JPS5856524B2 - Ethylene polymerization method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an ethylene polymer that simultaneously produces two or more products with different molecular weights each having a wide molecular weight distribution and excellent physical properties from two or more polymerization vessels with high productivity. The present invention relates to a polymerization method.

Producing polyethylene polymers with a wide molecular weight distribution with high productivity is very useful from an economic point of view, but it is difficult to obtain sufficiently high productivity with normal polymerization, and one method is a two-stage polymerization method. Polymerization methods have been tried.

Polymers produced by this method generally have stiffness, E
Polymers with a good balance of SCR properties (environmental stress cracking resistance) can be obtained, but conversely, one-through two-stage continuous polymerization generally has the disadvantage that gel appears on the surface when molded into a film. be.

As a method for improving this, attempts have been made to perform multistage polymerization in which polymerization vessels are further connected in series, or a two-stage circulation continuous polymerization method in which the contents of the latter stage polymerization vessel are circulated to the first stage.

Regarding these methods, see Japanese Patent Publication No. 46-11349,
Japanese Patent Publication No. 48-42716, Japanese Patent Application Publication No. 51-47079, and Japanese Patent Application Publication No. 52-19788 are known.

However, in these two-stage and multi-stage continuous polymerization methods, most of the molecular weights of the polymers polymerized in each stage are outside the commonly used range, and only the polymer obtained from the final stage can be used as a product. Of those available, only one type of polymer can be obtained from at least two polymerization vessels.

Therefore, if the process is stopped due to unexpected trouble or other reasons, the polymer in the polymerization vessel other than the last stage, especially the first stage, will be lost.

Furthermore, as mentioned above, in conventional two-stage and multi-stage polymerization, at least two or more polymerization vessels are required to obtain one type of polymer. The amount of spec-out polymer that is generated when switching to the above grade also increases.

Therefore, if the polymer obtained in two-stage and multi-stage polymerization is
It is possible to obtain two or more types of polymers (products) using two or more polymerizers, remove lost polymers due to sudden troubles or other shutdowns, reduce out-of-spec polymers when changing grades, and further improve operations. This is extremely useful in terms of reducing the amount of inventory required by increasing the flexibility of

The present inventors have discovered that by carrying out multi-stage cyclic continuous polymerization under appropriate polymerization conditions, the productivity is sufficiently high, the molecular weight distribution is wide, the physical properties are good, and furthermore, two polymers with different molecular weights with less gelation can be produced.
We have discovered that more than one type of polymer can be produced simultaneously from two or more polymerization vessels, and have accomplished the present invention.

That is, the present invention provides a polymerization method for producing polyethylene of different molecular weights in two or more polymerization vessels connected in series using a catalyst consisting of a transition metal compound and an organometallic compound. While circulating the contents of the vessel from the latter polymerization vessel to the former polymerization vessel, products with different molecular weights are simultaneously taken out from each polymerization vessel, (ii) the flow rate (v) of the polymerization contents to be circulated at this time;
) and the product extraction amount (u) (v/u) is adjusted to 1 to 50, and (iii) the ratio (r) of the molecular weight of polyethylene produced in each polymerization vessel is adjusted to 5 to 100. Adjust the ratio of amounts to 7:3-3 near.

This invention relates to an ethylene polymerization method characterized by the following.

The catalyst composed of a transition metal compound and an organometallic compound used in the present invention is
-36788, 52-36790゜52-36791
．． 52-36792.52-50070.52-367
94.52-36795゜52-36796.52-3
6915.52-36917.53-6019, JP-A-50-21876.50-31835.50-7204
4゜50-78619.53-40696 is effective, and these are (1) general formula % formula % (where α is 0 or a number larger than 0, p, q.

r and s are O or a number larger than 0, p 1q + r
+s=mα''-2β, M is a metal element belonging to Groups 1 to 2 of the periodic table, R1 and R2 are hydrocarbon groups having the same or different numbers of carbon atoms, and X.

