Process for the polymerization of propylene

Abstract

The invention relates to a process for the preparation of polypropylene having: a molecular weight of 450,000-950,000, a molecular weight distribution of 3-6, and xylene soluble content of 2-6 wt %, by converting propylene into the polypropylene without pre-polymerization in the presence of a polymerization catalyst under a condition where the volume ratio of H.sub.2 to propylene is at most 0.0020, wherein the catalyst comprises a catalyst component and a co-catalyst, wherein the catalyst component is obtained by a process wherein a compound with formula Mg(OAlk).sub.xCl.sub.y wherein x is larger than 0 and smaller than 2, y equals 2−x and each Alk, independently, represents an alkyl group, is contacted with a titanium tetraalkoxide and/or an alcohol in the presence of an inert dispersant to give an intermediate reaction product and wherein the intermediate reaction product is contacted with titanium tetrachloride in the presence of an internal donor.

Claims

1. A process for the preparation of polypropylene comprising: converting propylene into the polypropylene without pre-polymerization in the presence of a polymerization catalyst under a condition where the volume ratio of H.sub.2 to propylene is at most 0.0020; wherein the catalyst comprises a catalyst component and a co-catalyst, wherein the catalyst component is obtained by a process wherein a compound with formula Mg(OAlk).sub.xCl.sub.y wherein x is larger than 0 and smaller than 2, y equals 2−x and each Alk, independently, represents an alkyl group, is contacted with a titanium tetraalkoxide and/or an alcohol in the presence of an inert dispersant to give an intermediate reaction product and wherein the intermediate reaction product is contacted with titanium tetrachloride in the presence of an internal donor; wherein the polypropylene has a molecular weight of 450,000 to 950,000; a molecular weight distribution of 3 to 6; a melt flow in the range of 7 to 14 dg/min measured with a load of 21.6 kg at 230° C. or 0.05 to 2 dg/min measured with a load of 2.16 kg at 230° C.; and a xylene soluble content of 2 to 6 wt %.

2. The process according to claim 1, wherein the volume ratio of H.sub.2 to propylene is at most 0.0010.

3. The process according to claim 1, wherein the volume ratio of H.sub.2 to propylene is substantially 0.

4. The process according to claim 1, wherein the co-catalyst is an organoaluminium compound.

5. The process according to claim 4, wherein the co-catalyst is triethyl aluminium.

6. The process according to claim 1, wherein the catalyst further comprises an external donor.

7. The process according to claim 6, wherein the external donor is cyclohexylmethyldimethoxysilane.

8. The process according to claim 7, wherein the molar ratio of the co-catalyst to the external donor is 0.33 to 0.52.

9. The process according to claim 8, wherein the molar ratio of the co-catalyst to the external donor is 0.38 to 0.44.

Description

1. CATALYST PREPARATION

(1) In all examples below, the catalyst prepared by the following process was used.

(2) A. Grignard Formation Step

(3) A stainless steel reactor of 91 volume was filled with magnesium powder 360 g. The reactor was brought under nitrogen. The magnesium was heated at 80° C. for 1 hour, after which a mixture of dibutyl ether (1 liter) and chlorobenzene (200 ml) was added. Then iodine (0.5 g) and n-chlorobutane (50 ml) were successively added to the reaction mixture. After the colour of the iodine had disappeared, the temperature was raised to 94° C. Then a mixture of dibutyl ether (1.6 liter) and chlorobenzene (400 ml) was slowly added for 1 hour, and then 4 liter of chlorobenzene was slowly added for 2.0 hours. The temperature of reaction mixture was kept in interval 98-105° C. The reaction mixture was stirred for another 6 hours at 97-102° C. Then the stirring and heating were stopped and the solid material was allowed to settle for 48 hours. By decanting the solution above the precipitate, a solution of phenylmagnesiumchloride reaction product A has been obtained with a concentration of 1.3 mol Mg/l. This solution was used in the further catalyst preparation.

