Chromium phyllosilicate clay alpha-olefin catalysts

Abstract: A process for preparing pillared chromium phyllosilicate clay α-olefin catalysts is disclosed This process utilizes palygorskite and sepiolite clays. The pillaring of said clays comprise the steps of: (a) preparing a hydrolyzed first solution by dissolving a chromium salt and a base in water, heating said first solution to a temperature in the range of about 20°C to about 100°C while stirring continuously until the solution reaches a pH in the range of about 1.5 to about 2.5 and thereby producing a master batch; (b) diluting said master batch with water to produce a diluted second solution and heating said diluted second solution to produce a heated second solution; (c) adding a solid clay selected from the group consisting of sepiolites and palagorskites to said heated second solution, and continuing heating; (d) recovering said pillared chain silicate clay; (e) drying said pillared chain silicate clay to form first product; The activation of said clays comprise the steps of: (a) heating said first product at a temperature in the range of about 150°C to about 500°C and for a time period in the range of about 30 minutes to about 10 hours in an inert atmosphere; (b) thereafter reheating said first product at a temperature in the range of about 500°C to about 900°C and for a time period in the range of about 1 hour to about 50 hours in an oxidizing atmosphere and recovering said catalyst composition. This results in clay catalysts which polymerize α-olefins.

Description: This invention relates to a process for forming clay catalysts that can be used in a catalyst system for the polymerization of α-olefins. In one aspect, the present invention relates to preparing polymerization catalysts, which are useful in a process for polymerizing α-olefins. BACKGROUND OF THE INVENTION The preparation of pillared interlayer clay compositions by reacting a smectite-type clay with an aqueous solution of suitable polymeric cationic hydroxy metal complexes of metals, such as aluminum, titanium, zirconium and chromium is known, as illustrated in U.S. Patent Nos. 4,665,045, 4,742,033. Further, U.S. Patent No. 4,665,045, Pinnavaia et al. discloses that such pillared interlayed clay compositions that are prepared with chromium can be used in olefin polymerization. Another process for the polymerization of ethylene, under slurry polymerisation conditions, is described in GB-A-2 099 005. A catalyst comprising chromium oxide supported on a silica-support material is used along with either an organ-aluminium or a dihydrocarbylmagnesium compound. However, there is an ever present need to develop pillared interlayered clays with new processes that result in different catalysts. Equally important is the need to develop a process to produce efficient clay catalysts on a commercial scale. Further, a better understanding of the considerable diversity within this group of clays is needed such that the type of polymers produced can be explored for special or unique properties. SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a novel method for preparing catalyst compositions, which are useful as catalyst compositions well-adapted for the polymerization of α-olefins, thereby improving the process for the polymerization of α-olefins. This object of the present invention will become apparent from the disclosure and claims herein provided. In accordance with the present invention, there is provided a novel method for preparing a catalyst composition efficient for use in the polymerization of α-olefins by preparing a pillared phyllosilicate clay comprising the following steps of: (a) preparing a hydrolyzed first solution by dissolving a chromium salt and a base in water, heating said first solution to a temperature in the range of 20°C to 100°C while stirring continuously until the solution reaches a pH in the range of 1.5 to 2.5 and thereby producing a master batch; (b) diluting said master batch with water to produce a diluted second solution and heating said diluted second solution to a temperature from 20 to 100°C to produce a heated second solution; (c) adding a solid phyllosilicate clay selected from dioctahedral and trioctahedral smectites to said heated second solution, and continuing heating; (d) recovering said pillared phyllosilicate clay; and (e) drying said pillared phyllosilicate clay to form a first product. In a further embodiment there is provided the activation of said clay comprising the following steps of: (a) heating said first product