Activated Alumina Desiccant: Grades and Where Each One Fits

An activated alumina desiccant is chosen by the stream it has to dry, not by a single number. Alumina is a porous aluminium oxide with a very large specific surface area and a rich microporous structure, which is what gives it its strong water uptake. In practice the "grade" is selected by duty: compressed air, process gases, transformer and lubricating oils, the working solution in hydrogen peroxide production, water treatment, or as a catalyst carrier. This page sets out where each duty fits and what to put on the order.

What Activated Alumina Is

Our activated alumina (also sold as alumina desiccant) is supplied as white spherical particles. It is non-toxic, odourless, non-pulverising and insoluble in water, and it is used for the deep drying of industrial gases and liquids. It is a strong water adsorbent rather than a sachet desiccant: the form and grade are matched to a packed bed, a vessel or a process stream, not to a carton.

Where Each Duty Fits

Alumina earns its place in five broad duties:

• Industrial gas drying. Compressed air drying, where it prevents the rust and freezing of pneumatic equipment; purification of oxygen, hydrogen, CO₂, natural gas and cracked gas; and instrument air systems where absolute dryness is required.
• Liquid drying and purification. Transformer oil and lubricating oil, where it removes trace moisture; organic solvents such as ethanol and benzene; and hydrogen peroxide production, where it is a major application as an adsorbent in the working solution.
• Water treatment. Fluoride removal from drinking water, where the surface chemistry rather than the pore volume does the work.
• Catalyst carrier. As a carrier material for petrochemical applications.
• Protective beds. As a robust desiccant where a stream is wetter or harsher than a silica-based bed handles well.

Choosing Between Alumina and Silica Gel

Alumina and silica gel are not interchangeable, and the choice is the one a buyer most often gets wrong. Alumina is supplied in bulk bead form for packing beds and drying process streams and liquids; silica gel covers everything from the same kind of bulk drying to sachets, canisters and unit-dose packaging. If your job is a packed bed or a liquid stream, compare the two directly in alumina desiccant vs silica gel. Where you need a very low dew point or a separation by molecular size rather than bulk drying, the answer is usually a molecular sieve instead — see 3A, 4A, 5A and 13X explained.

What to Specify When You Order

• End use — compressed air, natural gas, transformer oil, hydrogen peroxide, water treatment or catalyst carrier. This drives the grade more than any other answer.
• Form — spherical particles, and the size suited to your vessel and acceptable pressure drop.
• Stream conditions — gas or liquid, and how wet the stream enters the bed.
• Packing and quantity — composite bag or drum; other packaging on request.

Tell us the stream you are drying, the vessel and the conditions, and we will recommend the grade and form and quote it. Prices are on request. For the fuller explanation of how alumina behaves and where it sits against other adsorbents, read our activated alumina guide.