DE2931775C2 - Batch process for the polymerization of monomers - Google Patents

Description

+ a AT)

is sufficient where Κ _μ ο the basic gain that can be set as a parameter, a is a constant between 0 and 10 and Δ Taxe is the difference between the temperature of the polymerization mixture and the mean jacket temperature.

2. Batch process according to claim 1, characterized in that a RegeJkorrektor is provided is, which constantly detects changes in the temperature of the polymerization mixture and the controller behavior and processes them in such a way that the Changeover from heating to cooling and vice versa initiated in good time as well as temperature disturbances by changing the controller output is counteracted.

3. Batch process according to claim 1 or 2, characterized in that the continuous measurement of the temperature of the polymerization mixture and the mean jacket temperature with Help of the integral criteria

ydr = j

jTdt ^ (T, -T _} -T _Ka ) -t _x

and

'j
I.

^Q ¥ ^d ' ⁼

O O

is constantly evaluated, where fi and ft mean two fixed times, after which a further increasing integral value no longer indicates a critical state and Q is the amount of heat removed, K is the heat transfer coefficient, ΔΤ is the difference between the temperature of the polymerization mixture and the mean jacket temperature, T, the desired target temperature of the polymerization mixture, Ti the cold water _{temperature and Γ «Μ} the temperature reserve as setting parameters.

4. Batch process according to claim 3, characterized in that an alarm is triggered in the event of an overdose of monomers and / or initiator in the agitator pressure autoclave and / or deterioration in the K number of the agitator pressure autoclave.

5. Batch process according to one of claims 1 to 4, characterized in that the integral component of the controller is held between an upper and a lower limit value, the lower Limit value is formed by the cold water temperature 7}.

The invention relates to a batch process for the polymerization of monomers in the liquid phase in stirred pressure autoclaves with double jacket for Beauf beat with water, with the double jacket in a A heating phase with hot water and in the actual polymerization phase with cooling water to set an essentially constant one The temperature of the polymerization mixture in the autoclave is applied.

The process for the polymerization of vinyl chloride in aqueous suspension according to DK-OS 22 12 9b2 is in carried out a stirred pressure autoclave, which heated via a flow-through of water or coolable double jacket is allowed lasting during the approximately one-third of the total polymerization cycle heating phase, the temperature of the reactor wall is no longer of than 20 ⁰ C above the temperature Polymerization mixture lie, and during the In the polymerization phase, the temperature of the reactor wall must be lower than the temperature of the polymerization mixture, the temperature of the mixture in the polymerization phase being essentially the same should be constant.

Furthermore, from DE-OS 22 22 929 a batch process for solution and emulsion polymerization in a reaction vessel equipped with a stirrer with a double jacket is known in which the double jacket a brine flows through it during the polymerization in such a way that the temperature of the reaction mixture during the reaction is in a range of rC is kept constant, the brine flow through the double jacket by a computer automa table depending on the measured temperature is regulated.

The disadvantage of the known methods that the type-specific internal temperature is not maintained precisely enough at all times. So For example, a rapid decrease in the heat of reaction causes supercooling in the reaction vessel up to 3 ° C. which, because of the resulting decrease in the rate of polymerization, extends the running time per batch up to 45 minutes and more in addition, the product quality is negatively influenced.

It is therefore the object of the invention to provide a batch process for the polymerization of monomers in which the predetermined internal temperature in the reaction vessel is precisely maintained during the polymerization phase. This is achieved according to the invention by keeping the set temperature of the polymerization mixture essentially constant in the polymerization phase by adaptive cascade control by changing the gain K _{p of} the master controller so that it corresponds to the relationship

K _n = Kp ₀ (I + a) ■ ΔΤ) is sufficient, where K _Pt o is the adjustable parameter

Basic gain, a is a constant between 0 and 10 and Δ T is the difference between the temperature of the polymerization mixture and the mean jacket temperature.

The batch process according to the invention can optionally also be designed in that

a) a control corrector is provided which constantly detects changes in the temperature of the polymerization mixture and the controller behavior and processes them in such a way that the switch from heating to cooling and vice versa is initiated in good time and temperature disturbances are counteracted by changing the controller output; ' ⁵

b) the continuous measurement of the temperature of the polymerization mixture as well as the average Manicl temperature with the help of the integral criteria for which the effectiveness can be adjusted. in the the corrector works according to the relationship

Q γ

and

20th

25th

30th

is constantly evaluated, where u and f2 mean two fixed times, after which a further increasing integral value no longer indicates a critical condition, and Q is the amount of heat removed, K is the heat transfer coefficient, Δ 7 is the difference between the temperature of the polymerization mixture and the mean jacket temperature, r , the specified target temperature of the polymerization mixture, Ti the cold water temperature and 7>"the temperature reserve as setting parameters;

c) in the case of an overdosing of monomers and / or initiator into the stirred pressure vessel and / or by worsening the K number of the An alarm is triggered due to an increase in the integral values caused by agitation pressure autoclaves;

d) the integral component of the controller is kept between an upper and a lower limit value, the lower limit value being formed by the cold water temperature Ti .

The batch process of the invention is ^J m especially when using large stirred autoclave, for example, from 90 content, appropriate because the control quality is so improved with him. that the specified internal temperature is precisely maintained in the polymerization phase. The control deviation in this phase is less than 0.05 ° C and is therefore below the measuring accuracy of the temperature sensor. This polymerization to is to ensure to ^b0 its termination consistent product quality from the start.