Y is the same or different group, halogen, OR3
,08iR'R5R6,NR7R8,SR9, R3, R4, R5, R6, R7, R8 are hydrogen atoms or hydrocarbon groups, R9 is a hydrocarbon group); ) at least 1
a titanium or vanadium compound containing halogen atoms; and (III) AZ t By is c e
t s n tTe, Sb halide compound (i)
A solid catalyst component obtained by reacting (1) and (ii) or (1) and (ii) and 011) of ~(iii) [
A, l] and an organometallic compound [B].

The organometallic compound is preferably a compound of Groups 1 to 1 of the periodic table, and in particular a complex containing an organoaluminium compound and an organomagnesium compound.

Catalyst component [AI and organometallic compound [B] acid component reaction is
It is also possible to add surrounding components to the polymerization system and allow the polymerization to proceed under the polymerization conditions, and may be carried out in advance prior to the polymerization.

Also, the reaction ratio of the catalyst components is [A] 1? Against [B
] It is preferable to carry out the component in a range of 1 to 3000 mmo, /-.

Instead of the catalyst component [A], a Ti compound supported on an inorganic Mg compound may be used.

The polymerization is carried out in saturated hydrocarbons having 4 to 10 carbon atoms.

(2) The polymerization temperature for both the second stage is 110°C or less, preferably 60°C.
It is carried out in the range of ~90°C.

In the first stage polymerization, a low molecular weight polymer is polymerized at a pressure of 1 to 30 kg/ff1G, preferably 5 to 20 kg/iG.

In the second stage polymerization, a high molecular weight is polymerized under a pressure of 1 to 3 oh/crita, preferably 1 to 20 ky/ff1G.

The molecular weight of the polymer produced in the first stage is 1ooo~500
00, preferably 5,000 to 30,000.

If the molecular weight is higher than this range, the molecular weight distribution will not be sufficiently wide, and if it is lower than this range, the concentration of hydrogen as a molecular weight regulator in the polymerization vessel will be high, resulting in a decrease in catalytic activity.

Furthermore, so-called wax increases, polymerization control becomes poor, and ethylene loss increases.

The ratio (r) of the molecular weights of the 72nd stage and the first stage is in the range of 5 to 100, preferably 10 to 60.

Next, a description will be given with reference to a drawing showing one of the typical flows of the present invention.

Ethylene, hydrogen, hexane, a catalyst, etc. are supplied to the first-stage polymerization vessel 1 through line 2, and a low molecular weight polymer is polymerized.

The slurry containing polymerized low molecular weight polyethylene is led to a flash drum 3, where unreacted ethylene and hydrogen are removed.

The removed ethylene and hydrogen are pressurized by a compressor 4 and returned to the polymerization vessel 1.

- A portion of the polymer slurry is extracted as a product from a line 6 by a pump 5, and a portion is introduced into a second stage polymerization vessel 7.

In the polymerization vessel 7, ethylene, hexane, catalyst components, etc. are supplied from a line 8, and high molecular weight polyethylene is polymerized.

A portion of the polymer slurry in the polymerization vessel 7 is extracted from a line 10 as a product by a pump 9-, and a portion is circulated through the first-stage polymerization vessel 1σ.

Due to this flow, polymerization is carried out continuously, and products with different molecular weights are obtained at the same time.

The ratio of the first stage production amount (W'+ ky/Hr) to the second stage production amount (W2 ky/Hr) is in the range of 7:3 to 3 near, preferably 6:4 to 4:6. It is best to polymerize within a range.

Polymer removal speed from the 1st stage to the 2nd stage (V1kg
/Hr) and the circulation speed from the second stage to the first stage (V2kg/
Hr) may be different, but usually the same speed (vkg/H
r).

On the other hand, the rate of withdrawal of the product from each polymerization vessel may also be different depending on the need for a polymer of a required molecular weight.

If we were to carry out the work at the same speed (ukg/hr), then, of course, 2u = wl + w2.

) Ratio of circulation speed (v) to product withdrawal speed U (v/u)
is 1-501, preferably 2-50.

If the value of (v/u) becomes larger than 50, the polymers produced in each stage will be the same, and the above-mentioned advantages will disappear.

