Reactor performance polymerization reactions

Performing polymerization reactions in perfectly mixed flow reactors leads to quite different results from those obtained in batch or plug flow reactors, as discussed in 1951 already by Denbigh [1951]. The key point concerns the relative lifetimes of the active propagating polymer species. If this is long relative to the mean holding time of the fluid in the reactor, the rules in Section... 

The effect of physical processes on reactor performance is more complex than for two-phase systems because both gas-liquid and liquid-solid interphase transport effects may be coupled with the intrinsic rate. The most common types of three-phase reactors are the slurry and trickle-bed reactors. These have found wide applications in the petroleum industry. A slurry reactor is a multi-phase flow reactor in which the reactant gas is bubbled through a solution containing solid catalyst particles. The reactor may operate continuously as a steady flow system with respect to both gas and liquid phases. Alternatively, a fixed charge of liquid is initially added to the stirred vessel, and the gas is continuously added such that the reactor is batch with respect to the liquid phase. This method is used in some hydrogenation reactions such as hydrogenation of oils in a slurry of nickel catalyst particles. Figure 4-15 shows a slurry-type reactor used for polymerization of ethylene in a sluiTy of solid catalyst particles in a solvent of cyclohexane. 

Reactor Design. The continuous polymerization reactions in this investigation were performed in a 50 ml pyrex glass reactor. The mixing mechanism utilized two mixing impellers and a Chemco magnet-drive mechanism. 

Some polymerization reactions are highly exothermic, so the problems of temperature control, which are the major emphasis of this book, are important in these systems. However, beyond the issue of temperature control, polymer reactors must produce a product with the desired properties. The final polymer product properties, such as viscosity, molecular weight distribution, particle size, and composition, are important for consistent performance of the polymer. These properties depend on more than just temperature and few can be measured online.12... 

In addition to the patent literature available on the production of BR in the gas-phase there is some scientific literature which mainly refers to the modeling of reaction kinetics. Details on the experimental procedure for the determination of the macroscopic kinetics of the Nd-mediated gas-phase polymerization of BD in a stirred-tank reactor are reported [568,569]. Special emphasis is given to video microscopy of individual supported catalyst particles, individual particle growth and particle size distribution (PSD). These studies reveal that individual particles differ in polymerization activity [536,537,570,571]. Reactor performance and PSD are modeled on the... 

Ring-opening polymerization reactions of several 2-substituted-2-oxazolines (i.e. 2-methyl, 2-ethyl, 2-nonyl, and 2-phenyl) in the presence of methyl tosylate as catalyst have been described by Schubert et al. (Scheme 14.14) [33-35]. The reactions were performed in the temperature range 80 to 200 °C inside a single-mode micro-wave reactor. In a typical run, 25 mL stock solutions of monomer-initiator-solvent were prepared before the polymerization. These stock solutions were divided among different reaction vials so each experiment was performed on a 1-mL scale. 

Synthesis of conjugated p-phenylene ladder polymers by means of a microwave-assisted reaction has been achieved by Scherf et al. (Scheme 14.35) [72]. The polymerization reactions were performed in THE solution at 130 °C in the presence of palladium catalyst with phosphine ligands with irradiation in a single-mode micro-wave reactor for 11 min. Compared with conventional thermal procedures, the reaction time was reduced from days to a couple of minutes and molecular weight distributions ( PDI ca 1.8) of the polymers were changed substantially. 

A polymerization reaction is usually accompanied by a reduction of the partial molar volume of the monomeric unit when it is incorporated in a polymeric chain. This phenomenon is utilized when the volume of the reactor contents is monitored with dUatomeCy [9] or the density with densitometry [10,11]. ITensity measurements are usually performed with Paar digital densitometers [10]. Similar... 

J. M. Castro, S. D. Lipshitz, and C. W. Macosko [AIChE J., 28, 973 (1982)] modeled a thermosetting polymerization reaction in a laminar flow reactor under several different operating conditions. Demonstrate your ability to simulate the performance of a plug flow reactor for this reaction under both isothermal and adiabatic reaction conditions. In particular, determine the reactor space times necessary to achieve 73% conversion for both modes of operation and the following parameter values for a (3/2)-order reaction (r = kc - ). 

Since the first report on controlled radical polymerization by Matyjaszewski et al. [18], efforts in the area have increased dramatically, with many attempts having been made to perform these types of reaction in micro-reactors. It should be noted, however, that some of the problems associated with free radical polymerizations using micro-reactors would also apply to controlled polymerization reactions. In particular, slow reaction rates, low molar masses, and homogeneous systems would be limiting factors. The one aspect that might be of interest to investigate in micro-reactors would be the rapid mixing of the initiator complex with the monomer, as this would cause the initiation step to occur more rapidly. 

The concept of performing polymerizations in micro-reactors has led to dramatic new insights into the importance of heat and mass transport for those reactions, when rapid initiation and propagation rates are involved. To date, the micro-reactors examined have demonstrated huge differences in surface-to-volume ratios between... 

The scale-up of suspension polymerization reactors (i.e., from lab to pilot and then to industrial scale) is not straightforward or well established. Probably, the most significant problem in scale-up occurs when different physical processes become Umiting at different scales. For example, commercial-scale suspension reactors have to perform several functions simultaneously (dispersion, reaction and heat transfer), which do not scale-up in the same manner. Thus, heat removal can become a Umiting factor for reactor performance at large scales while it is rarely a problem for lab-scale reactors [86]. 

Nitroxide-mediated miniemulsion polymerization reactions can also be performed successfully in a tubular reactor [80]. The demonstrated case used a tubular reactor with an i.d. of 2 mm and a length of 170 m. Samples prepared in the tubular reactor are comparable to those made in a batch reactor in terms of kinetics and molecular weight characteristics. 

---