JPS62250010A - Production of polyethylene - Google Patents

Abstract

PURPOSE:To obtain the titled polymer having stabilized physical properties, by detecting and inputting temperature, pressure, component composition and catalyst concentration of a reaction system to a computer, performing calculation, controlling the melt flow and density and polymerizing ethylene in the presence of a coordination compound based catalyst and hydrogen. CONSTITUTION:A coordination compound based catalyst 6, hydrogen 2, ethylene 3 and a comonomer 4 are fed to a polymerization reactor 1 and temperature, pressure, component composition in a liquid phase and catalyst concentration in the reactor 1 are detected by a temperature sensor 16, pressure sensor 15 and gas chromatographies 13 and 13'. Signals indicated by the detected values are then input to a computer 14 to estimate, calculate and indicate the melt flow index and density in the reactor 1 based on formula I [MFR is the melt flow index; T is the temperature ( deg.C) in the reactor 1; CAT is catalyst concentration (mmol/l-solvent); k, a, b and c are empirically determined constants] and formula II (D is the density; k', a', b' and c' are empirically determined constants). The resultant data are then compared with given present values to determine the target values of molar ratio of the hydrogen to the ethylene in the liquid phase at the same time and the feed ratio of the ethylene is controlled to afford the aimed polymer.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a method for producing polyethylene having predetermined physical properties using a ligand compound-based catalyst, and in particular, for determining parameters related to the physical properties of polyethylene using a sensor and gas chromatography. It relates to a method of manufacturing polyethylene having predetermined physical properties by detecting the detection signal and calculating and controlling the detection signal using a computer.

[Technical Background of the Invention] In the production of polyethylene, industrially, a continuous method is used to produce polyethylene of a predetermined specification, that is, with predetermined physical properties, at a predetermined production rate in a polymerization reactor maintained at a predetermined temperature. It is generally desirable to operate the

When producing polyethylene using a ligand compound catalyst, there are various physical properties of the produced polyethylene that must be controlled, among which the melt flow index (hereinafter referred to as MFR) and density are the most important factors.

The VFR and density (I) are indicators of the molecular weight of polyethylene, are set appropriately depending on the use of polyethylene, and are important indexes for consumers to select a brand of polyethylene.

Normally, polyethylene is manufactured using a continuous polymerization method, in which a predetermined amount of catalyst, a predetermined amount of ethylene, and a predetermined amount of hydrogen gas are supplied into a polymerization reactor maintained at a predetermined temperature, and the specified physical properties and therefore the predetermined specifications are achieved. Operated to produce polyethylene.

Supplying a predetermined amount of catalyst, a predetermined amount of ethylene, and a predetermined amount of hydrogen gas as described above is a method for maintaining a reaction system in a predetermined state, but in reality, simply supplying a predetermined amount of gas will not affect the reaction system. It is impossible to keep it in a predetermined state. For example, the ethylene concentration increases due to minute changes in the catalyst, decrease in activity, etc., and the VFR of the polyethylene to be produced decreases. There are many such minute disturbances for which the reason is unclear. If polyethylene is produced that exceeds the predetermined MFR or density range due to this disturbance, it will be disposed of as a non-standard product. Therefore, in order to prevent this loss, a polymer sample sampled from a conventional beam actor was analyzed using an MFR meter and a density gradient tube to determine the MFR of the produced polymer.
and density data, and depending on the value, hydrogen supply valve,
A technique was used to direct the operation of the ethylene supply valve. However, this method has the disadvantage that analysis takes time (MFR 1 hour, density 3 hours), and this time delay delays response and increases the number of non-standard products.
Furthermore, measurement equipment and personnel were required.

Therefore, a method of directly monitoring the inside of the reaction system has been proposed, but polymerization occurs before samples can be taken from the polymerization reactor, making it impossible to accurately grasp the state inside the reaction system (U.S. Patent No. 3,835,106). There are some drawbacks.

Note that there is also a known technique for monitoring the inside of the reaction system and measuring its pressure to homogenize the composition of the final product, ethylene copolymer (US Pat. No. 3,691,142); It is not a suitable technique for producing polyethylene with MFR and/or density.

