• Journal of Microbiology and Biotechnology
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• v.23 no.9
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• pp.1221-1228
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• 2013

Two lipase genes (bpl1 and bpl3) from Antarctic Bacillus pumilus strains were expressed in Bacillus subtilis. Both recombinant lipases BPL1 and BPL2 were secreted to the culture medium and their activities reached 3.5 U/ml and 5.0 U/ml, respectively. Their molecular masses apparent using SDS-PAGE were 23 kDa for BPL1 and 19 kDa for BPL3. Both lipases were purified to homogeneity using ammonium sulfate precipitation and HiTrap SP FF column and Superose 12 column chromatographies. The final specific activities were estimated to be 328 U/mg for BPL1 and 310 U/mg for BPL3. Both lipases displayed an optimum temperature of $35^{\circ}C$, similar to other mesophilic enzymes. However, they maintained as much as 70% and 80% of the maximum activities at $10^{\circ}C$. Accordingly, their calculated activation energy at a temperature range of $10-35^{\circ}C$ was 5.32 kcal/mol for BPL1 and 4.26 kcal/mol for BPL3, typical of cold-adapted enzymes. The optimum pH of BPL1 and BPL3 was 8.5 and 8.0, respectively, and they were quite stable at pH 7.0-11.0, showing their strong alkaline tolerance. Both lipases had a preference toward medium chain length ($C_6-C_{10}$) fatty acid substrates. These results indicate the potential for the two Antarctic B. pumilus lipases as catalysts in bioorganic synthesis, food, and detergent industries.

• Korean Chemical Engineering Research
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• v.48 no.3
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• pp.332-336
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• 2010

Ionic liquid immobilized on mesoporous amorphous silica was prepared from the coupling of 1-(triethoxysilylpropyl)-3-n-alkyl-imidzolium halides with tetraethyl orthosilicate(TEOS) through template-free condensation under strong acidic conditions. The immobilized 1-n-butyl-3-methyl imidazolium bromide ionic liquid on amorphous silica(BMImBr-AS) was proved to be an effective heterogeneous catalyst for the synthesis of dimethyl carbonate(DMC) from transesterification of ethylene carbonate(EC) with methanol. High temperature, high carbon dioxide pressure and long reaction time were favorable for the reactivity of BMImBr-AS. Kinetic studies based on two step reactions revealed that the proposed reaction model fitted well the experimental data. The apparent activation energy was estimated to be 67.4 kJ/mol.

• Korean Journal of Materials Research
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• v.5 no.1
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• pp.3-11
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• 1995

$(TiO_{2})$ thin films were deposited on p-Si(100) substrate by APMOCVD using titanium isopropoxide as a source material. The deposition mechanism was well explained by the simple boundary layer theory and the apparent activation energy of the chemical reaction controlled process was 18.2kcal /mol. The asdeposited films were polycrystalline anatase phase and were transformed into rutile phase after postannealing. The postannealing time and the film thikness as well as the postannealing temperature also affected the phase transition. The C-V plot exhibited typical charateristics of MOS diode, from which the dielectric constant of about 80 was obtained. The capacitance of the annealed film was decreased but those of the Nb or Sr doped films were not changed. I-V characteristics revealed that the conduction mechanism was hopping conduction. The postannealing and the doping of Nb or Sr cause to decrease the leakage current and to increase the breakdown voltage.

• Korean Chemical Engineering Research
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• v.52 no.3
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• pp.395-401
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• 2014

In this work, the reaction characteristics for the non-catalytic esterification of palm fatty acid distillate were analyzed. The esterification reaction was assumed as the pseudo homogeneous $2^{nd}$ order reversible reaction and 'reaction effectiveness factor (${\eta}$)' was used to take accounts into evaporation and reaction of water and methanol, which take place simultaneously in the liquid phase. The nonlinear programming was used to derive appropriate kinetic parameters, the reaction rate constant and mass transfer coefficient, minimizing the error between experimental data and the numerical values. Based on these parameters, the apparent activation energy was calculated to be 43.98 kJ/mol.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.11
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• pp.882-889
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• 2011

In this study, we have investigated the effects of Co doping on I-V curves, bulk trap levels and grain boundary characteristics of ZnO-$Bi_2O_3$ (ZB) varistor. From I-V characteristics the nonlinear coefficient (a) and the grain boundary resistivity (${\rho}_{gb}$) decreased as 32${\rightarrow}$22 and 18.4${\rightarrow}0.6{\times}10^9{\Omega}cm$ with sintering temperature (900~1,300$^{\circ}C$), respectively. Admittance spectra and dielectric functions show two bulk traps of zinc interstitial, $Zn_i^{{\cdot}{\cdot}}$(0.16~0.18 eV) and oxygen vacancy, $V_o^{{\cdot}}$ (0.28~0.33 eV). The barrier of grain boundaries in ZBCo (ZnO-$Bi_2O_3-Co_3O_4$) could be electrochemically single type. However, its thermal stability was slightly disturbed by ambient oxygen because the apparent activation energy of grain boundaries was changed from 0.93 eV at the 460~580 K to 1.13 eV at the 620~700 K. It is revealed that Co dopant in ZB reduced the heterogeneity of the barrier in grain boundaries and stabilized the barrier against the ambient temperature.