(4) B. Preparation of the First Intermediate Reaction Product (Mg(OAlk).sub.xCl.sub.y)

(5) The solution of reaction product of step A (360 ml, 0.468 mol Mg) and 180 ml of a solution of tetraethoxysilane (TES) in dibutyl ether (DBE), (55 ml of TES and 125 ml of DBE), were cooled to 10° C., and then were dosed simultaneously to a mixing device of 0.45 ml volume supplied with a stirrer and jacket. Dosing time was 360 min. Thereafter the premixed reaction product A and the TES-solution were introduced to a reactor. The mixing device (minimixer) was cooled to 10° C. by means of cold water circulating in the minimixer's jacket. The stirring speed in the minimixer was 1000 rpm. The stirring speed in reactor was 350 rpm at the beginning of dosing and was gradually increased up to 600 rpm at the end of dosing stage.

(6) On the dosing completion the reaction mixture was heated up to 60° C. and kept at this temperature for 1 hour. Then the stirring was stopped and the solid substance was allowed to settle. The supernatant was removed by decanting. The solid substance was washed three times using 500 ml of heptane. As a result, a pale yellow solid substance, reaction product B (the solid first intermediate reaction product; the support), was obtained, suspended in 200 ml of heptane. The average particle size of support was 22 μm and span value (d90−d10)/d50=0.5.

(7) C. Preparation of the Second Intermediate Reaction Product

(8) Support activation was carried out as described in Example IV of WO/2007/134851 to obtain the second intermediate reaction product.

(9) In inert nitrogen atmosphere at 200° C. a 250 ml glass flask equipped with a mechanical agitator is filled with slurry of 5 g of reaction product B dispersed in 60 ml of heptane. Subsequently a solution of 0.22 ml ethanol (EtOH/Mg=0.1) in 20 ml heptane is dosed under stirring during 1 hour. After keeping the reaction mixture at 200 C for 30 minutes, a solution of 0.79 ml titanium tetraethoxide (TET/Mg=0.1) in 20 ml of heptane was added for 1 hour.

(10) The slurry was slowly allowed to warm up to 300 C for 90 min and kept at that temperature for another 2 hours. Finally the supernatant liquid is decanted from the solid reaction product (the second intermediate reaction product; activated support) which was washed once with 90 ml of heptane at 30° C.

(11) D. Preparation of the Catalyst Component

(12) A reactor was brought under nitrogen and 125 ml of titanium tetrachloride was added to it. The reactor was heated to 90° C. and a suspension, containing about 5.5 g of activated support in 15 ml of heptane, was added to it under stirring. The reaction mixture was kept at 90° C. for 10 min. Then add 0.866 g of ethyl acetate (EA/Mg=0.25 mol). The reaction mixture was kept for 60 min (I stage of catalyst preparation). Then the stirring was stopped and the solid substance was allowed to settle. The supernatant was removed by decanting, after which the solid product was washed with chlorobenzene (125 ml) at 900 C for 20 min. Then the washing solution was removed by decanting, after which a mixture of titanium tetrachloride (62.5 ml) and chlorobenzene (62.5 ml) was added. The reaction mixture was kept at 900° C. for 30 min (II stage of catalyst preparation), after which the stirring was stopped and the solid substance was allowed to settle. The supernatant was removed by decanting, after which a mixture of titanium tetrachloride (62.5 ml) and chlorobenzene (62.5 ml) was added. Then 0.5 g of 9,9-bis-methoxymethyl-9H-fluorene (flu) (flu/Mg=0.05 mol) in 3 ml of chlorobenzene was added to reactor and the temperature of reaction mixture was increased to 1150° C. The reaction mixture was kept at 1150° C. for 30 min (III stage of catalyst preparation), after which the stirring was stopped and the solid substance was allowed to settle. The supernatant was removed by decanting, after which a mixture of titanium tetrachloride (62.5 ml) and chlorobenzene (62.5 ml) was added. The reaction mixture was kept at 1150° C. for 30 min (IV stage of catalyst preparation), after which the solid substance was allowed to settle. The supernatant was removed by decanting and the solid was washed five times using 150 ml of heptane at 600 C, after which the catalyst component, suspended in heptane, was obtained.

