Solvents dehydration through absorption on molecular sieves (zeolites)

The solvent dehydration process on zeolite beds occurs by feeding wet solvents through absorbers containing, indeed, molecular sieves. Wet solvents, crossing the zeolites bed are dehydrated by water present in the mixture, and come out anhydrous from absorption bed. Molecular sieves during the process absorb water until saturation, thanks to their porosity.

The exothermic reaction generated during water absorption enables automation systems installed in the plant to control zeolites beds saturation, so that the quality of dehydrated solvent exiting from adsorbers can always be controlled.

The most used zeolites in these applications are of 3A type due to the suitable dimensions of micropores, that ensure the adsorption of water molecules only, while solvents molecules are not absorbed. Once saturated, molecular sieves bed are regenerated using inert gas, as done for active carbon.

Molecular sieves regeneration through inert gas

The technology used to desorb water from molecular sieves is the same desorbing technology with inert gas (nitrogen) used for active carbon. Nitrogen is heated through a heat exchanger placed on the forced circulation of a fan until reaching a temperature of about 210°C, and is then conveyed to the adsorber containing molecular sieves saturated with water.

Once water has evaporated from the sieves, it is first condensed through refrigeration in condensation batteries because it has a high solvents content, while in a second phase it is sent to a guard bed and next in the atmosphere.

This treatment allows to restore the absorption capacity of the zeolites, as in origin.