Furthermore, a method has been proposed in which the hydrogen and ethylene concentrations in the reaction system are monitored, a computer-based monitoring and control system is introduced, and the amount of hydrogen and ethylene to be supplied is controlled (U.S. Pat. No. 4,469,853, Special Public Service 1986-2
8285), the reaction rate of the amount of comonomer copolymerized is low, such as the recently developed linear low-density polyethylene, and it is difficult to control the physical properties in a production system that uses a large amount of comonomer and recycled. It is difficult to obtain a polyolefin with predetermined physical properties by controlling .

[Object of the Invention] The present invention has been made in view of such conventional difficulties.
When producing polyethylene having a predetermined VFR and density by polymerizing ethylene and optionally a comonomer in the presence of a ligand compound system and hydrogen, a stable predetermined VFR can be obtained by estimating and calculating the physical properties of the reaction system using a computer. and a method for producing polyethylene having a density.

[Summary of the Invention] In order to achieve the above object, the present inventors developed operational data, that is, reaction system We created a calculation formula to estimate the VFR and density based on the hydrogen and ethylene ratio, temperature, comonomer amount and catalyst concentration, etc.
We developed a system and program to calculate 31 based on this calculation formula.

The calculation formula that we found empirically is expressed by the following formula.

i) When there is no comonomer, MFR=hx([o, ] / [c, ])'KariT
)bX(CAT)'------(1)D=to'X(
[H2] / [C2] )”X(T)”X(CA
T)c”・(II)ij) When there is a comonomer, MFR=kX([H2]/[C2])aX(T)b
X(CAT)CX exp(dX [Cxl / [C
9] ) ・”...(II) D”k' X([
H2] / [C2] )"X(1')"X(
CAT)"X exp(d' [Cxl / [C3]
...(IV) However, stakes, a, b
, c, d, k', a', b', c', and d' are constants determined empirically based on each operating condition.

[H2] / [C2] is the molar ratio of hydrogen and ethylene in the liquid phase, [Cxl / EC2] is the molar ratio of comonomer and ethylene in the liquid phase, T is the temperature inside the reactor (°C), and CAT is the catalyst concentration ( By comonomer is meant here a small proportion of olefins copolymerized with ethylene, specifically propylene <C,,), butene (C4) and methylpentane (C
s) is used.

The proportion of the comonomer used is preferably 30 mol% or less, preferably 10 mol% or less, based on the monomer ethylene. The ligand compound catalyst used in the production of polyethylene of the present invention is usually (a) Mendele
It is a catalyst whose main components are a compound of a transition metal of Groups 1 to 2 of the Periodic Table of Ljeff, and (b) an organometallic compound or a hydrogen compound of Groups 1 to 2 of the Periodic Table. Particularly preferred are catalysts whose main components are a halogen compound of titanium or vanadium and an organometallic compound of aluminum. The above components (a) and/or (b)
) may be supported on a carrier, or may be treated with a modifier such as an electron donor.

Examples of such ligand compound catalysts include, for example, U.S. Pat. No. 3,257,332, U.S. Pat. No. 3,826,792,
U.S. Patent No. 3113115, U.S. Patent No. 354613
No. 3, U.S. Patent No. 4,125,698, U.S. Patent No. 407
No. 1672, US Pat. No. 4,071,674, US Pat. No. 3,642,746, US Pat. No. 3,051,690, US Pat.
The catalysts described in No. 49 can be used.

The amount of the catalyst used in the polymerization of ethylene is generally 0.0% in terms of titanium atoms per IQ of polymerization solvent. 0.8 mmol.

The ethylene polymerization reaction using the catalyst of the present invention can be carried out in the same manner as the ethylene polymerization reaction using a conventional ligand compound catalyst. That is, all reactions are conducted in a state where oxygen, water, etc. are substantially excluded. A suitable inert solvent such as an aliphatic hydrocarbon such as propane, butane, pentane, hexane, heptane, kerosene is used, into which the catalyst and ethylene and optionally further comonomers are introduced to carry out the polymerization. . When polymerizing ethylene, a polymerization temperature of 50 to 90°C is usually employed. The polymerization is preferably carried out under pressure, and is generally carried out at 1 to 10 kg/cd.

IO- [Embodiments of the Invention] Preferred embodiments of the present invention will be described in detail below with reference to the drawings.

The drawing shows a block diagram of the method for producing polyethylene of the present invention, in which a polymerization reactor 1 includes a hydrogen supply line 2 for supplying hydrogen gas to the polymerization reactor, an ethylene supply line 3 for supplying ethylene, and a comonomer supply line. A comonomer supply line 4 for supplying hexane as a solvent, a solvent supply line 5 for supplying hexane as a solvent, a catalyst supply inlet 6 for supplying a catalyst, and an outlet line 7 for taking out polyethylene as a product from the polymerization reactor 1 are provided, respectively.

