JP3189340B2 - Method for producing polyolefin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polyolefin. Specifically, Ziegler catalysts,
When polymerizing an olefin in the polymerization zone in the presence of hydrogen using a Philips catalyst or the like, the physical properties, particularly the density value, of the polyolefin obtained by the polymerization reaction are measured, and the measured values and the operation data of the reaction conditions are computerized. To estimate the reaction state through arithmetic processing, predict the transition of the density value of polyolefin produced in the reactor in the future based on the estimated value, and change the operating conditions by comparing the predicted value with the target value The present invention relates to a method for producing a polyolefin having a predetermined density value by calculating an amount and directly controlling a reaction condition under a predetermined condition based on the calculated amount.

[0002]

2. Description of the Related Art Hitherto, polyolefins have been molded by various molding methods and used for various purposes. Depending on these molding methods and applications, it is desired that the polyolefin has various physical properties, particularly a melt flow rate (melt flow index; referred to as “MFR” in this specification) and a density. Generally, to adjust these properties,
There are known methods for changing the type, composition, amount, etc. of the catalyst and changing the polymerization conditions.

In order to produce a polyolefin on an industrial scale, a predetermined amount of a catalyst and a cocatalyst, a predetermined amount of an olefin, a predetermined amount of hydrogen, and a solvent are placed in a polymerization zone maintained at a predetermined temperature. The feed is run under conditions such that a polyolefin having a predetermined specification, ie, a predetermined MFR and density, is continuously produced.

[0004] However, even if continuous polymerization is carried out under the conditions where the feed rates are kept constant as described above, it is difficult to keep the state in the polymerization zone constant. For this reason, it is almost impossible to produce a polyolefin having a predetermined physical property specification at a constant production amount. That is, the olefin concentration in the polymerization zone changes due to a minute change in the catalyst or a change in the activity due to the uncertain disturbance. For example, when the activity of the catalyst decreases, the olefin concentration in the zone increases, the ratio of the concentration of hydrogen and the olefin, which are molecular weight regulators, decreases, and the density of the generated polyolefin decreases. . Frequent minute disturbances for which the reason is not clear often occur, which changes the olefin concentration in the polymerization zone and the physical properties of the resulting polyolefin, especially the MFR
And the density and the like will fluctuate.

Conventionally, various methods for improving such a problem have been proposed. For example, there are the following methods. A method for measuring the olefin concentration and the hydrogen gas concentration in the liquid phase portion of a polymerization reactor (US Pat. No. 3,835,106)
issue). A method for monitoring the polymerization reaction system and measuring the pressure to homogenize the composition of the ethylene copolymer as the final product (U
SP 3, 691, 142). A method for monitoring the ethylene and hydrogen concentrations in the gas phase or liquid phase of a polymerization reactor, incorporating this into a control system using a computer, and controlling the ethylene and / or hydrogen supply amounts (US Pat. No. 4,469,853, 1962-25
0010).

[0006]

SUMMARY OF THE INVENTION Among the above conventional methods,
However, the method (1) has a problem that the polymerization reaction progresses until the sample is collected from the reactor and the state in the reaction system cannot be accurately grasped.

Further, the method of the present invention is characterized in that desired physical properties, particularly MF
It is not a suitable technique for producing polyethylene having R and / or density.

In the method of (1), when a minute disturbance occurs in the polymerization zone, the reaction state changes. Therefore, it is only necessary to control the ethylene and hydrogen concentrations in the gas phase or liquid phase to a predetermined amount. It is difficult to obtain a polyolefin having an MFR or density.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a polymerization reaction operation support device for producing a polyolefin capable of obtaining a polyolefin having a predetermined density value stably and reliably. .

[0010]

The process for producing a polyolefin according to the present invention comprises the steps of: producing a polyolefin having a predetermined density by polymerizing an olefin and a comonomer in a polymerization zone in the presence of a catalyst and hydrogen; , The supply amounts of comonomer, hydrogen and catalyst, the olefin concentration in the gas phase, the comonomer concentration, the hydrogen concentration and pressure, and the temperature and liquid level in the liquid phase. At the same time, the density of the polyolefin product flowing out of the polymerization zone is measured, and the measured signal is input to a computer.
Using the measured values and the operation data, the following equation (1):
Based on (6), the density of the polyolefin instantaneously generated in the polymerization zone is dynamically and sequentially estimated by the arithmetic processing, and the γ value in the equation (6) is calculated from the estimated value, and the γ value is used. In the polymerization zone, the molar ratio of hydrogen / olefin or the molar ratio of comonomer / olefin in the gas phase in the polymerization zone is predicted by comparing the density value in the future with the density target value predetermined in the density prediction value. Calculating and controlling the supply amount of the olefin, comonomer or hydrogen or the supply amount of the catalyst to the polymerization zone by a computer control output performed based on the calculated value to produce a polyolefin having a predetermined density. Features.

