Faujasite

Faujasite is a mineral from the family of zeolites. It occurs in natural form and is also synthesized industrially.

History

Faujasite was discovered in 1842 by Damour and is named for Barthélemy Faujas de Saint-Fond, a French geologist and volcanologist.¹⁾.

Structure

The faujasite framework consists of sodalite cages which are connected through hexagonal prisms. The pores are arranged perpendicular to each other. The pore, which is formed by a 12-membered ring, has a relatively large diameter of 7.4 Å. The inner cavity has a diameter of 12 Å and is surrounded by 10 sodalite cages. The unit cell is cubic with a length of 24.7 Å. Zeolite Y has a void fraction of 48 % and a Si/Al ratio of 2.43. It thermally decomposes at 793 °C.²⁾

Synthesis

Faujasite is synthesized as other zeolites from alumina sources such as sodium aluminate and silica sources such as sodium silicate. Other alumosilicates such as kaolin are used as well. The ingredients are dissolved in a basic environment such as sodium hydroxide aqueous solution and crystallized at 70 to 300 °C (usually at 100 °C). After crystallization the faujasite is in it is sodium form and must be ion exchanged with ammonium to improve stability. The ammonium ion is removed later by calcination which renders the zeolite in its acid form.

Use

Faujasite is used above all as a catalyst in fluid catalytic cracking to convert high-boiling fractions of petroleum crude to more valuable gasoline, diesel and other products. Zeolite Y has superseded zeolite X in this use because it is both more active and more stable at high temperatures due to the higher Si/Al ratio. It is also used in the hydrocracking units as a platinum/palladium support to increase aromatic content of reformulated refinery products.

External links

• ¹⁾ "Synthese und katalytische Charakterisierung von Zeolith Y mit untereschiedlicher Kristallgröße", Dissertation by Christine Berger (German with English prologue)
• ²⁾ The Chemical Engineering Zeolite Page

Literature

• Subhash Bhatia, Zeolite Catalysis: Principles and Applications, CRC Press, Inc., Boca Raton, Florida, 1990.
• Ribeiro, F. R., et. al., ed., Zeolites: Science and Technology, Martinus Nijhoff Publishers, The Hague, 1984.