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How to choose adsorbent types of PSA oxygen plant in Sichuan

source:本站 2020-05-20


The adsorption performance of the adsorbent for each gas component is evaluated by measuring the isothermal adsorption curve under static state and the outflow curve under dynamic state. The good adsorption performance of adsorbent is the basic condition of adsorption separation process.

In the process of PSA, the choice of adsorbent should also consider to solve the contradiction between adsorption and desorption. For example, for strong adsorbates such as benzene and toluene, it is necessary to use adsorbents such as silica gel with weak adsorption capacity, so as to make the adsorption capacity appropriate and facilitate the desorption operation. For weak adsorbates, such as methane, nitrogen, carbon monoxide, etc., it is necessary to select adsorbents with strong adsorption capacity, such as molecular sieves, in order to have larger adsorption capacity. Another key point of selecting adsorbent is that the separation coefficient between components should be as large as possible.

In the adsorption equilibrium of a component, the total amount in the adsorption bed has two parts: one is in the dead space; the other is adsorbed by the adsorbent. The sum is called the retention of a component in the adsorption bed. The ratio of the amount of weak and strong adsorption components in the dead space to the retention in the adsorption bed is called separation coefficient. The larger the separation coefficient, the easier the separation. The separation coefficient of the two components separated in PSA should not be less than 2.

The main components in the air are nitrogen and oxygen. Therefore, adsorbents with different adsorption selectivity for nitrogen and oxygen can be selected, and appropriate process can be designed to separate nitrogen and oxygen to produce oxygen. Nitrogen and oxygen have quadrupole moment, but the quadrupole moment of nitrogen (0.31 Å) is much larger than that of oxygen (0.10 Å), so the adsorption capacity of nitrogen on zeolite molecular sieve is stronger than that of oxygen. When the air passes through the adsorption bed with zeolite adsorbent under pressure, nitrogen is adsorbed by the zeolite, and oxygen is enriched in the gas phase and flows out of the adsorption bed due to less adsorption, so that oxygen and nitrogen can be separated to obtain oxygen.

At present, the common VPSA oxygen making adsorbents are LiLSX lithium based adsorbent and 5A oxygen making adsorbent. LiLSX lithium based adsorbent has good performance, long service life and good sulfur resistance; the common 5A adsorbent has poor performance, large dosage and short service life and needs desulfurization (the desulfurizer needs to be replaced regularly).