JPS6340802B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for producing a polyolefin having predetermined physical properties using a Ziegler catalyst. The present invention relates to a method and apparatus for producing polyolefin having predetermined physical properties by controlling detection signals using a computer.

In the production of polyolefin, industrially, it is generally operated in a continuous manner in a polymerization reactor maintained at a predetermined temperature at a predetermined production rate to produce polyolefin of predetermined specifications, that is, with predetermined physical properties. desirable.

When producing a polyolefin using a Ziegler catalyst, there are various physical properties of the produced polyolefin that must be controlled, among which the melt index and density are the most important factors.

The melt index and density are indicators of the molecular weight of the polyolefin, and are appropriately set depending on the use of the polyolefin, and are important indexes for consumers to select a brand of polyolefin.

The melt index is measured by the method described in ASTM D1238, and is usually measured at 190°C for polyethylene and 230°C for polypropylene.

Once the type of catalyst used and the polymerization temperature are determined, the production rate of polyolefin is independently proportional to the catalyst concentration and olefin concentration.

When a Ziegler catalyst is used as a catalyst, the melt index of the polyolefin is controlled by hydrogen gas as a chain transfer agent. The melt index of the polyolefin produced is determined by the ratio of hydrogen gas concentration to olefin concentration (factors such as the type of catalyst used, polymerization temperature, and size and shape of the polymerization reactor affect the melt index). give).

On the other hand, the density of polyolefin is ASTM D1505
- Measured by the method described in 67. Density is usually determined by factors such as the type of catalyst used to polymerize the olefin, the polymerization temperature, the size of the polymerization reactor, and the amount of comonomer.

The density is controlled by adjusting the molar ratio of olefin and comonomer. usually,
As the amount of comonomer increases, the density decreases.

Under these circumstances, polyolefins are usually manufactured using a continuous polymerization method, in which a predetermined amount of catalyst, a predetermined amount of olefin, and a predetermined amount of hydrogen gas are supplied into a polymerization reactor maintained at a predetermined temperature. physical properties,
Therefore, it is operated so as to produce a polyolefin of a predetermined specification.

Supplying a predetermined amount of catalyst, a predetermined amount of olefin, and a predetermined amount of hydrogen gas as described above is a method for maintaining the reaction system in a predetermined state, but in reality, simply supplying a predetermined amount will not affect the reaction system. It is impossible to keep it in a predetermined state. For example, minute changes in the catalyst,
The olefin concentration increases due to a decrease in activity, and the melt index of the resulting polyolefin decreases. There are many such minute disturbances for which the reason is unclear.

The melt index of the produced polyolefin changes sensitively to changes in the ratio of olefin concentration to hydrogen gas concentration.

For example, in the case of polyethylene, depending on the type of Ziegler catalyst used and polymerization conditions such as polymerization temperature, under industrially adopted polymerization conditions, the gas phase partial pressure ratio changes and the melt index (MI) changes accordingly. is roughly as follows.

ΔMI/MI/Δ(H ² /C ₂ )/(H ² /C ₂ )=3
~4 In the case of polyethylene, if polyethylene is produced that exceeds the range of ±10% of the set melt index value, it is usually disposed of as a substandard product.

Therefore, in order to prevent this loss, Δ(H ₂ /
C ₂ ) must be ±3%. Conventionally, the melt index of the polyethylene produced was measured,
A technique was adopted in which the hydrogen supply valve and ethylene supply valve were instructed to operate according to the value. However, this method has a serious drawback in that it requires about one hour for measurement and the response is slow.

However, a method of directly monitoring the inside of the reaction system has been proposed, but this method involves actually measuring the olefin concentration and hydrogen gas concentration in the liquid phase. This method is not suitable for the following reasons.

(1) Since the polymerization part is a solid-liquid slurry, a solid-liquid separation operation is required, and at this time, the components to be measured tend to scatter from the liquid, so it is necessary to know the absolute values of the olefin concentration and hydrogen concentration. is difficult.

(2) It is necessary to have a sampling line in order to collect a sample, but polymerization occurs before the sample is collected from the polymerization reactor, making it impossible to accurately determine the state inside the reaction system (US Patent No. 3835106) .

Furthermore, in controlling the density of polyethylene, a technique has been used in which the density of the polyethylene to be produced is actually measured and the operation of the ethylene and comonomer supply valves is instructed according to the measured value. However, this method also had a very serious drawback in that it required about one hour for measurement and the response was slow. In this case, similar to the melt index,
Direct monitoring within the reaction system has been proposed, but is not a preferred technique for the reasons discussed above in the case of melt indexing.

