Activated alumina is used for a wide range of adsorbent and catalyst applications including the adsorption of catalysts in polyethylene production, in hydrogen peroxide production, as a selective adsorbent for many chemicals including arsenic, fluoride, in sulfur removal from gas streams (Claus Catalyst process).
Use as a desiccant, it works by a process called adsorption. The water in the air actually sticks to the alumina itself in between the tiny passages, as the air passes through them. The water molecules become trapped so that the air is dried out as it passes through the filter. This process is reversible, and if the alumina desiccant is heated to about 200°C it will release all of the water stored in it. This process is called regenerating the desiccant. Air always has some water in it; one way to measure the amount of water in the air is the air's dew point.
Activated alumina is also widely used to remove fluoride from drinking water. In the US, there are widespread programs to fluoridate drinking water. However, in certain regions, such as the Jaipur region of India, there is enough fluorine in the water to cause fluorosis. Activated alumina filters can easily reduce fluoride levels from .5 ppm to less than .1 ppm. The amount of fluoride leached from the water being filtered depends on how long the water is actually touching the alumina filter media. Basically, the more alumina in the filter, the less fluoride will be in the final, filtered water. Lower temperature water, and lower pH water (acidic water) are filtered more effectively too.
Activated alumina, when used as a fluoride filter, can be regenerated by a solution of lye (sodium hydroxide; NaOH), sulfuric acid (H2SO4), or alum (KAl(SO4)2).
In high vacuum applications, activated alumina is used as a charge material in foreline traps to prevent oil generated by rotary vane pumps from backstreaming into the system.
Activated alumina is an excellent all-purpose desiccant for drying air and most other gases with
high relative humidities. Dewpoints of -100°F can be achieved (depending on dryer).
Activated alumina can be used in both heated and heatless/pressure swing dryers.Activated
alumina has: excellent porosity creating tortuous paths and extended surface area; high strength
against crushing; and very stable physical and chemical characteristics, even in high temperature and
corrosive environments. Activated Alumina-100°F dew points obtainable Unaffected by catastrophic liquid
water loading Ideal for both heatless and heat regenerated systems Low regeneration temperature 250°F to 500°F.
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