JPH075669B2 - Polypropylene impact copolymer reaction control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for copolymerizing propylene and another alpha olefin such as ethylene, and more specifically, the present invention relates to the production of a copolymer in a polypropylene impact copolymer production system. A method and apparatus for controlling velocity and composition.

Although the present invention is described herein with respect to making propylene and ethylene copolymers, the present invention is readily adaptable to the control of other copolymers such as propylene-butadiene copolymers and propylene-hexene copolymers. Here, the "polypropylene impact copolymer" is a polymer composed of a polypropylene homopolymer phase intimately mixed with one or more ethylene-propylene copolymers.
This mixture can produce products with good impact resistance and good stiffness.

PRIOR ART Impact copolymers are typically produced by two or more reactors arranged in series. The first reactor typically produces polypropylene homopolymer, which is then sent to the second reactor. Alternatively, the first reactor can be used to produce a random copolymer, which product is then sent to the second reactor. In the second reactor (and subsequent reactors if necessary) the reactant composition is such that the copolymer is produced in each reactor as having different fractions of ethylene and propylene and the polymer from the previous reactor. Intimately mixed with.

The reactions in the reactors are typically catalyzed by transition metal catalysts. In most cases, the transition metal is titanium.
The reactor itself may be a gas phase reactor, but is not limited thereto.

The production rate in these reactors can be controlled by the catalyst feed rate or the monomer partial pressure. The composition of the polymer produced in a particular reactor is typically determined by the relative partial pressure (partial pressure ratio) of the monomers in the reactor. However, if the second reactor and subsequent reactors depend only on the residual catalyst contained in the polymer from the preceding reactor, the partial pressure of the monomer in the particular reactor is Determines the reaction rate in the reactor and the relative ratio of ethylene and polypropylene in the copolymer produced therein.

FIG. 1 shows a two reactor polymerization apparatus for producing polypropylene impact copolymer (polypropylene impact copolymer). The two reactor system in the diagram is the first reactor RX-
A catalytic exothermic reaction (e.g., using a fluidized bed 14) is conducted in 1 to convert the gaseous feed to a solid product. Raw materials (propylene, ethylene, nitrogen, hydrogen, catalyst, co-catalyst, and selectivity adjusting agent) are supplied from the inlet 2 to the reactor X-1. The heat of reaction is removed by circulating the gaseous feed stream 12 through the cooler 10. The reaction temperature is adjusted by removing heat from the circulating gas feed stream 12 by adjusting the water flow in the cooler 10. The solid product in the form of a polypropylene homopolymer or a random copolymer containing the active catalyst is removed from the reactor RX-1 by discharging it from the fluidized bed 14 in small portions periodically to the product extractor 4. To be done.

The second reactor RX-2 of the two-reactor system of FIG. 1 is the first reactor.
It is designed to produce propylene-ethylene copolymers in a homogeneous mixture system with solid homopolymers or random copolymers synthesized with RX-1. In this example, the first
The product stream 16 (eg homopolymer and active catalyst) from reactor RX-1 is fed to second reactor RX-2. The raw materials (eg ethylene and polypropylene) are fed into the second reactor RX-2 from the raw material inlet 18 and polymerized by the still active catalyst in the homopolymer or random copolymer in the product stream 16 of the reactor RX-1. To be done.

In the second reactor RX-2, ethylene and propylene are copolymerized with the polypropylene homopolymer or random copolymer in the form of an intimate mixture to form an impact copolymer. This process is maintained by the addition of the components from the first reactor RX-1 and the inlet 18 and the cooling is provided by the circulation of the gas stream 8 through the cooler 20. Product is extractor 6
Be withdrawn regularly.

The catalyst fed to the first reactor RX-1 catalyzes the polymerization of propylene (and optionally ethylene). The amount of polymer produced by a given amount of catalyst is approximately constant. Therefore, the production rate of the first reactor RX-1 is usually controlled by changing the catalyst supply rate (flow rate) to the reactor.

