DE10037153C2 - Device for polymerization in a loop reactor - Google Patents

Description

The invention relates to a device for controlling a Polymerization, especially for suspension polymerization in a loop reactor.

It is known to run batchwise for the polymerization de use suspension processes in which a monomer in is stirred in a stirred kettle. Disadvantage of this known method is that there is a risk of being relative sticky polymerizing drops are formed, the toppings on walls of the stirred tank and the like. in the In extreme cases, this deposit formation can lead to constipation of the entire system. Furthermore, this is known Process disadvantageous that large material sales only in be limited scope are possible and the setting of a ge desired bead size distribution is relatively difficult.

Furthermore, a clever device is known from EP 0 819 709 A2 use reactor for continuous polymerization, which is a comparatively improved automation and egg enables increased sales.

However, this known loop reactor is limited to the conversion of gaseous monomers, differing che reaction zones are provided. Furthermore, it is relative consuming the gas from solid components in the second re separate the action zone. Furthermore, the known loop re actuator an uneven distribution of the monomers or around put on polymers.  

A loop reactor is known from US Pat. No. 6,144,897 is used for suspension polymerization. The loop Reactor is assigned a temperature control, which the Reak tion temperature in a certain temperature range. A kalori is used to calculate the reaction rate cal heat balance used. For the circulation of the used A pump is provided with a fixed component Speed is operated.

The object of the present invention is therefore a Vorrich device for polymerization in a loop reactor as white that a continuous polymerization process with a relatively high turnover or reaction rate speed and improved mixing of the used Components is realized.

To achieve this object, the invention has the features of claim 1.

The special advantage of the device according to the invention be is that a calorimetric evaluation with a relatively great accuracy takes place that is an optimal substance sales in the loop reactor. By a delay Low-maintenance and continuous measurement can be dangerous pro Process conditions are calculated in advance and through controlled intervention be prevented.

According to the invention, the temperature is regulated in the Loop reactor by means of a two-point control, so that a compact and efficient temperature control is created.

Further advantages of the invention result from the others Dependent claims.

An embodiment is described below with reference to the drawing gene explained in more detail.

Show it:

Fig. 1 is a schematic representation of a Schlaufenreak tors,

Fig. Peraturregelung 2 is a block diagram of a TEM according to the invention,

Fig. 3, a heat quantity / time diagram,

Fig. 4 is a turnover / time diagram and

Fig. 5 is a timing diagram of several state parameters.

A loop reactor 1 consists essentially of a ring line 2 into which a medium can be supplied or discharged via an inlet / outlet line 3 . In the Ringlei device 2 , a pump 4 is integrated, by means of which the medium can be continuously circulated.

For temperature control of the medium, the ring line 2 has a heat exchanger 6 on longitudinal sections 5 , which cools or heats up the medium in the ring line depending on the control.

The loop reactor 1 is preferably used for suspension polymerization of monomers, such as vinyl acetate. The medium consists of water with dissolved stabilizer and initially liquid monomer mixed with an initiator.

To ensure continuous chemical conversion, the pump 4 can be activated in a pulsating manner. the pump is preferably controlled periodically and intermittently, so that a constant and constant circulation is achieved and the formation of deposits is prevented by the shear flow. As a result, the solid particles are kept in suspension, so that the chemical implementation process is promoted.

Fig. 2 shows a block diagram of the device for controlling the loop reactor, in which a two-point regulator 7 acts on the heat exchanger 6 via a thermostat 8 . An input signal T _Soll , which is set to, for example, 50 ° Celsius, is present at an input of the two-point controller 7 . At another input of the two-point controller 7 there is an input signal T _Ist , which represents the _reactor temperature T _reactor . For this purpose, a temperature sensor is introduced in the ring line 2 of the loop reactor 1 , which measures the current reactor temperature T _reactor and forwards a corresponding electrical signal to a PID controller 9 . The PID controller 9 is matched to the controlled system and brings about a rapid regulation of the reactor temperature T _reactor to the predetermined target temperature T _target , whereby unstable states of the system are reliably avoided.

The two-point controller periodically generates switching signals ON and OFF, the length of which depends on the additional heat development in the reactor 1 . As better ersicht of FIG. 5 is Lich, shortens the switching signal as soon as one generated in the reactor 1, reaction heat quantity Q _R ei nem to time t _1, is present. In this case, the heating time t _H shortens or the cooling time t _{K increases} . During the heating time t _H, the thermostat 8 acts on the heat exchanger 6 in the sense that it supplies a quantity of heat Q _to the loop reactor 1 . During the cooling time t _K , no heat is supplied to the loop reactor 1 via the heat exchanger 6 .

The two-point controller 7 and the PID controller 9 are part of a control circuit R. The thermostat 8 serves as a setting unit which acts on the heat exchanger 6 in the sense of a heat supply Q _to and heat dissipation Q _from .

As can be seen from FIG. 5, the shortening of the heating time t _{H in} response to the increase in the heat of reaction Q _R released in the system enables the reactor temperature T _R to remain within a tolerance band of +/- 0.075 ° Celsius and thus no undesirably high deviations from the target value T _target .

