Adsorption and desorption dynamics of CF4 on activated carbon beds: Validity of the linear driving force approximation for pressure-changing steps

Abstract

Adsorption and desorption dynamics of CF4 on an activated carbon bed were studied experimentally and theoretically, focusing on pressure-changing steps. The theoretical model used the ideal adsorbed solution (IAS) theory and the linear driving force (LDF) approximation as equilibrium and mass transfer models, respectively. Adsorption breakthrough curves of raw CF4 gas (500, 1,000, and 1,500 ppm) were well predicted by the theoretical model and the diffusion time constant for CF4 was found to be 3.3×10−3 s−1 from breakthrough curve fitting. Changes in the CF4 concentration during depressurization could be easily predicted using the above mathematical model when the half-cycle time (θ c ) was above 0.1. However, significant discrepancies were observed between the predicted CF4 concentrations and the experimental data when θ c was 0.1. Nakao and Suzuki also reported that proportional constant of LDF approximation (=KD e /R p 2) needs to be modified when θ c is less than 0.1.