• Bulletin of the Korean Chemical Society
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• v.23 no.6
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• pp.837-845
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• 2002

Based on ab initio calculations at the MP2(FULL)/6-31+G**//RHF/6-31G** level, we compare the energetic and mechanistic features of a model reaction for catalytic action of Δ?-3-ketosteroid isomerase (KSL,E.C.5.3,3.1) with those of a corresponding nonenzymatic reaction in aqueous solution. The results show that the two catalytic acid residues,Tyr14 and Asp99, can lower the free energy of activation by 8.6kcal/mol, which is in good agreement with the experimentally predicted~9 kcal/mol,contribution of electrophilic catalyses to the whole enzymatic rate enhancement. The dienolate intermediate formed by proton transfer from the substrate carbon acid to the catalytic base residue (Asp38) ins predicted to be stabilized by 12.0 kcal/mol in the enzymatic reaction, making its formation thermodynamically favorable. It has been argued that enzymes catalyzing the reactions of carbon acids should resolve the thermodynamic problem of stabilizing the enolate intermediate as well as the kinetic porblem of lowering the free energy of activation for porton abstraction. We find that KSI can successfully overcome the thermodynamic difficulty ingerent in the nonenzymatic reaction through the electrophilic catalyses of the two acid residues. Owing to the stabilization of dienolate intermediate, the reketonization step could influence the overall reaction rate more significantly in the KSI- catalyzed reaction than in the nonenzymatic reaction, further supporting the previous experimental findings. However, the electrophilic catalyses alone cannot account for the whole catalygic capability (12-13 kcal/mol), confiming the earlier experimental implications for the invement of additional catalytic components. The present computational study indicates clearly how catalytic residues of KSI resolve the fundamental problems associated with the entropic penalty for forming the rate-limiting transition state and its destabilization in the bulk solvation environment.

• Clean Technology
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• v.14 no.4
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• pp.287-292
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• 2008

In this study, computer simulation works have been performed for the capture process of the $CO_2$ and $H_{2}S$ gases contained in the effluent stream using methanol aqueous solution. In order to increase the solubilities of the $CO_2$ and $H_{2}S$ in the methanol aqueous stream, the operating pressure of the absorber was raised to 30 bar and the feeding temperature of the solvent was lowered to $-20^{\circ}C$ by using refrigeration cycle. NRTL liquid activity coefficient model was used to estimate the liquid phase nonidealities for methanol and water. Soave-Redlich-Kwong equation of state was used for the vapor phase nonidealities. Henry's law option was also used to calculate the solubilities of the supercritical noncondensible gases into the methanol aqueous solvent stream.

• Journal of Korean Society on Water Environment
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• v.22 no.1
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• pp.116-121
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• 2006

Fundamental investigations have been carried out to find the applicability of manganese nodule as an adsorbent of nickel ion with an intention that nickel can be secured in manganese nodule along with the treatment of wastewater. The average content of manganese in nodules which used in the experiments was about 27%. The content of nickel in manganese nodules was observed to increase up to 4 times higher with comparison to its original value after adsorption. When the initial concentration of nickel ion in artificial wastewater was lower than 500 mg/L, its adsorbed amount on manganese nodule was shown to increase continuously. However, no more than about 82 mg/L of nickel was attained at higher initial nickel ion concentration than 500 mg/L. The adsorption of nickel ion was increased with temperature under experimental conditions and as the size of manganese nodule particles became smaller more nickel ion was adsorbed on adsorbent. Regarding the effect of pH, the adsorption of nickel ion was more hindered as the solution became acidic. Adsorption behavior of nickel ion on manganese nodule was found to follow the Freundlich model well and kinetic analysis showed that the adsorption reaction of nickel ion was second order. Thermodynamic parameters for the nickel ion adsorption were estimated on the basis of thermodynamic equations and they were in good agreement with experimental results.

• Journal of the Korean Chemical Society
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• v.39 no.11
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• pp.837-841
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• 1995

Thermodynamic parameters for the hydrogen bonding between thiopropionamide(TPA) and proton donors such as triethylphosphine oxide(TEPO), triphenylphosphine oxide(TPPO), trimethylphosphate(TMP), and tributyl phosphate(TBP) in dilute carbon tetrachloride solution have been measured by near-IR spectroscopy. The νa + amide Ⅱ combination band of TPA has been resolved into two Lorentzian-Gaussian product components which have been identified with monomeric TPA and 1 : 1 hydrogen bonded complex. The equilibrium constants and thermodynamic parameters for the formation of 1 : 1 hydrogen bonded complex have been obtained by the analysis of concentration and temperature dependent spectra. The standard enthalpies for the 1 : 1 hydrogen bonded complex formation of TPA with TEPO, TPPO, TMP, and TBP in CCl4 have been found to be - 21.4, - 16.8, - 12.8, and - 12.9 kJ/mol, respectively. The results are explained by the inductive and steric effects of substituents.

