Evaluation on Adsorption Separation of Low Concentration Xe and Kr by Activated Carbon Through Static and Dynamic Methods

Abstract

Radioactive Xe isotopes are located at the heavy mass peaks of the fission mass distribution curves of 235U and 239Pu, with the characteristics of high fission yields and moderate half-life times, which have important application value in environmental radiation monitoring, international nuclear arms control and other nuclear event monitoring. The accuracy and reliability of nuclear data of radioactive Xe isotopes are valuable for its application, but there is often interference of radioactive Kr isotopes when measuring radioactive Xe isotopes. At present, cryogenic distillation is the main method for separating inert gas Xe and Kr in industry; however it is expensive and requires complex engineering control, which is not suitable for the preparation of nuclear data measuring gas sources. The adsorption separation method has been widely used in the separation and purification of various gas mixtures because of its maturity and low energy consumption. In order to prepare high activity Xe source for the measurement, the separation of low concentration Xe and Kr on CF-1450 activated carbon at room temperature and atmospheric pressure was studied. The pore structure characterized by N2 adsorption-desorption isotherm at −196 ℃ shows that the BET specific surface area of CF-1450 activated carbon is 1680 m2/g and the dominant pore size distribution is smaller than 2 nm. The capacity of CF-1450 activated carbon for separating Xe and Kr was evaluated by static adsorption and dynamic adsorption-desorption methods. The Xe and Kr henry coefficients of CF-1450 activated carbon at 25 ℃ are 0.21 mmol/(g·kPa) and 0.02 mmol/(g·kPa), respectively. The henry selectivity factor of Xe/Kr on CF-1450 activated carbon is 10.5, which is in agreement with the IAST selectivity(10.6, y(Xe)∶y(Kr)=50∶50) under the same conditions. The zero-point isosteric heats of Xe and Kr on CF-1450 activated carbon are 35.7 kJ/mol and 13.9 kJ/mol, respectively. Based on the dynamic separation capacity of low concentration Xe and Kr on CF-1450 activated carbon, an attractive procedure was proposed and showed good performance for preparing high activity Xe source. The recovery of Xe is 79% and the decontamination factor of Kr is 195.

Keywords

• activated carbon
• low concentration gas
• xe
• kr
• adsorption
• separation