A model
for studying the catalyst fragmentation in the early stages
of olefin polymerization is presented. The model is based on measurable
and observable parameters of the catalyst and on the energy balance
for the fragmentation phenomenon. The model allows the fragmentation
behaviors to be discriminated regarding the influence of particle
size, polymerization rate, and active site distribution. The results
are supported by experimental studies available in the literature
indicating the deterministic nature of the model and its capabilities
of prediction. The performance of the model allows the optimization
of the catalyst synthesis in terms of the nature of the support as
well as particle and pore morphology.
The presence of pharmaceuticals in aqueous environmental matrices often requires efficient and selective preconcentration procedures. Thus, silicas (SILs) were synthesized by a molecular imprinting technique using an acid-catalyzed sol-gel process and the following drugs as templates: fluoxetine, gentamicin, lidocaine, morphine, nifedipine, paracetamol, and tetracycline. The materials were subjected to sorbent extraction assisted by ultrasonic treatment to remove the drugs and the consequent formation of molecular imprinted cavities. The surface area of the resulting materials ranged from 290 to 960 m(2)/g. Adsorption tests were performed with the molecular imprinting phases. In terms of the potential selectivity, the SILs were subjected to the adsorption of drugs from samples such as potable and surface water. The adsorption capacity remained in the range between 55 and 65% for both matrices, while for the nonimprinted SIL it remained between 15 and 20%.
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