• Resources Recycling
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• v.21 no.6
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• pp.74-81
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• 2012

The Influence of temperature on the recovery reaction of silver in aqueous solution was investigated based on Pourbaix diagram constructed by thermodynamic calculation at different temperatures. It was observed that the stability of water is more strongly affected by pH variation and the stable region of ${Ag^+}_{(aq)}$ is diminished at higher temperature. It was shown that the recovery of $Ag_{(aq)}$ in the forms of $Ag_{(s)}$ and $Ag_2O_{3(s)}$ is more advantageous thermodynamically at lower temperature, however, the recovery of $Ag_{(aq)}$ in the forms of $Ag_2O_{(s)}$ 및 $Ag_2O_{2(s)}$ is more advantageous as temperature increases. The rise of temperature is considered to demote the recovery of silver thermodynamically in strong acidic condition ($pH{\leq}2$), but more silver is regarded to be recovered with temperature above pH 2. Finally, The recovery of silver in the elemental state is shown to be more sensitively influenced by temperature variation compared with the recovery of silver in its oxide form.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.2
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• pp.66-73
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• 2017

This study was to evaluate the influential parameters such as intial Cs concentration, reaction temperature, contact time and pH variation of solution on Cs adsorption. Using the experimental data, adsorption kinetics, isotherms and thermodynamic properties were analyzed. The Cs ion adsorption of the zeolite X was effective in the range from pH 5 to 10 and reached equilibrium after 60 minutes. The adsorption kinetics and isotherms of Cs ion with the zeolite X was described well by the pseudo-second-order kinetic and Langmuir isotherm model. The maximum adsorption capacities of Cs ion calculated from Langmuir isotherm model at 293~333 K were from 303.03 mg/g to 333.33 mg/g. It was found that thermodynamic property of Cs ion absorption on the zeolite X was spontaneous and endothermic reaction. The experimental data were fitted a second-order polynomial equation by the multiple regression analysis. The values of the dependent variable calculated by this best fitted model equation were in very good agreement with the experimentally obtained values.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.3
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• pp.1502-1511
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• 2013

In this study, simulation works have been performed for the modeling of $CO_2$ removal process contained in the DME production process through an absorber-stripper system using methanol aqueous solution. Aspen Plus release 7.3 in AspenTech company was utilized as a simulation tool and PC-SAFT modeling equation of state was used as a thermodynamic model. Fitting parameters built-in PC-SAFT model was determined by regressing experimental data, predicted results using PC-SAFT model were compared with experimental data in order to verify the exactness of the thermodynamic model. Optimization works have been performed to reduce the utility consumptions using solvent circulation rate, column operating pressure and feed stage location as manipulated variables.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1197-1205
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• 1988

An analytical method to predict qualitative performance characteristics of the Stirling Engines in the preliminary design stages is investigated. Both the expansion and the compression cylinder are treated as adiabatic and piston motions are approximated as saw-toothed waves. Basic equations which were originally proposed by Finkelstein consist of mass conservation and energy balances for each adiabatic cylinder. The approximation on piston motions and physical conditions make it possible to divide an engine cycle into four fundamental processes. In each process, first, pressure can be expressed as a function of the crank angle by solving a nonlinear first order ordinary differential equation and other thermodynamic variables are determined in turn. Application of the cyclic steady condition to the whole processes can complete a cycle. Also, further analysis results in analytic expressions for cyclic work and heat transfer in terms of the engine parameters and thermodynamic variables at boundary points. The results are expected useful as a quick reference for the engine performances. Finally, the present method can be applied to the other adiabatic analyses on the Stirling Engines with piece wise linear piston motions, if mass variations are predictable.

• Applied Chemistry for Engineering
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• v.25 no.1
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• pp.20-26
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• 2014

The interaction of p-halogenated phenol derivatives with the micellar system of tetradecyltrimethylammonium bromide (TTAB) was studied by the UV/Vis spectrophotometric method. Effects of substituents, additives, and temperatures on the solubilization of phenol derivatives have been measured. The results show that all the values of ${\Delta}G^o$ and ${\Delta}H^o$ were negative and the values of ${\Delta}S^o$ were positive for all phenol derivatives within the measured temperature range. The calculated thermodynamic parameters depended on the size, the electro-negativity, and the hydrophobic property of halogen substituents. The addition of n-butanol results in the decrement in tthe Ks values and the addition of NaCl caused the increment in the Ks values for all the phenol derivatives. From these changes we can postulate that the solubilization sites of the phenol derivatives in the micelle depend severely on properties of the halogen-substituent.

• Membrane and Water Treatment
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• v.9 no.2
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• pp.95-104
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• 2018

Copper pollution around the world has caused serious public health problems recently. The heavy metal adsorption on traditional membranes from wastewater is limited by material properties. Different adsorptive materials are embedded in the membrane matrix and act as the adsorbent for the heavy metal. The carbonized leaf powder has been proven as an effective adsorbent material in removing aqueous Cu(II) because of its relative high specific surface area and inherent beneficial groups such as amine, carboxyl and phosphate after carbonization process. Factors affecting the adsorption of Cu(II) include: adsorbent dosage, initial Cu(II) concentration, solution pH, temperature and duration. The kinetics data fit well with the pseudo-first order kinetics and the pseudo-second order kinetics model. The thermodynamic behavior reveals the endothermic and spontaneous nature of the adsorption. The adsorption isotherm curve fits Sips model well, and the adsorption capacity was determined at 61.77 mg/g. Based on D-R model, the adsorption was predominated by the form of physical adsorption under lower temperatures, while the increased temperature motivated the form of chemical adsorption such as ion-exchange reaction. According to the analysis towards the mechanism, the chemical adsorption process occurs mainly among amine, carbonate, phosphate and copper ions or other surface adsorption. This hypothesis is confirmed by FT-IR test and XRD spectra as well as the predicted parameters calculated based on D-R model.