JPH0348209B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyolefin manufacturing method and an olefin polymerization apparatus.

In detail, when polymerizing olefins by constant pressure polymerization using a solvent in the presence of hydrogen using Ziegler catalysts, Phillips catalysts, etc., the polymerization conditions, especially the polymerization reaction pressure (gas phase pressure), are stabilized. In particular, it relates to a method for producing homogeneous polyolefins and a polymerization apparatus used in the method.

Conventionally, in order to polymerize olefin by a solvent polymerization method in the presence of hydrogen using the catalyst as described above, a polymerization reactor is supplied with olefin as a raw material, hydrogen as a molecular weight regulator, a catalyst, and a solvent. , reaction temperature 50~300℃, reaction pressure normal pressure ~ several hundred
It is carried out batchwise or continuously at kg/ ^cm2 .

When polymerizing olefins as described above, unless the polymerization conditions such as polymerization temperature and pressure are kept constant, the degree of polymerization or melt index of the resulting polyolefin will change, making it impossible to obtain a polyolefin with a uniform degree of polymerization. becomes.

For this reason, in conventional polymerization reactors, a jacket cooling method using a jacket provided in the polymerization reactor, a coil cooling method in which a cooling coil is provided for passing a heat removal medium through the interior of the polymerization reactor, and a cooling method in which the contents inside the polymerization reactor are The external cooling method involves extracting a portion of the polymer, cooling it using an external cooling device, and returning it to the polymerization reactor. The polymerization reaction temperature is controlled to be kept constant by a reflux cooling method in which unreacted olefin is cooled and returned to the polymerization reactor, or by a combination of these methods.

In addition, the polymerization reaction pressure is controlled by monitoring the gas phase pressure and adjusting the supply amount of the materials that define the reaction pressure, such as catalyst, olefin, hydrogen, and solvent, according to changes in the gas phase pressure. It is made to be.

In conventional polymerization reactors, the polymerization reaction temperature and polymerization reaction pressure are controlled by different control systems. That is, changes in the polymerization reaction temperature are detected, for example, by a temperature sensor installed in the polymerization reactor, and this is transmitted as a control signal by a reaction temperature controller to a cooling water temperature controller, etc., to control the cooling water temperature. Cascade control was used to control the polymerization reaction temperature by changing the target value.

In addition, the polymerization reaction pressure is controlled by feedback control in which, for example, the gas phase pressure is detected with a pressure detector and the supply amount of catalyst, olefin, hydrogen, solvent, etc. is changed in response to pressure fluctuations to control the polymerization reaction pressure. was.

However, even when polymerization is carried out using such a conventional control system, the polymerization conditions, especially the polymerization reaction pressure, fluctuate relatively widely, and it often takes a long time to return to the target value pressure. It was difficult to carry out the polymerization.

In other words, it is difficult to say that polyolefins with a uniform degree of polymerization are stably produced.

The inventors of the present invention have conducted extensive studies in order to eliminate the drawbacks of the conventional polyolefin manufacturing methods described above and to provide a method for continuously and stably manufacturing excellent polyolefins with a uniform degree of polymerization. discovered problems with the conventional polymerization reaction pressure control system, solved the problems by using a special control system, and completed the present invention.

That is, the gist of the present invention is to detect temperature changes in the liquid phase and predict subsequent pressure changes in the gas phase based on the temperature changes when continuously producing olefin in the presence of a catalyst, a solvent, and hydrogen. , a polyolefin manufacturing method characterized by changing the predicted pressure change, and a polymerization apparatus used in the method.

An example of the method of the present invention will be explained in more detail below with reference to the drawings.

Figure 1 is a block diagram of an example of a control device system applied to the method of the present invention, and Figure 2 A, B, C, and D are for controlling the polymerization reaction temperature and gas phase pressure using separate control systems using conventional methods. Figure 3 is a graph conceptually showing an example of changes in polymerization reaction temperature (a), cooling water temperature (b), gas phase pressure (c), and catalyst supply amount (d) when
D, E, and E are the polymerization reaction temperature when the polymerization reaction temperature and gas phase pressure are controlled by a control system linked to each other according to the method of the present invention, cooling water temperature B, gas phase pressure C, catalyst supply amount D, and gas phase pressure. It is a graph conceptually showing an example of a change in E.