In the example of Figure 1, no catalyst is added to the second reactor RX-2. The reaction in the second reactor RX-2 is completely catalyzed by the catalyst contained in the polymer coming from the first reactor RX-1. Since the amount of catalyst in the second reactor RX-2 cannot be generally controlled, the reaction rate is controlled by other means such as adjusting the partial pressure of the reaction product in the circulating gas.

The purpose of use of the second reactor RX-2 (or later described) in the series reaction method using the multistage reactor shown in FIG.
The value of the fraction F _c of the final product (for example, impact polypropylene) produced in the second reactor and the value of the fraction E _c of ethylene contained in the copolymer produced in the reactor RX-2 are Including maintaining at a predetermined value.

Fc (fraction having a total product of the second reactor RX-2 product produced by) generally propylene (C ₃ H ₆ - hereinafter referred to as C3) and ethylene (C ₂ H ₄ - or less C2 Call it) 2nd reactor RX
-2 depending on the combination of partial pressures present. However, in some catalyst systems, a catalyst or cocatalyst is added to the second reactor to remove Fc.
May be controlled. Ec (fraction of ethylene contained in the copolymer produced in the second reactor RX-2) depends on the partial pressure ratio of ethylene and propylene.

Generally, increasing the C3 / C2 ratio decreases Ec and decreasing this ratio increases Ec. It is necessary to adjust the interacting process conditions for Fc and Ec to obtain the desired product properties. An optimal process controller must have a high degree of control over each of these variables, yet compensate for the effects of their interaction.

(Object of the invention) Accordingly, the object of the present invention is to obtain Fc (fraction of the product in the second reactor) in a polymerization apparatus for producing an impact copolymer.
It is to provide a method of controlling Ec (fraction of ethylene in the copolymer produced in the second reactor).

Still another object of the present invention is to provide a polymerization control method in consideration of interaction between Fc and Fc control in a polypropylene impact copolymer production apparatus.

(Summary of the Invention) The above object of the present invention is to model the relationship between Ec and ethylene and propylene partial pressure ratios, model the relationship between ethylene and propylene partial pressures and Fc, and then analyze the substances produced in the reactor. Achieved by a polypropylene impact copolymer manufacturing device equipped with an Fc, Ec controller configured to calculate the quantity and predict the Ec value using the above two modeled relationships and measured process conditions. It The predicted Ec is corrected using the measurement results obtained from the laboratory analysis of the product sample to calibrate the model relationship. Fc is controlled by a production rate controller whose set point is set in proportion to the production rate of the first reactor to achieve a predetermined value. The Ec is controlled by an Ec controller whose set point is adjusted according to the product recipe to achieve the desired value. The calculated production rate and the predicted Ec value are fed back to the production rate controller and the Ec controller and used as if they were measured values.

The preferred production rate controller is configured to control the production rate by adjusting desired relationships such as propylene and ethylene partial pressures and relative propylene and ethylene reactivity. The Ec controller is configured to control the value of Ec by adjusting the partial pressure ratio of propylene and ethylene. A computer is used to convert the output values from the production rate controller and the Ec controller into partial pressure set points for propylene and ethylene, and to decouple or compensate for the interaction between these highly related control parameters. Can be used by programs.

(Detailed Description of the Invention) FIG. 2 illustrates an apparatus for controlling Ec and Fc in a reactor for producing a propylene impact copolymer.

Shown in Figure 2 is the second reactor RX-2, which may be a fluidized bed. Reactor RX-2 can be the second reactor of a two-reactor propylene impact copolymer polymerizer (shown in Figure 1). Alternatively, the second reactor
RX-2 may be the final or intermediate reactor in a multi-reactor (those with three or more reactors) system. For purposes of this description, the second reactor will be the second reactor in a two reactor system.

In the example of Figure 2, a propylene homopolymer or random copolymer feed stream 20 containing about 20 to 1000 ppm of active catalyst is fed to the second reactor RX-2. Feed stream 21 may supply additional feedstock such as ethylene, propylene and the like. Generally, the temperature in the second reactor RX-2 is about 40-120 ° C and the pressure is about 40-500 psia (0.28-35 kg / cm ² ).

