The Effects of Inorganic Solids and Certain Gases on the Thermal Decomposition of Catechol
In order to investigate the effects of calcium carbonate and iron oxide on the thermal decomposition of solid fuels, we have constructed an isothermal flow reactor to perform experiments on the model compound catechol (ortho-dihydroxybenzene), a phenol-type compound representative of coal, wood and biomass. Calcium carbonate and iron oxide are inorganic components of coal and wood, which have demonstrated catalytic properties in thermal reactions and are commercially used to enhance the conversion of solid fuels. In this study, the effects of the inorganic solids on pyrolysis and combustion are conducted through identification and quantification of the products formed after subjecting vapor-phase catechol to temperatures that range from 300 to 600 °C at a residence time of 7.36 seconds inside the flow reactor. A carrier gas consisting of either (1) pure nitrogen for pyrolytic experiments, (2) 1540-ppm oxygen, and (3) 1320-ppm 1,3-butadiene in nitrogen, are utilized to generate a stream with constant catechol concentration. To investigate the role of the inorganic solids on the reactions, the inorganic solids are placed between quartz wool and installed near the reactor’s exit end. Reaction products are then collected at the exit end and analyzed using gas chromatography with mass spectrometric and flame ionization detection, non-dispersive infrared analyzers, and reversed-phase high performance liquid chromatography with diode-array ultraviolet-visible absorbance detection. The experimental results demonstrate the catalytic activities of calcium carbonate and iron oxide. In both cases, interaction with the inorganic solid enhances catechol conversion. For calcium carbonate, increase in the conversion of catechol is attributed to the enhanced scission of catechol’s O-H bond. The scission, in turn, promotes phenol, 1,3-butadiene, naphthalene, phenanthrene, anthracene, and pyrene formations. For iron oxide, deactivation occurs during catechol reactions in the reducing environments of pyrolysis. In the presence of 0.15% O2, iron oxide enhances catechol conversion through the cis-cinnamaldehyde formation pathway. To enhance our understanding of catechol conversion, the effects of residence time and presence of 1,3-butadiene are also investigated. The results support previously reported reaction mechanisms that include H elimination of catechol, phenol formation, benzoquinone formation, and the aromatic growth pathway of aliphatic addition.
NDIR, GC, HPLC, combustion, oxidation, pyrolysis, wood, coal, biomass, chromatography, iron oxide, solid fuel, catechol, calcium carbonate
Networked Digital Library of Theses and Dissertations