• Journal of Korean Society of Environmental Engineers
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• v.27 no.6
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• pp.657-662
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• 2005

Iron sulfide(FeS) is significantly produced through both abiotic and biotic processes in natural sediments and pore waters. In this study, chromium(VI) reaction with iron sulfide at various initial concentrations and at pH values of 4 and 8 was conducted to better understand the interactions between Cr(VI) and Fe(II) species dissolved from iron sulfide in both the aqueous and solid phases. Also, the removal efficiency of iron sulfide was compared with zero valent iron and other iron bearing oxides such as ${\alpha}-Fe_2O_3$, ${\alpha}-FeOOH$ and $Fe_3O_4$. The Cr(VI) removal rate by iron sulfide was higher at pH 4 than at pH 8 because more dissolved Fe(II) existed at pH 4 than at pH 8. Chromium and iron(oxyhydroxide) could be identified on the iron sulfide surface with transmission microscopy imaging and energy dispersive spectroscopy. The removal capacity of iron sulfide was much higher than zero valent iron and other iron oxide minerals due to the synergic effect of hydrogen sulfide and ferrous iron.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.1
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• pp.79-86
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• 2010

Effects of operating parameters such as applied voltage, solution conductivity, ferrous ion concentration, electrode material on phenol degradation by pulsed corona discharges were investigated in laboratory scale experiments. The increase of applied voltage enhanced the phenol degradation by generating more energetic electrons. The solution conductivity inversely affected phenol removal rate in the tested ranges because the increase of conductivity decreased the electric field strength through the liquid phase. The addition of ferrous sulfate promoted the phenol degradation through the OH radical production by the Fentonlike reactions between ferrous ion and hydrogen peroxide generated by pulsed corona discharges. Catechol and hydroquinone were detected as primary intermediates of phenol degradation and the decrease of pH and the increase of conductivity were observed probably due to the generation of organic acids. Almost all of the initial phenol was disappeared and 29% of total organic corbon (TOC) was removed in the condition of 0.5 mM of ferrous sulfate after approximately 230 kJ of discharge energy transferred to the reactor.

• Korean Chemical Engineering Research
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• v.53 no.6
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• pp.677-681
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• 2015

Aluminum alloy was examined as a material of low weight reactor for hydrolysis of $NaBH_4$. Aluminum is dissolved with alkali, but there is NaOH as a stabilizer in $NaBH_4$ solution. To decrease corrosion rate of aluminum, decrease NaOH concentration and this result in loss of $NaBH_4$ during storage of $NaBH_4$ solution. Therefore stability of $NaBH_4$ and corrosion of aluminum should be considered in determining the optimum NaOH concentration. $NaBH_4$ stability and corrosion rate of aluminum were measured by hydrogen evolution rate. $NaBH_4$ stability was tested at $20{\sim}50^{\circ}C$ and aluminum corrosion was measured at $60{\sim}90^{\circ}C$. The optimum concentration of NaOH was 0.3 wt%, considering both $NaBH_4$ stability and aluminun corrosion. $NaBH_4$ hydrolysis reaction continued 200min in aluminum No 6061 alloy reactor with 0.3 wt% NaOH at $80{\sim}90^{\circ}C$.

• Clean Technology
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• v.26 no.1
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• pp.72-78
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• 2020

The use of fossil fuel and biogas production causes air pollution and climate change problems. Research endeavors continue to focus on converting methane and carbon dioxide, which are the major causes of climate change, into quality energy sources. In this study, a novel plasma-carbon converter was proposed to convert biogas into high quality gas, which is linked to photovoltaic and wind power and which poses a problem on generating electric power continuously. The characteristics of conversion and gas production were investigated to find a possibility for biogas conversion, involving parametric tests according to the change in the main influence variables, such as O₂/C ratio, total gas feed rate, and CO₂/CH₄ ratio. A higher O₂/C ratio gave higher conversions of methane and carbon dioxide. Total gas feed rate showed maximum conversion at a certain specified value. When CO₂/CH₄ feed ratio was decreased, both conversions increased. As a result, the production of solar fuel by plasma oxidation destruction-carbon material gasification conversion, which was newly suggested in this study, could be known as a possibly useful technology. When O₂/C ratio was 0.8 and CO₂/CH₄ was 0.67 while the total gas supply was at 40 L min^-1 (VHSV = 1.37), the maximum conversions of carbon dioxide and methane were achieved. The results gave the highest production for hydrogen and carbon dioxide which were high-quality fuel.

