Scientia Iranica
Volume:26 Issue: 3, May-Jun 2019

A well-defined, amphiphilic poly(styrene-block-acrylic acid)  (PSt-b-PAA) block copolymer to prepare a magnetic nanocomposite was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The synthesized PSt and PSt-b-PAA copolymer were characterized using FTIR and 1H NMR spectroscopies as well as GPC analysis. Afterward, a PSt-b-PAA/Fe3O4 magnetic nanocomposite was fabricated through the incorporation of Fe3O4 nanoparticles (NPs) into the synthesized block copolymer. The morphology of the fabricated magnetic nanocomposite was observed using SEM and TEM. The SEM image revealed that the PSt-b-PAA/Fe3O4 magnetic nanocomposite has spherical morphology with the mean diameter of 100 nm approximately. In addition the thermal properties of the synthesized polymers as well as magnetic nanocomposite were studied using DSC and TGA analysis. The developed nanocomposite may be applied for enzyme immobilization and cell separation.

An effective solvent- and catalyst-free method was introduced for synthesis of symmetrical N, N’-alkylidene bisamides as high usage compounds in organic chemistry. In order to show the generality, the synthesis was done with various benzamides and aldehydes to obtain various derivatives in high yields.

An improved and efficient method for the synthesis of 1- & 5-substituted 1H-tetrazole derivatives has been described in the presence of nano-ordered MCM-41-SO3H as an effective heterogeneous catalyst. This metal-free protocol, [2+3] cycloaddition of sodium azide to various nitriles or ethyl N-phenyl formimidate intermediate under mild reaction conditions, afford a wide range of 1H-tetrazoles in good to excellent yields. The catalyst was reused for five times without significant loss of catalytic activity.

Several methods have been developed for the modification of natural polymers. Most of the reported methods are expensive since the chemical reactions are carried out using chemical additives along with stabilizers. Microwave assisted synthetic strategies gained significant importance for materials synthesis due their eco-friendly nature. Guar gum is one of the important naturally occurring non-ionic polysaccharide, which has incredible industrial and commercial applications. A rapid method for protecting the hydroxyl group in sterically hindered gum was developed by microwave-assisted synthesis (MAS). An efficient synthesis of different novel guar gum derivatives such as (acetate, butyrate and propionate; GG1-GG3) was performed. A significant higher yield of ester was achieved for 15 min at 600 W using iodine as a reaction promoter. Gum ester formation was carried out at various concentrations and for different reaction intervals. The synthesized products were characterized using FTIR, NMR, and SEM techniques. The efficiency of adopted synthesis method was evaluated based on swelling ratio, gelation ability and solubility. The study indicates that the guar gum can be modified using acid anhydride under microwave irradiation with enhanced physic-chemical properties. Moreover, microwave modification is an eco-friendly approach.

Solvent-free ball-milling synthesized porous metal-organic framework Cu2(BDC)2(DABCO) (BDC: benzene-1,4-dicarboxylic acid, DABCO: 1,4-diazabicyclo[2.2.2]octane) proved to be a practical catalyst for facile and convenient synthesis of 1,2,3–triazole derivatives via multicomponent reaction of terminal alkynes, benzyl or alkyl halides, and sodium azide in ethanol. Avoidance of usage and handling of hazardous organic azides, using ethanol as an easy available solvent and catalyst simple preparation and its recycling makes this procedure truly a scale-up-able method. The high loading of copper ions in the catalyst causes efficient catalytic activity and hence its low weight usage in reaction. The catalyst was recycled and reused several times without significant loss of its activity. Furthermore, novel derivatives were examined to investigate their potential antimicrobial activity via microdilution method.

The aim of the present research is the shaping of zeolite 13X and study the effect of singular and binary system of binders. For this purpose, zeolite 13X was successfully synthesized under hydrothermal conditions. Different combinations of polyvinyl alcohol (PVA) and polyethylene glycol (PEG) have been used for shaping. Physical properties of granules were measured by nitrogen adsorption-desorption and results showed that increasing the binder content up to a certain amount, enhanced the physical properties but with a further increase in binder content surface area decreases. Also it was found that mechanical strength was decreased with increasing binder content after burnout.

An experimental study was carried out on synthesis and performance of the MTES (methyltriethoxysilane) templated and template free nanostructure silica membranes for hydrogen separation. The permeance of hydrogen, carbon dioxide and nitrogen pure gases and permselectivity and separation factor of gas mixtures were investigated at 25 °C, 100 °C and 200 °C. Activated molecular sieve with positive and negative sign and Knudsen diffusion were respectively the dominant transport mechanisms in hydrogen, carbon dioxide and nitrogen gas molecules permeances.  Although, the hydrophobic property of templated membrane is a good option for gas separation in hydrothermal conditions, the dense structure of the membrane results in lower permeances and permselectivities in comparison with template free one. Hydrogen permeance at 200 ºC and 3 bar which was measured 30.5×10-8  for template free silica membrane, decreased to 2.37  for MTES templated silica membrane. Permselectivity and separation factor of H2/N2 at the same conditions, which were 31.2 and 21 for template free membrane, reached to 21.5 and 8 for templated membrane. In addition, H2/CO2 permselectivity at the same conditions was measured for template free and templated membranes, 23.4 and 13.9, respectively.

