Patent Publication Number: US-5021386-A

Title: Compositions involving V2 O3 -ZRO2 -TIO2

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to compositions involving V 2  O 3  -ZrO 2  -TiO 2 . 
     SUMMARY OF THE INVENTION 
     The present invention pertains to novel solid solutions involving V 2  O 3 , ZrO 2  and TiO 2  and the method for their preparation. The solid compositions involving V 2  O 3 , ZrO 2  and TiO 2  fall within the shaded area of a polygon in a ternary composition diagram of V 2  O 3 , ZrO 2  and TiO 2  as shown in the drawing herein e.g. FIG. 1. The polygon has the vertices and corresponding coordinates in weight percent as shown in the following Table I. 
     
                       TABLE I                                                     
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        Coordinates (wt %)                                                
Vertices  V.sub.2 O.sub.3                                                 
                        ZrO.sub.2                                         
                                TiO.sub.2                                 
______________________________________                                    
A         50            50       0                                        
B         24            50      26                                        
C         24            10      66                                        
D         32             2      66                                        
F         98             2       0                                        
______________________________________                                    
 
    
     The compositions involving V 2  O 3 , ZrO 2  and TiO 2  are depicted by the shaded area circumscribed by ABCDF as shown in FIG. 1. These novel solid solutions involving V 2  O 3 , ZrO 2  and TiO 2  are made by the process involving the steps of: 
     (1) heating V 2  O 5  powder having a particle size of less than about 50 microns in an atmosphere in which the partial pressure of oxygen is in the range of 10 -8  to 10 -10  atmosphere while gradually increasing the temperature stepwise over a temperature range of about 600° C. to 1300° C., and holding the temperature at about 1300° C. for a period to ensure complete reduction of all vanadium to V 3+  ; 
     (2) heating TiO 2  and ZrO 2  powders each having a particle size of less than about 50 microns for a period of about 10 to 14 hrs. at a temperature in the range of about 600° C. to 800° C. for TiO 2  and about 1000° C. to 1200° C. for ZrO 2  ; 
     (3) thoroughly grinding together about 24 to 98 wt. % of V 2  O 3  from (1), with about 2 to 50 wt. % of ZrO 2  and about 0 to 66 wt. % of TiO 2  from (2) to produce a mixture having a grain size of less than about 50 microns, 
     (4) pelletizing the mixture from (3) at a pressure of about 5,000 psi; and 
     (5) heating and reacting together the pellets from (4) at a temperature in the range of about 1100° C. to 1700° C. for a period in the range of about 1/2 to 48 hrs., in an atmosphere in which the partial pressure of oxygen is in the range of 10 -10  to 10 -5  atmosphere to produce said compositions involving V 2  O 3 , ZrO 2  and TiO 2 . 
     In one embodiment, the pellets from step (5) are cooled to ambient temperature while at substantially the same partial pressure of oxygen as in step (5). Preferably, to prevent undue oxidation and moisture pickup, the cooled pellets are stored in a sealed container. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The drawing e.g. FIG. 1 depicts a ternary composition diagram showing a polygon shaped shaded area circumscribed by ABCDF within which useful compositions involving V 2  O 3  -ZrO 2  -TiO 2  are found. 
    
    
     DESCRIPTION OF THE INVENTION 
     New solid solutions have been synthesized by the subject invention in which the nature and extent of the formation of solid solutions involving V 2  O 3 , ZrO 2  and TiO 2  have been characterized. This work has led to synthesizing new phases in which vanadium in several oxidation states are accommodated such as to render crystalline phases thermodynamically stable over a wide range of oxygen pressures at elevated temperatures. 
     The newly synthesized solid compositions involving V 2  O 3  -ZrO 2  -TiO 2  are shown in the enclosed figure (drawing) as circumscribed by the polygon shaped shaded area ABCDF in the ternary composition diagram. The oxidation states of vanadium in the solid solutions are mainly +3 and +4. 
     The polygon shaped shaded area has the following vertices and corresponding coordinates in weight percent: 
     
         ______________________________________                                    
        Coordinates (wt %)                                                
Vertices  V.sub.2 O.sub.3                                                 
                        ZrO.sub.2                                         
                                TiO.sub.2                                 
______________________________________                                    
A         50            50       0                                        
B         24            50      26                                        
C         24            10      66                                        
D         32             2      66                                        
F         98             2       0                                        
______________________________________                                    
 
