Measurement of diffusivity and solubility of olefins in polypropylene by gas chromatography

Abstract

The classical gas chromatographic technique is applied to measure the solubility and diffusivity of ethylene and propylene in polypropylene. The polymer particles were used as supplied by the producers to pack the chromatographic columns. This allows a direct measurement of the interested properties in a particle with the same morphology obtained at the reactor outlet. Moreover, the apparatus was adapted to carry out measurements at pressures and temperatures close to those typical of the reaction conditions. The measured values of solubility and diffusivity compare favorably with those predicted by literature relationships for semicrystalline polymeric matrices. Moreover, the estimated diffusivities indicate the diffusion in the polymer microparticles as the rate determining step and a diffusive characteristic length comparable with the particle diameter, i.e., larger than expected in the frame of a multigrain particle schematization. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 464–473, 2000

Sorption studies of propylene in polypropylene. Diffusivity in polymer particles formed by different polymerization processes

“…The diffusion coefficient is increasing with increasing particle size and is nearly independent with respect to propylene pressure at higher sorption temperature. The same effect was also observed by Sliepcevich et al10. The dynamic sorption characteristics of polymer particles at 343 K for different sorption pressure are shown in Figure 5.…”

“…We used the gravimetric method with a magnetic suspension balance. This sorption method was also used by Garmatter,3 Bartke,4 by Schabel et al,5 Weickert et al,6 Gorval and Svejda,7 Sato et al,8 and Kosek et al9 Further sorption methods are the inverse gas chromatography applied by Sliepcevich et al10 and the pressure decay method used by Sato et al11…”

Particle Growth during the Polymerization of Olefins on Supported Catalysts. Part 2: Current Experimental Understanding and Modeling Progresses on Particle Fragmentation, Growth, and Morphology Development

“…In fact, the discrepancies between morphology of real particles (see Figure ) and the one assumed by MGM model (i.e., as the agglomerate of microparticles of the size around 1 µm with the catalyst fragments located in its center) could result in significant inaccuracies in description of transport phenomena through the particle. For instance, it has been demonstrated using inverse gas chromatography (IGC) that the length scale for diffusion of species could be as large as particle size, which is higher than one expected from MGM model, or only a fraction of that size depending on the particle in question. As a result, in order to be able to study the transport phenomena inside the growing particles, one needs to be able to define its morphology in a more accurate manner.…”

X‐Ray Tomography Imaging of Porous Polyolefin Particles in an Electron Microscope

“…The existence of large compact domains of polymer in porous polyolefin particles was experimentally confirmed1–3 and has considerable implications: (i) the characteristic diffusion length in the particles is comparable with their size,4, 5 (ii) degassing characteristics of polyolefin powders have non‐Fickian character,6 (iii) monomer transport limitations are significant not only in the initial stage of polymerization, but also in fully grown particles,7 (iv) particle morphology cannot be simplified to a pseudo‐homogeneous medium or to an agglomerate of small grains with identical diameter (multi‐grain model).…”