Vinyl chloride polymerization in microdroplet reactor - Les thÃ¨ses en ...

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Chapter I : Bibliographic review Emulsion Latex may be directly usable High polymerization rates possible Usable, small-particle size possible Usable in producing soft and solid particles Polymer may require additional cleanup and purification Difficult to eliminate entrenched coagulants, emulsifiers, surfactants etc. Often requires rapid agitation Precipitation Suspension Molecular weight distribution maintained by control of polymerization environment Easy agitation Higher-purity product when compared to emulsion May require solution and reprecipitation of product to remove unwanted material Precipitation may act to limit molecularweight disallowing formation of ultrahighmolecular-weight products Sensitive to agitation Particle size difficult to control Table I- 1: Characteristics of the main vinyl chloride polymerization methods I.C. Physical Considerations On Vinyl Chloride Monomer At ambient temperature and pressure, vinyl chloride (VCM) is a colorless gas, with its boiling temperature of -13.8 °C and a sweet, ethereal odor according to Blout et al. (1949). VCM is stored or shipped as a liquid, which has a vapor pressure of about 3 bar at ambient temperatures. VCM is highly flammable and forms explosive mixtures with air. Hazardous properties of VCM are its narcotic effect in the case of inhalation of high concentrations and its carcinogenity, causing angiosarcomas (Cameron et al., 1981). The toxicological data on VCM are presented in Appendix A1 of this thesis. The solubility of VCM in water is about 8.8·10 -3 P/P 0 (kg/kg water), where P is the partial pressure and P 0 the saturation pressure of VCM. The liquid density at 25 °C is 901.3 kg/m 3 and the density of technical PVC falls into the range of 1390-1400 kg/m 3 . The heat of polymerization has been determined to be ∆H p = -97.6 kJ/mol (Saeki and Emura, 2002). The interfacial tension at the water/VCM interface without additives is found to be 32 mN/m (Nilsson et al., 1985). I.D. Vinyl Chloride Suspension polymerization The suspension polymerization process of vinyl chloride (S-PVC) is a process carried out in millions of ‘small reactors’ represented by the monomer droplets themselves. 20
Chapter I : Bibliographic review Actually, the term ‘suspension polymerization’ is a misnomer in the sense that it expresses the status of the dispersed system at the end of the polymerization. Before and during most of the polymerization process, this system is essentially a liquid-liquid dispersion – which is by definition, an emulsion. A typical recipe for S-PVC process has the following ingredients and parameters, which will be all discussed further in detail: Polymerization degree 1000 VCM 100 parts Water (de-mineralized) 120 parts Suspending agent (PVA, etc.) 0.05-0.10 parts Initiator (peroxi compounds, etc.) 0.03-0.16 parts Polymerization temperature 57°C Conversion 85-90% Pressure at end of polymerization 5 bar Polymerization time 8h Table I- 2: Suspension polymerization recipe from Alexopoulos et al. (2007) In S-PVC, the liquid vinyl chloride under its autogeneous pressure is dispersed in the aqueous continuous phase and divided in small droplets (30 – 50 µm) by vigorous stirring (see Figure I- 2). The protective colloids added inhibit them to coalesce. The polymerization is initiated by organic initiators, like peroxides or azo-compounds. Primary stabilizer Secondary stabilizer Primary particle Basic particle Microscale Macroscale Figure I- 2: Macro and micro scale representation of reactor, monomer droplets and primary particlesprocesses from Alexopoulos et al. (2007) Consequently, the polymerization takes place in each monomer droplet. The reaction is carried out at polymerization temperatures in the range of 40 – 70°C under the saturated pressure of VCM. The pressure in the autoclave remains therefore constant until the liquid monomer phase is consumed. At this point, a critical conversion (referred to as X f ) is reached and polymerization only proceeds in the 21
Page 1: THÈSE En vue de l'obtention du DOC
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Chapter II: Development of the micr
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CHAPTER III: ON-LINE KINETIC MONITO
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Chapter III: On-line kinetic monito
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CHAPTER IV: MORPHOLOGIC CHARACTERIS
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Chapter IV: Morphologic characteris
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GENERAL CONCLUSION AND PERSPECTIVES
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General conclusion and perspectives
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General conclusion and perspectives
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Appendix 1 APPENDIX 1 Vinyl chlorid
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Appendix 1 Kidney, stomach and skin
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Appendix 1 EPA. Integrated Risk Inf
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Appendix 2 APPENDIX 2 Modelling of
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Appendix 2 Conversion degree 1 0,9
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Appendix 2 K 11 /γ m = 0 V ) m (T
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Bibliographic references BIBLIOGRAP
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Bibliographic references C Cameron,
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Bibliographic references Ehrfeld W.
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Bibliographic references K Kamachi
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Bibliographic references McAdams W.
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Bibliographic references Z Zerfa M.
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