JPH0574601B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for removing polymerization heat when monomers are polymerized to produce a polymer, and more specifically, the present invention relates to a method for removing heat of polymerization when producing a polymer by polymerizing monomers. , relates to a method of condensing and utilizing this to remove polymerization heat and control polymerization temperature.

(Prior art) It is known that the polymerization heat generated during a polymerization reaction is removed through the wall of the reactor or by installing a heat exchanger inside the reactor. Since the area cannot be large, a method using a reflux condenser that utilizes the latent heat of the liquid medium is also known. Furthermore, it has been proposed that a reflux condenser has a large cooling capacity and can remove polymerization heat with good responsiveness by adopting specific control values (Japanese Patent Publication No. 45961/1983).

(Problem to be solved by the invention) However, even if the above method is used, the amount of heat that must be removed by the reflux condenser is large in a large reactor, so it is difficult to slightly vary the flow rate of the coolant flow. It is difficult to control the polymerization heat at a constant level, even if we set up several coolant flow lines with different flow rates and control the flow rate of the coolant flow with a small flow rate to deal with small fluctuations in the amount of heat removed. It was extremely difficult to do so.

(Means for Solving the Problems) As a result of intensive studies by the present inventors on methods for solving the above problems, the inventors of the present invention have found that by controlling specific parts, the heat of polymerization can be removed with excellent controllability, and the temperature can be maintained at a constant temperature. The present invention was completed by discovering that it is possible to carry out a polymerization reaction.

That is, the present invention condenses the vapor generated in the presence of a volatile liquid medium in a reflux condenser, and returns the condensed liquid separated from non-condensed gas to the reactor to remove the polymerization heat and control the polymerization temperature. In doing so, the non-condensable gas is returned to the reactor to control the polymerization temperature and a portion of the non-condensable gas is returned to the non-condensable gas discharge line from the reflux condenser via a control valve, and , the control valve is configured to adjust the flow rate of the non-condensable gas returning from the cooler to the non-condensable gas line and the flow rate of the coolant introduced into the cooler, depending on the temperature of the reactor. The present invention provides a method for controlling polymerization temperature.

The control method of the present invention can be applied to the polymerization of any monomer as long as the polymerization is carried out using a reactor equipped with a reflux condenser, and is particularly applicable to the polymerization of bulk polymers in which the monomer itself is a volatile liquid medium. When applied to legal polymerization reactions, the amount of polymerization heat that must be removed by the reflux condenser is large, making it even more effective.

Examples of monomers used in polymerization include those with a relatively large heat of polymerization, such as propylene, vinyl chloride, vinylidene chloride, butene-1, hexene-1, styrene, and p-methylstyrene, in which double bonds polymerize through addition reactions. Furthermore, it can be applied when copolymerizing the above monomers with each other or copolymerizing with ethylene.

Furthermore, although the polymerization reaction can be applied either batchwise or continuously, it is particularly effective to apply it to a continuous polymerization reaction in which it is difficult to predict changes in the generation pattern of polymerization heat in advance.

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

In the polymerization tank 1 the monomers are polymerized in the presence of a volatile liquid medium. The vapor of the volatile liquid medium heated by the heat of polymerization is introduced into the reflux condenser 2 via line 4, and the coolant is introduced into the reflux condenser 2 via line 7 via the flow control valve 14, and is discharged via line 8. Possibly condenses steam. The condensed liquid returns to the polymerization tank 1 via the line 6, and the non-condensed gas that did not condense is pressurized by the blower 3. A part of the liquid returns to the polymerization tank 1 via the flow rate control valve 10 and the line 9, and the remainder passes through the flow rate control valve 11. It is then returned from line 5 to line 15. Flow control valve 11, 10, 14
are each controlled by a controller 13 according to a thermometer (detection end) 12 that detects the temperature of the polymerization tank.
Note that in the above description, instead of the blower 3, other mechanical transfer means, such as various compressors, can also be used.

Various known methods can be applied to control the control valves 10, 11, and 14, which operate according to the temperature detected by the thermometer 12. There are no particular restrictions on the conversion method or arithmetic processing method to create a signal proportional to temperature, but usually a specific limit value is set for the rate of change of temperature in the polymerization tank, and when the temperature is below the limit value, the control valve is closed. 10 and 11, and when the limit value is exceeded, the control valve 14 is operated in conjunction with the control valves 10 and 11. In the present invention, a large change in the amount of heat removed is mainly dealt with by a change in the flow rate of the coolant, and a small change is dealt with by a change in the flow rate of the non-condensable gas.