In the batch process according to the invention, a control corrector can be provided, which under Recognition of the disturbance variable acting on the control loop influences the controller in such a way that the effect the disturbance variable is quickly regulated. The control corrector is to be understood as an additional control parameter,

Y'dt,

where \ XJ {is the amount of control deviation, Y 'is the differentiated controller output signal, Z is a parameter between 0 and 1 and {is the running time.

In the case of the batch process according to the invention, integral criteria can serve to increase the safety of the process and ensure product quality. The value of the integrals increases if the heat transfer coefficient K deteriorates in the course of the process. The integrals are also increased if too large an amount of monomer or an excessive amount of initiator has been charged.

The attached drawing shows an arrangement for carrying out the batch process according to the invention (FIG. I) and the effect of the dus tegelkorrektors in a graphic representation (FIG. 2). An autoclave 1 (see FIG. 1) is provided with a stirrer 2 and a double jacket 3. The annular space between the outer wall of the autoclave 1 and the double jacket 3 is provided with cooling water via a ring line 4 in which a circulation pump 5, a heat exchanger 6 and an automatically actuatable steam inlet valve 7 are arranged . Hot water can be applied. Cold water can be passed through the heat exchanger 6 via pipelines (8, 9), an automatically actuatable valve 10 being arranged in the pipeline 8

Three temperatures are continuously measured, namely the autoclave internal temperature Ti, the annulus inlet temperature Tj and the cold water temperature Ti. The measured temperature values are fed to processing blocks which control a slave controller that sends commands to the steam inlet valve 7 and valve 10

In. The individual processing blocks are as follows:

Subtracter Sß 1:

Calculates the temperature difference between Ti and Tj

Subtractor SS 2:

Calculates the control deviation X », ie the temperature difference between the setpoint Ts ₀ H and the actual value 7Ί

Start-up switch AF:

Start-up circuit for the heating-up phase, structure conversion or time indicator for the setpoint; an output transfers the information to the switching stage LOG as to whether the heating phase is active or ended (switching from K _p );

Setting parameters : Setpoint Tsou for the polymerisation phase

Integrator INT 1:

To improve the mean jacket temperature with the help of the integral criteria

Adder / multiplier AX:

To calculate the gain K _n ; Setting parameters'-: constant a (between 0 and 10)

Differential DIF 1.

To calculate the differential component of the controller, output signal smoothed;

Setting parameters: derivative time 7 ", ι
Integrate INT2:

To calculate the integral component of the controller, the integration being stopped, ie the instantaneous output value is held at the temperature 7 "i or an upper limit value OG if the output is l <T _s or l>OG;
Setting parameters: Reset time: T _n .,

Multiplier X3:

To calculate the product μ from the amount of control deviation X _w and the differentiated output signal V for the control corrector;
Setting parameters: Exporent χ

Comparator VG-.

Comparison of the current value of INT1 with two adjustable comparison values (see patent claim 3);

Setting parameters: temperature reserve Tr ^ t \ and ti as points in time at which a further increasing integral value no longer represents a critical state

Multiplier X 2:

To calculate the product of the gain Kp of the master controller and the basic gain / Cpoals setting parameters

Setting parameters Kp.f.

The gain K _{p that is} effective during the setpoint control in the heating phase

Adder A D-.

Adder for calculating the controller output Y '

Integrator INT3:

Represents the rule corrector;
Setting parameters: reset time T ". ₂

Level A NOISE:

Operates the horn or similar when the integral criteria are met

Limiter BG:

Limits the controller output;

Setting parameters: Lower limit UG and upper limit OG

Switching stage LOG.

During the heating-up phase, "'Kp.i" is effective for setpoint adjustment, while after the end of the heating-up time Io and in the event of a control deviation X <0.2%, the system _{switches to K r} (processing block X 2)

Multiplier XI:

To calculate the controller output Y = K _n ■ Y \ '"differentiator DIF2:

To calculate V for the rule corrector

PID:

PID controller as slave controller

^Γι In Fig. 2 indicate the dashed lines at the time profile of the temperature Tj and the associated control deviation AV for the case in which the PID controller is operated without control corrector. The solid lines, on the other hand, give the corresponding

- "'The relevant data for the case that the PID controller with Control corrector is operated. Accordingly, the checkered and straight hatched areas show the summed ones Control deviation without control corrector and the checkered hatched areas only represent the total control deviation > Correction with corrector according to the formula

at. The numerical values for the curves at hand are:

Without rule corrector: 444Ks.
With rule corrector: 320Ks.

For this purpose 2 sheets of drawings

Claims (1)

Patent claims: 1. Batch process for the polymerization of monomers in the liquid phase in a stirred pressure autoclave with a double jacket for exposure to water, the double jacket! in a heating phase amounting to at most one third of the entire polymerization cycle, hot water is applied and in the actual polymerization phase cooling water is applied to set an essentially constant temperature of the polymerization mixture in the autoclave, characterized in that in the polymerization phase the target temperature of the polymerization mixture is adjusted by adaptive cascade control in keeps essentially constant by changing the gain K _{9 of} the master controller so that it corresponds to the relationship