فهرست مطالب مهدی پورافشاری چنار

In this study, PES/Pebax composite membranes were prepared by coating the porous PES support layers by Pebax-1657. Film casting and pouring methods were used for coating Pebax layer. The effects of coating technique and conditions including coating solution concentration and curing temperature on CO2 and CH4 gas permeabilities of prepared composite membranes were investigated. SEM images were used to investigate the structure of the prepared membranes. Pure CH4 and CO2 gases were used to investigate the gas permeation properties of the prepared membranes at different trans-membrane pressures (1-11 bar) and feed temperatures (25-55°C). The obtained data showed that the prepared PES supports did not provide any CO2/CH4 selectivity. The results also showed the CO2/CH4 selectivity for the membrane prepared via pouring technique was higher than that of the film casting procedure due to the defect-free Pebax layer formation. CO2 and CH4 permeance increased as the feed temperature increased from 25 to 55°C. The results also showed that CO2 permeance increased from 6.8 to 10.1GPU with an increase in feed pressure from 2 to 12barg, while CH4 permeance remained almost constant and CO2/CH4 selectivity increased from 27 to 42.

Ammonia is one of the most common pollutants in urban and industrial wastewaters and due to various problems it generates, it is necessary to remove it from wastewaters. In this study, a laboratory scale once-pass membrane contactor system was designed and constructed using PPO hollow fiber membranes and the effect of various operating parameters such as the feed passage side (the lumen-side or the shell-side), feed flow rate and temperature on the efficiency of the process for synthetic wastewater was investigated. Since the petrochemical units are of the main sources of wastewaters containing ammonia at high concentrations, in the second part of this study, the efficiency of the process to remove ammonia from Khorasan Petrochemical wastewater was also investigated. Experimental results showed that low feed flow rate, high feed temperature and feed passage through the lumen side increased the ammonia removal percentage. Also, the ammonia removal percentage variations with the feed velocity and temperature were the same as that of synthetic wastewater. By comparing the ammonia removal percentages of synthetic and real wastewaters, it was obtained that ammonia removal percentages for real petrochemical wastewater at 20 and 40 ºC, were respectively about 25 and 19% lower than that of synthetic wastewater.

Process design and simulation of different natural gas dehydration processes including membrane systems، absorption، and adsorption were investigated in the current study and the results of the economic assessments of these processes were compared with each other. The absorption process was simulated by means of Aspen-Hysys and the modeling and simulation of membrane system were implemented by MATLAB. All of the processes were designed to reduce the water content of natural gas to less than 7 lb/MMSCF. According to the results، under assumed operating conditions، the total separation cost of membrane separation system was lower than that of other dehydration processes at low feed flow rates. The difference decreased with increasing feed flow rates followed by a decrease in the total separation costs of absorption and adsorption processes. In addition، under the operating conditions assumed in this study، the membrane systems showed lower total separation costs than the adsorption processes. According to the economic evaluation and optimization of membrane-absorption and membrane-adsorption hybrid processes، the use of membrane system on the upstream of other dehydration processes would result in a significant decrease in total separation costs depending on the operating conditions in each dehydration unit.

In the present investigation, nanosized silicalite-1 powder was first synthesized as a seed with mean diameter of 40 nm by the hydrothermal method. Seeding of nanosized zeolite crystals on the support surface is one of key steps in the secondary growth synthesis method. Therefore, in order to increase the quality of the zeolite membrane, subsequent seeding steps were investigated by dip-coating technique. The seeded supports and silicalite-1 nanoparticles were characterized by X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), N2-BET adsorption/desorption isotherm,Fourier Transform Infrared Spectroscopy (FT-IR), Thermo Gravimetric Analysis (TGA) and Differential Scanning Calorimeter (DSC). Examination of the number of seeding steps showed that three subsequent seeding steps would improve the quality of seed layer.

According to the position of Iran in the global gas reserves and the development of the country, natural gas sweetening process has a significant importance. Natural gas often contains contaminations such as CO2 and H2S that must be removed or lowered in content to the standard limits, before being delivered to the gas pipelines. Development of membrane technology in the world in the recent decades has made this technology more competitive with the conventional gas sweetening processes. The aim and objective of this study is providing economic boundaries between amine, hybrid and membrane technologies for sweetening of mixed gases containing CH4, CO2 and H2S. Simulation of the amine plant has been done using the Aspen-Hysys software and the membrane system has been precisely modeled and simulated using the MATLAB software. Configuration of membrane system was considered as a 2- stage process using a recycled flow. The influence of different parameters, including gas inlet pressure, permeate pressure, composition and the effect of inlet gas flow on the cost of membrane and amine systems, has also been studied. The results showed that for the CO2/CH4 feed, economic boundaries include three zones: Amine, membrane, hybrid and in all range of concentrations the membrane unit is economically efficient. For the CO2/H2S/CH4 feed, economic boundaries include two zones: amine & hybrid that all gas refineries in our country are placed in the economic area of amine now.

The advantages of membrane system, such as low initial investment, low space requirements and ease of scale up, has led to take into consideration the use of membranes for gas sweetening in recent decades. For this purpose, the membrane system, separately or in combination with amine unit is used. In the design of gas sweetening processes, economic evaluation and optimization are amongst important parts. The aim of this article is economic evaluation and optimization of the membrane systems for applications in gas refineries. In this regard, important optimization parameters (the ratio of membrane surfaces and permeate pressures of the stages) of two stage membrane system are determined firstly, and it will try to find their optimum values based on the inlet gas information of a refinery. Thereafter, the optimum content of the acid gases must be removed by membrane section of hybrid systems will be determined. Optimization results showed that at low to moderate concentrations of acid gases (less that 12%), for a feed gas rate equal to 70 MMSCFD, hybrid system containing two-stage membrane system presents lower cost than that of containing single-stage membrane system.

In the present study, ZSM5 zeolite membranes were synthesized on porous αaluminasupport by secondary growth hydrothermal method. Membranes synthesized were tested by structural characterization and single gas permeation experiments. To prepare zeolite membranes, nanosized silicalite-1 powder was first synthesized as seed with mean diameter of 40 nm from a clear solution. Silicalite nanoparticle slurries were purifiedby repeated centrifugation followed by redispersion by ultra-sound in deionized water. The effects of synthetic parameters such as synthesis time and aluminum content are studied. It was found that the membranes quality was sensitive to the aluminum content. Investigation of different synthesis times showed that the best film was obtained during 36 hours. The permeation properties of the support and membranes were measured over the pressure range of 1-4bar at room temperature. The ZSM-5 membranes were examined by permeation measurements using single CO2, N2, CH4 and H2 gases. Under optimum synthetic conditions, the permselectivity at 300K for H2/CH4, H2/CO2 and H2/N2 were 3.8, 3.5 and 4.4, respectively.