Thermal Degradation Catalysts

Phosphonium salts are typically stable crystalline soHds that have high water solubiUty. Uses include biocides, flame retardants, the phase-transfer catalysts (98). Although their thermal stabiUty is quite high, tertiary phosphines can be obtained from pyrolysis of quaternary phosphonium haUdes. The hydroxides undergo thermal degradation to phosphine oxides as follows ... 

Synthesis Temperature. Because of the exothermic nature of the ammonia synthesis reaction, higher temperatures increase reaction rates, but the equihbrium amount of ammonia decreases. Thermal degradation of the catalyst also increases with temperature. 

Anionic Polymerization of Cyclic Siloxanes. The anionic polymerization of cyclosiloxanes can be performed in the presence of a wide variety of strong bases such as hydroxides, alcoholates, or silanolates of alkaH metals (59,68). Commercially, the most important catalyst is potassium silanolate. The activity of the alkaH metal hydroxides increases in the foUowing sequence LiOH < NaOH < KOH < CsOH, which is also the order in which the degree of ionization of thein hydroxides increases (90). Another important class of catalysts is tetraalkyl ammonium, phosphonium hydroxides, and silanolates (91—93). These catalysts undergo thermal degradation when the polymer is heated above the temperature requited (typically >150°C) to decompose the catalyst, giving volatile products and the neutral, thermally stable polymer. 

Thermal Degradation and Sintering Thermally iaduced deactivation of catalysts may result from redispersion, ie, loss of catalytic surface area because of crystal growth ia the catalyst phase (21,24,33) or from sintering, ie, loss of catalyst-support area because of support coUapse (18). Sintering processes generally take... 

This comprehensive article supplies details of a new catalytic process for the degradation of municipal waste plastics in a glass reactor. The degradation of plastics was carried out at atmospheric pressure and 410 degrees C in batch and continuous feed operation. The waste plastics and simulated mixed plastics are composed of polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile butadiene styrene, and polyethylene terephthalate. In the study, the degradation rate and yield of fuel oil recovery promoted by the use of silica alumina catalysts are compared with the non-catalytic thermal degradation. 9 refs. lAPAN... 

The product yield of LDPE and HDPE for the same degradation time is in the order of ZSM-5 catalyst > RFCC catalyst > thermal, and the cumulative yield of liquid product from LDPE was greater than that from HDPE. 

Thermal operations such as distillation, decomposition, transformation, and rectification often cause thermal degradation. Furthermore, with these processes quantitative catalyst recovery is generally not possible, which results in loss of productivity. 

The objective of this work is to study the potential of modified ZSM5 zeolite, MCM41 mesoporous silica, hydrotalcites (HD) and HD originated mixed oxides as catalysts for degradation of PE, PP PS and PVC using thermal analytical measurements and laboratory reactor experiments. 

The TG analysis for pure PP proves a steep weight loss with a maximum in the DTG curve placed at 520 °C, which corresponds with the thermal degradation of this polyolefin. Fig 1 and 2 show TG analysis of PP/H-ZSM5 and PP/Ti-MCM41 catalyst mixture with 10 % catalyst content. 

For PP degradation (Fig. 5), the non-acidic Ti-MCM41 and the Fe-ZSM-5 samples produced liquid hydrocarbons with yields about 90%, which is higher than that of non-catalytic thermal degradation. Similar results have been obtained for PS degradation, however, the activity of the catalyst with small pore sizes (ZSM-5) have had lower activity (no reaction observed below 350 °C). 

The low melting point and high surface mobility of NiS also accelerate the sintering process of Ni crystallites. Since the formation of NiS is exothermic, activity loss can be partially recovered by raising the reaction temperature, which, however, also accelerates thermal degradation of the catalyst and increases carbon formation through cracking reactions. 

Uses. Solvent for polymers polymerization catalyst stabilizer against thermal degradation in polystyrene UV stabilizer in polyvinyl and polyolefin resins... 

The choice of the appropriate catalyst system will have an impact on the potential formation of the heavy polymers and coke. Cracking the high molecular weight precursors catalytically will significantly reduce the possibility of thermally degrading these components. The zeolite activity should be optimized in combination with an active matrix selective to upgrading the heavy feed components. 

Thermal Degradation Catalyst sintering can occur at flue gas temperatures > 800°F. This will result in the pore distribution shifting to larger pores. The loss of small pores will generally not have a large effect on activity since diffusion is not a critical parameter. The majority of conversion occurs on the exterior surface of the catalyst. 

Continuous exposure of catalysts to high temperatures may cause an alteration in its components and gradually lead to its deactivation. Thermal degradation may have an undesirable impact on both the catalyst substrate and noble metal load in various ways. Thermal degradation covers two phenomena sintering and solid-state transformation. 

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