Steady state experiments with vinyl

Continuous Emulsion Polymerization—Steady State and Transient Experiments with Vinyl Acetate and Methyl Methacrylate... 

An understanding of the transient hehavior of continuous reactors is important for start-up and reactor control considerations. Continuous oscillations have been observed by a number of workers. Figures 10 and 11 show data for styrene and methyl methacrylate. Gerrens and Ley (1974) reported continuous, undamped oscillations in surf e tension during a styrene emulsion polymerization run which lasted for more than 50 mean residence times. Nearly five complete cycles were observed during this run. Berens (1974) conducted experiments with vinyl chloride in whidi the measured panicle size changed with time. No steady state was achieved with the data shown in Fig. 12. 

Greene, R. K., Gonzalez, R. A., and Poehlein, G. W. (1976) Continuous emulsion polymerization - steady state and transient experiments with vinyl acetate and methyl methacrylate, in Emulsion Polymerization (eds I. Piirma and J. Gardon), ACS, Washington, pp. 341-358. 

Greene R, Gonzalez RA, Poehlein GW. Continuous emulsion polymerization-steady state and transient experiments with vinyl aeetate and methyl methacrylate. ACS Symp Ser 1976 24 341-358. 

Figures 3 through 6 show conversion-time data for a number of vinyl acetate runs. The start-up procedure for these experiments consisted of filling the reaction vessel with degassed water prior to introducing any feed streams. Periodic samples were taken and the monomer conversion measured gravimetrically. As can be seen, some of the conversion transients did not reach a steady state. Tendency toward unsteady behavior and the magnitude of the oscillations seemed to increase with increasing initiator concentration and mean residence time. The influence of changing the emulsifier concentration is not clear.

As a fast, albeit incomplete, probe of potential catalyst activity, the initiation rates of the catalysts presented in Figure 3.1 were measured via reaction with butyl vinyl ether (BVE) [27]. This assay does not describe the behavior of the catalysts in full detail and certainly says nothing about Z selectivity nevertheless, it was a relatively quick experiment that we hoped would shed light on the structural factors governing catalyst activity. It should also be noted that unlike the initiation behavior of phosphine-based Ru catalysts, which is easily explained by the steady-state approximation, the initiation behavior of catalysts with Hoveyda-type oxygen chelates, such as 1 and 7, is much less well defined. In these cases, initiation rates depend heavily on the nature of the catalyst, the reacting olefin, and several other factors [28]. Thus, it can be challenging to explain the initiation of these catalysts in terms of a simple associative or dissociative mechanism. 

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