To control the monomer supply, a metering unit D is provided, by means of which a predetermined amount m of a monomer can be supplied to the ring line 2 . The given quantity m results from a calculation in a computing unit C, in which a value for the reaction speed in the loop reactor 1 is determined from the proportional condition t _k / (t _k + t _H ) ~ Q _R , which is proportional to the reaction heat quantity Q _R. On the basis of a corresponding table stored in the computing unit, an amount of monomer (mass) can be determined which is fed to the ring line.

To determine the heating time t _H and cooling time t _K , a time detection unit Z is provided, at the input of which the switching signals of the two-point controller 7 can be applied. From this, the times t _H , t _K can then be recorded and fed to the computing unit C. The computing unit C can be designed as a personal computer. The period T = t _H + t _K is in a range of two minutes.

A calorimetric evaluation of the reaction in a pilot plant or production reactor is suitable because the great accuracy and the possibility of delay low-maintenance, continuous measurement to control the Re actuator. Dangerous conditions can be calculated in advance and appropriate times for intervention in the process when using dosing and temperature control strategies Find.

The developed calorimeter allows one of the warmth transfer from the reaction medium to the heat transfer medium in the re independent calorific evaluation.

The on-line measured values can be obtained from a connected Com computer recorded and used for regulation.

Due to the heat balance, which also the jacket cycle is a low inertia and accurate measurement of the Heat flow and the heat transfer value even with strong Viscosity increase of the reaction mass possible.

The calorimeter belongs to the group of isothermal calorimes ter (more precisely: heat balance calorimeter). It owns which gave way to the investigation of polyreactions are.

The reactor jacket is encased in a coolant circuit tet. This circuit is connected to a cooling or heating device tion coupled, which is a low-inertia control of the reac Gate temperature allowed.

The coolant flow is constant (5 l / min).  

The reactor and coolant circuit are for thermal Insulation with insulation material (Armaflex®) and aluminum foil wraps.

By integrating the jacket cycle into the heat balance a calorimetric evaluation is possible, based on the heat passage between reaction medium and coolant in the man telraum is independent.

The calorimeter was calibrated at constant flow speed of the reactor medium. With the good achieved The reactor temperature (+ -0.075 ° C) could be kept constant over the Heating times of the thermostat on the heat development and thus with known enthalpy of polymerization also on the Sales of the reaction can be closed. The thermostat (DMT from Haake), which could be operated as a Kryomat, turned off at intervals of about 2 minutes and on.

The heating time is t _H and the time in which the heating of the thermostat was switched off is the cooling time t _K. There is a linear relationship between the relative cooling time t _K / (t _K + t _H ) and the heat development in the reactor. The calorimeter could be calibrated by means of defined heat emission via built-in heating cartridges to the reactor medium and measurement of the resulting relative cooling times.

The batchwise suspension polymerizations were carried out with the following recipe at a reactor temperature T _reactor of 50 ° C.
1177.6 g vinyl acetate
20.77 g AIBN (azobisisobutyronitrile)
5400 g dist. water
5.65 g Mowiol 18/88

It was in the absence of oxygen by means of nitrogen gas solution worked.

A sales / time curve obtained is shown in Figure x provides.

Medium is continuously supplied via the feed line 3 for the polymerization. During a first time segment, heat Q must be supplied continuously to the system, see FIG. 3. After this first period, which comprises approximately a third of the total running time, the heat supply can be drastically reduced. Now the turnover U, which increased asymptotically in the first section, only increases slowly. Nonetheless, sales after a total runtime of 6 hours are more than 99 percent by weight of the medium.

Claims (4)

1.Device for controlling a polymerization, in particular a suspension polymerization, in a loop reactor ( 1 ) with an airtight ring line ( 2 ), a supply and discharge line and a pump ( 4 ) for circulating the medium in the ring line, the pulsie rend can be controlled, heat can be supplied to or removed from the loop reactor via a heat exchanger ( 6 ) and a coolant circuit coupled to the heat exchanger, and a periodically switching two-point controller ( 7 ) is provided to adjust the reactor temperature (T _reactor ) to one constant nominal value (T _soll) to regulate the duration of toddlers of one switching state of the Zweipunktreg a heating time (t _H), while the gate of the reac heat is supplied, further comprising a time detecting unit (Z) is provided, the heating time on on the basis of the duration of this one switching signal and forwards it to a computing unit (C), which, depending on the heating time detected, calculates a switching signal corresponding to the reaction rate of the chemical reaction, which is fed to a metering unit (D) which, depending on this switching signal, supplies a quantity of substance to the reactor. 2. Device according to claim 1, characterized in that the actual temperature value (T _actual ) can be determined by means of a PID controller ( 9 ), at the input of which the reactor temperature (T _R ) measured in the ring line ( 2 ) is present. 3. Device according to claim 1 or 2, characterized in that the two-point controller ( 7 ) is designed as a Schmitt trigger with a hysteresis function. 4. Use of the device according to one of claims 1 to 3 as a computer-controlled laboratory or company reactor.