(13) The catalyst has the following composition:

(14) TABLE-US-00001 TABLE 1 Ti Mg Mg/Ti EtO DNBP D10 D50 D90 Mean wt % wt % MR wt % wt % Microns 2 19.6 19.3 0.44 7.8 11.1 19 28.3 19 Ti = Titanium loading on the catalyst Mg = Magnesium EtO = Ethanol DNBP = Internal Donor content D10 = 10.sup.th percentile of catalyst particle size. Mean = Average catalyst particle size

2. POLYMERIZATION IN PILOT PLANT

(15) Propylene was polymerized using the catalyst component obtained according to step D. The polymerization was performed continuously in a gas phase reactor in the presence of a catalyst comprising the catalyst component according to step D, triethylaluminium and cyclohexylmethyldimethoxysilane. The polymerization period was 3 hours. The concentration of the catalyst component was 4 cc/hr; the concentration of triethylaluminium was 0.07 kg/hr. The concentration of cyclohexylmethyldimethoxysilane is shown in the Table 3, along with the molar ratio of triethylaluminium to cyclohexylmethyldimethoxysilane.

(16) The reactor used for the polymerization was a Unipol Gas Phase Pilot Plant Reactor. This is a continuous reactor which can produce PP resin up to 20 kg/hr as a maximum production capacity. In this example, the production rate was 15 kg/hr. The reactor conditions are described in Table 2:

(17) TABLE-US-00002 TABLE 2 REACTOR CONDITIONS Bed Temperature (° C.) 63 Reactor Pressure (Barg) 29 C3 Partial Pressure (Bara) 24 Bed wt. (mbar) 30 SGV (superficial gas 0.34 velocity) (m/s) Catalyst Flow (cc/hr) 4 TEAL flow (kg/hr) 0.07 Carrier Flow (kg/hr) 4 Production Rate (kg/hr) 15

(18) Four experiments were performed. In experiment 1 (comparative), the reaction was performed under the presence of H.sub.2. The volume ratio of H.sub.2 to propylene was 0.0038. In example 2, the reaction was performed under a reduced amount of H.sub.2. The volume ratio of H.sub.2 to propylene was 0.0019. In example 3 and 4, the reaction was performed without H.sub.2.

(19) The productivity, bulk density (BD), xylene solubles content, average particle size, melt flow index measured at 2.16 kg, Mn and Mw are presented in Table 3. The molecular weight and molecular weight distribution were characterized utilizing Waters 2000 Alliance Gel Permeation Chromatograph at 160° C. The melt flow index was measured utilizing Zwick 4106 melt index instrument. The xylene solubles content was measured according to ASTM D-5492, at 23° C. Resin bulk density and average particle size were measured according to ASTM D792 and ASTM D4513-11, respectively.

(20) TABLE-US-00003 TABLE 3 External donor conc. mol ratio co- Produc- H.sub.2/C.sub.3 catalyst to tivity APS Refer- Vol. external Kg PP/g BD XS mi- ence Ratio Kg/hr donor cat .Math. hr g/l wt % crons Ex 1 0.0038 0.35 0.33 25 431 2.9 743 (comp) Ex 2 0.0019 0.32 0.36 23 434 3.4 871 Ex 3 0 0.28 0.41 22.9 460 3.1 888 Ex 4 0 0.22 0.52 17.5 441 5.8 588 Refer- MFI (2.16 kg) Mn Mw ence g/10 min g/mole g/mole MWD Ex 1 3.9 62,500 359,500 5.8 (comp) Ex 2 1.8 79,000 451,500 4.2 Ex 3 0.09 140,250 911,000 5.4 Ex 4 0.2 139,000 806,000 5.8

(21) Properties of the polyethylene of Ex. 1 (comp.) and Ex. 3 were measured.

