(1) Selective adsorption according to the size and shape of the molecules, that is, only those molecules smaller than the molecular sieve pore size are adsorbed.
(2) For small polar molecules and unsaturated molecules, it has selective adsorption performance, and the greater the polarity, the higher the degree of unsaturation, and the stronger the selective adsorption.
(3) It has strong water absorption. At higher temperatures, higher airspeeds and lower water content, there is still a relatively high amount of water absorption.
The use of several common molecular sieves is described below.
1, 3A molecular sieve
The cracking gas generally contains 400-700ppm of water, which will form ice during cryogenic separation operation. In addition, under high pressure and low temperature, water can also be formed with lower alkanes (such as CH4, C2H6 and C3H8). White crystalline hydrocarbon hydrate. Crystals of ice and hydrocarbon hydrates can cause blockages in pipes and equipment, causing parking. Therefore, the petroleum cracking gas must be subjected to deep dehydration drying before cryogenic separation to reduce the water content in the cracked gas to less than 5 ppm (i.e., its dew point is lower than -60 ° C). At present, the most ideal deep-drying adsorbent recognized and widely used at home and abroad is 3A zeolite molecular sieve. Because it only adsorbs water molecules in the cracking gas, it does not adsorb larger hydrocarbon molecules (such as C2H6, C2H4, C3H8 and C3H6, etc. Therefore, it is possible to avoid coking of the olefin compound inside the pores of the molecular sieve, thereby prolonging the service life of the adsorbent.
2, 4A molecular sieve
Uses: For the drying of Freon refrigerant and other dehydration drying of substances with molecular size greater than 4.8.
3, 5A system (rich) oxygen molecular sieve
Uses: It is used as an efficient oxygen-nitrogen separation adsorbent in the air separation oxygen industry. The oxygen purity of the production can be controlled between 50-90%. It is widely used in powdered n-alkanes (ie dewaxing) in petroleum and its fractions. Excellent performance quality dewaxed oil having a low freezing point of aviation kerosene, separating normal paraffins (paraffins) can be used as chemical raw materials of synthetic detergents.
4, 13X molecular sieve
Uses: Used in desulfurization of petroleum gas and natural gas (H2S, SO2, mercaptans and thiophenes), and at the same time is an excellent desiccant. Note: For the 1.5-1.7mm strip molecular sieve, the nominal length of the finger is 1-6mm sample; for the 3.0-3.3mm strip molecular sieve, the nominal length of the finger is 2-9mm sample.
5, 13X air separation molecular sieve
Uses: It is used in the air separation industry. The oxygen and nitrogen feed gas in the air has extremely high efficiency. It can completely remove a small amount of CO2 and H2O impurities that affect the oxygen-nitrogen separation performance in the air. It is a special adsorbent for the air separation industry.
6. Cu--13X molecular sieve
Uses: This product is mainly used to remove a trace amount of organic sulfur (thiol) from aviation kerosene. Cu--13X molecular sieve is used in aviation kerosene desulfurization under the process conditions: temperature >130 ° C, pressure 2-3Kg / cm2, space velocity 4h-1, which can reduce the thiol content from 50ppm to 10ppm. Note: 1. The nominal length of the 1.5-1.7mm strip molecular sieve is 4-12mm; the rated length of the 3.0-3.3mm strip molecular sieve is 6-14mm.
7, 10X molecular sieve
Uses: Mainly used for adsorption separation of aromatic hydrocarbons and paraffin purification.
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