• Korean Chemical Engineering Research
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• v.46 no.3
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• pp.619-625
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• 2008

The effects of thermal cycling on residual stresses in both inorganic passivation/insulating layer that is deposited by plasma enhanced chemical vapor deposition (PECVD) and organic thin film that is used as a bonding adhesive are evaluated by 4 point bending method and wafer curvature method. $SiO_2/SiN_x$ and BCB (Benzocyclobutene) are used as inorganic and organic layers, respectively. A model about the effect of thermal cycling on residual stress and bond strength (Strain energy release rate), $G_c$, at the interface between inorganic thin film and organic adhesive is developed. In thermal cycling experiments conducted between $25^{\circ}C$ and either $350^{\circ}C$ or $400^{\circ}C$, $G_c$ at the interface between BCB and PECVD $ SiN_x $ decreases after the first cycle. This trend in $G_c$ agreed well with the prediction based on our model that the increase in residual tensile stress within the $SiN_x$ layer after thermal cycling leads to the decrease in $G_c$. This result is compared with that obtained for the interface between BCB and PECVD $SiO_2$, where the relaxation in residual compressive stress within the $SiO_2$ induces an increase in $G_c$. These opposite trends in $G_cs$ of the structures including either PECVD $ SiN_x $ or PECVD $SiO_2$ are caused by reactions in the hydrogen-bonded chemical structure of the PECVD layers, followed by desorption of water.

• Korean Chemical Engineering Research
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• v.50 no.6
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• pp.1015-1020
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• 2012

Lignite of low rank coal and petroleum coke of high sulfur content can be high potential energy sources for coal gasification process because of their plentiful supply. The steam gasification of lignite, anthracite, and pet coke has been carried out in both an atmospheric thermobalance reactor and a lab-scale fludized bed reactor (0.02 m i.d. ${\times}$ 0.6 m height). The effects of gasification temperature ($600{\sim}900^{\circ}C$) and partial pressure of steam (0.15~0.95 atm) on the gasification rate and on the heating value of product gas have been investigated. The modified volumetric reaction model was applied to the experimental data to describe the behavior of carbon conversion, and to evaluate kinetic parameters of char gasification. The results shows that higher temperature bring more hydrogen in the product syngas, and thus increased gas heating value. The feed rate of steam is needed to be optimized because an excess steam input would lower the gasification temperature which results in a degradation of fuel quality. The rank of calorific value of the product gas was anthracite > lignite > pet coke. Their obtained calorific value at $900^{\circ}C$ with 95% steam feed were 10.0 > 6.9 > 5.7 $MJ/m^3$. This study indicates that lignite and pet coke has a potential in fuel gas production.

• Journal of the Korean Electrochemical Society
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• v.2 no.3
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• pp.144-149
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• 1999

The two distinct adsorption sites and transition between the under and over-potentially deposited hydrogen (UPD H and OPD H) on the polycrystalline iridium (poly-Ir) surface in the 0.2 M LiOH electrolyte have been studied using the phase-shift method. At the forward and backward scans, the UPD H peak occurs on the cyclic voltam-mogram. The transition region on the phase-shift profile or the Langmuir adsorption isotherm occurs at ca. -0.80 to -0.95 V vs. SCE. At the transition region (-0.80 to -0.95 V vs. SCE), the equilibrium constant (K) for H adsorption transits from $7.9\times10^{-2}\;to\;1.5\times10^{-4}$ and vice versa. Similarly, the standard free energy $({\Delta}G_{ads})$ of H adsorption transits from 6.3 to 21.8kJ/mol and vice versa. The UPD H and OPD H on the poly-Ir surface act as two distinguishable electroadsorbed H species. Both the UPD H peak and the transition region are attributed to the two distinct adsorption sites of the UPD H and OPD H on the poly-Ir surface.

