Resin : Cation Anion

Resin, not to be confused with rosin, is a hydrocarbon secretion of many plants, particularly coniferous trees. It is valued for its chemical constituents and uses, such as varnishes and adhesives, as an important source of raw materials for organic synthesis, or for incense and perfume. Fossilized resins are the source of amber.

The term is also used for synthetic substances of similar properties. Resins have a very long history and are mentioned by both ancient Greek Theophrastus and ancient Roman Pliny the Elder, especially as the forms known as frankincense and myrrh. They were highly prized substances used for many purposes, especially perfumery and as incense in religious rites.

Uses

The hard transparent resins, such as the copals, dammars, mastic and sandarac, are principally used for varnishes and cement, while the softer odoriferous oleo-resins (frankincense, elemi, turpentine, copaiba) and gum resins containing essential oils (ammoniacum, asafoetida, gamboge, myrrh, and scammony) are more largely used for therapeutic purposes and incense.

Resin in the form of rosin is used for the upkeep of bows for stringed instruments (i.e. violin, viola, cello, double bass), because of its quality for adding friction to the hair. Ballet dancers may apply crushed rosin to their shoes to increase grip on a slippery floor.

Resin has also been used as a medium for sculpture by artists such as Eva Hesse, and in other types of artwork.

Also, resin is used in some skateboard decks. It makes the skateboard more durable, making it less likely to get pressure cracks, chippings, or break in half.

Conservators use resins to consolidate fragile items such as bone found on archaeological sites. The resin acts to bind the fragile material inside its molecular structure. In Pompeii, resin is now used instead of plaster to recreate the bodies of Mount Vesuvius' victims, because it is more durable.

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Activated Alumina

Activated alumina is manufactured from aluminium hydroxide by dehydroxylating it in a way that produces a highly porous material; this material can have a surface area significantly over 200 square metres/g. The compound is used as a desiccant (to keep things dry by absorbing water from the air) and as a filter of fluoride, arsenic and selenium in drinking water. It is made of aluminium oxide (alumina; Al2O3), the same chemical substance as sapphire and rubies (but without the impurities that give those gems their color). It has a very high surface-area-to-weight ratio. That means it has a lot of very small pores, almost like tunnels, that run throughout it.


Uses

* Catalyst applications

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).

* Desiccant

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.

* Fluoride absorbent

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).

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Molecular Sieve: Activated Carbon

Activated carbon, also called activated charcoal or activated coal, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions. [1] The word activated in the name is sometimes substituted by active. Due to its high degree of microporosity, just one gram of activated carbon has a surface area of approximately 500 m², as determined typically by nitrogen gas adsorption. Sufficient activation for useful applications may come solely from the high surface area, though further chemical treatment often enhances the adsorbing properties of the material. Activated carbon is usually derived from charcoal.

Applications:

Activated carbon is used in gas purification, gold purification, metal extraction, water purification, medicine, sewage treatment, air filters in gas masks and filter masks, filters in compressed air and many other applications.

One major industrial application involves use of activated carbon in metal finishing field. It is very widely employed for purification of electroplating solutions. For example, it is a main purification technique for removing organic impurities from bright nickel plating solutions. A variety of organic chemicals are added to plating solutions for improving their deposit qualities and for enhancing properties like brightness, smoothness, ductility, etc. Due to passage of direct current and electrolytic reactions of anodic oxidation and cathodic reduction, organic additives generate unwanted break down products in solution. Their excessive build up can adversely affect the plating quality and physical properties of deposited metal. Activated carbon treatment removes such impurities and restores plating performance to the desired level.

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Molecular Sieve: Zeolite

Zeolites (Greek, zein, "to boil"; lithos, "a stone") are hydrated aluminosilicate minerals and have a micro-porous structure.

The term was originally coined in the 18th century by a Swedish mineralogist named Axel Fredrik Cronstedt who observed, upon rapidly heating a natural mineral, that the stones began to dance about as the water evaporated. Using the Greek words which mean "stone that boils," he called this material zeolite.