There is also a known technology that monitors the inside of the reaction system and measures its pressure to homogenize the composition of the final product, ethylene copolymer (US Pat. No. 3,691,142).
The fact is that there is still no suitable technique for producing polyolefins having the desired physical properties, especially melt index and/or density.

Therefore, an object of the present invention is to employ a technique for measuring components in a gas phase provided in a polymerization reactor when polymerizing an olefin in the presence of a Ziegler catalyst and hydrogen to produce a polyolefin having predetermined physical properties. By doing so, it is an object of the present invention to completely eliminate the drawbacks of the method for measuring the liquid phase described above, and to provide a method and apparatus for producing a polyolefin that is extremely stable and has predetermined physical properties.

Another object of the present invention is to polymerize an olefin in the presence of a Ziegler catalyst and hydrogen to produce a polyolefin having a predetermined melt index, by measuring components in a gas phase provided in a polymerization reactor. An object of the present invention is to provide a method and apparatus for producing a polyolefin having an extremely stable predetermined melt index.

Another object of the present invention is to polymerize an olefin in the presence of a Ziegler catalyst and hydrogen to produce a polyolefin having a predetermined density, by measuring components in a gas phase provided in a polymerization reactor. An object of the present invention is to provide a method and apparatus for producing polyolefin having a stable predetermined density.

That is, the present invention is a method for producing a polyolefin having predetermined physical properties by polymerizing an olefin in the presence of a Ziegler catalyst and hydrogen. At least two parameters, the concentration of one or more olefins in the polymerization reactor and the concentration of hydrogen gas, are detected by gas chromatography.

The sensed signal that correlates to the parameter is
The signal is input to a computer, and the signal is compared with a predetermined set value corresponding to the physical property, and the calculation control output of the computer determines the amount of hydrogen supplied to the polymerization reactor. pressure,
The olefin concentration and/or hydrogen gas concentration are controlled by adjusting the olefin feed rate and/or catalyst feed rate to the polymerization reactor to produce a polyolefin having the predetermined physical properties.

In this way, gas chromatography is used to measure the olefin concentration and hydrogen gas concentration, and if high-speed gas chromatography is used as the gas chromatography and the response is obtained by measuring the gas phase every minute, for example, Hunting of physical properties is no longer recognized. In addition, based on the measured values using high-speed gas chromatography, the hydrogen supply amount, pressure,
It is impossible to manually adjust the amount of olefin supplied (for example, even if measurements are made every minute using high-speed gas chromatography, manual control cannot follow the measurements, resulting in hunting of physical properties). The method of the present invention incorporates a computer for automatic feed rate and pressure control.

Further, according to the present invention, when producing a polyolefin having a predetermined melt index by polymerizing an olefin in the presence of a Ziegler catalyst and hydrogen, the parameters of the concentration of olefin and the concentration of hydrogen gas in the polymerization reactor are determined by gas chromatography. Detected by tographies.

A detected signal correlated to the parameter is input to a computer, and the signal is compared with a predetermined set value corresponding to the melt index, and the calculation and control output of the computer is performed. The amount of hydrogen supplied to the polymerization reactor, the pressure within the polymerization reactor, and in some cases the amount of catalyst supplied are adjusted to adjust the olefin concentration and hydrogen gas to produce a polyolefin having the predetermined melt index. The concentration is controlled.

Further, according to the present invention, when producing a polyolefin having a predetermined density by polymerizing two or more types of olefins in the presence of a Ziegler catalyst and hydrogen, the parameter of the concentration of the olefin in the polymerization reactor is determined by gas chromatography. Detected by The detected signal correlated to the parameter is input to a computer, and the signal is compared with a predetermined set value corresponding to the density, and the polymerization reaction is controlled by the arithmetic control output of the computer. The amount of the olefin fed to the vessel is adjusted to control the concentration of the olefin to produce a polyolefin having the predetermined density.

In the method and apparatus of the present invention, a gas phase portion is provided in the polymerization reactor, and the olefin concentration and/or hydrogen gas concentration of the gas phase components is measured by gas chromatography.

The polymerization temperature in the reactor is held constant, and the olefin concentration and/or hydrogen gas concentration are controlled so as to produce a polyolefin with predetermined melt index and/or physical properties such as density at the polymerization temperature. .

The gas chromatography used is such that the time required to detect olefin is 10 minutes or less, preferably 5 seconds to 1 minute.

The olefins used in the polyolefin manufacturing method of the present invention include ethylene, propylene, 1-butene,
α-olefin such as 4-methyl-1-pentene, preferably α-olefin having 2 to 6 carbon atoms. Moreover, the polyolefin refers to a homopolymer of the above-mentioned olefins, a copolymer of olefins, or a copolymer of at least one of the above-mentioned olefins and diolefin.