The reaction or production rate in the second reactor RX-2 depends on the repartition pressure of C2 and C3 as all the catalyst flows in with the solids from the first reactor RX-1. Reactor RX-2
The fraction Ec (ethylene content rate) of the product produced in (1) depends on the C3 / C2 partial pressure ratio in the reactor RX-2. Regardless of the change in the re-partial pressure, the production rate and Ec are affected, and controlling these amounts has a strong interaction.

The present invention accurately controls the manufacturing process of impact copolymers by "decoupling" or "deinteracting" the interaction between ethylene partial pressure and propylene partial pressure, as well as the control of Fc and Ec. A method and apparatus are provided. Before describing this "decoupling" operation, the method of monitoring and controlling Fc and Ec is first described.

Regarding the control of Fc, various operating conditions of the second reactor EX-2 such as pressure, temperature, flow rate and composition are taken out and given to the production rate calculator 22 (see arrow 23 in FIG. 2), where the reactor is placed. Calculate the actual generation rate in RX-2. This value may be calculated using heat and mass balance calculation techniques well known in the art.

The calculated production rate of reactor RX-2 is provided to the comparison controller 24 to compare it with the production rate set point. This set point is the target Fc given to the prescriber 28 and the first
Based on the production rate of the first reactor calculated by the production rate calculator 25 of the reactor, it is calculated in the production rate set point calculator 26. Alternatively, the generation rate set point may be directly entered by the user, such as by computer input. The production rate set point is compared in the comparison controller 24 with the actual production rate from the production rate calculator 22.

In parallel with the calculation and comparison of generation rate, the predicted Ec
It is calculated at 30, on the one hand compared with the Ec setpoint in the Ec comparison controller 32 and, on the other hand, stored in the prediction history file 38. The Ec set point is based on the target Ec from the prescriber 28 and the Ec set point calculator 34
To achieve the desired Ec calculated at. Alternatively, the Ec set point may be entered directly by the user, for example from computer input.

Since the known Ec setting technique requires a long time (about 2 to 8 hours), the average Ec is predicted in the example of FIG. Periodically (eg, every 5 minutes) the instantaneous Ec value is predicted from the measured process parameters using the calibrated process model.
The current average value Ec is then the instantaneous Ec value and the predicted history file.
From the data stored in 38, it is calculated using the ideal stirred tank mixing model well known in the art.

Reactor RX-2 periodically (eg, every hour) during the process
Sample extraction from the extractor 35 of the well-known laboratory analyzer
The actual Ec is measured by 36. Predicted average when sampling
Ec is extracted from the prediction history file 38 and compared with the measured Ec by the comparator 40. The error between the historical prediction Ec and the measured Ec is passed by the well known numerical filter 42. This passed error value is used to recalibrate the Ec prediction model, which is used to correct the prediction history file 38. Current Floor Average Ec from Predicted Ec Calculator 30
The value is provided to the Ec comparison controller 32 and compared to the Ec set point 34.

The predictive history technique shown in Figure 2 is desirable because it reduces long sample analysis times and provides timely and accurate predictions of Ec.
However, the present invention also works effectively by supplying the measured Ec value directly to the comparison controller 32 (without using a prediction history file or the like). Better and faster measurement techniques will reduce the need for such predictions.

By comparing the predicted Ec and the Ec set point with the Ec comparison controller 52 and comparing the calculated actual generation speed and the generation speed set point with the generation speed comparison controller 24, these set point and calculated value are obtained. And the difference between Ec and
-Adjustment value of ethylene (C2) and / or propylene (C3) partial pressure is calculated in the production rate decoupling calculator 50 to adjust Ec and / or production rate. In the case of the example of FIG. 2, these adjustment values are converted into ethylene and propylene concentration set points, respectively.

Thereafter, the respective set point values are provided to the ethylene and propylene concentration controllers 44, 46, respectively, and the reactor RX-2
Adjust the relative value of ethylene and process fed to
Thereby, Ec and Fc are controlled.

