Polymerization batch systems

Suppose that the reactivity of the A and B endgroups is independent of the chains to which they are attached. This is a form of the equal reactivity assumption that is needed for almost all analytical solutions to polymer kinetic problems. If it is satisfied, we can ignore the details of the polymerization and just concentrate on the disappearance of the endgroups. For a batch system. 

Theoretical calculations were also conducted on the influence of/-functional initiators on DB in SCVCP [72]. In the semi-batch system, DB is only sHghtly affected by the presence of polyinitiator and is mostly governed by the comonomer content. The calculations are also applied to polymerizations from surface-bound initiators (see later). 

This was derived assuming uniform concentration because good mixing is important for this relationship to hold. It also assumes a constant temperature. Both these assumptions are only approached in most batch systems. Further, stirring becomes more difficult as conversion increases so that both control of localized temperature and concentration become more difficult. In reality, this relationship holds for only a few percentage points of conversion. Overall, temperature is a major concern for vinyl polymerizations because they are relatively quite exothermic. This is particularly important for bulk polymerizations. This, coupled with the general rapid increase in viscosity, leads to the Trommsdorff-like effects. 

The available data from emulsion polymerization systems have been obtained almost exclusively through manual, off-line analysis of monomer conversion, emulsifier concentration, particle size, molecular weight, etc. For batch systems this results in a large expenditure of time in order to sample with sufficient frequency to accurately observe the system kinetics. In continuous systems a large number of samples are required to observe interesting system dynamics such as multiple steady states or limit cycles. In addition, feedback control of any process variable other than temperature or pressure is impossible without specialized on-line sensors. This note describes the initial stages of development of two such sensors, (one for the monitoring of reactor conversion and the other for the continuous measurement of surface tension), and their implementation as part of a computer data acquisition system for the emulsion polymerization of methyl methacrylate. 

Yoshida and coworkers also developed a microreaction system for cation pool-initiated polymerization [62]. Significant control of the molecular weight distribution (Mw/Mn) was achieved when N-acyliminium ion-initiated polymerization of butyl vinyl ether was carried out in a microflow system (an IMM micromixer and a microtube reactor). Initiator and monomer were mixed using a micromixer, which was connected to a microtube reactor for the propagation step. The polymerization reaction was quenched by an amine in a second micromixer. The tighter molecular weight distribution (Mw/M = 1.14) in the microflow system compared with that of the batch system (Mw/M > 2) was attributed to the very rapid mixing and precise control of the polymerization temperature in the microflow system. 

Polymer-supported TADDOL-Ti catalyst 79 prepared by chemical modification was poorly active in the Diels-Alder reaction of 3-crotonoyloxazolidinone with cyclo-pentadiene (Eq. 24) whereas polymeric TADDOL-Ti 81 prepared by copolymerization of TADDOL monomer 80 with styrene and divinylbenzene had high activity similar to that of the soluble catalyst. In the presence of 0.2 equiv. 81 (R = H, Aryl = 2-naphthyl) the Diels-Alder adduct was obtained in 92 % yield with an endolexo ratio of 87 13. The enantioseleetivity of the endo product was 56 % ee. The stability and recyclability of the catalyst were tested in a batch system. The degree of conversion, the endolexo selectivity, and the enantioseleetivity hardly changed even after nine runs. Similar polymer-supported Ti-TADDOLate 82 was prepared by the chemical modification method [99]. Although this polymer efficiently catalyzed the same reaction to give the (2R,2S) adduct as a main product, asymmetric induction was less than that obtained by use of a with similar homogeneous species. 

Experiments using no emulsifier were conducted in tbe same stainless steel autoclave equipment described above (Machi et nf.. 1975). Stable latices were obtained, believed to be achieved by hydroxyl end groups and adsorbed hydroxyl ions. As with a number of the experiments with emulsifiers the polyethylene had a considerable cross-linked gel content. Finally, the same group of workers studied tbe radiation-induced emulsion polymerization of ethylene in a flow system (Kodama et al, 1974). Both potassium inyristate and ammonium perfluorooctanoate were used as emulsifiers. At longer residence times (above 0.2 hr) the rate of polymerization was essentially constant. As with the batch system it was assumed that the number of particles remained constant. In this region the rate was found to be proportional to tbe 0.3 power of the potassium myristate concentration and the 0.5 power of the dose rate, not too different from the batch systems. The kinetics was developed and estimates of tbe propagation rate constants obtained. Despite other similarities between the two systems, these were quite different, however, from those extracted from the batch experiment. 

