Emulsion steady-state characteristics

Let us consider the steady state characteristics of continuous emulsion polymerization of styrene in the first stage reactor. The steady state value of the number of polymer particles formed in the first stage reactor can be calculated using the following equations. From Eqs. (1) and (2), we have ... 

Emulsion polymerization is usually carried out isothermally in batch or continuous stirred-tank reactors. Temperature control is much easier than for bulk or solution polymerization because the small ( 0.5 fim) polymer particles, which are the locus of the reaction, are suspended in a continuous aqueous medium. This complex, multiphase reactor also shows multiple steady states under isothermal conditions. In industrial practice, such a reactor often shows sustained oscillations. Solid-catalyzed olefin polymerization in a slurry batch reactor is a classic example of a slurry reactor where the solid particles change size and characteristics with time during the reaction process. 

This can be explained by the fact that the flow in the CCTVFR became closer to plug flow as the Taylor number was dropped closer to. Therefore, the steady-state particle number and the steady-state monomer conversion could be arbitrarily varied by simply varying the rotational speed of the inner cylinder. Moreover, no oscillations were observed, and the rotational speed of the inner cylinder could be kept low, so that the possibility of shear-induced coagulation could be decreased. Therefore, a CCTVFR with these characteristics is considered to be highly suitable as a pre-reactor for a continuous emulsion polymerization process. In the case of the continuous emulsion polymerization of VAc carried out with the same CCTVFR, however, the situation was quite different [365]. Oscillations in monomer conversion were observed, and almost no appreciable increase in steady-state monomer conversion occurred even when the rotational speed of the inner cylinder was decreased to a value close to. Why the kinetic behavior with VAc is so different to that with St cannot be explained at present. 

An approach similar to that taken by Nomura and Harada was used by Samer to quantify the effects of droplet nucleation on emulsion polymerization kinetics in a CSTR. In their simplified analysis, it was assumed that radical capture by particles and droplets is proportional to the ratio of particle and droplet diameters. This assumption is reliable at low to moderate residence times, when polymer particles still closely resemble monomer droplets with respect to composition and surface characteristics. For predominant droplet nucleation, the maximum particle generation is limited by the concentration of monomer droplets in the feed. In Fig. 11 the steady state particle generation is given as a function of the residence time and temperature. Nucleation efficiency is defined as the number of particles divided by the number of droplets in the... 

The time scale for the dynamic development of a cef in model asphaltene-heptane—toluene emulsions with water is illustrated in Fig. 19, in which solutions of Arab Heavy (AH) asphaltenes (0.5-1.0% w/w) in 40-50% toluene-in-heptol are emulsified with 30% water, and the cef is monitored as a fimction of time. As should be apparent, there is a characteristic time scale for the cef to rise markedly towards its steady-state value which varies with asphaltene concentration and solvation state of the asphaltenes. The time scale is most rapid at the limit of solubility (40% toluene) and with the higher concentration of asphaltenes (1% versus 0.5%). As concentration is reduced, the time required to reach the near-steady value decreases. Interestingly, it appears to be the same value, regardless of concentration (= 1.2 kV/cm). Also, as the toluene concentration is increased from 40 to 50%, the time scale increases and the long-term value of the cef decreases. This is consistent with a reduced driving force for adsorption of aggre-... 

---