The hydrogen supply line 2 has a control valve 2a that controls the amount of hydrogen supplied, the ethylene supply line 3 has a control valve 3a that controls the amount of ethylene that supplies comonomer, and the inlet 4 has a control valve 4a that controls the amount of comonomer that is supplied. However, the solvent supply line 5 is provided with a control valve 5a for controlling the amount of solvent supplied, and the catalyst supply line 6 is provided with a control valve 6a for controlling the amount of catalyst supplied. The opening degrees of the valve 3a and the comonomer supply valve 4a are controlled by control signals from a computer, which will be described later, in order to change the ethylene concentration, hydrogen residue concentration, and amount of comonomer so as to produce polyethylene with a predetermined MFR.

A sampling line 8 is provided in the polymerization reactor 1, and the sample introduced into the sampling line 8 is passed through a heat exchanger 9 and an accumulator 1 for removing reaction heat from the system.
It is separated into a gas phase and a liquid phase through O, and each is recycled to the reactor 1. The temperature of the outlet of the heat exchanger 9 is 50-3
It is automatically adjusted to a certain predetermined value in the range of 0° C. and separates the sample into gas and liquid phases. The separated gas phase and liquid phase (including solids) are returned from the accumulator 10 to the polymerization reactor 1 via recycle lines 11 and 12.

The gas phase is led to gas chromatographs 13 and 13' in the middle of the recycle line 11, and the gas chromatography 13 measures the hydrogen gas concentration and ethylene concentration, and the gas chromatography 13' measures the comonomer concentration.

Methylpentane having 6 carbon atoms in the comonomer is measured from the liquid phase via a line 11' and a vaporizer in a gas chromatography 13' for comonomers.

As the gas chromatography, high-speed gas chromatography is used, which is set so that the time it takes to detect olefins (retention time) is less than the residence time of the reactants in the polymerization reactor (olefin detection time is less than IO minutes, preferably (gas chromatography for 5 seconds to 1 minute). The measured component signals based on the hydrogen gas concentration and olefin concentration measured by the gas chromatography 13 are sent to the computer 1.
4 is input.

The polymerization reactor 1 is equipped with a pressure measuring device 15 and a thermometer 16 as sensors, and the respective measured values are inputted to the computer 14 as electrical signals. Specifically, the pressure measuring device 15 that outputs a measured value as an electric signal may be a transmitter type pressure n1, and the thermometer 16 may be a thermocouple type temperature side. Next, the estimation system using the computer 14 will be explained.

The computer 14 consists of a calculation section 117, a calculation section 18, a control section 119, and a control section [20].
Based on the measured component signal from gas chromatography 11 and the pressure and temperature measurement signals, the molar ratio of hydrogen to ethylene in the liquid phase [82] / [C2] and the molar ratio of comonomer to ethylene [Cx] / [C21 Estimate. Next, the calculation section [1B calculates the catalyst concentration CA'r calculated from the amount of solvent supplied and the amount of catalyst supplied, the temperature T inside the polymerization reactor, the previously estimated molar ratio of hydrogen and ethylene [H2] / [C2], and the comonomer. and ethylene molar ratio [Cx] / EC2
], based on the pre-blocked estimation formula, M
Estimate FR and density. The estimated value is displayed as a graph on the display device 21, for example, every minute, and is also displayed on the printer 22.
It is printed out and further stored in the storage device 23.

The estimated values of VFR and density are compared with preset melt flow index MFR and standard setting values indicating density in the control unit I20, and [L] / [C
2] The target value of the value and the target value of the [Cxl/EC,l value are set and input to the control unit 17. Control unit 11
17 compares the set target value of [)I,] / [C2] value and the target value of [Cxl / [C2] value with the estimated value of the molar ratio previously estimated by the calculation unit 117, and calculates the difference between the two. outputs a signal according to the difference between the two. Based on this signal, the hydrogen supply valve 2 is controlled by the current/pneumatic converter or manually.
a, operate the ethylene supply valve 3a and the comonomer supply valve 4a, respectively.