Furthermore, the amount of circulation becomes extremely large, which is not a good idea in terms of equipment or energy (operating costs).

The ratio (v) of this circulation speed (v) to the product withdrawal speed (u)
/u), the ratio of the molecular weights of the polymers polymerized in the second stage and the first stage (r), and the ratio of the amounts produced in the first stage and the second stage, depending on the product obtained from the first stage and the second stage. Most of the molecular weight and other physical properties of the polymer are controlled.

In other words, when the ratio (r) of the molecular weights of the first and second stages is small, when (v/u) increases, both the first and second stages have almost the same molecular weight, and (r) is very If it is small (3), the molecular weight distribution will not be sufficiently broadened.

When (r) is large, unless the value of (v/u) is 1 or more, the polymer obtained from the first stage may not be usable because the molecular weight is below the commonly used molecular weight; )
When the value of is larger than 50, the molecular weights of the polymers obtained from the first and second stages become almost the same.

Therefore, the molecular weight ratio of the polymer obtained from the first stage can be freely changed depending on the value of (V/U).

Furthermore, low molecular weight polymers polymerized in the first and second stages,
The molecular weight of the polymer obtained from each stage also differs depending on the ratio of production rates of high molecular weight polymers, which also affects other physical properties.

In other words, in general, the faster the production rate of a low molecular weight polymer, the faster the production rate of a high molecular weight polymer.If you try to match the molecular weight of the polymer in each polymerization vessel, it will be difficult to match the molecular weight of the polymer in terms of physical properties (for example, in the case of a film gel). Also (V/
It is necessary to take a large value for U).

Appropriate ranges for these factors are the aforementioned ranges.

As can be seen from the above, this point is the most important point of the present invention, and by controlling these factors, it is possible to simultaneously obtain polymers with different molecular weights in a wide range from each polymerization vessel.

These include, for example, polymers for blow molding applications, polymers for high molecular weight film applications, or polymers for injection molding applications.

In addition to ethylene homopolymerization, the polymerization of the present invention includes propylene,
Olefins such as butene, hexene, octene etc. from 0.5 to
By copolymerizing within the range of 20 molar ratios, products with characteristic physical properties can be obtained.

The ability to simultaneously produce two or more types of polymers with different molecular weights from two or more polymerization vessels has a great effect on reducing grade changeover losses and reducing the amount of inventory required.

In other words, when switching from one molecular weight grade to another, a large number of polymers that do not belong to either grade (with different molecular weights, different physical properties such as fine density) are produced during the transition stage, but these polymers do not meet the specifications. Usually processed as an outpolymer.

According to the method of the present invention, two or more grades can be produced at the same time, so even if you think about it simply, the changeover loss will be less than half, and in reality, two or more grades can be produced at the same time, which increases flexibility and production planning. - There will be more margin in the operating grade cycle, and the reduction in switching loss will be even greater.

As can be seen from the above description and the examples below, the characteristics of the present invention are that it has extremely high productivity through the multistage cyclic continuous polymerization method, has a sufficiently wide molecular weight distribution, and has an environmental stress cracking resistance (ESCR). ) - Two or more types of polymers with different molecular weights having good physical properties such as rigidity balance and good film properties such as less gelation can be simultaneously produced from two or more polymerization vessels.

This has a significant effect on reducing grade changeover losses and reducing required inventory.

The present invention will be explained in more detail with reference to Examples below.
The present invention is not limited in any way by these Examples.

The symbols and measurement conditions shown in the present example and comparative example will be explained.

MI: Melt index, ASTM D
-1238, measured at a temperature of 190°C and a load of 2.16 to 9.

MIR: Means the quotient obtained by dividing the value measured under MI measurement conditions with a load of 21.6 kg by MI, and is one measure of molecular weight distribution, and the larger the value, the wider the molecular weight distribution.

FR: Value measured under MI measurement conditions with a load of 5 kg (
This is called MMI), which means the quotient obtained by dividing the value measured at a load of 21.6 kg, and like MIR, it is a measure of molecular weight distribution, and the larger the value, the wider the molecular weight distribution.

