Batch Reactor Design for Polystyrene Production

Abstract

In this paper, batch reactor design is described. Suspension polymerization reaction is themost preferred element for EPS production. In suspension polymerization, the particle sizeobtained from the reaction is very important. Parameters such as mixing speed, stirrer shape,reactor size and reactor geometry, reaction temperature and pressure affect the particle size.Furthermore, since suspension reaction is an exothermic reaction, temperature and pressureincrease during the reaction. This sitution negatively affects the reaction. Therefore, thereaction should be carried out at constant pressure and temperature. A batch reactor design hasbeen made considering this sitution and the necessary parameters.

Full text

Batch Reactor Design for Polystyrene Production
Corresponding autor aNihayet Koçyiğit, bNecati Yalçın
aBatman Üniversitesi, KimyaTek Meslek Yük. Okulu,72060 Batman/Türkiye
E-mail: nihayet.kocyigit@batman.edu.tr, Tel: +90 488 2132782
bGazi Üniversitesi, Teknoloji Fakültesi, Malzeme Müh. Teknik Okullar, Beşevler Ankara/Türkiye,
E-mail: neyalcın@gazi.edu.tr, Tel:+90 312 2028808
Abstract
In this paper, batch reactor design is described. Suspension polymerization reaction is the
most preferred element for EPS production. In suspension polymerization, the particle size
obtained from the reaction is very important. Parameters such as mixing speed, stirrer shape,
reactor size and reactor geometry, reaction temperature and pressure affect the particle size.
Furthermore, since suspension reaction is an exothermic reaction, temperature and pressure
increase during the reaction. This sitution negatively affects the reaction. Therefore, the
reaction should be carried out at constant pressure and temperature. A batch reactor design has
been made considering this sitution and the necessary parameters.
Key words: Expandable Polystyrene, Polystyrene, Reactor Design, Polymerization
1.introduction
The expandable polystyrene (EPS) is one of the industrial polymer foams and is also known
as Strofoil in our country. EPS is increasingly becoming attractive in practical use day by day
due to its lightness and economy in the plastics sector [1]. Isolation and packaging are the
most preferred areas where it is utilized, but it is also used in automotive industry, agriculture
sector, marine sector, visual arts and advertising sector, health sector, refrigeration sector. EPS
is produced from porous polystyrene (PS) granules by a series of processes such as aging,
molding, cooling, re-aging. PS granules used in EPS production are produced from styrene
(C8H8) monomers by polymerisation reactions. The size distribution of polystyrene (PS) beads
used in EPS production is one of the significant parameters determining the quality of the
product [2]. Therefore, in order for the size distribution to be uniform and all the beads to be
the same size, the parameters such as the suspending agents, the reaction initiator, the mixing

speed and the mixer shape, the reaction temperature and the reaction pressure as well as the
parameters such as the reactor size and the geometry must be selected accurately and the
reactor design must be made correctly. If these parameters are not set correctly, PS beads of
different sizes or unwanted size are obtained [3]. Therefore, before starting work to make the
correct reactor design, we must seek answers for the following questions [3];
What kind of reaction should be done?
Which type and size of reactor is required according to reaction type?
What are the reaction conditions (temperature, pressure, viscosity, density, etc.)?
Is the reaction endothermic or exothermic? What should be provided for the heating?
How must cooling be provided?
If it is necessary to heat and then cool before the reaction takes place, can an
arrangement be established to provide both heating and cooling?
What are the physical states (solid, liquid or gas) and properties (porosity, particle
size) of the substances used in the reactor?
Is the reaction medium homogeneous or heterogeneous?
Do we need to add catalyst to the reaction?
Is the process continuous or not?
Do we need to return to reach the desired turnaround?
Are the used chemicals corrosive?
How much does the reactor cost?
Going through the literature on the reactor, we can come across with F. Langner, HU Moritz,
KH Reichert, Masocha Tanaka et al.. They found that mixing speed, particle size affect
distribution of polystyrene particles with respect to reactor diameter, the effect on the height
and size of reactors allowing the reactors to take into account the polymerisation parameters
for EPS production, Vakili et al. investigated the turbulent flow field in an industrial
suspension polymerization reactor. Aziz et al. performed a temperature control on a control
engineering criterion problem of a polymerization reactor controlled by Chylla and friend
Chylla and Haase, which determined the optimum operating conditions in the mixing reactors.
We designed a 5 liter cut off reactor from stainless steel and determined the optimum reaction
parameters.
2.Reactor Design
Different types of reactors are used in industry for different purposes.These reactors are
produced in different sizes and geometries taking into account the characteristics and reaction

