Bulk polymerization of styrene

One of the few attempts to examine a polymerization reactor in periodic operation experimentally is the work of Spitz, Laurence and Chappelear (X6)who reported the influence of periodicity in the initiator feed to the bulk polymerization of styrene in a CSTR. To induce periodicity the initiator feed was pulsed on-and-off and the reactor output compared with steady-state operation with the same time-averaged initiator input. 

There is an interior optimum. For this particular numerical example, it occurs when 40% of the reactor volume is in the initial CSTR and 60% is in the downstream PFR. The model reaction is chemically unrealistic but illustrates behavior that can arise with real reactions. An excellent process for the bulk polymerization of styrene consists of a CSTR followed by a tubular post-reactor. The model reaction also demonstrates a phenomenon known as washout which is important in continuous cell culture. If kt is too small, a steady-state reaction cannot be sustained even with initial spiking of component B. A continuous fermentation process will have a maximum flow rate beyond which the initial inoculum of cells will be washed out of the system. At lower flow rates, the cells reproduce fast enough to achieve and hold a steady state. 

FIGURE 13.7 Performance of a laminar flow, tubular reactor for the bulk polymerization of styrene Tin = 35°C and F = 1 h. (a) Stability regions, (b) Monomer-conversion within the stable region. 

Bulk Polymerization of Styrene with 2,2 -Azobisisobutyronitrile in a Dilatometer... 

The bulk polymerization of styrene to give a narrow molecular weight distribution has appeared in a U.S. patent [45]. The polydispersity reported was... 

Several references to the bulk polymerization of styrene are worth consulting [46-50], Most consider a continuous bulk polymerization apparatus with some using spraying of the monomer through a nozzle. The controlled evaporation of unreacted monomer is one method of removing the heat of reaction. 

Example 5.7 A CSTR is commonly used for the bulk polymerization of styrene. Assume a mean residence time of 2h, cold monomer feed (300 K), adiabatic operation (UAext = 0), and a pseudo-first-order reaction with rate constant... 

Hamielec, Hodgins, and Tebbins (25) justified and used the PSSA with the solution and bulk polymerization of styrene. They calculated that the steady state was approached in a few thousandths of a second. Their equations for dead polymer were numerically integrated for 5000 species and, as previously mentioned, experimentally confirmed. 

As a sequel to the simple reactor model described above, two-zone cases for the bulk polymerization of styrene were also studied. Polymerizations in straight, empty tubes give rise to unfavorable temperature and velocity profiles which can lead to hydrodynamic or thermal instabilities. These instabilities may be avoided or postponed by manipulating the wall temperature. 

For the bulk polymerization of styrene using thermal initiation, the kinetic model of Hui and Hamielec (13) was used. The flow model (Harkness (1)) takes radial variations in temperature and concentration into account and the velocity profile was calculated at every axial point based on the radial viscosity at that point. The system equations were solved using the method of lines with a Gear routine for solving the resulting set of ordinary differential equations. 

Bylina et al. [105] have studied the bulk polymerization of styrene initiated by diacyl diperoxides... 

In Figure 1 are shown experimental conversion histories from bulk polymerization of styrene, methyl methacrylate, and vinyl acetate. It appears that with any of these monomers the rate of polymerization increases substantially during reaction, i.e. gel-effect is important in bulk polymerization of these monomers. The effect is particularly pronoimced with methyl methacrylate. 

Crystal polystyrene is produced by thermally initiated (Section 6.5.4) bulk polymerization of styrene at temperature of I20°C or more. (The term crystal refers to the optical clarity of products made from this polymer, which is not crystalline.) The rate of polymerization would decrease with increasing conversion and decreasing monomer concentration if the reaction were carried out at constant temperature. For this reason, the polymerization is performed at progressively increasing temperatures as the reaction mixture moves through a series of reactors. The exothermic heat of polymerization is useful here in raising the reaction temperature to about 250°C as the process nears completion. 

In the case of photo-initiated polymerizations bimodal distributions can occur as a result of concurrent free-radical and cationic growth, these intermediates not being in chemical equilibrium. This arises in the bulk polymerizations of styrene photo-initiated in the presence of tetracyanobenzene and also in the radiation-induced polymerization of alkyl-substituted styrenes.In the former system the higher molecular weight fraction is attributed to a cationic... 

Bulk polymerization of styrene using a TEMPO-based unimolecular initiator (Scheme 4)... 

Fig. 3.4 Experimental apparatus for bulk polymerization of styrene using TEMPO-based unimolecular initiators.

For the bulk polymerization of styrene, high-temperature initiators such as... 

In the bulk polymerization of styrene by ultraviolet radiation, the initial polymerization rate and degree of polymerization are 1.3x10 mol/L-s and 260, respectively, at 30°C. What will be the corresponding values for polymerization at 80°C The activation energies for propagation and termination of polystyryl radicals are 26 and 8.0 W/mol. What assumption, if any, is made in this calculation ... 

Problem 7.16 Bulk polymerization of styrene in the presence of 1 g/L of AIBN initiator at 60°C gave a measured polymerization rate of 5.92 mol/L-s. Predict the rate of copolymerization at 60°C of a mixture of styrene (Mi) and methyl methacrylate (M2) with 0.579 mole fraction styrene and the same initial concentration of the initiator as in the homopolymerization case. Compare the rates predicted from chemical control, diffusion control, and combined models with the experimental value of 4.8x10 mol/L-s [25]. Use relevant kp and kt values for homopolymerization from Table 6.7 and assume 0 = 15. [Other data ri = 0.52, T2 = 0.46 monomer density = 0.90 g/cm .]... 

In the experiments of Hamielec et al.8S) and of Soviet researchers86 87 the method of solving an inverse kinetic problem has been used to find the dependence of values of effective constants on conversion in the thermo-initiated bulk polymerization of styrene. 

Isothermal bulk polymerization of styrene is satisfactorily described by the model up to the limiting concentrations in the 100-200 °C temperature range. The model was later extended to cover the 200—230 °C temperature range without additional accounting for the reactions of polymer degradation88. ... 

In the study113) an attempt was made to model the whole process of thermal bulk copolymerization of styrene with polybutadiene up to high degrees of conversion. The calculations were based on the previously developed model of thermal bulk polymerization of styrene and supplemented with the reactions of chain transfer to rubber. 

A. Butakov, one of the authors of the study on which the above theoretical calculations are based, published in the same collection of articles a new investigation on the benzoylperoxide initiated bulk polymerization of styrene in laminar flow144). 

Bulk polymerization of styrene, initiated by photolysis of p-acetylbenzylidenetriphenylarsonium ylid has recently been shown to proceed by a free radical pathway [8a] the same initiator is useful for polymerization of methyl methacrylate [8b]. 

There is an interior optimum. In this numerical example it occurs when 40% of the reactor volume is in the initial CSTR and 60% is in the downstream PFR. The model reaction is chemically unrealistic but illustrates behavior that can arise with real reactions. An excellent process for the bulk polymerization of styrene consists of a CSTR followed by a tubular postreactor. 

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