The current article presents a numerical study for local solutions of Sisko liquid flow by bidirectional stretched surface. Additionally, the analysis of relaxation times for the heat and mass transfer mechanisms are made by utilizing modified heat flux and mass diffusion models. These improved relations are the generalized form of Fourier's and Fick's laws in which the time space upper-convected derivative are employed to portray the heat conduction and mass diffusion mechanisms. Appropriate transformations lead to a strongly nonlinear differential system of equations which is then solved numerically by employing the applications of bvp4c package in Matlab software. Another numerical method namely shooting technique with RK45 Fehlberg and Newton-Raphson method is utilized to authenticate the results. Graphical illustrations demonstrating the impacts of sundry physical parameters with required discussion highlighting their physical effect are also a part of this exploration. It is perceived that the temperature and concentration of Sisko liquid are diminishing functions of relaxation times for the heat and mass transfer mechanisms. It is also fascinating to perceive that the temperature and concentration of Sisko liquid are higher in case of classical form in comparison with an improved constitutive relations.

Existing liquid holdup models are generally based on low gas and liquid velocities. In order to extend the applicable range of existing liquid holdup prediction models and improve its prediction accuracy, a of gas-liquid two-phase flow experiment was carried out using a pipe of inner diameter 60mm and length of 11.5m. The superficial gas and liquid velocity ranges were 14.07~56.50m/s and 0.205~1.426m/s, respectively. The results indicate that the liquid holdup decreases with the increase of the superficial gas velocity and increases with the increase of the superficial liquid velocity. A new annular flow model for calculating low liquid holdup in horizontal pipe was developed and presented considering the relationships between the friction factor ratio of liquid phase and gas-liquid interface as well as the superficial Reynolds number of gas and liquid. The predictions of the model are found to be accurate with an average absolute error of 4.8%. Further, on the basis of the Beggs-Brill model and the horizontal pipe model established in this paper, a new liquid holdup model for different angles was given. It was observed the resultant model is also accurate, and has an average absolute error of 10%.

The shortage of natural resources in the power industry, combined with their increasing usage, price, and negative impact on the environment necessitate the search for new techniques of producing liquid fuel. One such possibility is the production of fuel and chemical products from coal via hydrogenation. The transformation of coal into liquid fuel is a complex technical process that requires saturating the initial substance with oxygen. Therefore, the purpose of this study is to determine the optimal conditions for the catalytic hydrogenation of a mixture of coal, primary coal tar (PCT) and heavy oil residues with an end-boiling point of 300°C. The results show the optimal conditions for producing liquid fuel. The proposed technique allows achieving a complete homogenization of all components and producing a highly stable coal paste. This technique also allows significantly reducing the negative impact on the environment.

Local velocities and aspect ratios of rising bubbles were measured to investigate the effects of bubble detachment shape on rising bubble hydrodynamics. Two types of capillary were employed to generate bubbles of identical volume: one glassy nozzle aligned vertically and the other stainless steel needle aligned horizontally. Horizontally injected bubbles had spherical initial shape and their values of aspect ratio slightly fluctuated around unity. However, vertically injected bubbles had surface-stretched initial shape and their values of aspect ratios decreased sharply from 1.1 to 0.65. There is a notable correspondence between the variation of local velocities and aspect ratios which reflects the relevance of the detachment shape of the bubbles to their surface energy. Correlations of Taylor & Acrivos and Vakhrushev & Efremov for aspect ratio were examined by experimental data.

The effect of two different crystal species of alumina on hydrodesulfurization activity of the corresponding CoMo catalysts was studied. Cylindrical extruded alumina with two different crystal structures i.e. γ-Al2O3 and δ-Al2O3 was prepared using boehmite and nitric acid as a peptizing agent by calcination at 550 ˚C and 900 ˚C, respectively. The Al2O3 support were impregnated with 9 wt.% of Mo and 2 wt.% Co via incipient wetness impregnation method. The CoMo/Al2O3 catalysts were used for hydrodesulfurization (HDS) and hydrodenitrification (HDN) of Iranian straight-run gas oil (ISRGO). The supports and catalysts were characterized by nitrogen adsorption-desorption isotherm, XRD, UV-vis-DRS, TPD, TPR and ICP-OES. The HDS activity of CoMo/γ-Al2O3 catalyst was higher than that of CoMo/δ-Al2O3 and was found to be 95.74%. This result was due to the formation of larger CoMoO4 and MoO3 crystals in CoMo/δ-Al2O3 catalyst which reduces the active metal phase dispersion and the performance of the catalyst. The HDS activity of CoMo/γ-Al2O3 catalyst was remarkable as the metal content of the catalyst was low. The HDN activity of CoMo/γ-Al2O3 was also about 66%.