[0011]

(Equation 2)

That is, the present inventors have solved the above-mentioned problems of the prior art, and quickly grasped the reaction state even when the reaction state was changed due to disturbance or the like, and determined a predetermined state in accordance with the state amount. As a result of intensive studies to provide a method for producing a polyolefin which can be changed to reaction conditions for obtaining a polyolefin having physical properties, operation data in the polymerization zone and actual measured values of the density of the polyolefin obtained in the polymerization zone are loaded into a computer and subjected to arithmetic processing. Then, the density of the polyolefin instantaneously generated in the polymerization zone is dynamically and sequentially estimated, and a change in density in the future is predicted based on the estimated value, and the density prediction value and a target value corresponding to a predetermined density are predicted. By contrast with
The inventors have found that the above problems can be solved by calculating the target value of the reaction conditions and adjusting the reaction conditions in the polymerization zone based on the calculated target value, and have completed the present invention.

Hereinafter, the present invention will be described in detail.

The catalyst used for producing the polyolefin according to the present invention includes a Ziegler catalyst, a Phillips catalyst and the like. An organic aluminum compound is used as a promoter. If desired, a third component such as an electron donating compound may be used.

As the solvent, inert hydrocarbon solvents such as aliphatic hydrocarbons such as hexane and heptane, aromatic hydrocarbons such as benzene, toluene and xylene, and alicyclic hydrocarbons such as cyclohexane and methylcyclohexane are used.

Examples of the olefin include α-olefins such as ethylene, propylene, butene-1, hexene-1, and 4-methylpentene-1.

The comonomer means a small proportion of other olefins copolymerized with these olefins. For example, when ethylene is used as the olefin, propylene, butene-1 and the like are used as the comonomer. The use amount of the comonomer is 30 mol% or less, preferably 10 mol% or less based on the olefin.

The olefin polymerization reaction is carried out by supplying a predetermined amount of an olefin, a comonomer, hydrogen, a catalyst and a cocatalyst, a solvent and a third component, if desired, to a polymerization zone.
The reaction is carried out at a temperature of ° C., a pressure of 0.1 to 100 kg / cm ² G and a hydrogen / olefin molar ratio in the gas phase of 0.01 to 1000. Of course, the reaction conditions are appropriately selected within the above range according to the desired properties of the polyolefin.

Hereinafter, embodiments of the method of the present invention will be described in more detail with reference to the drawings. FIG. 1 is a block diagram of a polyolefin production process illustrating an embodiment of the present invention.

In FIG. 1, a hydrogen supply line 2, an olefin supply line 3, a comonomer supply line 20, a solvent supply line 4, a catalyst supply line 5, a promoter and a third component supply line 5 'are connected to a polymerization reactor 1. A predetermined amount of hydrogen, olefin, comonomer, solvent, catalyst, co-catalyst, third component, and the like are continuously supplied according to the density of the polyolefin to be produced.

A liquid phase portion 1a and a gas phase portion 1b are formed inside the polymerization reactor 1 by the above-mentioned feed, and the olefin is polymerized while being stirred by the stirrer 1c.

The produced polyolefin is continuously extracted from the polyolefin extraction line 6, supplied to a degassing tank or a gas separator 12, and after separating unreacted gas from a pipe 12A, passes through a supply line 6A. The solvent is supplied to the solvent separator 13, and the solvent is separated from the pipe 13A. Next, it is supplied to the dryer (dryer) 14 via the feed line 6B, and is made into a dried polyolefin solid. This is supplied to the extruder 15 through the feed line 6C and pelletized,
Withdraw from polyolefin pellet extraction line 16.

In the present invention, the polyolefin extracted from the polymerization reactor 1, preferably, the polyolefin pellets extracted from the extraction line 16 are sampled from the sampling lines 16A and 16B at predetermined time intervals. The MFR and the density of the produced polyolefin are guided to the density measuring device 18 and measured. A signal based on this measured value (actually measured value) is input to the computer 30 (signals K ₁ and K ₂ ).