To further describe the control method of the control valve in the present invention, it is usually a function proportional to the difference from a set value.
The valve opening degree is controlled according to three functions: a function obtained by differentiating the difference with respect to time, and a function obtained by integrating the difference with respect to time. At this time, which of the above three functions is weighted is not specified depending on the equipment and polymerization system, but if the difference from the set value is less than a certain value and the absolute value of the differential value is less than a certain value, only valve 11 is changed. When the absolute value of the differential value is above a certain value, the valve 14 is varied, and when the differential value is below a certain value, the valve 14 is kept constant and the valve 11 is varied. Here, the setting function of the valve opening degree corresponding to the temperature change can also be changed by the above-mentioned integral value over a certain period. The valve 11 may be held constant, or may be held in the middle of the fluctuation range, or may be closed in conjunction with the valve 14, or may be opened to absorb a part of the fluctuation in the amount of heat removed due to changes in the valve 14. is also possible. These may be determined depending on the controllability of the reactor, etc.

The reason why the polymerization temperature can be controlled with good controllability by removing the polymerization heat in the method of the present invention is because the amount of steam introduced into the reflux condenser is controlled by controlling the amount of non-condensable gas that does not condense in the reflux condenser. In other words, it is presumed that this is because the amount of steam to be condensed can be finely controlled (that is, the amount of heat removed can be finely controlled), so that the polymerization temperature can be controlled to be constant.

(Effects of the invention) According to the method of the present invention, the controllability of the reaction temperature of the reactor is extremely high, and it is possible to carry out the polymerization reaction at a constant temperature, and the quality of polyvinyl chloride, polypropylene, etc. changes greatly depending on the polymerization temperature. Even polymers can be manufactured with constant quality. In addition, in the bulk polymerization method, a change in temperature immediately results in a change in pressure, which causes problems in transferring slurry, etc. However, this method solves such problems and is extremely valuable as a method for industrial implementation.

Examples Next, the present invention will be explained in more detail based on examples.

Example: Internal volume 40 with temperature control method shown in Figure 1
Bulk polymerization was carried out continuously using a m ³ polymerization tank using liquid propylene as the liquid medium using a catalyst consisting of titanium trichloride and diethylaluminium chloride.

The polymerization tank is covered with a cooling jacket (maximum heat removal amount: 600 Mcal/H), and by introducing a certain amount of cooling water at a nearly constant temperature, a part of the polymerization heat is removed. The structure is such that the reflux condenser (maximum heat removal amount: 2000 Mcal/H) is controlled by the polymerization tank temperature.

Using this polymerization tank, the catalyst was charged as titanium trichloride at 1.2 kg/h and continuous polymerization was carried out so that polypropylene was produced at 24 T/h per hour while controlling the slurry to have a volume of approximately 30 ^m3 . did. At this time, the molecular weight of the polypropylene charged and obtained is controlled so that the hydrogen concentration in the gas phase is 7%.

Under the above conditions, polymerization was carried out for 10 hours while controlling the polymerization temperature to 70°C. For comparison, an operation was also conducted with the control valve 11 closed and the control valve 10 open. Figure 2 shows the temperature change during 10 hours of operation. In comparative experiments, there were large temperature changes, which made it difficult to drain the slurry from the polymerization tank when the temperature was low and the pressure was low, and when the temperature and pressure were high, the amount of slurry discharged was large and the volume of the slurry was reduced. In addition to being difficult to maintain constant, the stereoregularity of the resulting polypropylene was reduced.

In this embodiment, the control valves 10, 11, and 14 were controlled in the following manner based on the detected temperature.

The polymerization tank temperature detected by the detection end 12 is compared with a set temperature of 70°C in the controller 13, and if it is higher than the set temperature and the rate of change in the polymerization tank temperature is below the limit value, the valve opening degree of the control valve 11 is further reduced. , above the specific limit value, the valve opening of the control valve 14 was increased and the valve opening of the control valve 11 was adjusted.

On the other hand, if the polymerization tank temperature is lower than the set temperature, the control valve is used to perform the reverse operation.

Further, when the rate of change in temperature of the polymerization tank is processed by the controller 13, the control valve 10 is feedback-controlled by a function of the rate of change in temperature, thereby increasing the stability of the control system.

[Brief explanation of the drawing]

Figure 1 shows one of the polymerization apparatuses used in the method of the present invention.
As an example, FIG. 2 is a graph showing the relationship between operation time and reaction temperature when polymerization was carried out by the method of the present invention and the conventional method, respectively. Explanation of symbols, 1... Polymerization tank, 2... Reflux condenser, 3... Blower, 4, 5, 6, 7, 8, 9,
15... Line, 10, 11, 14... Flow control valve, 12... Thermometer, 13... Controller.

Claims (1)

[Claims] 1. The vapor generated in the presence of a volatile liquid medium is condensed in a reflux condenser, and the condensate separated from the non-condensed gas is returned to the reactor to remove the heat of polymerization and reduce the polymerization temperature. In order to control the non-condensable gas, the non-condensable gas is returned to the reactor to control the polymerization temperature, and a portion of the non-condensable gas is returned to the non-condensable gas discharge line from the reflux condenser via a control valve. and the flow rate of the non-condensable gas returning to the non-condensable gas line from the cooler and the flow rate of the coolant introduced into the cooler via the regulating valve is adjusted according to the temperature of the reactor. A method for controlling polymerization temperature, characterized in that: 2. The method according to claim 1, wherein the volatile liquid medium is a monomer.