Heterogeneous Catalysts for Olefin Polymerization: Mathematical Model for Catalyst Particle Fragmentation

Fragmentation-Oriented Design of Olefin Polymerization Catalysts: Support Porosity

The development of catalysts for the production of polyethylene and polypropylene is ordinarily accomplished on a trial-and-error experimentation program. From the point-of-view of the fragmentation performance, support porosity is the key property affecting the mechanical support resistance, and, therefore, it determines the fragmentation process during the early moments of polymerization. The design of the support porosity can be more accurately determined by applying the theoretical knowledge acquired from previous research, but this is not consolidated for catalyst design. This article reports a methodology to optimize the support porosity using a simple fundamental model of the fragmentation process. Using this approach, the design of fragmentation-oriented supports can be achieved for polymerization reactors.

Early-stage particle fragmentation behavior of a commercial silica-supported metallocene catalyst

Olefin polymerization starts at the outer surface and at the macropores walls. Here fragmentation occurs by peeling off the catalyst in a layer-by-layer mode with, in ideal conditions, the simultaneous formation of bisection-type fractures across the catalyst inner domains.

Development of a Simple Reversible-Flow Method for Preparation of Micron-Size Chitosan-Cu(II) Catalyst Particles and Their Testing of Activity

A simple flow system employing a reversible-flow syringe pump was employed to synthesize uniform micron-size particles of chitosan-Cu(II) (CS-Cu(II)) catalyst. A solution of chitosan and Cu(II) salt was drawn into a holding coil via a 3-way switching valve and then slowly pumped to drip into an alkaline solution to form of hydrogel droplets. The droplets were washed and dried to obtain the catalyst particles. Manual addition into the alkaline solution or employment of flow system with a vibrating rod, through which the end of the flow line is inserted, was investigated for comparison. A sampling method was selected to obtain representative samples of the population of the synthesized particles for size measurement using optical microscopy. The mean sizes of the particles were 880 ± 70 µm, 780 ± 20 µm, and 180 ± 30 µm for the manual and flow methods, without and with the vibrating rod, respectively. Performance of the flow methods, in terms of rate of droplet production and particle size distribution, are discussed. Samples of 180 µm size CS-Cu(II) particles were tested for catalytic reduction of 0.5 mM p-nitrophenol to p-aminophenol by 100-fold excess borohydride. The conversion was 98% after 20 min, whereas without the catalyst there was only 14% conversion.

Comparative Study on Kinetics of Ethylene and Propylene Polymerizations with Supported Ziegler⁻Natta Catalyst: Catalyst Fragmentation Promoted by Polymer Crystalline Lamellae

The kinetic behaviors of ethylene and propylene polymerizations with the same MgCl₂-supported Ziegler–Natta (Z–N) catalyst containing an internal electron donor were compared. Changes of polymerization activity and active center concentration ([C*]) with time in the first 10 min were determined. Activity of ethylene polymerization was only 25% of that of propylene, and the polymerization rate (R_p) quickly decayed with time (t_p) in the former system, in contrast to stable R_p in the latter. The ethylene system showed a very low [C*]/[Ti] ratio (<0.6%), in contrast to a much higher [C*]/[Ti] ratio (1.5%–4.9%) in propylene polymerization. The two systems showed noticeably different morphologies of the nascent polymer/catalyst particles, with the PP/catalyst particles being more compact and homogeneous than the PE/catalyst particles. The different kinetic behaviors of the two systems were explained by faster and more sufficient catalyst fragmentation in propylene polymerization than the ethylene system. The smaller lamellar thickness (<20 nm) in nascent polypropylene compared with the size of nanopores (15–25 nm) in the catalyst was considered the key factor for efficient catalyst fragmentation in propylene polymerization, as the PP lamellae may grow inside the nanopores and break up the catalyst particles.