In the figure, 1 is a polymerization reactor, 1a is a liquid phase part, 1b is a gas phase part, 1c is a stirrer, 1d is a jacket, 2 is a catalyst supply line, 2a is a catalyst supply pump, 3 is an olefin supply line, and 4 is hydrogen Supply line, 5 is a solvent supply line, 6 is a polyolefin extraction line,
7 is a cooling water supply line, 7a is a cooling water supply valve, 8
is the cooling water discharge line, 9 is the cooling water circulation line, 1
0 is a reaction temperature change detection device, 11 is a cooling water temperature controller, 12 is a pressure detector, 13 is a gas phase pressure target value setting device, 14 is a catalyst introduction amount regulator, 15 is a reaction pressure change detection device, and 16 is a A feed forward controller and 17 each represent a reaction temperature target value setting device.

The polymerization reactor 1 exemplifies a typical solvent slurry polymerization method, and a jacket 1d using cooling water is provided on the outside of the polymerization reactor 1, which controls the temperature of the liquid phase and the pressure of the gas phase. Although a case will be described using a method of controlling by changing the amount of catalyst supplied, the present invention is not limited to this.

As shown in Fig. 1, a catalyst supply line 2, an olefin supply line 3, a hydrogen supply line 4, and a solvent supply line 5 are connected to a polymerization reactor 1, and catalysts, olefins, hydrogen, solvents, etc. are to be produced. A predetermined amount is continuously supplied depending on the polyolefin. Inside the polymerization reactor 1, a liquid phase portion 1a and a gas phase portion 1b are formed by the above-mentioned feed materials, and the olefin is polymerized while being stirred by a stirrer 1c. The produced polyolefin is continuously extracted from a polyolefin extraction line 6.

When producing polyolefin by such a continuous method, it is well known that the polymerization reaction temperature and polymerization reaction pressure in the polymerization reactor 1 are extremely important factors in producing a uniform polyolefin.
For this reason, while a cooling jacket 1d or the like is conventionally provided in the polymerization reactor 1, the polymerization reaction temperature is monitored and when the polymerization temperature changes, the temperature of the cooling medium in the cooling jacket 1d is changed to compensate for the polymerization reaction temperature. , the gas phase pressure is monitored, and when the gas phase pressure changes, the amount of feed material such as a catalyst is changed to compensate for the polymerization reaction pressure.

There are various possible causes for changes in the polymerization reaction temperature, gas phase pressure, etc., but they are collectively referred to as disturbances.

Examples of disturbances include changes in the amount of catalyst poison components (e.g., water) in the raw material olefin, changes in catalyst concentration, changes in catalyst activity when catalyst lots are changed, changes in catalyst activity due to changes in co-catalyst, and other uncertain disturbances. .

When there is a disturbance as mentioned above, the main conditions of polymerization conditions, such as polymerization reaction temperature and polymerization reaction pressure, change.
According to studies conducted by the present inventors, it has been found that there is a certain regularity in the variation of polymerization conditions due to this disturbance.

The regularity is that when a disturbance is applied during polymerization, the polymerization reaction temperature changes sensitively, but the change in the polymerization reaction pressure appears much later in time than the change in the polymerization reaction temperature.

For example, regarding the conventional method, if there is some kind of disturbance at point A in Figure 2 and the state of the polymerization reaction system changes, the polymerization reaction temperature will immediately change as shown in Figure 2 A. This temperature change is immediately detected by a temperature detector, and the temperature of the cooling water introduced into the cooling jacket is changed as shown in Figure 2 (b), thereby compensating the polymerization temperature, and the polymerization temperature quickly returns to its original temperature. Return. Therefore, it appears that the isothermal reaction was carried out accurately and that no trouble occurred in the polymerization reaction.

However, in such cases, a change in gas phase pressure occurs after a certain time. That is, the gas phase pressure does not show any change at time A when the disturbance occurs, but changes appear after a considerable amount of time, ie, after time B, as shown in FIG. 2C.

