Difference Between Activated Alumina and Molecular Sieve

 The key difference between activated alumina and molecular sieve is that activated alumina contains a considerably high number of pores, whereas molecular sieve has comparatively a low number of pores.

Activated alumina and molecular sieve are materials that are useful in absorbing water as adsorbents. These materials have a strong adsorption capacity for water vapour.

CONTENTS

1. Overview and Key Difference
2. What is Activated Alumina
3. What is Molecular Sieve
4. Side by Side Comparison – Activated Alumina vs Molecular Sieve in Tabular Form
5. Summary

What is Activated Alumina?

Activated alumina is a highly porous material made of aluminum oxide. This material is manufactured through the dihydroxylation of aluminum hydroxide. The surface area of this material is very high, about 200 square meters per gram. Activated alumina is important as a desiccant that can keep substances dry by absorbing water from surrounding air. Moreover, this material can be used as a filter of fluoride, arsenic and selenium in drinking water.

Activated alumina has a large surface-area-to-weight ratio. This is because this material has many “tunnel-like” pores.

There are many applications of activated alumina, including catalyst applications, using as a desiccant, as a fluoride adsorbent, in vacuum systems, as a biomaterial, and in defluoridation. In catalyst applications, activated alumina is useful as a catalyst in polyethylene production, hydrogen peroxide production, etc. As a desiccant, activated alumina is useful for adsorption because the water in the air sticks to the alumina itself inside the pores. Then, the water molecules become trapped. In addition, this material is useful in removing fluoride from drinking water.

What is Molecular Sieve?

Molecular sieve is a porous material having pores with uniform sizes. The diameter of these pores is similar to the size of very small molecules. Therefore, large molecules cannot pass through these pores, and they are adsorbed, but smaller molecules can pass through these pores. We can measure the diameter of a molecular sieve using the unit Angstrom or nanometers.

When a mixture of molecules is migrating through the stationary bed of porous and semi-solid substance (the sieve), the components having a high molecular weight tend to leave the bed first; then comes the successively smaller molecules. Therefore, these molecular sieves are useful in chromatography. Some types of molecular sieves are useful as desiccants.

Concerning the applications of molecular sieve material, we can use it in the petroleum industry for drying gas streams. We can use this substance to dry solvents which includes aggressive desiccants. Moreover, there are catalytic applications that can catalyze isomerization, alkylation, and epoxidation. In addition, we can use molecular sieves for the filtration of air supplies in breathing apparatus such as scuba divers and firefighters.

What is the Difference Between Activated Alumina and Molecular Sieve?

Activated alumina and molecular sieves are highly porous materials. Activated alumina is a highly porous material made of aluminum oxide while molecular sieve is a porous material having pores with uniform sizes. Therefore, the key difference between activated alumina and molecular sieve is that activated alumina contains a considerably high number of pores, whereas molecular sieve has comparatively a low number of pores.

Below is a summary of the difference between activated alumina and molecular sieve in tabular form.

Summary – Activated Alumina vs Molecular Sieve

Activated alumina and molecular sieve are materials that are useful in absorbing water as adsorbents. The key difference between activated alumina and molecular sieve is that activated alumina contains a considerably high number of pores, whereas molecular sieve has comparatively a low number of pores.

Reference:

1. “Molecular Sieve.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., Available here.

Image Courtesy:

1. “Active Al2O3” By GOKLuLe 盧樂 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Molecular Sieve5” By Psiĥedelisto – Own work (Public Domain) via Commons Wikimedia