مجله فرآیند نو
پیاپی 40 (زمستان 1391)

Membrane technology is one of the most widely used methods in separation processes (gas separation, i.e). Considering the time and costs spent in experimental studies, CFD could efficiently predict the fluid behavior without conducting the experiment. In this work, separation of H2/N2 gas mixture is carried out with palladium-silver membrane deposited on ceramic support, using COMSOL Multiyphysics software for simulation purposes. The findings of this work indicate that an increase in the feed pressure, hydrogen mole fraction and the feed flow rate in the shell side would lead in an enhancement of the hydrogen permeate flux crossing over the membrane in the tube side. The results also reveal that there is a good compatibility of the present findings with the experimental data.

Asphaltene is known as the heaviest fluid component of crude oil and has a significant impact on its resistance behavior. In recent years, determining the nature of asphaltene in oil has been the target of many researches. Some investigators believe that the structure of asphaltene is colloidalmaterial which is suspended by stabilizing factors in oil. In this article, asphaltene, separated by normal alkanes and its structure is examined. In this regard, various methods, including the IP143 method of oil standard institute, introduced as an efficient method of separating asphaltene, have been studied. In this paper, it has been tried to collect all information related to asphaltene through surveying its structure andseparation methods, to be available as a reference.

This paper provides an overview of the most important researches carried out during 1981 to 2012 in the case of heat transfer in different models of metal hydride storage tanks. In metal hydrides, which are used for hydrogen storage, the adsorption is carried out by metal in an exothermic reaction mechanism. So, heat transfer is a very important factor to improve storing process. In this paper, different types of metal hydride storage tanks with straight, spiral and finned tubes and different methods of hydrogen storage are analyzed.According to the studies, the use of cooling fluid inside storage tanks would have a greater impact on the adsorption process. Moreover, if the fluid is used outside storage tanks, the rate of heat transfer will be better in comparison to the use of finned tubes.

An overview of the literature from 1975 up to now on hollow fiber membrane contactors for gas-liquid systems and common polymeric membranes, applied in this technology, has beenpresented. Glass transition temperature of polymers is usually determined based on their chemical structures, including chain flexibility and chain reactions. Generally, the factors which cause Tg, Tm or crystallinity of the membranes to be increased, improve their thermal and chemical stabilities. The most important parameters of membrane contactors for acid gases removal, CO2 and H2S, including hydrophilicity and hydrophobicity of the absorbent materials in the membranes, and various models, presented in the literature, have also been presented. In addition, advantages and disadvantages of gas-liquid contactor membranes in acidic gases separation have been studied and the technology has been compared to the traditional methods of separation. Current status and future directions of the technology have been shown and some approaches for future research have been recommended to commercialize this technology.

In this research, Nanoemulsions of water droplets in gas oil have been prepared using combination of nonionic surfactants. Three formulations of the emulsion containing various amount of water as 5, 10 and 14 volume fractions (based on 100 volume fractions of gas oil) have been prepared, clear and stable, using a mixture of two surfactants containing sorbitan monooleate (20%) and sorbitan trioleate polyoxyethylene (20 mole ethoxylated) (80%) and adjusting the system HLB at 10. The effect of water content on droplets size, fuel calorific value, amount of gas emissions (environmental pollutants) and the exhaust gas temperature have been studied in a diesel engine, and it has been found that the amount of nitrogen oxide, soot, particulates, unburnt hydrocarbons and carbon monoxide are reduced. This study shows that the average droplet size of water formed (being 19.3-39 nanometers in this research) depends on the total concentration of surfactants and the amount of water used.

Hydroxyapatite has been recognized as an effective sorbent for a variety of heavy metals, radionuclide and organic contaminants such as phenol from water and wastewater. In this paper hydroxyapatite application in chemical industries, particularly in wastewater treatment has been investigated and the effect of solution’s PH, heavy metal type, initial metal concentration and hydroxyapatite physicochemical properties on Hydroxyapatite sorption capacity have been studied.

Study on the results of the different membranes performance used in the hydrogen purification and comparing them at the trade off curve for H2/N2 system, have shown that palladium membranes have situated at the suitable position of the curve, so that high permeability (104-105 Barrer) and selectivity (103- 104) have been achieved by the Pd membranes for the hydrogen purification. The permeability of silica membranes has also been at the range of 103 to 104 Barrer and their selectivity has been even more than 104 that situated them after Pd membranes at the trade off curve. The permeability of hydroxy sodalite zeolite membranes has been comparable to Pd membranes and at the range of even more than 104 Barrer, but very low selectivity of even less than 10 has been achieved for this kind of membranes. Certainly, it should be mentioned that so desirable selectivities and even infinite selectivity of these membranes have been achieved for the H2/Hydrocarbon systems which are presented at the different sources. Despite of so suitable selectivity, polymeric membranes have very low permeability of hydrogen which should be modified. Although, mixed matrix nanocomposite membranes could solve this problem to some extent.