at a temperature in the range of 150°C to 550°C and for a time period in the range of 30 minutes to 10 hours in an inert atmosphere; (b) thereafter heating said first product at a temperature in the range of 500°C to 900°C and for a time period in the range of 1 hour to 50 hours in an oxidizing atmosphere and recovering said catalyst composition. In further accordance with the present invention, there is provided an improved method for the polymerization of α-olefins which results in polymer compositions and which comprises: contacting at least one mono-1-olefin having 2 to 8 carbon atoms per molecule with said catalyst; optionally copolymerizing with a comomomer having from 3 to 8 carbon atoms per molecule; and optionally combining said catalyst with an organo-metal cocatalyst. DETAILED DESCRIPTION General Preparation of Chromium - Pillared Clays The clays employed in the present invention are the dioctahedral and trioctahedral smectites which have a platelet morphology containing extended sheets of silica tetrahedra and alumina octahedra (smectites) or sheets of silica tetrahedra and magnesia octahedra joined together. The natural abundance and commercial availability of clays make them an inexpensive alternative to more costly synthetic silicas presently used for olefin polymerization. The method employed consists of considerable modifications to the process disclosed in Pinnavaia et al of U.S. patent 4,665,045. One differentiating factor is that Pinnavaia is limited to "...an aqueous slurry of a layer lattice clay." The present invention provides a novel process for preparing a pillared phyllosilicate clay; the first step of which is preparing a hydrolyzed first solution by dissolving a chromium salt and a base in water, heating said first solution to a temperature in the range of 20°C to 100°C while stirring continuously until the solution reaches a pH in the range of 1.5 to 2.5 and thereby producing a master batch. The heating accomplishes in a reasonable time the hydrolytic polymerization of chromium while the pH indicates when to stop heating so as to optimize the concentration of the highly polyhydroxy chromium oligomers. Using the pH of said first solution to determine when heating is sufficient is a novel method of accomplishing what is referred to in prior patents as "aging". Preferably, the heating is conducted at a temperature of about 90°C while stirring continues until said first solution reaches a pH of about 2.3. Said base is selected from sodium carbonate, ammonium carbonate, sodium hydroxide and ammonium hydroxide with preference given to sodium carbonate. Said salt is selected from chromium nitrate and chromium acetate with preference given to chromium nitrate. The second step is diluting said master batch with water to produce a diluted second solution and heating said diluted second solution to a temperature from 20 to 100°C to produce a heated second solution. It was discovered that achieving said diluted master batch facilitates the goal of producing said pillared phyllosilicate clay on a commercial scale. Pinnavaia discloses the preparation of a clay slurry to be contacted with a chromium solution. In accordance with the present invention, said master batch containing chromium in solution is diluted, and dry (i.e. powdered or free flowing) clay is added. When said pillared phyllosilicate clay is prepared on a commercial scale, the liquid volume required to slurry such quantities is too great to be viable. It is unexpected that by diluting said master batch in lieu of slurrying said clay, the liquid volume required is reduced to less than one-fourth of that otherwise required. The dilution step also provides a means whereby the chromium content of the final catalyst can be controlled. When known methods of preparing pillared silicate clays are used, the final clay product is high in chromium content; and when this product is utilized as a polymerization catalyst, an unacceptably high amount of Cr(VI) is present. Possible health hazards associated with Cr(VI) are diminished, when the initial chromium content is controlled via the method of the present invention. Said dilution is carried out such that said first solution is diluted to the ratio of 0.5 ml H₂O to 10 ml H₂O to about 1 ml master batch, with a preferred amount of H₂O being 4 ml H₂O to about 1 ml master batch. Said said second solution is heated to a temperature in the range of 20°C to 100°C with a preferred heating at about 90°C. The third step comprises adding a solid clay selected from