The point at which the pressure change width reaches a certain value (point P)
It is detected that there has been a change in the gas phase pressure, and at that point, in order to compensate for the pressure change, a process is taken to increase the amount of catalyst supplied, as shown in FIG. 2D, for example. By changing the catalyst supply amount,
Eventually, at point C, the gas phase pressure change is completely compensated with a considerable time delay.

In this way, in the conventional method, a de facto constant-temperature reaction is realized, but the quality of the polymer changes during the period when the gas phase pressure deviates significantly from the constant pressure value, that is, from B to C.

For example, when the polymerization conditions change in a direction that inhibits polymerization due to a disturbance, the polymerization in the solvent will not proceed as planned and the liquidus temperature will immediately drop, but if the polymerization is Although there is a capacity delay until the exhausted olefin moves to the gas phase and a new vapor-liquid equilibrium is reached, and the liquid phase temperature change is sufficiently large compared to the detection limit of the instrument,
Since the gas phase pressure does not change significantly, a detection delay occurs.

It was estimated that due to the combination of these two delays, the liquid phase temperature change and gas phase pressure change were detected with a difference of about 20 to 30 minutes.

Therefore, using a conventional control method, the temperature of the liquid phase and the pressure of the gas phase are detected respectively, the temperature of the liquid phase is adjusted by changing the temperature of the cooling jacket, etc., and the pressure of the gas phase is adjusted. When adjusting by changing the supply amount of catalyst, etc., it takes a long time for the polymerization conditions to stabilize due to the delay described above, and it also causes changes in temperature in the liquid phase and pressure in the gas phase. It was expected to change over a fairly wide range of fluctuations.

The present inventors have conducted various studies and further investigated the causal relationship between the above-mentioned changes in polymerization reaction temperature and changes in gas phase pressure. ) and the amount of change, and the timing and amount of change in gas phase pressure have a certain relationship, and it was found that the timing and amount of change in gas phase pressure can be predicted fairly accurately from the time and amount of change in polymerization reaction temperature. .

The relationship between the timing and amount of change in the polymerization reaction temperature and the timing and amount of change in gas phase pressure is expressed, for example, by the following approximate equation.

ΔPπ(S)/ΔT ₂ (S)e ^-STd1 KP ₁ /1+STp1
...(a) In the formula, ΔPπ (S): Change in gas phase pressure (Kg/cm ² ) ΔT ₂ (S): Change in liquid phase temperature (cooling water temperature) (℃) Tp1: Time constant (hr) Td1 : Dead time (hr) Kp1: Gain (Kg/cm ² /〓) S: Indicates the Labrus operator.

The above approximation formula is a first-order lag approximation formula, but any other approximation formula can be adopted, such as a second-order lag approximation formula, a third-order lag approximation formula, etc. If a formula is used, a predicted value that is closer to the actual gas phase pressure change can be obtained, but in reality, a predicted value using a first-order lag approximation formula provides sufficient accuracy and is easy to handle with a calculator, etc. Therefore, it is good to adopt this.

In the present invention, based on the gas phase pressure change predicted as described above, the polymerization conditions are manipulated so as to cancel out the predicted gas phase pressure change before this gas phase pressure change actually occurs. be.

When carrying out a continuous polymerization reaction at constant temperature and constant pressure, subtle changes in the polymerization reaction temperature become changes in the cooling water temperature without delay, and are detected in an enlarged form (however, the sign of the temperature change is opposite). Rather than directly detecting changes in reaction temperature, it is more convenient to indirectly detect changes in cooling water temperature.

The method of the present invention will be explained with reference to FIG. 3. When the polymerization reaction temperature changes due to a disturbance as shown in FIG. 3A, the cooling water temperature actually changes as shown in FIG. 3B. This cooling water temperature is usually maintained for an appropriate period of time (usually 2~
The detected temperature is compared with the previous detected temperature, and if the difference (absolute amount or slope) exceeds a certain value, it is detected that a disturbance has occurred. has been done.

Suppose now that a disturbance is detected at point Q in FIG. 3B.