• Journal of the Korean Electrochemical Society
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• v.19 no.1
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• pp.14-20
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• 2016

Vanadium redox flow battery (VRFB) is an energy conversion device in which charging and discharging are alternatively carried out by oxidation and reduction reactions of vanadium ions with different oxidation states. VRFB consists of electrolyte, electrode, ion-exchange membrane, etc. The role of ion-exchange membranes in VRFB separates anolyte and catholyte and provides a high conductivity to hydrogen ions. Recently much attention has been devoted to develop ideal ion-exchange membranes for VRFB. A number of developed ion-exchange membranes should be evaluated to find out ideal ion-exchange membranes for VRFB. Long-term durability test is a crucial characterization of ion-exchange membranes for commercialization, but is very time-consuming. In this study, the life time prediction protocol of ion-exchange membranes in VRFB cell tests was developed through short-term single cell performance evaluation (real total operation time, 87.5 hrs) at three different current densities. We confirmed a decrease in test time up to 96.2% of real durability tests (expected total operation time, 2,296 hrs) and 5~6% of relative error discrepancy between the predicted and the real life time in a unit cell.

• Journal of Environmental Health Sciences
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• v.21 no.4
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• pp.1-9
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• 1995

This study was carried to investigate the biodegradability of phenol in the wastewater with the two sludge blanket-packed bed reactor in series. Each reactor had a dimension of 0.09 m i.d. and 1.5 m height and consisted of two regions. The lower region was a sludge blanket of 0.5 m height and the upper region was a packed-bed of 1 m height. The packed bed region was charged with ceramic raschig rings of 10 mm i.d., 15 mm o.d. and 20 mm length. The reactors were operated at 35$\circ$C and the hydraulic retention time(HRT) was maintained 24 hours. The synthetic wastewater composed of glucose and phenol as major components was fed into the reactor in a continuous mode with incereasing phenol concentration. In addition, the nutrient trace metals($Na^+, Mg^{2+}, Ca^{2+}, PO_4^{3-}, NH_4^+, Co^{2+}, Fe^{2+}$ etc.) were added for growing anaerobes. The phenol concentration of the effluent, the overall gas production, the composition of product gas, the efficiency of COD reduction and the duration of acclimation period were measured to determine the performance of the anaerobic wastewater treatment system as the phenol concentration of the influent was increased from 600 to 2400 mg//l. Successfully stable biodegradation of phenol could be achieved with the anaerobic treatment system from 600 to 1, 800 mg/l of the influent phenol concentration. The upper level of influent phenol loading was high enough to meet most of the practical requirement. The duration of acclimation increased with the phenol loading. At steady state of the influent phenol concentration of 1800 mg/l, the treatment performance indicated the phenol reduction efficiency of 99%, the COD reduction efficiency of 99% and the gas production rate of 37 l/day. At the influent phenol concentration of 2400 mg/l, however, the operation of the treatment system was noted unstable. While the concentration of methane in biogas decreased with increasing the influent phenol loading, the carbon dioxide was increased. However, the concentration of hydrogen was varied negligibly. The concentration of methane was high enough to be used as a fuel. As a result, it is suggested that anaerobic phenol wastewater treament was economical in the sense of energy recovery and wastewater treatment.

• Applied Chemistry for Engineering
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• v.29 no.5
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• pp.589-593
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• 2018

In this paper, an economic evaluation with the uncertainty analysis using a Monte-Carlo simulation method was performed for the glycerol steam reforming to produce $H_2$ at a capacity of $300m^3h^{-1}$. Fluctuations in a unit $H_2$ production cost were identified based on the variation of key economic factors at ${\pm}10-{\pm}40%$ and the probability of 30.9% was obtained for a previously reported unit $H_2$ production cost of 5.10 $ $kgH{_2}^{-1}$. In addition, fluctuations in the B/C ratio were obtained by varying the fixed capital investment (${\pm}20%$), cost of manufacturing (${\pm}20%$), revenue (${\pm}20%$), and discount rate (2-10%) and the probability ranging from 17 to 55% was observed to meet a minimum B/C ratio of 1 for the economic feasibility of the glycerol steam reforming to produce $H_2$.