Process for polymerisation of ethylene

Abstract

The present invention is directed to a process for the production of high density polyethylene by polymerisation of ethylene in the presence of a supported chromium oxide based catalyst which is modified with an organic compound comprising oxygen and a nitrogen atom which is selected from the group consisting of saturated heterocyclic organic compounds with a five or six membered ring, amino esters and amino alcohols. Such organic compounds allow manufacturing of HDPE with increases molecular weight distribution and increased molecular weight.

Claims

1. A process for the production of high density polyethylene by polymerizing ethylene in the presence of a supported chromium oxide-based catalyst that is modified with an organic compound comprising an oxygen and a nitrogen atom, wherein the organic compound is an amino alcohol, wherein the amino alcohol has the formula: ##STR00003## wherein each R, independently the same or different, is a C.sub.1-C.sub.8 alkyl group, a C.sub.6-C.sub.10 aryl group, a C.sub.1-C.sub.8 cycloalkyl group, or a trifluoromethyl group, and R.sup.1 is a C.sub.1-C.sub.8 alkyl group, a C.sub.3-C.sub.8 cycloalkyl group, a C.sub.6-C.sub.10 aryl group or a C.sub.4-C.sub.16 alkyl substituted cycloalkyl group.

2. The process according to claim 1, wherein the amino alcohol is 4-(cyclohexylamino) pentan-2-ol, 4-(methylamino)pentan-2-ol, 4-(phenylamino)pentan-2-ol, 4-(isopropylamino)pentan-2-ol, 3-(methylamino)-1-phenylbutan-1-ol, 1,1,1-trifluromethyl-4-(methylamino) pentan-2-ol and/or 4-[(2-methylcyclohexyl)amino]pentan-2-ol.

3. The process according to claim 1, wherein the molar ratio of chromium to amino alcohol ranges between 1: 0.05 and 1:3.

4. The process according to claim 1, wherein the supported chromium oxide based catalyst is modified with a mixture of the amino alcohol and an organoaluminum compound having the formula R.sup.l.sub.nAlX.sub.3-n, wherein R.sup.l represents an alkyl group having from 1 to 10 carbon atoms, X represents a halogen atom and 1n3.

5. The process according to claim 4, wherein the molar ratio of chromium to aluminium ranges between 1:0.1 and 1:1.

6. The process according to claim 1, wherein the process is a slurry process.

Description

EXAMPLES

(1) The properties of the polymers produced in the Examples were determined as follows:

(2) Flow Index:

(3) Melt Index (2.16): ASTM D-2338 Condition E measured at 190 C. reported as grams per 10 minutes.

(4) Flow Index: (FI.sub.21) ASTM D-1238 Condition F measured at 190 C. using 10 times the weight as used in Melt Index above.

(5) MFR: melt flow ratio is the flow index/melt index

(6) Density:

(7) The polymer density (g/cm.sup.3) was determined as specified in ASTM D 1505-68.

(8) Gel Permeation Chromatography (GPC):

(9) Polymer molecular weight and its distribution (MWD) were determined by Polymer Labs 220 gel permeation chromatograph. The chromatograms were run at 150 C. using 1,2,4-trichlorobenzene as the solvent with a flow rate of 0.9 ml/min. The refractive index detector is used to collect the signal for molecular weights. The software used is Cirrus from PolyLab for molecular weights from GPC. The calibration of the HT-GPC uses a Hamielec type calibration with broad standard and fresh calibration with each sample set.

Examples I-XII and Comparative Examples A-B

(10) Catalyst Preparation

(11) A silica supported chromium oxide based catalyst with 0.5% by of chromium, 4% by weight of titanium, a surface area of 300 m.sup.2/g and a pore volume of 1.5 cm.sup.3/g was activated in an atmosphere of dry air at a temperature of 825 C. for 3 hours using a tube furnace.

(12) 2.5 grams of previously activated catalyst was placed in a 50 ml flask. Dry degassed hexane was added in an amount just enough to obtain a slurry. The hydrocarbon solution comprised catalyst modifier, diethylaluminum chloride (DEAC) or tri isobutylaluminum (TIBAL) was added via syringe in a molar ratio as indicated in Table 1. Then the mixture was reacted for 1 hour at 50 C. with occasional shaking of the flask. The slurry was then dried under high vacuum or with a nitrogen purge. The modified catalyst was stored under nitrogen away from light until used.

(13) Ethylene Polymerization

(14) An autoclave with a volume of 2 liters was purged with nitrogen at 150 C. for 20 minutes. After cooling the autoclave to 90 C., one liter of isopentane was introduced to the reactor and then the reactor was pressurized up to 15 bar with ethylene. Then 0.15 ml of TEAL solution (1M) was injected into the reactor to scavenge the impurities that could deactivate the catalyst, followed by 0.30 g of the solid catalyst according to any one of the Examples I-XII and Comparative Examples A-B slurried in 20 ml of isopentane. The reactor temperature was raised to 102 C. Ethylene polymerization was carried out for 1 hour, with ethylene supplied on demand to maintain the total reactor pressure at 15 bars. Upon completion of the polymerization, the reactor was vented and cooled to ambient temperature to recover the polymer.

