Multiobjective Optimization Based on “Distance-to-Target” Approach of Membrane Units for Separation of CO2/CH4

Ricardo Abejón,Aurora Garea,Clara Casado-Coterillo

doi:10.3390/pr9111871

Ricardo Abejón, Aurora Garea + Show 1 more

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https://doi.org/10.3390/pr9111871

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Abstract

The effective separation of CO2 and CH4 mixtures is essential for many applications, such as biogas upgrading, natural gas sweetening or enhanced oil recovery. Membrane separations can contribute greatly in these tasks, and innovative membrane materials are being developed for this gas separation. The aim of this work is the evaluation of the potential of two types of highly CO2-permeable membranes (modified commercial polydimethylsiloxane and non-commercial ionic liquid–chitosan composite membranes) whose selective layers possess different hydrophobic and hydrophilic characteristics for the separation of CO2/CH4 mixtures. The study of the technical performance of the selected membranes can provide a better understanding of their potentiality. The optimization of the performance of hollow fiber modules for both types of membranes was carried out by a “distance-to-target” approach that considered multiple objectives related to the purities and recovery of both gases. The results demonstrated that the ionic liquid–chitosan composite membranes improved the performance of other innovative membranes, with purity and recovery percentage values of 86 and 95%, respectively, for CO2 in the permeate stream, and 97 and 92% for CH4 in the retentate stream. The developed multiobjective optimization allowed for the determination of the optimal process design and performance parameters, such as the membrane area, pressure ratio and stage cut required to achieve maximum values for component separation in terms of purity and recovery. Since the purities and recoveries obtained were not enough to fulfill the requirements imposed on CO2 and CH4 streams to be directly valorized, the design of more complex multi-stage separation systems was also proposed by the application of this optimization methodology, which is considered as a useful tool to advance the implementation of the membrane separation processes.

Highlights

Membrane separation processes are considered to be of great potential in addressing the drawbacks of conventionally based amine processes for CO2 capture and for natural gas sweetening or biogas upgrading [1,2]
These CO2 /CH4 -selective membranes can be employed for different application where the separation of both gases is required, such as biogas upgrading, natural gas sweetening or enhanced oil recovery
The mathematical model developed in this work has been successfully applied to represent the performance of membrane separation units with two types of innovative membranes for CO2 /CH4 separation

Summary

Introduction

Membrane separation processes are considered to be of great potential in addressing the drawbacks of conventionally based amine processes for CO2 capture and for natural gas sweetening or biogas upgrading [1,2]. Among the most representative materials studied for CO2 /CH4 separation, it was pointed out that cellulose acetate was the most used polymer for large scale CO2 separation, despite a significant selectivity reduction when processing a highly pressurized natural gas mixture in comparison to single gas permeability data. This is due to a possible effect of plasticization, it being the scope for investigating other polymeric materials that are more stable at process conditions, such as polydimethylsiloxane (PDMS) [11]. The development of new membrane materials, including polymers and hybrid materials, will rely on a multidisciplinary approach that embraces the broad fields of chemical and materials engineering, polymer science and materials chemistry, as well as accurate process understanding in order to close the gap with their implementation in large scale applications [5,12]

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