The state estimation technique can also be incorporated into the design of optimal batch polymerization control system. For example, a batch reaction time is divided into several control intervals, and the optimal control trajectory is updated online using the molecular weight estimates generated by a model/state state estimator. Of course, if batch reaction time is short, such feedback control of polymer properties would be practically difficult to implement. Nevertheless, the online stochastic estimation techniques and the model predictive control techniques offer promising new directions for the improved control of batch polymerization reactors. 

For example, borane reduction of butyrophenone using the polymeric catalyst 24 gave the alcohol in quantitative yield with 97% ee [71 ] (Scheme 15). Since the polymeric catalyst is crosslinked and insoluble in the organic solvent used, this catalyst can be used not only in a batch system, but also in a continuous flow system, in which the ketone is converted into the enantio-enriched alkoxybo-rane by passing it through a column filled with the polymeric catalyst. 

The example is taken from a polymerization batch process and has also been referred to previously by Dahl et al. [1999] and Kosanovich et al. [1996], The dataset consists of 50 batches from which eight process variables are measured over approximately 120 time intervals. From this set of batches, two quality variables on the final product were also available. Both process and quality variables are listed in Table 10.7. The reactor in this chemical process (see Figure 10.26) converts the aqueous effluent from an upstream evaporator into a polymer product. The reactor consists of an autoclave and a cooling/heating system. It also has a vent to control the vapor pressure in the autoclave. The recipe specifies reactor and heat source pressure trajectories through five stages. 

Although originally designed as a batch process, the direct amidation of the nylon 6,6 salt has been adapted to continuous polymerization by a wide variety of process modifications developed over the past 40 years. Many of these are quite different from an engineering standpoint, but all involve essentially the same chemistry as the batch system. 

Temperature and pressure limits vary according to manufacturers specifications and usually depend on the physical and chemical properties of materials employed in the construction of reaction vessels. In batch systems the recommended upper temperature is usually between 200 °C (vessels fabricated from polymeric materials such as PTFE, for example) and 300 °C (quartz vessels). Most commercial... 

Recently, Ryu, Studer and colleagues also reported the use of highly sterically hindered amines [217, 218] for the NMP of styrene and butyl acrylate in a flow microreactor [219]. The polymerization in the flow microreactor is faster than that in the batch system, although polymers with slightly smaller molecular are obtained in flow. 

Therefore, it is important to control these steps. However, in conventional batch systems, control of polymerization is difhcult due to local concentration gradients. In contrast, flow microreactor systems enable such control (Fig. 32)... 

Despite the unfavorable experimental conditions in a batch system for kinetic controlled reactions, a selectivity of 80% in n-butane was achieved through ethylation of ethane. The results show, however, that to succeed in the direct alkylation the following conditions have to be met (1) The olefin should be totally converted to the reactive cation (incomplete protonation favors the polymerization and cracking processes) this means the use of a large excess of acid and good mixing. (2) The alkylation product must be removed from the reaction mixture before it transfers a hydride to the reactive cation, in which case the reduction of the alkene is achieved. (3) The substrate to cation hydride transfer should not be easy for this reason the reaction shows the best yield and selectivity when methane and ethane are used. 

This is the scheme of a polymerization reaction by addition of radicals. Although this system is complex and usually solved by numerical methods, the general solution using the integral method will be shown here. This is the easiest way to identify the kinetic parameters involved and indicate a general solving method for complex reactions of this type, although the numerical solution is more appropriate. We should start from a batch system (constant volume), whose equations for the rates of reactants and products are described as follows ... 

To achieve this balance between rate and MW, rates of polymerization (monomer consumption rates) at low conversion are of order 10 -10 mol s such that approximately 10 -10 s is required to take a batch system to complete conversion. Faster rates can be achieved by increasing Pinit. but at the expense of decreased polymer MW. 

In continuous polymerizations, temperature and pressure are controlled in much the same way as in batch systems. Obviously temperature trajectories are not employed in continuous reactors. Instead, the various vessels in a series of polymerization reactors may operate at different temperatures. The polymerizing mixture, then, will see different temperatures as it passes from one vessel to the next. Likewise, monomer trajectories are replaced, in continuous systems, with intermediate injection of a more reactive monomer between polymerization vessels. This strategy can be exploited to adjust the copolymer composition distribution. 

Trifluoromethanesulfonic acid (TfOH) is an effedive initiator for cationic polymerization. For example, TfOH-initiated polymerization of isobutyl vinyl ether (IBVE) in 1,2-dichloroethane using a macroscale batch system (20 mL scale) [46] is complete within lOsat—25°C. The molecular weight distribution is, however, rather broad and Mw/Mn ranges from 2.73 to 4.71, presumably because of chain transfer readions due to the high readivity of the polymer ends. 

Continuous Polymerization Control Strategies hi continuous polymerizations, temperature and pressure are controlled in much the same way as in batch systems. 

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