نشریه علوم و مهندسی جداسازی
سال هفتم شماره 1 (پیاپی 13، بهار و تابستان 1394)

Absorption of hydrogen sulfide with aqueous amine solution is one of the most important processes in refinery units. Tray and packed columns are widely used for removal of hydrogen sulfide. For modeling of these kind equipments, equilibrium and rate-based techniques can be used. Since, the hydrogen sulfide absorption with amine solutions is a reactive absorption; using equilibrium-based models would not attain appropriate results. In this study, the wetted wire column was properly introduced; low pressure experimental setup of hydrogen sulfide absorption with amine solutions was constructed and then different type of experiments were performed. the heat transfer coefficient, the gas phase mass transfer coefficient were determined experimentally based on liquid flow-rate, inlet liquid and gas temperatures, amine weight percent and also hydrogen sulfide loading. Also by assuming laminar liquid film over the wires, velocity distribution and liquid phase mass transfer coefficient were calculated based on liquid flow-rate and mean gas-liquid flow temperatures. For modeling the process the general computer code was created. There is a good consistency between experimental data and simulation results; additionally, the effect of different parameters such as liquid flow rate and gasliquid phase temperature on absorption amount were examined.

A single-drop liquid-liquid extraction system in the presence of carbon nanotubes was studied in this investigation. Carbon nanotubes have a striking effect on heat transfer and due to the similarities between mass and heat transfer, these nanotubes were investigated in a mass transfer system. Furthermore, carbon nanotubes were compared with silica nanoparticles to specify the effects of molecular structure on mass transfer. Toluene, acetic acid and nanoparticles as dispersed phase and ionized water as continuous phase were chosen. The surface of carbon nanotubes were modified using dodecyl iodide in order to provide appropriate stability in the dispersed phase. The FT-IR test showed the acceptable modification of nanotubes. The angle of hydrophobicity which was measured by contact angle test, was 134º. Terminal velocity and drop size slightly decreased with nanoparticle concentrations. Equivalent drop diameters and terminal velocity were in the ranges 0.55-0.7 cm and 10.5- 11.4 cm/s, respectively. The maximum enhancements of 27% and 119% for overall mass transfer coefficient were achieved in carbon nanotubes and silica nanoparticles, respectively. The increment in drops’ diameter increased the overall mass transfer coefficient.

Carbon dioxide as one of the important combustion product of various industrial units is a greenhouse gas which has a significant influence on global warming. In recent years, porous inorganic membranes have extended for carbon dioxide separation from flue gas. In this study, the microporous silica membrane with nanometer size pores was prepared by template assisted sol-gel method using methyltriethoxysilane (MTES) as organic template and influence of the surface modification on the membrane separation performance was investigated. To fabricate the membrane, α-alumina macroporous support was prepared by gel casting method using ceramic alumina powder. The uniform γ-alumina mesoporous layers were selected as surface modification strategy, in which the supports were coated by alkoxide boehmite sol via dip coating method. The morphology of membrane layer was investigated by scanning electron microscope, indicating the formation of a uniform layer from γ-Al2O3 and silica. Permeance characteristics of the synthesized membrane were studied in two parts: permeance of pure gases such as carbon dioxide, nitrogen and hydrogen, and separation of 50/50 ratio (vol%) mixture of carbon dioxide and nitrogen. For the modified templated silica membrane, the CO2/N2 ideal selectivity and pure CO2 permeance were achieved 11 and 4×10-8 mol/m2.s.Pa, respectively. The real selectivity of CO2 in the mixture (CO2 and N2) with 50/50 ratio (vol%) was achieved 5.3.