More than 150 zeolite types have been synthesized, and 48 naturally occurring zeolites are known. Zeolites have an "open" structure that can accommodate a wide variety of cations, such as Na+, K+, Ca2+, Mg2+ and others. These positive ions are rather loosely held and can readily be exchanged for others in a contact solution. Some of the more common mineral zeolites are: analcime, chabazite, heulandite, natrolite, phillipsite, and stilbite. An example mineral formula is: Na2Al2Si3O10-2H2O, the formula for natrolite.

Natural zeolites form where volcanic rocks and ash layers react with alkaline groundwater. Zeolites also crystallized in post-depositional environments over periods ranging from thousands to millions of years in shallow marine basins. Naturally occurring zeolites are rarely pure and are contaminated to varying degrees by other minerals, metals, quartz or other zeolites. For this reason, naturally occurring zeolites are excluded from many important commercial applications where uniformity and purity are essential.

Zeolites are the aluminosilicate members of the family of microporous solids known as "molecular sieves". The term molecular sieve refers to a particular property of these materials, i.e. the ability to selectively sort molecules based primarily on a size exclusion process. This is due to a very regular pore structure of molecular dimensions. The maximum size of the molecular or ionic species that can enter the pores of a zeolite is controlled by the diameters of the tunnels. These are conventionally defined by the ring size of the aperture, where, for example, the term "8ring" refers to a closed loop that is built from 8 tetrahedrally coordinated silicon (or aluminium) atoms and 8 oxygen atoms. These rings are not always perfectly flat and symmetrical due to a variety of effects, including strain induced by the bonding between units that are needed to produce the overall structure, or coordination of some of the oxygen atoms of the rings to cations within the structure. Therefore, the pore openings for all rings of one size are not identical.

Uses:

* Commercial and Domestic

Zeolites are widely used as ion-exchange beds in domestic and commercial water purification, softening, and other applications. In chemistry, zeolites are used to separate molecules (only molecules of certain sizes and shapes can pass through), as traps for molecules so they can be analyzed.

Zeolites have the potential of providing precise and specific separation of gases including the removal of H2O, CO2 and SO2 from low-grade natural gas streams. Other separations include: noble gases, N2, O2, freon and formaldehyde. However at present, the true potential to improve the handling of such gases in this manner remains unknown.

* Petrochemical industry

Synthetic zeolites are widely used as catalysts in the petrochemical industry, for instance in fluid catalytic cracking and hydro-cracking. Zeolites confine molecules in small spaces, which causes changes in their structure and reactivity. The hydrogen form of zeolites (prepared by ion-exchange) are powerful solid-state acids, and can facilitate a host of acid-catalyzed reactions, such as isomerisation, alkylation, and cracking. The specific activation modality of most zeolitic catalysts used in petrochemical applications involves quantum-chemical Lewis acid site reactions. Catalytic cracking uses a furnace and reactor. First crude oil distillation fractions are heated in the furnace and passed to the reactor. In the reactor the crude meets with a catalyst such as zeolite. It goes through this step three times, each time getting cooler. Finally it reaches a step known as separator. The separator collects recycled hydrogen. Then it goes through a fractionator and becomes the final item.

* Nuclear Industry

Zeolites have uses in advanced reprocessing methods, where their micro-porous ability to capture some ions while allowing others to pass freely allow many fission products to be efficiently removed from nuclear waste and permanently trapped. Equally important are the mineral properties of zeolites. Their alumino-silicate construction is extremely durable and resistant to radiation even in porous form. Additionally, once they are loaded with trapped fission products, the zeolite-waste combination can be hot pressed into an extremely durable ceramic form, closing the pores and trapping the waste in a solid stone block. This is a waste form factor that greatly reduces its hazard compared to conventional reprocessing systems. [1]

* Agriculture

In agriculture, clinoptilolite (a naturally occurring zeolite) is used as a soil treatment. It provides a source of slowly released potassium. If previously loaded with ammonium, the zeolite can serve a similar function in the slow release of nitrogen. Zeolites can also act as water moderators, in which they will absorb up to 55% of their weight in water and slowly release it under plant demand. This property can prevent root rot and moderate drought cycles.