(15) Table 1 below compares the catalyst productivity for the catalysts according to Examples I-XII and Comparative Examples A and B.

(16) TABLE-US-00001 TABLE 1 Productivity Cr/M/Al (gPE/ Example Catalyst Modifier (M) molar ratio gCat/hr) I ethyl 2-isopropyl-3- 1/0.25/0.5 370 (isopropylamino) butanoate + DEAC II 2-pyrrolidone + DEAC 1/0.25/0.5 927 III 2-pyrrolidone + DEAC 1/0.5/1 333 IV 2-pyrrolidone + TIBAL 1/0.35/0.5 570 V 2-pyrrolidone + TIBAL 1/0.25/0.5 917 VI* 2-pyrrolidone 1/0.75/0 387 VI-a 2-pyrrolidone 1/0.75/0 760 VII 2-pyrrolidone + ethyl 2- 1/0.125/ 800 isopropyl-3- 0.125/0.5 (isopropylamino)butanoate + TIBAL VIII 3-cyclohexyl-4,6-dimethyl-1,3- 1/0.25/0.5 943 oxazinane + DEAC IX* 3-cyclohexyl-4,6-dimethyl-1,3- 1/0.75/0 150 oxazinane IX-a 3-cyclohexyl-4,6-dimethyl-1,3- 1/0.75/0 405 oxazinane X 2-oxazolidone + DEAC 1/0.44/0.44 1143 XI 4-(cyclohexylamino)pentan-2-ol 1/0.75/0 1011 XII 4-[(2- 1/0.75/0 859 methylcyclohexyl)amino]pentan- 2-ol A none 950 B TIBAL 1/0/0.5 1350

(17) With respect to examples VI* and IX* the present inventors observed an unexpected low productivity and suspected the catalyst was contaminated. The experiments were repeated, see VI-a and IX-a and the results show higher productivities confirming the suspected contamination of the catalyst.

(18) The Table 1 above shows that in comparison to a process where no catalyst modifier was used, i.e. Comparative Example A the productivity of the catalyst is still at an acceptable level. Comparative example B in fact is a modified catalyst as it is modified with TIBAL (tri-isobutylaluminium). Because of this modification the productivity is relatively high.

(19) Table 2 below summarises the polyethylene properties that were obtained with the catalysts according to examples I to XII and comparative examples A and B.

(20) TABLE-US-00002 TABLE 2 Bulk density MWD (g/cm.sup.3) Mw Mn () I 0.27 356357 9124 39 II 0.30 250080 8329 30 III 0.29 312127 7583 41.2 IV 0.35 268632 9360 28.7 V 0.37 246232 10227 24 VI* VI-a 0.34 335067 9256 36.2 VII 0.33 190960 19925 9.8 VIII 0.30 221252 8626 25.6 IXI* 0.35 266343 9758 27.3 IXI-a X 0.34 310676 10320 30.1 XI 0.42 302873 10858 27.9 XII 0.40 336908 9880 34.1 A 0.31 192397 11803 16.3 B 0.36 214484 15883 13.5

(21) According to Table 2 the modification of chromium oxide based catalysts with the catalyst modifier according to the invention results in an increase of the molecular weight and molecular weight distribution. Example VII shows a MWD of 9.8 which is significantly lower compared to the other Examples and the Comparative Examples. The cause for this unexpected behaviour is not entirely clear. Without being bound by it, the present inventors suspect that the combined use of the two modifiers according to the invention in combination with tri-isobutylaluminium led to a narrowing of the diversity of the chromium active sites, which consequently resulted in a narrow MWD of the produced resin.

(22) With respect to comparative example B it is noted that even though said catalyst shows a relative high catalyst activity, the MWD is significantly lower than the MWD of the polyethylenes produced with a modified catalyst according to the present invention. In addition, the Mw is lower than most of the polyethylenes produced with a modified catalyst according to the present invention

(23) To study the effect of the molar ratio of chromium to catalyst modifier experiments as described in Table 3 below were carried out.

(24) TABLE-US-00003 TABLE 3 Bulk Polymer Cr/M* Productivity density Density molar ratio (g PE/g cat/1 hr) (g/cm.sup.3) (g/cm.sup.3) No modifier 1653 0.36 0.9521 1/0.5 1980 0.39 0.9549 1/1 895 0.36 0.9575 1/1.25 653 0.33 0.9583 1/1.5 290 0.30 E 530 0.39 0.9593 M*2-Pyrrolidine

(25) The modifier that was used was 2-Pyrrolidine.

