Polymerization reactions continuous flow stirred

In this short initial communication we wish to describe a general purpose continuous-flow stirred-tank reactor (CSTR) system which incorporates a digital computer for supervisory control purposes and which has been constructed for use with radical and other polymerization processes. The performance of the system has been tested by attempting to control the MWD of the product from free-radically initiated solution polymerizations of methyl methacrylate (MMA) using oscillatory feed-forward control strategies for the reagent feeds. This reaction has been selected for study because of the ease of experimentation which it affords and because the theoretical aspects of the control of MWD in radical polymerizations has attracted much attention in the scientific literature. 

Continuous-flow stirred-tank reactors (CSTRs) can be cooled in three ways. The most elegant method is to allow boiling of the monomer or solvent so that the heat of reaction is removed in an overhead condenser. The pressure in the vessel is set to give the desired temperature. The condensate can be returned to the vessel or recycled back to the feed. This process is commonly used for polystyrene. Chilling the feed is another means for managing the exotherm in a CSTR. Refrigeration to -40°C has been used for the bulk, continuous polymerization of PMMA. Laboratory reactors and small-scale industrial reactors can be cooled using jackets or internal coils, but this method scales up poorly. 

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. 

Both polyol and chain extenders were dehydrated before use by drying under vacuum at 100°C for 1 h. The quasi synthesis technique was used where the required amount of diisocyanate was first dissolved in part of the polyol component with the reactants being held in a round-bottomed polymerization-type reaction flask equipped with a dropping funnel and a stirrer and located in an oil bath at 120X with a steady flow of dry nitrogen passing continuously over the mixture and thus forming a blanket of gas this formed the quasi-prepolymer. This reaction mixture was stirred continuously for approximately 30 min, after which the formation of the prepolymer was considered complete. 

Automatic Continuous Online Monitoring of Polymerization Reactions was adapted to monitoring a homogeneous continuous stirred tank reactor (HCSTR) to verify the quantitative predictions concerning f, M, and r, as a function of the flow and kinetic parameters, to determine the kinetic parameters themselves, to ascertain the ideality of mixing in the reactor, to assess the effects of feed and reactor fluctuations, and to approximate a fully continuous tube-type reactor [38],... 

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. 

Example 4-8 An ideal continuous stirred-tank reactor is used for the homogeneous polymerization of monomer M. The volumetric flow rate is O, the volume of the reactor is V, and the density of the reaction solution is invariant with composition. The concentration of monomer in the feed is [M]o. The polymer product is produced by an initiation step and a consecutive series of propagation reactions. The reaction mechanism and rate equations may be described as follows, where is the activated monomer and P2, . . , P are polymer molecules containing n monomer units ... 

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