conditions of the product to be produced.The classification of these reactors used in industry
is as in Figure 1.
Figure1: Reactors Classification
Figure1: Classification of Reactors
Although there are many reactors for different purposes in the industry, the batch reactor was
decided to be the most suitable reactor at the end of the literature research, considering the
parameters of the suspension polymerization reaction and the properties of the product to be
produced because batch reactors are used in a wide range of applications such as product
mixing, chemical reactions, distillation, crystallization, liquid-liquid extraction,
polymerization, etc., which are widely used in industrial applications. A typical batch reactor
structure includes a tank, mixer, internal heating and cooling systems. These containers can
range from 15000 liters to less than 1 liter. They can be produced from stainless steel, glass
and composite materials. In the batch reactor, excellent homogeneity occurs throughout the
reaction. The process stops when the desired conversion rate is reached. In small-scale pilot
plants, batch reactors can be used to obtain preliminary information. Besides, batch reactors
are preferred in production of new products in small quantities, which are developed with
higher efficiency. Industrial reactors are widely used in pharmaceutical, biochemical and paint
industries [4-6].
Classication of
Reactors
Catalyst
Based
Classicatio
n
Sized
Based
Classicati
on
Used Based
Classicatio
n
Phased
Based
Classicatio
n
Operation
Based
Classicatio
n
Simple
Phase
Multi
Phase
Homojen
Reactors
Heterojen
Reactors
Polymerizatio
n
Reactors
Biological
Reactors
Electrochemic
al Reactors
Laboratory
Reactors
CTJ Reactors
GL Reactors
SA Reactors
Agitated Tanks
Batch
Reactor
Semi-batch
Reactor
Continuous
Reactor

Figure 2: Chemical batch reactor [4].
Batch reactors have advantages such as easy installation, small cost, comfortable application
conditions. The biggest disadvantage of batch reactors is the operating cost. Loss of time in the process
of evacuating the reactor and cleaning the reactor before putting the product back are two major
operating cost problems. It is also necessary to heat up to a certain temperature in the event of a
reaction. When the reaction is completed, the product must be cooled. Significant energy and time are
needed to provide them. Another disadvantage is the difficulty in controlling heat transfer and
ensuring continuity of product quality. Chemical reaction rate usually increases with increase in
temperature. The mechanical stirrers attempt to reduce the occurrence of film resistance in the
container walls by providing mass transfer with heat flow propulsion. In addition, the stirrer also
prevents small solid particles from becoming agglomerated. The purpose of mixing is to make the
substances come into contact with mixture in a homogeneous way. Temperature, viscosity, physical
states and density of the products and pressure are the factors affecting the operation of the reactor [7].
As the batch reactor, it was designed because it was a pilot work in laboratory conditions. The reactor
was from stainless steel.
Stirring speed: The size of drops was significantly affected by the agitation speed. If
the mixing speed is high, small beads are obtained, but if the mixing speed is low,
there is accumulation between the beads.Therefore, the speed of the mixer must be set
correctly. The mixer types that can be used in the reactors are shown in Figure 3.

Mixing Peddler Stirrer Axial flow Impeller Ribbon Stirrer Dispersing Homogenizing
Stirrer
Anchor type Stirrer Overhead Stirrer Radikal Flow Impeller 3-Blade Impeller
Turbine Stirrer
S
piral Flow Impeller Radikal Flow Impeller Overhead Stirrer
Figure 3: Figure 3: Stirrer types used in reactors [8]
The most suitable stirrer for the batch reactor that will carry out the polymerization reaction is
spiral propeller bladed (Fig.4)

Figure 4: Designed Impeller[9]
 Temperature control: The suspension polymerization reaction which will take place in the
reactor is an exothermic reaction in which temperature control is very important [9,10]. The
suspension polymerization will be carried out at 70 oC. However, because the reaction is
exothermic and the reactor is heated, the temperature does not remain constant at 70 oC; thus it can
rise up to 100 oC . This situation causes the resulting product to deteriorate. In order to control the
temperature of the reaction medium, the jacket is made for heating and cooling out of the reactor
tank. With the help of hot water inlet and cold water inlet and outlet, temperatures of the reaction
medium were kept constant at 70 oC. A thermometer was installed in the reactor cap to monitor the
temperature flactuations during the reaction.
Pressure control: The safety valve was installed for safety against pressure build up. A
thermometer and a barometer were fitted to the reactor lid so as to measure the temperature of the
reactor and see the pressure of the reactor, respectively. A safety valve was installed in the reactor
to prevent the reactor from explosion due to inside pressure rise. In addition, a barometer was
installed on the reactor cover to monitor the pressure during the reaction.
One of the biggest problems in the suspension reaction is clustering. In order to prevent
agglomeration of the beads, two wave breakers are placed in the reactor.
Figure 5: Wavebreakers in batch reactor
In some reactor designs, these components are mounted on a separate panel outside the reactor.In this
case, the reactor takes up more space and the reactor also cost is higher. All parts were placed on the

reactor lid to avoid this situation [11-17]. In view of all necessary parameters and literature research,
our produced the batch reactor is as in figure 5.
Barometer
Engine
Security valve
Thermometer
Agitator
Inside the Batch Reactor

Figure 6: Produced Batch Reactor
4. Conclusion
After determining the parameters required for the suspension polymerization and the design
of the batch reactor required for the pilot application, the reactor has been produced. In order
to check that the reactor is running, a small amount of water has been put into the reactor and
the reactor is operated. During operation, leakage has been detected at the point where the
mixer has been connected to the motor. In order to solve this problem, the connection point is
compressed. Apart from this problem, there is no problem in the reactor.The batch reactor
produced is ready for polymerization production.
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