MOLECULAR WEIGHT DISTRIBUTION ADJUSTMENT OF POLYETHYLENE BY EXTERNAL ELECTRON DONOR

Abstract

The present invention relates to a process to control the molecular weight distribution of polyethylene and to reduce the smoke quantity during the formation of polyethylene, wherein the process for preparing polyethylene having narrow molecular weight distribution, comprising the following steps: a) continuously polymerizing ethylene by subjecting ethylene stream, hydrogen, solvent, Ziegler-Natta catalyst comprising titanium, co-catalyst, external electron donor selected from alkoxysilane compound into the reactor to produce polymer slurry; b) removing residue reaction gas from the polymer slurry stream obtained from a) and c) separating polymer stream in b) from the solvent.

Claims

1. A process for preparing polyethylene having a narrow molecular weight distribution, comprising the following steps: a) continuously polymerizing ethylene by subjecting an ethylene stream, hydrogen, a solvent, a Ziegler-Natta catalyst comprising titanium, a co-catalyst, and an external electron donor selected from an alkoxysilane compound into a reactor to produce a polymer slurry; b) removing a residue reaction gas from the polymer slurry stream obtained from a); and c) separating the polymer stream in b) from the solvent.

2. The process according to claim 1, wherein the external electron donor is selected from alkoxysilane as shown in structure (I):
R.sub.nR.sub.mSi(OR).sub.4-n-m(I) wherein, R, R and R represent a substitution group independently selected from an alkyl group having 1-10 carbon atoms, a cyclic group, or an aromatic group, when n and m are an integer of 0-4, and n+m<4.

3. The process according to claim 1 or 2, wherein the external electron donor is selected from the group comprising tetraethoxysilane, dimethoxy diphenylsilane, dicyclopentyl dimethoxysilane, isobutylisopropyl dimethoxysilane, trimethoxy propylsilane, isobutyldimethoxy methylsilane, and trimethoxy-2-methyl propylsilane, or a mixture thereof.

4. The process according to claim 1, wherein the external electron donor is dicyclopentyl dimethoxysilane.

5. The process according to claim 1, wherein the mole ratio of silicon in alkoxysilane to titanium in the Ziegler-Natta catalyst is in a range of 0.1-20.

6. The process according to claim 5, wherein the mole ratio of silicon in alkoxysilane to titanium in the Ziegler-Natta catalyst is in the range of 0.25-1.

7. The process according to claim 1, wherein the co-catalyst is an alkyl aluminum compound.

8. The process according to claim 7, wherein the co-catalyst is triethylaluminum.

9. The process according to claim 1, wherein the concentration of the catalyst is in a range of 0.005-0.1 mmol/L.

10. The process according to claim 9, wherein the concentration of the catalyst is in the range of 0.03-0.05 mmol/L.

11. The process according to claim 1, wherein the concentration of the co-catalyst is in a range of 0.1-2 mmol/L.

12. The process according to claim 1, wherein the concentration of the co-catalyst is in the range of 0.2-1 mmol/L.

13. The process according to claim 1, wherein the polymerization of ethylene in step a) is operated at a temperature in a range of 60-90 C. and a pressure in a range of 1-8 bars.

14. The process according to claim 1, further comprising adding an -olefin having 3-10 carbon atoms into the reactor in step (a).

15. The process according to claim 14, wherein the concentration of the -olefin is in a range of 0.1-10% by weight of polyethylene.

16. The polyethylene prepared from the process according to any one of the preceding claims, wherein the molecular weight of polyethylene is in a range of 40,000-300,000 g/mole, and the molecular weight distribution (Mw/Mn) is in a range of 4-8.

17. The polyethylene prepared from the process according to any one of the preceding claims, wherein the density of polyethylene is in a range of 0.940-0.965 g/cm.sup.3, and the melt flow rate (2.16 kg/190 C.) is in a range of 0.1-30 g/10 min.

Description

DESCRIPTION OF THE INVENTION

[0014] The present invention discloses the method for controlling the molecular weight distribution of polyethylene by the use of Ziegler-Natta catalyst together with silane compound as the external electron donor.

[0015] Any aspect being shown here means to include its application to other aspects of this invention unless stated otherwise.

[0016] Technical terms or scientific terms used here have definitions as by a person skilled in the art unless stated otherwise.

[0017] Any tools, equipment, methods, or chemicals named herein mean tools, equipment, methods, or chemicals being used commonly by a person skilled in the art unless stated otherwise that they are tools, equipment, methods, or chemicals specific only in this invention.

[0018] Use of singular noun or singular pronoun with comprising in claims or specification means one and including one or more, at least one, and one or more than one.

[0019] All compositions and/or methods disclosed and claims in this application aim to cover embodiments from any action, performance, modification, or adjustment without any experiment that significantly different from this invention, and obtain with object with utility and resulted as same as the present embodiment according to a person ordinary skilled in the art although without specifically stated in claims. Therefore, substitutable or similar object to the present embodiment, including any little modification or adjustment that clearly seen by a person skilled in the art should be construed as remains in spirit, scope, and concept of invention as appeared in appended claims.

