نشریه شیمی و مهندسی شیمی ایران
سال سی و دوم شماره 4 (پیاپی 70، زمستان 1392)

Silica gel with low density can be prepared via various methods. According to abundance and low price, using sodium silicate as a silicon source in order to prepare initial seeds is one of the suitable and native methods. In this research, a suitable method based on the cheap raw materials and the ease of preparation was selected. In this method, as in the conventional one, primarily hydrosol was prepared through the reaction of sodium silicate and sulfuric acid. Then after conducting varius tests, the effective factors in reduction of the silica gel density such as: the time of rapid setting, alkalinizing the washing medium of the hydrogel, using solvents with low surface tension to prepare alcogel or acetogel, and curing them in the critical point temperature and pressure of the mentioned solvents were studied. Finally, a product with 0.18 g/cm3 density, 7.5% adsorption capacity in 60% relative humidity, 17 micron particle size and 230 m2/g surface area at super critical point of aceton, was synthesized.

In present investigation, ruthenium was deposited on cobalt supported alumina catalyst by Chemical Vapor Deposition (CVD) of Ru3(CO)12 for Fischer-Tropsch Synthesis (FTS). The 15.0 wt% Co/γ-Al2O3 catalyst was prepared by wet impregnation of cobalt nitrate aqueous solution, and then dried and calcined at 400oC for 4 h. To optimize the CVD operating conditions in which Ru3(CO)12 starts to decompose on surface of the catalyst, the decomposition products of the CVD processwere passed through a gas cell of FT-IR. In a specific temperature range, ruthenium deposited selectively on the surface of cobalt active phase.The CVD of ruthenium onto Co/γ-Al2O3 catalyst increased the catalyst reducibility which in turnled to a higher CO hydrogenation activity in FTS process. Furthermore, the promoted cobalt catalyst showed a better selectivity towards heavy hydrocarbons than the reference unpromoted catalyst. The effects of temperature (210oC-240oC) and H2 /CO ratio (1-3) for all catalysts were examined. For the all operating conditions, the promoted catalyst performed much better than the unpromoted catalyst.

A sensitive glutamate biosensor is prepared based on glutamate dehydrogenase/vertically aligned carbon nanotubes (GLDH, VACNTs). Vertically aligned carbon nanotubes were grown on a silicon substrate by Direct Current Plasma Enhanced Chemical Vapor Deposition (DC-PECVD) method. Glutamate dehydrogenase covalently attached on tip of VACNTs. The electrochemical performance of the electrode for detection of glutamate was investigated by cyclic and differential pulse voltammetry. The linear calibration curve of the concentration of glutamate versus peak current is investigated in a wide range of 0.1–500 mM. The mediator-less biosensor has a low detection limit of 57 nM and two linearranges of 0.1–20 mM with a sensitivity of 0.976 mA/mM cm2 and 20–300 mM with a sensitivity of 0.182 mA/mM. cm2. The effects of the other biological compounds on the voltammetric behavior of the prepared biosensor and its response stability are investigated. The results are demonstrated that the GLDH/VACNTs electrode even without electron mediator is a suitable basic electrode for detection of glutamate.

In this work a novel Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic equation has been proposed for hydrodesulfurization (HDS) and used an unusual hydrodenitrogenation (HDN) kinetic equation. These equations include inhibitive effect of nitrogenous compounds (basic and nonbasic) on the HDS reaction and the activating effect of H2S concentration on HDN reactions (basic and nonbasic). Three phase reactor model that incorporates the effect of hydrodynamics has been developed. The concentration profiles obtained using the proposed kinetics for hydrotreating reactions were compared with other kinetic models and pilot plant experimental data available in the literature. The predicted value showed a very good agreement with the experimental data. The average absolute error for all predictions is <1.5% while the published value in the literature is <2%.

In this paper, particles coating system in fluid bed have been studied. This system includes two process of coating and drying in the bed and used for coating of sodium per carbonate particles by liquid sodium silicate. This is a top spray coating system and batch type. Response Surface Method (RSM) was applied for experiment design by means of Minitab software, version 15. The fluidization hydrodynamics of particles and air flow was studied. The optimum operating conditions was determined. The effect of particles fluidization height, air and liquid flow rates on coating efficiency was investigated. The experimental results showed that, the mass of particles coating, was proportional to the liquid value and indirectly to the air flow rates. Experimental correlation of coating mass is proportional with fluidized air and liquid flow rates and atomization air flow. Also RSM tables and contours for process optimization, for investigation of system performance were derived. The result of fluidized height of particles based on time and coating mass with different air and liquid flow rates for the best case of particles coating was calculated and investigated and optimized coating information was obtained.

