JPH01308410A - Copolymerization of ethylene - Google Patents

Abstract

PURPOSE: To enhance the physical properties and the economy by subjecting ethylene and specific ethylene comonomers to a copolymerization process in the presence of a catalyst which is dispersed in liquid propane.

CONSTITUTION: Etylene (A) and a 3-18C 1-olefin comonomer (B) which is preferably 1-butene, 1-hexene, 1-octene are subjected to a copolymerization process at 75-85°C in the presence of a polymerization catalyst (D) dispersed in liquid propane (C), and a linear low density PE is obtained as isolated solid particles under such a condition as dispersed in the C-component and having a density of 0.90-0.945g/cc and a molecular weight distribution of 4 or less (measured by RD value).

COPYRIGHT: (C)1989,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to improvements in the process of copolymerizing ethylene with other olefins. In particular, the present invention relates to an improved process for copolymerizing ethylene with other olefins to obtain linear low density polyethylene copolymers.

J, S., published on April 30, 1963.

Scoggin U.S. Patent i-MS, 087.91
No. 7 discloses a process for polymerizing ethylene in the presence of a liquid reaction medium and a catalyst to obtain the polymer product in the form of solid particles that are dispersed in the reaction medium during its formation.

This type of reaction process is known to those skilled in the art as a "slurry" polymerization process and is widely used in the production of high density polyethylene.

One such slurry method typically uses isobutane, pentane, hexane or similar saturated aliphatic hydrocarbons as the liquid reaction medium (also referred to as the "diluent"). However, one conventional slurry method involving so-called "particulate forms" is used for the production of ethylene/olefin copolymers, particularly of the type known as "linear low density polyethylene (LLDPE)". When applied, it presents certain drawbacks; for example, at elevated temperatures, linear low density polyethylene liquefies and adversely affects heat transfer and production rates, which limits the reaction temperatures that can be operated. Complete separation from the reaction medium is difficult, and the copolymer products generally have a relatively broad molecular weight distribution and contain undesirably high amounts of wax. Polymers tend to be low in bulk density.

One objective of the present invention is to overcome one & more of the above problems.

According to the invention, by copolymerizing ethylene and at least one other 1-olefin in the presence of a catalyst and a liquid proton, the copolymer or terpolymer is formed in the form of solid particles. Manufactured. These products are generally about 0.90
It has a density in the range ~0.9459/cc. The process of the invention is particularly suitable for the production of so-called linear low-density polymers (1) ethylene copolymers -CX.

The process of the present invention is more economical than slurry processes using isobutane, hexane or other liquid diluents and provides copolymer products with more desirable physical properties.

Other objects and benefits will become apparent to those skilled in the art from the description below.

The present invention will be described in detail below.

In accordance with the present invention, ethylene and at least one olefin comonomer of about 3 to 18 carbon atoms are copolymerized in the presence of a polymerization catalyst and liquid bromine. Also has a high degree of short chain branching, approximately α90~
It is particularly suitable for the production of linear low density polyethylene copolymers which are ethylene/1-olefin copolymers with densities in the α945 p/cc range.

Various benefits are derived from the improved method of the present invention. For example, propane is less expensive and has a lower heat of vaporization than liquid diluents such as isobutane and hexane that have been used in traditional slurry polymerization processes.

Additionally, in the synthesis of linear low-density polymers, the use of propane in the so-called "particle form" allows reactors to be operated at higher temperatures than isobutane without blockage or fouling of the reactor. Make it. Furthermore, since propane is more volatile, there is more residual sensible heat, thereby allowing for more efficient flash separation of the polymer product from the diluent.

Butene and hexene are ideal comonomers for the copolymerization of ethylene according to the present invention. In the case of butenes, simple flash evaporation allows almost complete separation of the polymer product from comonomer and reaction medium.

In the case of 1-hexene, additional drying may be required, but the load on the dryer is much less than when using inbutane or other conventional diluents.

Since propane is a relatively poor solvent for linear low density polyethylene, the viscosity of the product/reaction medium slurry is low, thus making the reaction mixture easy to mix and allowing immediate removal of the heat of polymerization. The use of Pronokun allows the polymerization reaction to be carried out at a relatively high temperature without clogging the reactor, and at the same time the relatively high catalyst Reactivity is brought about.

In addition, surprisingly, copolymers and terpolymers made by the slurry method using propane as the liquid diluent typically have an LS value of less than 50, and even less than 50. It exhibits significantly lower elasticity compared to higher conventional methods, and Polymer Engineering
and 5science, Vol, 11, tk
2, p. 124-128 (1971), it was found to exhibit a fairly narrow molecular weight distribution as determined by rheological dispersion (R[)) as described by Fern et al. The RD value of the product made according to the present invention is typically less than or equal to 4.0, preferably less than or equal to 5.5, which is in contrast to the conventional process value of >4.0 (
>5.0) in most cases.

