A novel process for CO2/CH4 gas separation on activated carbon fibers--electric swing adsorption.

Equilibrium and breakthrough adsorptions on activated carbon fibers (ACF) were conducted for CO2 and CH4 gas mixtures and the selective separation of CO2 was demonstrated. An electric swing adsorption process (ESA) was exploited to effect the rapid desorption of adsorbed gas at atmospheric pressure. Also, the relationship between the electrical behavior and desorption characteristics of ACF is discussed. In a single component adsorption experiment, the amount of adsorbed CO2 reached up to 40 mg/g-ACF, twice as much as that of adsorbed CH4. Therefore, the separation factor, defined as the ratio of adsorbed CO2 to adsorbed CH4, was 2.0. Multicomponent experiments showed a higher separation factor of 5.2, owing to a roll-up phenomenon. The temperature increase is not linearly proportionate to the power input, while the passage of higher electrical voltage (30 V) caused the ACF temperature to exceed 200 degrees C within 30 s. CO2 desorption at low voltage was well accomplished by heating the ACF to temperatures <60 degrees C. An ACF adsorption bed regenerated with ESA showed a constant regeneration efficiency of over 85% with a regular breakthrough curve. The ESA method increased desorption efficiency by over 20%, compared with the vacuum method.

Effect of acidic treatment on metal adsorptions of pitch-based activated carbon fibers.

In this work, the pitch-based activated carbon fibers (ACFs) were prepared by nitric acid to investigate the multi-metal adsorption in interfacial and textural points of view. N2/77 K adsorption isotherm characteristics, including the specific surface area and micropore volume, were studied by BET specific surface area and t-plot methods, respectively. As a result, the specific surface area of the almost neutral ACFs in nature significantly decreased with nitric acid treatment, probably due to the widening of micropores. However the total acidity, including the carboxyl groups, on carbon surfaces was extremely induced during the acidic surface treatment. From the adsorptions of Cu2+ and Ni2+, it was revealed that the adsorption capacity of metal ions was mainly influenced by the weakly acidic functional groups such as lactones on the carbon surfaces at pH < pI (isoelectric point), and by the strongly acidic functional groups such as carboxyl groups at pH > pI.

Studies on pore structures and surface functional groups of pitch-based activated carbon fibers.

The present study concerns the physical activation and chemical oxidation of pitch-based activated carbon fibers (ACFs) as ways to improve the adsorption properties. The surface oxides of the ACFs studied were determined by Boehm's titration and the pore structures were studied by the BET method with N(2)/77 K adsorption. Also, the adsorption properties of the ACFs were investigated with chromium ion adsorption by different adsorption models. As a result, it was observed that carboxyl groups were largely created after nitric acid treatment on ACFs. The affinity for chromium ions increases with increasing specific surface area, micropore volume, and surface functionalities of ACFs as the activation time increases.