* Animal Welfare

In Concentrated Animal Growing facilities, the addition of as little as 1% of a very low sodium clinoptiloite was shown to improve feed conversion, reduce airborne ammonia up to 80%, act as a mycotoxin binder and improve bone density. See US Patents 4,917,045 and 6,284,232. Can be used in general odor elimination for all animal odors.

* Medical

Zeolite-based oxygen concentrator systems are widely used to produce medical grade oxygen. The zeolite is used as a molecular sieve to create purified oxygen from air using its ability to trap impurities, in a process involving the absorption of undesired gases and other atmospheric components, leaving highly purified oxygen and up to 5% argon. QuikClot® brand hemostatic agent, which continues to be used successfully to save lives by stopping severe bleeding[1], contains a calcium loaded form of zeolite.

* Heating and refrigeration

Zeolites can be used as solar thermal collectors and for adsorption refrigeration. In these applications, their high heat of adsorption and ability to hydrate and dehydrate while maintaining structural stability is exploited. This hygroscopic property coupled with an inherent exothermic (heat producing) reaction when transitioning from a dehydrated to a hydrated form, make natural zeolites useful in harvesting waste heat and solar heat energy.

* Detergents

The largest single use for zeolite is the global laundry detergent market. This amounted to 1.44 million metric tons per year of anhydrous zeolite A in 1992.

* Construction

Synthetic zeolite is also being used as an additive in the production process of warm mix asphalt concrete. The development of this application started in Europe (Germany) in the 1990s. It helps by decreasing the temperature level during manufacture and laying of asphalt concrete, resulting in lower consumption of fossil fuels, thus releasing less carbon dioxide,aerosols and vapours. Other than that the usage of synthetic zeolite in hot mixed asphalt leads to easier compaction and to a certain degree allows cold weather paving and longer hauls. When added to Portland Cement as a Pozzolan, it can reduce chloride permeability and improve workability. It reduces weight and helps moderate water content while allowing for slower drying which improves break strength.[2]

* Gemstones

Thomsonites, one of the rarer zeolite minerals, have been collected as gemstones from a series of lava flows along Lake Superior in Minnesota and to a lesser degree in Michigan, U.S.A.. Thomsonite nodules from these areas have eroded from basalt lava flows and are collected on beaches and by scuba divers in Lake Superior.

These thomsonite nodules have concentric rings in combinations of colors, black, white, orange, pink, red and many shades of green. Some nodules have copper as inclusions and rarely will be found with copper "eyes". When polished by a lapidary the thomsonites sometimes display chatoyancy.[3]

* Aquarium keeping

Zeolites are marketed by pet stores for use as a filter additive in aquariums. In aquariums, zeolites can be used to absorb ammonia and other nitrogenous compounds. However, due to the high affinity of some zeolites for calcium, they may be less effective in hard water and may deplete calcium. Zeolite filtration is used in some marine aquaria to keep nutrient concentrations low for the benefit of corals adapted to nutrient-depleted waters.

Where and how the zeolite was formed is an important consideration for aquariums. Northern hemisphere natural zeolites were formed when molten lava came in contact with sea water, thereby 'loading' the zeolite with Na (sodium) sacrificial ions. These sodium ions will speciate with other ions in solution, thus the takeup of nitrogen in ammonia, with the release of the sodium. In southern hemisphere zeolites, such as found in Australia, which were formed with fresh water, thus the calcium uptake on formation.

Zeolite is an effective ammonia filter, but must be used with some care, especially with delicate tropical corals which are sensitive to water chemistry and temperature.

* Space hardware testing

Zeolites can be used as a molecular sieve in cryosorption pumps for rough pumping of vacuum chambers which can be used to simulate space-like conditions in order to test hardware bound for space.

* Cat litter

Non-clumping cat litter is often made of zeolite or diatomite.

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Molecular Sieve: Silica Gel

Silica gel is a granular, porous form of silica made synthetically from sodium silicate. Despite the name, silica gel is a solid.

