JPS6358846B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves polymerizing an olefin in the presence of a Ziegler catalyst and hydrogen to increase the melt index.
A polyolefin of MI ₂ is produced by a continuous process, and then the melt index is adjusted in the same polymerization reactor.
This invention relates to a transition operation method for changing polymerization conditions to produce a polyolefin with MI ₂ different from MI ₁ by a continuous process. In the present invention, polyolefins include, for example, ethylene,
Refers to a homopolymer of α-olefin such as propylene, 1-butene, 4-methyl-1-pentene, or a copolymer thereof. The melt index is a measure of the molecular weight of a polyolefin, and is appropriately set depending on the use of the polyolefin, and is an important index for consumers to select a brand of polyolefin. and measured, for example, by the method described in ASTM D 1238, typically for polyethylene.
Measured at 190°C, 230°C for polypropylene. As is well known, the production rate of polyolefin depends on the type of catalyst used, the polymerization temperature, the catalyst concentration,
The olefin concentration is independently proportional to each. The melt index of the polyolefin produced is determined by the ratio of hydrogen gas concentration to olefin concentration (H ₂ /C ₂ ). Therefore, in order to produce a polyolefin with a melt index of MI ₂ rather than a melt index of MI ₁ , the polymerization conditions should be controlled to a hydrogen gas concentration and an olefin concentration that will produce a polyolefin with a melt index of MI ₂ . If the residence time in the polymerization reactor is long, or if the difference between melt index MI ₁ and melt index MI ₂ is large, simply produce a polyolefin with melt index MI ₂ rather than melt index MI ₁ . Simply controlling the hydrogen gas concentration and olefin concentration will not achieve the intended purpose due to large transition loss. Note that the allowable range of melt index is appropriately selected depending on the use of the polymer to be produced, and in the case of polyethylene, it is MI±10%. In the present invention, a polyolefin with a melt index of MI ₁ is produced in a continuous process, and then in the same polymerization reactor, a polyolefin with a melt index of MI ₂ (where MI ₁ ≠
MI ₂ . ) When producing polyolefins using a continuous process, first the melt index is MI ₃ .
(Here, when MI ₁ > MI ₂ , MI ₂ > MI ₃ , and MI ₁
When <MI ₂ , MI ₂ < MI ₃ . ), the hydrogen concentration and olefin concentration are changed to produce a polyolefin of When the temperature almost coincided with MI ₂ , the polymerization conditions in the polymerization reactor were changed to minimize transition loss by changing the hydrogen gas concentration and olefin concentration so that a polyolefin with a melt index of MI ₂ was produced. It is something. According to the present invention, the average melt index of the polyolefin in the polymerization reactor is calculated by a computer, and the value is displayed if desired, so that the average melt index of the polyolefin in the polymerization reactor that changes over time can be calculated. The desired melt index can be determined smoothly without waste and without transition loss.
It becomes possible to change the polymerization conditions to produce MI ₂ . When this transition operation is performed by conventional techniques without the use of a computer,
It is necessary to measure the average melt index of the polyolefin in the polymerization reactor and, based on the measured melt index value, judge whether or not to change the polymerization conditions to produce MI ₂ . At this time, it takes about one hour to know the actual melt index after sampling the polyolefin in the polymerization reactor, so the average melt index value in the polymerization reactor is the desired value. i.e.
In reality, it takes one hour after the average melt index of the polyolefin in the polymerization reactor reaches around MI _{2 to judge that it has reached around MI 2 .} Moreover, even though the average melt index in the polymerization reactor is MI ₂ , it takes one hour to confirm this, resulting in an hour of operation under polymerization conditions that produce MI ₃ . As a result, the average melt index greatly deviates from MI ₂ , and there are many cases where further time is lost. The polyolefin produced during this lost time becomes a substandard product. The only way to avoid this is to rely solely on the operator's long experience, but not being able to immediately know what's inside the actual polymerization reactor places an extremely heavy burden on the operator, and leads to frequent so-called operational errors. do. In the method of the present invention, the above-mentioned time loss is completely eliminated by using a computer, and the burden on the operator is also drastically reduced.