Furthermore, in the present invention, the term "monomer" refers to an olefin that accounts for the main proportion of the olefin in the polymerization system, and the term "comonomer" refers to an olefin and/or diolefin that accounts for a small proportion of the olefins other than the monomer.

When producing a polyolefin by copolymerizing a monomer and a comonomer, the comonomer is preferably at most 30 mol%, preferably at most 10 mol%, based on the monomer.

Examples of the diolefin include conjugated diolefins such as butadiene and isoprene, and non-conjugated diolefins such as dicyclopentadiene and ethylidene norbornene.

Particularly preferred olefins are ethylene or mixtures of ethylene with other olefins and/or diolefins in an amount of not more than 30 mol %, preferably not more than 10 mol %, based on ethylene. The Ziegler catalyst used in the production of the polyolefin of the present invention is usually composed of (a) a compound of a transition metal of Mendelejeff's periodic table, and (b) an organometallic compound of a metal of group 1 or group of the periodic table, or hydrogen. It is a catalyst whose main component is a compound. Particularly preferred are catalysts whose main components are a halogen compound of titanium or panadium and an organometallic compound of aluminum. Ingredients (a) and (or) above
(b) may be supported on a carrier, or may be treated with a modifier such as an electron donor.

Such Ziegler catalysts include, for example, US Pat. No. 3,257,332, US Pat. No. 3,826,792, US Pat. No. 3,113,115, US Pat. No. 3,546,133, US Pat. , U.S. Pat. No. 3,642,746, U.S. Pat.
Catalysts described in US Pat. No. 3,051,690, US Pat. No. 3,058,963 and British Patent No. 1,140,649 can be used.

The amount of the catalyst (a) used in the polymerization of olefin is generally 0.001 to 100 mmol in terms of titanium atoms per polymerization solvent, and the amount of the catalyst (b)
The amount of the organometallic compound or hydride of group metal or hydride used as a component is selected to be 0.1 to 1000 times, preferably 0.2 to 100 times, by mole relative to (a).

The olefin polymerization reaction using the catalyst of the present invention can be carried out in the same manner as the olefin polymerization reaction using a conventional Ziegler 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 hexane, heptane or kerosene is used, into which a catalyst and an olefin, optionally a diolefin, are introduced to proceed with the polymerization.

When polymerizing olefins, the polymerization temperature is usually 20 to 200°C, preferably 50 to 180°C. The polymerization is preferably carried out under pressure, and is generally carried out at a pressure of 2 to 100 kg/cm ² .

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 of the attached drawings shows a block diagram of the method and apparatus for producing polyolefin of the present invention, in which a polymerization reactor 1 maintained at a constant temperature is equipped with a liquid phase section 1a and a gas phase section 1b. . The polymerization reactor 1 includes a hydrogen supply line 2 for supplying hydrogen gas to the polymerization reactor 1, an olefin supply line 3 for supplying olefin, a catalyst supply line 4 for supplying a catalyst,
A solvent supply line 5 for supplying a solvent, a depressurization line 6 for depressurizing the polymerization reactor 1, and an outlet line 7 for taking out the polyolefin product from the polymerization reactor 1 are provided.

The hydrogen supply line 2 has a control valve 2a that controls the amount of hydrogen supplied, the olefin supply line 3 has a control valve 3a that controls the amount of olefin supplied, and the catalyst supply line 4 has a control valve 4 that controls the amount of catalyst supplied.
a, the solvent supply line 5 is provided with a control valve 5a for controlling the amount of solvent supplied, the depressurization line 6 is provided with a depressurization valve 6a for controlling the pressure inside the reactor, and the outlet line 7 is provided with an on-off valve 7a. Of these, the hydrogen supply valve 2a, the olefin supply valve 3a, and the pressure relief valve 6 are
In some cases, the opening degree of the catalyst supply valve 4a is controlled by a control signal from a computer, which will be described later, in order to change the olefin concentration and hydrogen gas concentration so as to produce polyolefin with a predetermined melt index.

A sampling line 8 is provided in the gas phase portion 1b of the polymerization reactor 1, and the hydrogen gas and olefin in the gas phase portion 1b are led to a gas chromatograph 9 via an on-off valve 8a, and the gas chromatograph 9 collects hydrogen. Measure gas concentration and olefin concentration. As the gas chromatography, use high-speed gas chromatography that is set so that the time it takes to detect olefin (retention time) is less than the residence time of the reactant in the polymerization reactor (olefin detection time is 10 minutes or less). , preferably 5 seconds to 1 minute (gas chromatography). Measured component signals based on the hydrogen gas concentration and olefin concentration measured by the gas chromatograph 9 are input to the computer 11 . Polymerization conditions for producing polyolefin with a predetermined melt index are programmed in the computer 11, and calculations are performed according to changes in the signal amount, and the hydrogen supply valve 2a, depressurization valve 6a, and olefin supply are controlled according to the signals from the computer 11. Valve 3a, optionally catalyst supply valve 4
a to control the olefin concentration and hydrogen gas concentration so as to produce a polyolefin with a predetermined melt index. At this time, the measured value of the gas chromatograph 9 is recorded with a recorder 10, and the control signal of the computer 11 is recorded with a recorder 12.

