Batch reactors styrene polymerization

Continuous stirred-tank reactors can behave very differently from batch reactors with regard to the number of particles formed and polymerization rate. These differences are probably most extreme for styrene, a monomer which closely follows Smith-Ewart Case 2 kinetics. Rate and number of particles in a batch reactor follows the relationship expressed by Equation 13. 

The rate of polymerization with styrene-type monomers is directly proportional to the number of particles formed. In batch reactors most of the particles are nucleated early in the reaction and the number formed depends on the emulsifier available to stabilize these small particles. In a CSTR operating at steady-state the rate of nucleation of new particles depends on the concentration of free emulsifier, i.e. the emulsifier not adsorbed on other surfaces. Since the average particle size in a CSTR is larger than the average size at the end of the batch nucleation period, fewer particles are formed in a CSTR than if the same recipe were used in a batch reactor. Since rate is proportional to the number of particles for styrene-type monomers, the rate per unit volume in a CSTR will be less than the interval-two rate in a batch reactor. In fact, the maximum CSTR rate will be about 60 to 70 percent the batch rate for such monomers. Monomers for which the rate is not as strongly dependent on the number of particles will display less of a difference between batch and continuous reactors. Also, continuous reactors with a particle seed in the feed may be capable of higher rates. 

Peaking and Non-isothermal Polymerizations. Biesenberger a (3) have studied the theory of "thermal ignition" applied to chain addition polymerization and worked out computational and experimental cases for batch styrene polymerization with various catalysts. They define thermal ignition as the condition where the reaction temperature increases rapidly with time and the rate of increase in temperature also increases with time (concave upward curve). Their theory, computations, and experiments were for well stirred batch reactors with constant heat transfer coefficients. Their work is of interest for understanding the boundaries of stability for abnormal situations like catalyst mischarge or control malfunctions. In practice, however, the criterion for stability in low conversion... 

In this work, the characteristic "living" polymer phenomenon was utilized by preparing a seed polymer in a batch reactor. The seed polymer and styrene were then fed to a constant flow stirred tank reactor. This procedure allowed use of the lumped parameter rate expression given by Equations (5) through (8) to describe the polymerization reaction, and eliminated complications involved in describing simultaneous initiation and propagation reactions. 

This paper presents the physical mechanism and the structure of a comprehensive dynamic Emulsion Polymerization Model (EPM). EPM combines the theory of coagulative nucleation of homogeneously nucleated precursors with detailed species material and energy balances to calculate the time evolution of the concentration, size, and colloidal characteristics of latex particles, the monomer conversions, the copolymer composition, and molecular weight in an emulsion system. The capabilities of EPM are demonstrated by comparisons of its predictions with experimental data from the literature covering styrene and styrene/methyl methacrylate polymerizations. EPM can successfully simulate continuous and batch reactors over a wide range of initiator and added surfactant concentrations. 

In this work, a comprehensive kinetic model, suitable for simulation of inilticomponent aiulsion polymerization reactors, is presented A well-mixed, isothermal, batch reactor is considered with illustrative purposes. Typical model outputs are PSD, monomer conversion, multivariate distritution of the i lymer particles in terms of numtoer and type of contained active Chains, and pwlymer ccmposition. Model predictions are compared with experimental data for the ternary system acrylonitrile-styrene-methyl methacrylate. 

Emulsion Polymerization in a CSTR. Emulsion polymerization is usually carried out isothermally in batch or continuous stirred tank reactors. Temperature control is much easier than for bulk or solution polymerization because the small (. 5 Jim) polymer particles, which are the locus of reaction, are suspended in a continuous aqueous medium as shown in Figure 5. This complex, multiphase reactor also shows multiple steady states under isothermal conditions. Gerrens and coworkers at BASF seem to be the first to report these phenomena both computationally and experimentally. Figure 6 (taken from ref. (253)) plots the autocatalytic behavior of the reaction rate for styrene polymerization vs. monomer conversion in the reactor. The intersection... 

Polymerization conditions batch reactor initially containing toluene with 20 mL of styrene at 50 C, MAO catilyst ratio (atomic) = 300. 

Tlie rubber latex is usually produced in batch reactors. The rubber can be polybutadiene [9003-17-2] or a copolymer of 1,3-butadiene [106-99-0] and either acrylonitrile [107-13-1] or styrene [100-42-5]. The latex normally has a polymer content of approximately 30 to 50% most of the remainder is water. In addition to the monomers, the polymerization ingredients include an emulsifier, a polymerization initiator, and usually a chain-transfer agent for molecular weight control. 