There are no erroneous operations. The actual value of the melt index of the polyolefin in the polymerization reactor is only used to confirm the value calculated by the computer, and what is more, the value calculated by the computer and the actual value match extremely well. Of course, if the hydrogen gas concentration and olefin concentration are directly changed in the polymerization conditions to produce a polyolefin with a melt index of MI ₂ , the transition loss will be large. That is, Fig. 1 shows a typical example of the operating situation when MI ₂ > MI ₁ , and Fig. 2 shows a typical example of the operating situation when MI ₂ < MI _1. The vertical axis shows the melt index (MI). , and time (T) is plotted on the horizontal axis.
In each figure, the solid line represents the average MI of the polyolefin in the polymerization reactor, the dashed line represents the MI of the polyolefin actually produced in the polymerization reactor, and the dotted line represents the MI of the polyolefin actually produced in the polymerization reactor in D. shows the average MI of polyolefins. In addition, when the polymerization conditions are changed directly to the melt index without using the method of the present invention, and the hydrogen gas concentration and olefin concentration are changed so as to produce a polyolefin of MI ₂ , the curve shown by the two-dot chain line is shown and the transition loss is big. If a computer is not used, the system will be as shown in FIG. 3, for example. In fact, the dash-dotted line, horizontal axis, and vertical axis used here are the same as in FIGS. 1 and 2.
It is at point D, one hour later, that the average MI at point F is found to match MI ₂ by actual measurement. However _, depending on how MI ₃ is set at this time, the average melt index of the polyolefin in the polymerization reactor is likely to deviate considerably from MI ₂ , so the operator must (point E). The operator determines that the average melt index of the polyolefin in the polymerization reactor is definitely MI ₂ based on the melt index value actually measured based on sampling at point G. It will be at point H after 1 hour. Therefore
Polyolefins produced along the solid line connecting AFDGH are considered substandard products. According to the method of the present invention, in order to measure the hydrogen gas concentration and olefin concentration in the polymerization reactor for controlling polymerization conditions, for example, a gas phase is formed in the polymerization reactor, and the gas phase is measured using high-speed gas chromatography. For example, measurements are taken every minute, and a computer is installed to automatically control the opening and closing of the hydrogen supply valve and olefin supply valve when controlling the hydrogen gas concentration and olefin concentration. FIG. 4 is a block diagram illustrating preferred embodiments of the apparatus used in carrying out the method of the present invention, in which a polymerization reactor 1 maintained at a constant temperature has a liquid phase portion 1a and a gas phase portion. 1b.
The polymerization reactor 1 includes a hydrogen supply line 2 that supplies hydrogen gas to the polymerization reactor 1, an olefin supply line 3 that supplies olefin, a catalyst supply line 4 that supplies a catalyst, a solvent supply line 5 that supplies a solvent, and a depressurization line. A depressurization line 6 for carrying out the process and an outlet line 7 for taking out the polyolefin product from the polymerization reactor 1
are provided for each. The hydrogen supply line 2 has a hydrogen supply valve 2a.
However, the olefin supply line 3 has an olefin supply valve 3a, and the catalyst supply line 4 has a catalyst supply valve 4a.
