JPS62124107A - Control of molecular weight - Google Patents

Abstract

PURPOSE:To enable the control of molecular weight of polypropylene in high efficiency suppressing the loss of material based on the fact that the hydrogen consumption per unit weight is constant at constant molecular weight in the polymerization of propylene in a reactor provided with a reflux condenser using hydrogen as a molecular weight controller. CONSTITUTION:Propylene is polymerized in a reactor provided with a reflux condenser by bulk-polymerization process using hydrogen as a molecular weight controller and propylene as a liquid medium at a constant temperature while removing at least a part of polymerization heat by condensing propylene vapor with the reflux condenser. In the above process, the molecular weight of the polymer is controlled by controlling the feeding rate of hydrogen according to the consumption of hydrogen per unit propylene in the reactor. The hydrogen consumption corresponds to the molecular weight of polypropylene and is calculated from the polymerization ratio calculated from heat generation and a preliminarily determined relationship between the molecular weight of polypropylene and the consumption of hydrogen.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a process for the polymerization of propylene. Specifically, the present invention relates to a method of controlling the molecular weight of polypropylene obtained by using hydrogen in a specific polymerization method and polymerizing propylene itself.

It is well known that the molecular weight of polypropylene obtained when propylene is polymerized using a Cheekler-Kenatsuta catalyst can be controlled by controlling the amount of hydrogen added during the polymerization (for example, J. Polymer Sci., C2109).
(1974)) There is a certain relationship between the hydrogen concentration in the gas phase and the molecular weight of the polypropylene obtained (for example, J, Poly
mer Sci, Part Al vol 8271
7 (1970)), polypropylene is usually produced by controlling the molecular weight of polypropylene, which provides the hydrogen concentration in the gas phase, to a constant value so that it becomes a desired value.

On the other hand, when producing polypropylene using a large reactor, it is difficult to remove the heat of polymerization simply through the walls of the reactor or by installing a heat exchanger inside the reactor, so it is difficult to remove the heat of polymerization in a liquid form. Methods using reflux condensers that utilize the latent heat of the medium are also known.

Problems to be Solved by the Invention However, when propylene is polymerized using a reactor equipped with the above-mentioned reflux condenser, the hydrogen concentration in the gas phase changes greatly depending on the load on the reflux condenser. If hydrogen is introduced and/or discharged so that the hydrogen concentration is constant, hydrogen will be introduced and discharged frequently, and the amount of hydrogen and propylene entrained during discharge will be large. There was a problem that.

The present inventors have diligently studied methods to solve the above problems, and by implementing a method for specifying results, hydrogen and/or
Alternatively, they discovered that the molecular weight of polypropylene can be controlled without loss of propylene, and completed the present invention.

It is an object of the present invention to provide a method for producing polypropylene of controlled molecular weight without loss of raw materials.

A third means to solve the problem, that is, the present invention, is a bulk polymerization method using a reaction tank equipped with a reflux condenser, hydrogen as a molecular weight regulator, and propylene itself as a liquid medium, to absorb at least a part of the polymerization heat. In the method of polymerizing propylene at a constant temperature by removing propylene vapor by condensing it in a reflux condenser, the relationship between the amount of polymerization calculated from the calorific value, the predetermined molecular weight of the polypropylene obtained, and the consumption amount of hydrogen. Molecular weight control characterized by controlling the amount of hydrogen charged in accordance with the consumption amount of hydrogen in a reaction tank derived from the consumption amount of hydrogen per unit propylene corresponding to the desired molecular weight of polypropylene derived from the formula. It's a method.

The method of the present invention uses a reaction tank equipped with a reflux condenser,
It is extremely important when polymerizing propylene using hydrogen as a molecular weight regulator.

This is because in a reaction tank that does not use a reflux condenser, the gas phase and liquid phase are in vapor-liquid equilibrium, and the gas phase is in a nearly uniform state, so the gas in the gas phase is sampled to determine the hydrogen concentration. If you measure it, you can accurately know the hydrogen concentration in the gas phase, so compare the detected hydrogen concentration with the desired hydrogen concentration using a comparison means, and introduce the insufficient hydrogen concentration into the reaction tank by operating the hydrogen introduction valve. This is because it is possible to completely control the molecular weight of the polypropylene obtained by this method.

In the present invention, the polymerization of propylene includes not only homopolymerization of propylene but also copolymerization of propylene with ethylene, butene-1, hexene-1, and the like.

