Improving the Separation of CO2/CH4 Using Impregnation of Deep Eutectic Solvents on Porous Carbon

The separation of CO2/CH4 using porous carbon can be increased by the presence of a functional group of nitrogen on the carbon surface. This study explores the potential of porous carbon derived from the palm kernel shell (C-PKS) impregnated with a deep eutectic solvent (DES), which is one of the chemicals containing a nitrogen element. The DES was composed of a quaternary ammonium salt of choline chloride (ChCI) and a hydrogen bond donor of alcohol. Three alcohols of 1-butanol (-ol), ethylene glycol (-diol), and glycerol (-triol) were employed to study the effects of a number of hydroxyl groups in the separation performance. The research steps included (i) the preparation of DES-impregnated porous carbon synthesized from the palm kernel shell (DES/C-PKS), (ii) characterization of the material, and (ii) a separation test of CO2/CH4 with a breakthrough system. Materials were characterized using scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX), N-2-sorption analysis, and Fourier transform infrared (FTIR) spectroscopy. SEM images showed a significant morphological difference of pristine carbon and DES/C-PKS. There was a significant decrease in the range of 67-73% of a specific surface area with respect to pristine carbon, having initially 800 m(2)/g. However, the N element on the carbon surface increased after impregnation treatment, which was shown from the intensity of the FTIR graphs and EDX analysis. Adsorption isotherm revealed that DES/C-PKS could enhance up to 1.6 times the adsorption capacity of CO2 at 1 atm and 30 degrees C while increasing the selectivity of CO2/CH4 up to 125%. The breakthrough experiment showed that all DES/C-PKS materials displayed a better performance for the separation of CO2/CH4, indicated by a longer breakthrough time and enhancement of CO2 uptake. The best separation performance was achieved by DES/C-PKS using glycerol as a hydrogen bond donor with 15.4 mg/g of CO2 uptake or equivalent to 95% enhancement of the uptake capacity compared to pristine porous carbon. Also, the cycling test revealed that DES/C-PKS can be used repetitively, which further highlights the efficiency of the material for the separation of CO2/CH4.

Automated summary

The study investigated the use of nitrogen-functionalized porous carbon derived from palm kernel shell impregnated with a deep eutectic solvent for CO2/CH4 separation. The DES/C-PKS material showed increased CO2 adsorption capacity and selectivity, with glycerol as the hydrogen bond donor exhibiting the best separation performance. The cycling test demonstrated the material's reusability and effectiveness for CO2/CH4 separation.