An experiment was conducted to show the difference between silica gel orange-green and molecular sieves 4A and 13X when used in an adsorber. For the experiment, 0.5kg of each of the desiccants was tested at a mass flow rate of 46.6 g/h. This is calculated using a volume flow of 50l/min, a temperature of 20°C and a relative humidity of 90%. Due to the lack of a humidity indicator, key figures for the color change are determined for the molecular sieves. The behavior of the breakthrough curve of molecular sieves differs from that of silica gel.

For low loadings, this has a value of approximately 0.
Towards the maximum load, the breakthrough curve of the molecular sieve rises steeply to the value 1. The steeper rise of the breakthrough curve indicates a more complete loading of the molecular sieve.

The maximum loading of the molecular sieves is lower than that of the silica gel and is reached more quickly due to the steeper breakthrough curve. The maximum loading of molecular sieve 13X is higher than that of molecular sieve 4A. Due to the flatter breakthrough curve, the water sum at low loadings is lower than that of the silica gel. Only when the maximum loading is reached does the water absorption rise steeply, since from this point on no more water is absorbed.

Figure 1: Dependence of the DBK on the load for different adsorbents

Figure 2: Dependence of DBK on time for different adsorbents

Figure 3: Dependence of the water sum on the load for different adsorbents

The use of molecular sieves, especially the MS 13X, provides better protection for the plant to be ventilated. Due to the strong binding of water, the entire incoming humidity is adsorbed. At the same time, the 13X molecular sieve has a higher maximum loading than the 4A molecular sieve. Both molecular sieves have more favorable adsorption properties than the silica gels at low loadings, which leads to faster saturation. In addition, the lack of a color indicator is disadvantageous for use in an aeration dryer.