Modeling Of Carbon Dioxide and Nitrogen Removal From Natural Gas Using Membrane Processes

Removal of carbon dioxide and nitrogen from natural gas is very critical processes.
The carbon dioxide contributes to the corrosive problem to the pipeline and
equipments when react with water while nitrogen needs to be reduced less than 4 %
in order to meet the pipeline specifications. The objectives of this project are to
develop a mathematical model for carbon dioxide and nitrogen removal from natural
gas and to study the effects of PEBAX membrane pore size, mole fraction of gas
speciesand operating pressure on permeability of gas species. Three factors including
membrane pore size, mole fraction and operating pressure have been analyzed. The
permeability models are developed by incorporating three main mechanisms that are
viscous diffusion, Knudsen diffusion and surface diffusion. The modeling result
shows the permeability of carbon dioxide was found to be highest followed by
nitrogen and methane. At small pore size of 0.2 nm, the permeability of gases is
dominated by surface diffusion while Knudsen diffusion overlook at large pore size
of larger than 2 nm. Meanwhile the viscous flow is slightly increases with increasing
pore size. The composition of mole fraction in the feed influenced the permeability of
binary mixture. The permeability of CO2/CH4 mixture lay in between of pure carbon
dioxide and pure methane permeability. Similarly the binary mixture of CO2/N2 and
CH4/N2 lay in between the pure gases. For the tertiary mixture, the permeability of
carbon dioxide and methane at fixed nitrogen concentration increases a bit compared
to the binary mixture. At the mean time, increasing the operating pressure slightly
increases the methane permeability whilst the permeability of carbon dioxide and
nitrogen were found out almost independent. As the conclusion, the developed
models were able to predict the permeability of pure carbon dioxide, methane,
nitrogen and the mixtures of these gases.