As shown in FIG. 2, the output of the Ec comparison controller 32 is C3 / C.
It is a ratio of two partial pressures, and the output of the production speed comparison controller 24 is a partial pressure scaled in consideration of a function of decoupling control which will be described in detail below. These values are provided to the decoupling calculator.

To accurately calculate the desired partial pressure on calculator 50, the C3 / C2 reactivity ratio and reactor pressure are included in the calculation model. C3 / C2
The reactivity ratio can be determined empirically, but the pressure is determined directly. For example, as an example, the reactivity ratio is about 0.277 (a value obtained by removing the reactivity of C3 by the reactivity of C2), and the reactor pressure is in the range of 40 to 500 psia (0.28 to 35 kg / cm ² ). Generally, reaction characteristics such as selectivity and operating conditions differ depending on the type of polymerization catalyst used.

When the C2 and / or C3 partial pressure changes, the production speed and Ec vary, so in the present invention, the desired partial pressure set point is obtained from the individual control outputs obtained from the production speed comparison controller 24 and the Ec comparison controller 32. To calculate. The C3 / C2 reactivity ratio is adapted to compensate for the interaction between the partial pressures of C3 and C2 included in the calculation.

FIG. 3 shows a control diagram for debinding (eliminating) the influence of C3 and C2 partial pressures on the production rate and Ec. The algorithm of FIG. 3 is recorded in the software of the computer inside the calculator 50.

Derivation of Decoupling Formula A method of deriving a relational formula used in the algorithm of FIG. 3 will be described below. The following equation of motion can be used to express the polymerization reaction of the monomer a.

W = Kp · Pa · ([TM] · Vr) /1.0+Kd· [THETA]) where, W = reaction rate of monomer a (kg / hour) Kp = polymerization rate constant of monomer a (kg) / Hour / (kg / cm ² ) / (T
M mol)) Pa = Partial pressure of monomer a (kg / cm ² ) [TM] = Active transition metal concentration in catalyst (MOL / m ³ ) Vr = Reactor volume (m ³ ) Kd = Polymerization rate decay Constant (1 / h) THETA = residence time in reactor (h) The overall polymerization rate in reactor RX-2 consists of the reaction of C2 and C3, so the above equation applies to these two components. Can be applied to calculate the production rate.

PP2 = KC3 / PC32 / ([TM] / Vr) /1.0+Kd/ [THET
A]) ＋ KC2 ・ PC22 ・ ([TM] ・ Vr) / (1.0 ＋ Kd ・ THET
A) Here, PR2 = total reactor reaction rate in RX-2 (kg / hr) KC3 = C ₃ H ₆ polymerization rate constant (kg / hr ^{/ (kg / cm 2) /} (TM mol)) KC2 = C ₂ H ₄ polymerization rate constant (kg / h / (kg / cm ² ) / (TM mol)) PC32 = C ₃ H ₆ partial pressure (kg / cm ² ) PC22 = C ₂ H ₄ partial pressure (kg / cm) ² ) By transposing and solving for the term including partial pressure, KC3 ・ PC32 ＋ KC2 ・ PC22 ＝ PR2 ・ (1 ＋ Kd ・ THETA) ／ [T
M] ・ Vr ・ KC2 and divide by RR = KC3 / KC2, and PPR = PC32 / PC2
Putting 2, PC22 ・ (1.0 ＋ RR ・ PPR) ＝ PR2 ・ (1.0 ＋ Kd ・ THETA /
([TM] ・ Vr ・ KC2) Now, in the steady state, the term (1.0 + Kd ・ THETA / ([T
M] · Vr · KC2) can be assumed to be almost constant, so the above equation is as follows.

PR2 = X ・ [PC22 ・ (1.0 + RR ・ PPR)] where X = ([TM] ・ Vr ・ KC2) / (1.0 + Kd ・ THET
A) This equation shows the direct proportional relationship between the generation rate and the scaled partial pressure (right side of the above equation). Therefore, it can be used as a basis for decoupling calculations.