The above-mentioned hydrogen supply line 2, olefin supply line 3, comonomer supply line 20, and solvent supply line 4 have supply valves 2a,
3a, 20a, and 4a, and flow detectors 2b, 3b, 20b, and 4b that detect the supply amounts of the respective detectors are provided, and detection signals correlated with the flow rates from the flow detectors 2b, 3b, 20b, and 4b ( K ₃ , K ₄ , K ₅ , K ₆ ) are input to the computer 30. On the other hand, according to control signals S _{1 to} S ₄ from the computer 30 to be described later, the olefin concentration,
In order to change the comonomer concentration and the hydrogen concentration, the stroke of the catalyst supply pump 5a, the olefin supply valve 3
a, the opening degree of the comonomer supply valve 20a and the hydrogen supply valve 2a is controlled.

Further, a sampling line 7 is provided in the gas phase portion 1b of the polymerization reactor 1, and the gas in the gas phase portion 1b is guided to an analyzer 8 such as gas chromatography via an on-off valve 7a. The analyzer 8 measures the hydrogen concentration, olefin concentration and comonomer concentration in the gas. A signal (K ₇ ) based on the hydrogen concentration, the olefin concentration and the comonomer concentration measured by the analyzer 8 is also input to the computer 30.

Reference numerals 9 and 10 denote detectors for the pressure in the gas phase and the temperature in the liquid phase of the polymerization reactor 1, and detection signals (K) correlated with the pressure and temperature from the pressure detector 9 and the temperature detector 10, respectively. ₈ , K ₉ ) are also input to the computer 30.

Reference numeral 11 denotes a supply line for supplying cooling water to the polymerization reactor 1. The supply line 11 is provided with a supply valve 11a for adjusting the supply amount and a flow detector 11b for detecting the supply amount. A detection signal (K ₁₀ ) correlated with the flow rate from 11b is input to the computer 30. The cooling water supply valve 11a is also the control signal S ₅ from the computer 30 to be described later, to produce a polyolefin of a predetermined density, in order to change the polymerization temperature, the opening degree is controlled.

Further, a solvent supply line 18 is connected to the degassing tank 12 for adjusting the slurry concentration. A supply valve 18a for adjusting the supply amount and a flow detector 18b for detecting the supply amount are provided. The detection signal (K ₁₁ ) correlated with the flow rate from the flow rate detector 18 b is
Input to 0.

The pipe 19A is a line for returning hot water to the cooling tower, and the pipe 19B is a line for circulating hot water.

As described above, in the present invention, the operation data signals (K _{3 to} K ₁₀ in this embodiment) of the reaction conditions in the polymerization reactor 1 are taken into the computer.
The polyolefin discharged from the polymerization reactor 1, desirably the polyolefin pellets obtained through the degassing tank 12, the solvent separator 13, the dryer 14 and the extruder 15 is subjected to MFR
The signals (K ₁ , K ₂ ) of the measured MFR value and the measured density value measured by the measuring device 17 and the density measuring device 18 are taken into a computer, and the prediction model formula (5) described later is used by using the measured values and the operation data. The density of the polyolefin instantaneously generated in the polymerization reactor is dynamically and sequentially estimated by the arithmetic processing based on (1) to (1), and the density estimated value and the following equation (6) are used to calculate the density in the following equation (6). Calculate the γ value. By using the γ value and the operation data of the reaction conditions of the polymerization reactor 1 or the change amount thereof, the polyolefin produced in the polymerization reactor 1 in the future (future) by the calculation processing of the following equation (6) → the following equation (1) The transition of the density value is predicted, the predicted value of the density is compared with the target value, and the reaction condition of the following formula (6) is changed until the predicted value matches the target value, and the following formulas (6) and (1)
The prediction of the change in the density is repeated by a trial and error method by the arithmetic processing by the formula, and the target value of the reaction condition in the following formula (6), in particular, the hydrogen / olefin molar ratio or the comonomer / olefin in the gas phase of the polymerization reactor 1 is calculated. Calculate the target value of the molar ratio of
The supply amount of olefin, hydrogen, comonomer, or catalyst in the polymerization reactor 1 is controlled by the control output of a computer performed based on the calculated value (control signals S _{1 to} S
₄ ) By doing so, the density of the polyolefin produced in the polymerization reactor 1 is adjusted to a predetermined range.