Polymers made according to the present invention exhibit desirable high @v properties.

The copolymer and terpolymer products of the present invention can be categorized as discrete particles with size and shape characteristics substantially similar to conventional methods, which are highly heterogeneous in size and shape and often in agglomerated form. In contrast to the products of

Comonomers useful in the process of this invention include about 3 to 18 carbon atoms.
Consisting of one or more 1-olefins. Suitable 1-olefin comonomers include furopylene, 1
-butene, 1-pentene, 1-hexene, 4-methyl-
Examples include, but are not limited to, 1-pentene, 1-octene, 1-decene, 1-dodece/and 1-tectadecene. 1-butene, 1-hexene or 1-
Preferably, octene is used to produce linear low density polyethylene.

As is well known in the art, the comonomer/ethylene ratio can be varied to provide a copolymer product with a desired density. For example, by selecting the proportions of butene, hexene or octene comonomers, linear low density polyethylene can be produced. In the case of 1-butene, the proportion of butene that should be present in the copolymer product is about 1 to 10 mole percent. 1-
For hexene, the corresponding proportion is approximately O,S ~ 10 mol%
, in the case of 1-octene, it is approximately α5 to 5 mol%.

Linear low-density polyethylene typically has substantially no long chain branching and a high degree of short chain branching, from about Q, 90 to (L 94
Ethylene/1− with density in the range 5 f//eC
Defined as an olefin copolymer.

The polymerization reaction can be carried out in any convenient type of reactor, such as a loop reactor, autoclave or tubular reactor. The reaction is carried out under polymerization conditions of temperature and pressure such that the propane remains liquid. The critical temperature of propane is about 948°C and is independent of pressure. It is therefore preferable to carry out the reaction below this critical temperature.

Although the reaction can be carried out at lower temperatures, around 75-8
It has been found that reaction at 5°C, preferably 76-82°C, results in significantly higher catalytic activity.

Generally, the reaction is carried out by dispersing the catalyst in liquid propane in the presence of ethylene and comonomer. The copolymer or terpolymer product is made in particulate form that is dispersed as a slurry in liquid propane.

Some conventional methods for producing low density ethylene copolymers require a prepolymerization step.

In that process, ethylene (up to about 20×t relative to the total amount of ethylene and 1-olefin to be polymerized) is a catalyst dispersed in a slurry in a liquid diluent before co-merging with the 1-olefin comonomer. is prepolymerized in the presence of This prepolymerization results in a catalyst slurry mixed with catalyst and ethylene homopolymer.

According to the present invention, such a prepolymerization step is neither necessary nor desirable. In the process of the present invention, propane diluent, catalyst, and ethylene and 1-olefin comonomers can be introduced simultaneously into the reactor. Also advantageously, the copolymerization reactions of the present invention are carried out in one step, as opposed to the two-step copolymerization reactions of conventional methods.

After the reaction is complete, the polymer is physically separated from the liquid propane and comonomer by any suitable means. Because propane is considerably more volatile than traditional diluents, it is well suited for flash evaporative separation of polymers from diluents and comonomers. If the comonomer has a relatively high carbon number, additional drying may be necessary, but the load on the dryer is much lower than in conventional systems.

If desired, separation of the product from the diluent can be accomplished by mechanical means, such as centrifugation.

Propane's high volatility also aids in separating propane from higher molecular weight comonomers.

Since propane is a significant poor solvent in the product, relatively high polymerization temperatures can be used without fenestrated reactor blockage. Blockage of the reactor causes costly process interruptions and reactor downtime.

Any polymerization catalyst suitable for producing ethylene/1-olefin copolymers of the type commonly referred to as "linear low density polyethylene" and illustrated herein can be used in the present invention. Such catalysts include modified Ziegler catalysts, but modified chromium catalysts such as chromium oxide catalysts commonly referred to as "Phillips" catalysts are not suitable for producing linear low-density polyethylene copolymers. This is because it results in products with an undesirably broad molecular weight distribution.

Suitable catalysts include Pu1lukat et al.
US Pat. Line kPul
No. 4.499.198 to Lukat et al.
These documents are included in this document (published on February 12, 1985), so please refer to these documents as necessary.

A preferred catalyst is a so-called Ziegler catalyst containing a transition metal selected from Groups I and V of the Periodic Table, which is used in conjunction with an alkyl aluminum promoter. More preferred is a titanium-containing catalyst. Catalysts useful in the present invention may be supported or unsupported.

