سال:1393 | دوره: | شماره: |تعداد مقالات:11

Cellulose sulfuric acid as a bio-polymer based solid catalyst efficiently catalyzes the selectively oxidation of sulfides to sulfoxides and thiols to disulfides using hydrogen peroxide as a green oxidant with good yields at room temperature. The developed method offers a number of advantages such as high selectivity, mild reaction conditions, simple operation, cleaner reaction profiles, low cost and biodegradability of the catalyst.

A binuclear macrocyclic ligand containing dissimilar N(amine) 2O2 and N (imine) 2O2 coordination sites sharing two phenolic oxygen atoms, was prepared by cyclic condensation of dialdehyde precursor L1H2 with 1, 3-diaminopropane. The ligand includes two propionitrile pendant arms on the amine nitrogen atoms. The homobimetallic complex [ZnL2Zn (OAc)] PF6 was synthesized by one step procedure. Heterobimetallic complexes [ZnL2M (OAc)] PF6 that M= Cu(II) and Ni (II), were prepared by a trans-metallation reaction. The prepared complexes were characterized on the basis of molar conductance measurement, elemental analysis, IR, NMR and UV-Vis spectroscopy techniques. Characterization results showed that the nitrogen atoms of propionitrile pendant arms are not involved in the coordination to the metal center and also the two metal ions are bridged by two phenolic oxygen atoms and an acetate group.

Recently, with increasing public awareness of food safety, developments of some valid and rapidly analytical methods are required for the determination of residual pesticides in crops. This study was conducted on validation of a reliable, accurate and precise method for multi analysis of pesticides residue in melon as a main fruit in Iranian food basket. A reliable, and valid method based on spiked calibration curves and modified QuEChERS sample preparation was developed for determination of 12 pesticide residues in melon by Gas Chromatography Mass Spectrometry (GC/MS). The interested pesticides are, diazinon, dimethoate, chlorothalonil, pirimicarb, chlorpyrifos-methyl, metalaxyl, a-endosulfan, b-endosulfan, permethrin 1, 2 and fenvalerate 1, 2 that are belonged to different chemical groups of pesticides. Triphenylmethane (TPM) is used as internal standard. Use of spiked samples for constructing the calibration curve substantially reduced adverse matrix-related effects. The recovery of pesticides at 3 concentration levels (n=3) was in range of 79.8-97.6%. The method was proved to be repeatable with RSD lower than 20%. The limits of quantification for all pesticides were <25 ng/g. The recoveries and repeatabilities were in accordance with the criteria set by SANCO Guideline (Commission of the European Communities, 2006). Using spiked samples for preparation of calibration curves is a sensitive, selective, rugged, rapid and accurate method in pesticides analysis.

The work focuses on the removing of Cu (II) from aqueous solution by Linde F (K) zeolite. The zeolite is synthesized from fly ash by hydrothermal process. The adsorption experiments discuss several factors including the optimal solution pH, zeolite dosage, adsorption temperature, adsorption kinetics and adsorption isotherm equation. The results show that, the optimal solution pH is 6 and the efficient zeolite dosage is 4g/L. Higher reaction temperature could favor the removal of Cu (II). The adsorption of Cu (II) on Linde F (K) zeolite is monolayer adsorption. The experiment data could be calculated by pseudo-second-order model and Langmuir isotherm. The adsorption process is endothermic and spontaneous and the system disorder increases with temperature.

Spherical mesoporous silica MCM-41 was synthesized for adsorptive removal of sulfur compounds from fossil fuels using 1mM solution of dibenzothiophene (DBT) in dodecane as model oil. The prepared silica adsorbent has been characterized by nitrogen adsorption-desorption analysis as well as Small Angle X-ray Scattering (SAXS), and transmission and Scanning Electron Microscopy (SEM) methods. Results showed that the prepared mesoporous adsorbent has ordered pore structures with surface area of 1106 m2/g and mean pore diameter of 3.54 nm. SEM micrographs indicated that prepared mesoporous silica (MCM-41) has spherical morphology with the narrow size distribution in the range of 200-300 nm. Hexagonal structure of pores has also been confirmed by high resolution transmission electron microscopy and SAXS pattern. High performance liquid chromatography analysis has also been utilized to study the kinetics of the DBT adsorption from dodecane solution by means of the synthesized silica. Results showed that 0.03 g/mL of mesoporous silica has capability to adsorb more than 42% of DBT (a sulfur containing compound) from dodecane solution. The improvement of mass transfer via adsorption DBT by the prepared nanosorbent is an efficient method for enhancement of biodesulfurization kinetic.

