(73b) Fundamental Chemistry, Kinetics and Mass-Transfer Aspects of the Emerging Sulfate-Radical Based Environmental Technologies for Pollution Control

Pollutants emitted from combustion sources are of great public concern due to their detrimental effects on human health and ecosystems. Although multipollutants’ reductions from flue gas using different processes such as selective catalytic reduction, lime/limestone wet flue gas desulfurization and activated carbon, respectively for NO_x, SO₂ and Hg removal, are efficient purification techniques, these complex treatment processes require high construction and operational costs, and large installation space. It is desirable to develop cost-effective especially those capable of providing simultaneous multipollutants’ control. Such technologies, which could also possibly be retrofitted to existing power plant are believed to be more cost-effective. Sulfate-radical (SO₄^•-) based advanced oxidation processes (AOPs) have drawn increasing attention in research and successful applications in water treatment and soil remediation as well as in flue gas purification for multipollutant treatments. The persulfate (PS) or peroxydisulfate anion (S₂O₈^2-) is a strong oxidant, kinetically slow at ordinary conditions but activation by heat, ultraviolet (UV), ultrasound, microwave, transition metal ions, electrodes, nanoparticles or base (and alkaline pH) resulting in the generation of SO₄^•- and subsequent production of hydroxyl (OH^•) radicals. As a cheap, naturally abundant and environmentally friendly material, iron (Fe(0), Fe(II), Fe(III)) activation has been preferentially used to generate. The activation by Fe(II) requires a relatively lower energy (14.8 kcal/mol) than the thermal energy (33.5 kcal/mol), so the PS/(Fe(II) reaction system has greater potential for destruction of target pollutants. This work evaluates the chemistry, reaction pathways, kinetics and removal efficiencies of NO and SO₂ from flue gas induced by the combined temperature and Fe²⁺ activation of aqueous PS. The work involves experimental studies and the development of a kinetic-mass transfer model utilizing a comprehensive reaction scheme for process evaluation. The mathematical model utilizes the Bodenstein or pseudo-steady-state approximation (PSSA) and equilibrium-state hypothesis (ESH) techniques, which have broad applications in modeling reaction kinetics in chemical, biochemical, and environmental reacting systems. The model equations were solved numerically using the fourth order Runge-Kutta method in Matlab. The model results, which appeared to fit the experimental results remarkably well, were used to predict species concentrations, NO and SO₂ mass transfer coefficients, new kinetic data and other process parameters at different temperatures for the NO_x-S(IV)-S₂O₈^2--Fe²⁺system.

References:

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