Method for improving the operability of an olefin polymerization reactor

Abstract

The present technology relates to a method of introducing a supported antistatic compound that does not comprise a transition-metal-based catalyst component for use in an olefin polymerization reactor. In some embodiments, the methods disclosed herein avoid the formation of polymer agglomerates in the reactor and minimize potentially negative effects on catalyst yield.

Claims

1. A supported antistatic compound comprising an antistatic compound and a support, wherein the antistatic compound is a hydroxyester with at least two free hydroxyl groups, and wherein the supported antistatic compound: (i) does not comprise a transition-metal-based catalyst component; and (ii) the support is not suspended in a solvent, wherein the supported antistatic compound has a residual moisture content less than 5% by weight, based on the total weight of the supported antistatic compound.

2. The supported antistatic compound of claim 1, wherein the antistatic compound is glycerol monostearate.

3. A process for the preparation of the supported antistatic compound of claim 1, comprising the step of contacting an antistatic compound with a support in the absence of a transition-metal-based catalyst component to form the supported antistatic compound, wherein the supported antistatic compound has a residual moisture content less than 5% by weight, based on the total weight of the supported antistatic compound.

4. The process of claim 3, wherein the antistatic compound is contacted with the support at a concentration of 10-60% by weight per gram of support.

5. The process of claim 3, wherein the antistatic compound is contacted with the support at a concentration of 20-50% by weight per gram of support.

6. The process of claim 3, wherein the antistatic compound is contacted with the support at a concentration of 30-40% by weight per gram of support.

7. A process for polymerizing an olefin, comprising the step of polymerizing an olefin in a reactor by adding the supported antistatic compound of claim 1 to a polymerization mixture containing an olefin to form a polymer, wherein the supported antistatic compound reduces the formation of polymer on equipment of the polymerization plant.

8. The supported antistatic compound of claim 1, wherein the support is silica gel.

Description

EXAMPLES

(1) Test Methods:

(2) Melt Index E (MIE):

(3) Determined according to ASTM-D 1238, condition E (190? C./2.16 kg).

(4) Poured Bulk Density (PBD):

(5) Determined according to DIN-53194.

(6) Particle Size Distribution (PSD):

(7) Determined by using a Tyler Testing Sieve Shaker RX-29 Model B available from Combustion Engineering Endecott, provided with a set of six sieves, according to ASTM E-11-87, of numbers 5, 7, 10, 18, 35, and 200, respectively.

Example 1

(8) Silica Dehydration

(9) Silica was loaded into a vessel and was dehydrated at 200? C. under vacuum (26 mbar) for 8 hours (lab conditions) with a residual water content of between 2000 and 5000 ppm.

(10) Antistatic (GMS) Support:

(11) Iso-hexane was loaded into a stirred reactor and was heated up to 55? C. GMS was loaded in the reactor up to the amount of 75 g/L. After 3 hours, silica support was loaded in the reactor up to the amount of 175 g/L with respect to the starting iso-hexane, with a total load of GMS and silica of 250 g/L and a ratio between GMS and silica of 30%/70% by weight. After 30 minutes of contact between the dissolved GMS and silica, the drying step started. The equipment was placed under vacuum (26 mbar) in order to remove the iso-hexane and the temperature was raised according to a ramp up to 90? C. in order to remove all iso-hexane. The solid (GMS on silica) was then cooled to room temperature and unloaded from the vessel.

