loading of ZnO on ceramic filters for desulphurisation of hot coal gas has also been reported (Steinike et al., 3rd European Powder Diffraction Conference, Vienna, Sept 25-28, 1994). The ceramic matrix consists of mullite, quartz and metakaolinite etc. obtained from thermal degradation of kaolinite clay. The adsorbents are prepared by calcination of ZnO impregnated kaolinite clay. A high porosity of the filters was maintained by mixing polyurethane foams, which on calcination formed cavities. However, since the surface of kaolinite clay is neutral, such a supported system of ZnO would have inherent problem of nonuniform distribution of solids, because the driving force for mixing the solids is only mechanical not chemical or electrostatic in nature.
In an another patent, Burgess and Coates (British Patent 1,273, 738 - 1972) reported the preparation of an adsorbent formulation for sulphur bearing gases from a paste consisting of ZnO, bentonite, Fe oxide and H20, which are then extruded, dried and calcined at 350°C. This invention although involves bentonite (a smectite group of clay) the amount of clay used is very low (in amount 4.8% w/w with following ingredients ratios ZnO:Fe203:H20:Clay = 76.7:4.03:4.8 :14.6) and hence the clay acts here as a simple binder only.
Formation of active ZnO particles from Zn-AI type mixed metal
layered hydroxide (MMLH) has been reported by Baird et al. (J. Chem. Soc. Faraday Trans., 91(18), 3219, 1995), however presence of Aluminium in the precursor structure led to the formation of highly stable Zn-AI spinel rather than active ZnO and consequently there is lowering of the sulphur adsorption ability. From this perspective Zn-Cr type mixed metal layered hydroxide undertaken in the present work is advantageous as oxidic phases formed on thermal decomposition of parent MMLH can react with H2S which is evidenced in XRD pattern by the presence of ZnCr2S4 (Powder Diffraction File, International Center for Diffraction Data, Pennsylvania, USA, No 16 - 507)
Like adsorption of H2S at high temperature by different metal
oxides, adsorption of SO2 by oxidic adsorbents at high temperature is
also highly important. Since, SO2 is mainly produced during
gasification of low grade coals, residual oil and coke oven gas etc.
(Baruah et al. J. of Sci. & Ind. Res. 59, October, 2000), it is desirable
to remove it from hot stage, otherwise if there is lowering of
temperature during adsorption there would be loss of thermal
efficiency which is highly detrimental to industrial processes like hot
gas clean up. But most of the desulphuhsation processes operate at
ambient or lower temperatures only. In an Indian patent Abram et
al. (No 171664, 1988) have described a method for
adsorption of S02 in Mg(OH)2 suspension. As the. process involves bubbling gas stream through aqueous medium there would be cooling down of the gas resulting in loss of thermal efficiency during hot gas clean up stage. SO2 adsorption on MgO-AI203 based mixed oxide adsorbents derived from Hydrotalcites have been reported (Corma et al. Appl. Catal. B Env. 4, 1994, 29 - 43).
N2O is another highly toxic gas which is of urgent environmental
concern. The lethal Green-House effect of the gas can be understood from the fact that one mole of N20 in the atmosphere is 270 times more harmful than the same amount of CO2 (Hitzler G. and Bargende M. FKFS Sttutgart, Feb 2000 from Web Page). N20 is formed as an undesired product in aged catalytic converters in cars, in nitric acid production, in adipic acid production, in circulating bed fluidised combustion, in non-selective catalytic reduction of NOx with cyanuric acid or urea. In US in 1999 N20 emission from automobile combustion totaled 63.4 Tg C02 eq. or 15% of US N20 emissions. In compliance with Kyoto declaration of 1997, G8 countries of the world is bound to bring down its level at least 5% below 1990 level during the period 2008 to 2012 (Agarwal S B and Partha Sarathy R: Proc. of Seventh NCB Int. Sem. on Cement and Build. Mat., New-Delhi 21-24 Nov. 2000). One of the promising class of material for catalytic decomposition of N20 is mixed metal layered hydroxides. Perez-Ramirez et al. (Appl. Catal B Env, 25, 2000, 191-203) has described a Co-Rh-AI based system capable of decomposing N20 to N2 and 02. Similarly, Swamy et al. (Appl. Catal. B Env., 7, 1996, 397-406) has reported that Co-AI hydrotalcites on thermal decomposition produces a high surface area material which is quite effective for catalytic decomposition of N20 under simulated conditions typical for emissions found in Nylon 6,6 productions. Dandl and Emig (Appl. Catal. A Gen., 168, 1998, 261-268) have reported that Co-La-AI type hydrotalcites form very good catalysts for decomposition of N20 to N2 and 02. They have also reported CoO-MgO impregnated over silica is extremely good for decomposition of N20 to N2 and 02.
Main object of the present invention is to provide a process for the