(26) Catalyst preparation was carried out in the same manner as for Examples I to XII.

(27) The catalyst of comparative example E is a Silylchromate (S-2) catalyst and was prepared by placing 2.5 grams of previously dehydrated silica (600 C.) in a 50 ml flask. Then 30 ml of dry degassed isopentane was added into the flask. 83 mg silylchromate was added and the mixture was stirred for 1 hour at 50 C. Then diethyl aluminum ethoxide was added via syringe to give an Al/Cr molar ratio of 2:1. Then slurry was dried under high vacuum or with a nitrogen purge. The chromium loading was 0.27 wt %.

(28) The polymerisation conditions were as follows:

(29) An autoclave with a volume of 2 liter was purged with nitrogen at 150 C. for 20 minutes. After cooling the autoclave to 90 C., one liter of isopentane was introduced to the reactor and then the reactor was pressurized up to 290 psi with ethylene. Then 1M solution of triethyl aluminum (TEAL), just enough to scavenge unwanted catalyst poisons such as oxygen and moisture, were added to the reactor. After that, the catalyst slurried in isopentane was injected into the reactor. The reactor temperature was raised to 102 C. Ethylene polymerization was carried out for 1 hour, with ethylene supplied on demand to maintain the total reactor pressure at 20 bar. Upon completion of the polymerization, the reactor was vented and cooled to ambient temperature to recover the polymer.

(30) From Table 3 it is clear that upon increasing ratio of Cr/M, meaning from 1/1.5 to 1/0.5, the productivity increases. Said in another way, at lower relative modifier levels the productivity increases.

(31) The inventors further studied the effect of the molar ratio of chromium to catalyst modifier on the molecular weight and molecular weight distribution, the results of which can be found it Table 4.

(32) TABLE-US-00004 TABLE 4 Cr/M* molar ratio Mw Mn MWD Mz + 1 Mz No modifier 190069 11733 16.2 1647090 949438 1/0.5 212298 9258 22.9 2488233 1243931 1/0.75 258821 8366 30.9 3320769 1681422 1/1 302120 8549 35.3 3409073 1841619 1/1.25 351947 9285 37.9 3645504 1930072 E 313985 8928 35.1 3502230 1967113 M*2-Pyrrolidone

(33) From Table 4 it is clear that compared to the no modifier example a catalyst modifier allows the molecular weight distribution and molecular weight to be varied, more specifically to be broadened and increased respectively. When compared to Comparative Example E it is further clear that the invention enables production of a polyethylene which has similar molecular weight and molecular weight distribution as silylchromate catalyst based produced polyethylene.

(34) In addition the present inventors studied the effect of the molar ratio of chromium to catalyst modifier on the productivity, bulk density, flow index and polymer density for the catalyst modifier 4-(cyclohexylamino)pentan-2-ol. The results of can be found it Table 5.

(35) TABLE-US-00005 TABLE 5 Cr/M** Productivity (g PE/ Bulk density Density molar ratio g cat/1 hr) (g/cm.sup.3) FI (g/cm.sup.3) No modifier 1653 0.36 1.57 0.9521 1/0.5 2160 0.44 2.39 0.9554 1/1 1180 0.40 3.4 0.9565 1/1.25 814 0.34 1.25 0.9589 1/1.5 354 0.30 0.69 E 530 0.39 1.17 0.9593 M**4-(cyclohexylamino)pentan-2-ol

(36) The results of the experiments were in line with the experiments carried out for catalyst modifier 2-pyrrolidone in Table 3.

(37) From Table 5 it is clear that upon increasing ratio of Cr/M, meaning from 1/1.5 to 1/0.5, the productivity increases.

(38) The inventors further studied the effect of the molar ratio of chromium to catalyst modifier on the molecular weight and molecular weight distribution, the results of which can be found it Table 6.

(39) TABLE-US-00006 TABLE 6 Cr/M** molar ratio Mw Mn MWD Mz + 1 Mz No modifier 190069 11733 16.2 1647090 949438 1/0.5 218438 12859 17 2671117 1244475 1/1 286565 7980 35.9 4255635 2079459 1/1.25 316905 8505 37.4 4329903 2232212 1/1.5 361584 9144 39.5 3819371 2182846 E 313985 8928 35.1 3502230 1967113 M**4-(cyclohexylamino)pentan-2-ol

(40) From Table 6 it is clear that compared to the no modifier example a catalyst modifier allows the molecular weight distribution and molecular weight to be varied, more specifically to be broadened and increased respectively. When compared to Comparative Example E it is further clear that the invention enables production of a polyethylene which has similar molecular weight and molecular weight distribution as silylchromate catalyst based produced polyethylene.