Hereinafter, using the actual measured value of the density of the polyolefin produced in the polymerization reactor 1 and operation data of the polymerization reaction conditions (hereinafter sometimes referred to as “process state quantity”),
A method for estimating the density of the polyolefin instantaneously generated in the polymerization reactor by the arithmetic processing based on the prediction model will be described in detail.

Each symbol indicates the following. G _L1 : Liquid phase capacity of polymerization reactor 1 G _L2 : Liquid phase capacity of degassing tank 12 _GL3 : Liquid phase capacity of solvent separator 13 C _P1 : Polymer concentration of polymerization reactor 1 C _P2 : Degassing tank 12 C _P3 : Polymer concentration of solvent separator 13 F _P1 : Instantaneous reaction amount of polymerization reactor 1 F _Ol1 : Olefin supply amount of polymerization reactor 1 F _S1 : Solvent supply amount of polymerization reactor 1 F _S2 : Desorption Amount of solvent supplied to gas tank 12 F _S3 : Amount of solvent supplied to solvent separator 13 S _Ol1 : Amount of olefin dissolved in solvent of polymerization reactor 1 ρ ₁ : Instantaneous density of polymerization reactor 1 ρ ₂ : Polymerization reactor Density at 1 outlet ρ ₃ : density at outlet of degassing tank 12 ρ ₄ : density at outlet of solvent separator 13 ρ ₅ : density at outlet of dryer 14 ρ ₆ : density at outlet of extruder 15 L: delay time k: powder Drop-off coefficient k = f (additive type and concentration, extruder specific energy, etc.) First, a polymerization reactor 1, a degassing tank 12, a solvent separator 13,
The material balance of the dynamic characteristics of the density of polyolefin in the dryer 14 and the extruder 15 is represented by the following prediction model formula.

(1) Polymerization reactor 1 During unsteady operation (when starting or stopping polymerization reaction, when disturbance occurs, or when changing polymerization reaction conditions, etc.)

[0034]

(Equation 3)

At the time of steady operation (C _L1 , C _P1 , F _P1 , S
_Ol1 is constant)

[0036]

(Equation 4)

(2) Degassing tank 12 during unsteady operation

[0038]

(Equation 5)

During normal operation ( _GL2 and _CP2 are constant)

[0040]

(Equation 6)

(3) Solvent separator 13 During unsteady operation

[0042]

(Equation 7)

During steady operation

[0044]

(Equation 8)

(4) Dryer 14

[0046]

(Equation 9)

(5) Extruder 15

[0048]

(Equation 10)

[0049] Here, for example, by density measuring instrument 18 the polyolefin pellets withdrawn from the extruder 15 (granules) was sampled every predetermined time and measuring the density of the polyolefin, using the measured value [rho _6, Equation (5) →
The density of the polyolefin instantaneously generated in the polymerization reactor 1 can be estimated by performing the sequential processing based on the formula (4) → the formula (3) → the formula (2) → the formula (1). A γ value is calculated from the estimated density value ρ ₁ and the following equation (6).
(Each sign in equation (6) is as described above.) Log ρ (t) = B
₁ log (H ₂ / Ol) _G + B ₂ log (Co / Ol) _G + B ₃ MFR _l + γ ...
(6) Next, this γ value and the process state quantity of the polymerization reactor 1
That is, by using the operation data of the reaction conditions or the amount of change thereof, the transition of the density value of the polyolefin generated in the polymerization reactor 1 in the future (future) is predicted by the arithmetic processing of the equation (6) → the equation (1). I do.

The predicted value of the density change is compared with the target value of the density, and the process state quantity in the equation (6) is changed until the predicted value matches the target value. The prediction of the transition of the density value is repeated by a trial and error method by the arithmetic processing according to 1), and the process state quantity in the equation (6), that is, the target value of the reaction condition, particularly the target value of the comonomer / olefin molar ratio in the gas phase, is calculated. calculate.

Based on the target value, control signals S _{1 to} S ₅ are output from the reaction condition set value changing unit 38 and the control unit 36 to supply the olefin, comonomer, hydrogen, catalyst or cocatalyst in the polymerization reactor 1. By changing the set values such as the amount, a polyolefin having a predetermined density value can be produced.

Note that MFR ₁ (instantaneously generated MFR) in the above equation (6) is obtained from the measured MFR value of the MFR measuring device 17.
It can be calculated from the following equation (7).