(12) Preparation of Prepolymerized Catalyst

(13) A magnesium chloride and alcohol adduct containing about 3 mols of alcohol was prepared following the method described in Example 2 of U.S. Pat. No. 4,399,054, but working at 2000 rpm instead of 10000 rpm. The adduct was subjected to a thermal treatment, under nitrogen stream, over a temperature range of 50-150? C. until a weight content of 25% of alcohol was reached. Into a 2 L four-necked round flask, purged with nitrogen, 1 L of TiCl.sub.4 was introduced at 0? C. Then, at the same temperature, 70 g of a spherical MgCl.sub.2/EtOH adduct containing 25 wt % of ethanol and prepared as described above were added under stirring. The temperature was raised to 140? C. over 2 h and maintained for 60 min. The stirring was discontinued, the solid product was allowed to settle and the supernatant liquid was siphoned off. The solid residue, having an average particle size of about 60 micrometers, was then washed once with heptane at 80? C. and five times with hexane at 25? C., dried under vacuum at 30? C. and analyzed. Into a 260 cm.sup.3 glass reactor provided with stirrer, 351.5 cm.sup.3 of hexane at 20? C. and 7 g of the catalyst prepared as above described were introduced and stirred at 20? C. The internal temperature was kept constant and 5.6 cm.sup.3 of tri-n-octylaluminum (TNOA) in hexane (about 370 g/l) were slowly introduced into the reactor, with the temperature brought to 10? C. After 10 minutes of stirring, 10 g of propylene were carefully introduced into the reactor and kept at the same temperature for 4 hours. The consumption of propylene in the reactor was monitored and the polymerization was discontinued when a theoretical conversion of 1 g of polymer per g of catalyst was reached. The whole contents of the reaction vessel were filtered and washed three times with hexane at a temperature of 20? C. (50 g/l). After drying the resulting pre-polymerized catalyst was analyzed and found to contain 1.1 g of polypropylene per g of catalyst.

(14) Preparation of Catalyst Suspension

(15) A dispersion tank with an internal diameter of 14.5 cm is used. This tank is equipped with a stirrer, an external water jacket for the temperature regulation, a thermometer and a cryostat. The following components were used to prepare the catalyst suspension: the above indicated Ziegler-Natta catalyst powder; and white oil (Winog 70) having a viscosity of 70 cStokes at 40? C.

(16) 1005 g of white oil were fed into the dispersion tank at room temperature (25? C.). Successively, 300 g of catalyst powder were loaded to the tank containing the oil, while continuously maintaining the dispersion tank under stirring conditions.

(17) After the introduction of the catalyst, the resulting suspension is maintained under stirring conditions for 30 minutes, with the temperature of the dispersion tank reduced to 13? C. The velocity of the stirring device is adjusted to 85 rpm during the mixing of the components of the suspension.

(18) The obtained suspension has a catalyst concentration of about 252 g/l (grams of catalyst for liter of oil). The catalyst suspension contains the antistatic compound in a weight ratio GMS90/catalyst of 0.13.

(19) Preparation of Catalyst Paste

(20) 431 g of molten Vaseline? grease BF (thickening agent) were fed to the dispersion tank containing the catalyst suspension at a feed temperature of 80? C. The molten thickening agent is slowly fed for 3 minutes, while stirring the catalyst suspension in the dispersion tank with a velocity of 85 rpm. The catalyst suspension is maintained at a temperature of 13? C. during the addition of the molten Vaseline? grease. The molten thickening agent rapidly solidifies on contact with the catalyst suspension. After the introduction of the molten Vaseline?, the components of the catalytic paste were maintained under stirring at 85 rpm for a time of 90 minutes. During this time the temperature in the dispersion tank is kept at 13? C.

(21) The resulting catalytic paste has a weight ratio grease/oil of about 0.43, while the concentration of the solid (catalyst+antistatic) in the catalytic paste is equal to about 170 g/l.

(22) Catalyst Activation

(23) The catalytic paste is withdrawn from the dispersion tank by a dosing syringe and is then continuously transferred by means of two dosing syringes to a first catalyst activation vessel, then to a second, then to a third. Triisobutyl-aluminum (TIBAL) is used as the cocatalyst with a weight ratio of TIBAL/catalyst of 1.5. No external donor is used and propane is fed as a diluent to the activation vessels. The components were pre-contacted in three activation vessels at a temperature of 40? C. for 19, 44 and 25 minutes, respectively. The activated catalytic paste is discharged from the activation vessel and is continuously fed to a gas-phase fluidized bed reactor for the polymerization of olefins.

