Separation of nitrogen from methane by multi-stage membrane processes: Modeling, simulation, and cost estimation

Abstract

This study focuses on the application of multi-stage membrane separation processes for the removal of nitrogen from natural gas. Reliable modeling and process simulation are essential for the analysis of the gas separation process. A mathematical model was developed using thermodynamic models, like lattice fluid (LF) and non-equilibrium lattice fluid (NELF), for gas sorption and transfer model for gas diffusion in the membrane. The proposed mass transfer model was validated with the experimental data for the gas solubility and permeability in various glassy and rubbery membranes. Then the proposed model was coupled with Aspen Plus software (Aspen Tech) for simulation of different proposed configurations of the multi-stage membrane processes. The performance of various gas separation configurations was investigated in terms of product purity, methane recovery, total capital investment, and total annual cost. The results indicated that the membranes with higher permeability had more suitable economic parameters. For example, the total annual cost for the AF1600 membrane was seven times the total annual cost value for the PTMSP membrane in the single-stage membrane separation process. It was observed that the methane purity of above 96 %mol and methane recovery of 90% could not be achieved by the single-stage process. However, the specified separation criteria can be achieved via the multi-stage membrane processes by two or three membranes. The best configuration was selected from various proposed configurations by evaluating the economic parameters.