dioctahedral and trioctahedral smectites to said heated second solution. The clay is added in solid form for the reasons set out supra. The liquid volume of said second solution is in the range of 1 ml to 50 ml per gram of clay and contains an amount of chromium in the range of 0.001 g to 0.01 g per ml of said second solution, with a preferred volume of said second solution being about 5 ml per g of clay and containing about 0.002 g of chromium per ml of said second solution. The pillared clay obtained according to the invention may be recovered by conventional methods well known to those skilled in the art. However, it is preferred that said pillared phyllosilicate clay be washed and centrifuged with an initial series of washes being conducted with H₂O and a secondary series of washes being conducted with an alcohol for the purpose of removing unbound H₂O before the final drying step and thereby minimizing the collapse of the clay pore structure due to the surface tension of the H₂O during the drying process. This produces a first product which is thereafter dried using any method known to those of skill in the art such as oven or vacuum, or freeze drying. Other methods to remove water include azeotrope drying or spray drying. General Activation of Chromium-Pillared Clays The dried chromium pillared clays can be activated to achieve a catalyst system by performing the following steps which comprise: (a) heating said first product at a temperature in the range of 150°C to 550°C and for a time period in the range of 30 minutes to 10 hours in an inert atmosphere, with a preferred temperature of about 500°C for a time period of about 1 hour; (b) thereafter heating said first product at a temperature in the range of 500°C to 900°C and for a time period in the range of 1 hour to 50 hours in an oxidizing atmosphere and recovering a second product, with a preferred temperature of about 650°C for a time period of about 3 hours. Optionally, the activation may further comprise cooling said second product to a temperature in the range of 300°C to 500°C and for a time period in the range of 1 minute to 5 hours in a reducing atmosphere, with a preferred temperature of about 350°C for a time period of about 30 minutes. The optional heating accomplishes a more productive olefin polymerization catalyst than that which is made via a one-step continuous heating. General Polymerication Process Utilizing Novel Catalyst System A polymerization process to be carried out with the catalyst obtained according to the present invention requires that at least one mono-1-olefin having 2 to 8 carbon atoms per molecule be contacted with said novel catalyst system. The olefin is selected from ethylene, propylene, 1-pentene, 1-hexene, and 1-octene. Preferably said olefin is predominantly ethylene. A comonomer may be copolymerized with ethylene to form an ethylene copolymer. Said comonomer can be selected from propylene, 1-butene, 1-pentene, 1-hexene, and 1-octene. Preferred copolymers are those of ethylene and 0.4 to 1 weight percent of a comonomer selected from C₄ to C₁₂ mono-1-olefins, most preferably hexene. Additionally, said catalyst system may be combined with an organo-metal cocatalyst selected from triethylaluminum, triethylboron, and diethylsilane. Preferred cocatalyst is triethylaluminum. EXAMPLES Preparation of Chromium-Smectite Dioctahedral Pillared Clay Example I The clay used was the Wyoming bentonite, HPM-20, obtained from American Colloid Company. The analysis supplied by the vendor indicates that the dioctahedral clay was comprised of the following compounds, calculated in oxide form: 63.02 weight percent SiO₂; 21.08 weight percent Al₂O₃; 3.25 weight percent Fe₂0₃, 0.35 weight percent FeO; 2.67 weight percent MgO; 2.57 weight percent Na₂O; 0.65 weight percent CaO; 0.07 weight percent TiO; and 5.64 weight percent H₂O. The cation exchange capacity was measured at 68.7 meq/100g. Nitrogen pore size distribution measurements showed a surface area of 34 m²/g and a pore volume of 0.15 ml/g. Preparation of Master Batch : Dissolved were 1333 g (3.33 moles) of Cr(NO₃)₃·9H₂O in 13.3 liter of deionized water to which was added slowly, while stirring, a solution made by dissolving 353 g (3.33 moles) of Na₂CO₃ in 6.7 liter of deionized water. While stirring continuously, the mixture was heated to 90-95°C for 15 to 24 hours replenishing any water lost because of evaporation. The mixture was cooled and stored at ambient temperature. 