Method for altering melt flow ratio of ethylene polymers

Abstract

A method for altering the melt flow ratio (MFR) of ethylene copolymers made in a gas phase reactor using a supported Ziegler-Natta catalyst treated with a catalyst modifier. The method involves changing the amount of the catalyst modifier added to the supported Ziegler-Natta polymerization catalyst to effect changes in the MFR of the resulting polymer.

Claims

1. A method for altering the melt flow ratio of an ethylene polymer or copolymer, said method comprising: i) introducing a polymerization catalyst into a gas phase reactor, said polymerization catalyst comprising: a) a Ziegler-Natta catalyst and an inert support: ii) feeding from 1 to 100 ppm of a catalyst modifier into the reactor based on the weight of the ethylene polymer or copolymer produced, the catalyst modifier comprising a compound having the formula: R.sup.1R.sup.2.sub.xN((CH.sub.2).sub.nOH).sub.y where R.sup.1 is a hydrocarbyl group having from 5 to 30 carbon atoms, R.sup.2 is hydrogen or a hydrocarbyl group having from 1 to 30 carbon atoms, x is 1 or 0, y is an integer, the sum of x and y is 2 and each n is independently an integer from 1 to 30; iii) polymerizing ethylene and optionally an alpha olefin to give the ethylene polymer or copolymer; wherein the melt flow ratio of said ethylene polymer or copolymer is altered by changing the amount of the catalyst modifier in said polymerization catalyst by at least 5 ppm (based on the weight of the ethylene polymer or copolymer produced).

2. The method of claim 1 wherein the catalyst modifier comprises at least one compound of the formula: R.sup.1N((CH.sub.2).sub.nOH) ((CH.sub.2).sub.mOH) where R.sup.1 is a hydrocarbyl group having from 5 to 30 carbon atoms, and n and m are integers from 1 to 20.

3. The method of claim 1 wherein the catalyst modifier comprises at least one compound of the formula: R.sup.1N((CH.sub.2).sub.xOH).sub.2 where R.sup.1 is a hydrocarbyl group having from 6 to 30 carbon atoms, and x is independently an integer from 1 to 20.

4. The method of claim 1 wherein the catalyst modifier comprises at least one compound of the formula: R.sup.1N((CH.sub.2).sub.xOH).sub.2 where R.sup.1 is a hydrocarbyl group having from 6 to 30 carbon atoms, and x is 2 or 3.

5. The method of claim 1 wherein the catalyst modifier comprises at least one compound of the formula: R.sup.1N(CH.sub.2CH.sub.2OH).sub.2 where R.sup.1 is a hydrocarbyl group having from 8 to 22 carbon atoms.

6. The method of claim 1 wherein the catalyst modifier comprises a compound of the formula: C.sub.18H.sub.37N(CH.sub.2CH.sub.2OH).sub.2.

7. The method of claim 1 wherein the catalyst modifier comprises compounds of the formulas: C.sub.13H.sub.27N(CH.sub.2CH.sub.2OH).sub.2 and C.sub.15H.sub.31N(CH.sub.2CH.sub.2OH).sub.2.

8. The method of claim 1 wherein the catalyst modifier comprises a mixture of compounds of the formula: R.sup.1N(CH.sub.2CH.sub.2OH).sub.2 where R.sup.1 is a hydrocarbyl group having from 8 to 18 carbon atoms.

Description

EXAMPLES

(1) Catalyst Modifier

(2) Armostat 1800 was purchased from Akzo Nobel. The reagent was dissolved in toluene and the resulting solution was dried over activated molecular sieves for several days before use. Toluene and pentane were purchased as anhydrous grades and were further dried over activated molecular sieves.

(3) Preparation of Comparative-1 Catalyst:

(4) 50 g of silica (38 m average particle size, 316 m.sup.2/g surface area, 1.54 mL/g pore volume) which had been dehydrated substantially as described in U.S. Pat. No. 6,140,264, was added to a 500 mL flask in a glove box. To the flask was added approximately 190 mL of pentane. The slurry was stirred and 12.0 g of a 25.3 wt % triethyl aluminum in hexane solution was added over approximately 5 minutes. The mixture was stirred for 1 hour at ambient temperature. 35.5 g of a 19.6 wt % butyl ethyl magnesium in heptane solution which contains 1.4 wt % triethyl aluminum was added to the slurry over approximately 10 minutes. The mixture was stirred for 2 hours at ambient temperature. The slurry was cooled to maintain a temperature below 20 C. while 11.7 g of dried t-butyl chloride containing <50 ppm water diluted to 35 wt % in pentane was added over about 20 minutes. The mixture was stirred for 2 hours after the addition was completed. 1.5 g of TiCl.sub.4 diluted to approximately 10 wt % in pentane was added to the flask at ambient temperature over about 5 minutes and the mixture was stirred further for 2 hours. 5.1 g of tetrahydrofuran (THF) diluted to 25 wt % in pentane was added over 10 minutes, providing a THF:Ti molar ratio of 9:1. The mixture was stirred for 1 hour at room temperature. A 25.8 wt % tri-n-hexyl aluminum (TnHAL) in hexane solution was added over 10 minutes at ambient temperature in an amount that would provide a TnHAL:Ti molar ratio of 3.0-3.5:1. After the addition was completed, the mixture was stirred for 45 minutes. A vacuum was then applied to remove the solvent. The catalyst was further dried by vacuum at 50 C.