Density: True density measured by ASTM D-1505.

ESCR: Represents environmental stress cracking resistance, and the measurement method is 5.
Fill 00cc bottles (weight 42?, wall thickness 0.8 inches) with 10 times the internal volume of nonionic surfactant, place them in an oven at 60°C, and apply a constant internal pressure until 50% of the test bottle is filled.
time until destruction.

Bottle molding conditions: Molded product shape 500CC round bottle (JISZ
-1703), machine used: 50 mφ, hollow molding machine, cylinder temperature 160°C, mold temperature, surface temperature 40°C.

Film gel: A film with a thickness of 40 μm was drawn using an ordinary blown film forming machine (50 mrtwfi), and visually judged.

Izod impact strength: Measured according to ASTM D-256.

Example 1 (a) Catalyst synthesis Di-n-butylmagnesium 1381 and triethylaluminum 19P with 2t of n-hebutane in a volume of 4t
The composition AtMg6 (C2H5) 3 (n c4I(9)
An organoaluminium-magnesium complex of 1, , , was synthesized.

An n-heptane solution 800I711 containing 400 mmot (54P) of this complex and 800 ml of an n-hebutane solution containing 400 mmo7 titanium tetrachloride were replaced with dry nitrogen to remove moisture and oxygen, and then reacted at -20°C with stirring for 4 hours. Ta.

The resulting hydrocarbon-insoluble solid was isolated and washed with n-hebutane. A solid was obtained.

The solid thus obtained was diluted with n-hexane,
used for polymerization.

(b) 1.3 m of the above solid catalyst is placed in the polymerization vessel 1 with an internal polymerization volume of 300 t.
At a rate of mot (Ti atom standard)/Hr, 20 mmo7
Triethylaluminum was supplied at a rate of (based on metal atoms)/Hr, purified hexane was supplied at a rate of 40t/Hr, and ethylene was supplied at a rate of 7NM3/Hr and hydrogen at a rate of 0.25NM3.
/Hr, and polymerization is carried out under the conditions of a polymerization temperature of 85° C. and a total pressure of 15 to 9/cIrLG.

The content of the polymer slurry produced by this polymerization was
kg/criLG, is introduced into a flash drum at a temperature of 75° C., and after separating unreacted ethylene and hydrogen, is introduced into the polymerizer 7.

On the other hand, polymer is extracted as a product from the flash drum.

The ratio of the speed at which the polymer is introduced into the polymerization vessel 7 from the flash drum and the speed at which it is withdrawn as a product is 5:1.

The polymerization vessel 7 had an internal volume of 250 t, triethylaluminum was supplied at a rate of 7.5 mmo/Hr (based on metal atoms), purified hexane was supplied at a rate of 30 t/Hr, and ethylene was introduced at a rate of 7NM/Hr. Continuous polymerization is carried out under the conditions of a temperature of 80° C. and a pressure of 8 kg/crrtG.

The contents of the polymer slurry in the polymerization vessel γ are pressurized and circulated to the polymerization vessel 1 by a pump, and at the same time, the polymer is extracted from the polymerization vessel 7 as a product.

The ratio of the rate of circulation to the polymerization vessel 1 and the rate of withdrawal as a product is 6:1.

Note that the ratio of polymerization rates in each polymerization vessel was 1:1.

In this way, polymerization is carried out while circulating the contents of the two polymerization vessels, and MIo and 25 are obtained from polymerization vessel 1, and MMI is obtained from polymerization vessel 7.
o.35 polymer was obtained.

MIR and FR, which are considered to be measures of molecular weight distribution, are as follows: MIR of the polymer obtained from polymerization vessel 1 is 85;
The FR of the polymer obtained was 32.

The polymer from polymerization vessel 1 had good physical properties as a hollow molding grade, and the polymer from polymerization vessel 7 had good properties as a high molecular weight film grade with little gelation.

Regarding other physical properties, the density obtained from polymerization vessel 1 for use in hollow molding is 0.966 L? /cni1 bottle ESCFt
was 10 hours.