350 ml of dionized water was heated to 90-95°C. To this hot solution were added 50 ml of master batch. After the 90°C temperature of the solution was reestablished, 20 g of (bentonite) clay was added slowly while continually stirring. After the addition of the clay, stirring and heating of the solution was continued for 90 minutes. After cooling to ambient temperature the mixture was transferred to a 1 liter centrifuge bottle. The mixture was centrifuged and washed six times with 500 ml portions of deionized water followed by four times with 500 ml portions of methanol. The pillared clay was dried in a vacuum oven set at 52°C with a nitrogen purge for 40 hours. The sample was ground using a Laboratory mill (Janke & Kunkel KG, Type A10) and passed through a No. 50 sieve to achieve Product A. Activation Example II Product A was activated for polymerization in a laboratory sized fluidized bed (48 mm O.D. quartz tube) at elevated temperatures by sequential treatment with a stream of dry nitrogen for one hour at 500°C, followed by a stream of dry air for three hours at 650°C. After activation, the catalyst was cooled under a stream of dry nitrogen to ambient temperature, recovered and stored in dry nitrogen until ready for use to produce Catalyst A1. Example III Activated in a similar manner to A1 except after air oxidation, the catalyst was cooled under nitrogen to 350°C, at which temperature a stream of dry CO is passed through the catalyst bed for 30 to 45 minutes. The CO was then purged with dry nitrogen while cooling to ambient temperature. Catalyst was recovered and stored as above to produce Catalyst A2. Preparation of Chromium-Smectite Trioctahedral Pillared Clay Catalysts, An example of a smectite trioctahedral clay used, was the hectorite, Imvitone 38H, obtained from Industrial Mineral Ventures of Las Vegas, Nevada. Example IV The process as described in Example I was repeated, except that 20 g of hectorite clay were used instead of the bentonite to achieve Product B. Activation Example V Product B was activated as described in Example II to produce Catalyst B1. Example VI Product B was activated as described in Example III to produce Catalyst B2. Example VII Product B was activated in the manner described in Example II except that Product B was heated to 650°C for four hours without the preparatory nitrogen step to produce Catalyst B3. Polymerization Example VIII The polymerization of ethylene alone or in admixture with hexene-1 comonomer was carried out in a particle form process employing a 2.6 liter stainless-steel jacketed reactor. After flushing the clean reactor with dry nitrogen and dry isobutane vapor, one liter of dry, liquid isobutane was added as diluent. The sealed reactor was heated to the specified temperature after which a weighted amount of catalyst (0.03 to 1 g) was charged and a solution of cocatalyst, if used, amounting to 1.0-2.0 ml of a 0.5 weight percent organometal compound such as triethylaluminum, triethylboron, diethylsilane or a mixture thereof. The reactor was then pressurized to 3.9 MPa (550 psig) with ethylene and maintained at that pressure throughout the reaction with ethylene flow being regulated by the rate of polymerization. Polymerization time was normally one hour. The productivity is calculated by dividing the weight of the dried reactor product by the weight of catalyst for a one-hour run and is expressed in terms of g per polymer per g catalyst per hour. Polymerization times deviating from 60 minutes are normalized to 60 minutes by assuming a linear polymerization response during the run. Thus, the uncorrected productivity value is corrected to 60 minutes by multiplying it with 60 and dividing that result by the actual polymerization time in minutes. The catalyst, polymerization conditions, results and selected properties of the polyethylenes obtained are presented in Table I. Polymerization Results and Polyethylene Properties Catalyst No.(a) Temp. °C Adjuvant (ppm) Polymer Properties Productivity g/g/hr HLMI Density g/cm³ A1 95 TEA(5) 300 A2 95 TEA(5) 400 0.02 B1 95 TEA(5) 1100 0.06 B2 95 TEA(5) 780 0.27 B2 95 TEA(5) 520 0.23 0.946 B3 95 TEA(5) 650