The output of the Ec comparison controller is logically interpreted as the voltage division ratio (ie, the PPR defined above), and the output of the production rate comparison controller is the scaled partial pressure value, ie [X · PC22 · (1.0
+ RR / PPR)]. With the outputs of the comparators 24, 32 thus defined, the decoupling calculation can be defined using the values for the reactivity ratios to obtain the partial pressure set points of C2 and C3. Reactivity ratios (or relative reactivity) are usually calculated from data obtained from reactor or off-line experiments.

The output of the Ec comparator controller is then multiplied by the reactivity ratio RR and then
Add 1.0 and multiply by X to obtain the term (1.0 + RR · PPR) · X in the above equation.

If the output of the production speed comparison controller is divided by this term, the desired partial pressure C2 (PC2 ') can be obtained as is apparent from the above equation.
Since the amount of X is divided by itself during the calculation of the present invention, it does not need to be explicitly determined as it does not mathematically appear on the surface.

Multiply the output PPR of the Ec comparator controller by the partial pressure of C2 to obtain the desired C3.
A partial pressure is obtained.

PC3 ′ ＝ PC2 ′ ・ PPR Finally, dividing both partial pressures by the current reactor total pressure PT gives the concentration set point% C3 = 100 ・ PC3 '/ PT% C2 = 100 ・ PC2' / PT .

Decoupling Method The operation of the calculator 50 (FIG. 2) will be described with reference to FIG. The steps illustrated in FIG. 3 may be performed by a computer for calculator 50.

If there is a difference between the desired Ec and the calculated Ec (Ec of the comparison controller 32 of Figure 2), this indicates that the propylene C3 / ethylene C2 ratio is incorrect. Therefore, a predetermined operation is performed to adjust the ratio of the partial pressure of propylene (PC3) to the partial pressure of ethylene (PC2), and thus the adjusted value of the output of the Ec comparison controller 32 is calculated. The output of the Ec comparison controller 32 is calculated in the form of the ratio (PPR) of the partial pressure of C3 (PC3) and the partial pressure of C2 (PC2) in order to avoid the fluctuation of the generation speed when the Ec changes. Container 50
Is supplied to. Calculator 50 then calculates the correct C3 and C2 partial pressures to achieve the desired Ec without changing the production rate.

If there is a difference between the desired production rate and the calculated production rate (the output of the production rate comparison controller 24 in FIG. 2), this will result in C3 partial pressure and
Indicates that the C2 partial pressure is incorrect. Therefore, a predetermined operation is performed and the adjustment values of the propylene partial pressure (PC3) and the ethylene partial pressure (PC2) are calculated.

In order to avoid the fluctuation of Ec when the generation speed fluctuates,
The output of the production speed comparison controller 24 is supplied to the calculator 50 in the form of a scaled partial pressure value (SPC2). The calculator 50 then calculates the correct C3 and C2 partial pressures to achieve the desired production rate without changing Ec.

If both the production rate and Ec deviate from desired values, both adjustments are performed simultaneously.

Step I in FIG. 3 is PC3 / PC from the Ec comparison controller 32 in FIG.
2 = Input process of PPR (partial pressure ratio). The partial pressure ratio PPR is then multiplied in step II by a predetermined reactivity ratio (RR).
Then, the value of 1 is added to the product RR × PPR in step V to obtain the relationship (1 + PP × PPR) described in the derivation of the decoupling equation.
Derive.

The output of the generation speed comparison controller 24 is the scaled partial pressure value SPC2
= PC2 x (1.0 + RR x PPR) to give a particular overall reaction for a particular partial pressure ratio (step IV). This scaled partial pressure value is returned to the original scale in the decoupling process. That is, the scaled partial pressure value is divided by the output (1.0 + RR × PPR) from the process V in the process VII to obtain the desired C2.
A partial pressure value PC2 'is produced. In step VIII, the desired C2 partial pressure values PC2 'and PPR are multiplied to obtain the desired C3 partial pressure (PC3').
To calculate. The% concentrations of C2 and C3 (% C2,% C3) are then calculated by dividing the C2, C3 partial pressure values PC2 ', PC3' by the total pressure PT in steps IX and X, respectively. These new density values PC2 '/ PT and PC3' / PT are the density controllers 46 and 44, respectively.
The flow of C2 and C3 supplied to (Fig. 2) and supplied to the reactor is adjusted to correct Ec and Fc to desired values.

