• Applied Chemistry for Engineering
• /
• v.25 no.6
• /
• pp.648-653
• /
• 2014

Cr(VI)-heterocyclic complex (2,4'-bipyridinium chlorochromate) was synthesized by the reaction between heterocyclic compound(2,4'-bipyridine) and chromium trioxide, and characterized by IR and ICP analysis. The oxidation of benzyl alcohol using 2,4'-bipyridinium chlorochromate in various solvents showed that the reactivity increased with the increase of the dielectric constant (${\varepsilon}$), in the order : N,N-dimet-hylformamide (DMF) > acetone > chloroform > cyclohexene. In the presence of DMF solvent with acidic catalyst such as hydrochloric acid (HCl solution), 2,4'-bipyridinium chlorochromate oxidized benzyl alcohol (H) and its derivatives (p-$CH_3$, m-Br, m-$NO_2$). Electron-donating substituents accelerated the reaction rate, whereas electron acceptor groups retarded the reaction rate. The Hammett reaction constant (${\rho}$) was -0.67 (303 K). The observed experimental data have been rationalize the proton transfer occurred followed the formation of a chromate ester in the rate-determining step.

• Membrane Journal
• /
• v.25 no.3
• /
• pp.256-267
• /
• 2015

The goal is to compare two different aeration strategies for a pilot scale operation of submerged microfiltration with respect to the minimization of membrane fouling. A constant aeration (65 L/min) was examined parallel with a step-wise increase in airflow rate (40 to 65 L/min). The airflow rate was stepped to a higher rate every 5 min and the step-aeration cycles were repeated at regular intervals of 15 min. The comparative filtration runs were conducted with synthetic water containing powdered activated carbon (~10 g/L) and/or kaolin (~20 g/L) at a constant flux of 80 LMH. The extent and mechanisms of fouling in the microfiltration were identified by determining hydraulic resistance to filtration and the fouling reversibility after cleaning. Results showed that the step-aeration effectively alleviated fouling in the microfiltration of synthetic water compared to when using constant aeration. A substantial decrease in fouling was achieved by combining with coagulation using aluminum salts regardless of the aeration strategies. The constant aeration resulted in increased pore blocking likely due to increased accumulation of particles on the surface of membrane.

• Membrane Journal
• /
• v.17 no.3
• /
• pp.254-268
• /
• 2007

Sodium type faujasite(FAU) zeolite layers with diverse materials characteristics(Si/Al ratio, thickness, and structural discontinuity) were hydrothermally grown on a porous $\alpha-Al_2O_3$ tube, and then the $CO_2/N_2$ separation was evaluated at $30^{\circ}C$ for an equimolar mixture of $CO_2$ and $N_2$. Among hydrothermal conditions, $SiO_2$ content in hydrothermal solution seriously affected materials characteristics: with an increment in the $SiO_2$ content, Si/Al ratio, thickness, and structural discontinuity of grown FAU zeolite layer simultaneously increased. The present study reveals that structural discontinuity(intercrystalline voids due to an incomplete densification and cracks induced by GIS Na-P1 phase) is the most important variable affecting the $CO_2/N_2$ separation. Also, it was suggested that the $CO_2$ desorption in permeate side be the rate-determining(slowest) step in the overall $CO_2$ permeation.

• Resources Recycling
• /
• v.26 no.3
• /
• pp.39-46
• /
• 2017

AlN powder was prepared by carbon reduction and subsequent nitridation method through lab- scale experiments. AlN powder was synthesized using the mixture of high purity $Al_2O_3$ powder and carbon black at $1,600{\sim}1,700^{\circ}C$ for 0.5~6 hours under nitrogen atmosphere (flow rate of nitrogen gas: $4.7{\times}10^{-6}{\sim}20{\times}10^{-6}m^3/sec$) with variation of charged height of the mixture powder. Experimental results showed that size of the synthesized particles grows with increasing of temperature. The reaction activation energy was calculated as 382 kJ/mol at the temperature range, and it was considered that chemical reaction is the rate determining step. Content of oxygen and nitrogen of the prpared samples were 0.71~0.96 wt% and 30.7~35.1 wt%. The results was similar with those of the commercial AlN product.

