Modeling and simulation of natural gas sweetening process by methyldiethanolamine (MDEA) absorbent in the hollow fiber membrane contactor using COMSOL software

Membrane separation processes are interesting compared with the traditional processes such as distillation, extraction, absorption, etc. due to their superior advantages. Development and simulation of a precise mathematical model for description of phenomena occurred during permeation and transfer of components through membrane could enable one to improve their design, application and operation. In this research a two-dimensional model was used for simulation of CO2 and H2S removal from their mixture with CH4 (as a representative of natural gas sweetening) by absorption on MDEA aqueous solution in polypropylene hollow fiber membrane contactors. The model was solved and simulated using computational fluid dynamic (CFD) in COMSOL software by finite element method. Validation of the simulated CO2 fluxes (0.4 - 2.5 × 10-3 mol/m2.s) through the membrane vs. liquid phase velocity vs. experimental data reveled minimum, average, and maximum errors of 3.45, 9.56, and 17.45 % and those for the gas phase velocity were 2.64, 4.31, and 5.59 %, respectively. The results showed that the gas and liquid absorbent phases’ velocities are the most important affecting factors on the acid gas removal. Also, the liquid phase mass transfer resistance was found determining. With increase in membrane porosity, absorbent concentration and gas phase temperature, the gas outlet’s CO2 concentration were reduced by 45, 68, and 17.5 %, respectively. Increment in the gas and absorbent velocities, reduced and increased the CO2 absorption flux by 15 % and 4.5-fold, respectively. Simultaneous removal of H2S and CO2 reduces the only CO2 removal efficiency by ~ 8 %.