Example 2 The solid catalyst used in Example 1 was 1.0 mmo, 4/H
Polymerization was carried out in the polymerization vessel 1 under the same conditions as in Example 1, at a rate of 0.20 NM3/Hr, and in the polymerization vessel γ, the pressure was 12 kg/crtt G and 0.02 NM3/Hr.
Polymerization was carried out in the same manner as in Example 1, except that the polymer was supplied at a rate of NM3/Hr, and the other conditions were the same as in Example 1.

However, the ratio of circulation speed to product withdrawal speed is 8:l.

The polymer obtained from each polymerization vessel was MIo, 55
(Polymerizer 1) and MIo, 20 (Polymerizer 7).

The MIR was 80.95 for each. The polymer from polymerizer 1 had no film gel and was good as a film or tape grade, and the polymer from polymerizer 7 had good physical properties as a hollow molding grade.

The density of the polymer for hollow molding obtained from the polymerization vessel 7 is 0.
．． 95? /crt1. , bottle ESCR was 30 Hr.

Comparative Example 1 Homopolymerization was carried out using the catalyst used in Examples 1 and 2 to obtain a polymer with an MIo of 25 and the same molecular weight as the polymer obtained from polymerization vessel 1 in Example 1. The molecular weight distribution was narrow with an MIR of 38 compared to the MIR of 85 for the polymer, and the amount of heat generated during hollow molding was large, making it unsuitable for bottle bottom molding.

The finished product has melt fractures on the bottle surface and has no commercial value.

Comparative Example 2 Homopolymerization was carried out using the catalyst used in Examples 1 and 2 to obtain a polymer with an MMIo of 28 having almost the same molecular weight as the polymer obtained from the polymerization vessel γ of Example 1. The molecular weight distribution was narrow with FRI 5 compared to FR32 of Polymer No. 1, and it was impossible to form a film due to the extrusion amount during film formation.

Comparative Example 3 Ratio of circulation speed and product withdrawal speed (v/u) in Example 1
was carried out at 0.5, and the polymers were extracted from each polymerization vessel. Polymerization vessel 1 yielded a polymer with an MI of 44, and polymerization vessel 7 yielded a polymer with an MMI of 35.

The polymer from polymerizer 1 had a low molecular weight and a narrow molecular weight distribution that was inappropriate for hollow molding grade and film grade, and the molecular weight was slightly too high for injection molding grade, and the Izod impact strength was 1.8 kg - cm
It is weak at 7cm.

On the other hand, although the FR of the polymer from polymerization vessel 7 was 35 and the molecular weight distribution was satisfactory, gel was formed on the film surface when it was formed into a film.

Comparative Example 4 In Example 2, when (v/u) was carried out at lOO and the polymer was extracted from each polymerization vessel, MI=
A polymer of 0.21 was obtained, and MI=0 from the polymerizer 7.
．． Twenty polymers were obtained.

The MIR of each polymer is 85 and 82, the density is both 0.953, and the ESCR is 31 Hr and 33H.
Both the polymers and r have good physical properties, but both the first and second stages are made of almost the same polymer.

[Brief explanation of the drawing]

The drawings are flow sheets illustrating embodiments of the invention.

Claims (1)

[Scope of Claims] 1. A polymerization method for producing polyethylene of different molecular weights in two or more polymerization vessels connected in series using a catalyst consisting of a transition metal compound and an organometallic compound, comprising: (i) While circulating the contents of the polymerization vessel from the latter polymerization vessel to the former polymerization vessel, products with different molecular weights are taken out from each polymerization vessel at the same time. (11) Flow rate (v) of the polymerization contents to be circulated and product extraction Adjust the ratio v/u of 1(u) to 1-50,
(iiD) An ethylene polymerization method characterized by further adjusting the molecular weight ratio (r) of polyethylene produced in each polymerization vessel to 5 to 100, and adjusting the production amount ratio to 7:3 to 3. 2. The ethylene polymerization method according to claim 1, in which there are two polymerization vessels connected in series. 3. The method according to claim 1 or 2, in which the value of v/u is 2 or more. Polymerization method of ethylene.