E-M-HG2-S-V1_04
Rotronic AG
Bassersdorf, Switzerland
Document code
Unit
HygroGen2 humidity and temperature
generator: Instruction Manual
Instruction Manual
Document Type
Page
17
of 46
Document title
© 2009-2010; Rotronic AG
17
E-M-HG2-S-V1_04
2.7 Regeneration of Molecular Sieve Desiccant
Molecular sieve desiccant may be regenerated by heating, however unless effectiveness of the
regenerated molecular sieve can be determined it is recommended that new molecular sieve desiccant
is used. This can be ordered from ROTRONIC.
To regenerate molecular sieve remove it from the desiccant cell and heat it at 175 °C for at least 3…5
hours in a dry environment (do not use a gas oven). After heating, transfer the desiccant to a sealed
container and allow cooling to room temperature. Check the effectiveness of the regeneration by
measuring the % relative humidity of the dried desiccant prior to recharging the desiccant cell.
2.8 Silica Gel Desiccant
Silica gel is an amorphous form of silicon dioxide, which is synthetically produced in the form of hard
irregular granules (having the appearance of crystals) or hard irregular beads. A micro porous structure
of interlocking cavities gives a very high surface area (800 square metres per gram). It is this structure
that makes silica gel a high capacity desiccant. Water molecules adhere to the gel surface because it
exhibits a lower vapour pressure than the surrounding air. When equilibrium of equal pressure is
reached, no more adsorption occurs. Thus the higher the humidity of the surrounding air, the greater
the amount of water that is adsorbed before equilibrium is reached. Self-indicating silica gel changes
colour once it has become saturated offering an easy method of checking if it is necessary to replace.
Silica gel does not perform well at low temperatures and rapidly becomes saturated at low relative
humidity. Silica gel is suitable for approximately ambient temperature use, where relative humidity
below approximately 30% is not required. There is minimal health and safety implications, non-
indicating (white), and orange to green self-indicating silica gels are non-toxic.
2.9 Regeneration of Silica Gel Desiccant
As a general rule saturated silica gel desiccant will require a minimum of 4-6 hours at a temperature of
between 105-130 °C throughout the entire desiccant bed for the reactivation process to be effective and
reduce the adsorbed moisture to less than 2% by weight. Heating to higher temperatures will damage
the desiccant. Reactivation should be carried out in a ventilated electric oven. A sealed oven will limit
the moisture liberated and prevent efficient reactivation. Gas ovens and microwave cookers are not
suitable for reactivation. After reactivation the desiccant must be placed in a sealed container and
allowed to cool.
For most situations it recommended that new silica gel is used unless a proven process for regeneration
can be implemented. Regeneration can be carried out repeatedly, although eventually the beads will
lose their colour. Replacement Orange to Green self-indicating silica gel can be ordered from ROTRONIC.
2.10 Drierite Desiccant
Drierite is anhydrous calcium sulphate. It is of neutral pH, constant in volume, chemically inert except
towards water, insoluble in organic liquids and refrigerants, non-disintegrating, non-wetting, non-toxic,
non-corrosive, non-channelling, generally recognized as safe (GRAS) by the FDA, not regulated by OSHA,
economical to use, and can be regenerated repeatedly for reuse. Moisture absorption is good across the
range of conditions encountered in the HygroGen.
