Pyrolysis reactor, oxidation

Process development on fluidized-bed pyrolysis was also carried out by the ConsoHdation Coal Co., culminating in operation of a 32 t/d pilot plant (35). The CONSOL pyrolysis process incorporated a novel stirred carbonizer as the pyrolysis reactor, which made operation of the system feasible even using strongly agglomerating eastern U.S. biturninous coals. This allowed the process to bypass the normal pre-oxidation step that is often used with caking coals, and resulted in a nearly 50% increase in tar yield. Use of a sweep gas to rapidly remove volatiles from the pyrolysis reactor gave overall tar yields of nearly 25% for a coal that had Eischer assay tar yields of only 15%. 

FIGURE 12.1. Schematic of tubular reactor setup for pyrolysis/catalytic/oxidation studies coupled to a molecular-beam mass spectrometer sampling system. 

S.G Davis, C.K. Law, and H. Wang. Propene Pyrolysis and Oxidation Kinetics in a Flow Reactor and Laminar Flames. Combust. Flame, 119 375-399,1999. 

The neutral species gas-phase chemistry in diamond CVD reactors generally consists of a well-understood set of pyrolysis and oxidation reactions, long studied in the combustion community. Several detailed combustion mechanisms exist for non-sooting conditions typically encoim-tered in diamond as summarized by Coltrin and Dandy,I J and... 

Davis SG, Law CK, Wang H Propene pyrolysis and oxidation kinetics in a flow reactor and laminar flames. Combust Flame 119(4) 375-399, 1999. 

Residence Time. Eor cost efficiency, residence time in the reactor should be minimized, but long enough to achieve complete combustion. Typical residence times for various thermal processes are incineration (0.1 s to 1.5 h), catalytic incineration (1 s), pyrolysis (12—15 min), and wet air oxidation (10— 30 min) (15). 

Determination of oxygen. The sample is weighed into a silver container which has been solvent-washed, dried at 400 °C and kept in a closed container to avoid oxidation. It is dropped into a reactor heated at 1060 °C, quantitative conversion of oxygen to carbon monoxide being achieved by a layer of nickel-coated carbon (see Note). The pyrolysis gases then flow into the chromatographic column (1 m long) of molecular sieves (5 x 10-8 cm) heated at 100 °C the CO is separated from N2, CH4, and H2, and is measured by a thermal conductivity detector. 

Recently, Stair and coworkers [10, 11] developed a method to produce gas-phase methyl radicals, and used this to study reactions of methyl groups on Pt surfaces [12] and on molybdenum oxide thin films [13]. In this approach, methyl radicals are produced by pyrolysis of azomethane in a tubular reactor locat inside an ulttahigh vacuum chamber. This method avoids the complications of co-adsorbcd halide atoms, it allows higher covraages to be reached, and it allows tiie study of reactions on oxide and other surfaces that do not dissociate methyl halides effectively. 

The expulsion of CO from ketocyclohexadienyl radical is also reasonable, not only in view of the data of flow-reactor results, but also in view of other pyrolysis studies [64], The expulsion indicates the early formation of CO in aromatic oxidation, whereas in aliphatic oxidation CO does not form until later in the reaction after the small olefins form (see Figs. 3.11 and 3.12). Since resonance makes the cyclopentadienyl radical very stable, its reaction with an 02 molecule has a large endothermicity. One feasible step is reaction with O atoms namely,... 

Previous studies in conventional reactor setups at Philip Morris USA have demonstrated the significant effectiveness of nanoparticle iron oxide on the oxidation of carbon monoxide when compared to the conventional, micron-sized iron oxide, " as well as its effect on the combustion and pyrolysis of biomass and biomass model compounds.These effects are derived from a higher reactivity of nanoparticles that are attributed to a higher BET surface area as well as the coordination of unsaturated sites on the surfaces. The chemical and electronic properties of nanoparticle iron oxide could also contribute to its higher reactivity. In this work, we present the possibility of using nanoparticle iron oxide as a catalyst for the decomposition of phenolic compounds. 

---