(22) The melt strength was measured using capillary rheolmeter equipped with pulley according to ASTM D 3835. The melt strength of the sample of Ex. 3 was around 10, which was 2-3 times higher than the sample of Ex. 1.

(23) The zero shear viscosity was measured according to ASTM D4440. The zero shear viscosity of the sample of Ex. 3 was 75 KPa-second, which was about 18 times higher than that of the sample of Ex. 1. The zero shear viscosity of the sample of Ex. 2 and of Ex. 4 was also measured and was found to be about 9 KPa-second and 38 KPa-second, respectively.

(24) The elongational viscosity was measured using Advanced Rheometric Expansion System (ARES) equipped with an extensional viscosity fixture (EVF). The elongational viscosity of the sample of Ex. 3 was 400 KP-second at 170° C., which was about 15 times higher than that of the sample of Ex. 1.

(25) The crystallization temperature, the crystallinity and the melting temperature were measured according to ASTM D3418-08 at a heating rate of 10° C./min in DSC. The sample was heated up to 200° C. (first heating) and then cooled (to measure the crystallization temperature and crystallinity) and then heated (second heating to measure the melting temperature and heat diffusion. TA DSC-Q-1000, Q2000 and Q20 instruments. The crystallinity level of the samples of Ex. 3 was about 48%, which was 3% lower than the sample of Ex. 1. The crystallization and melting temperatures of the sample of Ex. 3 were 118° C. and 163° C., respectively. These temperatures were very similar to the samples of Ex. 1. The same trend was observed when using a lower heating rate of about 2° C./min from 50° C. to 260° C.

3. PROCESSING OF POLYPROPYLENE INTO ARTICLE

(26) 3.1 Extrusion

(27) The polypropylene obtained by Experiments 1 and 3 were processed using a co-rotating twin screw extruder for continuous compounding of polymeric materials equipped with a hopper feeder: Brabender-TSE 35/17D.

(28) Polypropylene from comparative experiment 1 was processable with an output of 20 kg/h, at a melt temperature of 220° C. and a melt pressure of 960 psi. For processing polypropylene from experiment 3, the melt temperature was about 10° C. higher and the melt pressure was about 50% higher compared to processing polypropylene from comparative experiment 1.

3.2 Blow Molding

(29) The polypropylene obtained by Example 3 was processed by blow molding. The polypropylene obtained by Example 3 was stabilized by using phenolic and phosphites antioxidants and acid scavenger (Irganox 101, Irgafos 168 and DHT-4A). The PP base resin and additives were blended in a Henshel mixer for 5 minutes prior to extrusion. Sample was melt compounded on a 30-mm twin screw extruder (ZSK 30 type form MPM) at melt temperature 227° C. and screw speed of 200 rpm. The molten PP was processed on Battenfeld blow molding machine to produce bottles (0.5 L). The melt temperature was 240° C.

(30) It is therefore shown that the polypropylene having a relatively high molecular weight can be processed by conventional equipment. The article formed had good properties such as good environmental stress cracking (ESCR) of about >1000 hours at 100% Igebal, higher transparency measured as % haze of about 20% for 2 mm thickness on a BYK Gardner Haze-gard Plus hazemeter in accordance with ASTM D1003, good gloss>80 according to ASTM D2457 and lower weight (180 g).

3.3 Injection Molding

(31) The polypropylene obtained by Ex. 1 (Comp) and Ex. 3 were also injection molded by using Battenfield injection molding machine with a general-purpose screw to produce samples for measuring flexural modulus and Izod impact strength. The injection pressure was 800 bar and the temperature was 200-225° C., the nozzle temperature being 225° C. The injection speed was 10 mm/s and the injection time was 2.50 second.

(32) The stiffness and the impact strength were measured according to ASTM D1043-D and ASTM D256, respectively. The sample from PP of Ex. 1 (Comp.) had a stiffness of 1370 MPa and an impact strength of 26 J/m, whereas the sample from PP of Ex. 3 had a stiffness of 1320 MPa and an impact strength of 90 J/m. The sample according to the invention had an excellent Impact strength/stiffness balance.