Conversion distribution in diffusion‐governed chlorination of poly(vinyl chloride)

Abstract

Conversion distribution in particles of chlorinated poly(viny1 chloride) (CPVC) is conceptually described based on balance equations involving mass transfer and chemical reaction. In the physical sorption of chlorine in poly(viny1 chloride) (PVC) as measured by the constant volume cell method. eauilibrium concentration and diffusion rate obeved Henrv's law and Fick's law. The rate process of photo chlorination of PVC, which was investigated by the gravimetric method, could be well predicted by theoretical calculation of chlorine diffusion in PVC accompanying the infinitely fast chemical reaction. In a free grain of PVC synthesized by suspension polymerization, the chlorination rate was governed by the polymer-phase diffusion within agglomerates of coalesced primary particles.To produce homogeneously chlorinated PVC, a periodic photo-irradiation method was theoretically proposed and experimentally demonstrated. The effect of the periodic operation on the thermal property of CPVC was evaluated by DSC.Tokyo 113, Japan hv C12 -2 CI C1* + -(CHZ -CHC1)---(CH -CHC1)-+ HCI (2)

An analysis of the reaction-diffusion mechanism governing the chlorination process of poly(vinyl chloride)

“…This slowdown leads to an intermediate "linear" regime between the "exponential" tails, corresponding to the start of the reaction and the final saturation. Furthermore, the shapes for the chlorine uptake displayed by curves (c) and (d) match the shapes obtained for the chlorine uptake in many previous experiments on PVC films, [2][3][4][5][6][7] shapes that were left unexplained. In each of these experiments, when K S is determined for the particular values of T and P Cl 2 , K T can easily be adjusted to reproduce the kinetics of chlorination.…”

“…The reaction then is more likely to occur near the surface, and this diffusion-limited reaction mechanism can be seen as a source of the final heterogeneity. 2 In what follows, we consider a PVC film or a PVC sphere in contact with chlorine gas. As soon as the gas starts to diffuse in the material, the chain reaction is initiated and chlorination occurs.…”

“…If L is the characteristic length of the PVC sample (half the thickness of the PVC film or the radius of the PVC sphere), the characteristic time of diffusion is D ϭ L 2 /D Cl 2 21 and the two constitutive equations can be written as…”

“…Under certain conditions, the chlorine uptake in the polymer grows exponentially at the beginning, then linearly before saturation. [2][3][4][5][6][7] In addition, the average conversion ratio (the chlorine content of the final CPVC after a fixed reaction time) depends nonlinearly on the chlorine external pressure or the film thickness. 4 -6 In order to bring a better understanding to the dry chlorination process, we are examining the connections between the external parameters and the characteristics of the chlorinated product.…”

China goes green: cleaner production of chemicals

“…The reported processes of CPVC synthesis mainly include solvent process, aqueous-suspension process and gas-solid process [69] . The solvent process has been eliminated because of the serious pollution associated with the toxic solvent.…”