All molecular sieves are composed of sodium and aluminosilicate, which are grown to form a three-dimensional crystal structure. It's this crystalline structure that allows molecular sieve to adsorb some molecules while rejecting other molecules that are too large to fit inside the crystal.
When A-Type crystals are grown, they initially are all Type 4A, meaning the pore openings are four Angstroms in diameter with an A-Type crystal structure. These 4A crystals are capable of adsorbing molecules that are smaller than 4 angstroms in diameter, such as water, while allowing larger molecules, such as methane, to pass along to the desired product stream. The pore size of Type 4A can be manipulated, which allows molecular sieve to be used to adsorb, or exclude, certain molecules depending on the new pore size and the desired results.
Type X crystals are shaped differently from Type A crystals are tend to offer much larger pore sizes, about 9 Angstroms in diameter. 13X molecular sieve is often used to produce oxygen or in cryogenic distillation processes to deeply dehydrate LNG and LPG streams. It is critical to remove all water from these streams to prevent blockage and freezing in pipelines. There are many variations of Type X crystals with most being Type 13X.
While all molecular sieves serve the purpose of selectively adsorbing smaller molecules from larger ones, it's critical to select the right product for your application. Quality of material and close care to specifications are essential to helping you optimize your process, increase efficiency, and get the high return on your investment.