Bead Polymerization Bulk reaction proceeds in independent droplets of 10 to 1,000 pm diameter suspended in water or other medium and insulated from each other by some colloid. A typical suspending agent is polyvinyl alcohol dissolved in water. The polymerization can be done to high conversion. Temperature control is easy because of the moderating thermal effect of the water and its low viscosity. The suspensions sometimes are unstable and agitation may be critical. Only batch reactors appear to be in industrial use polyvinyl acetate in methanol, copolymers of acrylates and methacrylates, polyacrylonitrile in aqueous ZnCb solution, and others. Bead polymerization of styrene takes 8 to 12 h. 

Although theoretical models seem to be quite adequate for styrene emulsion polymerization in either batch reactors or CSTR s, such is not the case with other monomers like vinyl acetate, methyl acrylate, methyl methacrylate, vinyl chloride, etc. One of the early papers to discuss scane of the important mechanisms involved with these other moncaners was written by Priest ( ). He studied the emulsion polymerization of vinyl acetate and identified most of the key mechanisms involved. Priest s paper has been largely overlooked, however, perhaps because of the success of the Smith-Ewart approach to styrene. 

Polystyrene can be easily prepared by emulsion or suspension techniques. Harkins (1 ), Smith and Ewart(2) and Garden ( ) have described the mechanisms of emulsTon polymerization in batch reactors, and the results have been extended to a series of continuous stirred tank reactors (CSTR)( o Much information on continuous emulsion reactors Ts documented in the patent literature, with such innovations as use of a seed latex (5), use of pulsatile flow to reduce plugging of the tube ( ), and turbulent flow to reduce plugging (7 ). Feldon (8) discusses the tubular polymerization of SBR rubber wTth laminar flow (at Reynolds numbers of 660). There have been recent studies on continuous stirred tank reactors utilizing Smith-Ewart kinetics in a single CSTR ( ) as well as predictions of particle size distribution (10). Continuous tubular reactors have been examined for non-polymeric reactions (1 1 ) and polymeric reactions (12.1 31 The objective of this study was to develop a model for the continuous emulsion polymerization of styrene in a tubular reactor, and to verify the model with experimental data. 

The mechanism of particle formation at submicellar surfactant concentrations was established several years ago. New insight was gained into how the structure of surfactants influences the outcome of the reaction. The gap between suspension and emulsion polymerization was bridged. The mode of popularly used redox catalysts was clarified, and completely novel catalyst systems were developed. For non-styrene-like monomers, such as vinyl chloride and vinyl acetate, the kinetic picture was elucidated. Advances were made in determining the mechanism of copolymerization, in particular the effects of water-soluble monomers and of difunctional monomers. The reaction mechanism in flow-through reactors became as well understood as in batch reactors. Computer techniques clarified complex mechanisms. The study of emulsion polymerization in nonaqueous media opened new vistas. 

The major problem in temperature control in bulk and solution batch chain-growth reactions is the large increase in viscosity of the reaction medium with conversion. The viscosity of styrene mixtures at I50°C will have increased about 1000-fold, for example, when 40 wt % of the monomer has polymerized. The heat transfer to a jacket in a vessel varies approximately inversely with the one-third power of the viscosity. (The exact dependence depends also on the nature of the agitator and the speed of fluid flow.) This suggests that the heat transfer efficiency in a jacketed batch reactor can be expected to decrease by about 40% for every 10% increase in polystyrene conversion between 0 and 40%. 

Determine the molecular weight distribution for the formation of polystyrene for an initiiUor concentralwn of 10 molar and a monomer concentration of 3 molar. What are M , M , and the polydispersity, D, after 40 hrs How would the change if chain transfer were neglected The polymerization of styrene is carried out in a batch reactor. Plot the mole fraction of polystyrene of chain length 10 as a function of time for an initial concentration of 3M and 0.0 IM of monomer an initiator respectively, The solvent concentration is 10 molar,... 

Yoshida et al. [36] have studied the effect of fast mixing of miscible systems by measuring the selectivity towards mono-alkylation in the Friedel-Crafts alkylation of aromatics. They observed a 20-fold increase in the relative selectivity of the mono-alkylate over the di-alkylated system when using a micromixer instead of a conventional batch reactor. In the cycloaddition of the N-acyHminium ion to styrene [36], 50-80% of the cycloadduct is typically lost towards polymeric byproducts. Using an interdigital micromixer, the yield to the cycloadduct increased from 20-50% to almost 80%. 

The simple batch reactor for homogeneous reactions is the most common type. From this kind of reactor, many kinetic data have been obtained. AU the reactants are charged in at the beginning of the reaction, with no mass transfer occurring until the reaction is complete. Examples of batch reactions are the ammonolysis of nitrochlorobenzenes, hydrolysis of esters, and polymerization of butadiene and styrene in aqueous suspension. These will be treated in more detail in later chapters. 

Example 10.7 Calculate the time required for 10% polymerization of pure styrene at 60°C with benzoyl peroxide as the initiator in a batch reactor. Asstrme that the irritiator concentration rerrrairrs constant. Data ... 

