  In the field of directional dark matter experiments, SF6 has emerged as an
ideal target gas. A critical challenge with this gas, and with other proposed
gases, is the effective removal of contaminant gases. This includes radon which
produce unwanted background events, but also common pollutants such as water,
oxygen, and nitrogen, which can capture ionisation electrons, resulting in loss
of detector gas gain over time. We present here a novel molecular sieve (MS)
based gas recycling system for the simultaneous removal of both radon and
common pollutants from SF6. The apparatus has the additional benefit of
minimising gas required in experiments and utilises a Vacuum Swing Adsorption
(VSA) technique for continuous, long-term operation. The gas system's
capabilities were tested with a 100 L low-pressure SF6 Time Projection Chamber
(TPC) detector. For the first time, we present a newly developed
low-radioactive MS type 5A. This material was found to emanate radon at 98%
less per radon captured compared to commercial counterparts, the lowest known
MS emanation at the time of writing. Consequently, the radon activity in the
TPC detector was reduced, with an upper limit of less than 7.2 mBq at a 95%
confidence level (C.L.). Incorporation of MS types 3A and 4A to absorb common
pollutants was found successfully to mitigate against gain deterioration while
recycling the target gas.
