Layered double oxide/activated carbon-based composite adsorbent for elevated temperature H2/CO2 separation

A layered double oxide/activated carbon-based composite adsorbent for H2/CO2 separation at elevated temperatures is presented for the first time. The CO2 adsorbent is synthesized from commercially available activated carbon, which is loaded with Mg-Al hydrotalcite using the urea or co-precipitation methods. Samples are comprehensively characterized using various techniques, including XRD, BET and SEM. The results show that the co-precipitation method is more efficient for the synthesis of the composite adsorbent. Compared with activated carbon and hydrotalcite as single-composition adsorbents, the composite adsorbent has a comparatively larger adsorption capacity and faster kinetics at elevated temperatures. The adsorption capacity of the composite adsorbent reaches 0.185 mmol/g at 200 °C and 1 atm for the second adsorption/desorption cycle, and 86% of the total CO2 is adsorbed within 20 min. Additionally, K2CO3 is loaded on the surface of the composite adsorbent via impregnation to further promote the adsorption performance. The adsorption isotherm data show that the K2CO3-promoted composite adsorbent has an adsorption capacity of 1.741 mmol/g at 200 °C and 3 MPa, which is higher than that for activated carbon (1.410 mmol/g) and for the composite adsorbent without K2CO3 (1.638 mmol/g). This result further proves that the developed adsorbent is a promising candidate for H2/CO2 separation within the elevated temperature pressure swing adsorption process.