Figures 3a-3b show a preferred embodiment of a control device for carrying out the method of the invention. 3a-3b, elements that are the same as those shown in FIG. 1 are designated by corresponding reference numbers.

Generally speaking, in the method of the present invention, olefin gas and hydrogen gas are sampled from the gas phase portion 1b of the polymerization reactor 1 via the sampling line 8, and detected by the process gas chromatography 9, and the detected signal is is input into the computer 11, and the hydrogen supply valve 2a, depressurization valve 6a, and olefin supply valve 3a are controlled by the arithmetic control output of the computer.
The purpose is to control the concentrations of olefin and hydrogen gas to produce a polyolefin having predetermined physical properties.

First, the sampling line 8 will be explained. As shown in FIG. 3a, the sampling line 8 includes two sampling lines 8a' and 8a''.

Basically, the sampling line 8a' is used to directly measure the gas in the gas phase 1b of the reactor 1. In this line, the sample gas is passed through block valve 1 for switching to sampling line 8a''.
3 and is flushed by a pressure control valve 14 which reduces the sample gas pressure to a predetermined value, and then is completely vaporized by a sample vaporizer 15. Note that 16 detects the pressure of the sample gas with a transmitter 17 and operates the pressure control valve 14.
PID (proportional−plus−intergral−plus−
It is a PID controller that controls (derivative).
The sample gas in this line is monitored by a flow transmitter 18, such as an orifice flow meter, and a flow indicator 19 to see if the flow rate is within a specified value. Then, the sample gas is passed through a two-stage pressure reducing valve 20, a filter 21 and a pressure reducing valve 2.
A pretreatment unit 22 comprising a filter 21a and a filter 21a performs pretreatment, and the operating conditions of the process gas chromatograph 9 are set. This pretreatment unit 22 is assembled in a constant temperature bath 23 to prevent condensation of the sample, and this constant temperature bath 23 is kept at a certain temperature within the range of 40 to 150 degrees Celsius by a temperature controller 24. has been done.

In this manner, according to the sample line 8a', dry gas can always be injected into the detector 25 of the process gas chromatograph 9 even during operation using a monomer having a boiling point similar to that of the solvent.

Furthermore, depending on the specification or brand of the polyolefin to be produced, only monomers having a large boiling point difference from the solvent may be used. In this case, by operating the sampling line 8a'' provided in front of the pressure control valve 14, stable process gas chromatography measurement can be performed more reliably.

That is, in the sampling line 8a'', the sample gas collected from the gas phase portion 1b of the reactor 1 is transferred to the sample condenser 26 and the sample receiver 2.
7 condenses and separates the solvent in the sample.
The sample temperature controller 28 at the outlet of the sample condenser 26 automatically adjusts it to a certain predetermined value in the range -15 to 10°C.
Therefore, the gas coming out of the sample receiver 27 is flashed under reduced pressure by the pressure control valve 14, and when heated by the vaporizer 15, it is easily completely vaporized. On the other hand, the separated solvent returns to the reactor 1 via line 8b. A block valve 13a is inserted in front of the sampling line 8a', and together with the block valve 13, switching is performed to selectively use the lines 8a' and 8a''.

Adoption of such a sampling method has the advantage that normal operation of the process gas chromatography can be ensured without paying great consideration to the situation of the sampling line.

However, in this case, the sample gas composition and the gas composition within the reactor are different. However, as in this embodiment, the temperature of the reactor and the outlet temperature of the sample condenser 26 are controlled separately, so if a simple gas-liquid equilibrium calculation is performed in advance, the temperature obtained from the sample gas can be adjusted. The gas composition of the reactor can be easily estimated from the composition.

Thus, in this example, the sample gas to the process gas chromatography is completely vaporized. Therefore, if high-boiling components in the reactor gas flow into the sampling line as a liquid or condense in the sampling line, as in the past, the sample gas for gas chromatography will contain droplets. Gas chromatography, which exhibits fluctuations in its readings and sometimes becomes clogged in the line and becomes unable to measure, is completely eliminated. This means that the stability of gas chromatography operation is improved and that the gas concentration in the gas phase of the reactor can be accurately measured.

