Process simulation and optimal design of membrane separation system for CO2 capture from natural gas

In order to avoid carbon dioxide (CO2) built up in the atmosphere, the major source of global warming, CO2 capture must be applied to large point sources including natural gas processing. Membrane process, a relatively new technology among other available techniques, can be used for the purpose of CO2 capture from natural gas. Over the decades, the membrane performance has been described by different mathematical models, but there is limited work done in the field of process simulation where membrane models can be incorporated with other unit operations using a commercially available simulator. In this paper, mathematical model for cross flow membrane separation has been proposed to be incorporated with ASPEN HYSYS as a user defined unit operation in order to design and optimize the membrane system for the separation of CO2 from natural gas. The proposed simulated model is validated by published experimental and simulated data. Parameter sensitivities, along with process economics, have been studied by changing the operating conditions (feed composition and pressure) and membrane selectivity for different design configurations such as single stage (with and without recycle) and multiple stages (with permeate and retentate recycle) systems. It has been observed that double stage with permeate recycle system gives the optimum design configuration due to minimum process gas cost involved with it. The ASPEN HYSYS user defined unit operation proposed in the current paper has potential to be applied for the design, optimization and scale up of complex membrane systems.