Tubular seed generation reactor

It would also be possible to use a tubular seed generation reactor as suggested by Greene, Gonzales and Poehlein L] 1, although the improved mixing characteristics of the CSTR would seem to be preferable. In either case, control of the proper split of monomer and water between this first and the second reactor is essential to achieve the desired number of particles. Nomura and Harada [ ] have also noted that relative monomer to water split in the first few reactors would alter the number of particles produced and that a certain split would maximize this number. 

Gonzalez (6,7) used a tubular pre-reactor upstream of a CSTR to generate a particle seed to feed into the CSTR. The motivation for this work was to control the conversion oscillations often observed in CSTR systems. A tube-CSTR series has a number of potential advantages which will be reviewed in this paper. 

One of the most promising ways of dealing with conversion oscillations is the use of a small-particle latex seed in a feed stream so that particle nucleation does not occur in the CSTRs. Berens (3) used a seed produced in another reactor to achieve stable operation of a continuous PVC reactor. Gonzalez used a continuous tubular pre-reactor to generate the seed for a CSTR producing PMMA latex. 

The data on particle size distributions for both PVA and PMMA emulsions suggest that small particles could be quite important in the kinetic scheme, and that the larger particles probably grow by internal polymerization and by flocculation with smaller particles. The experiments with the tubular reactor installed upstream of the CSTR demonstrate a practical way to eliminate uncontrolled transients with continuous systems. We believe that the particles generated in the tube prevent CSTR oscillations by avoiding the unstable particle formation reactions in the CSTR. Berrens (8 ) accomplished the same results by using a particle seed in the feed stream to a CSTR with PVC emulsion polymerizations. 

To resolve this instability problem, adopting a feed stream of seed latex particles [62] or installing a continuous tubular reactor, which generates seed particles, upstream of the continuous stirred tank reactor [53] have been proved quite effective (Figure 7.4b). For the latter approach, small latex particles form as a seed latex before the reacting stream enters the continuous stirred tank reactor when the monomer conversion at the exit of the tubular reactor is maintained at an adequate level. As a result, the continuous emulsion polymerization system can be operated at a stable steady state. The work of Nomura and Harada [54] also suggests that a tube-stirred tank reactor series... 

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