Moreover, in this embodiment, the sampling line 8
Since a' and 8a'' are switched and used for each specification of the olefin to be produced, it is possible to cope with a wide range of operation methods using different monomers for each such specification. The gas sampling method simultaneously satisfies the requirements of gas chromatography for detecting gas concentrations and the production process requirements depending on the specifications of the polyolefin produced.

Next, the detector 25 of the process gas chromatography 9 will be explained using ethylene polymerization as an example. A sample gas adjusted to specifications for gas chromatography by the sample pretreatment unit 22 is injected into the separation column of the detector 25.
Next, each component in the sample gas is detected by a thermal contact detector constituted by a resistive bridge, and its detection output shows a response as shown in FIG. For example, ethylene (C ₂ H ₄ )
When used as a monomer, it originally responds in the form of hydrogen (H ₂ ), methane (CH ₄ ), ethane (C ₂ H ₀ ), and ethylene (C ₂ H ₄ ) over time;
A diagram that uses gas chromatography with three separation columns connected in series and parallel, with ethane and ethylene bypassed to a separation column with a fast response speed, and these response peaks intervening between the response peaks of hydrogen and methane. It is structured so that the responses appear in the following order. As a result, the detection time can be shortened.

This response output is applied to the control section 28. Fourth
The response outputs of hydrogen (H ₂ ) and ethylene (C ₂ H ₄ ) shown in the figure, for example, occur sequentially at fixed times with constant elapsed intervals due to the unique characteristics of the detection unit 25, so the control unit 28 In this step, the peak value of the response output is measured for each gas component at the corresponding time, and the peak value of the response output is individually outputted as a DC voltage signal. The peak value of each component indicates the parameter of each gas concentration. This DC voltage signal varies from 1 to 1 depending on the magnitude of the peak value.
Y1', Y for each component after being converted to 5V DC voltage
It is output as 2'.

In addition, in order to produce polyolefin by a continuous polymerization method, the measurement period of the gas chromatography 9 must be fast as described above, and should be 10 minutes or less per sample gas, preferably 5 seconds to 3 minutes. is preferred. In this example, the gas chromatograph used was Yamatake Honeywell Co., Ltd., Tokyo, Japan, Model H-1000TE.

The model H-1000TE used in the method of the present invention has a high-speed measurement cycle of 2 minutes or less, and during implementation, sample measurements are automatically repeated every 60 seconds as shown in Figure 4. I was able to do that.

Therefore, a response as shown in FIG. 4 is obtained from the detector 25 at each measurement period, and then the control section 28
The peak value of the response is measured separately for each gas component, and depending on the size of the peak value,
It is held and output continuously as a 5V DC voltage signal at each measurement period.

The model H-1000TE used in this example can measure, for example, hydrogen (H ₂ ), monomer A, monomer B, and monomer C per sample gas, and each continuous DC voltage signal is ，
Let them be Y2', Y3', and Y4'.

In this way, by separating the response output signal from the detector 25 into each gas component in the control unit 28, holding it, and continuously outputting it, there is no need for the computer to perform complicated processing, and the system This simplifies the process, lowers costs, and improves overall reliability.

The signal separated into each component by the control section 28 is recorded by a recorder 29.

The DC voltage signals Y1' to Y4' are sent to the computer 11.
(FIG. 3b) and is also connected to the multipoint recorder 10 for recording.

Next, the process computer control device will be described with reference to FIG. 3b.

Continuous voltage signals Y1 _' , Y2', Y3' for each component H2, monomer A, monomer B, and monomer C output from the gas chromatograph 9 described above,
Y4' (1-5V each) and output voltage signal from pressure transmitter 30 of reactor 1 (1-5V)
is connected to the input terminal section 32 of the computer 11.

The computer 11 includes a scanning section (not shown) that automatically periodically scans the above five types of signals, an A/D (analog/digital) converter section 34, and linear processing of signals from the converter. linear processing units 35, 36, 37,
Arithmetic units 38, 39, which process the output signals;
40, and control units 41, 42, and 43 that compare and control the signal from the calculation unit and a predetermined reference setting value.
It is equipped with

In this embodiment, such a computer 1
1, model TDCS-2000 manufactured by Yamatake Honeywell Co., Ltd. located in Tokyo, Japan was adopted.

Next, control of the physical properties of polyolefin produced using this process computer control device will be specifically explained.

First, the control loop for the melt index (MI) of polyolefin will be explained in detail using ethylene polymerization as an example. As mentioned above, polymer
The MI value is basically a function of the molar ratio of hydrogen in the gas phase portion 1b of the reactor 1 to monomer A. Below, hydrogen (H ₂ ) and ethylene (C ₂ H ₄ ) as monomer A are used.
When producing polyethylene using
Display as H ₂ /C ₂ . ) Describe the control loop.

