(712e) Modeling and Sensitivity Analyses of Reactive Processes Involved in the Removal of Nitric Oxide and Sulfur Dioxide Synchronously By Thermally Activated Aqueous Persulfate

It is well-known that diesel engines used as propulsion units in maritime vessels emit high levels of air pollutants such as sulfur dioxide (SO₂), nitric oxides (NO_x and particulate matters (PMs). These pollutants which are emitted from combustion sources are of great public concern due to their detrimental effects on human health and ecosystems. As a result, the International Maritime Organization has set stringent limits on SO₂ and NO_x emissions for international navigation ships. While current commercial processes for multi-pollutants’ flue gas treatment systems employ different control units such as selective catalytic reduction NO_x and lime/limestone wet flue gas desulfurization for SO₂ are efficient purification techniques, they tend to have high construction and operational costs, and large installation space. It is desirable to develop a novel, single and integrated post-treatment technique to remove SO₂ and NO_x simultaneously, which could be cost-effective technology and could be used as a short-term solution or could possibly be retrofitted to existing pollution control units. Sulfate radical technology is an example of advanced oxidation technologies (AOTs) based on the generation highly oxidative radicals - mainly the hydroxyl radical (·OH), is currently receiving world-wide attention for applications in multicomponent flue gas pretreatments. 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, biochars, electrodes, nanoparticles or base (and alkaline pH). The activation results in the generation of sulfate radical () and subsequent production of mainly hydroxyl (OH^•) but other reactive oxygen species including superoxide anion radical (O₂^.-), hydrogen peroxide (H₂O₂) and singlet oxygen could also be generated depending on the activation method. Despite the recent numerous studies of the on the individual and/or simultaneous removal of SO₂, nitric oxide (NO) and mercury (Hg⁰) by activated persulfate, the mechanisms as to the contributions of the main free radicals compared other process parameters such as temperature, pH and reactive mass transfer effects, are still not well understood. This work involves experimental studies and the development of a kinetic-mass transfer utilizing a comprehensive reaction scheme for process evaluation of the simultaneous aqueous-phase removal of SO₂ and NO in a simulated flue gas by heat-activated persulfate in a bubble-column reactor. For the first time, a sensitivity analysis and rate of production analysis are used to access the contributions of each homogeneous reaction to the SO₂ and NO oxidation in the detailed mechanisms to reveal the dominant pathway(s), and evaluate the effects on the predicted concentrations of key products. This talk will comprehensively evaluate the chemistry, kinetics and the mass transfer aspects, oxidant utilization, and economic viability of the sulfate radical technology for flue gas cleanup; and outline directions for future developments of this innovative technology for potential large-scale treatment applications.

References:

• Adewuyi, Y.G. and Khan, M.A., Modeling the Synchronous Absorption and Oxidation of Nitric Oxide and Sulfur Dioxide by Heat-Activated Aqueous Peroxydisulfate in a Lab-scale Bubble Reactor, Separation and Purification Technology, 2022, 300, 121841.
• Adewuyi, Y.G., and Khan, M.A., Simultaneous NO and SO₂ Removal by Aqueous Persulfate Activated by Combined Heat and Fe²⁺: Experimental and Kinetic-Mass Transfer Model Studies, Environmental Science and Pollution Research, 2020, 27: 1186-1201.
• Adewuyi, Y.G., Sakyi, N.Y., and Khan, M.A. Simultaneous Removal of NO and SO₂ from Flue Gas by Combined heat and Fe²⁺ Activated Aqueous Persulfate Solutions. Chemosphere, 2018, 193: 1216-1225.
• Adewuyi, Y.G., and Khan, M.A., Nitric Oxide Removal by Combined Aqueous Persulfate and Ferrous-EDTA Systems: Effects of Persulfate and EDTA Concentrations, Temperature, pH, and SO₂, Chemical Engineering Journal, 2016, 304: 793-807.
• Adewuyi, Y.G., and Khan, M.A., Nitric Oxide Removal by Combined Aqueous Persulfate and Ferrous-EDTA Reaction Systems, Chemical Engineering Journal, 2015, 281: 575-587.