Perfluorocompounds (PFCs), which are indispensable materials for semiconductor manufacturing, are considered to be contributors to global warming. Countries that ratify the Kyoto Protocol commit to reduce their emissions of these gases. Therefore, it is desirable that used PFCs should be collected, refined, and reused. To realize this recycling system, it is necessary to establish a method to separate PFCs from other gases and to recover pure PFCs. To meet this requirement, we have developed a new separation technique for PFCs by modifying the technique applied to un-reacted fuels (tritium and deuterium) in the fuel cycle system of fusion reactors.
The Continuous Circulation Chromatograph method (Fig. 2-15) is used for the separation and recovery of PFCs. The device consists of several special adsorbent columns and open-closed valves to separate the mixture of PFC into component gases using the difference in adsorption affinity among the component gases. Component gases are time-sequentially separated using the open-closed valves because the time required for a gas to pass through a column is determined by adsorption affinity.
Based on existing knowledge and many experimental data, we have manufactured a large-sized testing device (Fig. 2-16). Experimental results verify efficient and continuous separation of CF4-C2F6 mixtures into their component gases. High recovery rates of more than 99% are obtained, and the impurity level in each PFC is lower than 0.01% (Fig. 2-17). |
