5A Molecular Sieve

5A is the separation-and-purification grade of molecular sieve. Its main jobs are gas separation in PSA and VPSA units — pulling nitrogen out of air to make oxygen, and cleaning up hydrogen — plus separating normal paraffins from branched and cyclic ones in refining. It also dries and sweetens sour natural gas, taking out water, carbon dioxide, hydrogen sulfide and light mercaptans in one bed while keeping COS low. Anywhere a process has to split a gas mixture or strip acid gases along with water, 5A is the grade to use.

It works on shape and size. The roughly 5 angstrom pore is just wide enough for a straight-chain paraffin to thread in, but a branched or ring-shaped molecule of the same carbon number is too bulky to enter. Run a mixture of normal and iso paraffins through a 5A bed and the straight chains are held inside while the branched and cyclic ones pass on through. The trapped normal paraffins are then recovered in a separate desorption step. This is the basis of molecular-sieve dewaxing and normal-paraffin recovery from naphtha and kerosene.

An oxygen concentrator runs on pressure swing adsorption. Compressed air is pushed through a 5A bed, where the sieve grabs nitrogen and lets oxygen slip past, so the gas coming off is oxygen-rich. Once the bed fills with nitrogen the pressure is dropped, the nitrogen is released, and the sieve is ready again — two beds swap back and forth for a steady flow. The strong calcium sites and even pore size give 5A the nitrogen affinity and fast cycling a concentrator needs, and a well-run unit reaches oxygen in the mid-nineties percent.

5A comes back to life by heating or by dropping the pressure. A thermal bake at roughly 250 to 350 degrees Celsius under a dry sweep clears water and acid gases, while in a PSA unit the sieve is regenerated by pressure alone on every cycle. Either way it holds up over a long run of swings. The bead and pellet diameters we stock are set out in the table above, so pick the size that fits your PSA vessel or packed bed. Send the separation or drying duty and the flow and we will size the fill.