Date of Award

2012

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

First Advisor

Adewuyi, Yusuf G. Dr.

Abstract

Nitric Oxide (NO) is regarded as a pollutant with multiple effects. These include visibility impairment, respiratory problems, declined crop yield, greenhouse effect and stratospheric ozone depletion. Together with SO2, NO is a major contributor to acid rain, ground-level ozone and photochemical smog. Of much recent concern for NOx (all oxides of nitrogen together) is its ability to form ground-level ozone with volatile organic compounds (VOC) in the presence of heat and sunlight. Consequently, the Environmental Protection Agency (EPA) is becoming stringent in terms of standards for NOx emissions to protect human health and the environment. Past and current existing methods for NOx control have high operating cost, strict temperature requirements, and disposal problems. Current federal regulations require that all the utility power plants (some were previously exempted) control their emissions, therefore, much attention has shifted to a less expensive alternative; the use of scrubbing solutions. In this research work, the absorption and oxidation of NO by aqueous Na2S2O8 activated by temperature and Fe2+ have been studied in a bubble column reactor operated in a semi-batch mode. Experiments were conducted to investigate the effects of persulfate (0.01-0.2 M), Fe2+ (0- 0.1 M), and gas-phase NO (500-1000 ppm) concentrations. The effects of temperature (23-90°C), presence of SO2 and the scrubbing solution’s pH were also investigated. In addition, mechanistic reaction pathways were proposed, and a previously developed xiv model was applied to include the case of temperature-Fe2+ activation. From these the kinetic rate constants were determined and the activation energies were subsequently estimated. The absorption rate model was also used to obtain the kinetic rate expression. In the presence of 0.01 M Fe2+ , 0.1 M persulfate remains the suitable concentration for NO removal by activated persulfate. Overall, presence of 0.01 M Fe2+ significantly improved NO removal by about 10% compared to temperature alone activation. The presence of SO2 gas greatly improved NO removal for temperature activated persulfate and worked best at near neutral pH. SO2 gas was completely absorbed in all cases, and the rate of reaction of NO with persulfate (S2O8 2- ) was found to be first order with respect to NO and zero order with respect to S2O8 2- ( ) at 23, 40 and 50°C. The results demonstrate the feasibility of removing NOx and SO2 by activated persulfate.

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