Byoung Sung Ahn

Mathematical modeling of silver extraction by an emulsion liquid membrane process

Abstract A general physical model of a typical batch extraction system employing an emulsion liquid membrane process for the extraction of silver has been developed. The model takes into account the extraction reaction between the silver ion and the carrier molecules at the external interface, the diffusion of the complex in the membrane phase, the stripping reaction at the internal interface and the reaction of silver ion with the reagent, HCL, in the internal phase to yield silver chloride incapable of permeating through the membrane phase. In addition, the leakage of the internal aqueous phase to the external aqueous phase due to membrane breakage has been incorporated in this model. The batch extraction of silver using D2EHPA as a carrier has been carried out under various experimental conditions. The experimental data can be well explained by the present model.

Synthesis of dimethyl carbonate by vapor phase oxidative carbonylation of methanol over Cu-based catalysts

Abstract Dimethyl carbonate (DMC) synthesis reaction by oxidative carbonylation of methanol has been studied using vapor phase flow reaction system in the presence of Cu-based catalysts. A series of Cu-based catalysts were prepared by the conventional impregnation method using activated carbon (AC) as support. The effect of various promoters and reaction conditions on the catalytic reactivities were intensively evaluated in terms of methanol conversion and DMC selectivity. The morphological analysis by X-ray diffraction and SEM was also conducted in order to characterize the emloyed catalysts. Regardless of catalyst compositions, the optimal reaction temperature for oxidative carbonylation of methanol was found to be around 120–130°C. The reaction rate was too slow below 100°C, while too much by-products was produced above 150°C. Among the various catalysts employed, CuCl 2 /NaOH/AC catalyst with the molar ratio of OH/Cu=0.5–1.0, has shown the best catalytic performance, which appears to have a strong relationship with the formation of intermediate species, Cu 2 (OH) 3 Cl.

A study on the hydrodechlorination reaction of dichlorodifluoromethane over PdAlF3 catalyst

Abstract The hydrodechlorination reaction of dichlorodifluoromethane (CF2Cl2) has been studied under an atmospheric pressure at 130–210°C over Pd AlF 3 catalyst. The effects of various reaction conditions on the catalyst performance in terms of the reaction rate and product distributions were extensively investigated and the adsorption behaviours of H2, CF2Cl2, CHF2Cl, CH2F2 and CH3F on the catalyst surface are compared. In addition, the plausible reaction scheme has been proposed based on the experimental observations. Under the assumption that the formation of two main products, CH2F2 and CH4, proceeds through the hydrogenation of intermediate species, CF∗2∗, the reaction rate constants have been calculated by fitting the experimental data with the reaction rate expression.

Mathematical modeling of penicillin G extraction in an emulsion liquid membrane system containing only a surfactant in the membrane phase

An extraction experiment of penicillin G was performed in an emulsion liquid membrane system in which only ECA 4360J exists in the organic membrane phase without a predominant carrier, Amberlite LA-2, used in our previous works and it functions as a carrier as well as a surfactant. A permeation model for the present system has been developed as a primary study to examine the transport mechanism of penicillin G in the previous batch and continuous systems with two carriers of Amberlite LA-2 and ECA 4360J. The model takes into account the mass transfer in the external aqueous film, the extraction reaction between penicillin G and ECA 4360J at the external interface, the diffusion of penicillin G in the emulsion phase, the stripping reaction at the internal interface and the pH change of internal aqueous solution containing Na2CO3 with penicillin G transported into the internal phase. The experimental data were well fitted with the present model. Also, an expression for the reaction of penicillin G with ECA 4360J was obtained through a series of equilibrium measurements in liquid–liquid extraction system.

The role of copper chloride hydroxides in the oxidative carbonylation of methanol for dimethyl carbonate synthesis

Abstract Dimethyl carbonate (DMC) synthesis by oxidative carbonylation of methanol has been studied using vapor phase flow reaction system in the presence of CuCl 2 /NaOH/AC (AC, activated carbon) catalysts. A series of CuCl 2 /NaOH/AC catalysts have been prepared by the conventional impregnation method with varying the molar ratio of OH/Cu from 0.0 to 1.0. The catalytic activity of CuCl 2 /NaOH/AC catalysts has been found to increase continuously with the increase of OH/Cu molar ratio as compared with CuCl 2 /AC catalyst. The morphological analysis by X-ray diffraction, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) has shown that the improved performance of CuCl 2 /NaOH/AC catalysts was closely related with the existence of copper chloride hydroxides (Cu 2 (OH) 3 Cl). Two different crystal habits of Cu 2 (OH) 3 Cl were observed in the catalyst surface based on the OH/Cu molar ratio. One is α-Cu 2 (OH) 3 Cl (atacamite) which is orthorhombic, while the other is γ-Cu 2 (OH) 3 Cl (paratacamite) which is rhombohedral. The catalyst phase was revealed to change from α-Cu 2 (OH) 3 Cl to γ-Cu 2 (OH) 3 Cl with the increase of OH/Cu molar ratio. The catalyst phase was α-Cu 2 (OH) 3 Cl dominant at the molar ratio of OH/Cu=0.5, while at the molar ratio of OH/Cu=1.0, γ-Cu 2 (OH) 3 Cl dominant. The γ-type catalyst was found to be more favorable to DMC synthesis than the α-type catalyst. The CO temperature-programmed desorption (TPD) experiments on the employed catalysts also strongly supported these observations.

