AIR POLLUTION CONTROL

INTRODUCTION

    Air pollution is one of the most serious environmental problems this planet is facing nowadays.  Human activities have drastically changed the air we are breathing by introducing materials into the atmosphere in a great quantity every second, and subsequently changed the entire environment (e.g. weather, ecosystem).  As the residents in the planet, human beings are unavoidably affected by this change (e.g. health problems, reduced visibility, property damage).  To improve the environment and the quality of our life, it is important to develop technologies to control the air pollution we produce.
    In our research on air pollution, we focus on the (1) understanding the mechanisms of pollutant formation, and (2) development of new technology to control air pollution, especially using aerosol science and particle technology.  Following are some examples.
 

METAL BEHAVIOR IN COMBUSTION SYSTEMS

    Heavy metals such as lead, arsenic or mercury are present in the waste we incinerate or coal we burn to generate energy.  Although they are in trace amount, they pose significant adverse health problems because of their high toxicity.  Unlike organic compounds, these metals are destroyed in combustion systems and typically they will form fine particles due to their high boiling points.  However, the formation depends on the operating conditions of the combustor (e.g. temperature) and the materials in the combustor (e.g. chlorine content).  To better control them in combustion system, the first step is to understand their behavior in combustion systems.  Thermodynamic calculations and experiments are conducted to evaluate the behavior of these metals in combustion systems.  They are also used to evaluate the impact of the components in flue gas such as HCl and SO2.

Related Publication:

1.          Wu, C. Y. and Biswas, P., "An Equilibrium Analysis to Determine the Speciation of Metals in an Incinerator", Combustion and Flame, 93, 31-40, 1993.

 

DEVELOPMENT OF INNOVATIVE SORBENT TECHNOLOGY TO CONTROL HEAVY METALS

Sorbent materials, such as Al2O3, SiO2 or TiO2, have been found to be effective to remove heavy metals.  Bulk materials such as bauxite or kaolinite have been used.  However, their effective area is on the surface and hence a high quantity is required to control the heavy metal emission.  Using an aerosol technology, agglomerated sorbent materials with a much larger surface area can be generated to in-situ capture heavy metals in combustion environment.  Currently, the foci of the group are: (1) CCA-treated wood (Cr, Cu and As) and (2) As, Mo and V from coal combustion.

Related Publication:

2.          Owens, T., Wu, C. Y. and Biswas, P., "An Equilibrium Analysis for Reactions of Metal Compounds with Sorbents", Chemical Engineering Communications, 133, 31-52, 1995.

3.          Biswas, P. and Wu, C. Y., "Control of Toxic Metal Emissions from Combustors using Sorbents: A Review", J. Air & Waste Management Association, 48, 113-127, 1998.

4.          Wu, C. Y. and Barton, T., "A Thermodynamic Equilibrium Analysis to Determine the Potential Sorbent Materials for the Control of Arsenic Emissions from Combustion Sources", Environmental Engineering Science, 18(3), 179-192, 2001.

5.          Lee, S. R. and Wu, C. Y., "Study of Vanadium Emission Control in Combustion Systems by Thermodynamic Equilibrium Analyses", Advanced in Environmental Research, 7(1), 1-10, 2002.

6.          Cho, K. and Wu, C. Y., "Control of Molybdenum Emission by Sorbents: An Equilibrium Analysis", submitted to J. Env. Eng., February 2002.

7.          Iida, K., Pierman, J., Tolaymat, T. Townsend, T. and Wu, C, Y., "Control of Heavy Metal Emissions and Leaching from Incineration of CCA-Treated Woods Using Mineral Sorbents", submitted to J. Env. Eng., June 2002.

 

DEVELOPMENT OF NOVEL CATALYST/PHOTOCATALYST TO CONTROL MERCURY EMISSION

      Mercury is a unique metal in combustion systems.  While most other metals are emitted as particulate matters, mercury is mainly emitted as elemental mercury vapor, especially from coal fired power plants.  Therefore, particle control devices are not capable of capturing it.  Meanwhile, it is insoluble, making scrubber useless in removing it from flue gas.  Currently, EPA has specified Activated Carbon to be the Maximum Available Control Technology.  However, it’s not an ideal material (e.g. it requires 3 kg of the best carbon to remove 1 g of Hg).  Hence, advanced technologies are being developed for effective capture of mercury in combustion systems. 

      The major process involves oxidation using strong oxidants such as hydroxyl radicals.  Under UV light, semiconductor materials such as TiO2 or ZnO can generate reactive hydroxyl radicals on their surface that can be used to oxidize mercury (forming mercury oxide).  Mercury oxide is attached to the surface of the photocatalyst and is also more soluble (hence more desired).  One application of the material is to in-situ generate nano-photocatalyst in agglomerated form, thus the surface area is high.  The other way that is being developed is to use nano-structured silica network doped with TiO2 that will have both functions of adsorption and photocatalysis.  The third process being developed is to add a third function which is to facilitate recycle and reuse of the material.  Ultimately, a “smart” material will be developed to detect, remove and signal the completion of its mission (i.e. the system is clean of Hg or other pollutant).

      Another materials being investigated include nanosized Fe2O3 and CuO.  They are activated by thermal energy instead of photons.  Therefore it is important to identify the optimal temperature for the best performance.  Additionally, these metal oxides can also be engineered to improve their properties. 


The mechanisms of the photocatalytic process in the system.

Related Publication:

8.          Wu, C. Y., Lee, T. G., Arar, E., Tyree, G. and Biswas, P., "Capture of Mercury in Combustion Environments by In-Situ Generated Titania Particles with UV Radiation", J. Environmental Engineering Science, 15(2), 137-148, 1998.

9.          Pitoniak, E., Wu, C. Y., Londeree, D., Mazyck, D., Bonzongo, J.-D., Powers, K. and Sigmund, W., “Nanostructured Silica-Gel Doped with TiO2 for Hg Vapor Control”, submitted to Journal of Nanoparticle Research, December 2002.

 

DEVELOPMENT OF HIGH SURFACE AREA CATALYST FOR MOBILE SOURCES

      Nanosized catalysts are important in the control of automobile exhaust due to their high surface area and reactivity.  However, the application requires their deposition on durable substrates.  Currently the group is working on the development of ceramic fiber coated with high surface area by coating binary nanosized catalysts on the surface.  The experimental results show that a higher surface area fiber can be fabricated with good dispersion of nanoparticles.

 

 

 

 

 


 Raw fiber before processing                                     Fiber coated with 2% (wt) nanosized particles

 

DEVELOPMENT OF INNOVATIVE MAGNETIC PHOTOCATALYST COMPOSITE

      Photocatalyst such as TiO2 is a very effective material to decompose organic pollutants.  Its application is important especially when limited supply of chemicals is allowed.  In collaboration with other UF researchers, we developing photocatalyst coated on magnet for use in microgravity environment.  The developed composite can be used in magnetic fluidization that does not rely on fluid flow.