Faujasite
Encyclopedia
Faujasite is a mineral group in the zeolite
family of silicate minerals. The group consists of faujasite-Na, faujasite-Mg and faujasite-Ca. They all share the same basic formula: (Na2,Ca,Mg)3.5[Al7Si17O48]·32(H2O) by varying the amounts of sodium, magnesium and calcium. It occurs as a rare mineral in a several locations worldwide and is also synthesized industrially.
, Kaiserstuhl
, Baden-Württemberg
, Germany
. The sodium modifier faujasite(Na) was added following the discovery of the magnesium and calcium rich phases in the 1990s. It was named for Barthélemy Faujas de Saint-Fond
(1741-1819), French geologist and volcanologist.
Faujasite occurs in vesicles within basalt
and phonolite
lava
and tuff
as an alteration or authigenic mineral. It occurs with other zeolites, olivine
, augite
and nepheline
.
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; Pearson symbol
cF576, symmetry Fd3m, No.227, lattice constant 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.
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. Depending on the silica-to-alumina ratio of their framework, synthetic faujasite zeolites are divided into X and Y zeolites. In X zeolites that ratio is between 2 and 3, while in Y zeolites it is 3 or higher. The negative charges of the framework are balanced by the positive charges of cations in non-framework positions. Such zeolites have ion-exchange, catalytic and adsorptive properties. The stability of the zeolite increases with the silica-to-alumina ratio of the framework. It is also affected by the type and amount of cations located in non-framework positions. For catalytic cracking
, the Y zeolite is often used in a rare earth-hydrogen exchanged form.
By using thermal, hydrothermal or chemical methods, some of the alumina can be removed from the Y zeolite framework, resulting in high-silica Y zeolites. Such zeolites are used in cracking
and hydrocracking catalysts. Complete dealumination results in faujasite-silica.
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.
Zeolite
Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...
family of silicate minerals. The group consists of faujasite-Na, faujasite-Mg and faujasite-Ca. They all share the same basic formula: (Na2,Ca,Mg)3.5[Al7Si17O48]·32(H2O) by varying the amounts of sodium, magnesium and calcium. It occurs as a rare mineral in a several locations worldwide and is also synthesized industrially.
Discovery and occurrence
Faujasite was first described in 1842 for an occurrence in the Limberg Quarries, SasbachSasbach
Sasbach may refer to two towns in Baden-Württemberg, Germany:*Sasbach , in the Ortenau district*Sasbach am Kaiserstuhl, in the district of Emmendingen...
, Kaiserstuhl
Kaiserstuhl
The „Kaiserstuhl“ is a relatively low mountain range – a Mittelgebirge – with a maximal height of 556.6 m above sea level. It is of volcanic origin and located in the South West of Baden-Württemberg, Germany in the districts of Emmendingen and Breisgau-Hochschwarzwald...
, Baden-Württemberg
Baden-Württemberg
Baden-Württemberg is one of the 16 states of Germany. Baden-Württemberg is in the southwestern part of the country to the east of the Upper Rhine, and is the third largest in both area and population of Germany's sixteen states, with an area of and 10.7 million inhabitants...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
. The sodium modifier faujasite(Na) was added following the discovery of the magnesium and calcium rich phases in the 1990s. It was named for Barthélemy Faujas de Saint-Fond
Barthélemy Faujas de Saint-Fond
Barthélemy Faujas de Saint-Fond , French geologist and traveller, was born at Montélimar. He was educated at the Jesuit's College at Lyon; afterwards he went to Grenoble where he studied law and was admitted as an advocate to the parlement.He rose to be president of the seneschal's court in...
(1741-1819), French geologist and volcanologist.
Faujasite occurs in vesicles within basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
and phonolite
Phonolite
Phonolite is a rare igneous, volcanic rock of intermediate composition, with aphanitic to porphyritic texture....
lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
and tuff
Tuff
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
as an alteration or authigenic mineral. It occurs with other zeolites, olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
, augite
Augite
Augite is a single chain inosilicate mineral, 2O6. The crystals are monoclinic and prismatic. Augite has two prominent cleavages, meeting at angles near 90 degrees.-Characteristics:Augite is a solid solution in the pyroxene group...
and nepheline
Nepheline
Nepheline, also called nephelite , is a feldspathoid: a silica-undersaturated aluminosilicate, Na3KAl4Si4O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites...
.
Structure
The faujasite framework consists of sodaliteSodalite
Sodalite is a rich royal blue mineral widely enjoyed as an ornamental gemstone. Although massive sodalite samples are opaque, crystals are usually transparent to translucent...
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; Pearson symbol
Pearson symbol
The Pearson symbol, or Pearson notation, is used in crystallography as a means of describing a crystal structure, and was originated by W.B. Pearson. The symbol is made up of two letters followed by a number. For example:* Diamond structure, cF8...
cF576, symmetry Fd3m, No.227, lattice constant 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.
Synthesis
Faujasite is synthesized, as are other zeolites, from alumina sources such as sodium aluminateSodium aluminate
Sodium aluminate is an important commercial inorganic chemical. It works as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium aluminate is a white crystalline solid having a formula variously given as NaAlO2, NaAl4 , Na2O·Al2O3, or Na2Al2O4...
and silica sources such as sodium silicate
Sodium silicate
Sodium silicate is the common name for a compound sodium metasilicate, Na2SiO3, also known as water glass or liquid glass. It is available in aqueous solution and in solid form and is used in cements, passive fire protection, refractories, textile and lumber processing, and automobiles...
. Other alumosilicates such as kaolin
Kaolinite
Kaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O54. It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra...
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
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
to improve stability. The ammonium ion is removed later by calcination which renders the zeolite in its acid form. Depending on the silica-to-alumina ratio of their framework, synthetic faujasite zeolites are divided into X and Y zeolites. In X zeolites that ratio is between 2 and 3, while in Y zeolites it is 3 or higher. The negative charges of the framework are balanced by the positive charges of cations in non-framework positions. Such zeolites have ion-exchange, catalytic and adsorptive properties. The stability of the zeolite increases with the silica-to-alumina ratio of the framework. It is also affected by the type and amount of cations located in non-framework positions. For catalytic cracking
Cracking
Cracking may refer to:* Cracking, the formation of a fracture or partial fracture in a solid material* Fluid catalytic cracking, a catalytic process widely used in oil refineries for cracking large hydrocarbon molecules into smaller molecules...
, the Y zeolite is often used in a rare earth-hydrogen exchanged form.
By using thermal, hydrothermal or chemical methods, some of the alumina can be removed from the Y zeolite framework, resulting in high-silica Y zeolites. Such zeolites are used in cracking
Cracking
Cracking may refer to:* Cracking, the formation of a fracture or partial fracture in a solid material* Fluid catalytic cracking, a catalytic process widely used in oil refineries for cracking large hydrocarbon molecules into smaller molecules...
and hydrocracking catalysts. Complete dealumination results in faujasite-silica.
Use
Faujasite is used above all as a catalyst in fluid catalytic crackingFluid catalytic cracking
Fluid catalytic cracking is the most important conversion process used in petroleum refineries. It is widely used to convert the high-boiling, high-molecular weight hydrocarbon fractions of petroleum crude oils to more valuable gasoline, olefinic gases, and other products...
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.
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.