Title of Invention

AN IMPROVED PROCESS FOR THE PREPARATION OF STYRENE.

Abstract

The invention relates to an improved process for the preparation of styrene .Process steps are: passing a feed consisting of ethyl benzene and air/oxygen on a preheated BED at a temperature in the range of 350 to 650°C of transition metal doped stabilized zirconia catalyst consisting coprecipitating zirconium, yttrium and transition metal hydroxides/carbonates/oxalates at Weight Hourly Space Velocity (WHS) in the range of 0.4 to 5.0 per hr, collecting styrene by conventional method such as herein described.

Full Text

The present invention relates to an improved process for the preparation of styrene. The present day art of the preparation of styrene is by dehydrogenation of ethyl benzene using a suitable catalyst. Initially iron oxide promoted by potassium was used by Lee et al.(Lee E.H., Catalyst Review Science Engineering, 8, 285, 1973). Alternatively, structural promoters like alumina, chromia and promoters for selectivity like oxides of vanadium, cerium, tungsten and/or lithium(Hirano T, Applied Catalyst, 28, 119, 1986). Dehydrogenation of ethyl benzene to styrene has been reported by M. Muhler, J. Schutze, M. Wesemann, T. Rayment, A. Dent, R. Schlogi and G. Erti, J.of Catalysis, 126, 339-360, 1990. Using thin active layer of KFeO2 supported on a solid structure of K2Fe22O34 in Fe3O4 wherein 50% conversion of ethyl benzene to styrene is reported at 600 C. The process is endothermic and therefore higher temperature favours the formation of styrene. Also reduced pressure favours the reaction. These conditions are achieved by having a fixed bed of catalyst maintained at 600-700°C over which the mixture of vapours of ethylbenzene and superheated steam in a conveniently fixed ratio is passed. The resulting product is cooled which contains mainly benzene, toluene, unreacted ethylbenzene and styrene among other products. The products are then separated by distillation. The use of steam serves various purposes in the process. It helps in maintaining the temperature of the catalyst bed which might get lowered by endothermic nature of the reaction, secondly, it reduces the partial pressure of ethylbenzene and hydrogen during the reaction, favouring the products and lastly steam is useful to keep the surface of the catalyst "clean" maintaining its active nature. Oxides or their mixtures, are used industrially for the dehydrogenation reaction. For example Fe2O3 + Cr2O3. The process is energy intensive. Reaction is carried out at around 600°C. The disadvantages of this route are: 1. High temperature of reaction and hence the need for high energy inputs. 2. Large number of water molecules per ethyl benzene molecule are required to be processed for increasing the yield of the product. 3. The catalyst can be poisoned by CO2, a reaction product. 4. The catalyst can get deactivated by coke formation on its surface. 5. High temperature of reaction leads to the low molecular weight degradation products affecting selectivity of the reaction and hence low yield of the product. Styrene can also be made by the oxydehydrogenation of ethylbenzene. The oxydehydrogenation of ethylbenzene to styrene on different acid catalyst has been studied by various researchers the study has been made on different catalyst such as, Na-SiO2, alumina, silica, Ni-P, Sn-P, as seen in the following references (7) .Tomohiko Tagawa, Kazuyoshi Iwayama, Yuzuru Ishida, Tadashi Hattori, and Yuichi Murakami., (2). Auslegeschrift 17807666, The Badger Co., Cambridge, Mass., 1977. (3). U.S.Pat. 3935126, The Dow Chemical Co., 1976. (4). Fiedorow.R., Przystajko, W., Sopa.M., and Dalla Lana. I.G., J. of catalysis., 68,33(1981). In the oxydehydrogenation route a redox reaction on the surface of the catalyst is taking place. The reduction on the surface removes the oxygen from the lattice or otherwise present on the surface. The vacant sites, however, gets coupled again with oxygen in the oxidation step. Examples of oxydehydrogenation catalyst are Sb2O3, Fe2O3, A12O3, ZrP, Ni/W oxide on A12O3, NiP, SnO2 - P2O5 etc. In general, cracking and oxidation of EB is attributed to the strong acid sites in these catalysts. It has been reported in literature that the carbonaceous layer formed on the surface of the catalyst, can also have the catalytic property. The carbonaceous layer has a composition containing species like C, CH and O. The latter forms redox system to convert ethylbenzene to styrene with low efficiency. The chemistry of the process in ox dehydrogenation is different from dehydrogenation route. Primarily it is an exothermic reaction. Some of the disadvantages of the dehydrogenation route are overcome in this route i.e. ox dehydrogenation thereby making it more advantageous for reasons given below: 1. It requires low temperature, around 500°C, for conversion of ethylbenzene to styrene. 