Adsorption separation of CF4, O2, CO2, and COF2 from an excimer gas mixture

Abstract

The use of adsorbents is explored as an option for the removal of trace impurities of CO2, CF4, COF2, and O2 from F2, Kr, and Ne for applications in excimer lasers. Due to the incompatibility of many adsorbents to F2 and HF, aluminas and polymeric adsorbents were selected as potentially compatible materials. To determine the adsorption potential of these adsorbents in the low concentration region, the concentration pulse chromatographic technique was chosen to determine the Henry’s Law constants of CO2, CF4, and O2 gases with three polymeric adsorbents (HayeSep Q, HayeSep B, and Fluorinated DVB) and two aluminas (AA-300, and Alumina A). The results were plotted and compared on van’t Hoff plots (the natural logarithm of Henry’s Law constants as a function of inverse absolute temperature) with the heat of adsorption values being calculated from the lines of best fit for all gases and adsorbents tested in this study. Due to the large energies required to operate the excimer lasers, a cryo-cooler was determined to be feasible to precool the feed stream before separation, which increases the adsorption capacity and the compatibility of the adsorbents to F2 and HF. The van’t Hoff plots were extrapolated to colder temperatures to determine the Henry’s Law constants to analyze the potential of using the cryo-cooler. From this study, it was determined that HayeSep Q was the best polymeric adsorbent with significant adsorption of CO2 at temperatures below −50 °C while being the best performing CF4 adsorbent. AA-300 was the best performing alumina in this study while having significant adsorption of CF4 at temperatures below −135 °C. However, from a compatibility standpoint, both of these materials need to be tested to determine their robustness in the presence of F2 and HF at room and reduced temperatures.