High pressure adsorption of CO2 on MCM-41 grafted with quaternary ammonium ionic liquids

- [thepAm][Br] and [VBTMA][Cl] were successfully bonded to MCM-41.
- The grafted MCM-41 showed high CO2 adsorption at high pressure.
- The grafted MCM-41 acted as a selective separation agent to CO2 over CO.
- The adsorption-desorption indicated stability of the hybrid adsorbent.
- The high pressure adsorption showed complete separation of CO2 from a mixture.

In order to improve CO2 absorption capacity and selectivity in ionic liquids (ILs), grafting two quaternary ammonium ILs, (vinyl benzyl) trimethylammonium chloride ([VBTMA][Cl]) and tetra-n-heptyl ammonium bromide ([thepAm][Br]), on mesoporous MCM-41 was studied in this work. Results from the characterization of FT-IR, TGA, BET, TEM and elemental analysis showed that the ILs were successfully grafted on MCM-41. Gas excess loading (from 0.1 MPa to 8.0 MPa) was studied by using the high-pressure quartz spring method. Grafting the ILs on the supports caused loss in mesoporosity, resulting in slight decrease in CO2 adsorption capacity, but enhanced the CO2/CO selectivity. Meanwhile, the adsorbents grafted with [VBTMA][Cl] performed better in terms of excess CO2 loading (3.90 mmol/g) and CO2/CO selectivity (95) than those grafted with [thepAm][Br] corresponding to 3.65 mmol/g for CO2 loading and 21 for CO2/CO at 30.0 °C and 5.0 MPa. An adsorption-desorption (9.0 MPa) procedure at 30.0 °C was implemented to examine the selective CO2 capture from the H2, CO and CO2 mixture by using the [VBTMA][Cl] grafted adsorbent and showed almost complete separation of CO2 from the mixture.

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