In this work, effect of maleic anhydride grafted- LDPE (PE-g-MA) on the mechanical, morphology and flow behavior of biodegradable LDPE-thermoplastic corn starch (TPS) blends were investigated. TPS was prepared by mixing neat starch and glycerol (35wt. %) at room temperature. The mixture then was melt-compounded using an internal mixer at 140oC, rotor speed of 60 rpm for 8 minutes. LDPE-TPS blends containing different contents of TPS (0-40wt. %) with (3wt. %) and without the addition of PE-g-MA, were prepared using a single-screw extruder. Surface morphology of the prepared blends was investigated by Scanning Electron Microscopy (SEM). Also, mechanical properties and flow behavior of the prepared samples were carried out by means of related standard test methods. Scanning electron micrographs of the samples show improvement in dispersion of the starch particles in LDPE matrix in the presence of PE-g-MA as a compatibilizer. Also, the results of mechanical properties indicate that as TPS concentration increases, the ultimate tensile strength, elongation at break, Young’s modulus and relative impact strength of the blends decrease. However, the compatibilized blends represent higher mechanical properties than the blends without any compatibilizer. Furthermore, the addition of starch to LDPE decreases the melt flow index values of the samples and subsequently increases their apparent viscosity.The results of rheological tests also indicate that as shear rate increases, the apparent viscosity of the samples decreases (shear thinning).

In the present research, a square bubble column has experimentally been utilized in order to quantify the important hydrodynamic properties of bubbly liquid/gas two phase flows, such as bubble velocity and diameter, flow pattern as well as oscillation frequency of the gas phase via the high-speed video recorder. Results were then processed using new techniques of image processing. The column was fabricated from plexy-glass which was dimensionally 205120cm (cross sectionheight). Results indicated that gas superficial velocity varied from 0.1 to 0.7 cm/s. Three cameras with different speeds were employed (20, 500 and 600 frames per second) to evaluate the bubble characteristics and MATLAB 7.4 (2007a) was used for image analysis. Oscillation frequency of gas phase was obtained using a new method with accuracy close to 95%. At coalescence condition, Mean Sauter Diameter (MSD) of bubbles was calculated with accuracy of about 99.8%. For the first time, bubble velocity was computed by "minimum distance with upper limit" method in the bubble column.

In this paper, the effect of presence of nano-microbubbles on flotation recovery of chalcopyrite fine particles (-38+5µm) has been studied. Comparative flotation tests were performed both in the presence and absence of nano-microbubbles (conventional flotation) to evaluate recovery changes of chalcopyrite. Methyl IsoButyl Carbinol (MIBC) was used as frother and Potassium Amyl Xanthate (KAX) as collector at pH= 10. Nano-microbubbles were generated using a nano-microbubble generator based on cavitation phenomenon in venturi tubes. Changes in size distribution, zeta potential and stability of nano-microbubbles were measured as a function of time. Results showed that the interval between generation time and 10 minutes after that, simultaneous with reduction of the absolute value of zeta potential increased the average size of nano-microbubbles from 358 nm to 13.24 μm. The results in the presence of nano-microbubbles showed increased flotation recovery of chalcopyrite fines by 16-21% and reduction of chemicals reagent (up to 75% of collector and 50% of frother). In addition, the effect of nano-microbubbles on promoting the recovery of ultrafine particles (-14.36+5 μm), has been higher than fine particles (+14.36-38 μm).

In this research, the thermo economic analysis of a PSOFC/GT hybrid cycle was taking place regarding a sustainable approach. Initially, the proposed cycle was accurately introduced and then the modeling methodology was presented. Furthermore, the cycle simulation was presented with the development of a thermodynamic model in EES software based on the mass, energy and economic equations, those were solved simultaneously. With introducing electrical and overall efficiencies, a comprehensive analysis of thermodynamics was done, which was contributed to a dynamic economic model, which was proposed and analyzed in after-steps. In order to determine effects of change in main parameters, a parametric study was prepared. By these means, the results show that the electrical efficiency of 61.3 % and overall efficiency of 77.65 % are achievable within 1962 kW net output power, where, HRSG heat recovery capacity is equal to 436.8 kW and HPR was calculated 22.27 %. This cycle with producing 310.9 g/kWh CO2, reduces the CO2 emissions by 30.3 % comparing with the conventional gas fired combined cycles.

Membrane bioreactors (MBR Process) are now considered as one of the main new processes in wastewater treatment. Membranes used for wastewater purification are fabricated from different oil based polymers including PVC, polysulphonates, polyamides and many other synthetic polymers. Fabrication technology is advanced and only in possession of very few multinational companies. For these reasons, membranes are expensive and not easily available. This study was carried out to test an innovative, locally made filter element for separation of flocks in an MBBR reactor. This innovative filter is seen as a viable replacement to a conventional settling tank that may be even as effective as synthetic polymer membranes. The filter’s element was made very cheaply and had important advantages in installing and operation. Experiments were carried out using a laboratory scale MBBR unit as the biological aerated reactor, fixed with filter elements inside aeration chamber, similar to a MBR installation. The filter elements consisted of 3 plastic filter tubes with perforations and covered with dense cotton-polyester yarns and were placed inside the aeration chamber. The bioreactor was run over a period of 10 months with usual conditions resembling a real biological wastewater treatment unit. Reactor performance was measured regularly and the results indicated that 99% of suspended solids are separated under normal conditions. Filter clogging, a very familiar problem with membrane bioreactors, was not seen as an obstacle in bioreactor operation. Outflow TSS was lower than 12 mg/L, while overall organic removal was over 95 percent. Next set of experiments were carried with fewer filter elements and higher value of TSS in the effluent was observed, indicating that filters surface area (or number of filter elements) have a profound effect on treatment efficiency as could be well expected. Overall the experiments indicated that locally made MBR can easily be applied in existing plants, saving money and operational difficulties.