Isomerization catalyst of group 8 metal/ZrO2/SiO2/WO2, and isomerization process using it

Abstract: A catalyst composition useful in isomerization of C₅+ feeds comprises a Group VIII metal, preferably a Group VIII noble metal, and a zirconia support impregnated with silica and tungsten oxide. The composition's use in an isomerization process is described.

Description: FIELD OF THE INVENTION Isomerization catalysts disclosed in the prior art continue to suffer major disadvantages when applied, for example, to long chain hydrocarbons e.g., C 7 +. For instance, large amounts of byproducts, consisting predominantly of cracked hydrocarbon materials, form in prior art isomerization methods along with the desired isomerate product. Cracking decreases the amount of long chain paraffins available for isomerization, thereby reducing the ultimate yield. Applicants have discovered that a catalyst composition comprising a Group VIII metal, preferably a Group VIII noble metal, and a zirconia support having both silica and tungsten oxide simultaneously present produces a solid acid catalyst that behaves differently from one having a Group VIII metal with either silica or tungsten oxide alone on the zirconia support. At 450°C, Group VIII noble metal-containing zirconia impregnated with silica alone is not active for nC 7 isomerization compared with either Group VIII noble metal containing tungsten oxide impregnated zirconia or Group VIII noble metal containing zirconia impregnated with both tungsten oxide and silica simultaneously. The tungsten oxide and silica impregnated Group VIII noble metal containing zirconia has comparable activity at 350°C to a tungsten oxide impregnated zirconia at 250°C; however, the selectivity to cracked product is substantially higher on zirconia impregnated with only tungsten oxide than on zirconia impregnated with both silica and tungsten oxide. Therefore, applicants have discovered a new catalyst which can act as a solid acid catalyst useful in isomerization reactions and leading to much lower selectivity to undesirable cracked products. SUMMARY OF THE INVENTION The invention is directed to a catalyst composition comprising a Group VIII metal, preferably a Group VIII noble metal, and a zirconia support impregnated with a mixture of silica and tungsten oxide. The invention is further directed to the use of the catalyst composition in an isomerization reaction. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the conversion (line A) and cracking (line B) selectivity in an isomerization reaction, of a zirconia support having impregnated therein tungsten oxide alone and containing 0.5% platinum and run at 250°C and the conversion (line C) and cracking selectivity (line D) of a zirconia support having both silica and tungsten oxide simultaneously impregnated therein and containing 0.5% platinum and run at 350°C. The figure shows that the impregnation of both tungsten oxide and silica affords a catalyst with lower cracking selectivity and comparable conversion. DETAILED DESCRIPTION The catalysts of this invention may be prepared by techniques well-known in the art, such as incipient wetness, impregnation, etc., the choice being left to the practitioner. When using the impregnation technique, the impregnation solution is contacted with the support material for a time sufficient to deposit the precursor material onto the support either by selective adsorption or alternatively, the excess solvent may be evaporated during drying leaving behind the precursor salt. Advantageously, incipient wetness techniques may also be used. The choice of catalyst preparation method is left to the practitioner. The catalyst of the present invention may be prepared from precipitated zirconium hydroxide. For example, ZrOCl 2 .8H 2 O can be dissolved in water and Zr(OH) 4 precipitated with ammonium hydroxide. Other compounds reacting to produce Zr(OH) 4 may also be used. The solid Zr(OH) 4 is then separated, for example, by filtration, washed and dried. A Group VIII metal may then be incorporated, for example, via the incipient wetness technique using a solution of chloroplatinic acid. The amount of Group VIII metal incorporated can range from 0.01 to 10 wt%, preferably 0.01-2 wt%, and most preferably from 0.3 to 1.0 wt%. The Group VIII metal may be selected from any of the Group VIII metals, and mixtures thereof. Preferably the Group VIII metal will be a noble metal selected from platinum, palladium, ruthenium, iridium, osmium, and mixtures thereof. Tungsten oxide and silica may then be impregnated into the support. Tungsten oxide and silica may be incorporated directly or any compounds of tungsten and silicon capable of forming tungsten oxide and silica upon calcination may be used to provide these oxides. Preferably the tungsten oxide and silica will be incorporated simultaneously. For example, a solution containing ammonium metatungstate as the source or precursor of tungsten oxide, and aqueous colloidal silica can be prepared and the Zr(OH) 4 or Zr(OH) 4 containing Group VIII metal immersed therein. Generally 5 to 25 wt%, preferably 10 to 15 wt% tungsten oxide will be added to the support. The amount of silica impregnated will range form 1 to 10 wt%, preferably 3 to 5 wt% based on the catalyst composition. Following impregnation of the oxides, or oxide precursors, and the Group VIII metal, the catalyst is dried and calcined to convert the Zr(OH) 4 to zirconia and the oxide precursors to oxides. Drying is conducted at temperatures of about 100°C to about 150°C and calcination at temperature of about 300°C to about 900°C. Preferably calcination temperatures will be about 400°C to about 600°C. Calcination time will be at least 1 hour, preferably about 4 hours. The impregnation of Group VIII metal, tungsten oxide and silica can be performed simultaneously or in any sequence. Though it is preferable to incorporate the Group VIII metal first, the order of addition is merely a matter of choice. The catalysts of the present invention are particularly useful for an isomerization reaction. The catalysts may be contacted with a C 5 + feedstream. Preferably a feedstream comprising C 5 to C 10 paraffins will be used. Isomerization can be conducted at temperatures below about 400°C, 0,69 to 20,7 MPa (100 to 3000 psi) H 2 , 4/1 to 10/1 H 2 /n-paraffin, and 0.1 to 10.0 LHSV, preferably the reaction is carried out at temperatures between about 300°C and 400°C, 5/1 H 2 /n-paraffin, and 1 to 2 W/W/hr. The invention is illustrated by the following example which is not limiting in any way. EXAMPLE 1: Preparation of Platinum Solution: 6.25 g of chloroplatinic acid containing 40% platinum, were dissolved in and diluted to one liter with water. The resultant solution contains 0.05 g Pt/20 cc of solution. Preparation of Zr(OH) 4 : 360 g of ZrOCl 2 .8H 2 O were dissolved in 2800 cc of water. Concentrated ammonium hydroxide solution ( ∼ 14M) was added with stirring at which point a precipitate forms. The addition of ammonium hydroxide solution is continued until the pH of solution reaches ∼ 10. The resulting slurry is then left to settle for two hours. The precipitate is filtered, washed with distilled water twice, then with water containing a sufficient quantity of ammonium hydroxide to keep the pH at ∼ 10. In order to remove any residual chloride, the solid is then reslurried into a 1M solution of ammonium hydroxide, the slurry is heated to 60°C, stirred and after one hour filtered and washed with water. The solid is then dried at 110°C overnight. Preparation of Pt/Zr(OH) 4 : 40 g of Zr(OH) 4 were immersed into 80 cc of the chloroplatinic acid solution, stirred and mixed for 5 minutes, filtered and dried overnight at 110°C. Preparation of Pt/ZrO 2 /WO 3 : A solution was prepared containing 4 g of ammonium metatungstate (Sylvania 92.2% WO 3 ) dissolved in 40 cc of water. 20 g of Pt/Zr(OH) 4 was immersed into this solution, stirred and mixed for five minutes, filtered and dried at 110°C overnight. This was then calcined at 600°C for three hours in air. Preparation of Pt/ZrO 2 /(WO 3 -SiO 2 ), platinum on zirconia containing tungsten oxide and silica. A solution was prepared by dissolving 2 g of ammonium metatungstate (92.2% WO 3 ) and 3.5 g of Ludox HS-40 colloidal silica (Dupont) into 20 cc of water. 10 g of Pt/Zr(OH) 4 was immersed into this solution, stirred and mixed for 5 minutes, filtered and dried at 110°C overnight. This was then calcined at 600°C for three hours in air. The Pt/ZrO 2 /WO 3 and Pt/ZrO 2 /(WO 3 -SiO 2 ) catalysts were then compared in an isomerization reaction using a n-heptane feed. The results, which are depicted in Figure 1 show that the silica tungsten oxide mixture (line C) has comparable activity at 350°C relative to the tungsten oxide only zirconia catalyst (line A) run at 250°C. However, the selectivity to cracked product is substantially higher on the tungsten oxide only zirconia (line B) than on the tungsten oxide-silica zirconia (line D). As used herein, conversion means the fraction expressed as % of feed converted, selectivity means the wt% of product formed/wt% of feed converted measured in %, activity is a measure of the amount in grams of feed converted per gram of catalyst per unit time.

Claims: A catalyst composition comprising a Group VIII metal and a zirconia support impregnated with silica and tungsten oxide. A catalyst composition according to claim 1 wherein said zirconia support is impregnated with a mixture comprising silica and tungsten oxide (or precursor(s) thereof). A catalyst composition according to claim 1 or claim 2 wherein said silica is present in an amount of from 1 to 10 wt%. A catalyst composition according to any one of claims 1 to 3 wherein said tungsten oxide is present in an amount of from 5 to 25 wt%. A catalyst composition according to any one for claims 1 to 5 wherein said Group VIII metal is present in an amount of from 0.01 to 10 wt%. A catalyst composition according to any one of claims 1 to 5 Group VIII metal is a Group VIII noble metal selected from the group consisting of platinum, palladium, ruthenium, osmium, iridium, and mixtures thereof. A catalytic isomerization process comprising contacting a C 5+ feed, under isomerization conditions, with a catalyst composition according to any one of claims 1 to 6. A catalytic isomerization process according to claim 7 wherein said C 5+ feed comprises C 5 to C 10 paraffins. A catalytic isomerization process according to claim 7 or claim 8 wherein said Group VIII metal is a Group VIII noble metal.

Inventors: GATES WILLIAM ELLIS, IGLESIA ENRIQUE, SOLED STUART LEON, GATES, WILLIAM ELLIS, IGLESIA, ENRIQUE, SOLED, STUART LEON
Applicants: EXXON RESEARCH ENGINEERING CO, EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1993
Main classification: B01J23
IPC codes: C07C5, C10G45, B01J23, C07B61