Modeling ofN2 Separation From Natural Gas Using Alumina Membrane

• Main Author: Abdul Karim, Marcella
• Format: Final Year Project
• Language: English
• Published: Universiti Teknologi Petronas 2004
• Subjects: TP Chemical technology
• Online Access: http://utpedia.utp.edu.my/8623/1/2004%20-%20Modeling%20of%20Manufacturing%20Assembly%20Line%20for%203%20Pin%20Power%20Plug.pdf; http://utpedia.utp.edu.my/8623/

Purification of natural gas is very crucial step for upgrading the current value of natural gas, which contain about 5-20% of nitrogen. Petroleum refineries currently employ cryogemcs, pressure swing adsorption (PSA), and membrane systems for hydrogen recovery. Each of these technologies has limitations: cryogenics is generally used only in large-scale facilities with liquid hydrocarbon recovery, because of its high capital cost; and PSA typically recovers less of the feedstream and is limited to modest temperatures. Due to this reasons, alternative approach using membrane technology is to be explore. The purpose of this study is to develop a mathematical model for predicting the permeability and separation of nitrogen from natural gas. The parameters of concerns are operating pressure and temperature, feed composition and membrane pore size. Simulated results shows that increase in temperature gives rise to a strong increase in membrane segmental motions, causing the pore diameter to become larger resulting the selectivity will be lower. The effective diffusivity is either determined experimentally without knowledge of the porosity or tortuosity or use of predictive method for ordinary molecular diffusivity. It considers the normal molecular diffusivity and the Knudsen diffusivity. Operating conditions can be very important; an excellent membrane will achieve a poor performance if the operating conditions have not been properly selected. Selectivity is controlled by the properties of the active layer, and the porous supporting layer improves mechanical properties of the membrane only. The membrane used in this study is alumina. The equation used to calculate the permeability for pure gases consider the effect of viscous, Knudsen and surface diffusion. The total permeability of gases will increase as the membrane pore size increased. At 323.25 K, and pressure 60 bar, the permeability of methane at rp =0.2nm is 4.8313xl0"11 molls and the value increase to 1.76xl0.10 molls at rp=2nm.The effect of pressure and temperature were also studied, where increase in feed pressure will in result increase the total permeability. The effect of temperature shows the opposite trend where the total permeability decreased as the temperature increased.The permeability of the binary mixture of methane and nitrogen is very close to permeability of pure methane. Pure methane attained the highest permeability. As the membrane pore size increase, more gas molecules can diffuse through the membrane and as a result, the total permeability of gases increased. Due to increase value in permeability of both methane and nitrogen, the separation process will be less selective and thus it decrease with increase in pore size. As the flow rate at the retentate side is higher, the percentage removal will decrease. Thus in order to achieve high nitrogen removal, the stage cut must be low.