Molecular gas filtration: chemisorption versus physisorption

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Courtesy of Bioconservacion SA

Advantages of chemisorption over physisorption in molecular gas filtration.

To remove pollutant compounds in air, both spherical and pelletized solid products are widely used. Examples of their application include Indoor Air Quality, Corrosion in Control Rooms, In Vitro Fertilisation, and Odours. What all these applications have in common are low concentrations of pollutants and relatively high flow rates.

According to the way they work there are two types of absorbents:

Firstly, products based on physical adsorption -physisorption-, basically activated carbon. In this case the compound is trapped in the pores of the filter but remains intact.

Secondly, products based on chemical reactions that involve an active ingredient and a support. In this case the pollutant is removed through an irreversible chemical reaction, or chemisorption. The main advantages of chemisorption are the following:

  • The pollutant is irreversibly captured.
  • It is independent of temperature and a broad range of relative humidity.
  • It is independent of the compound's molecular weight. It also works with small molecules.
  • The product's effectiveness is relatively independent of the concentration of the compound to be eliminated.

However, in chemisorption the efficiency of the product usually is somewhat lower than in physisorption, as it is a slower and more complex process.

Typically, physisorption products exhibit a high degree of efficiency initially, but this drops off relatively rapidly with use.  Nevertheless, certain factors such as changes in temperature frequently cause the desorption of previously eliminated  pollutants. For this reason its disadvantages are:

  • It requires the lowest relative humidity possible, at least less than 50%.
  • It is strongly dependent on temperature.
  • The removal effciency of the product is highly dependent on the concentration of the compound to eliminate. The lower the concentration, the lower the adsorption capacity.
  • Permanent adsorption is not usually achieved with low-molecular-weight compounds. In fact, as a general rule, the greater the molecular weight the better the retention by adsorption.

Bioconservacion has a broad portfolio that includes physisorption-based products (such as the Bi On AC range); products based on chemisorption (like Bi On R8, R12, and the entire Bi On Isorb, Bi On ACPA, Bi On Clear, and Bi On Sigma range), and high-capacity products based on catalytic processes (such as Bi On Oxyl, Bi On Delta, Bi On DOD, and Bi On Carb OX). Bioconservacion's philosophy is to always offer the best solution, with technical and innovative proposals for solving the different problems. To do this, we have an action protocol that we adapt to the particular needs of each client and case, ensuring our clients benefit before, during, and after the installation of the filtration system.

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