[0020] Throughout this application, term about means any number that appeared or showed here that could be varied or deviated from any error of equipment, method, or personal using said equipment or method.

[0021] Hereafter, invention embodiments are shown without any purpose to limit any scope of the invention.

[0022] The process for preparing polyethylene having narrow molecular weight distribution according to the invention comprising the following steps: [0023] a) continuously polymerizing ethylene by subjecting ethylene stream, hydrogen, solvent, Ziegler-Natta catalyst comprising titanium, co-catalyst, external electron donor selected from alkoxysilane compound into the reactor to produce polymer slurry; [0024] b) removing residue reaction gas from the polymer slurry stream obtained from a) and [0025] c) separating polymer stream in b) from the solvent.

[0026] In one aspect of the invention, the Ziegler-Natta catalyst comprises at least one titanium compound.

[0027] In another aspect of the invention, the Ziegler-Natta catalyst is magnesium chloride supported titanium tetrachloride catalyst.

[0028] In one aspect of the invention, the process according to the invention comprises the polymerization under condition with organic solvent selected from, but not limited to, propane, butane, isobutane, pentane, hexane, heptane, octane, benzene, and toluene, preferably hexane.

[0029] In one aspect of the invention, the external electron donor comprises at least one silane compound.

[0030] In one aspect of the invention, the external electron donor is selected from alkoxysilane as shown in structure (I):

R.sub.nR.sub.mSi(OR).sub.4-n-m(I);

[0031] wherein, R, R and R represent a substitution group independently selected from alkyl group having 1-10 carbon atoms, or cyclic group, or aromatic group, when n and m are integer of 0-4, and n+m<4.

[0032] In one aspect of the invention, the external electron donor is selected from the group comprising tetraethoxysilane, dimethoxy diphenylsilane, dicyclopentyl dimethoxysilane, isobutylisopropyl dimethoxysilane, trimethoxy propylsilane, isobutyldimethoxy methylsilane, and trimethoxy-2-methyl propylsilane, or mixture thereof.

[0033] In one aspect of the invention, the external electron donor is dicyclopentyl dimethoxysilane.

[0034] In one aspect of the invention, the mole ratio of silicon in alkoxysilane to titanium in the Ziegler-Natta catalyst is in a range of 0.1-20.

[0035] In one aspect of the invention, the mole ratio of silicon in alkoxysilane to titanium in the Ziegler-Natta catalyst is in the range of 0.25-1.

[0036] In one aspect of the invention, the process according to the present invention further comprises alkyl aluminum compound as a co-catalyst. Preferably, the co-catalyst is triethylaluminum.

[0037] In one aspect of the invention, the concentration of the catalyst is in a range of 0.005-0.1 mmole/L. Preferably, the concentration of the catalyst is in the range of 0.03-0.05 mmole/L.

[0038] In one aspect of the invention, the concentration of the co-catalyst is in a range of 0.1-2 mmole/L. Preferably, the concentration of the co-catalyst is in the range of 0.2-1 mmole/L.

[0039] In one aspect of the invention, the polymerization of ethylene in step a) is operated at the temperature in a range of 60-90 C. and the pressure in a range of 1-8 bars.

[0040] In one aspect of the invention, the process further comprises the addition of -olefin having 3-10 carbon atoms into the reactor in step (a), and the concentration of -olefin is in the range of 0.1-10% by weight of polyethylene.

[0041] In one aspect of the invention, the molecular weight of polyethylene prepared from the process according to the invention is in the range of 40,000-300,000 g/mole, and the molecular weight distribution (Mw/Mn) is in the range of 4-8.

[0042] In one aspect of the invention, the density of polyethylene prepared from the process according to the invention is in the range of 0.940-0.965 g/cm.sup.3, and the melt flow rate (2.16 kg/190 C.) is in the range of 0.1-30 g/10 min.

[0043] In one aspect of the invention, the polymerization of ethylene further comprises the addition of the additive selected from processing aid, mold release, antioxidant, light stabilizer, heat stabilizer, or mixture thereof into the polymer mixture.

[0044] In one aspect of the invention, the polyethylene prepared from the process according to the invention can be formed into product by injection molding process, extrusion blow molding, and rotational molding process.

[0045] In one aspect of the invention, the polyethylene can be applied to be formed into product or article, including but not limited to rope, fiber, or nonwoven.

[0046] The following examples are for demonstrating one aspect of this invention only, not for limiting the scope of this invention in any way.

[0047] Testing for Selecting Suitable External Electron Donor

[0048] Preparation of Comparative Sample

[0049] Hexane (1,000-3,000 mL) was added into the reactor. Triethylaluminum was added with controlled concentration in a range of 0.2-1.0 mmole/L. The PZ type Ziegler-Natta catalyst (produced by Mitsui Chemicals Inc.) was added with controlled concentration in a range of 0.01-0.05 mmole/L. Then, hydrogen gas and ethylene gas were fed into the reactor. The temperature and pressure of the reaction were controlled from 60-90 C. and 1.0-8.0 bars, respectively, which the reaction time 2-3 hours. Then, the temperature was reduced to the room temperature. The prepared polymer was subjected to drying process and extruded into pellet.

