Degradation, high temperature avoidance

Heterogeneous catalysts are more common. However, they degrade and need replacement. If contaminants in the feed material or recycle shorten catalyst life, then extra separation to remove these contaminants before the feed enters the reactor might be justified. If the cataylst is sensitive to extreme conditions, such as high temperature, then some measures can help to avoid local hot spots and extend catalyst life ... 

At a holdup time longer than 10—15 min at a high temperature, resin degradation is avoided by keeping the rear of the cylinder at a lower temperature than the front. At short holdup times (4—5 min), cylinder temperatures are the same in rear and front. If melt fracture occurs, the injection rate is reduced pressures are in the range of 20.6—55.1 MPa (3000—8000 psi). Low backpressure and screw rotation rates should be used. 

Sample Preparation. The UHMWPE used in this study was a HiFax 1900 (Himont, Inc.) with an average molecular weight of 2-8 x 10. The UHMWPE was added to paraffin oil to concentrations from 2 to 5% w/w. To avoid polymer degradation at high temperatures, the polymer was stabilized with approximately 0.5% of BHT antioxidant. The mixture was stirred at 150 C. A solution was obtained that was clear until it was cooled to about 120 C when it became opaque and transformed into a gel-like or pseudo-gel. 

In order to avoid agglomeration of micronized particles, and thermal degradation of nifedipine at high temperatures (175 and 185°C), the hydrophilic polymer PEG 4000 was added to nifedipine to reduce its melting point. Micronization at pre-expansion temperatures between 50 and 70°C was possible and fine powdered co-precipitates of nifedipine/PEG 4000 were obtained. Their dissolution rate was twice as high as that for pure micronized nifedipine. 

Generally, recovery increases with the increase in temperature and then levels off after a certain point. For thermally labile compounds, analyte degradation occurs at high temperatures and results in low recovery. Excessively high temperatures lead to matrix decomposition in polymer extractions and should be avoided. In general, pressure is not a critical parameter in MAE. It changes with the solvent system and the temperature used and is acceptable below a preset limit. 

ETFE resins have a good thermal stability however, for high-temperature applications thermal stabilizers are often added67 A wide variety of compounds, mostly metal salts, such as copper oxides and halides, aluminum oxide, and calcium salts, will act as sacrificial sites for oxidation. Addition of certain salts can alter the decomposition from oligomer formation to dehydrofluorination. Iron and other transition metal salts accelerate the dehydrofluorination. Hydrofluoric acid itself destabilizes ETFE at elevated temperatures and the degradation becomes self-accelerating. For that reason, extrusion temperatures higher than 380°C (716°F) should be avoided.68... 

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