Zeolite membranes: properties, applications, and performance

Zeolite Membranes

Catalyst

Catalyst is a substance that can cause a change in the rate of a chemical reaction itself being consumed in the reaction; the changing of the reaction rate by use of a catalyst is called catalysis. Substances that increase the rate of reaction are called positive catalysts or, simply, catalysts, while substances that decrease the rate of reaction are called negative catalysts or inhibitors.

Zeolites

Compositionally, zeolites are similar to clay minerals. More specifically, both are alumino-silicates. They differ, however, in their crystalline structure. Many types of clay have a layered crystalline structure (similar to a deck of cards) and are subject to shrinking and swelling as water is absorbed and removed between the layers. In contrast, zeolites have a rigid, 3-dimensional crystalline structure (similar to a honeycomb) consisting of a network of interconnected tunnels and cages. Water moves freely in and out of these pores but the zeolite framework remains rigid. Another special aspect of this structure is that the pore and channel sizes are nearly uniform, allowing the crystal to act as a molecular sieve.

Why is a Catalyst important?

Many important chemical reactions require inputs of energy to proceed. If a catalyst is present less energy will be required to complete the reaction. Catalysts are substances that are mixed in with materials that are to be reacted, but they themselves do not, in the end, change chemically. They establish a local environment that promotes one or more chemical reactions to take place.

A catalyst is important in many industrial processes. Sulfuric acid, which is used to produce batteries, detergents, dyes, explosives, plastics, and many other produces, is commonly produced using a catalyst called vanadium oxide. Ammonia, a primary component of many fertilizers, could not be produced economically without the use of iron oxide which speeds up the reaction.

The process of catalyst also affects the state of our global environment. Automobiles use catalytic converters to treat exhaust. The metals platinum and palladium facilitate the chemical conversion of noxious gases to more inert forms, greatly decreasing the environmental impact of combustion engines.

Probably the most important impact of catalyst is on life itself. All important biochemical reactions are catalyzed by molecules called enzymes. Most enzymes are proteins which catalyze specific reactions within cells. Some examples include polymerases, which synthesize DNS and RNA, peptidases, which digest protein, and ATP syntheses, which produce energy for the many different cell activities.

When zeolite was discovered and who discovered it?

The first zeolite, stilbite, was discovered in 1756 by a Swedish chap called Cronstedt, who found that the mineral lost water rapidly on heating and seemed to boil. The name zeolite comes from the Greek words zeo (to boil) and lithos (stone), literally meaning "the rock that boils."

Why this is an important catalyst?

Zeolites are important catalysts used in petrochemistry industry where zeolites are used in oil refining as cracking catalysts and in the Methanol to Gasoline (MTG) catalytic conversion process.

Use of Zeolites

Health

Toothpaste

Nutrition

Fertilizer

Animal Nutrition

Construction

Latent Hydraulic Additive

Energy

Solar Energy Use

Environment

Waste Water Treatment

Ammonia removal in municipal sludge / waste water

Heavy metal removal

Septic leach fields

Waste Gas Treatment

Industry

Oxygen Production

Transportation

Petroleum Production

Hygiene

Water Softening

What are its advantages?

The high cation exchange capacity (CEC) make zeolite particularly valuable in holding and slow releasing valuable nutrients to plants, mainly ammonium nitrogen (NH4+), potassium (K+) and magnesium (Mg+), calcium (Ca+) and trace elements.

Promotes better plant growth by improving the value of fertilizer. Helps prevent plant burning from over use of fertilizers by trapping and slowly releasing valuable nutrients when and as the plants need them.

Improves the cation exchange capacity of soil resulting in less fertilizer requirements.

Natural zeolites make an excellent soil amendment, and are environmentally friendly for landfill dump sites (with the exception of zeolite that has been used as a molecular sieve or filter medium for the removal of radioactive waste or the removal of heavy chemical toxins deemed hazardous by government regulations.)

Reduces nutrient and fertilizer loss through heavy rains, leaching and irrigation, resulting in less environmental damage through water runoff.

The water retention capability of zeolites allows less irrigation applications.

Zeolite is used to reduce offensive odors, especially ammonia from sewage, animal manure and waste water situations.

This retained valuable nitrogen improves the quality of the resulting manures and sludges making them worthwhile in fertilizers.

Improves water quality and filtration in aquaculture.

Increases the biological activity of sewage treatment and improves the value of resultant sludges.