preparation of active zinc-, magnesium- and Nickel oxide bearing composites useful as toxic gas adsorbents or decomposition catalyst of toxic gases, which combines reacting oxides and salts of metals in a known manner so as to produce mixed metal layered hydroxides (MMLH) such as Zn-Cr, Mg-AI, Ni-AI type possessing positive layer charge; adding swellable clay such as montmorillonite, laponite, hectorite, nontronite, saponite etc. having a negative charge, in the ratio of MMLH to clay 1:0.25 to 0.25:1 by weight in dry states followed by homogenizing in water till the completion of hydration; drying at 40 to 250°C, followed by calcination at 350 to 750°C for 15 - 60 minutes to obtain active metal oxide composites useful as solid adsorbent or catalyst.
In an embodiment of the present invention active zinc-, magnesium-and Nickel oxide bearing composites obtained has actve ZnO, MgO and NiO in the range of 0.25 to 0.75% by wt of clay.
In an embodiment of the present invention the amount of water added ranges from 10 to 25 times the weight of total solid in the slurry.
In an embodiment of the present invention the drying is effected preferably at a temperature in the range of 50oC - 65 °C for 10 to 1 hour and calcination is carried out at 350 to 750°C for 15 - 60 minutes.
Accordingly, the present invention provides a process for the preparation of active metal zinc-, magnesium- and Nickel oxide bearing composites useful as toxic gas adsorbent or decomposition catalyst of toxic gases, which combines reacting oxides or salts of metals in a known manner so as to produce mixed metal layered hydroxides (MMLH) such as Zn-Cr, Mg-AI, Ni-AI type possessing positive layer charge; adding swellable clay such as montmorillonite, laponite, hectorite, nontronite, saponite etc. having a negative charge in ratio of MMLH to clay 1:0.25 to 0.25:1 by weight in dry states followed by homogenising in water till the completion of hydration; drying at 50 to 250°C followed by calcination at 350 to 750°C for 15 - 60 minutes to obtain active metal zinc-, magnesium-and Nickel oxide bearing composites useful as solid adsorbent or decomposition catalyst.
In present invention the starting material Zn-Cr MMLH was synthesised by reacting ZnO with an aqueous solution of CrCl3. 6H20 at 60°C. The pink coloured product was filtered and dried. The dried MMLH was then mixed thoroughly in a ratio of clay to MMLH (1:0.25 to 0.25:1 weight/weight). The dry mix was homogenised in water in a Hamilton beach mixture. The homogenised slurry was allowed to hydrate and dry followed by calcination in an electric furnace at 350°C to 750°C. Allowed to cool gradually to obtain active ZnO particles projected up from the surface of clay matrix (as evaluated by XRD & SEM-EDXA). ZnO like particles obtained from Zn-Cr MMLH is due to formation of a solid solution of Zn and Cr giving some ZnO like non-stoichiometric oxide particles. On increasing the calcination temperature the active oxide formed segregates to bivalent oxide (e.g. ZnO) and spinel (e.g. ZnCr204). However, at active oxide stage
the trivalent ion (Cr3+) from the MMLH precursor accommodates itself with bivalent oxide structure in the form of a solid solution. The synthesised composite acts as a strong adsorbent at high temperature (about 600°C) for adsorpotion of sulphur from H2S.
In invention a Mg-AI MMLH was synthesised by reacting
AI(N03)3.9H20 with Mg(N03)2.6H20 at 80°C in presence of NaOH at pH 10. The white product was filtered and dried. The dried MMLH was then mixed thoroughly with montmorillonite clay. The dry mix was homogenised in water in a Hamilton beach mixture. The homogenised slurry was allowed to hydrate and dry followed by calcination in an electric furnace. Cooling was done gradually to obtain some non-stoichiometric oxides of Mg and Al which have structural similarity with MgO. The synthesised composite acts as a strong adsorbent for S02 at 700°C giving MgS04 (as evidenced by XRD). Which can be decomposed at 850°C to give back MgO.
In present invention a Ni-AI MMLH was synthesised by reacting AI(N03)3.9H20 with Ni(N03)2.6H20 in presence of NaOH at pH 10 at 80°C. The green coloured product was filtered and dried. The dried MMLH was then mixed thoroughly with montmorillonite clay. The dry mix was homogenised in water in a Hamilton beach mixture. The homogenised slurry was allowed to hydrate and dry, followed by calcination in an electric furnace and cooling was done slowly to obtain active NiO particles projected up from the surface of ceramic matrix (as evaluated by XRD & SEM-EDXA). The synthesised adsorbent acts as a catalyst for decomposition of N20 to N2 and 02 at 500°C.
The following examples are given by the way of illustrations of the present invention and should not be construed to the limit of the scope of the present invention,
Examples : (1)
To a suspension of 40 g (0.49 M) ZnO in 1000 cm3 water, 200 cm3 of 1 M aqueous solution of CrCl3.6H20 was added in drops under stirring condition at 60°C. The slurry was stirred for 2 hours. The decolorised supernatant liquid was decanted off and 200 cm3 of fresh 1 M CrCl3.6H20 solution was added in drops under stirring condition. The process was repeated once. The pink coloured product was filtered, washed with water and dried in an air oven at 40°C for 48 hours. The synthesised MMLH was found to give XRD patterns typical of layered structures with high intensity (001) peaks at regular interval of d-spacings alongwith specific positions for other (hkl) reflections. The dried MMLH (5 g) was then mixed thoroughly with 5 g of montmorillonite clay (M/S LOBA Chemie, India) for more than 1 hour in a mortar. The dry mix was then homogenised in 300 ml water in a Hamilton beach mixture for about fifteen minutes at 14000 rpm. The homogenised slurry was then kept for hydration for about 7 days after which it was dried in an air oven at 110°C; the dried mass was then gradually calcined in an electric furnace at 500°C for 30 minutes. Cooling was done slowly to obtain active ZnO projected surface matrix (as evaluated by XRD & SEM-EDXA).