Silica gel is most commonly encountered in everyday life as beads packed in a semi-permeable plastic. In this form, it is used as a desiccant to control local humidity in order to avoid spoilage of some goods. Because of poisonous dopants (see below) and their very high adsorption of moisture, silica gel packets usually bear warnings for the user not to eat the contents. If consumed, the pure silica gel is unlikely to cause acute or chronic illness, but would be problematic nonetheless. However, some packaged desiccants may include fungicide and/or pesticide poisons. Food-grade desiccant should not include any poisons which would cause long-term harm to humans if consumed in the quantities normally included with the items of food. A chemically similar substance with far greater porosity is aerogel.

Applications:

* Desiccant
In many items from leather to pepperoni, moisture encourages the growth of mold and spoilage. Condensation may also damage other items like electronics and may speed the decomposition of chemicals, such as those in vitamin pills. By adding packets of silica gel, these items can be preserved longer.

Silica gel may also be used to keep the relative humidity inside a high frequency radio or satellite transmission system waveguide as low as possible. Excessive moisture buildup within a waveguide can cause arcing inside the waveguide itself, damaging the power amplifier feeding it. Also, the beads of water that form and condense inside the waveguide change the characteristic impedance and frequency, impeding the signal. It is common for a small compressed air system (similar to a small home aquarium pump) to be employed to circulate the air inside the waveguide over a jar of silica gel.

Silica gel is also used to dry the air in industrial compressed air systems. Air from the compressor discharge flows through a bed of silica gel beads. The silica gel adsorbs moisture from the air, preventing damage to the compressed air users due to condensation or moisture. The same system is used to dry the compressed air on railway locomotives, where condensation and ice in the brake air pipes can lead to brake failure.

Silica gel is sometimes used as a preservation tool to control relative humidity in museum and library exhibitions and storage.

* Chemistry
In chemistry, silica gel is used in chromatography as a stationary phase. In column chromatography the stationary phase is most often composed of silica gel particles of 40-63 μm. In this application, due to silica gel's polarity, non-polar components tend to elute before more polar ones, hence the name normal phase chromatography. However, when hydrophobic groups (such as C18 groups) are attached to the silica gel then polar components elute first and the method is referred to as reverse phase chromatography. Silica gel is also applied to aluminum, glass, or plastic sheets for thin layer chromatography.

Chelating groups have also been covalently bound to silica gel. These materials have the ability to remove metal ions selectively from aqueous media. Chelating groups can be covalently bound to polyamines that have been grafted onto a silica gel surface producing a material of greater mechanical integrity. Silica gel is also combined with alkali metals to form a M-SG reducing agent.

* Cat Litter
Silica gel is also used as cat litter, by itself or in combination with more traditional materials, such as clays including bentonite. It is trackless and virtually odorless, albeit expensive.

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Molecular Sieve: Lime (mineral)

Lime is a general term for various naturally occurring minerals and materials derived from them, in which carbonates, oxides and hydroxides of calcium predominate. It is also name for single mineral (native lime) of the CaO composition, occurring very rarely. The word 'lime' originates with its earliest use as building mortar and has the the sense of 'sticking or adhering'. [1]

These materials are still used in large quantities as building and engineering materials (including limestone products, concrete and mortar) and as chemical feedstocks, among other uses. Lime industries and the use of many of the resulting products date from prehistoric periods in both the Old World and the New World.

The rocks and minerals from which these materials are derived, typically limestone or chalk, are composed primarily of calcium carbonate. They may be cut, crushed or pulverized and chemically altered. "Burning" (calcination) converts them into the highly caustic material quicklime (calcium oxide, CaO) and, through subsequent addition of water, into the less caustic (but still strongly alkaline) slaked lime or hydrated lime (calcium hydroxide, Ca(OH)2), the process of which is called slaking of lime.

When the term is encountered in an agricultural context, it probably refers to agricultural lime. Otherwise it most commonly means slaked lime, as the more dangerous form is usually described more specifically as quicklime or burnt lime.

Lime Production Process:

* Limestone is extracted from quarries or mines.
* Part of the extracted stone, selected according to its chemical composition and granulometry, is calcinated at about 1000°C in different types of kiln, fired by such fuels as natural gas, coal, fuel oil, lignite, etc.

