Comparative assessment of the ability of a microwave absorber nanocatalyst in the microwave-assisted biodiesel production process

In this study, a carbon-supported KOH/Ca₁₂Al₁₄O₃₃ nanocomposite was fabricated via the microwave combustion method, in which dextrose was used as a carbon source, and its activity in the microwave-assisted transesterification reaction as a microwave absorption material was assessed. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry, Brunauer–Emmett–Teller (BET), field-emission scanning electron microscopy, and energy dispersive X-ray analyses. The results showed that the carbonate and noncarbonate samples had a calcium aluminate (Ca₁₂Al₁₄O₃₃) structure as a support. Different carbon groups were formed during preparation of the carbon-supported KOH/Ca₁₂Al₁₄O₃₃ nanocomposite, which improved its surface area and porosity. Although the samples presented similar basicity, the carbonated nanocomposite exhibited twice as much activity as the KOH/Ca₁₂Al₁₄O₃₃ nanocatalyst for conversion of canola oil to biodiesel in the microwave-assisted transesterification reaction at 270 W microwave power. The nanocomposite with a larger pore size made active sites easily accessible and exhibited higher catalytic ability where the conversion of 98.8% was obtained under the optimized conditions of 270 W microwave power, methanol/oil molar ratio of 15, 4 wt% of the nanocomposite, and 30 min of reaction time. The carbon-supported nanocatalyst can be reused for at least four times with less reduction in activity. Furthermore, the obtained biodiesel showed that it met the standard values (EN 14214 and ASTM D-6751) with respect to the density, kinematic viscosity at 40 °C, acid number, and flash point.     

Evaluation of adsorption of nonionic surfactants blend at water/oil interfaces

The inherent biocompatibility of Span and Tween surfactants makes them an important class of nonionic emulsifiers that are employed extensively in emulsion and foam stabilization. The adsorption of Span-Tween blend at water/oil surface of emulsion has been investigated using a population balance model for the first time. Destability of emulsion was modeled by considering sedimentation, coalescence and interfacial coalescence terms in population balance equation (PBE). The terms of coalescence efficiency and interfacial coalescence time were considered as a function of surface coverage of droplets by surfactant molecules. The surface coverage at different surfactant concentrations was determined by minimization of difference between the model predictions and experimental average droplet sizes. After optimization, the surface coverage outputs were fitted with different adsorption isotherms to evaluate the adsorption behavior of Span-Tween surfactants blend at water/oil surface. The results show that Freundlich isotherm can predict the adsorption behavior of closer to the experimental observation. Moreover, fitted parameters imply the favorable adsorption of Span-Tween blend at water/oil interface.     

Detecting high-potential conditions of asphaltene precipitation in oil reservoir

Crude oil contains a wide range of components with different chemical natures. Complex molecules consisting of associated groups of polyaromatic sheets and alkyl side chains are known as asphaltene. Asphaltenes are insoluble in solvents such as n-heptane and n-pentane and soluble in benzene and toluene. Asphaltene causes serious damages around the wellbore and the reservoir by reducing permeability and plugging the pores. This paper includes a natural depletion test, performed on the bottom-hole sample and on a carbonate-core sample. The main emphasis is to identify high potentially damaged conditions in the reservoir from the asphaltene precipitation point of view. Stability of asphaltene was investigated by Saturates-Asphaltenes-Resins-Aromatics (SARA) analysis; moreover, asphaltene composition, permeability reduction, and porosity reduction were measured using the natural depletion in 4500, 3000, 2500, and 1450 psig via both static and dynamic approaches. At the pressures above the bubble point, asphaltene precipitation decreases as pressure increases, and the solubility model becomes dominant; on the other hand, below the saturation pressure, decrease in the pressure would decreases asphaltene precipitation and let the colloidal model dominate. It can be concluded that the maximum amount of asphaltene precipitation occurs near the saturation pressure. Asphaltene precipitation was then investigated through the core sample, using a novel scaling equation.     

Statistical analysis of instantaneous turbulent heat transfer in circular pipe flows

Turbulent heat transfer in circular pipe flow with constant heat flux on the wall is investigated numerically via Large Eddy Simulations for frictional Reynolds number Re _τ  = 180 and for Prandtl numbers in the range 0.1 ≤ Pr ≤ 1.0. In our simulations we employ a second-order finite difference scheme, combined with a projection method for the pressure, on a collocated grid in cylindrical coordinates. The predicted statistical properties of the velocity and temperature fields show good agreement with available data from direct numerical simulations. Further, we study the local thermal flow structures for different Prandtl numbers. As expected, our simulations predict that by reducing the Prandtl number, the range of variations in the local heat transfer and the Nusselt number decrease. Moreover, the thermal flow structures smear in the flow and become larger in size with less sharpness, especially in the vicinity of the wall. In order to characterize the local instantaneous heat transfer, probability density functions (PDFs) for the instantaneous Nusselt number are derived for different Prandtl number. Also, it is shown that these PDFs are actually scaled by the square root of the Prandtl number, so that a single PDF can be employed for all Prandtl numbers. The curve fits of the PDFs are presented in two forms of log-normal and skewed Gaussian distributions.     

