Part 1. Evaluation of combustion processes for production of feedstock chemicals from ammonium sulfate and ammonium bisulfate, and, Part 2. An assessment of polychlorinated dibenzo-p-dioxins and furans in raw materials for cement production.

摘要

Ammonium sulfate and ammonium bisulfate are produced in large quantities annually during various commercial chemical manufacturing processes. A major portion of these salts are disposed of as waste in deep wells at considerable cost to the chemical industry and represents a potential long-term environmental hazard. This problem can be reduced or eliminated by converting ABS/AS into feed stock chemicals through cost-effective conversion processes.;Combustion of ABS and AS in hydrocarbon-air flames was studied as a conversion process. Flame stoichiometry was varied from 120% excess oxygen to 40% oxygen deficiency. It was seen that with stoichiometric or excess oxygen flames all of the sulfur in the salts was converted to SO2. Such flames produced nitrogen oxides (NOx) at few hundred ppm level as well. SO 2 was also produced with sub-stoichiometric flames; however, the amount of NOx produced in such flames was significantly lower. These flames also resulted in formation of reduced sulfur species such as H2S and COS. The concentration of these species was dependent on oxygen deficiency and the presence of catalytic surfaces. When the oxygen deficiency was <20% the principal product of AS/ABS combustion was SO2 in the presence or absence of a catalyst. Only a small portion (<0.2% by volume) of the ABS/AS sulfur was converted to H2S and COS. Whereas, combustion in sub-stoichiometric flames with oxygen deficiencies of >30% and presence of suitable catalytic surfaces nearly all of the AB/ABS sulfur was converted to reduced sulfur species (H2S and COS). Alumina (Al2O 3) was found to be an efficient catalyst.;The conversion of H2S and COS to methanethiol (CH3SH) was investigated. The reaction was found to proceed efficiently only in the presence of suitable catalyst. Metal oxides such as niobium and tantalum supported on titania were investigated. Niobium oxide was found to give best yields.;Part two of this work was directed at an investigation into the release of dioxins from cement raw materials and its relationship to dioxins in the emissions. Results indicated that dioxins/furans were found in deep rock formations, indicating that dioxins/furans were formed and deposited at the time of rock formation rather than subsequently transported. A probable route for the presence of PCDDs/PCDFs is the release of previously bound molecules during cement manufacturing.