(5) Preparation of Inventive Catalyst (Catalyst A)

(6) In a round-bottom flask equipped with an overhead stirrer, 60 g of the Comparative-1 Catalyst prepared above was slurried in 250 mL of dried pentane. While the slurry was being stirred, 8.30 g of an 18.55 wt % Armostat 1800 in toluene solution was added to the slurry to provide 2.5 wt % loading of Armostat 1800 in the finished catalyst. The slurry was stirred for 30 minutes at ambient temperature. The solvents were removed by applying a high dynamic vacuum first at 30 C. to remove pentane, and then at 60 C. to remove toluene. The drying process was completed when 500 mTorr was achieved, resulting in a free flowing powder.

(7) Preparation of Comparative-2 Catalyst:

(8) This catalyst was prepared in the same manner as the Comparative Catalyst-1, except that a silica with 40 m average particle size, 311 m.sup.2/g surface area and 1.62 mL/g pore volume was used as the catalyst support.

(9) Preparation of Inventive Catalyst (Catalyst B)

(10) In a round-bottom flask equipped with an overhead stirrer, 60 g of the Comparative-2 Catalyst prepared above was slurried in 250 mL of dried pentane. While the slurry was being stirred, 4.93 g of an 18.55 wt % Armostat 1800 in toluene solution was added to the slurry to provide 1.5 wt % loading of Armostat 1800 in the finished catalyst. The slurry was stirred for 30 minutes at ambient temperature. The solvents were removed by applying a high dynamic vacuum first at 30 C. to remove pentane, and then at 60 C. to remove toluene. The drying process was completed when 500 mTorr was achieved, resulting in a free flowing powder.

(11) Preparation of Inventive Catalyst (Catalyst C)

(12) This catalyst was prepared in the same manner as the Catalyst B, except that the loading of Armostat 1800 in the finished catalyst was 2.5 wt %.

(13) General Polymerization Conditions

(14) Continuous ethylene/1-hexene gas phase copolymerization experiments were conducted in a 56.4 liter technical scale reactor (TSR) in continuous gas phase operation (for an example of a TSR reactor set up see European Patent Application No. 659,773A1). Ethylene polymerizations were run at 88 C., ethylene partial pressure of 800 kilo pascal gauge (kPag) and total operating pressure of 2067 kPag. Ethylene gas phase composition in the reactor was controlled via closed-loop process control to a value of 38 mole percent. Hexene to ethylene molar flow ratio to the reactor was controlled via closed loop process control to values from 0.065 to 0.086. Hydrogen to ethylene molar flow ratio to the reactor was controlled from 0.029 to 0.037. Nitrogen constituted the remainder of the gas phase mixture. Triethylaluminum (TEAL) was fed to the reactor continuously, as a 4.0 wt % solution in hexane at a rate of approximately 120 parts per million (ppm) with respect to production rate as a co-catalyst and impurity scavenger. The residence time in the reactor is held at 1.5 to 1.8 hour, with a production rate range from 2.3 to 2.8 kg of polyethylene per hour (kg/hr).

(15) Polymer Analysis

(16) Melt index, I.sub.2, in g/10 min was determined using a Tinius Olsen Plastomer (Model MP993) in accordance with ASTM D1238 condition F at 190 C. with a 2.16 kilogram weight. High load melt index, I.sub.21, in g/10 min was determined in accordance with ASTM D1238 condition E at 190 C. with a 21.6 kilogram weight.

(17) Polymer density was determined in grams per cubic centimeter (g/cc) according to ASTM D1928.

(18) Polymerization Results

(19) The data shown in Table 1 clearly show that the addition of a catalyst modifier to a supported Ziegler-Natta catalyst useful in gas phase polymerization of ethylene and alpha-olefins has the effect of increasing the melt flow ratio (I.sub.21/I.sub.2) of the resulting polymer. The increase in MFR is dependent upon the amount of catalyst modifier added to the catalyst. A catalyst with 1.5 wt % Armostat 1800 produced a polymer with an MFR that was 4.83% higher than the polymer produced under the same conditions using the same catalyst but without added Armostat 1800. Adding 2.5% Armostat 1800 to the catalyst produced an even higher percentage increase in MFR, ranging from 4.66 to 9.29%. Alteration of the support used appears to have no effect on the ability of a catalyst modifier to increase the MFR of a resin produced with a similar catalyst.

(20) TABLE-US-00001 TABLE 1 Armostat % 1800 in I.sub.2 change Catalyst Density (g/10 in Catalyst (wt %) (g/cc) min) I.sub.21/I.sub.2 I.sub.21/I.sub.2 Comparative- None 0.9158 0.73 27.9 1 A 2.5 0.9228 0.52 29.2 4.66 A 2.5 0.9204 0.68 29.6 6.10 Comparative- None 0.9214 0.63 26.9 2 B 1.5 0.9218 0.56 28.2 4.83 C 2.5 0.9236 0.33 28.4 5.58 C 2.5 0.9213 0.45 29.4 9.29