Quicklime is produced according to the reaction: CaCO3 + heat --> CaO + CO2

* Quicklime can be hydrated, i.e. combined with water.

Hydrated lime is produced according to the reaction: CaO + H2O --> Ca(OH)2

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Molecular Sieve: Clay

Clay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired. Clay deposits are mostly composed of clay minerals (phyllosilicate minerals), minerals which impart plasticity and harden when fired and/or dried, and variable amounts of water trapped in the mineral structure by polar attraction. Organic materials which do not impart plasticity may also be a part of clay deposits.[1]

Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks (usually silicate-bearing) by low concentrations of carbonic acid and other diluted solvents. These solvents (usually acidic) migrate through the weathering rock after leaching through upper weathered layers. In addition to the weathering process, some clay minerals are formed by hydrothermal activity. Clay deposits may be formed in place as residual deposits, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation. Clay deposits are typically associated with very low energy depositional environments such as large lake and marine deposits.

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Molecular sieve: Desiccant

Desiccant

A desiccant is a substance that absorbs water. It is most commonly used to remove humidity that would normally degrade or even destroy products sensitive to moisture.

Desiccation refers to the state of extreme dryness, or the process of extreme drying. A desiccant is a substance that absorbs or adsorbs water. It is most commonly used to remove humidity that would normally degrade or even destroy products sensitive to moisture. Silica gel, calcium sulfate, montmorillonite clay, and molecular sieves are commonly used as desiccants.

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Molecular Sieve: 13X

Type 13X
Composition 1 Na2O: 1 Al2O3 : 2.8 ±
Description The sodium form represents the basicstructure of the type X family, with an effective pore opening in the 910¼ r range. Will not adsorb(C4F9)3N, for example.
Major
Applications Commercial gas drying, air plantfeed purification (simultaneous H2O and CO2 removal) and liquid hydrocarbon/natural gas sweetening (H2S and mercaptan removal).

13X Molecular Sieve

13X Molecular sieve is a sodium form of type X crystal and has a larger pore opening than type 4A molecular sieve. 13X adsorbs molecules with a kinetic diameter of less than 9 Angstrom (0.9nm) and excludes larger molecules.

3A Molecular Sieve Typical Chemical Formula

* Silicon Dioxide: < 60 %
* Aluminum Oxide: < 40 %
* Sodium Oxide: < 20 %
* Magnesium Oxide: < 5 %

3A Molecular Sieve Applications

* Oxygen generators: medical or bulk Oxygen production
* 13X molecular sieve traps CO2 and moisture
* Compressed air drying

13X Molecular Sieve Regeneration

13X Molecular Sieve is regenerated by purge air in desiccant air dryers. Purge air temperature must be atleast 250°C - 300°C to regenerate the sieve. 13X molecular sieve can maintain dewpoints below -100°F.

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Molecular Sieve: 5A

Type 5A
Composition 0.6 K2O: 0.40 Na2O : 1 Al2O3 : 2.0 ±
Description Divalent calcium ions in place of sodium cations give apertures of ~5Å, e.g., all 4-carbon rings, and iso-compounds.
Major
Applications Separation of normal paraffins frombranched-chain and cyclic hydrocarbons; removal of H2S, CO2 and mercaptans from natural gas.

5A Molecular Sieve

Type 5A small oxygen enrich molecular sieve is a kind of appropriative molecular
sieve specially designed for medical or healthy oxygen generator - a mini PSA plant for medical application. The product has the character of high purity of oxygen concentrating and long lasting working span. It is already widely used in the medical care field.

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Molecular Sieve: 4A

Type 4A
Composition 1 Na2O: 1 Al2O3: 2.0 ±
Description This sodium form represents the type A family of molecular sieves. Effective pore opening is 4Å, e.g., propane
Major
Applications Preferred for static dehydration in closed liquid or gas systems, e.g., in packaging of drugs, electric components and perishable chemicals; water scavenging in printing and plastics systems and drying saturated hydrocarbon streams.Adsorbed species include SO2, CO2, H2S, C2H4, C2H6, and C3H6. Generally considered a universal drying agent in polar and nonpolar media.