One of the main limitations and the reason for the slow dissolution kinetic of chalcopyrite in acidic ferric sulfate solutions is surface passivation at potentials higher than critical values. In order to optimize the operating parameters of chalcopyrite bioleaching, the effect of redox controlling on the recovery of copper from chalcopyrite concentrate was evaluated. The used flotation concentrate was mainly contained chalcopyrite (45.7%), pyrite (23.4%) and secondary copper sulfides (10.8%). Bioleaching and electrobioleaching experiments were performed in a continuous set-up containing a preparation tank and three bioreactors using moderate thermophile bacteria. Results of conventional bioleaching experiments indicated that the recovery of copper was low. To increase the copper recovery, the effect of redox potential on the leaching of chalcopyrite was investigated by electrochemically controlling of redox potential. The results of experiments conducted in different redox potential ranges showed that reducing the redox potential from high levels to optimum window (420-440mV Ag/AgCl) caused a 75% increase in copper recovery compared to conventional bioleaching. In the best conditions studied in this research (7-days residence time, 420-440 mV redox window, acidity of 55 Kg/ton and 30μm particle size) copper recovery was approximately 94%.

Purification of a desired protein from fermentation broth containing a wide variety of biomolecules is one of the major challenges in the biotechnology industry. The aim of this work was partitioning of lipase using aqueous two phase systems (ATPS). ATPS has proved to be a valuable tool for separating and purifying mixtures of biomolecules. In this study, the various aqueous two phase systems containing poly ethylene glycol 4000, 8000 and potassium oxalate and sodium-potassium tartrate were examined for extraction of lipase from fermentation broth. The results show that, the best operating system was contained the 17.5%(w/w) PEG4000,19.5%(w/w) potassium oxalate, 10.2%(w/w) crude fermentation broth loading and pH=5, resulted in partition coefficient (Ke) of 1.29, enzyme activity recovery of 84.93%, purification factor of 17.59 and specific activity of 22.22.

Mineralogical studies on the Zaylik gold ore of Eastern Azerbaijan showed that silica and iron were major phases in ore. To identify the phase accompany gold, SEM studies, analytical Map and magnetic separation method were used. Experimental results showed that using two stages of magnetic separation, led to the elimination of more than 69% by weight of the original feed to tailing with grade lower than 0.9 ppm gold. Also a concentrate with approximately 31% by weight of the original sample with recovery of about 93% gold obtained. In other words, about 7% of gold lost in total tailing, but due to the removal of a significant portion of the silicate compound from ore, magnetic separation has an important role in reducing chemical consumption and operating costs for leaching processes.

Modeling of drying process is usually carried out by using the heat and mass transfer equations for prediction of moisture variations of drying material during drying. In this paper, convective air drying of a single body has been modeled using a thermodynamic approach. The proposed model was validated by the experimental data obtained from drying of small spherical potatoes and green tea leaves in a pilot scale dryer. Drying samples were dried at temperatures between 35 and 60°C. The proposed model predicts the temperature and moisture variations and the entropy generation and exergy in the drying sample. The results showed that the air velocity didn’t have a pronounced effect on the drying rate. The surface temperature of the drying material increased rapidly at first, and then reached slowly to the drying air temperature. Also the entropy generation increased at the early stages of drying and then decreased at the end of the drying. Exergy and energy increased during the drying. Comparison of the predictions of the proposed model with the experimental data showed the validity of the proposed model. The average relative error between the predictions of the proposed model and the experimental data (MRE) for humidity and temperature were between, 3.9 and 3.1% for green tea and between 3 and 3.9% for potato samples, respectively.

In this study, the effect of MIL-53 particles on CO2/CH4 separation of Matrimid was investigated. MIL-53 used as an additive due to its especial pore structure and considerable selectivity respect to CO2. For the purpose of mixed matrix membrane structure with different weight percent of MIL-53 on CO2/CH4 separation, membranes fabricated with symmetric and asymmetric structure. Morphology of membranes studied with cross sectional SEM images and a performance of membranes in gas separation evaluated through permeability measurement. SEM images showed that a proper compatibility between particles and polymer along with proper dispersion of particles within polymer matrix were achieved. Results from gas permeation test demonstrated that increasing in weight percent of MIL-53 in membranes led to the permeability and selectivity enhancement. Moreover, permeability results showed that the CO2 permeability was increased from 0.056 GPU in neat symmetric membrane up to 0.113 GPU in mixed matrix membrane that containing 15 wt. % of MIL-53 particles. CO2/CH4 selectivity also increased 85% compared to neat membrane and reached to 51.8. In addition, permeability results illustrated that the gases permeability in asymmetric membranes was 100 times higher than those in symmetric membranes.