Other preferred catalysts are those disclosed in U.S. Pat. No. 4.499.198 to Pullukat et al. and U.S. Pat. 4.38 to No. 119 (published on May 10, 1983) or 2'Jg or more of magnesium silylamide compounds (please refer to this document as necessary) and period 4 of the periodic table. and 1st II of 5 cycles
The catalyst is prepared by reacting a compound of a transition metal selected from Groups B, IVB, VB and VIB and Groups ①B and ②B of the fourth period with at least 1''S. may optionally contain one or more of a Lewis acid, a Lewis base, a hydrogen halide, or a zirconium tetrachloride in addition to the magnesium and titanium transition metal compounds.

The transition metal compound of the catalyst used in the present invention is
It is important that the selection be made for its ability to produce a linear low density polyethylene product with a molecular weight distribution commonly referred to in the art as "narrow."

According to the invention, products with a narrow molecular weight distribution can be obtained, characterized in that they have a rheological dispersity (RD) of less than 4.

The symbols used herein are as follows: HMDS
- Hexamethyldisilazane LLDPE - Linear low density polyethylene L3 - Elasticity measure MI - Melt index RD - Rheology ° - Dispersibility TIBAL - Triisobutylaluminum Examples The following examples illustrate the method of the invention and its advantages over conventional methods. However, none of the embodiments should be construed as limiting the invention.

All polymerization tests in the examples below were carried out as described in British Patent No. 2,068,007 to Pulukat et al.
As described in k), hexamethyldisilazane (H
MDS)-treated chestnuts were treated with titanium and triisobutylaluminum (T I
BAL) co-catalyst (aluminum/titanium ratio 7.0)
The experiment was carried out using a catalyst system prepared using

The procedure for making the catalyst is illustrated below: To a nitrogen purged flask was added hexamethyldisilazane treated Davison 952 brand silica 1-2Ii. After 30 minutes of nitrogen purge, 20 ml of heptane was added to form a slurry.

To this slurry, add 10X 6.5HMaga in heptane.
a (T'exas Alkylg) solution was added (65HMagala = [(n-C4H,)2Mg
]6.5-AI(02H,), ).

By addition of Magala, t 88 mM Mll/
li silanized silica was obtained.

This slurry was mixed for 30 minutes and then raw titanium tetrachloride (TiC14) was added. The additional scenery is t
88 mM Ti/fi silanized silica was to be obtained. Therefore, the magnesium/titanium molar ratio is t
It was o.

The slurry was then stirred for 30 minutes. The catalyst was dried at 90°C with a nitrogen flush. The catalyst was a free-flowing dark brown powder with a titanium concentration of approximately 5.6% by weight.

The polymerization test procedure is described below: The two reactors are purged with nitrogen and brought to the desired temperature.

The catalyst and cocatalyst solutions were then added to the reactor under a nitrogen atmosphere. The reactor was closed and 1 [100 d] of diluent (propane or isobutane) was pressurized into the reactor. Then,
Hydrogen gas was added as a molecular weight regulator (10-50 p
si). Then, at the same time, 1-hexene was measured via a sight glass and ethylene was added to the predetermined reactor pressure K. This pressure was maintained by adding ethylene to the reactor as needed.

The temperature was adjusted to ±tO 0 C for a 1 hour polymerization period.

The reaction was stopped by turning off the ethylene gas and venting the reactor to the catchpot via the remotely controlled bottom pulp. Depending on the reaction medium used, the amount of 1-hexene and the temperature, the polymer may contain diluent and 1-hexene, if any.
- Very "wet" with hexene, so filtered to remove excess 1-hexene, and - dried overnight. This time was sufficient to obtain dry polymer.

The concentration of ethylene was adjusted by changing the partial pressure of ethylene in the system. Vapor pressures for propane and isobutylene can be found in the Physical Properties of
Hydroearbons (R,W, Ga1lan
Author: Gulf Pu, Hyuston, Texas
(published by blishing).

Examples A-F (comparative) Several ethylene/1-hexene copolymers were performed using inbutane as a diluent. Details of reactor temperature, ethylene partial pressure, hydrogen partial pressure and 1-hexene concentration are shown in the table below.

Examples AC were carried out at 54.4<0>C and Examples D-F at 65.5<0>C. In each case, the polymer separated from the reaction mixture was washed to remove excess 1-hexene. Despite this procedure, the polymer still contained significant 1-hexene.

Upon final drying, the polymer fed at 65.5°C was very sticky and had poor particle size and shape properties (example product shown in Figure 1). On the other hand, 54.4
The polymer made at °C had better particle size and shape properties and was less sticky. However, at this temperature, the reactivity was quite low and large amounts of isobutane and 1-hexene remained in the polymer.

Polymer rheology for the three samples shows that these samples have fairly high elasticity, as evidenced by high L3 values (a measure of elasticity). The polymers also have (in the case of Ziegler catalysts) a fairly broad molecular weight distribution.