H ₂ A/D converted by converter 34
A signal Y1' indicating the mol% and a signal _Y2 ' indicating the mol% of C2 are applied to linear processing units 35 and 36, respectively. The output signal of the gas chromatograph 9 is the fourth
Since the peak height of the response shown in the figure is measured, linear processing is performed in linear processing units 35 and 36 to calibrate each to an accurate mol% concentration.

Note that the control unit 28 of the gas chromatograph 9
If the signal from the detection unit 25 is subjected to integral processing, accurate mol% concentration can be measured, and therefore, in such a case, linearization processing on the computer side is unnecessary.

The linearization processing in the linear processing units 35 and 36 employs a polygonal line approximation calculation method.

The output signal Y of these linear processing units 35 and 36
1 and Y2 correctly indicate the mol% concentration of each component of hydrogen (H ₂ ) and ethylene (C ₂ H ₄ ), respectively. These signals Y1 and Y2 are converted into analog signals again through the D/A converter 34 and taken out as voltage signals of 1 to 5 V, and then sent to the multipoint recorder 1.
2 and is also input to the calculation section 38. The calculation unit 38 calculates Y1/Y2, and the output of Y1/Y2 is input as an H ₂ /C ₂ value to the multipoint recorder 12 via the D/A converter 34 to be recorded. It is applied to the control unit 41 as a process variable.

A predetermined set value m corresponding to a predetermined melt index is input to the PID control unit 41 by an operator operating a data entry panel 44.

Then, the PID control unit 41 automatically performs PID control to compare the set value m and the input signal (H ₂ /C ₂ value) so that they match, and adjust the setting value m to 4 to 20 depending on the difference between the two.
Output as mA current signal.

This current signal is converted to 0.2 to 1.0 Kg/cm ² by the current/pneumatic converter 46 depending on the value of the current signal.
The signal is converted into a G air signal and supplied to the positioners of both the hydrogen supply valve 2a and the pressure relief valve 6a.
In controlling the positioners of valves 2a and 6a,
A control method called so-called split range is used. That is, as shown in FIG. 5, the valve positioner of the pressure relief valve 6a is fully opened when the input air signal pressure is 0.2 kg/cm ² G or less, and fully closed when the input air signal pressure is 0.6 kg/cm ² G or more, and the hydrogen supply valve 2a is set to 0.6 kg. /cm ² G or less, fully closed, 1.0Kg/cm ² G
With the above settings, the two control valves are set to be fully open, and one control signal pressure is used to operate the two control valves.

Note that the reference H ₂ /C ₂ set value may be input to the control unit 41 of the computer 11 through the data entry panel 44, but it may also be input to the H ₂ /C ₂ analog display meter 49 of the analog display device 48. You can do it even if you do it. This display meter 49 displays the H ₂ /C ₂ set at the same time and the H ₂ /C ₂ detected by the gas chromatography and calculated by the computer.
Analog display of match or difference.

In this way, according to the _H2 / _C2 control loop:
The H ₂ /C ₂ concentration in the gas phase 1b of the reactor 1 is automatically adjusted to the set value, and therefore polyethylene having a desired MI can be produced continuously, effectively controlling the MI. Therefore, it is called the MI control loop.

Therefore, when a gas phase section 1b is provided in the reactor 1 and a predetermined amount of monomer (ethylene) is supplied, if a disturbance such as a change in the activity of the Ziegler catalyst introduced via the catalyst supply line 5 occurs. , monomer (C ₂ )
As the partial pressure changes, the amount of monomer dissolved in the solvent that is correlated with the partial pressure changes, and the dissolved monomer flows out of the system as an unreacted monomer together with the solvent. In other words, even if the amount of monomer supplied is constant, the polymerization rate will change. Conventionally, when such a disturbance occurs, only the monomer (C ₂ ) partial pressure changes independently, resulting in a change in the H ₂ /C ₂ value and a change in MI. however,
In the present invention, as described above, since the H ₂ /C ₂ value is automatically controlled by the hydrogen supply valve 2a and the depressurization valve 6a, the MI is maintained constant even when such disturbances occur. . However, as a result, if this state is maintained, the polymerization rate of the olefin will remain out of the predetermined value, so the catalyst supply amount is manipulated to restore the monomer (C ₂ ) partial pressure to the original value. The change in activity is canceled out by the amount of catalyst supplied to restore the polymerization rate to a predetermined value. This _C2 partial pressure control loop will be explained below.

