Band 14, Heft 2 -

In this study, adsorption properties of arc produced Multi Walled Carbon Nanotubes (MWNT) were investigated for Bovine Serum Albumin (BSA) in aqueous phase. Solution pH, adsorbent amount and temperature effects were examined on protein adsorption. The results show that, the temperature and the adsorbent amount both increase the BSA adsorption, whereas the solution pH has a decreasing effect. The equilibrium behavior of protein adsorption was examined by Langmuir and Freundlich isotherms. The monolayer adsorption capacities at 40 °C for solution pH 4 and 5 were determined as 139.5 and 127.2 mg g −1 , respectively, which were much higher than the BSA adsorption capacities of various metal oxides investigated in our previous studies. The adsorption rate data were compared by the pseudo-first and the second-order kinetics equations. Evaluation of the experimental kinetics data have shown that the adsorption of BSA by MWNT followed the pseudo-first-order kinetics. The pseudo-first order adsorption rate constants at pH 4 and 5 decreased with an increase in temperature which results in a decrease in diffusion rate of BSA molecules across the external boundary layer, and favors the sorption process. The adsorption behavior of protein by carbon nanotubes was explained also using the zeta potential measurements. The adsorption capacity decreased with increasing pH due to the electrostatic repulsions. The thermodynamic parameters evaluated to predict the nature of adsorption confirmed the non-spontaneous and endothermic behaviour of the BSA/MWNT adsorption process. Adsorption standard enthalpy values were found as ∆ H 0 =59.5 kJ mol −1 and ∆ H 0 =14.3 kJ mol −1 for pH 4 and 5, respectively indicating that the protein molecules are adsorbed electrostatically on the carbon nanotubes.

In this study, the catalytic behavior of protonated clinoptilolite in propane-SCR-NO x was investigated. The experiments were carried out in the temperature range of 200–500 °C as a function of zeolite mesh size 20, 35 and 70 at different weights of zeolite (0.45–1 g) and flow rates (300–600 ml/min) and consequently at various gas hourly space velocities (GHSV). Group method of data handling (GMDH) and artificial neural network (ANN) system were applied for mathematical modeling of NO x conversion to N 2 in propane-SCR-NO x . The operating temperature (T), volumetric flow rate (F) and the weight of clinoptilolite zeolite (W) and the conversion of NO x to N 2 (X) were considered as the inputs and output, respectively. In order to evaluate the models performance, conversions of NO x obtained from the GMDH and ANN systems were compared with those obtained from the experimental method. It is concluded that the ANN could successively estimate the conversion and the results were in a good agreement with the experimental data.

Esterification of acrylic acid with ethanol, catalyzed by sulfuric acid has been carried out in stirred batch reactor under atmospheric pressure. Different parameters such as effect of initial molar ratios of the reactants, effect of catalyst concentration, initial water and effect of temperature has been studied in the batch reactor. Different catalyst loading system (1–3 vol%), reaction temperatures (50–70 °C), initial reactants molar ratio (1:1–1:3) and water concentration in feed (0–20 vol%) was used in the reaction system. The temperature dependence is exponential and expressed by Arrhenius type of relationship. Kinetics parameters such as equilibrium constant, rate constants, activation energy and reaction enthalpy and entropy were estimated by experimental data. The rate equation has a remarkable fit to the data and was able to describe the behavior of the system at various reaction temperatures. Hydrochloric acid (HCl) and hydro iodic acid (HI) were also compared with sulphuric acid as catalyst for esterification of acrylic acid with ethanol. Sulphuric acid was found to be more efficient catalyst for esterification as it induces the maximum conversion of acrylic acid.

A composite catalytic membrane (CCM), as a heterogeneous catalyst, was prepared from sulfonated polyethersulfone (SPES) and polyethersulfone (PES) impregnating polyphenylene sulfide (PPS) non-woven fabric by solvent evaporation method, which was employed to produce butyl acetate from continuous esterification of acetic acid with n-butyl alcohol in a flow-through mode. The pervaporation-assisted esterification was also carried out to promote forward reaction of the esterification through online removing the water produced. The results showed that the n-butyl alcohol conversion was over 95.0 % at the reaction temperature of 363 K, the initial acetic acid/n-butyl alcohol molar ratio of 4:1 and the residence time of 4,000 s in single flow-through mode. In the pervaporation-assisted esterification, an obvious enhancement in conversion was achieved compared with the esterification without pervaporation. And the CCMs presented a good catalytic activity and stability.

An unsteady two-dimensional laminar forced convection heat transfer around a square cylinder with rounded corner edge is numerically investigated for Prandtl Number, Pr=0.01–1,000 and non-dimensional corner radius, r =0.50–0.71 at low Reynolds number, Re=100. The effect of gradual transformation of square cylinder into circular cylinder on heat transfer phenomenon is studied. The lateral sides of the computational domain are kept constant to maintain the blockage as 5 %. A structured non-uniform mesh is used for the computational domain and the Finite Volume Method (FVM) based commercial software Ansys FLUENT is used for numerical simulation. The heat transfer characteristics over the rounded corner square cylinder are analyzed with the isotherm patterns, local Nusselt number (Nu local ), average Nusselt number (Nu avg ) at various Pr and various corner radii. It is found that the heat transfer rate of a circular cylinder can be enhanced 14 % by introducing a new cylinder geometry of corner radius, r =0. 51.