Claims: A process for preparing a pillared phyllosilicate clay which comprises: (a) preparing a hydrolyzed first solution by dissolving a chromium salt and a base in water, heating said first solution to a temperature from 20 to 100°C while stirring continuously until the solution reaches a pH of 1.5 to 2.5 and thereby producing a master batch; (b) diluting said master batch with water to produce a diluted second solution and heating said diluted second solution to a temperature from 20 to 100°C to produce a heated second solution; (c) adding a solid phyllosilicate clay selected from dioctahedral and trioctahedral smectites to said heated second solution, and continuing heating; (d) recovering said pillared phyllosilicate clay; and (e) drying said pillared phyllosilicate clay to form a first product. The process of claim 1 wherein said base is selected from sodium carbonate, ammonium carbonate, sodium hydroxide and ammonium hydroxide, in particular wherein said base is sodium carbonate. The process of any of the preceding claims wherein said salt is selected from chromium nitrate and chromium acetate, in particular wherein said salt is chromium nitrate. The process of any of the preceding claims wherein said heating of said first solution in step (a) is conducted at a temperature of about 90°C while stirring continues until said first solution reaches a pH of about 2.3. The process of any of the preceding claims wherein said first solution is diluted in step (b) to the ratio of 0.5 to 10 ml H₂O to about 1 ml master batch, in particular wherein said first solution is diluted to the ratio of about 4 ml H₂O to 1 ml master batch. The process of any of the preceding claims wherein said second solution in step (b) is heated to a temperature of about 90°C. The process of any of the preceding claims wherein the liquid volume of said second solution in step (b) is from 1.0 to 50 ml per gram of clay and contains an amount of chromium from 0.001 to 0.01 gram per ml of said second solution. The process of any of the preceding claims wherein the liquid volume of said second solution in step (b) is about 5 ml per gram of said dioctahedral smectite and contains about 0.002 gram of chromium per ml of said second solution. The process of claims 1 to 7 wherein said liquid volume of said second solution in step (b) is about 9 ml per gram of said trioctahedral smectite and contains about 0.0022 gram of chromium per ml solution. The process of claims 1 to 8 for preparing said pillared phyllosilicate clay which comprises: (a) preparing a hydrolyzed first solution by dissolving chromium nitrate and sodium carbonate in water, heating said first solution to a temperature of about 90°C while stirring continues until said first solution reaches a pH of about 2.3 and thereby producing a master batch; (b) diluting said master batch with water to achieve a ratio of about 4.0 ml H₂O to about 1 ml master batch to produce a diluted second solution and heating said diluted second solution at a temperature of about 90°C; (c) adding solid dioctahedral smectite clay to said second solution in a ratio of about 5.0 ml of second solution per gram of clay wherein said second solution contains 0.002 gram of chromium; (d) recovering said pillared phyllosilicate clay to produce a first product by washing and centrifuging said second solution and thereafter drying said first product. The process of any of the preceding claims further comprising activating said pillared phyllosilicate clay first product to produce a catalyst. The process of claim 11 wherein said activating of said first product comprises: (a) heating said first product at a temperature from 150 to 550°C and for a time period from 30 minutes to 10 hours in an inert atmosphere; (b) thereafter reheating said first product at a temperature from 500 to 900°C and for a time period from 1 hour to about 50 hours in an oxidizing atmosphere and recovering a second product. The process of claim 12 wherein said first product is heated at a temperature in an inert atmosphere of about 500°C for a time period of about 1 hour; and said first product is reheated at a temperature of about 650°C for a time period of about 3 hours in an oxidizing atmosphere. The process of claim 12 or 13 further comprising treating said second product at a temperature from 300 to 500°C and for a time period from 1 minute to 5 hours in a reducing atmosphere, in particular wherein said second product is treated at a temperature of about 350°C for a time period of about 30 minutes in a reducing atmosphere. The process of any of claims 11 to 14 further comprising combining said catalyst with an organo-metal cocatalyst, in particular wherein said organo-metal cocatalyst is selected from triethylaluminum, triethylboron, and diethylsilane, more particularly triethylaluminum.

Inventors: SHVEIMA JOSEPH SAMUEL, SHVEIMA, JOSEPH SAMUEL
Applicants: PHILLIPS PETROLEUM CO, PHILLIPS PETROLEUM COMPANY
Application year: 1992
Main classification: C08F10
IPC codes: C08F4, C08F10, C01B33