Preparation and Characterization of Activated Carbons from Bamboo Sawdust and Its Application for CH4 Selectivity Adsorption from a CH4/N2 System

A series of activated carbons were prepared by H 3 PO 4 -mechanical force activation and characterized by N 2 adsorption/desorption isotherms, SEM, FTIR, CO/CO 2 -TPD, and XPS. Adsorption isotherms of CH 4 and N 2 were measured in the range of 25–760 mmHg at 20 °C and fitted by Langmuir model to calculate separation coefficient of CH 4 against N 2 (α CH 4 /N 2 ). Results showed that H 3 PO 4 -mechanical force activation had significantly enhanced the micropore volume of activated carbons (ACs), in which the highest micropore volume (0.8 cm 3 /g) and BET specific area (1966 m 2 /g) were obtained under the optimum condition of phosphoric acid impregnation ratio of 1:1, activation temperature of 400 °C, and activation time of 60 min. The micropore volume and surface properties of ACs affected its selectivity adsorption ability toward CH 4 . The ACs with higher micropore volume had a larger adsorption amount of CH 4 . And the larger the O/C ratio of the ACs was, the larger the oxygen-containing groups on the ACs would be, which can improve the surface polarity of ACs and enhance the adsorption ability of N 2 with certain polarity, and thus make the ACs having the smaller separation factor of α CH 4 /N 2 . Among all of the samples, AC-1-400 with the largest micropore volume and O/C ratio had the highest CH 4 adsorption amount but the smallest α CH 4 /N 2 .