Specifically, according to the apparatus diagram shown in FIG.
The reaction temperature subtracter provided at 0 is compared with the target value preset in the reaction temperature target value setting device 17 to find the deviation, and an output signal is issued to the cooling water temperature controller 11. The cooling water temperature controller 11 is activated and selects an appropriate cooling water temperature target value.

On the other hand, when the cooling water temperature target value is changed by the signal from the reaction temperature change detection device 10, the cooling water temperature controller 11 issues an output signal to compensate for the difference, and the output signal causes the cooling water supply valve 7a to
is opened and closed to adjust the amount of cooling water supplied.

The temperature of the cooling water entering the jacket 1d is determined by the ratio between the amount of cooling water circulating through the cooling water circulation line 9 and the amount of cooling water supplied from the cooling water supply line 7.

The cooling water temperature can be changed as described above, and the cooling water temperature controller detects the change in the cooling water temperature at appropriate intervals as described above, and checks for the presence or absence of disturbance.

For example, suppose that a change in the cooling water temperature is detected as a substantial disturbance exceeding a predetermined value at point Q in FIG. 3B. When a disturbance is detected, the pressure change calculator 16A immediately calculates the timing and amount of change in gas phase pressure based on the amount of change in the cooling water temperature using the above relational expression. Through this calculation, the pressure change can be approximately predicted as shown by the solid line in FIG. 3C.

If a change in gas phase pressure occurs, the conditions for constant pressure polymerization will change, making it impossible to obtain a uniform polyolefin. Therefore, it is necessary to prevent this gas phase pressure change from actually occurring, or at least reduce the range of change as much as possible. Must.

As conventionally done, the pressure detector 12 monitors the gas phase pressure change, and when the gas phase pressure change is detected as a disturbance (at point P in FIG. 2 C or 3 C, In the method of changing the catalyst supply amount as shown in the dashed line in Figure 3 (D), the result is the same as when a disturbance occurs between the time the catalyst supply amount is changed and the time when the gas phase pressure actually starts to be compensated. Since there is a response delay, the gas phase pressure changes greatly as shown in FIG. 2C.

In the present invention, such large gas phase pressure changes are prevented from occurring. That is, instead of waiting until time P to change the polymerization conditions, at time Q, we change the predicted pressure change (the value shown by the solid line in Figure 3C) and the opposite change (the value shown by the dashed line in Figure 3C). The polymerization conditions are changed at an early stage in order to increase the

For example, if it is predicted that the gas phase pressure will change approximately as shown by the solid line in Figure 3C, the polymerization conditions may be manipulated to change the gas phase pressure as shown by the dashed line in Figure 3C. Amount adjustment calculator 16
The calculation is performed in B, and the catalyst introduction amount regulator 14 is operated to change the polymerization conditions.

This is done, for example, by varying the stroke of the catalyst supply pump 2a and manipulating the catalyst supply amount as shown by the solid line in FIG. 3D.

The above operation is not limited to changing the amount of catalyst supplied, and other feed materials such as olefin, hydrogen, and solvent may also be changed; however, changing these feed materials may change the amount of polyolefin produced, or Since the ratio of olefin and hydrogen is an important requirement for polymerization conditions, problems arise such as difficulty in controlling it, so a method of varying the amount of catalyst supplied is usually adopted.

When the catalyst supply rate is changed as shown by the solid line in Figure 3D, the gas phase pressure change due to disturbance is canceled by the gas phase pressure change due to the catalyst supply rate change, and in reality the pressure changes as shown in Figure 3E. There are almost no changes. Since there is some difference between the actual gas phase pressure change and the approximately predicted gas phase pressure change, only a very small pressure change appears. Second
As is clear from a comparison between Figure C and Figure 3 E, the present invention is characterized by not only a small width of gas phase pressure change, but also a greatly shortened period of change from B→C to B→D. be. The amount of change in catalyst supply is obtained by calculation by the introduction amount adjustment calculator using an approximation formula similar to the approximation formula used to predict the gas phase pressure change described above.