5.0 g calcined MMLH-clay powder ( two ends of the tube were fixed with outlet and inlet tubes in a leak-proof manner with the help of epoxy resins. The tube was placed inside a cylindrical furnace, and a flow of dry hydrogen sulphide gas was maintained at a flow-rate of 40 cm3/minute. The temperature of the reactive zone of the tube containing the adsorbent plug was maintained at 600°C for a period of 60 minutes. The flow of hydrogen sulphide gas was also maintained during cooling and was continued till the temperature of reactor came down to 200°C. The cooled powders were subjected for different physico-chemical analysis.
In order to compare the efficacy of the supported system with a non-supported one, a neat sample of Zn-Cr MMLH was calcined at 500°C in a similar way as that of calcined MMLH-clay system. 5.0 g of the calcined product (particle size Example 2 188.32 g (0.502 M) of AI(NO)3.9H20 and 230.79 g (0.9 M) of Mg(NO)2- 6H20 were dissolved in 700 cm3 water. A mixture of 280 cm3 of 12.5 M NaOH solution and 1000 cm3 of 1 M Na2C03 solution was added in drops over a period of 4 hours under stirring condition maintaining a pH of 9.5. The slurry was rolled in a roller oven for 24 hours at 65°C. The product was filtered, washed to free of sodium ion
and dried at 100 ± 5°C for 24 hours in an air oven to obtain dried Mg-AI MMLH. The dried MMLH (5 g) was then mixed thoroughly with 5 g of montmorillonite clay (M/S LOBA Chemie, India) for more than
1 hour in a mortar. The dry mix was then homogenised in 300 ml
water, in a Hamilton beach mixture for about fifteen minutes at
14000 rpm. The homogenised slurry was then kept for hydration for
about 7 days after which it was dried in an air oven at 110°C;
the dried mass was then gradually calcined in an electric furnace at
500°C for 30 minutes. Cooling was done slowly to obtain active MgO
particles projected up from the surface of clay matrix (as evaluated
by XRD &SEM-EDXA).
1 g of MMLH-clay powder ( 2 hours. The temperature of the composite was decreased under N2
flow from 750 to 700°C. The composite was reacted with a mixture of
SO2 and air at 700°C under a flow rate of SO2 25 ml min"1 and air
10 ml min"1 and subsequently the temperature of the substance was
decreased to 300°C under S02 flow. Ultimately the composite was
cooled down to room temperature under N2 atmosphere. XRD
evaluation of the product showed formation of well crystallised
MgS04 {Powder Diffraction Data File no 74-13641(c)}.
Example 3:
60.02 g (0.16 M) of AI(N03).9H20 and 130.86 g (0.45 M) of Ni(N03)2- 6H20 were dissolved in 320 cm3 water. The solution was heated at 80°C. 400 cm3 of 1.8 M Na2C03 solution was added in drops under stirring condition maintaining the pH between 7 and 8. The process of addition was completed in 6 hours. The slurry was set aside for 12 hours. The pale green product was filtered, washed and dried in an air oven at 40°C for 48 hours. The dried MMLH (5 g) was then mixed thoroughly with 5 g of montmorillonite clay (M/S LOBA Chemie, India) in a mortar for a period of more than one hour. The dry mix was then homogenised in 300 ml water in a Hamilton beach mixture for about fifteen minutes at 14000 rpm. The homogenised slurry was dried in an air oven at 110°C and the dried mass was gradually calcined in an electric furnace at 500°C for 30 minutes. Cooling was done slowly within the furnace to obtain layered NiO particles projected up over ceramic matrix of montmorillonite clay ( as evaluated by XRD & SEM-EDXA).
30 g calcined MMLH-clay powder ( has been observed that there is 98% and 94% conversion after 9 hours and 0.5 hours respectively. The effectiveness of the catalyst was observed even after 13 hours of reaction at 500°C. In the present invention a system of MMLH and montmorillonite clay in an aqueous medium is used, which is a self organising system due to interaction of positive and negative layer charges present in the MMLH and montmorillonite clay respectively. This helps in the exfoliation of MMLH layers to discreet layers by the bridging of two montmorillonite layers. The mechanism of bridging is visualised by remarkable rise of thixotropy in such suspensions (Felixberger J, Recent Advances in Oilfield Chemistry 84 - 98, Royal Society of Chemistry, Cambridge, 1994). Such a fully extended thixotropic suspension on calcination at proper temperature gives metal oxide particles in the form of layers.
The main advantages of the present invention are
1. Highly reactive metal oxide particles over a ceramic matrix can be prepared easily.
2. Surface active ZnO particles obtained from Zn-Cr MMLH-montmorillonite show very high adsorption of sulphur from H2S gas.
3. After sulphurisation the adsorbent may be regenerated easily by thermal treatment.