A LBM–DEM solver for fast discrete particle simulation of particle–fluid flows

The lattice Boltzmann method (LBM) for simulating fluid phases was coupled with the discrete element method (DEM) for studying solid phases to formulate a novel solver for fast discrete particle simulation (DPS) of particle–fluid flows. The fluid hydrodynamics was obtained by solving LBM equations instead of solving the Navier–Stokes equation by the finite volume method (FVM). Interparticle and particle–wall collisions were determined by DEM. The new DPS solver was validated by simulating a three-dimensional gas–solid bubbling fluidized bed. The new solver was found to yield results faster than its FVM–DEM counterpart, with the increase in the domain-averaged gas volume fraction. Additionally, the scalability of the LBM–DEM DPS solver was superior to that of the FVM–DEM DPS solver in parallel computing. Thus, the LBM–DEM DPS solver is highly suitable for use in simulating dilute and large-scale particle–fluid flows.     

Mass flow rate prediction of pressure–temperature-driven gas flows through micro/nanoscale channels

In this paper, we study mass flow rate of rarefied gas flow through micro/nanoscale channels under simultaneous thermal and pressure gradients using the direct simulation Monte Carlo (DSMC) method. We first compare our DSMC solutions for mass flow rate of pure temperature-driven flow with those of Boltzmann-Krook-Walender equation and Bhatnagar-Gross-Krook solutions. Then, we focus on pressure–temperature-driven flows. The effects of different parameters such as flow rarefaction, channel pressure ratio, wall temperature gradient and flow bulk temperature on the thermal mass flow rate of the pressure–temperature-driven flow are examined. Based on our analysis, we propose a correlated relation that expresses normalized mass flow rate increment due to thermal creep as a function of flow rarefaction, normalized wall temperature gradient and pressure ratio over a wide range of Knudsen number. We examine our predictive relation by simulation of pressure-driven flows under uniform wall heat flux (UWH) boundary condition. Walls under UWH condition have non-uniform temperature distribution, that is, thermal creep effects exist. Our investigation shows that developed analytical relation could predict mass flow rate of rarefied pressure-driven gas flows under UWH condition at early transition regime, that is, up to Knudsen numbers of 0.5.     

An Efficient Synthesis of 8-Hydroxy-6,7-dimethoxy-3-methylisocoumarin (6-O-methylreticulol)

An efficient synthesis of 8-hydroxy-6,7-dimethoxy-3-methylisocoumarin (6-O-methylreticulol), a metabolite of several fungal species possessing phosphodiesterase inhibitor, topoisomerase I inhibitor activities and antitumor efficacy, has been described. 3,4,5-Trimethoxyhomophthalic acid was refluxed with acetic anhydride in dry pyridine and the resulting 2,3,4-trimethoxy-6-(2-oxopropyl)benzoic acid was smoothly cyclodehydrated to 6,7,8-trimethoxy-3-methylisocoumarin using acetic anhydride. Regioselective demethylation of the latter yielded the 6-O-methylreticulol. __________ Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1644–1648, November, 2005.     

Synthesis of 7,8-benzo-9-aza-4-oxabicyclo[3.3.1]nonan-3-ones by sequential ‘condensation–iodolactonization’ reactions of 1,1-bis(trimethylsilyloxy)ketene acetals with isoquinolines

Functionalized 7,8-benzo-9-aza-4-oxabicyclo[3.3.1]nonan-3-ones were prepared by regio- and diastereoselective condensation of 1,1-bis(silyloxy)ketene acetals with isoquinolinium salts and subsequent regioselective and stereospecific iodolactonization.     

Cyclic voltammetric studies of the redox behavior of iron(III)-vitamin B6 complex at carbon paste electrode

Electrochemical redox behavior of Fe-vit B₆ complex is investigated in HEPES buffer in the pH range 5.1–13.1 using cyclic voltammetry. Well-defined anodic and cathodic peaks are observed in the voltammograms at pH 13.1. At pH 8.0, only one cathodic peak and at pH 5.1, only one anodic peak are found. At all the pH values, the peak potential separation is much higher than that of a reversible electrochemical reaction. The peak current ratio (i _pa/i _pc) is less than unity and decreases with the scan rate. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 6, pp. 691–697. The text was submitted by the authors in English.     

3-D finite element modeling of laser cladding by powder injection: effects of laser pulse shaping on the process

This paper introduces a 3-D transient finite element model of laser cladding by powder injection to investigate the effects of laser pulse shaping on the process. The proposed model can predict the clad geometry as a function of time and process parameters including laser pulse shaping, travel velocity, laser pulse energy, powder jet geometry, and material properties. In the proposed strategy, the interaction between powder and melt pool is assumed to be decoupled and as a result, the melt pool boundary is first obtained in the absence of powder spray. Once the melt pool boundary is obtained, it is assumed that a layer of coating material is deposited on the intersection of the melt pool and powder stream in the absence of the laser beam in which its thickness is calculated based on the powder feedrate and elapsed time. The new melt pool boundary is then calculated by thermal analysis of the deposited powder layer, substrate and laser heat flux. The process is simulated for different laser pulse frequencies and energies. The results are presented and compared with experimental data. The quality of clad bead for different parameter sets is experimentally evaluated and shown as a function of effective powder deposition density and effective energy density. The comparisons show excellent agreement between the modeling and experimental results for cases in which a high quality clad bead is expected.