A polymerization temperature of about 54.4° C. with this catalyst results in a density of 0.920 and a melt index (MI) of about 1 to
This is approximately the maximum polymerization temperature at which polymer No. 2 can be made without fear of clogging the reactor.

Above this temperature, the particle size and shape properties of the polymer rapidly deteriorate.

Several ethylene/1-hexene copolymers were performed using propane as a liquid diluent. The table below details the reactor temperature, ethylene partial pressure, hydrogen partial pressure and 1-hexene concentration. The product of Example 2 is shown in FIG.

Example L (Invention) Ethylene/1-butene copolymerization was carried out in liquid propane diluent using the catalyst described above. The reaction conditions are shown in the table below. The polymer had a density of about α901-α911 and was not sticky. The polymer particles had -like degree and shape characteristics.

Examples GL of the present invention demonstrate the use of relatively high polymerization temperatures with blockage of the reactor.

For example, the polymerization can be carried out at 82.2 DEG C. using 30 tX of 1-hexene in the reactor without blockage.

All of the resulting polymers have desirable -1 particle size and shape characteristics. Polymers made using liquid propane as a diluent have shown the additional and unexpected benefit of improved polymer properties. Polymers made in liquid propane diluent according to the present invention have lower elasticity and narrower molecular weight distribution (lower RD) as evidenced by the values compared to polymers made using isobutane diluent. have Both are highly desirable properties for LLDPE film resins.

A54.4 65 40 20 t4
0.931 5.5 >50BS4.5 120
50 40 t3 α929 4.7
>50C54, 41205040tOQ, 950 4
．． 7 >50D655 64 25 1
2.1 (L922 - -E65.5 6
5 25 20 [L67 0.925 -
-F655 80 50 40 α
52 α91B--Propane diluent (invention) G, 65.5 65 20 20 2.9 0.9
25 - -H7t1 75 15 20 α
65 0.927 5.0 2.0I7t1 55 1
5 50 α79 Q, 922 5.3 2B
J766 ss 10 30 α34 (
192B -- 822 60 10 50
α25 α92B--1-butene] 1% L7t1 70 5 15 51 α
910--The foregoing description is merely illustrative of the invention and is not intended to limit the invention thereby, and it will be apparent to those skilled in the art that modifications may be made within the scope of the invention.

[Brief explanation of the drawing]

FIG. 1 is a photograph showing the particle structure of a dense (L922.!il/cc) ethylene/1-hexene copolymer (Example D) prepared by a conventional slurry method using an inbutane diluent. Figure 2 shows the density α92'29/cc of ethylene/
It is a photograph showing the particle structure of a 1-hexene copolymer (Example ■). FIG, I Fig, 2 Procedural Amendment May 1985 310

Claims (1)

[Claims] 1. Ethylene and at least one 1-olefin comonomer having about 3 to 18 carbon atoms are dispersed in liquid propane at a selected temperature, pressure, and 1-olefin/ethylene ratio. Copolymerized in a single step in the presence of a polymerization catalyst, whereby a linear low density polyethylene product having a density in the range of about 0.90 to 0.945 g/cc is dispersed in the liquid propane and R_D A process for producing linear low density polyethylene comprising the steps of: forming the linear low density polyethylene as discrete solid particles having a narrow molecular weight distribution of 4 or less as measured by value. 2. The method according to claim 1, wherein the molecular weight distribution is 3.3 or less as measured by R_D value. 3. The copolymerization of ethylene and one comonomer is carried out at a temperature below the critical temperature of propane, and the solid particles of the product have a narrow molecular weight distribution of 4 or less as measured by R_D values and have low elastic properties. The first claim indicating
The method described in section. 4. The comonomer is propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-
4. The method according to any one of claims 1 to 3, wherein the method is selected from the group consisting of octene, 1-decene, 1-dodecene and 1-octadecene. 5. The method according to claim 4, wherein the comonomer is 1-butene. The ratio of 6,1-butene/ethylene is about 1 to 1 in the product.
6. The method of claim 5, wherein the amount of 1-butene is selected to be 0 mole percent. 7. The method according to claim 4, wherein the comonomer is 1-hexene. The ratio of 8,1-hexene/ethylene is approximately 0.8,1-hexene/ethylene in the product.
7. The method of claim 6, wherein the amount of 1-hexene is selected to be between 5 and 10 mole percent. 9. The method according to claim 4, wherein the comonomer is 1-octene. The proportion of 10,1-octene/ethylene in the product is approximately 0.
selected to be 5 to 5 mol% 1-octene;
The method according to claim 9. 11. A process according to any of claims 1 to 3, wherein the product is separated from the diluent after the reaction by evaporation of the diluent. 12. The method of claim 11, wherein the evaporation is carried out by flash drying under reduced pressure conditions.