[0050] Preparation of the Sample According to the Invention 1-12

[0051] The samples were prepared with the same method as being described in the comparative sample by adding the silane compound as external electron donor as shown in table 1.

TABLE-US-00001 TABLE 1 Testing of external electron donor from comparative sample and sample according to the invention Catalyst Molecular concentration weight Smoke Sample Type of external electron donor (mmole/L) distribution quantity* Comparative 0.030 8.68 10790.00 sample Sample Dimethoxydiphenylsilane 0.030 6.18 10201.93 according to the invention 1 Sample Dicyclopentyldimethoxysilane 0.040 6.24 10529.80 according to the invention 2 Sample Cyclohexyldimethoxymethylsilane 0.022 7.63 12079.37 according to the invention 3 Sample Diisobutyldimethoxysilane 0.045 7.50 12333.50 according to the invention 4 Sample Diisopropyldimethoxysilane 0.048 6.12 12681.53 according to the invention 5 Sample Isobutylisopropyldimethoxysilane 0.056 6.24 8842.15 according to the invention 6 Sample Trimethoxypropylsilane 0.040 7.38 10138.93 according to the invention 7 Sample Isobutyldimethoxymethylsilane 0.030 6.64 9174.67 according to the invention 8 Sample Tetraethoxysilane 0.030 7.08 9985.65 according to the invention 9 Sample Isobutyltriethoxysilane 0.048 6.01 11839.23 according to the invention 10 Sample Triethoxypropylsilane 0.016 7.09 13209.40 according to the invention 11 Sample Trimethoxy-2-methylpropylsilane 0.040 7.26 10556.47 according to the invention 12 *Area under curve analyzed by Gas chromatography-flame Ionization Detector (GC-FID)

[0052] Testing of Molecular Weight Distribution

[0053] The molecular weight distribution was analyzed by Gel permeation chromatography (GPC-IR) with triple detector (Polymer Char) according to the following steps:

[0054] Polymer (4.0-8.0 mg) was added into vial. Then, 8.0 mL of 1,2,4-trichloribenzene was added. Sample was injected into high pressure liquid chromatography and heated at 150-160 C.

[0055] Testing of Smoke Quantity

[0056] The smoke quantity was tested by extracting the low molecular weight polyethylene from the sample by soxhlet extraction with hexane (soxhlet extractor BUCHI B-S11). Then, the low molecular weight polyethylene was analyzed by Gas chromatography (Intuvo 9000 GC system, Agilent Technologies) according to the following steps.

[0057] About 10 g of polymer was added into thimble, and hexane was added into soxhlet for extraction. The extract was filtered and was analyzed by chromatography equipped with DB-5 MS UI column (30 m0.32 mm0.25 microns) at flow rate 6.0 mL/s and temperature at 300 C. The area under curve was collected for the quantification of smoke quantity.

[0058] From table 1, it was found that silane compound could reduce the molecular weight distribution. Moreover, the use of dimethoxy diphenylsilane, dicyclopentyl dimethoxysilane, isobutylisopropyl dimethoxysilane, trimethoxypropyl silane, isobutyldimethoxymethyl silane, tetraethoxysilane, and trimethoxy-2-methylpropylsilane can reduce the smoke quantity occurred in the process.

[0059] Testing of Suitable External Electron Donor Quantity

[0060] Preparation of Sample According to the Invention 13-16

[0061] Samples were prepared with the same method as the sample according to the invention 2, and dicyclopentyl dimethoxysilane was added to the sample as the concentrations shown in table 2.

TABLE-US-00002 TABLE 2 Testing of quantity of the external electron donor according to comparative sample and sample according to the invention Ratio of external electron donor to Catalyst Molecular catalyst concentration weight Sample (mole/mole) (mmole/L) distribution Sample according 0.125 0.030 6.65 to the invention 13 Sample according 0.250 0.030 5.84 to the invention 14 Sample according 0.500 0.035 5.64 to the invention 15 Sample according 0.750 0.050 5.50 to the invention 16 *Area under curve analyzed by Gas chromatography-flame Ionization Detector (GC-FID)

[0062] From table 2, it was found that the molecular weight distribution was narrower when the quantity of external electron donor was higher. The catalyst concentration is preferable in the range of 0.005-0.1 mmole/L, preferably 0.03-0.05 mmole/L. The amount of silicon in silane compound in molar ratio of titanium in Ziegler-Natta catalyst (Si/Ti ration) is in the range of 0.1-20.0 mole/mole, preferably 0.25-1.0 mole/mole.

[0063] From all above, the use of silane compound as an external electron donor benefits to narrow the molecular weight distribution of the polyethylene. Consequently, the polyethylene prepared by the process according to the present invention can be drawn at higher speed. Moreover, the smoke quantity occurred during the process can be reduced. Thus, the polymer according to the invention is suitable for using to the preparation of fiber in industrial scale.

Preferred Embodiment of the Invention

[0064] Preferred embodiment of the invention is as provided in the description of the invention.