However, the solvent supply line 5 is provided with a solvent supply valve 5a, the depressurization line 6 is provided with a depressurization valve 6a, and the outlet line 7 is provided with an on-off valve 7a, among which a hydrogen supply valve 2a and an olefin supply valve are provided. 3b, the pressure relief valve 6a, and in some cases the catalyst supply valve 4a, their valve openings are controlled by control signals from a computer, which will be described later. A sampling line 8 is provided in the gas phase section 1b of the polymerization reactor 1, and the hydrogen gas and olefin in the gas phase section 1b are led to a gas chromatograph 9 via an on-off valve 8a, and the gas chromatograph 9 collects the gas. Measure the hydrogen gas concentration and olefin concentration in the phase. Measured component signals based on the hydrogen gas concentration and olefin concentration measured by the gas chromatograph 9 are input to the computer 11 . The computer 11 is programmed to calculate the melt index of polyolefin produced at a certain time based on the measured component signals from the gas chromatograph 9. The program may be programmed to calculate the polyolefin production rate as required. Then, the melt index of the polyolefin produced in response to changes in the ratio of polyolefin concentration to hydrogen concentration (H ₂ /C ₂ ) in the polymerization reactor 1, the amount of polyolefin produced, and the amount of polyolefin produced before the polymerization conditions change. Based on the average melt index of the polyolefin present in the reactor 1 and the amount of the polyolefin present, the program is programmed so that the average melt index of the polyolefin after changing the polymerization conditions can be successively calculated. Once the type of polyolefin is determined, the relationship between the melt index of the polyolefin and the intrinsic viscosity [η] of the polyolefin is unique, and the average intrinsic viscosity of a mixed system of polyolefins with different intrinsic viscosities is determined by the additivity of the intrinsic viscosity. Since this holds true, the average melt index can be calculated by programming a computer using this law. In addition, since it is usually preferable to keep the production amount of polyolefin constant, it is preferable to operate so that the olefin concentration is kept constant and the polyolefin production rate is constant. There is no need to program computer 11 to calculate the production rate. In the following explanation, a case will be explained in which the olefin concentration is controlled so that the polyolefin production rate is constant. The transition operation of the present invention follows the following steps. That is, in FIG. 4, the hydrogen supply valve 2a and depressurization valve 6a are operated according to control signals from the computer 11 to keep the hydrogen concentration constant, and the olefin supply valve 3a and, in some cases, the catalyst supply valve 4a are operated. From a state where the olefin concentration is kept constant and polyolefin with a melt index of MI ₁ is produced, the hydrogen supply valve 2a and the pressure relief valve 6a are operated according to the control signal from the computer 11, and the polymerization conditions of the polymerization reactor 1 are set. Control the hydrogen gas concentration to produce a polyolefin with a melt index of MI ₃ . The ratio of olefin concentration to hydrogen concentration (H ₂ /C ₂ ) changes from moment to moment from polymerization conditions that produce a polyolefin with a melt index of MI ₁ to polymerization conditions that produce a polyolefin with a _melt index of MI 3. and time are input into the computer 11, and the computer 11 calculates the average melt index of the polyolefin in the polymerization reactor 1. This is the time from point A to point B in FIGS. 1 and 2. The time during this period can be arbitrarily determined depending on the size of the polymerization reactor 1 by controlling the degree of opening and closing of the hydrogen supply valve 2a and the pressure relief valve 6a, but it is preferable that it be as short as possible. The average melt index is similarly calculated under the conditions under which polyolefin with a melt index of MI ₃ is to be produced, that is, at the time corresponding to the dashed line connecting BC in FIGS. 1 and 2. Then, at time C, if the average melt index value approximately matches MI ₂ , that is, within ±10% of the set melt index MI ₂ , the melt index will produce a polyolefin with MI ₂ . Then, the hydrogen supply valve 2a and the pressure relief valve 6a are controlled by the control output signal of the computer 11 to change the hydrogen concentration. During this time, it takes some time to reach a predetermined ratio of hydrogen concentration to olefin concentration (H ₂ /C ₂ ), but during this time, the average melt index value of the polyolefin in the polymerization reactor 1 is calculated in the same way. During this time, Figures 1 and 2
This is the time taken from C to D in the figure. This time can be arbitrarily controlled to some extent by the degree of opening and closing of the hydrogen supply valve 2a and the pressure relief valve 6a.
It is preferable that the time is as short as possible. In the method of the present invention, the polyolefin produced after point D in FIGS. 1 and 2 is used as a standard product. The polyolefins produced after point D are the polyolefins with melt index MI ₁ that have been present in the polymerization reactor at point A for a while, the polyolefins with melt index MI ₁ to MI ₃ produced along the dashed-dotted line ABCD, and It is a mixture of polyolefins with a melt index MI ₂ formed after point D. On the other hand, depending on the use of the polyolefins, a mixture of polyolefins having melt index values that are too different may not be suitable for the use even if the apparent melt indexes are the same. Therefore, the mutual relationship between melt indexes MI ₁ , MI ₂ , and MI ₃ is as follows:
If MI ₁ < MI ₂ then 1 < MI ₃ / MI ₂ ≦100 and 1 <
It is preferable that MI ₂ /MI ₁ ≦100, and more preferably 1<MI ₃ /MI ₂ ≦50 and 1<MI ₂ /MI ₁ ≦50.