4A Molecular Sieve

A common 4A molecular sieve application is dehydrating compressed air. In a desiccant air dryer molecular sieve is regenerated by heating and purging. Regeneration temperatures must be 400° to 600° F, but are not to exceed 1000° F. The degree of regeneration depends on the temperature reached in purge. Molecular sieve is often used as a polishing layer in air dryers to reach dewpoints of -120° F.

The pore size for 4A molecular sieve is 4A. It is mainly used to adsorb
water, methanol, ethanol, sulfureted hydrogen, carbon dioxide, ethylene,
propylene, does not adsorb any larger molecular than 4A, and often used
as desiccant in industrials.

4A Molecular Sieve Features

* Dewpoints Down to 100° F. and Lower: molecular sieves are often used as a polishing layer in molecular sieve dryers to achieve dewpoints down to -120°F. Molecular sieve is the most effective desiccant for low inlet, relative humidities, generally below 30-35% RH.
* Uniform Size = Low Pressure Drop in a packed bed, molecular sieve provides a low pressure drop which minimizes channeling and maximizes utilization of the whole drying capacity of the compressed air dryer tower.
* Round Smooth Beads/Low Abrasion: Round and smooth beads contributes to a low pressure drop. Low abrasion means less dusting, migration / attrition and longer desiccant life.

4A Molecular Sieve Typical applications
1) Deep drying of air, natural gas, alkane and refrigerant
2) Generation and purification of argon
3) Static dehydration of electronic element, pharmaceutical and unstable materials
4) Desiccant for paint, dope and foul etc.

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Molecular Sieve: 3A

Type 3A
Composition 0.6 K2O: 0.40 Na2O : 1 Al2O3 : 2.0 ±
Description The 3A form is made by substituting potassium cations for the inherent sodium ions of the 4A structure, reducing the effective pore size to ~3Å
Major
Applications Commercial dehydration of unsaturated hydrocarbon streams, including cracked gas, propylene, butadiene, acetylene; drying polar liquids such as methanol and ethanol. Adsorption of molecules such as NH3 and H2O from a N2/H2 flow. Considered a general-purpose drying agent in polar and nonpolar media.

3A Molecular Sieve

The pore size of 3A molecular sieve is 3A. It does not adsorb any molecular larger
than 3A. According to the industrial application specialties, our products have
the characters of higher adsorption speed, stronger crushing and anti-contaminative
resistance, more cyclic times and longer work-span. All these advantages have
made it come to be the most essential and necessary desiccant in the fields
of the deep drying, refinery polymerization for cracked gasses, ethylene, propylene
and any other non-acidic gasses of liquids in petroleum and chemical industrials.

3A Molecular Sieve Formula
0.4K2O 0.6Na2O Al2O3 2.OSiO224.5H2O

3A Molecular Sieve Typical Applications
1) Dehydration of many kinds of liquids (such as ethanol)
2) Dehydration of air
3) Dehydration of refrigerant
4) Dehydration of natural gas or methane
5) Dehydration of cracked gas, ethylene, propylene or butadiene

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Molecular Sieve

A molecular sieve is a material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids.

Molecules small enough to pass through the pores are absorbed while larger molecules are not. It is different from a common filter in that it operates on a molecular level. For instance, a water molecule may be small enough to pass through while larger molecules are not. Because of this, they often function as a desiccant. Molecular sieve can absorb water up to 22% of its own weight.

Often they consist of aluminosilicate minerals or synthetic compounds that have open structures through which small molecules can diffuse, such as clays, porous glasses, microporous charcoals, active carbons etc...

Molecular sieves are usually utilized in the petroleum industry, especially with purification of gas streams. The mercury content of natural gas is extremely harmful to the aluminum piping and other parts of the liquefaction apparatus - silica gel is used in this case.

Methods for Regeneration of molecular sieves include by pressure change as in oxygen concentrators or by heating and purging with a carrier gas as when used in ethanol dehydration.

Molecular sieves types:

* Activated carbon
* Desiccant
* Clay
* Lime (mineral)
* Silica gel
* Zeolite

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