It has been proposed that to avoid possible health problems, the polystyrene used for drinking cups must contain less than 1% monomer. Polystyrene was prepared at 100°C by the thermal polymerization of 10 M styrene in toluene in a batch reactor. The shift operator stopped the reaction after 2.5 h. Is the product from this operation suitable for producing drinking cups without further purification ... 

The precipitation polymerization takes place in a batch reactor. Azoisobutyronitrile is used as the radical initiator, and styrene and divinylbenzene were chosen as monomers. A solution of the monomers in a long-chain hydrocarbon liquid is prepared [23]. After a clear solution has formed the megaporous glass Raschig rings are immersed in the solution, vacuum was used to remove the air from the pores, and the polymerization was initiated by heating. Fig. 8.7 shows the course of the precipitation polymerization in the pore volume of the carrier. 

RAFT polymerization in miniemulsion has been carried out in a tubular reactor. Emulsion is prepared in a batch reactor using sodium dodecyl sulfate (SDS, surfactant), Triton X-405 (surfactant), styrene (monomer), hexadecane... 

NMP of styrene and /i-butyl acrylate at 140°C has been performed in a continuous-flow microtubular reactor (Fig. 27) consisting of a stainless steel tube reactor and a back-pressure cartridge [212]. In the case of styrene polymerization, there is no difference between batch reactors and flow microreactors. However, for M-butyl acrylate, a better control of the polymerization has been observed in the flow microreactor (A/w/A/ of 1-80 for the batch reactor and 1.44 for the flow microreactor). Moreover, consumption of the monomer is much faster using the flow microreactor (Fig. 28). 

NMP of styrene in a miniemulsion can be also performed in a tubular reactor [213]. In the first step, a macroinitiator is prepared by bulk polymerization in a batch reactor and the subsequent miniemulsion polymerizatiOTi is carried out in a tubular reactor. The polymerization kinetics in the tubular reactor are similar to those in a batch reactor. It is also noteworthy that both preparatimi of a macroinitiator and a miniemulsion polymerization can be achieved in a crmtinuous tubular reactor to obtain polystyrene-h/ock-poly(butyl acrylate) diblock and polystyrene-h/ocA -poly (butyl acrylate)-h/ocA -polystyrene triblock copolymers [214],... 

An optimal predictive controller was developed and implemented to allow for maximization of monomer conversion and minimization of batch times in a styrene emulsion polymerization reactor, using calorimetric measiuements for observation and manipulation of monomer feed rates for attainment of control objectives [31]. Increase of 13% in monomer conversion and reduction of 28% in batch time were reported. On-line reoptimization of the reference temperature trajectories was performed to allow for removal of heater disturbances in batch bulk MMA polymerizations [64]. Temperature trajectories were manipulated to minimize the batch time, while keeping the final conversion and molecular weight averages at desired levels. A reoptimization procediue was implemented to remove disturbances caused by the presence of unknown amounts of inhibitors in the feed charge [196]. In this case, temperatiue trajectories were manipulated to allow for attainment of specified monomer conversion and molecular weight averages in minimum time. 

For butyl acrylate (BA), the molecular weight distribution was found to be narrower than that for the batch reactor, as can be seen in Figure 12.5. The PDI for this polymer is then lower in the microreactor system (Table 12.1). The difference was smaller but still noticeable for benzyl methacrylate (BMA) and methyl methacrylate (MMA) and almost zero for vinyl benzoate (VBz) and styrene (St) (Table 12.2). The authors claimed that the observed results are directly related to the superior heat transfer ability of the microtube reactor. The more exothermic the polymerization reaction. 

Figure 2.3.5 shows the conversion-time data for the batch reactor polymerization of styrene in ether and acetone under FRRPP conditions (80°C). The half-life of the V501 initiator used in the ether system is about 130 min (Wako Chemicals, 1987). It is evident that there is a sharp rise in conversion at the beginning, followed by a period of reduced conversion rate. The onset of reduced conversion rate occurs at around 25%. 

Block Copolymerization. A polymerization with long chain lives can be used to make block copolsrmers (qv). An important commercial example is styrene/butadiene blocks produced by anionic polymerization (qv). A solution polymerization is done in a batch reactor, starting with one of the two monomers. That monomer is reacted to completion and the second monomer is added while the catalytic sites on the chains remain active. This produces a block copolymer of the AB form. Early addition of the second monomer produces a tapered block. If the second monomer is reacted to completion and replaced by the first monomer, an ABA triblock is obtained. This process is not easily converted to continuous operation because polsrmerizations inside tubes rarely approach the piston-flow environment that is needed to react one monomer to completion before adding the second monomer. Designs using static mixers (also known as motionless mixers) are a possibility. 

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