The above calculation is repeated periodically.

Computer control To adjust the partial pressure of C3 and C2 to control the production rate of the reactor RX-2, and to adjust the two partial pressure doors to control Ec (see Figure 3), Computer control can be performed. It is also possible to monitor the heat generated in the fluidized bed of the reactor RX-2, the solid feed portion from the first reactor RX-1, and the propylene-ethylene equilibrium in the gas phase during the reaction cycle by the system computer. From the data collected from a particular process, operating or / and structural parameters, the current reaction or production rate of the fluidized bed can be calculated.

In FIG. 2, device elements that are easily adaptable to computer software are shown in the portion labeled "Computer" above the horizontal dashed line in the figure. These may be implemented by a single computer or multiple computers. Also, the reactor elements are shown below the horizontal dashed line in the figure in the part labeled "Site".

Although the present invention has been described above with reference to a propylene-ethylene copolymer manufacturing apparatus, propylene-buden,
It can be easily applied to other copolymers such as propylene-hexene.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an apparatus for polymerizing a polypropylene impact copolymer by two reactors which can embody the present invention, and FIG. 2 is a schematic diagram showing an apparatus according to an embodiment of the present invention for controlling Ec and Fc in the above apparatus. FIG. 3, FIG. 3 is a method of converting production rate data and Ec data to concentration set points of propylene and ethylene according to the present invention so that the interaction of partial pressures of propylene and ethylene is decoupled. 2 is a flowchart showing

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor William Jyozi Chiado Henson Avenue 227, Henson Avenue, South Charleston, West Virginia, USA (56) References JP-A-55-142008 (JP, A) JP-A-57-168904 (JP, A) JP 60-28285 (JP, B2)

Claims (2)

[Claims] 1. A copolymer of propylene and an alpha olefin selected from ethylene, butene and hexene,
In producing in a reactor equipped with a propylene concentration controller and a concentration controller for the second alpha olefin, (a) the copolymer to be contained in the second alpha olefin produced in the reactor Selecting a target fraction, (b) selecting a target copolymer reaction rate based on the target fraction of all copolymers to be produced in the reactor, and (c) measuring the reactor effluent. Determining the actual fraction of the copolymer in the reactor containing the second alpha olefin, (d) calculating the copolymer reaction rate of the reactor, and (e) the measurement. Comparing the fraction of the second alpha olefin with the target fraction of the second alpha olefin, (f) comparing the measured reaction rate with the target reaction rate, (g) in the step (e) If there is a difference in the comparison, Calculating the partial pressure ratio of propylene to the second alpha olefin to adjust the fraction of the copolymer containing 2 alpha olefins towards the target fraction; (h) in step (f) above. Once the difference is determined by comparison, the partial pressure of the second alpha olefin is calculated to adjust the reaction rate of the copolymer towards the target copolymer reaction rate, (i) above (g) To meet the target fraction of the second olefin and the target reaction rate as a function of the polypropylene / second alpha olefin partial pressure ratio determined in (1) and the partial pressure determined in (h) above. Calculating the partial pressures of the modified propylene and the second olefin, and (j) the modified propylene and the second olefin from (i) above.
Alpha olefin partial pressure value to the propylene concentration controller and the second alpha olefin concentration controller, thereby controlling the production of polypropylene impact copolymer controlling the operating conditions of the reactor. Method. 2. Step (c) analyzes a sample of the product from (i) the reactor to determine the actual fraction of the product containing the second alpha olefin, and (ii) above (i) The predicted fraction obtained from the previous alpha olefin fraction prediction history file was predicted by an experimental relationship related to the process conditions of the second alpha olefin fraction process conditions. Including comparing with an average second alpha olefin fraction,
The method according to item 1.