A molecular sieve foreline trap can be regenerated by baking it while under low vacuum. A molecular sieve trap contains type 13X synthetic zeolite (mostly Aluminum Oxide) which effectively prevents oil back streaming and traps water vapor at room temperature. Type 13X zeolite will adsorb molecules with critical diameters up to 10 angstroms. The sieve charge can be regenerated (reactivated) by baking it in place when the desired vacuum in the isolated foreline or roughing manifold cannot be achieved. A valve should be used to isolate the manifold from the rest of the system during the bakeout cycle. During bakeout a mechanical pump removes the evolved gases from the sieve while it is being baked. To minimize down-time, bakeouts can be conducted during system off-hours. Oils trapped by the sieve material will not be evolved by baking. Periodic replacement of the sieve material is required whenever the sieve material exhibits evidence of hydrocarbon saturation as determined by foreline or roughing line pressure or visual observation. The sieve material is easily replaced (see basic instructions for TSR traps document). Molecular sieve traps can be mounted in a vertical or horizontal position. The trap’s built-in heater requires customer wiring to an appropriate source (110V or 220V outlet). Once turned on, the heater reaches and maintains a self-regulated and constant temperature (about 150 degrees C). Bakeout time depends on the amount of water vapor in the zeolite and can generally range from 2 to 12 hours. Ensure the setup consists only of the mechanical pump, the trap, a vacuum gauge that can measure in millitorr or millibar and the current vacuum plumbing between the components. Ensure this setup is isolated from the rest of the system. Start the mechanical pump and turn on the vacuum gauge. When the pressure stops going down, plug in the heater. There is no switch or temperature regulation on the heater. Let it heat to its full ability. The pressure will rise significantly on the vacuum gauge, level out, then decrease. When it stops decreasing, unplug the heater. After the trap is back to ambient temperature, the pressure should be at least in the single millitorr or millibar range. If it is not, and you are sure there are no vacuum leaks in the setup, replace the sieve and repeat the process. For vacuum purists, to ensure very little of the evolved gas does not condense in the manifold away from the trap, install a needle valve into the manifold as far toward the end of the manifold as possible. At the point in the process where the trap is hot and the pressure has stopped decreasing, open the needle valve to maintain a pressure of about 50-100 mTorr for about an hour, and then close the needle valve and unplug the trap after the pressure has gone back to a stable reading. Continue to pump on the trap until the trap has returned to ambient temperature as noted above.
More information on molecular sieve traps can be found at:
Molecular Sieve Traps
Category: Process
Sub-Category: None
Related Topics: Maintenance, Cleaning, foreline trap, regenerate, activate, reactivate
