Chang-Yu Wu

CeO2-TiO2 catalysts for catalytic oxidation of elemental mercury in low-rank coal combustion flue gas.

CeO(2)-TiO(2) (CeTi) catalysts synthesized by an ultrasound-assisted impregnation method were employed to oxidize elemental mercury (Hg(0)) in simulated low-rank (sub-bituminous and lignite) coal combustion flue gas. The CeTi catalysts with a CeO(2)/TiO(2) weight ratio of 1-2 exhibited high Hg(0) oxidation activity from 150 to 250 °C. The high concentrations of surface cerium and oxygen were responsible for their superior performance. Hg(0) oxidation over CeTi catalysts was proposed to follow the Langmuir-Hinshelwood mechanism whereby reactive species from adsorbed flue gas components react with adjacently adsorbed Hg(0). In the presence of O(2), a promotional effect of HCl, NO, and SO(2) on Hg(0) oxidation was observed. Without O(2), HCl and NO still promoted Hg(0) oxidation due to the surface oxygen, while SO(2) inhibited Hg(0) adsorption and subsequent oxidation. Water vapor also inhibited Hg(0) oxidation. HCl was the most effective flue gas component responsible for Hg(0) oxidation. However, the combination of SO(2) and NO without HCl also resulted in high Hg(0) oxidation efficiency. This superior oxidation capability is advantageous to Hg(0) oxidation in low-rank coal combustion flue gas with low HCl concentration.

Control of Toxic Metal Emissions from Combustors Using Sorbents: A Review

This paper constitutes a review of the control of toxic metal emissions using sorbents. The objective of sorbent-injection methods is to effectively capture the metal species (preferably transform it to an environmentally benign form) and to suppress the fraction in the submicrometer mode. The design of an effective sorbent-injection methodology thus requires an understanding of the fate of the metallic species and its transformation pathways (transfer to the gas phase, subsequent chemistry at high temperatures, and aerosol formation and growth dynamics) in the combustor. Several different sorbent methodologies used for metals capture are discussed, and a mechanistic description is provided. The need for further experimentation and pilot scale testing is also emphasized.

Role of flue gas components in mercury oxidation over TiO2 supported MnOx-CeO2 mixed-oxide at low temperature

MnO(x)-CeO(2) mixed-oxide supported on TiO(2) (Mn-Ce/Ti) was synthesized by an ultrasound-assisted impregnation method and employed to oxidize elemental mercury (Hg(0)) at 200°C in simulated coal combustion flue gas. Over 90% of Hg(0) oxidation was achieved on the Mn-Ce/Ti catalyst at 200°C under simulated flue gas representing those from burning low-rank coals with a high gas hourly space velocity of 60,000 h(-1). Gas-phase O(2) regenerated the lattice oxygen and replenished the chemisorbed oxygen, which facilitated Hg(0) oxidation. HCl was the most effective flue gas component responsible for Hg(0) oxidation. 10 ppm HCl plus 4% O(2) resulted in 100% Hg(0) oxidation under the experimental conditions. SO(2) competed with Hg(0) for active sites, thus deactivating the catalysts capability in oxidizing Hg(0). NO covered the active sites and consumed surface oxygen active for Hg(0) oxidation, hence limiting Hg(0) oxidation. Water vapor showed prohibitive effect on Hg(0) oxidation due to its competition with HCl and Hg(0) for active adsorption sites. This study provides information about the promotional or inhibitory effects of individual flue gas components on Hg(0) oxidation over a highly effective Mn-Ce/Ti catalyst. Such knowledge is of fundamental importance for industrial applications of the Mn-Ce/Ti catalyst in coal-fired power plants.

Dry particle coating using magnetically assisted impaction coating: modification of surface properties and optimization of system and operating parameters

Abstract The feasibility of using the magnetically assisted impaction coating (MAIC) device to coat fine silica guest particles onto the surface of larger cornstarch and cellulose host particles was examined. This was done to simultaneously improve the flowability of the host particles, as well as reduce their hydrophilicity, making them more suitable for use in foods and pharmaceuticals. The success of coating achieved by MAIC depends on the degree of “fluidization” of the host/guest particle system caused by the motion of the magnetic particles. To better understand the factors influencing this fluidizing behavior, several critical system and operating parameters were investigated. This was done using a model system consisting of PMMA host particles and alumina guest particles. The system parameters examined were magnetic particle size, mass ratio of magnetic particles to powder (host and guest particles) and guest particle size. The operating parameters were processing time, current (or voltage) and frequency. In addition to varying these parameters, enhanced image processing was used to measure the motion of the magnetic particles in order to study its effect on coating efficiency. The magnetic particles were observed to have both rotational and translational motion.