This paper describes the effects of induced magnetic field and partial slip on the peristaltic flow of a couple stress fluids in an asymmetric channel. The two dimensional equation of couple stress fluid are simplified by making the assumptions of long wave length and low Reynolds number. The exact solutions of reduced momentum equation and magnetic force function have been computed in wave frame. The expressions for stream function, magnetic force function and pressure rise per wave length have been also computed. Finally, the pressure rise, pressure gradient, velocity, magnetic force function and stream lines for different physical parameters of interest are plotted.

The design and optimization of hydrocyclones using CFD techniques are gaining popularity and the key to a successful simulation lies with the accurate description of the high turbulent swirling behavior of the flow. This paper presents a detailed comparison between the Omega RSM and the RNG k-e turbulence model, which are both derived specially for modeling swirling or rotational flow, in the simulation of a hydrocyclone. The predictions of velocity field, volume of vortexes, mass split and turbulent viscosity were obtained and compared. It is showed that in general both models gave similar predictions of the flow field under different inlet velocities, while the predictions of turbulent viscosity and in the core region of hydrocyclone were found more closely aligned with the reality using Omega RSM.

Due to high applicability of the fixed bed catalytic naphtha reforming reactors, hydrodynamic features of this kind of reactors with radial flow pattern are improved in this work by utilising computational fluid dynamics technique. Effects of catalytic bed porosity, inlet flow rate and flow regime through the bed on the flow distribution within the system are investigated. It is found that the first reactor among three fixed bed reactors in series is working inappropriately. It is due to the effects of recirculating flow on the hydrodynamics. In addition, flow distribution at the end of each bed is discovered to be non-uniform. By applying computational fluid dynamics technique to the system and manipulating effective parameters, not only vortices are removed at the end of each bed, but also flow distribution through the first reactor is considerably improved. A new internal modification for all reactors is proposed, which allows reactors to become overloaded with the catalyst. Subsequently, inlet flow rate can rise by 10-15 per cent over its current value.

The equation of state Soave-Redlich-Kwong (SRK) and its modification (predictive SRK or PSRK) are applied to simulate multicomponet distillation, which separate main component of spearmint essential oil. The simulation model is based on bubble point method, and the Wang-Henke algorithm. Spearmint essential oil is considered in the study and the original experimental data were obtained from pilot plant. The models were validated by continuous distillation column with trays of one to five numbers. The work allows concluding on the advantages, disadvantages and expected accuracy of SRK and PSRK equations of state for multicomponent distillation data in the system as those studied.

Constructing phase diagram and its subsequent quality lines for lean gas condensate reservoirs is always crucial and challenging topic in reservoir fluid studies. Due to small amounts of liquid drop-outs in lean gas condensates at reservoir conditions, full experimental tracking of phase diagram and its relevant quality lines is almost impossible for lean gas condensates. On the other hand, EOS models of reservoir fluid characterization softwares are always unable to estimate condensed liquid drop-outs at different pressures and temperatures precisely. This study aims to present a commingled experimental-simulation method which was designed to pinpoint and keep track full phase diagram with correspondent quality lines for a lean gas condensate fluid.

Fruit waste extract was selected as the sole substrate for carotenoid production and the effect of parameters like pH, temperature and agitation have been studied. A two-step simple sequential strategy was employed for the optimization of carotenoid production by Rhodotorula rubra. In the first step, one factor at a time was employed to evaluate the impact of pH on carotenoid production. The outcome revealed that pH has noteworthy influence on pigment production at ambient conditions with constant temperature and agitation. The prod-ced carotenoid was characterized and confirmed by UV-Visible and FT-IR spectroscopic analyses. A Box–Behnken design was then applied in the second step to optimize the pH, temperature and agitation to obtain high pigment yield. The statistical experimental design predicted the high yield conditions of different responses. The interaction between pH and temperature stood vital for improved carotenoid production (2.98±0.28 mg/L) with biomass yield of 7.83 mg/mL by the optimization of significant parameters. The optimum conditions followed for high yield carotenoids are pH (7.0), temperature (28.2oC), and agitation (150 rpm). Along with the above, biomass growth conditions were also studied and optimum parameter values were reported. The present work shows the effectiveness of abundantly available cheaper fruit waste extract as a sole substrate in obtaining carotenoids in significant amount by R. rubra.