Volume 1 Issue 2

Authors: Congxiao Shang; Mi Tian

Abstract: Titanium carbide (TiC) and molybdenum carbide (Mo2C) particles were selected to modify the hydrogen storage properties of magnesium hydride (MgH2). (MgH2+ 2 mol% TiC) and (MgH2+2 mol% Mo2C) mixtures were prepared using both cryogenic milling and high-energy ball milling. The morphology and crystallite structure of the mixtures were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The milled (MgH2+TiC) and (MgH2+Mo2C) composites consisted of γ-MgH2 and β-MgH2. TiC nanoparticles with the size of 10~20 nm after milling were deposited onto the surface or into the grain boundary of MgH2. Mo2C were uniformly distributed on the surface of MgH2 particles. Thermogravimetry and derivative thermogravimetric analyses showed that ~6.5 wt. % hydrogen was desorbed from (MgH2+TiC) mixture in the temperature range from 190 to 400 °C at a heating rate of 10 °C/min under He flow. The on-set and peak temperatures were 190 and 280 °C, respectively, for (MgH2+TiC) ball-milled up to 60 hrs after 8 hrs cryomilling. However, (MgH2+Mo2C) shows much higher desorption temperature of 300 °C (on-set) and 358 °C (peak), respectively, compared with those recorded for (MgH2+TiC). The hydrogen desorption activation energy of the milled (MgH2+TiC) mixture, 104 kJ/mol, was also substantially reduced, compared with that of the (MgH2+ Mo2C) mixture, 167 kJ/mol. The addition of TiC nanoparticles has greater effect on reduction of hydrogen desorption temperatures and acceleration of desorption kinetics.

Keywords: Hydrogen Storage; MgH2; TiC; Mo2C; Nanoparticles; Mechanical Milling; Cryogenic Milling

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Authors: A.S. Fouda; Y.A. Elewady; H.K. Abd El-Aziz

Abstract: The corrosion inhibition effect of cationic surfactants, namely cetyl trimethyl ammonium bromide: CTAB and dodecyl trimethyl ammonium chloride: DTAC, have been used as corrosion inhibitors for 1037 C-steel in 0.5 M HCl. The inhibition efficiency has been determined by weight loss and electrochemical measurements. The results show that the order of inhibition efficiency is CTAB > DTAC. Polarization curves indicate that all investigated surfactants are mixed inhibitors. Adsorption of these surfactants was in agreement with the Langmuir adsorption isotherm. The density function theory (DFT) was used to study the structural properties of the surfactants. The inhibition efficiencies of cationic surfactants showed a certain relationship to Pearson HSAB principle and Fukui indices.

Keywords: Carbon Steel; Electrochemical Calculations; DFT; Acid Corrosion

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Authors: Francisco Maugeri; Mónica Alvarado-Huallanco

Abstract: Modeling and simulation studies represent powerful tools, saving time and resources for the development of bioprocesses. Thus, studies of modeling, simulation and production of fructooligosaccharides, from sucrose, with fructosyl transferase from Rhodotorula sp. have been performed lately. In this paper, dynamic modeling of the synthesis process in continuous basket bioreactor was carried out, from mass balances and reaction kinetics, equally contemplating the resistance to mass transfer phenomena. The computational tools used were the Simulink programs of the MatLab 6.0 software, MathWork, Inc, USA. The model obtained, together with the simulation process, were used for the in silico optimization of the continuous production of fructooligosaccharides by fructosyl transferase immobilized in an inorganic support. A factorial design methodology was used, performing a central composite rotational design (CCRD). The optimum conditions obtained were: 4 Ui/mL of biocatalytic activity, stirring speed of 35 rpm, sucrose feed concentration of 550 g/L and residence time of 29 h. The other process conditions such as pH, temperature and substrate concentration were similar to those obtained in previous studies. Thus, in optimal conditions, the yield of FOS was around 31.2% and productivity around 5.4 gLh, sucrose feed concentration of 50%, 50C of temperature and pH 4.5. The results showed that, for the continuous reactor, the FOS yield was about 31%, lower than in batch process; however the main FOS fraction was GF4, around 30.4% of the total, a different result from those obtained by other types of reactors. Finally, biocatalytic activity and mass transfer coefficient had significant influence on the course of the reaction and on the FOS yield.

Keywords: Fructosyltransferase; Rhodotorula sp.; Fructooligosaccharides; Immobilized Enzyme; Continuous Basket Reactor; Mathematical Modeling; Simulation and Process Optimization

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