• Bulletin of the Korean Chemical Society
• /
• v.23 no.3
• /
• pp.381-384
• /
• 2002

Second-order-rate constants ($k_N$) have been measured spectrophotometrically for the reactions of 4-nitrophenyl 2-thiophenecarboxylate (1a) with a series of secondary alicyclic amines in H2O containing 20 mole % DMSO at 25.0 $^{\circ}C$ . The ester 1a is less reactive than 4-nitrophenyl 2-furoate (1b) but more reactive than 4-nitrophenyl benzoate (1c) except towards piperazinium ion. The Brønsted-type plots for the aminolyses of 1a, 1b and 1c are linear with a $\beta$nuc value of 0.92, 0.84 and 0.85, respectively, indicating that the replacement of the CH=CH group by a sulfur or an oxygen atom in the benzoyl moiety of 1c does not cause any mechanism change. The reaction of piperidine with a series of substituted phenyl 2-thiophenecarboxylates gives a linear Hammett plot with a large $\rho^-$ value ($\rho^-$ = 3.11) when $\sigma^- $ constants are used. The linear Brønsted and Hammett plots with large $\beta$nuc and $\rho^-$ values suggest that the aminolysis of 1a proceeds via rate-determining break-down of the addition intermediate to the products.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
• /
• v.2 no.1
• /
• pp.85-90
• /
• 1998

The reaction rate of $CO_2$ with 2-amino-2-methyl-1-propanol (AMP), MEA monoethanolamine(MEA) and diethanolamine (DEA) in aqueous solutions has been determined using a stirred vessel with a plane gas-liquid interface over a wide range of concentrations of amines at different temperatures. The results show that the overall reaction rate is first order with respect to both $CO_2$ and amine. The reaction rate constant varies with temperature according to the relationship which agrees with the experimental data. The proposed interpretation is that the kinetic rate determining step is a reaction of $CO_2$ with amine to form carbamic acid which is then totally and immediately ionized.

• Journal of Environmental Science International
• /
• v.2 no.1
• /
• pp.85-90
• /
• 1993

The reaction rate of $CO_2$ with 2-amino-2-methyl-1-propanol (AMP), MEA monoethanolamine (MEA) and diethanolamine (DEA) in aqueous solutions has been determined using a stirred vessel with a plane gas-liquid interface over a wide range of concentrations of amines at different temperatures. The results show that the overall reaction rate is first order with respect to both $CO_2$ and amino. The reaction rate constant varies with temperature according to the relationship which agrees with the experimental data. The proposed interpretation is that the kinetic rate determining step is a reaction of $CO_2$ with amine to form carbamic acid which is then totally and immediately ionized.

• Bulletin of the Korean Chemical Society
• /
• v.7 no.2
• /
• pp.111-113
• /
• 1986

The axial alcohol in trans-3,3,5-trimethylcyclohexanol was oxidized more readily than the equatorial alcohol in cis-3,3,5-trimethylcyclohexanol by NBS in aqueous dioxane. On the contrary, the equatorial alcohol was preferentially oxidized to the axial one by 10% aqueous sodium hypochlorite in the presence of tetrabutylammonium hydrogen sulfate (TBHS). The specificity indicates the presence of two different mechanism. In acidic medium, the cleavage of C-H bond is rate determining step while the reactivity of the alcohol is important in the presence of TBHS. The mechanism in basic medium without TBHS will be discussed.

• Bulletin of the Korean Chemical Society
• /
• v.16 no.9
• /
• pp.839-844
• /
• 1995

The kinetics and mechanism of the reactions of phenyl benzoates with benzylamines and pyrrolidine are investigated in acetonitrile. The variations of ρX (ρXY>0) and ρZ (ρYZ<0) with respect to the substituent in the substrate (σY) indicate that the reactions proceed through a tetrahedral intermediate, T±, with its breakdown in the rate determining step. The large magnitudes of ρZ, ρXY and ρYZ as well as the effects of secondary kinetic isotope effects involving deuterated nucleophiles are also in line with the proposed mechanism.

• Bulletin of the Korean Chemical Society
• /
• v.13 no.5
• /
• pp.547-550
• /
• 1992

The oxidation of benzaldehyde, 3,4-dimethoxy benzaldehyde, p-methoxy benzaldehyde, m-$NO_2$-benzaldehyde, and m-chlorobenzaldehyde by pyridinium chlorochromate (Corey's reagent) are reported. Michaelis-Menten behaviour is observed. The rate determining step appears to be the decomposition of a complex of benzaldehyde with PCC either through a loss of $H^+$ or $H^-$ ions.