As the polymerization catalyst used in the present invention, a known catalyst system consisting of a transition metal catalyst and an organometallic compound (combined with a stereoregularity improver if necessary) is used, and the transition metal catalyst is not particularly limited. Titanium trichloride obtained by reducing with a reducing agent such as aluminum, organoaluminum, or organomagnesium, or titanium trichloride obtained by further pulverization, treatment with an oxygen-containing organic compound, titanium tetrachloride treatment, etc.
Alternatively, examples include those in which titanium trichloride or titanium tetrachloride is supported on a carrier such as magnesium chloride, and examples of organic metal compounds include organic aluminum compounds such as trialkylaluminium, dialkylaluminum halide, alkyl aluminum sesquihalide, and alkylaluminum cybaride. , organic magnesium such as dialkylmagnesium, and the like.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of an apparatus for carrying out the method of the present invention. 1 is a mirror tank with a stirrer, 2 is a reflux condenser
3 is a jacket, 4-1 is a gas flow rate and temperature detector, 4-2 is a condensate flow rate and temperature detector, and 4-3 is a hydrogen gas introduction flow! Control valve 4-4 is for jacket cooling (
4-5 is a detector for the amount and temperature of cooling (or heating) water flowing into the jacket, and line 5 is a slurry introduction line (first line). line 6 (which becomes the catalyst slurry charging line)
7 indicates the slurry discharge line, and 7 indicates the propylene and catalyst charging line. 4-1.4-2.4-4.4-5 above
The signals aX b, c, and d detected in are inputted to the data processor 8, and the amount of heat dissipated and the like are corrected to calculate the polymerization t from the amount of heat generated. On the other hand, by determining the relationship between the amount of hydrogen consumed and the molecular weight of the obtained polypropylene (in Figure 2, the intrinsic viscosity is used as a measure of molecular weight), the consumption of hydrogen per unit weight of polypropylene corresponding to the desired molecular weight is determined in advance. Polypropylene with a constant molecular weight can be produced by determining t and introducing hydrogen corresponding to the product of the amount of polymerization determined above.

It goes without saying that when continuous polymerization is carried out using a polymerization machine with multiple tanks connected and polymerization is carried out while changing the molecular weight in the multiple tanks, it is necessary to correct the amount of hydrogen flowing in and out with the slurry.

At the start of polymerization, it is not possible to obtain the desired molecular weight by simply introducing all the hydrogen to meet the amount consumed. Therefore, the amount of hydrogen required is determined at once by considering the amount of hydrogen dissolved in propylene and the volume of the gas phase. After measuring the molecular weight of the charged polypropylene and making slight corrections, it is possible to produce polypropylene with a constant molecular weight by introducing hydrogen according to the amount of consumption mentioned above after reaching the desired molecular weight. becomes.

Effect: According to the present invention, the amount of hydrogen consumed when given to a certain molecule i1 is
Must be constant per unit weight. The concentration of hydrogen in the gas phase fluctuates depending on the load on the reflux condenser, and the apparent value fluctuates greatly, but on average, the equilibrium between the gas and liquid phases is maintained, and hydrogen can be introduced in proportion to consumption. It can be assumed that the molecular weight could be maintained at a constant value.

Example: The internal volume of the structure shown in FIG. 1 is 40W? Polymerization was carried out at 70° C. using a reactor using liquid propylene as a medium and a catalyst consisting of titanium trichloride and diethylaluminium chloride. At the start of polymerization, 35N- hydrogen was added all at once, and the amount of hydrogen introduced was slightly adjusted so that the intrinsic viscosity number was t7, and then the hydrogen was controlled to be introduced according to the amount of polymerization calculated from the calorific value. My friend. FIG. 3 shows the relationship between the value obtained by monitoring the gas phase hydrogen concentration by sampling gas in the gas phase from line 9 in FIG. 1 and the intrinsic viscosity of the obtained polypropylene (average 2.4 T/hour). Although the hydrogen concentration in the gas phase fluctuates, the intrinsic viscosity remains constant.

Effects of the Invention By carrying out the method of the present invention, polypropylene of a constant molecular weight can be obtained efficiently and with good controllability, which is of great industrial significance.

[Brief explanation of drawings]

Figure 1 shows an example of an apparatus for carrying out the method of the present invention, Figure 2 shows an example of the relationship between hydrogen consumption and intrinsic viscosity (example of polymerization at a constant temperature), and Figure 3 shows an example of an apparatus for carrying out the method of the present invention. It is a drawing showing the relationship between the passage of time, the gas phase hydrogen concentration, and the intrinsic viscosity of the obtained polypropylene in an example. Patent applicant: Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] A bulk polymerization method using hydrogen as a molecular weight regulator and propylene itself as a liquid medium using a reaction tank equipped with a reflux condenser, in which at least a part of the polymerization heat is removed by condensing propylene vapor with a reflux condenser. In the method of polymerizing propylene at a constant temperature, a unit corresponding to the desired molecular weight of polypropylene derived from the relational expression between the polymerization amount calculated from the calorific value, the predetermined molecular weight of the obtained polypropylene, and the consumption amount of hydrogen. 1. A method for controlling molecular weight, comprising controlling the amount of hydrogen charged in accordance with the amount of hydrogen consumed in a reaction tank, which is derived from the amount of hydrogen consumed per propylene.