Sehkyu Park

Enzymatic coproduction of biodiesel and glycerol carbonate from soybean oil in solvent-free system.

The enzymatic coproduction of biodiesel and glycerol carbonate by transesterification of soybean oil and dimethyl carbonate (DMC) has been studied in a solvent-free system. The effects on biodiesel and glycerol carbonate conversion of reaction conditions including the kind of enzyme, the amount of enzyme, the molar ratio of DMC to soybean oil, the reaction temperature, and water addition were investigated. The optimal conditions for biodiesel and glycerol carbonate were 20% Novozym 435, 10:1 molar ratio of DMC to soybean oil, and 0.7% water addition. Under these conditions, the conversions of 96.4% biodiesel and 92.1% glycerol carbonate have been achieved after 48h.

Electro-biocatalytic production of formate from carbon dioxide using an oxygen-stable whole cell biocatalyst

The use of biocatalysts to convert CO2 into useful chemicals is a promising alternative to chemical conversion. In this study, the electro-biocatalytic conversion of CO2 to formate was attempted with a whole cell biocatalyst. Eight species of Methylobacteria were tested for CO2 reduction, and one of them, Methylobacterium extorquens AM1, exhibited an exceptionally higher capability to synthesize formate from CO2 by supplying electrons with electrodes, which produced formate concentrations of up to 60mM. The oxygen stability of the biocatalyst was investigated, and the results indicated that the whole cell catalyst still exhibited CO2 reduction activity even after being exposed to oxygen gas. From the results, we could demonstrate the electro-biocatalytic conversion of CO2 to formate using an obligate aerobe, M. extorquens AM1, as a whole cell biocatalyst without providing extra cofactors or hydrogen gas. This electro-biocatalytic process suggests a promising approach toward feasible way of CO2 conversion to formate.

Micro-porous patterning of the surface of a polymer electrolyte membrane by an accelerated plasma and its performance for direct methanol fuel cells

Polymer electrolyte membranes (PEMs) have been used in various areas of electrochemical technologies such as fuel cells, chloroalkali processes, electrolysis, redox flow batteries, etc. They are made of either fluorinated or hydrocarbonbased polymers, and are either cationic or anionic. Among the proton exchange membranes based on fluorinated polymers, Nafion membranes are the most popular ones because they have a relatively high ionic conductivity, and are chemically and physically robust. There are also commercially available hydrocarbon-based membranes, but in general they suffer from physical and chemical weaknesses. One of the important issues in polymer electrolyte membranes is the selectivity toward certain ions. For use in direct liquid fuel cells (DLFCs), PEMs should have very high proton conductivity, but be resistant against the permeation of fuels such as methanol, ethanol, propanol, formic acid, etc. Among DLFCs, direct methanol fuel cells (DMFCs) are known to be most promising for practical applications and thus have been developed to replace batteries for portable electronics and small-scale power generators. One of the key issues that limit the performance improvement of DMFCs is methanol crossover through PEM from the anode to the cathode because the methanol crossover can cause a significant rise in cathodic overpotential as well as a loss in energy efficiency. The main factors that affect methanol crossover rates and protonic conductivity are degree of hydration, ion exchange capacity (IEC) and thickness of PEMs. Methanol crossover rate and protonic conductivity change almost in the same direction and extent because they pass through the same ion channels in the membranes. The size of ion channels are proportional to the degree of hydration which in turn is also affected by IEC. The size and shape of the ion channels vary depending on the type of polymer materials comprising the membranes. In general, hydrocarbon-based polymers such as sulfonated poly(ether ether ketone) has smaller ion channels and thus have lower methanol permeation rates than fluorinated polymers such as Nafion membranes. Therefore, many efforts have been devoted to reduce fuel crossover through membrane by modifying its surface properties. Mondal et al. modified the surface of Nafion 117 by dip-coating in a blend of polybenzimidazole (PBI) and partially sulfonated polyvinylidenefluoride-co-hfp polymer and achieved a reduced methanol crossover and improved electrical efficiency. Ma et al. deposited a thin layer of Pt/Pd-Ag/ Pt by sputtering on the surface of a Nafion membrane, and found that the modified membrane had a lower methanol crossover rate and a higher DMFC performance than a pristine one. Moon and Rhim modified Nafion membranes by coating polyallylamine hydrochloride to reduce methanol crossover to around one third of the pristine Nafion membrane. Kim et al. used an in situ sol-gel technique to fabricate composite membranes comprising of poly(arylene ether sulfone) (SPAES), phosphotungstic acid (PWA), and sulfonated silica (silica-SO3H) for DMFC. Plasma technologies have been used in various areas such as modification of the surface of polymer films to give hydrophilic or hydrophobic properties, reduction of inorganic materials and material specimen cut for analytical purposes. Bae et al. used a radio frequency plasma technique to modify the surface of a Nafion membrane for use in DMFCs. Song et al. used an electron beam irradiation technique to crosslink sulfonated poly(ether ether ketone) (SPEEK) membranes in the presence of various crosslinking agents in order to improve the thermal and hydration stability of the membranes for use in polymer electrolyte membrane fuel cells (PEMFCs). Michael and Stulik reported a surface topography development on a Teflon film induced by Xe plasma bombardment. Koh et al. used an accelerated plasma technique to bring about changes in the morphology and wettability of the surfaces of polymer films. They observed that the surfaces of polymer films became more hydrophilic and rugged by irradiating accelerated plasma because of the erosion by the plasma beam. The plasma techniques, however, have not been widely used to modify the PEMs for fuel cells. For the membrane-electrode assemblies that are used in electrochemical processes, the contact area between the membrane and the electrodes are crucial because it affects the performance of the MEA by varying the contact resistance. There have been some efforts to increase the surface areas DOI 10.1007/s13233-017-5008-x