We claim
1. A process for the preparation of active zinc-, magnesium- and
Nickel oxide bearing composites useful as toxic gas adsorbents or decomposition catalyst of toxic gases, which combines reacting oxides and salts of metals in a known manner so as to produce mixed metal layered hydroxides (MMLH) such as Zn-Cr, Mg-AI, Ni-AI type possessing positive layer charge; adding swellable clay such as montmorillonite, laponite, hectorite, nontronite, saponite etc. having a negative charge, in the ratio of MMLH to clay 1:0.25 to 0.25:1 by weight in dry states followed by homogenizing in water till the completion of hydration; drying at 40 to 250°C, followed by calcination at 350 to 750°C for 15 - 60 minutes to obtain active metal oxide composites useful as solid adsorbent or catalyst.
2. A process as claimed in claim 1, wherein active zinc-, magnesium-and Nickel oxide bearing composites obtained has active ZnO, MgO and NiO in the range of 0.25 to 0.75% by wt of clay.
3. A process as claimed in claims 1 & 2, wherein the amount of water added ranges from 10 to 25 times the weight of total solid in the slurry.
4. A process as claimed in claims 1 to 3, wherein the drying is effected preferably at a temperature in the range of 500C - 65 °C for 10 to 1 hour and calcination is carried out at 350 to 750°C for 15 - 60 minutes.
5. A process for the preparation of active zinc-, magnesium- and Nickel oxide bearing composites useful as toxic gas adsorbent and decomposition catalyst as herein substantially described with reference to examples.

Documents:

199-del-2002-abstract.pdf

199-del-2002-claims.pdf

199-del-2002-complete specification (granted).pdf

199-del-2002-correspondence-others.pdf

199-del-2002-correspondence-po.pdf

199-del-2002-description (complete).pdf

199-del-2002-form-1.pdf

199-del-2002-form-18.pdf

199-del-2002-form-2.pdf

199-del-2002-form-3.pdf

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Patent Number

235052

Indian Patent Application Number

199/DEL/2002

PG Journal Number

31/2009

Publication Date

31-Jul-2009

Grant Date

24-Jun-2009

Date of Filing

07-Mar-2002

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	RAJIB LOCHAN GOSWAMEE	REGIONAL RESEARCH LABORATORY, JOHRAT-785006, ASSAM.
2	DIPAK KUMAR DUTTA	REGIONAL RESEARCH LABORATORY, JOHRAT-785006, ASSAM.
3	KRISHNA GOPAL BHATTACHARYYA	REGIONAL RESEARCH LABORATORY, JOHRAT-785006, ASSAM.
4	ANDRE AYRAL	REGIONAL RESEARCH LABORATORY, JOHRAT-785006, ASSAM.

PCT International Classification Number

N/A

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA