Porous inorganic catalyst support

Abstract: Olefin polymerisation catalyst on a porous inorganic support comprising (i) 99.5 to 83.3 parts by weight of SiO 2 , (ii) 0.5 to 10 parts by weight of Titanium and 0.85 to 1.15 parts by weight of chromium, this catalyst having a pore volume of 0.9 to 1.15 cc/g, a surface area of 440 to 540 m 2 /g and a mean pore diameter of between 70 and 100 Angstroms.

Description: Field of the Invention The present invention relates to a porous inorganic catalyst support, to a catalyst, to a process for manufacturing a porous catalyst support and to a polymerisation process using said catalyst. Background of the Invention Supported chromium catalysts have long been used in olefin polymerisation. In such products key parameters are pore volume, surface area and pore diameter. Whilst surface area and pore volume can to some extent be varied independently of one other, the pore diameter of the resulting support or catalyst is directly related to the surface area and pore volume. In particular, assuming cylindrical pores the average pore size (APD) in Angstroms is calculated as 40,000 PV(cm 3 /g)/SA(m 2 /g). Thus all three parameters influence catalyst performance and particularly the structure of the polyethylene produced. In general terms higher surface areas, pore volumes and pore diameters result in increased activity, whereas the molecular weight of the resultant polymer decreases with increase in average pore diameter. Clearly, because APD is related to surface area and pore volume as indicated above, changes in molecular weight are also effected by changes in surface area and pore volume. US 4,981,831 discloses a process for manufacturing a catalyst wherein a support is first formed by forming a silica titania cogel which is then first aged at neutral pH and then aged an alkaline pH. The twice aged cogel is then spray dried to form a xerogel and is then impregnated with chromium. This process requires two ageing steps which altogether are typically between 13 and 23 hours long. The obtained catalyst has a low surface area (300 to 400 m 2 /g), a pore volume of between 0.7 and 1.1 cm 3 /g and a mean pore diameter of between 6 and 12 nm (60 and 120 Angstroms). There is therefore a need for a process which avoids a two-step ageing while producing a catalyst with the required mean pore diameter and a satisfactory activity. EP 661 299 discloses a supported chromium catalyst system wherein the support has a specified surface area to pore volume relationship. Preferred supports have a surface area of 100 to 300 m 2 /g and the preferred pore volume is 1 to 2 cm 3 /g. WO 93/23438 describes an alternative catalyst support system which is a cogel of silica and at least one other metal oxide. The pore volume is high (at least 2 cm 3 /g) and the support is prepared by displacing water in the cogel with an organic liquid before spray drying. It has now been discovered that it is possible to avoid a two step ageing process as well as a spray drying step while nevertheless obtaining a product, with an increased surface area and keeping a pore volume above 0.9 cm 3 / g and maintaining an average pore diameter of about 7 to 10 nm (70 to 100 Angstroms), which exhibits satisfactory activity. Tests and Definitions i) Surface Area Surface Area is determined using standard nitrogen adsorption methods of Brunauer, Emmett and Teller (BET). ii) Pore Volume The pore Volume is determined by liquid titration. A known weight of a previously heated sample is titrated with small amounts of Isopropyl Alcohol. (Reference to method - Innes WB Anal., Chem. Vo123 (1956) 759). iii) Mean Pore Diameter Mean pore diameter is calculated from Surface Area and Pore Volume measurements according to Mean Pore Diameter (nm) = 4000 PV(cm 3 /g) SA(m 2 /g) iv) Activity expressed as gPE/gcatalyst/hr MI measured according to ASTM D1238, Condition 190/2.16HLMI measured according to ASTM D1238, Condition 190/21.6MIR is the HLMI/MI ratio. General Description of the Invention It is a first object of the present invention to provide a porous inorganic catalyst support comprising, on dry basis, 99.2 to 83.3% by weight of SiO 2 , preferably 99.2 to 93.3% 0.5 to 10% by weight of Titanium, preferably 0.5 to 5%, most preferably 0.5 to 4%. and having a pore volume of 0.9 to 1.15 cm 3 /g, a surface area of 440 to 540 m 2 /g and a mean pore diameter of between 7 and 10nm (70 and 100 Angstroms), preferably between 7.5 and 10 nm (75 and 100 Angstroms). Even more preferably the porous inorganic catalyst support comprises, on dry basis, 96.0 to 95.3% by weight of SiO 2 2.4 to 2.8% by weight of Titanium and has a pore volume of 1.0 to 1.12 cm 3 /g, a surface area of 440 to 540 m 2 /g and a mean pore diameter of between 8 and 10 nm (80 and 100 Angstroms). Preferably also, the porous inorganic catalyst support has an average particle size of 50 to 110 µm, most preferably between 60 and 100 µm. It is a second object of the present invention to provide a catalyst on a porous inorganic support as hereabove described further comprising, on dry basis, 0.85 to 1.15% w/w of chromium, preferably 0.9 to 1.1% w/w of chromium. Therefore, the catalyst of the invention comprises, 99.2 to 83.3 parts by weight of SiO 2 , preferably 99.2 to 93.3 pbw, most preferably 96.0 to 95.3 pbw, 0.5 to 10 parts by weight of Titanium, preferably 0.5 to 5 pbw, more preferably 0.5 to 4 pbw, even more preferably 2.4 to 2.8 pbw. 0.85 to 1.15 parts by weight of chromium, preferably 0.9 to 1.1 pbw, this catalyst having a pore volume of 0.9 to 1.15 cm 3 /g, preferably 1.0 to 1.12 cm 3 /g, a surface area of 440 to 540 m 2 /g and a mean pore diameter of between 7 and 10 nm (70 and 100 Angstroms), preferably between 7.5 and 10 nm (75 and 100 Angstroms), more preferably between 8 and 10 nm (80 and 100 Angstroms). It is a third object of the present invention to provide a process for manufacturing a porous catalyst support comprising the steps of: a) preparing a silica titania hydro-cogel b) washing said hydro-cogel until a sodium content of less than 0.1% by weight of solids is reached c) aging said hydro-cogel at a pH within the range of 7.4 to 7.8 for a period of 16 to 8 hours d) flash drying the obtained aged hydro-cogel. Typically, the aged hydro-cogel has, before drying, a solid content of 15-18% by weight. By flash drying it is meant short residence time pneumatic drying including spray drying. Preferably the flash-dried hydro-cogel is milled and screened to get an average particle size of 50 to 110 µm, preferably between 60 to 100 µm. The catalyst of the invention is particularly useful in olefin polymerisation. It is therefore a fourth object of the present invention to provide a process for olefin polymerisation wherein the polymerisation is performed using a catalyst comprising, 99.2 to 83.3 parts by weight of SiO 2 , preferably 99.2 to 93.3 pbw, most preferably 96.0 to 95.3 pbw, 0.5 to 10 parts by weight of Titanium, preferably 0.5 to 5 pbw, more preferably 0.5 to 4 pbw, even more preferably 2.4 to 2.8 pbw. 0.85 to 1.15 parts by weight of chromium, preferably 0.9 to 1.1 pbw, this catalyst having a pore volume of 0.9 to 1.15 cm 3 /g, preferably 1.0 to 1.12 cm 3 /g, a surface area of 440 to 540 m 2 /g and a mean pore diameter of between 7 and 10nm (70 and 100 Angstroms), preferably between 7.5 and 10nm (75 and 100 Angstroms), more preferably between 8 and 10 nm (80 and 100 Angstroms). General Description of the Invention The present invention will be further described in the following examples. Example 1 Preparation of Hydro-cogel A sulphuric acid solution containing 1.18% by weight of Titanium is prepared by mixing 36 parts by weight of 50% sulphuric acid with 50 parts by weight a titanium sulphate solution (4.53% Ti) and diluting with 107 parts by weight of water. This is mixed with a solution of sodium silicate prepared by diluting 4 parts by weight of Crystal 79, a commercially available sodium silicate solution, with 3 parts by weight of water. Solutions are used at ambient temperature. They are mixed continuously using a high shear mixer to obtain a hydrosol having a pH of 5 and a temperature of 32°C. The gelation time is about 2 minutes and the resultant silica gel has a SiO 2 content of 12%w/w and a Ti content of 0.32%w/w. Washing and Aging the Hydro-cogel The hydro-cogel is washed, using a series of exchanges with Ammonium nitrate solutions, until a sodium content of less than 0.1% by weight of solids is obtained. Washing is performed at ambient temperature. The pH is then increased to pH 7.8 by the addition of ammonium hydroxide. The hydro-cogel is hydrothermally aged at pH 7.8 and a temperature of 80°C for 8 hours. At this stage the hydro-cogel is about 15%w/w SiO 2 and has a Ti content of about 0.4% w/w. Drying Water is removed directly from hydro-cogel by flash drying. The resulting xerogel has a Total Volatiles content measured at 500°C of 13.3% and a Pore Volume of 1.08 cm 3 /g. Milling and Screening The resulting granular xerogel is milled and screened at 38 and 150 µm (microns) to generate product with average particle size of 100 µm (microns). Chromium Impregnation Impregnation is performed using an aqueous solution of Cr (Acetate)3 to achieve 1% Cr on silica titania hydro-cogel. The obtained material is again submitted to a rapid drying to remove water. Product The obtained catalyst has the following characteristics: SiO 2 95.6 %w/w Ti 2.64 %w/w (4.4% TiO2) Cr 1.04 %w/w SA 514 m 2 /g PV 1.05 cm 3 /g Average particle Size 99 µm Average pore diameter 8.2nm (82 Angstroms) Soda 173 ppm The obtained catalyst exhibits the following Performance Data. The catalyst is activated in a fluidised bed reactor. Fluidising gas used is predried air and a final hold temperature of 700°C is maintained for 5 hours prior to cooling and switching from dry air to dry nitrogen. This activated catalyst is tested in ethylene polymerisation using a slurry reactor operating at 103°C and 4.1 mPa (600psi). Polymerisation is continued to a productivity of approximately 2000g/g. Values obtained for induction time (mins), catalyst activity (g/g/hr)and MI and HLMI values of resulting polymer are tabulated below. MI and HLMI values quoted are corrected to productivity of 2000 g/g. Test 1 Test 2 Induction time 4 4 Catalyst Charge 0.103g 0.136g Activity 1898 1978 MI 0.04 0.04 HLMI 6.1 5.0 MIR 152 126 Example 2 A xerogel as produced in example 1 was milled and screened and then impregnated with chromium to get a product having a surface area of 498 m 2 /g, a pore volume of 1.05 cm 3 /g, an average pore diameter of 8.4 nm (84 Angstroms) and an average particle size of 66 micrometers. The catalyst was then tested as in Example 1 at a catalyst charge of 0.132 g. The performances are summarized as follows: Test 3 Catalyst Charge (g) 0.132 Induction Time (min) 1 Activity (g/g/hr) 2660 MI 0.03 HLMI 6.5 MIR 217 Example 3: A sulphuric acid solution containing 2.26% Ti by weight of Titanium is prepared by mixing 39 parts by weight of a 77% sulphuric acid solution with 10 parts by weight of a titanium sulphate solution (4.8% Ti) and diluting with 38 parts by weight of water. This is mixed with a solution of sodium silicate prepared by diluting 4 parts by weight of Crystal 79, a commercially available sodium silicate solution, with 3 parts by weight of water. Solutions are mixed continuously using a high shear mixer to obtain a hydrosol having a pH of 5 and a temperature of 31°C. The hydrocogel is washed and aged as described in Example 1. The resulting hydrogel is about 15%w/w SiO 2 and has a Ti content of 0.78% w/w. Water is removed directly from the hydrocogel by flash drying. The resulting xerogel has a Total Volatiles content measured at 500°C of 8.5%, a Pore Volume of 0.95cm 3 /g, a Surface Area of 524m 2 /g and a Titanium content of 5.06%. The resulting granular xerogel is milled and screened as in Example 1. Chromium impregnation is performed using an aqueous solution of Cr(Acetate) 3 to achieve 1%w/w Cr. The resulting catalyst is activated in a fluidised bed reactor and tested in ethylene polymerisation using a slurry reactor as described in Example 1. The following performance characteristics were recorded. Test 4 Test 5 Catalyst Charge (g) 0.162 0.139 Induction Time (min) 0 5 Activity (g/g/hr) 2444 2283 MI 0.03 0.04 HLMI 5.6 5.3 MIR 187 133

