Desorption Kinetics of Naphthalene and Acenaphthene over Two Activated Carbons via Thermogravimetric Analysis

Activated carbon (AC) is a promising sorbent for adsorption removal of polycyclic aromatic hydrocarbons (PAHs) because of its cost effectiveness. The desorption kinetics of two-ring PAHs, naphthalene and acenaphthene, over bituminous-coal-based (AC_WY) and coconut-shell-based (AC_NT) activated carbons were investigated. The desorption kinetics were studied over the temperature range of 400–800 K at different heating rates (8–20 K/min) using thermogravimetric analysis techniques. The activation energy, pre-exponential factor, and kinetic model for each sorbate–sorbent pair were determined by applying analytical methods to the non-isothermal data. The Johnson–Mehl–Avrami (JMA) rate equation, <i>g</i>(α) = [−ln­(1 – α)]^<i>n</i> (in integral form, where α is fractional completion), following the nucleation and growth model, was found to best describe the PAH desorption from both sorbents. Strong molecular sieving effects were found to influence both adsorption capacity and desorption rates. AC_WY, with less micropore (<0.7 nm) volume and more larger pores (0.7–2 nm) compared to AC_NT, favors PAH adsorption and desorption rates, leading to different values of the kinetic exponent (<i>n</i>) and other kinetic parameters. Likewise, the sieving effects favor adsorption and desorption of naphthalene (kinetic diameter of 0.62 nm) over acenaphthene (kinetic diameter of 0.66 nm) for both carbons

Novel Wire-on-Plate Electrostatic Precipitator (WOP-EP) for Controlling Fine Particle and Nanoparticle Pollution

A new wire-on-plate electrostatic precipitator (WOP-EP), where discharge wires are attached directly on the surface of a dielectric plate, was developed to ease the installation of the wires, minimize particle deposition on the wires, and lower ozone emission while maintaining a high particle collection efficiency. For a lab-scale WOP-EP (width, 50 mm; height, 20 mm; length, 180 mm) tested at the applied voltage of 18 kV, experimental total particle collection efficiencies were found as high as 90.9–99.7 and 98.8–99.9% in the particle size range of 30–1870 nm at the average air velocities of 0.50 m/s (flow rate, 30 L/min; residence time, 0.36 s) and 0.25 m/s (flow rate, 15 L/min; residence time, 0.72 s), respectively. Particle collection efficiencies calculated by numerical models agreed well with the experimental results. The comparison to the traditional wire-in-plate EP showed that, at the same applied voltage, the current WOP-EP emitted 1–2 orders of magnitude lower ozone concentration, had cleaner discharge wires after heavy particle loading in the EP, and recovered high particle collection efficiency after the grounded collection plate was cleaned. It is expected that the current WOP-EP can be scaled up as an efficient air-cleaning device to control fine particle and nanoparticle pollution

Desorption of Polycyclic Aromatic Hydrocarbons on Mesoporous Sorbents: Thermogravimetric Experiments and Kinetics Study

The desorption performances of naphthalene and pyrene on mesoporous MCM-41, SBA-15, and CMK-3 sorbents are studied on the basis of temperature-programmed desorption experiments over the temperature range of 350–800 K at different heating rates. The kinetic parameters for each sorbate–sorbent pair are determined with combined model-fitting methods. The data for naphthalene and pyrene are best fitted with the same kinetic models on MCM-41 (with 1D mesopore channels), in contrast to those on SBA-15 and CMK-3, which have micropore–mesopore structures, leading to different desorption mechanisms for these two sorbates. SBA-15 with interconnectivity between adjacent mesopores not only shows high sorption capacities but also offers diffusion advantages in desorption, which contributes to the order of the degree of ease in desorption: SBA-15 > MCM-41 > CMK-3. CMK-3, with higher microporosity and hydrophobicity, shows stronger binding with the adsorbates while still benefiting in pyrene desorption from the consecutive mesoporosity