Vinyl chloride polymerization in microdroplet reactor - Les thèses en ...

Chapter I : Bibliographic review
polymer phase swollen with monomer (30% weight). With further increase in conversion, the pressure
gradually drops. These details are schematically represented in Figure I- 3.
Figure I- 3: Relationship between reactor pressure and monomer distribution from Xie et al. (1991a)
It will be then proper to say that the S-PVC process under the commercial temperatures is subject to
both isobaric as well as non-isobaric conditions. This pressure drop (measured as the difference
between VCM vapour pressure and the final pressure of the reactor) is a good indicator of the final
conversion of the reaction, as mentioned by Xie et al. (1991a).
Before the pressure drops in the reactor, there is still an equilibrium established between phases.
Therefore until all the liquid VCM is consumed, there will be no diffusion of monomer from vapour
phase to polymer phase. The number of moles of VCM in vapour phase will not decrease. Its volume
will increase as a result of the shrinkage of the volume of the reaction medium due to the density
difference between VCM and PVC. In order to maintain a constant pressure, the monomer in the
liquid phase must diffuse through the interface and through water phase into the vapour phase. When
VCM phase is completely diminished, the monomer concentration in polymer phase decreases
enabling monomer transfer from water and vapour phases to the polymer phase. The result is a
pressure drop corresponding to high conversion values. The mechanism of diffusion of monomer
among phases is shown in Figure I- 4.
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