That is, for example, the following formula (b) ΔPπ(S)/ΔC(S)e ^-STd2 KP ₂ /1+STP ₂
...(b) In the formula, ΔPπ(S): Change in gas phase pressure (Kg/cm ² ) ΔC(S): Change in catalyst supply amount (Kg-CAT/hr) TP ₂ : Time constant (hr) Td ₂ : Waste Time (hr) KP ₂ : Gain (Kg/cm ² /Kg-CAT/hr) S: Indicates Labrus operator.

You can get it by.

However, it is preferable to change the catalyst supply amount etc. immediately after detecting a change in the cooling water temperature, that is, at the time Q in FIG. 3D.

To explain specifically according to the device, when the reaction temperature change detection device 10 detects a change in cooling water temperature, that is, a disturbance, the cooling medium temperature controller 11 sends a signal to the feed forward controller 16 to detect the change in the cooling water temperature. A signal is emitted depending on the amount.

The feed/forward controller 16 includes a pressure change calculator 1 that predicts the pressure change in the gas phase of the polymerization reactor based on the magnitude of this signal using the above equation (a).
6A is provided, and this pressure electrification calculator predicts the timing and amount of change in pressure in the gas phase portion.

In addition, the feed forward controller 16 is provided with an input device that calculates and determines the timing and amount of the introduced material such as a catalyst so as to cancel out the gas phase pressure change predicted above using the equation (b). A quantity adjustment calculator 16B is provided, and the result of this calculation is outputted.

The output signal from the introduction amount adjustment calculator 16B is sent to the catalyst (supply material) introduction amount regulator 14,
The regulator controls the amount of catalyst etc. introduced into the polymerization reactor 1.

In this way, gas phase pressure changes are canceled out and
Stable polymerization takes place.

As described above, the control of the polymerization reaction pressure according to the present invention predicts the subsequent gas phase pressure change by detecting the polymerization reaction temperature change (cooling water temperature change), and according to this predicted value, the predicted gas phase pressure is This method changes the polymerization conditions (catalyst supply amount, etc.) to cancel out pressure changes, but adjusting the polymerization reaction pressure only with this method requires a very precise control system, and on the contrary, it increases the gas phase pressure. For some reasons, such as the fact that the gas phase pressure is not stable and the gas phase pressure changes repeatedly over a certain range, we have developed a feed system that detects the gas phase pressure and changes the polymerization conditions according to the changes in the gas phase pressure. It is better to perform back control in parallel.

As shown in FIG. 1, in the feed back control, a pressure detector 12 detects a gas phase pressure change, and a gas phase pressure target value setter 13 sets a gas phase pressure target value in advance and the detected value. The deviation is determined by a reaction pressure subtractor, and an output signal is generated from the reaction pressure change detection device 15 according to the magnitude of the deviation. Upon receiving the output signal, the supply material introduction amount regulator 14 is operated to adjust the polymerization conditions. It is subject to change.

In this way, it is desirable that the feed/forward controller 16 and the reaction pressure change detection device 15 are installed in parallel, and the timing of the operation of both is such that once the feed/forward controller 16 is activated due to a disturbance, the feed/forward controller 16 is activated due to a disturbance. - The forward controller 16 may be set not to operate for several tens of minutes to several hours, and the reaction pressure change detection device 15 for feedback control may be kept operating at all times.

According to the present invention, when producing polyolefins such as polyethylene and polypropylene by a continuous polymerization method under constant pressure, the change in gas phase pressure of the polymerization conditions can be made extremely small, and the recovery time after the change is also extremely short. As a result, uniform polyolefin can be produced extremely stably, and labor can be saved through automation, which is extremely useful in practice.

Note that the method and apparatus of the present invention are not limited to the apparatus shown in FIG. 1, in which a cooling jacket is provided outside the polymerization reactor, but also those in which a cooling jacket is provided inside the polymerization reactor, and those in which a cooling jacket is provided outside the polymerization reactor. It can also be applied to polymerization reaction methods and apparatuses such as the cooling method, the latent heat of vaporization cooling method, and the reflux cooling method.