[0053]

[Equation 11]

Symbol: MFR ₁ : MFR generated instantaneously MFR ₂ : MFR at reactor outlet Y: Exponent

[0055]

As described above, in the method of the present invention, the above-mentioned signals input to the computer are processed in the computer according to a preset program, and the partial pressure of hydrogen in the gas phase (1b in FIG. 1) is calculated. Calculated values of olefin partial pressure, comonomer partial pressure, hydrogen / olefin molar ratio, comonomer / olefin molar ratio, polyolefin polymerization amount in the polymerization reactor, polymer concentration, cocatalyst concentration, catalytic activity, etc. are calculated. The deviation is determined by comparing and calculating the calculated value and each target value set in advance for producing a polyolefin having a predetermined density, and a control signal based on the difference is used to determine, for example, a hydrogen supply valve (FIG. 1). 2a) to operate the gas phase part (1b)
The hydrogen concentration in the olefin feed valve or the olefin feed valve (3
a) controlling the stroke of the comonomer supply valve (20a) or the catalyst supply pump (5a) to adjust the olefin concentration or comonomer concentration of the gas phase portion (1b), and The hydrogen concentration, the olefin concentration, and the comonomer concentration are controlled so as to produce a polyolefin having a predetermined density by adjusting the molar ratio of the monomer or the comonomer / olefin molar ratio to a predetermined value.

[0056]

The present invention will be described in more detail with reference to specific control examples.

Example 1 A polyolefin was produced using the apparatus shown in FIG. 1 according to the control method described above.

FIGS. 2 and 3 show the measured MFR (a) and the estimated MFR (b) (FIG. 2) when the MFR and the density are directly controlled by the method of the present invention shown in FIG. and density measured value (c) and density estimates (d) Ri graph der showing a change in the (Figure 3), in Figure 3, a predetermined
This is an example in which the density is 0.947.

From these results, the measured and estimated values of MFR and density are in good agreement, and according to the method of the present invention,
It is clear that the desired MFR and density of polyolefin can be obtained simultaneously and easily.

[0060]

As described above in detail, according to the method for producing a polyolefin of the present invention, the olefin and the comonomer are polymerized in the polymerization zone in the presence of a catalyst and hydrogen to produce a polyolefin having a predetermined density reliably and stably. , And can be manufactured efficiently.

[Brief description of the drawings]

FIG. 1 is a block diagram of a polyolefin production process showing one embodiment of the present invention.

FIG. 2 shows measured values (a) and M of MFR when direct control of MFR and density is performed by the method shown in FIG.
It is a graph which shows transition of the estimated value (b) of FR.

FIG. 3 is a graph showing transitions of a measured density value (c) and an estimated density value (d) when direct control of MFR and density is performed by the method shown in FIG. 1;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 polymerization reactor 2 hydrogen supply line 3 olefin supply line 4 solvent supply line 5 catalyst supply line 6 polyolefin extraction line 7 sampling line 8 analyzer 12 degassing tank 13 solvent separator 14 dryer 15 extruder 17 MFR measuring device 18 Density measuring device 20 Comonomer supply line 30 Computer

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C08F 2 / 00,2 / 01

Claims (1)

(57) [Claims] 1. In producing a polyolefin having a predetermined density by polymerizing an olefin and a comonomer in the polymerization zone in the presence of a catalyst and hydrogen, supply amounts of the olefin, comonomer, hydrogen and the catalyst in the polymerization zone, Olefin concentration, comonomer concentration, hydrogen concentration and pressure, and the temperature and liquid level of the liquid phase are detected, and their operation data signals are input to a computer, and the polyolefin product flowing out of the polymerization zone is detected. The density is measured, the measured signal is input to a computer, and the following equation (1) is calculated using the measured value and the operation data.
Based on (6), the density of the polyolefin instantaneously generated in the polymerization zone is dynamically and sequentially estimated by the arithmetic processing, and the γ value in the equation (6) is calculated from the estimated value, and the γ value is used. In the polymerization zone, the molar ratio of hydrogen / olefin or the molar ratio of comonomer / olefin in the gas phase in the polymerization zone is estimated by comparing the density value in the future with the density target value predetermined in the density prediction value. Calculating the amount of olefin, comonomer or hydrogen supplied to the polymerization zone or the amount of supplied catalyst to produce a polyolefin having a predetermined density by an operation control output of a computer performed based on the calculated value. Characteristic polyolefin production method. (Equation 1)