Pressure transmitter 30 for pressure P ₀ in reactor 1
The output voltage signal (1 to 5 V) from the linear processing section 36 and the output signal Y2 indicating ethylene mole % from the linear processing section 36 are input to the calculation section 40, where the calculation of (P ₀ +1.03)Y2 is performed. In this formula, Katsuko ( )
The part indicated by is for converting to absolute pressure,
1.03 indicates atmospheric pressure, and if an absolute pressure gauge is used for the pressure transmitter 30 of reactor 1, ( )
The value 1.03 within is unnecessary.

The output from the calculation unit 40 is sent to the D/A converter 34.
is recorded on the multi-point recorder 12 via
C ₂ Used as an operating indicator for partial pressure.

On the other hand, this C ₂ partial pressure signal is applied to the PID control unit 43 similarly to the H ₂ /C ₂ control loop described above, and the operator can display the C ₂ partial pressure analog display on the data entry panel 44 or the analog display device 48. _The output signal (4 to 20 mA) is output to the D/A converter 3.
4 to the current/pneumatic converter 52;
The air signal serves as an operation signal for the stroke control unit 4a' of the catalyst supply pump 4a''. In this way, the H ₂ /C ₂ concentration is maintained at a predetermined value, and when a disturbance such as a change in catalyst activity occurs, The _C2 partial pressure can also be adjusted to a predetermined pressure.

Note that in the case of other olefins, the physical properties can be controlled by the same operation as described above.

Finally, as mentioned above, depending on the specification and brand of polyolefin to be produced, monomer A (e.g. ethylene) and comonomer B (e.g. propylene) or monomer A and comonomer C (e.g. 1-butene) can be used. It is required to produce a polyolefin having predetermined physical properties, especially a predetermined density, by keeping the ratio constant.

Such comonomer ratio control is based on the aforementioned H ₂ /
This is achieved by the same configuration as the C _binary control loop.

Signals from gas chromatography 9 for monomer A, comonomer B, and C components are expressed as Y2' and Y2', respectively.
3', Y4'. Signals Y3' and Y4' are alternatively input to the A/D converter 34 by means of a changeover switch (not shown). The case where signal Y3' is selected will be explained below.

Signals Y2' and Y3' of monomers A and B are input to linear processing units 36 and 37 and linearized, respectively, and the output signals Y2 and Y3 are recorded by recorder 12 via D/A converter 34. At the same time, it is applied to the arithmetic unit 39. The calculation unit 39 performs the calculation of Y2/Y3, and this calculation unit 39
The output from the controller 12 is recorded by the recorder 12 via the D/A converter 34, and is also input to the controller 42. In the control unit 42, this input signal is PID-controlled so as to match the reference set value d of the comonomer ratio given by the operator via the data entry panel 44 or the comonomer ratio analog display 51 of the analog display device. The output signal (4 to 20mA) for that purpose is sent to a cascade type controller 54 via a D/A converter 34.
The amount of comonomer supplied is adjusted by controlling the comonomer supply valve 3a'. In this manner, it is possible to continuously produce a polyolefin having a predetermined density by controlling the respective concentrations of monomer and comonomer.

In the above embodiment, the amount of olefin supplied as a monomer and the amount of solvent supplied are automatically controlled by the flow rate instruction control devices 56 and 58 via the olefin supply valve 3a and the solvent supply valve 5a, respectively. However, similar to the process computer control described above, these controls may be performed by the output from the computer 11 or by a combination of the flow rate indicating control devices 56, 58 and the output control from the computer 11. .

As explained above, since the polyolefin manufacturing method according to the present invention measures the gas phase, it is possible to accurately grasp the state inside the reaction system. By measuring the gas phase and performing the response (FIG. 4), hunting in physical properties such as melt index and/or density is hardly observed. Furthermore, since the present invention uses computer control, there is no instability that would occur with manual control, which relies on the operator's intuition. It is possible to obtain a polyolefin having uniform physical properties such as a predetermined melt index and/or density.

The solid line A in FIG. 2 shows the relationship between the melt index value and the polymerization time when polyethylene is continuously produced by the method of the present invention, and the dotted line B is based on the melt index value measured every 4 hours. ,
This figure shows the relationship between the melt index and polymerization time when the operator controls the melt index by specifying the operations of the hydrogen supply valve, ethylene supply valve, etc. Note that the polymerization time on the horizontal axis in FIG. 2 is not calculated from the polymerization start time, but is calculated from an arbitrary time during steady operation. As is clear from FIG. 2, it can be seen that according to the method of the present invention, a polyolefin having an extremely stable melt index value can be produced.

