Clay catalyst, activated analysis

With fresh activated-clay catalyst, endothermic peaks are observed at temperatures of about 300, 1200, and 1600°F. These three peaks are attributed to loss of physically adsorbed water, loss of chemically bound (hydroxyl) water, and collapse of the montmorillonite structure, respectively. The hydroxyl water originally present amounts to 3 or 4%. The magnitude of the peak at 1200°F. decreases if the sample is heated above 800°F. prior to thermal analysis, and disappears completely if the sample is calcined at 1100°F. The thermal-analysis curve for the dehydrated catalyst is flat up to the point at which the montmorillonite structure begins to disappear. If the catalyst has not been heated above 1450°F., it becomes rehydrated upon exposure to moisture and a new endothermic peak appears in the curve between 800 and 1000°F. The size of the new peak increases as that of the original hydroxyl-water peak decreases it corresponds to 1.5 to 2.0% sorbed water with catalyst that has been rehydrated after calcination at 1100°F. The rehydration capacity of the catalyst decreases as the catalyst becomes partially deactivated with use. 

The earliest catalyst developed for commercial use was produced from naturally occurring bentonitic-type clays. Such clays are carefully selected and further refined and activated by chemical means to bring out their latent cracking characteristics. A typical analysis of this type of commercial catalyst follows ... 

Preferred bentonite clays are those whose chief constituent is mont-morillonite, a mineral of the composition corresponding to the empirical formula, 4Si02-Al203 H20. The principal sources of raw clay for the manufacture of the presently most widely used natural catalyst (Filtrol Corporation) are deposits in Arizona and Mississippi. The clay from these deposits contains appreciable amounts of impurities, principally CaO, MgO, and Fe203, which replace part of the A1203 in the ideal montmorillonite structure. The catalyst is prepared by leaching the raw clay with dilute sulfuric acid until about half of the alumina and associated impurities is removed. The resulting product is then washed, partially dried, and extruded into pellets, after which it is activated by calcination. A typical analysis of the finished catalyst is as follows (Mills, 12). 

Incoronata Tritto studied stereospecific olefin polymerization in the group of Prof. Adolfo Zambelli at the Institute for Macromolecular Chemistry of the CNR and received her degree in polymer science at the Specialization School Giulio Natta at Politecnico di Milan (Italy) in 1981. In 1982, she joined as permanent researcher the Institute for Macromolecular Chemistry of the CNR In 1988, she spent 1 year in the group of Prof. Robert H. Grubbs at Caltech (USA), where she studied the relationship between metathesis and addition olefin polymerization. She is currently a senior research chemist at ISMAC-CNR. Her research interests focus on (1) synthesis and microstmctural characterization of stereospecific olefin and cyclic olefin homo- and copolymers by transition metal catalysts (2) activation and deactivation reactions ofthe homogeneous catalytic systems by in situ multinuclearNMR analysis and (3) synthesis of block copolymers and nanostructured hybrid polymers, in situ polymerization on clay and carbon nanotubes. 

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