2. Water/steam in the inputs is not essential. The main object of the present invention is to provide improved process for the preparation of styrene from ethylbenzene. Another object of the present invention is to make use of superionic conductors, particularly transition metal ion doped stabilized zirconia, as catalyst for ethyl benzene to styrene conversion. Accordingly the present invention provides an improved process for the preparation of styrene which comprises; passing a feed consisting of ethyl benzene and air/oxygen in a ratio in the range 0-(1,5) on a preheated bed at a temperature in the range of 350 to 650°C of transition metal doped stabilized zirconia catalyst consisting coprecipitating zirconium, yttrium and transition metal hydroxides/carbonates/oxalates at Weight Hourly Space Velocity (WHSV) in the range of 0.4 to 5.0 per hr, collecting styrene by conventional method such as herein described Stabilized zirconia has a defect structure with oxygen ion vacancies present in the lattice. This makes these materials to be good ionic conductors, as oxygen ions are mobile in the lattice. Also, oxygenation and dehydrogenation can be carried out simultaneously. The acidic or basic sites of the catalyst can be manipulated by suitable ion doping in stabilized zirconia. The acidity or basicity depends on the sizes of the doped ions and therefore there would be a good choice for manipulation of this property. This leads to decreased cracking products and better selectivity. The present invention utilizes the above mentioned features to develop a process for ethylbenzene conversion to styrene. The catalyst used in the process of the present invention is prepared from coprecipitating zirconium, yttrium and transition metal hydroxides/carbonates/oxalates, etc. and subsequent calcination at 600°C. The preparation of the catalyst is described in the copending Indian patent No.l95/DEL/93. The stoichiometric composition of the catalyst is ZrAYBTMc where A is in the range of 0.84 to 0.76, B is in the range of .16 to .08 and C is in the range of 0 to .16 where TM is the transition metal, so that A+B+C=1. The process can be fully described in the following steps: 1. Preparing the catalyst by conventional methods or according to copending Indian patent N0.195/DEL/93 or otherwise. 2. Arranging a fixed bed of catalyst which can be suitably heated to the desired temperature in the range of 200 to 650 C. 3. Mixing cthlybcnzcne vapours and air/oxygen in a suitable ratio. 4. Passing mixture as prepared in (3) over a hot bed as described in (2). 5. Condensing the products of reaction carried out in step (1) to (4) by heat exchanger. 6. Separating the products to their constituents and analysing them by conventional method. 7. In one of the embodiment the temperature of the catalyst bed may be maintained in the range 200 - 650 C. 8. In yet another embodiment, the ratio of ethylbenzene/air(oxygen) can be in the range 0- (1,5) so that it does not exceed the lower limit of the formation of explosive mixture. 9. In yet other embodiment, the WHSV (Weight Hourly Space Velocity) can be in the range 0.4 - 4. The invention is illustrated by the following examples which may not however be construed to limit the scope of present invention in any manner whatsoever. EXAMPLE- 1 A catalyst with a typical composition Zr.76Y.16Fe.08O2-d is prepared by coprecipitation method as described in copending Indian Patent 195/DEL/93. After confirming by X-ray diffraction that the catalyst powder shows the cubic structure (calcium fluorite type structure), it was mixed with porcelain beads of 4 mm (od) and loaded in a fixed bed reactor. The catalyst bed is maintained at 480°C. From the inlets above the bed, ethylbenzene and air were fed in [WHSV(Weight Hourly Space Velocity) = 0.437]. The product vapours were condensed below the bed by circulating coolant at 0°C. The condensed products were collected in a trap maintained at 0°C. The product showed the yield with the composition: EB conversion = 20.2%; Styrene yield = 18.2%, Selectivity for styrene = 90.01% EXAMPLE- 2 A catalyst with a typical composition Zr.76Y ,6Fe06Cr02O2-d is prepared by coprecipitation method as described in copending Indian patent 195/DEL/93. After confirming that the catalyst shows cubic structure, it was mixed with porcelain beads of 4 mm(od) and loaded in a fixed bed reactor. The catalyst bed is maintained at 500°C. From the inlets above the bed, ethylbenzene and air were fed in (WHSV (Weight Hourly Space Velocity) = 0.2722). The product showed the yield with the composition EB conversion = 33.6%, Styrene yield = 29.8%, Selectivity for styrene= 88.7% EXAMPLE- 3 A catalyst with a typical composition Zr0.76Y0.16Fe0.04V0.04O2-d, is prepared by coprecipitation method as described in copending Indian patent 195/DEL/93. After confirming that the catalyst shows cubic structure, it was mixed with porcelain beads of 4 mm (od) and loaded in a fixed bed reactor. The catalyst bed is maintained at 350 C. From the inlets above the bed, ethylbenzene and air were fed in (WHSV(Weight Hourly Space Velocity) = 0.2722). The product showed the yield with the composition. EB conversion = 17%, Styrene yield = 15%, Selectivity for styrene= 80.0%. We Claim: 1. An improved process for the preparation of styrene which comprises; passing a feed consisting of ethyl benzene and air/oxygen in a ratio in the range 0-(1,5) on a preheated bed at a temperature in the range of 350 to 650°C of transition metal doped stabilized zirconia catalyst consisting coprecipitating zirconium, yttrium and transition metal hydroxides/carbonates/oxalates at Weight Hourly Space Velocity (WHSV) in the range of 0.4 to 5.0 per hr, collecting styrene by conventional method such as herein described. 2. An improved process for the preparation of styrene as described substantially herein before with reference to the examples contained herein.

Documents:

91-del-2000-abstract.pdf

91-del-2000-claims.pdf

91-del-2000-correspondence-others.pdf

91-del-2000-correspondence-po.pdf

91-del-2000-description (complete).pdf

91-del-2000-form-1.pdf

91-del-2000-form-19.pdf

91-del-2000-form-2.pdf