[Brief explanation of drawings]

Figure 1 is a block diagram of an example of a control device system applied to the method of the present invention, and Figure 2 A, B, C, and D are for controlling the polymerization reaction temperature and gas phase pressure using separate control systems using conventional methods. Figure 3 is a graph showing an example of changes in polymerization reaction temperature (a), cooling water temperature (b), gas phase pressure (c), and catalyst supply amount (d) over time when
D and E are polymerization reaction temperature A, cooling water temperature B, gas phase pressure C, catalyst supply amount D, and gas phase pressure when the polymerization reaction temperature and gas phase pressure are controlled by a control system linked to each other according to the method of the present invention. It is a graph showing an example of e over time. In the figure, 1 is a polymerization reactor, 1a is a liquid phase part, 1b is a gas phase part, 1c is a stirrer, 1d is a jacket, 2 is a catalyst supply line, 2a is a catalyst supply pump, 3 is an olefin supply line, and 4 is hydrogen Supply line, 5 is a solvent supply line, 6 is a polyolefin extraction line,
7 is a cooling water supply line, 7a is a cooling water supply valve, 1
0 is a reaction temperature change detection device, 11 is a cooling water temperature controller, 12 is a pressure detector, 13 is a gas phase pressure target value setting device, 14 is a catalyst introduction amount regulator, 15 is a reaction pressure change detection device, and 16 is a A feed forward controller and 17 each represent a reaction temperature target value setting device.

Claims (1)

[Claims] 1. When polyolefin is continuously produced by constant pressure polymerization of olefin in the presence of a catalyst, a solvent, and hydrogen, a temperature change in the liquid phase is detected, and the subsequent gas phase is determined based only on the temperature change. 1. A method for producing a polyolefin, which comprises predicting a pressure change and changing polymerization conditions so as to cancel at least a part of the predicted pressure change. 2. The method according to claim 1, wherein the polymerization conditions are changed immediately after detecting a change in temperature of the liquid phase. 3. The method according to claim 1 or 2, characterized in that the polymerization conditions are changed so as to cancel out the entire predicted pressure change. 4. The method according to any one of claims 1 to 3, wherein the polymerization condition to be changed is the amount of catalyst supplied. 5. The method according to any one of claims 1 to 3, wherein the polymerization conditions to be changed are the amount of olefin supplied and the amount of hydrogen supplied. 6. The method according to any one of claims 1 to 3, wherein the polymerization condition to be changed is the amount of solvent supplied. 7. In an olefin polymerization apparatus having an introduction section for feed materials such as olefin, catalyst, solvent, and hydrogen, a polymerization reactor, a polyolefin outlet section, and a cooling device, a temperature sensor for detecting the temperature of the liquid phase of the polymerization reactor; A reaction temperature change detection device comprising a reaction temperature target value setting device and a reaction temperature subtracter for calculating the deviation between the temperature detected by the temperature detector and the reaction temperature target value, and based on the output of the reaction temperature change detection device. A pressure change calculator that predicts the pressure change in the gas phase portion of the polymerization reactor after a predetermined period of time, a timing for adjusting the amount of the feed substance to be introduced so as to cancel out the pressure change predicted from the output of the pressure change calculator, and An olefin polymerization apparatus comprising an introduction amount adjustment calculator for determining the amount of the introduced material, and a feed substance introduction amount adjustment device that operates in response to an output from the introduction amount adjustment calculator. 8. A cooling medium temperature controller that operates in response to an output signal from the reaction temperature change detection device, a cooling device that operates in response to an output signal from the controller, and a pressure change calculator that operates in response to an output signal from the reaction temperature change detection device. 8. The polymerization apparatus according to claim 7, wherein the signal from the polymerization apparatus is indirectly received via a cooling medium temperature controller. 9 A reaction consisting of a pressure detector that detects the pressure in the gas phase of the polymerization reactor, a reaction pressure target value setting device, and a reaction pressure subtractor that calculates the deviation between the pressure detected by the pressure detector and the reaction pressure target value. 9. The polymerization apparatus according to claim 7 or 8, wherein a pressure change detection device is connected such that an output from the pressure change detection device is inputted to a feed substance introduction amount regulator.