Thomas C. Ho

Mesoporous magnetic carbon nanocomposite fabrics for highly efficient Cr(VI) removal

We have demonstrated that magnetic carbon nanocomposite fabrics prepared by microwave assisted heating are advanced adsorbents in the removal of Cr(VI) with a much higher removal capacity of 3.74 mg g−1 compared to 0.32 mg g−1 for cotton fabrics and 0.46 mg g−1 for carbon fabrics. The enhanced Cr(VI) removal is attributed to the highly porous structure of the nanocomposites. The adsorption kinetics follow the pseudo-second-order model, which reveals a very large adsorption capacity and high adsorption rate. The removal process takes only 10 min, which is much faster than conventional adsorbents such as activated carbon and biomass that often requires hours of operation. The significantly reduced treatment time and the large adsorption capacity make these nanocomposite fabrics promising for the highly efficient removal of heavy metals from polluted water.

Metal Capture During Fluidized Bed Incineration of Wastes Contaminated with Lead Chloride

Abstract The emission of toxic metals during the incineration of solid wastes containing metals presents potential environmental and health hazards. Some of the metals in the effluent gases are of submicron size which conventional air pollution control devices may not always effectively collect. One of the alternative control technologies for heavy metal emissions is to use sorbents to capture metals through various mechanisms during incineration. Of the available incineration systems, the fluidized bed incinerator appears to be suitable for this purpose. The objective of this work was to experimentally study the characteristics of metal capture by various bed sorbents during fluidized bed incineration of wastes containing lead chloride. Experiments were carried out in a 76.2 mm ID fluidized bed of sand, limestone and aluminum oxide. Combustible test materials contaminated with lead chlorides were incinerated in the bed with different sorbents under different incineration conditions. The observed results ...

Metal capture by sorbents during fluidized-bed combustion

Abstract Metal capture experiments were performed in a 76 mm (3″) ID fluidized-bed combustor with limestone, sand and alumina serving as both the fluidized medium and metal capture sorbents. Wood pellets spiked with metal solutions were used to simulate the metal-containing combustible fuel. The tested metals were nitrate and chloride species of lead and cadmium. The experimental parameters included metal species and concentration, sorbent type and size, combustor temperature, air flow rate and combustion duration. Experimental results indicated that the technology is highly promising. In-furnace lead capture by limestone was observed to be as high as 95%. The capture efficiency, however, varied with experimental parameters and chemical additives. Most of the captured metals were observed to be TCLP nonleachable.

Metal volatilization and separation during incineration

Abstract The United States Environmental Protection Agency (U.S.EPA) has reported that metals can account for almost all of the identified risks from a thermal treatment process. Fundamental research leading to better understanding of their behavior and improved control of their emissions is greatly needed. This paper reports our studies on metal volatilization and separation during incineration. Metal volatilization studies were carried out in two separate experiments. In the first experiment, the dynamic volatilization characteristics of various metals during the combustion of metal-containing wood pellets were investigated in a high-temperature electric furnace. In addition to uncontrolled volatilization, the potential of employing chemical additives to bind metals and prevent them from volatilizing during combustion was also investigated. The second experiment involved the investigation of metal volatilization characteristics during the thermal treatment of metal-contaminated clay in a fluidized bed unit. The metal species tested in both experiments were compounds of lead and cadmium. Metal capture/separation studies were also carried out in two separate experiments. The first involved the use of sorbents in the combustion chamber to capture metals during the fluidized bed incineration of metal-containing wood pellets. The second experiments, however, employed sorbents to absorb metal vapors in a fluidized-bed waste-heat boiler. The objective of both the experiments is to characterize the metal absorption efficiency associated with the processes.

Waste minimization by process modification

Abstract A simulation of the Sohio process for the production of acrylonitrile from the catalytic ammoxidation of propylene has been performed, using published kinetic and thermodynamic data to illustrate the concepts of pollution prevention by process modification. The study has determined the reaction parameters which will minimize the production of by-products while maintaining the conversion of propylene above 80%. The reaction parameters studied were reactor type (plug flow reactor [PFR], continuous stirred tank reactor [CSTR], and fluidized bed reactor [FBR]), reaction temperature, residence time, and entering feed temperature. The minimum byproducts were produced in an FBR operating at 450°C at a residence time of 7 seconds for a conversion of 81%.

Metal behavior during fluidized bed thermal treatment of soil

The Superfund dumpsites are frequently composed of soils contaminated with hazardous organic constituents and toxic heavy metals. While thermal treatment is an effective method of remediating the contaminated soils, the major environmental concerns are the emissions of toxic metal fumes during the treatment and the leaching of metals from the treated soil. The US EPA has reported that metals can account for almost all of the identified cancer risks from waste incineration systems. Research leading to better understanding of their behavior and better controlling of their emissions is urgently needed. In this study, the behavior of metals during the fluidized bed thermal treatment of artificially prepared metal-contaminated clay was experimentally and theoretically investigated. The objective of the study was to evaluate the effects of operating conditions on metal volatilization and metal leachability associated with the process. Metal experiments were carried out in a well instrumented 76 mm (3 inch) i.d. fluidized bed incinerator. The metals involved were compounds of lead and cadmium and the operating parameters included metal concentration, air flow rate, treatment temperature and treatment duration. The observed results indicated that metal volatilization is mainly a function of treatment temperature and treatment duration. The degree of volatilization was observed to range from 5 to 40% depending on the operating conditions. Cadmium leachability was observed to be relatively high compared to that of lead. In addition to the experimental study, a theoretical model based on the laws of heat and mass transfer operations and reaction kinetics was derived to simulate the metal volatilization process. The derived model was found to predict reasonably well the experimental observations.