    
     A typical newly synthesized composition involving V 2  O 3 , ZrO 2  and TiO 2  having the formula Zr 0 .11 V 1 .89 Ti 0 .83 O 5 .00 is illustrated by point G in the drawing having the following coordinates in wt. %: V 2  O 3  64, ZrO 2  6, and TiO 2  30. 
     The subject compositions made from V 2  O 3 , ZrO 2  and TiO 2  are synthesized in the following manner. The identity of the reaction product, solid solutions involving V 2  O 3  -ZrO 2  -TiO 2 , may be confirmed by X-ray diffraction analysis. 
     First, V 2  O 3  is prepared by heating commercially available analytical-grade V 2  O 5  having a particle size of less than about 50 microns in a vertical tube furnace in an atmosphere of carefully selected oxygen pressure within the stability range of V 2  O 3  e.g. in the range of 10 -8  to 10 -10  atmospheres. This is accomplished by using a gas mixture of high-purity e.g. 99.9 mole% or more CO 2  and H 2  or CO 2  and CO or H 2  O and H 2  in controlled proportions. The CO 2  /H 2 , CO 2  /CO or H 2  O/H 2  ratio by volume is in the range of 10/1 to 1/1. The relatively low melting point of the starting vanadium oxide (V 2  O 5 ) e.g. about 690° C., necessitates heating the oxide slowly. Starting at a temperature of about 600° C., the temperature is gradually increased stepwise over a period of about 12 to 24 hrs. to a final temperature of about 1300° C. At a temperature of about 1300° C. the vanadium oxide is held at least about 24 hrs e.g. 24 to 30 hrs. to ensure complete reduction of all vanadium to V 3+ . 
     Preheated analytical-grade oxides having a particle size of less than about 50 microns are used as starting materials for the other components of the solid solutions to be synthesized. For example, TiO 2  is heated for about 10 to 14 hrs. at a temperature in the range of about 600° C. to 800° C. and ZrO 2  is heated for about 10 to 14 hrs. at a temperature in the range of about 1000° C. to 1200° C. prior to being used in preparation of the final mixtures. The oxides are thereby demoisturized. They may be then cooled to ambient conditions. 
     The mixtures of the three oxide components are thoroughly mechanically ground together under acetone in a an agate mortar to ensure thorough mixing and a sufficiently small grain size e.g. less than 50 microns. For example, about 24 to 98 wt. % of V 2  O 3  is ground together with about 2 to 50 wt. % of ZrO 2  and about 0 to 66 wt. % of TiO 2  to produce a mixture having a grain size of less than about 50 microns. Complete formation of the desired compounds in the succeeding heat treatment is thereby promoted. Next, the oxide mixtures are pelletized at a pressure of about 5,000 psi or higher. The pellets may have any conventional size e.g. 1/16&#34; to 1&#34;. The pellets are then heated and reacted together at a temperature in the range of about 1100° C. to 1700° C., such as about 1100° C. to 1200° C., for a period in the range of about 1/2 to 48 hrs., such as about 1/2 to 2 hrs. (depending on the nature and solidus temperature of the phase to be synthesized) in a vertical tube furnace with carefully controlled oxygen pressures, in the range of 10 -10  to 10 -5  atmosphere. In the manner described previously for preparing V 2  O 3 , the pellets are heated in a furnace atmosphere provided by a gas mixture of CO 2  and H 2  or CO 2  and CO or H 2  O and H 2  in various desired volumetric mixing ratios. For example, the volumetric ratio CO 2  /H 2 , CO 2  /CO, or H 2  O/H 2  is typically in the range of about 10/1 to 1/1. These selected ratios are kept constant for the duration of the synthesis by use of a differential manometer. By this method the oxygen pressure at the specified temperature can be controlled to better than ±1%. The thermodynamic data for the water-gas shift reaction (CO 2  +H 2  =CO+H 2  O), on which the calculations were based, are known with extremely high accuracy (better than 0.1%). Hence, the method used herein ensures reliable accurate control of the oxidation state of vanadium during the synthesis. This is extremely important for optimization of the properties of the finished product. 
     At the time of the high temperature reaction in the range of about 1100° C. to 1700° C., all of the oxide pellets may be in the solid state or at least one, two or three of the oxide constituents may be in the molten state. At the reaction conditions prevailing in the subject process, solid solutions may be made by solid-state reactions considerably below temperatures at which a liquid phase is present. However, the presence of a liquid phase or a solid-liquid phase improves the kinetics of the reaction. 