Partial oxidation (POX) reforming of gasoline for fuel-cell powered vehicles applications

As a part of the development of a gasoline processor for integration with a proton-exchanged membrane (PEM) fuel cell, we carried out the POX reforming reaction ofiso-octane, toluene and gasoline over a commercial methane reforming catalyst, and investigated the reaction conditions required to prevent the formation of carbon and the effect of fuel constituents and sulfur impurities in gasoline. The H2 and CO compositions increased with increasing reaction temperature, while those of CO2 and CH4 decreased. It is desirable to maintain an O/C molar ratio of more than 0.6 and an H2O/C molar ratio of 1.5 to 2.0 for vehicle applications. It has been found that carbon formation in the POX reforming ofiso-octane occurs below 620 °C, whereas in the case of toluene it occurs below 640 °C. POX reforming of gasoline constituents led to the conclusion that hydrogen production is directly related to the constituents of fuels and the operating conditions. It was also found that the coke formation on the surface of catalysts is promoted by sulfur impurities in fuels. For the integration of a fuel processor with PEM fuel cell, studies are needed on the development of new high-performance transition metal-based catalysts with sulfur and coke-resistance and the desulfurization of fuels before applying the POX reformer based on gasoline feed.

Kinetics of Dimethyl Carbonate Synthesis From Ethylene Carbonate and Methanol Using Alkali-Metal Compounds as Catalysts

Dimethyl carbonate (DMC) was synthesized by the ester exchange reaction of ethylene carbonate and methanol. K2 CO3 , KOH, LiOH and NaOH were used as catalysts for DMC synthesis and their catalytic abilities were compared in terms of kinetics. LiOH showed the best reaction rate among the catalysts. The rate constant was estimated to be 0.02538 (dm 3 /mol) 0.21 /min at 298 K.

Reversible olefin complexation by silver ions in dry poly(vinyl methyl ketone) membrane and its application to olefin/paraffin separations

Rapid and reversible olefin coordination to silver ions in AgBF4–poly(vinyl methyl ketone) membrane has been characterized using FTIR and UV spectroscopy.

Study on Dissolution and Regeneration of Poplar Wood in Imidazolium-Based Ionic Liquids

Abstract We tested dissolution and regeneration of poplar wood using 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and 1-butyl-3-methylimidazolium acetate ([C4mim]OAc). When 5wt% of poplar sawdust in [C4mim]OAc was stirred at 130°C, 96wt% of added poplar was dissolved in [C4mim]OAc, whereas 25.3wt% of poplar dissolved in [C4mim]Cl at the same reaction condition. Fourier transform infrared spectroscopy (FT-IR) and lignin content analysis revealed that poplar was partially delignified during the dissolution and regeneration processes. X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and microscopy were used to characterize raw poplar sawdust, undissolved poplar, and regenerated wood from the poplar-ionic liquid solution. The direct acetylation of poplar-[C4mim]OAc solution using acetyl chloride was also performed in the absence of any organic solvent. FT-IR analysis of the resulting wood sample revealed the formation of partially delignified acetylated-poplar.

Selective hydrogenolysis of chlorofluorocarbons by RhCl(PPh3)3

Abstract Factors affecting hydrogenolysis of CFC-113a (CF 3 CCl 3 ) catalyzed by RhCl(PPh 3 ) 3 were studied to have an insight on the mechanism of the reaction. A slightly polar solvent such as THF is found to be appropriate for selective hydrogenolysis of fluorochlorocarbons. Kinetic analysis showed the reaction was first-order with respect to the concentrations of catalyst and substrate, respectively. Reaction rates were dependent on the concentration of Cl − ions added; the reaction rate increased initially but remained constant at the higher Cl − concentration. Striking effect of halide ions were rationalized by increased nucleophilicity of [RhX 2 (PPh 3 ) 2 ] − (X = Cl, Br, I), a product from the initial reaction between catalysts and added halide ions, toward CFC-113a. Hydrogenolysis of CFC-113 (CF 2 ClCFCl 2 ) produced HCFC-123a (CF 2 ClCHClF) and chlorotrifluoroethene (CF 2 =CFCl), a product from β-elimination of HCFC-123a, indicating nucleophilic attack of metal complexes to more electropositive carbons actually occurred. These results appears to support the S N 2 mechanism for the oxidative addition of CFC-113a. Added amines decreased reaction rates most probably by inhibiting the formation of more nucleophilic complexes mentioned above. Added proton induced decrease in reaction rates. Effect of added phosphines is rather complicated; reaction rates initially decline to the range where the ratio of [PPh 3 ] to [catalyst] is 6 but increase thereafter. This rate enhancement strongly indicates the existence of an independent phosphonium-containing reaction cycle. Light brownish compound was actually isolated and was spectroscopically characterized as [Ph 3 P(CCl 2 CF 3 )]Cl. Plausible reaction cycles are proposed and the rate equations for this proposed mechanism are derived.