Looped carbon capturing and environmental remediation: case study of magnetic polypropylene nanocomposites

A waste-free process to recycle Fe@Fe2O3/polypropylene (PP) polymer nanocomposites (PNCs) is introduced to synthesize magnetic carbon nanocomposites (MCNCs) and simultaneously produce useful chemical species which can be utilized as a feedstock in petrochemical industry. The magnetic nanoparticles (NPs) are found to have an effective catalytic activity on the pyrolysis of PP. The PNCs (with a NP loading of 20.0 wt%) undergo a complete degradation with 2 h pyrolysis at 500 °C in a H2/Ar atmosphere and the degradation components exhibit a distribution of species with different numbers of carbon, while only 40% of pure PP is decomposed after applying the same pyrolytic conditions. The coked solid waste from the conventional process has been utilized as a carbon source to form a protective carbon shell surrounding the magnetic NPs. The magnetic carbon nanocomposites (MCNCs) pyrolyzed from PNCs containing 20.0 wt% NPs demonstrate extremely fast Cr(VI) removal from wastewater with the almost complete removal of Cr(VI) within 10 min. The pH effect on the Cr(VI) removal efficiency is investigated with a preferable value of 1–3. The adsorbent exhibits much higher adsorption capacity in acidic solutions than that in alkali solutions. The large saturation magnetization (32.5 emu g−1) of these novel magnetic carbon nanocomposites allows fast recycling of both the adsorbents and the adsorbed Cr(VI) from the liquid suspension in a more energetically and economically sustainable way by simply applying a permanent magnet. The significantly reduced treatment time required to remove the Cr(VI) makes these MCNCs promising for the efficient removal of the heavy metals from wastewater. Kinetic investigation reveals the pseudo-second-order adsorption of Cr(VI) on these novel magnetic carbon nanocomposite adsorbents.

Simultaneous capture of metal, sulfur and chlorine by sorbents during fluidized bed incineration

Metal capture experiments were carried out in an atmospheric fluidized bed incinerator to investigate the effect of sulfur and chlorine on metal capture efficiency and the potential for simultaneous capture of metal, sulfur and chlorine by sorbents. In addition to experimental investigation, the effect of sulfur and chlorine on the metal capture process was also theoretically investigated through performing equilibrium calculations based on the minimization of system free energy. The observed results have indicated that, in general, the existence of sulfur and chlorine enhances the efficiency of metal capture especially at low to medium combustion temperatures. The capture mechanisms appear to include particulate scrubbing and chemisorption depending on the type of sorbents. Among the three sorbents tested, calcined limestone is capable of capturing all the three air pollutants simultaneously. The results also indicate that a mixture of the three sorbents, in general, captures more metals than a single sorbent during the process. In addition, the existence of sulfur and chlorine apparently enhances the metal capture process.

Transparent anhydride–cured epoxy nanocomposites reinforced with polyaniline stabilized nanosilica

Transparent anhydride–bisphenol-A epoxy systems filled with pristine nanosilica were prepared and compared with the counterparts with the nanosilica coated with surface initiated polymerization (SIP) prepared phosphoric acid (H3PO4) doped polyaniline (PANI). The rheological investigation on the bisphenol-A epoxy nanosuspensions demonstrated that the surface coating increased the interaction between the nanosilica and the resin matrix. The tensile strength of anhydride–epoxy (83.79 MPa) was increased to 87.00 and 88.78 MPa for the epoxy with the as-received and functionalized nanosilica, respectively. The real permittivity of the nanocomposites was increased after the introduction of PANI functionalized nanosilica. The H3PO4 doped PANI decreased the heat release rate of epoxy from 563.0 to 508. 3 W g−1, confirming the fire retardancy behavior of the PANI coating. The obtained cured anhydride–epoxy nanocomposites filled with nanosilica are highly transparent in visible light, and have potential applications in the optical field.

Study of atmospheric mercury budget in East Asia using STEM-Hg modeling system

East Asia is the largest source region of global anthropogenic mercury emissions, and contributes to atmospheric mercury concentration and deposition in other regions. Similarly, mercury from the global pool also plays a role in the chemical transport of mercury in East Asia. Annual simulations of atmospheric mercury in East Asia were performed using the STEM-Hg modeling system to study the mass budgets of mercury in the region. The model results showed strong seasonal variation in mercury concentration and deposition, with signals from large point sources. The annual mean concentrations for gaseous elemental mercury, reactive gaseous mercury and particulate mercury in central China and eastern coastal areas were 1.8 ng m(-3), 100 pg m(-3) and 150 pg m(-3), respectively. Boundary conditions had a strong influence on the simulated mercury concentration and deposition, contributing to 80% of the concentration and 70% of the deposition predicted by the model. The rest was caused by the regional emissions before they were transported out of the model domain. Using different oxidation rates reported for the Hg(0)-O(3) reaction (i.e., by Hall, 1995 vs. by Pal and Ariya, 2004) led to a 9% difference in the predicted mean concentration and a 40% difference in the predicted mean deposition. The estimated annual dry and wet deposition for East Asia in 2001 was in the range of 590-735 Mg and 482-696 Mg, respectively. The mercury mass outflow caused by the emissions in the domain was estimated to be 681-714 Mg yr(-1). This constituted 70% of the total mercury emission in the domain. The greatest outflow occurred in spring and early summer.