A multiphase-Eulerian, three-dimensional (3-D), computational fluid dynamics (CFD) model was built to investigate the local hydrodynamics of a pilot-scale (0.29 m ID, 3 m height) Slurry Bubble Column Reactor (SBCR). The model was first validated against the gas holdup radial profiles in an air-water-glass beads system obtained in a 0.254 m ID and 2.5 m height column under ambient conditions at various superficial gas velocities by Yu and Kim (Bubble characteristics in the radial direction of three-phase fluidized beds. AIChE Journal 34, 2069–2072, 1988). The model was next validated against the gas holdup radial profile data for N 2 -Drakeol-glass beads system obtained in a 0.44 m ID and 2.44 m height reactor, including internals, operating under ambient conditions at various superficial gas velocities by Chen et al. (Fluid dynamic parameters in bubble columns with internals. Chemical Engineering Science 54, 2187–2197, 1999). The model was also validated against experimental data obtained in our lab for N 2 -Fischer Tropsch (F-T) reactor wax-Fe catalyst system obtained in a pilot-scale, Slurry Bubble column Reactor, SBCR (0.29 m ID, 3 m height) under pressures and temperatures up to 25.9 bar and 490 K, respectively. These three validations led to the selection of the turbulence and interphase drag coefficient models, and the optimization of the solution method, mesh size and structure and the step size. Moreover, the inclusion of RNG k-ε turbulence model coupled with the Wen-Yu (Mechanics of Fluidization. Chemical Engineering Progress Symposium Series 62, 100–111, 1966) / Schiller-Naumann (A drag coefficient correlation. Zeitung Ver. Deutsch. Ing 77, 318–320, 1935) drag correlations, and the mass transfer coefficients were found to provide the most accurate predictions of the experimental data. The CFD model was then used to investigate local gas holdup, liquid recirculation, local turbulence intensities, bubble diameters, and solids distribution throughout our pilot-scale SBCR, operating under typical F-T process conditions. The model predictions showed strong liquid recirculation and backmixing near the walls of the reactor, and the solid-phase velocity vectors closely followed those of the liquid-phase. A relatively high liquid turbulence intensities were observed in the vicinity of the sparger upon startup, however, after reaching a steady state, the liquid turbulence intensities became more evenly distributed throughout the reactor. The liquid turbulence intensities were slightly higher near the center of the reactor, and closely resembled the velocity vectors. Also, the Sauter mean bubble diameters increased, whereas the solids distribution decreased with reactor height above the gas distributor.

Computational fluid dynamics (CFD) was used to investigate the turbulent mixing performance in a vertical CJT in the range of Re=3,668−18,342. Energy source of hot water was centrally placed just below the top of the tank and temperature instead of concentration measurements were used to quantify mixing performance. The 95 % criterion for temperature equilibrium was employed to evaluate the local mixing degree, and the global mixing performance was evaluated based on the ratio of well-mixed volume to total fluid volume. It was obviously observed from the axial distributions of t 95 % that the macro-mixing times decreased slightly for z/H < 0.6 and a deep downward trends appeared with the increase of z/H with given r/R. The macro-mixing time in the jet mixing boundary layer were uniform which were a little longer than those in the bulk zones below z/H=0.5 and decreased sharply by 37.5−87.5 % than that in the bulk zone above z/H=0.5. The values of 95 % mixing time increased with the increase of r/R. The global t 95 % decreased with the increasing Reynolds number, and a power correlation between the global t 95 % values and Re was proposed. With the increasing logarithm of mixing time, the logarithm of segregation intensity rapidly decreased linearly in the slopes from –0.996 to –0.955. The segmentation intensity first decreased then increased with the increasing values of θ.

The utilization of CaSO 4 -based oxygen carrier suffers the deactivation problem caused by sulphur loss. To capture the gas sulphides and to improve the stability of CaSO 4 oxygen carrier, calcined limestone was introduced into the fuel reactor of Chemical Looping Combustion (CLC). Kinetic behaviors and thermodynamics of the combined process of coal gasification and oxygen carrier reduction using the mixed oxygen carrier CaSO 4 -CaO under different atmospheres were investigated. The effects of reaction temperature, gasification intermediate, and molar ratio of CaO to CaSO 4 on gas sulphide emissions, CO 2 generation, and distribution of other gas emissions and characterization of solid products are taken into account. It is found the CaO-based additive evidently suppressed the sulphur emissions, and improved both chemical reaction rate and CO 2 generation efficiency. The sulfation products, both CaS and CaSO 4 , can be used as oxygen carrier later. The optimum reaction parameters are evaluated and obtained in terms of gas sulphide emissions, CO 2 capture, other gas releases and maintenance of oxygen transfer capability.

In this investigation, time average local gas holdup and bubble dynamic data were achieved for three L/D ratios of slurry bubble column. The examined ratios were 3, 4 and 5 in 18″ diameter slurry bubble column. Air-water-glass bead system was used with superficial gas velocity up to 0.24 m/s. The gas holdup was measured using four tips optical fiber probe technique. The results showed that the gas holdup increases almost linearly with the superficial gas velocity in 0.08 m/s and levels off with a further increase of velocity. A comparison of the present data with those reported for other slurry bubble column having diameters greater than 18″ and L/D higher than 5 was made. The results indicated a little effect of diameter on the gas holdup. A local, section-averaged gas holdup increases with increasing superficial gas velocity, while the effect of solid loading are less significant than that of the superficial gas velocity. Chaos analysis was used to analyze the slurry system.