(24) Polymerization

(25) The activated catalytic paste and the supported GMS were introduced into the fluidized bed reactor, where ethylene is polymerized to produce high density polyethylene (HDPE). The polymerization is operated in the presence of propane as a polymerization diluent and hydrogen as the molecular weight regulator. The polymerization conditions and the composition of the gaseous reaction mixture are indicated in Table 1. The characterization of the HDPE discharged from the reactor is reported in Table 2.

Example 2C (Comparison)

(26) Example 1 is repeated, with the only difference that during the preparation of catalyst suspension 40 g of microbeads of GSM were added to the suspension of catalyst powder in oil, so that the resulting catalytic paste incorporates GMS and no supported GMS was used. The polymerization conditions and the composition of the gaseous reaction mixture are indicated in Table 1. The characterization of the HDPE discharged from the reactor is reported in Table 2.

Examples 3 and 4

(27) The procedure set forth in Example 1 was repeated, except that a different amount of GMS was used.

(28) The polymerization conditions and the composition of the gaseous reaction mixture are indicated in Table 1. The characterization of the HDPE discharged from the reactor is reported in Table 2.

Example 5C (Comparison)

(29) The procedure set forth in Example 2 was repeated, except that the same catalyst as in Examples 3 and 4 has been used.

(30) The polymerization conditions and the composition of the gaseous reaction mixture are indicated in Table 1. The characterization of the HDPE discharged from the reactor is reported in Table 2.

Example 6

(31) The procedure set forth in Example 1 was repeated, except that the catalyst components were pre-contacted in two activation vessels at a temperature of 40? C. for 19 and 44 minutes respectively, followed by a pre-polymerization treatment in a third vessel at a temperature of 40? C. for 35 minutes with a ratio ethylene/catalyst of 10 g/g.

(32) The polymerization conditions and the composition of the gaseous reaction mixture are indicated in Table 1. The characterization of the HDPE discharged from the reactor is reported in Table 2.

(33) By comparing the data on polymer particle size, the examples produced in accordance with the present technology significantly reduced the amount of fines versus the comparative examples, further resulting in a significant reduction of fouling inside the fluidized bed reactor and in the equipment arranged along the gas recycle line (compressor and heat exchanger). It is also notable that the examples produced in accordance with the present technology show a higher specific mileage.

(34) TABLE-US-00001 TABLE 1 Process conditions Example 1 2C 3 4 5C 6 T ? C. 80 80 80 80 80 80 P barg 24 24 24 24 24 24 Residence h 2.1 2.3 2.1 2.1 2.3 2.2 time GMS/HDPE ppm 89 97 55 92 99 73 C2 % mol 5.4 7.5 5.3 5.6 6.6 5.8 H2/C2 2.8 2.6 2.6 2.7 2.7 2.9 Mileage g/g 4252 4108 4500 4101 4027 4189 Specific g/g .Math. bar .Math. h 1466 942 1612 1385 1068 1303 Mileage

(35) TABLE-US-00002 TABLE 2 HDPE characterization Example 1 2C 3 4 5C 6 MIE g/10 118 145 132 143 159 139 PBD g/cc 0.448 0.492 0.449 0.459 0.483 0.451 P50 ?m 1375.6 1146.8 1244.4 1206.5 1220.6 1214.9 <500 % wt 3.7 8.1 9.7 14.2 5.6 12.3 <300 % wt 1.5 3.2 3.5 4.3 2.2 5.7 <180 % wt 0.6 1.2 1.2 1.4 0.8 2.1 <125 % wt 0.3 0.5 0.4 0.5 0.4 0.8 <106 % wt 0.2 0.3 0.2 0.2 0.3 0.4