SCR Atmosphere Induced Reduction of Oxidized Mercury over CuO–CeO2/TiO2 Catalyst

CuO-CeO2/TiO2 (CuCeTi) catalyst synthesized by a sol-gel method was employed to investigate mercury conversion under a selective catalytic reduction (SCR) atmosphere (NO, NH3 plus O2). Neither NO nor NH3 individually exhibited an inhibitive effect on elemental mercury (Hg(0)) conversion in the presence of O2. However, Hg(0) conversion over the CuCeTi catalyst was greatly inhibited under SCR atmosphere. Systematic experiments were designed to investigate the inconsistency and explore the in-depth mechanisms. The results show that the copresence of NO and NH3 induced reduction of oxidized mercury (Hg(2+), HgO in this study), which offset the effect of catalytic Hg(0) oxidation, and hence resulted in deactivation of Hg(0) conversion. High NO and NH3 concentrations with a NO/NH3 ratio of 1.0 facilitated Hg(2+) reduction and therefore lowered Hg(0) conversion. Hg(2+) reduction over the CuCeTi catalyst was proposed to follow two possible mechanisms: (1) direct reaction, in which NO and NH3 react directly with HgO to form N2 and Hg(0); (2) indirect reaction, in which the SCR reaction consumed active surface oxygen on the CuCeTi catalyst, and reduced species on the CuCeTi catalyst surface such as Cu2O and Ce2O3 robbed oxygen from adjacent HgO. Different from the conventionally considered mechanisms, that is, competitive adsorption responsible for deactivation of Hg(0) conversion, this study reveals that oxidized mercury can transform into Hg(0) under SCR atmosphere. Such knowledge is of fundamental importance in developing efficient and economical mercury control technologies for coal-fired power plants.

Investigation of speciated VOC in gasoline vehicular exhaust under ECE and EUDC test cycles

The emission factors and compositions of volatile organic compounds (VOC) in exhaust gas from in-use gasoline passenger cars were characterized using a chassis dynamometer. Three passenger cars were tested at the ECE and the EUDC drive cycles to represent both urban and suburban driving scenarios. Exhaust gas was collected in Summa canisters and analyzed by gas chromatography-mass spectrometry (GC-MS). Common gaseous emissions (CH(4), NOx, CO, and CO(2)) were measured by an on-board monitoring system. The VOC emission factors of different cars ranged from 0.10 to 0.25 g km(-1) at the ECE cycle, and 0.01-0.02 g km(-1) at the EUDC cycle. A total of 57 individual VOC were detected in the exhaust gas, and the weight percentages were very consistent among the three cars. Ethylene (11.80 wt.%), toluene (11.27 wt.%), and benzene (8.83 wt.%) were the most abundant VOC in exhaust gas. Aromatics (38.32%) dominated the low speed conditions (ECE), while alkanes (37.34%) were the major compounds at the high speed condition (EUDC). The total amount of alkenes did not change much between those two cycles, while ethylene is abundant in the ECE and EUDC cycles. Ozone formation potential (OFP) was calculated to estimate the ozone yield from VOC emissions by gasoline cars and the results showed that OFP of VOC emission at the ECE cycle was about ten times higher than that at the EUDC cycle.

Characterization of Biological Aerosol Exposure Risks from Automobile Air Conditioning System

Although use of automobile air conditioning (AC) was shown to reduce in-vehicle particle levels, the characterization of its microbial aerosol exposure risks is lacking. Here, both AC and engine filter dust samples were collected from 30 automobiles in four different geographical locations in China. Biological contents (bacteria, fungi, and endotoxin) were studied using culturing, high-throughput gene sequence, and Limulus amebocyte lysate (LAL) methods. In-vehicle viable bioaerosol concentrations were directly monitored using an ultraviolet aerodynamic particle sizer (UVAPS) before and after use of AC for 5, 10, and 15 min. Regardless of locations, the vehicle AC filter dusts were found to be laden with high levels of bacteria (up to 26,150 CFU/mg), fungi (up to 1287 CFU/mg), and endotoxin (up to 5527 EU/mg). More than 400 unique bacterial species, including human opportunistic pathogens, were detected in the filter dusts. In addition, allergenic fungal species were also found abundant. Surprisingly, unexpected fluorescent peaks around 2.5 μm were observed during the first 5 min use of AC, which was attributed to the reaerosolization of those filter-borne microbial agents. The information obtained here can assist in minimizing or preventing the respiratory allergy or infection risk from the use of automobile AC system.

Characterization of reaerosolization from impingers in an effort to improve airborne virus sampling.

Aims:  To assess the impact of reaerosolization from liquid impingement methods on airborne virus sampling.

Efficacy of photocatalytic HEPA filter on microorganism removal

UNLABELLED This study assessed the application of photocatalytic oxidation (PCO) to the high efficiency particulate air (HEPA) filter for disinfection of airborne microorganisms. Experiments were conducted at two TiO2 loadings (1870 +/- 169 and 3140 +/- 67 mg/m(2)) on the HEPA filter irradiated with UV-A at the intensity of 0.85 +/- 0.18 or 4.85 +/- 0.09 mW/cm(2) under two relative humidity conditions (45 +/- 5% and 75 +/- 5%). Inactivation and penetration of four microorganisms were tested, including Aspergillus niger, Penicillium citrinum, Staphylococcus epidermidis, and Bacillus subtilis. It was found that microorganisms retained on a photocatalytic filter were inactivated around 60-80% and even 100% for S. epidermidis when the PCO reactions occurred. Lower penetration was also found from the photocatalytic filter for all airborne microorganisms. High humidity decreased photocatalysis efficacy. Increasing TiO2 loading or irradiance intensity did not substantially affect its disinfection capability. PRACTICAL IMPLICATIONS The high efficiency particulate air filter is used widely to remove particulates and microorganisms from the air stream. However, the filter may become a source of microbes if those retained microorganisms proliferate and re-entrain back into the filtered air. This study demonstrates that such a problem can be handled effectively by using photocatalytic reactions to inactivate those confined microorganisms. A 60-100% microbe reduction can be achieved for a wide variety of microorganisms to provide better indoor air quality for hospitals, offices, and domestic applications.

Assessment of iodine‐treated filter media for removal and inactivation of MS2 bacteriophage aerosols

Aims:  To investigate the performance of an iodine‐releasing filter medium for use as a protective device against airborne pathogens.