Table 1 shown below shows representative 5 produced by the method of the present invention.
It shows the comparison between the estimated VFR and density of the brand and the MFR and density obtained by analysis, the number of analyzes per the previous production volume, and the amount of off-grade products (off-grade products) produced.The difference from the analytical values is M
The FR was 10% and the density was 0.2%, which were within the practical range.

Table 2 shows the results when the above brands were produced using conventional VFR and density analysis.1 Compared to the method of the present invention, both the number of analyzes and the amount of off-products produced are significantly greater.

(Table-1) (Table-2) -15= [Effects of the Invention] As explained above, the polyethylene manufacturing method according to the present invention can estimate the MFR and density of the currently produced product at any time based on operational data. Since the supply amount of hydrogen, ethylene and comonomer is controlled based on the calculation, the production of out-of-grade products can be minimized and polyethylene with specified physical properties can be produced, especially linear low-density polyethylene whose physical properties are difficult to control. This is a suitable manufacturing technique.

[Brief explanation of drawings]

The drawing is a block diagram implementing the method of the present invention. 1...Polymerization reactor 2...Hydrogen supply line 3...Ethylene supply line 4...
...... Comonomer supply line 5 ...... Solvent supply line 6 ...... Catalyst supply line 7 ...... Outlet line 8 ... ...Sampling line 9...
... Heat exchanger 10 ... Accumulator 11 ...
...Recycle line 12...Recycle line 13.13'...Gas chromatography 14...Computer 15...Pressure Measuring device (sensor) 16・
・・・・・・Thermometer (sensor) 17・・・・・・
・Calculating unit■ ]8......Calculating unit■ 19...Control unit■ 20...Control unit■ 21...... Display unit 22...Printer 23...Storage device agent Patent attorney Moritani -O = 1Q-

Claims (1)

[Claims] 1. Polymerize ethylene in the presence of a coordination compound catalyst and hydrogen to obtain a predetermined melt flow index (MFR) and density (D
), the temperature, pressure, and composition of components in the liquid phase within the reactor. The catalyst concentration is detected by a sensor and gas chromatography, a signal indicating the detected value is input into a computer, and based on formulas I and II, MFR=k×([H_2]/[C_2])^a×(T )
^b×(CA ding) ^c・・・(I)D=k′×(
[H_2]/[C_2])^a′×(T)^b×(CA
T) ^c'...(II) However, k, a, b, c, d
, k', a', b', c' are constants determined empirically based on each reaction condition, [H_2]/[C_2] is the molar ratio of hydrogen and ethylene in the liquid phase T is the temperature inside the reactor (°C) CAT estimates and displays the catalyst concentration (m mol/l-solvent), melt flow index and density in the reactor, and
Production of polyethylene, characterized in that the target value of the molar ratio of hydrogen and ethylene in the liquid phase is determined in comparison with the predetermined melt flow index and density, and the amount of ethylene supplied to the reactor is controlled. Method. 2. Polymerize ethylene and a comonomer in the presence of a coordination compound catalyst and hydrogen to obtain a predetermined melt flow index (MFR).
) and density (D), the temperature, pressure, component composition in the liquid phase, and catalyst concentration inside the reactor are detected by a sensor and gas chromatography, and a signal indicating the detected values is sent to a computer. Based on formulas III and IV, MFR=k×([H_2]/[C_2])＾a×(T)
^b×(CAT)^c×exp(d×[Cx]/[C_
2]・・・・・・(III) D=k′×([H_2]/[
C_2])^a'×(T)^b'×(CAT)^c'×
exp(d′×[Cx]/[C_2])・・・・・・(
IV) However, k, a, b, c, d, k', a', b', c
', is a constant determined empirically based on each reaction condition, [H_2]/[C_2] is the molar ratio of hydrogen and ethylene in the liquid phase, [Cx]/[C_2] is the mole of comonomer and ethylene in the liquid phase. The ratio T is the temperature inside the reactor (°C). CAT is the catalyst concentration (mmol/l-solvent). The melt flow index and density inside the reactor are estimated and displayed.
A target value of the molar ratio of hydrogen and ethylene in the liquid phase and a target value of the molar ratio of comonomer and ethylene in the liquid phase are determined in comparison with the predetermined melt flow index and density set in advance, and the target value of the molar ratio of comonomer and ethylene in the liquid phase is determined. A method for producing polyethylene, which comprises controlling the amount of ethylene and comonomer supplied to the polyethylene.