Jung-Gil Lee

Enhanced vapor transport in membrane distillation via functionalized carbon nanotubes anchored into electrospun nanofibres

To ascertain membrane distillation (MD) as an emerging desalination technology to meet the global water challenge, development of membranes with ideal material properties is crucial. Functionalized carbon nanotubes (CNTs) were anchored to nanofibres of electrospun membranes. Covalent modification and fluorination of CNTs improved their dispersibility and interfacial interaction with the polymer membrane, resulting in well-aligned CNTs inside crystalline fibres with superhydrophobicity. Consideration for the chemical/physical properties of the CNT composite membranes and calculation of their theoretical fluxes revealed the mechanism of MD: CNTs facilitated the repulsive force for Knudsen and molecular diffusions, reduced the boundary-layer effect in viscous flow, and assisted surface diffusion, allowing for fast vapor transport with anti-wetting. This study shows that the role of CNTs and an optimal composite ratio can be used to reduce the gap between theoretical and experimental approaches to desalination.

Evaluating the potential of superhydrophobic nanoporous alumina membranes for direct contact membrane distillation

HYPOTHESISnDirect contact membrane distillation (DCMD) processes exploit water-repellant membranes to desalt warm seawaters by allowing only water vapor to transport across. While perfluorinated membranes/coatings are routinely used for DCMD, their vulnerability to abrasion, heat, and harsh chemicals necessitates alternatives, such as ceramics. Herein, we systematically assess the potential of ceramic membranes consisting of anodized aluminum oxide (AAO) for DCMD.nnnEXPERIMENTSnWe rendered AAO membranes superhydrophobic to accomplish the separation of hot salty water (343u202fK, 0.7u202fM NaCl) and cold deionized water (292u202fK) and quantified vapor transport. We also developed a multiscale model based on computational fluid dynamics, conjugate heat transfer, and the kinetic theory of gases to gain insights into our experiments.nnnFINDINGSnThe average vapor fluxes, J, across three sets of AAO membranes with average nanochannel diameters (and porosities) centered at 80u202fnm (32%), 100u202fnm (37%), and 160u202fnm (57%) varied by < 25%, while we had expected them to scale with the porosities. Our multiscale simulations unveiled how the high thermal conductivity of the AAO membranes reduced the effective temperature drive for the mass transfer. Our results highlight the limitations of AAO membranes for DCMD and might advance the rational development of desalination membranes.

Experimental Investigation on the Reduction Characteristics of Nitric Dioxide(NO2) over Platinum-based Oxidation Catalyst

The reduction characteristics of NO2 to NO are experimentally studied over a platinum-based catalyst, especially at lower temperatures below about 200°C. In the present work, two types of steady-state experiments, engine bench and synthetic gas bench tests, are carried out in sequence. Steady-state engine bench tests with the DOC mounted on a light duty 4-cylinder 2.0 liter turbocharged diesel engine are performed and prove that CO plays a major role in NO2 abatement at temperatures below the light-off temperature of CO oxidation, about 200°C. Synthetic gas bench tests are then performed using synthetic gas mixtures with CO, C3H6, NO, NO2, O2, H2O and N2 in the 140~450°C T-range and show that both CO and C3H6 are capable of reducing NO2. It is noted that the reaction rate of NO2 with C3H6 is much higher than that with CO. At temperatures below about 200°C, the reduction of NO2 to NO is promoted with increasing CO concentration and NO2/NOX ratio and with decreasing O2 concentration, as well as with the presence of H2O.