In addition, the solid line C in FIG. 6 shows the relationship between density and polymerization time when polyethylene is continuously produced by the method of the present invention, and the dotted line D shows the relationship between the density and polymerization time when polyethylene is produced continuously by the method of the present invention. This figure shows the relationship between density and polymerization time when a person controls the density by instructing the operation of the ethylene supply valve as a monomer, the propylene supply valve as a comonomer, etc. Note that the polymerization time on the horizontal axis in FIG. 6 is not calculated from the polymerization start time, but is calculated from an arbitrary time during steady operation. As is clear from FIG. 6, it can be seen that according to the method of the present invention, a polyolefin having an extremely stable density value can be produced.

As is clear from the above examples, the present invention provides a method for producing polyolefins by polymerizing olefins in the presence of a Ziegler catalyst and hydrogen. It is useful as a technique for producing polyolefins having a certain density, and is suitable as a technique for providing standardized polyolefins having extremely stable desired physical properties, particularly desired melt index and/or density.

[Brief explanation of drawings]

Figure 1 is a block diagram of the method of the present invention, Figure 2 is a diagram showing the relationship between polymerization time and the melt index value of the polyolefin produced, and Figure 3a.
3 and 3b are block diagrams showing one embodiment of a control device for carrying out the method of the present invention, FIG. 4 is a diagram showing the response of a gas chromatography detector in the control device, and FIG. FIG. 6 is a diagram showing the control system of the supply valve and the pressure relief valve, and FIG. 6 is a diagram showing the relationship between the polymerization time and the density of the produced polyethylene. 1...Polymerization reactor, 1a...Liquid phase part, 1b...
Gas phase part, 2...Hydrogen supply line, 2a...Hydrogen supply valve, 3...Olefin supply line, 3a...Olefin supply valve, 4...Catalyst supply line, 4a...
...Catalyst supply valve, 6...Depressurization line, 6a...Depressurization valve, 7...Outlet line, 9...Gas chromatography, 11...Computer.

Claims (1)

[Claims] 1. In producing a polyolefin having a predetermined density by continuously polymerizing two or more olefins in the presence of a Ziegler catalyst and hydrogen, a gas phase section is provided in the polymerization reactor and the polymerization temperature is controlled. At the same time, the concentration of olefin in the gas phase portion is detected by gas chromatography, the detected signal correlating with the concentration is input into a computer, and the signal is converted into a predetermined signal corresponding to the density. The amount of olefin supplied to the polymerization reactor is adjusted by the arithmetic control output of the computer performed in comparison with a set value, and the olefin concentration is controlled to maintain the predetermined value at the constant polymerization concentration. A method for producing a polyolefin, the method comprising producing a polyolefin having a density. 2. When producing a polyolefin having a predetermined melt index and density by continuously polymerizing two or more types of olefins in the presence of a Ziegler catalyst and hydrogen, a gas phase section is provided in the polymerization reactor and the temperature is kept constant. At the same time, the olefin concentration and hydrogen gas concentration of the gas phase component are detected by gas chromatography, the detected signal correlated with the concentration is input into a computer, and the signal is converted into the melt index and density. The amount of hydrogen supplied to the polymerization reactor and the amount of olefin supplied to the polymerization reactor are adjusted by the calculation control output of the computer performed in comparison with corresponding predetermined set values, and the concentration of the olefin is adjusted. and hydrogen gas concentration and the olefin concentration are controlled so as to produce a polyolefin having the predetermined melt index and density at the constant polymerization temperature. 3. A polymerization reactor for producing a polyolefin having a predetermined melt index and/or density by continuously polymerizing an olefin at a constant polymerization temperature in the presence of a Ziegler catalyst and hydrogen; is provided with a hydrogen supply line for supplying hydrogen to the polymerization reactor, an olefin supply line for supplying olefin, a catalyst supply line for supplying catalyst, a depressurization line for depressurizing, and an outlet line for taking out the product polyolefin. , the hydrogen supply line, the olefin supply line, the catalyst supply line, and the depressurization line include a hydrogen supply valve that controls the hydrogen supply amount, an olefin supply valve that controls the olefin supply amount, and a catalyst supply valve that controls the catalyst supply amount; and a gas chromatograph for detecting the olefin concentration and/or hydrogen gas concentration of the components in the gas phase section provided in the polymerization reactor, and a gas chromatograph for detecting the olefin concentration and/or hydrogen gas concentration for the components in the gas phase section provided in the polymerization reactor, and The correlated sensed signals are compared to predetermined setpoints corresponding to the melt index, density, and the olefin concentration and density are adjusted to produce a polyolefin having the predetermined melt index and/or density. (or) a polyolefin manufacturing apparatus comprising: a computer that performs arithmetic control to adjust the opening degrees of the hydrogen supply valve, olefin supply valve, catalyst supply valve, and depressurization valve to change the hydrogen gas concentration; .