     The individual oxide components are heated to a sufficiently high temperature to expel absorbed or adsorbed water. Well defined starting materials for accurately weighing up mixtures is thereby produced. V 2  O 5  was heated slowly in several steps to a temperature of about 600° C. to 1300° C., such as about 1100° C. to 1300° C. at controlled Oxygen pressures in order to preferably decompose the V 2  O 5  slowly to V 2  O 3 . By this means, violent reactions are avoided at the highest temperatures, and most of the vanadium is produced in the desired oxidation state V 3+ . 
     The oxide mixtures were heated at temperatures in the range of about 1100° C.-1700° C. in order to promote reaction among the oxide components to the desired finished products consisting mainly of one or more (solid-solution) phases. In one embodiment, the mixture of solid particles was heated to a temperature below the solidus, for example to about 1200°. The phase assemblage of the final product was produced entirely by solid state reaction. Under such conditions, the crystals were relatively small, typically, of about 0.5-3.0 microns. In another embodiment, the mixtures were heated to a sufficiently high temperature e.g. about 1700° C. to produce partial or complete melting. This speeds up the reaction and produces (solid solution) phases (crystals) of larger size, typically in the range of about 2-100 microns. After heating the mixtures at this high temperature for a period of time, such as 1/2-2 hrs., the composition is cooled to ambient conditions. For example, the composition may be cooled slowly (over a period of 1/2-1 hr) to about 1200° C. From this temperature, the composition may be cooled rapidly (quenched) to room temperature. During these runs the oxygen pressure of the gas phase was controlled by using gas mixtures of CO 2  and H 2 , CO 2  and CO, or H 2  O and H 2  with volumetric ratios CO 2  /H 2 , CO 2  /CO or H 2  O/H 2  in the range of about 10/1-1/1. 
     In addition to oxygen pressure, one other parameter influencing the oxidation state of vanadium in oxide phases has been utilized in synthesizing the new phases. This is the provision of host structures which incorporate vanadium in one (or more) valence state(s) in strong preference to other valence states. In the present case, the ternary solid solution phase of pseudobrookite structure in the system V 2  O 3  -ZrO 2  -TiO 2  serves this purpose. In this solid solution vanadium is present partly in the trivalent state, and partly in the tetravalent state, as stabilized by the preferential substitution of V 4+  for Ti 4+ . 
     The pellets of the composition involving V 2  O 3  -ZrO 2  -TiO 2  may be used as an oxidation catalyst, offering improved activity and yields and greater stability over a wider temperature range e.g. about 1000° C. or higher than that which is offered by typical oxidation catalysts. For example, as an oxidation catalyst the subject pellets may be used in the conversion of oxylene to phthalic anhydride, butane to maleic anhydride, or alcohols to aldehydes or organic acids. 
     As a high temperature refractory or as an ingredient in a high temperature refractory material for lining a gasifier for the partial oxidation of ash-containing liquid hydrocarbonaceous and solid carbonaceous fuels, the subject material would have a long life, withstanding attack from V 2  O 5 . For example, a thermal refractory for lining the reaction zone of a partial oxidation gas generator may comprise the previously described composition involving V 2  O 3  -ZrO 2  -TiO 2  in the amount of about 1 to 25 wt. %, and the remainder of the refractory e.g. about 75 to 99 wt. % involving oxides with a cationic portion that is selected from the group consisting of Cr, Mg, Al, Mn, Si and mixtures thereof. The partial oxidation reactor operates in a reducing atmosphere and at a temperature in the range of about 1700° F. to 3000° F. 
     The subject composition involving V 2  O 3  -ZrO 2  -TiO 2  may also be used as an additive. About 0.01 to 0.2 wt. % (basis weight of ash in the fuel fed to the gas generator) of additive may be introduced into the refractory lined partial oxidation gas generator along with the fuel feed to stabilize said refractory. 
     Various modifications of the invention as herein before set forth may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be made as are indicated in the appended claims.