In particular, 1<MI ₃ /MI ₂ ≦10 and 1<MI ₂ /MI ₁
It is preferable to satisfy ≦10. Also, when MI ₁ > MI ₂ , 1 < MI ₂ / MI ₃ ≦100 and 1 < MI ₁ / MI ₂
It is preferable to satisfy ≦100, and more preferably 1<
It is preferable that _MI2 / _MI3 ≦50 and 1 _< MI1/ _MI2 ≦50, particularly 1< _MI2 / _MI3 ≦10 and 1< _MI1 / _MI2 ≦10. Furthermore, in the case of the present invention, the melt index MI ₃ does not need to be constant as shown by the dashed-dotted line connecting _BC in FIGS. I don't mind. In addition, if the residence time in the polymerization reactor is small,
MI ₂ = MI ₂ within the desired time as MI ₃ ±10%
Can be done within. Furthermore, even if the residence time in the polymerization reactor is long, if MI ₁ and MI ₂ are close values, even if MI ₂ = MI ₃ , MI ₂ ±
It can be within 10%. (The value of MI ₂ ±10% is within the range allowed for standard products.) Therefore, in the above case, the melt index MI ₃
No step is necessary to produce a polyolefin. In addition to controlling the hydrogen gas concentration and olefin concentration described above, the polymerization temperature may also be controlled. As can be seen from the above description, according to the present invention, transition loss is reduced and polyolefins having a predetermined melt index can be produced. Example Olefin: Ethylene Polyolefin: Polyethylene Reactor: 50 ^M3 tank reactor with stirrer Solvent: Aliphatic hydrocarbon catalyst: Ziegler catalyst Ethylene feed rate: 4 TON/H Solvent feed rate: 10 M ³ /H Temperature: 80°C Polymer residence time: 3HR [Table]

[Brief explanation of drawings]

FIG. 1 is a graph showing the operating situation when melt index MI ₂ >melt index MI ₁ . FIG. 2 is a graph showing the operating situation when melt index MI ₂ <melt index MI ₁ . FIG. 3 is a graph showing the case where the polymerization conditions were changed by manual control in the case of melt index MI ₂ >melt index MI ₁ . FIG. 4 is a block diagram illustrating the method of the present invention. FIG. 5 shows an embodiment of the present invention,
Melt Index MI ₂ > Melt Index
It is a graph showing the driving situation in the case of MI ₁ . DESCRIPTION OF SYMBOLS 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, 5
...Solvent supply line, 5a...Solvent supply valve, 6...Depressurization line, 6a...Depressurization valve, 7...Outlet line, 7a...
On-off valve, 8... Sampling line, 8a... On-off valve, 9... High speed gas chromatography, 10... Gas chromatography measurement recorder, 11... Computer, 12... Computer signal recorder.

Claims (1)

[Claims] 1 A polyolefin with a melt index of MI ₁ is produced by a continuous process by polymerizing an olefin in the presence of a Ziegler catalyst and hydrogen, and then in the same polymerization reactor, a polyolefin with a melt index of MI ₂ (where MI ₂ ≠ MI ₁ In the transition operation method in which the polymerization conditions are changed in order to produce polyolefin by a continuous process, the melt index is MI ₃ (here, when MI ₁ > MI ₂ , MI ₂ > MI ₃
and when MI ₁ < MI ₂ , MI ₂ < MI ₃ . ), change the hydrogen concentration and olefin concentration, enter the above polymerization conditions and operating time into the computer to produce a polyolefin with a melt index of MI ₃ , and record the elapsed operating time. The average melt index of the polyolefin in the subsequent polymerization reactor is calculated by the computer, and the average melt index is
Identical polyolefins with different melt indexes, characterized by changing _{the hydrogen gas concentration and olefin concentration so as to produce a polyolefin with a melt index of MI 2 ,} while at the same time changing the polymerization conditions of the polymerization reactor to produce a polyolefin with a melt index of MI 2. A transition operation method for continuous production using a polymerization reactor.