Pyrocarbonate species

Equation (14.69) has been included to account for the possible introduction of O2 at the feed/membrane side to boost CO2 permeation. A further reaction can be included to account for the formation of pyrocarbonate species (i.e., 205 [46]) at the feed/membrane and feed/permeate surfeces ... 

The term pyrolytic carbon can be applied to carbon filaments, carbon blacks, and carbon films, as well as to the more massive deposits which are the subject of this section. Pyrocarbon materials, made by chemical vapor deposition (CVD), vary in density, properties, and structure as much as the bulk materials discussed in 17.3.4.1. A heated hydrocarbon gas decomposes into an entire series of molecular species with a wide spectrum of carbon contents and molecular weights Within this pyrolyzing atmosphere, droplets form that pyrolyze and condense on a nearby surface, or large carbonaceous complexes may condense directly on the surface of the chamber. The former condition produces a fluffy, sooty, soft carbon, not far removed from carbon black, while the latter produces a hard solid carbon. The second of these materials is of primary interest here. The structure of the carbon produced by the CVD process has been shown to depend on the type of hydrocabon and its concentration, the pyrolysis temperature, the contact time, and the geometry of the pyrolyzing chamber. Of these, the pyrolysis temperature is perhaps the most important, but it is the nature of the chamber that conveniently divides the carbons produced into two distinct types. 

Kinetic studies of carbonization of a methane/carbon tetrachloride mixture at low pressure (2 kPa) at r< 800°C allowed one to assume that pyrocarbon was formed from chlorinated intermediate species with apparent activation energy of 180 kJ/mol (Gun ko and Leboda 2002). At higher temperatures, the apparent activation energy was lower (140 kJ/mol) and unsaturated hydrocarbons were the most probable carbon precursors (Feron et al. 1999). Chemical vapor infiltration of pyrocarbon was studied at 1100°C and methane or methane/hydrogen mixture pressures ranging from 5 to 100 kPa on porous alumina ceramic as a substrate (pore diameters from 1 to 36 pm)... 

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