close valve it is understood that a single throttle valve not shown could replace this valve combination the use of two valves restricts the flow of gas into an adsorbent bed 13 in cleaning chamber 12 when there is a large pressure difference and provide a u201c soft start u201d the use of the two valves is also wasteful when the outlet 44 of the recycle pump 26 is at atmospheric pressure and the adsorbent bed 13 is under vacuum at the start of the adsorption cycle the adsorbent bed comprises cf x wherein x is from about 0 9 to about 1 2 and is pelletized according to the methods described herein said cf x further comprising an amount of ptfe and optionally a pore forming agent according to the present invention valves 60 62 would be used when the inlet 38 of the recycle pump 26 is at vacuum and the adsorbent bed 13 is under pressure at the start of the bed regeneration cycle valves 60 and 62 control the flow of gas from the inlet 56 of the adsorbent bed 12 to the inlet 38 of the recycle pump 26 preferably valve 62 is a full flow open close valve and valve 60 is a restricted flow open close valve it is understood that a single throttle valve could replace this valve combination the two valves 60 62 work to restrict the flow of gas into the recycle.