• Bulletin of the Korean Chemical Society
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• v.32 no.7
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• pp.2267-2273
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• 2011

A novel energetic material, 1-amino-1-(2,4-dinitrophenylhydrazinyl)-2,2-dinitroethylene (APHDNE), was synthesized by the reaction of 1,1-diamino-2,2-dinitroethylene (FOX-7) and 2,4-dinitrophenylhydrazine in N-methyl pyrrolidone (NMP) at 110 $^{\circ}C$. The theoretical investigation on APHDNE was curried out by B3LYP/6-311+$G^*$ method. The IR frequencies analysis and NMR chemical shifts were performed and compared with the experimental results. The thermal behavior of APHDNE was studied by DSC and TG/DTG methods, and can be divided into two crystal phase transition processes and three exothermic decomposition processes. The enthalpy, apparent activation energy and pre-exponential factor of the first exothermic decomposition reaction were obtained as -525.3 kJ $mol^{-1}$, 276.85 kJ $mol^{-1}$ and $10^{26.22}s^{-1}$, respectively. The critical temperature of thermal explosion of APHDNE is 237.7 $^{\circ}C$. The specific heat capacity of APHDNE was determined with micro-DSC method and theoretical calculation method, and the molar heat capacity is 363.67 J $mol^{-1}K^{-1}$ at 298.15 K. The adiabatic time-to-explosion of APHDNE was also calculated to be a certain value between 253.2-309.4 s. APHDNE has higher thermal stability than FOX-7.

• Applied Chemistry for Engineering
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• v.10 no.4
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• pp.548-556
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• 1999

The thermal degradation of polyethylene has been studied using a nonisothermal thermogravimetric technique under a nitrogen atmosphere condition at several heating rates from 10 to $50^{\circ}C/min$. To obtain information on the kinetic parameters, the dynamic thermogravimetric analysis curve and its derivative have been analyzed by a variety of analytical methods such as Kissinger, Freeman-Carroll, Flynn-Wall, Coats-Redfern, Chatterjee-Conrad, Friedman, Horowitz-Metzger, Ozawa and Denq methods. The comparative works for the kinetic results obtained from various methods should be performed to determine the kinetic parameters, because three are tremendous differences in the calculated kinetic parameters depending upon the mathematical method taken in the analysis. From this work, it was found that the apparent activation energy of HDPE was larger than those of LDPE and LLDPE.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.765-774
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• 1995

The hot deformation behaviour of particulate reinforced aluminium 6061 Al composite were investigated by hot compression tests in the temperature range from 623K to 823K with strain rate of 10$^{-3}$ ~5.0 S$^{-1}$ . The effect of reinforced particulate volume fraction, mean diameter on the high temperature flow stress has also been studied. Experimental results showed that the increase in the volume fraction of reinforcement contributed to the rising of yield stress, but the stress above the yield point appeared to be steady state at all volume fractions. The apparent activation energy for deformation was 290KJ/mo1 for unreinforced 6061 Al, 327KJ/mo1 for 6061 Al-20vo1.% SiC composite and 531KJ/mo1 for 6061 Al-20vo1.%A1$_2$O$_3$composite. It appeared that $Al_2$O$_3$reinforced composites was more difficult to hot deform.

• Applied Chemistry for Engineering
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• v.3 no.2
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• pp.305-311
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• 1992

The experimental study on the reduction of $In_2O_3$ was performed by using thermogravimetric analyzer. The reduction of $In_2O_3$ was occurred at above $300^{\circ}C$. The reduction rates were rapidly increased with the reaction temperature, whilehardly affectedby the flow rate of hydrogen gas. It was found that the unreacted core model could be applied for the analysis of the reduction data and the rate control step was the chemical reaction of $In_2O_3$ with hydrogen on the surface of unreacted $In_2O_3$. The apparent activation energy for this reaction was 20kcal/g-mol $H_2$ and the rate equation of $In_2O_3$ reduction with hydrogen could be expressed in the following equation. ${\frac{dX}{dt}}=1.6{\times}10^5e^{-20000/RT}(1-X)^{2/3}$

• Korean Journal of Food Science and Technology
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• v.16 no.4
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• pp.451-456
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• 1984

Rheological properties of gelatinized rice starch solutions were investigated with Brookfield rotational viscometer. The 8% starch solution showed thixotropic behavior with yield stress. The alkali gelatinized starch was more thixotropic than the thermal gelatinized one. The time dependent characteristics of starch solutions followed Tiu's model. The value of rate constant $(a_1)$ in Tiu's model increased linearly with shear rate, and was exponentially dependent on concentration and temperature. Temperature dependency of rate constant and apparent viscosity followed Arrhenius type equation and the activation energy were about 14.3 and 6.8 Kcal/g mole, respectively. The $a_1-value$ was found to be useful to evaluate changes in structaral decay on the shearing time of gelatinized rice starch solutions.