Breakthrough adsorption study of activated carbons for CO2 separation from flue gas

Abstract

Granular activated carbons (GACs) were used to separate carbon dioxide (CO2) from N2-CO2 feed gas mixture employing a fixed bed column. Two grades of GAC (GAC-1 and GAC-2) were used as an adsorbents. The adsorbents were characterized using Micromeritics ASAP surface analyzer and a scanning electron microscope. The parameters considered for examining the breakthrough responses of GACs were the initial concentration of CO2 in feed, temperature, and feed flow rate. It was observed that breakpoint time decreases with increased column temperature and with the gas feed rate for GAC-1 and GAC-2. For both types of activated carbons, the breakthrough time (tb) slightly decreases with increased initial CO2 concentration (vol. %) from 1% to 2% in feed. It was suggested that longer breakthrough time contributes to a higher adsorption capacity of an adsorbents. The adsorption breakthrough occurs early for GAC-2 compared with GAC-1 when the bed was subjected to the same temperature of 25 °C because of the superior surface characteristics of GAC-1. A longer breakthrough time of 1640 sec for GAC-1 was observed compared with a slower breakthrough time of 760 s for GAC-2 at a constant bed temperature of 25 °C subjected to a feed rate of 3 L/min (Cfeed = 5%). It was concluded that GAC-1 breakthrough was delayed compared with that of GAC-2 when the column was controlled to the same initial concentration of CO2 in the feed. The breakthrough periods of 960 s and 270 s were observed at an initial CO2 concentration of 2% in feed for GAC-1 and GAC-2, respectively. The maximum CO2 adsorption capacity of 25.39 g/kg adsorbent was estimated at a CO2 partial pressure of 0.048 bars for GAC-1.