CO2 Desorption Performance from Imidazolium Ionic Liquids by Membrane Vacuum Regeneration Technology

Abstract

In this work, the membrane vacuum regeneration (MVR) process was considered as a promising technology for solvent regeneration in post-combustion CO₂ capture and utilization (CCU) since high purity CO₂ is needed for a technical valorization approach. First, a desorption test by MVR using polypropylene hollow fiber membrane contactor (PP-HFMC) was carried out in order to evaluate the behavior of physical and physico-chemical absorbents in terms of CO₂ solubility and regeneration efficiency. The ionic liquid 1-ethyl-3-methylimidazolium acetate, [emim][Ac], was presented as a suitable alternative to conventional amine-based absorbents. Then, a rigorous two-dimensional mathematical model of the MVR process in a HFMC was developed based on a pseudo-steady-state to understand the influence of the solvent regeneration process in the absorption-desorption process. CO₂ absorption-desorption experiments in PP-HFMC at different operating conditions for desorption, varying vacuum pressure and temperature, were used for model validation. Results showed that MVR efficiency increased from 3% at room temperature and 500 mbar to 95% at 310K and 40 mbar vacuum. Moreover, model deviation studies were carried out using sensitivity analysis of Henry's constant and pre-exponential factor of chemical interaction, thus as to contribute to the knowledge in further works.

Keywords: CO2 desorption; Ionic liquid [emim][Ac]; hollow fiber membrane contactor; membrane vacuum regeneration; modeling.

Figure 1

Experimental setup of the membrane vacuum regeneration (MVR) system. (1) Gear measuring pump; (2) solution tank with temperature control; (3) polypropylene (PP) HFMC; (4) condenser; (5) vacuum pump; (6) CO₂ analyzer; (7) flow measurement by variable volume vessel.

Figure 2

Experimental setup of the CO₂ absorption–desorption process with one absorption HFMC and one desorption HFMC for MVR. (1) Gas cylinder; (2) mass flow controller; (3) absorption PP HFMC; (4) and (10) CO₂ Analyzer; (5) gear measuring pump; (6) solution tank with temperature control; (7) desorption PP HFMC; (8) vacuum pump; (9) condenser; (11) flow measurement by variable volume vessel.

Figure 3

Diagram of CO₂ MVR process in a hollow fiber membrane contactor.

Figure 4

Proposed reaction of CO₂ and [emim][Ac]. Reprinted with permission from Zareiekordshouli et al. [35]. Copyright (2018) Elsevier Ltd.

Figure 5

CO₂ flux through the membrane vacuum regeneration (MVR) module over time in the CO₂ desorption test, using different ionic liquids (ILs) being (●) [emim][EtSO₄] and (■) [emim][Ac].

Figure 6

Change of CO₂ loading of ILs with regeneration time in the CO₂ desorption test, MVR process being (●) [emim][EtSO₄] and (■) [emim][Ac].

Figure 7

Effect of MVR vacuum pressure and temperature on desorption efficiency using [emim][Ac].

Figure 8

Effect of vacuum degree on the cyclic absorption capacity in a MVR process at different temperatures using [emim][Ac].

Figure 9

Correlation of CO₂ absorption efficiency with MVR cyclic efficiency. [(■) Room temperature (289 K) and (●) 310 K].

Figure 10

CO₂ outlet concentration (dimensionless) vs. time. Influence of regeneration stage in absorption process. [(●) only absorption stage and (■) absorption–desorption process].

Figure 11

(a) CO₂ dimensionless concentration in [emim][Ac] along fiber length. (b) CO₂ dimensionless concentration in [emim][Ac] along fiber radius.

Figure 11

(a) CO₂ dimensionless concentration in [emim][Ac] along fiber length. (b) CO₂ dimensionless concentration in [emim][Ac] along fiber radius.

Figure 12

Sensitivity analysis of Henry constant in terms of MVR efficiency at different set parameters. [Legend: the scattered data points (♦) represent experimental data for each set of operating parameters].

Figure 13

Sensitivity analysis of pre-exponential factor of the first-order reaction rate constant in terms of MVR efficiency at different set parameters. [Legend: the scattered data points (♦) represent experimental data for each set parameter].