Claims: Porous inorganic catalyst support comprising, on dry basis, 99.2 to 83.3% by weight of SiO 2 , 0.5 to 10% by weight of titanium, and having a pore volume, as determined by liquid titration using isopropanol, of 0.9 to 1.15 cm 3 g -1 , a BET surface area of 440 to 540 m 2 g -1 and a mean pore diameter of between 7 and 10 nm (70 - 100 Å). Porous inorganic catalyst support according to claim 1 characterised in having a content of SiO 2 in the range 99.2 to 93.3% by weight on a dry basis. Porous inorganic catalyst support according to claim 1 or 2 characterised in having a content of titanium in the range 0.5 to 5% by weight on a dry basis. Porous inorganic catalyst support according to any one of the preceding claims characterised in that the mean pore diameter is in the range 7.5 to 10 nm (75 - 100Å) Porous inorganic catalyst support according to claim 1 comprising, on dry basis, 96.6 to 95.3% by weight of SiO 2 , 2.4 to 2.8% by weight of titanium, and having a pore volume, as determined by liquid titration using isopropanol, of 1.0 to 1.12 cm 3 g -1 , a surface area of 440 to 540 m 2 g -1 and a mean pore diameter of between 8 and 10 nm (80 - 100 Å) Porous inorganic catalyst support according to any one of the preceding claims and having an average particle size of 50 to 110 µm. Porous inorganic catalyst support according to claim 6 characterised in that the average particle size is in the range 60 to 100 µm. Catalyst on a porous inorganic catalyst support comprising 99.2 to 83.3 parts by weight of SiO 2 , 0.5 to 10 parts by weight of titanium, 0.85 to 1.15 parts by weight of chromium, this catalyst having a pore volume, as determined by liquid titration using isopropanol, of 0.9 to 1.15 cm 3 g -1 , a surface area of 440 to 540 m 2 g -1 and a mean pore diameter of between 7 and 10 nm (70 - 100 Å) Catalyst according to claim 8 comprising 96.0 to 95.3 parts by weight of SiO 2 . Catalyst according to claim 8 or 9 comprising 2.4 to 2.8 parts by weight of titanium. Catalyst according to claim 8, 9 or 10 comprising 0.9 to 1.1 parts by weight of chromium. Catalyst according to any one of claims 8 to 11 characterised in having a pore volume, as determined by liquid titration using isopropanol, of 1.0 to 1.12 cm 3 g -1 . Catalyst according to any one of claims 8 to 12 characterised in having a mean pore diameter in the range 8 to 10 nm (80 - 100 Å) Process for manufacturing a porous catalyst support according to any one of claims 1 to 7 comprising the steps of a) preparing a silica titania hydro-cogel b) washing said hydro-cogel until a sodium content of less than 0.1% by weight of solids is reached c) ageing said hydro-cogel at a pH within the range of 7.4 to 7.8 for a period of 16 to 8 hours d) flash drying the obtained aged hydro-cogel. Process according to claim 14 characterised in that the flash-dried cogel is milled and screened to get an average particle size of 50 to 110 µm. Process according to claim 15 characterised in that the average particle size is in the range 60 to 110 µm. Process for olefin polymerisation characterised in that the polymerisation is performed using a catalyst according to any one of claims 8 to 13.

Inventors: MARSDEN CHRISTINE ELIZABETH, REGAN JOHN MICHAEL, MARSDEN, CHRISTINE ELIZABETH, REGAN, JOHN MICHAEL
Applicants: INEOS SILICAS LTD, INEOS SILICAS LIMITED
Application year: 1997
Main classification: C08F4
IPC codes: B01J23, C08F10, B01J35, C08F4