FAQs

Not all drying agents can be regenerated. Physically acting drying agents can be regenerated by heating the desiccant to drive the moisture from the molecule. Specific regeneration instructions are found in each section of the catalog where applicable.

Often the particle size of the drying agent is described in terms of mesh size. To better understand the relationship between mesh and millimeters, refer to this chart. For example, t.h.e. desiccant with a 12 mesh particle size will pass through a sieve with openings spaced 1.68mm apart.

Molecular sieves are a family of adsorbents that can be used to dry gases and organic liquids. They have a crystalline structure and come in different types depending on the size of the pores in the crystals. For example, type 3A is named for the size of the pores (3 Ångstroms), and is used to remove moisture from unsaturated hydrocarbons and polar fluids. These would include methanol, ethanol, and acetone. Type 3A will adsorb a molecule less than 3Å in size (e.g., water) and has an adsorption capacity or 22% by weight.

To dry polar liquids such as methanol, add a slight excess of drying agent to the liquid. The water specification (this can be found in the manufacturer's catalog or on a certificate of analysis) may state that the water content is 1.0%. This equates to 40 mL in a 4 liter bottle. 40 mL of water is equal to 40 g of water. 40 g divided by 22% = 181.8 g. To insure an excess, use 200 g of molecular sieve. Keep in mind that an opened bottle of methanol, which is very hygroscopic, would probably have a higher moisture content, depending on how many times the bottle has been opened for use. How often you would need to dry a solvent is dependent on your application, use, and humidity.

Add the determined amount of molecular sieve (for example, our part number MX1583D-1), mix thoroughly and allow the liquid to stand. After a few minutes, the drying agent settles to the bottom of the container. Separation can be completed by decanting or filtration (suction filtration would work best and fastest). After use, the molecular sieve can be regenerated (dried) by heating a thin layer in an oven at 350° to 500°F (~180° to 260°C) for about an hour. It is then once again ready for use.

A drying agent is a substance that absorbs water. Drying agents are grouped into two major classes: chemically acting and physically acting drying agents.

There are two subdivisions of chemically acting drying agents:

Chemically acting drying agents are substances that bind the water in the form of crystallization and may be regenerated by warming. Examples of these types of drying agents are calcium chloride, sodium sulfate, or magnesium perchlorate. The second subdivision of chemically acting drying agents are substances that react with water. Regeneration of these drying agents is not possible since the drying agent has undergone a chemical change. Examples of these types of drying agents are phosphorus pentoxide, sicacide, metals, and metal hydrides. Often by-products are formed.

Physically acting drying agents are substances that adsorb water on the surface and in the pores of the drying agent. These drying agents can be regenerated by warming or applying a vacuum. Examples of these types of drying agents are t.h.e. desiccant, silica gel, molecular sieve, and aluminum oxide.

Gases can be dried by passing the gas through large quantities of desiccant. The desiccant is contained in tubes, towers, or columns.

Solids can be dried by heating at an elevated temperature. A more gentle way to dry a solid is to place the material in a desiccator in the presence of a physically acting drying agent. In order to increase the effectiveness of the desiccator, a vacuum can be applied. Examples of common types of drying apparatus are found on the next page. In a dry atmosphere, the water in the solid material begins to escape in the form of water vapor from the surface of the material. The water vapor is absorbed onto the surface of the desiccant.

In the classical procedure for drying liquids, a slight excess of drying agent is added to the liquid. The solution is mixed thoroughly and allowed to stand or the liquid is refluxed. After a few minutes, the drying agent will settle to the bottom of the container. Separation can be completed by decantation, suction filtration, or distillation. Distillation is necessary when compounds are formed during drying by reaction of water with the drying agent and where such compounds subsequently dissolve in the solvent.

TYPE 3A: Potassium Ion with pore diameter of 3 Angstroms

ORGANIC LIQUIDS: Acetone, Acetonitrile, Methanol, Ethanol, 2-Propanol

GASES: Acetylene, Carbon Dioxide, Ammonia, Propylene, Butadiene,

Cracked Gas

TYPE 4A: Sodium Ion with pore diameter of 4 Angstroms

ORGANIC LIQUIDS: Chloroform, Dichloromethane, Diethyl Ether,

Dimethylformamide, Ethyl Acetate, Cyclohexane, Benzene, Toluene,

Xylene, Pyridine, Diisopropyl Ether

GASES: Natural Gas, Low pressure Air Drying

TYPE 5A: Calcium Ion with pore diameter of 5 Angstroms

ORGANIC LIQUIDS: Tetrahydrofuran, Dioxane

TYPE 13X: Sodium Ion with pore diameter of 10 Angstroms

GASES: Air plant feed purification to remove water and carbon dioxide simultaneously, Cracked Gas

Regeneration: Regeneration of molecular sieve should be carried out at a water uptake of a maximum of 20% by weight. Regeneration takes place in an oven at 300-350°C in a stream of dry inert gas such as nitrogen or argon or, preferably, in a vacuum. Special precautions must be taken before regeneration of a molecular sieve that has been in a flammable solvent.

Adsorptive capacity refers to the amount of water the desiccant can take in by physical means only. Physical means can be either capillary action or surface attraction. For example, consider a drying agent with an adsorptive capacity of 10% This means that the amount of water adsorbed amounts to 10% by weight of the desiccant. Simply, the capacity of a drying agent is the weight of water adsorbed per unit weight of desiccant.

When a drying agent is indicating, the drying agent will turn pink in the presence of water. For example, silica gel with indicator (blue gel) contains minute quantities of an indicator (cobalt (II) chloride) which is blue in the anhydrous state. Exhaustion of the gel is easily detectable from the pink color that develops upon saturation with water. After regeneration, the silica gel returns to its original blue color and can be used again.

t.h.e.® Desiccant

t.h.e.® desiccant is a high capacity desiccant used for all laboratory applications. Its high adsorptive capacity provides drier samples faster. This product is available in both indicating and non indicating form.

Adsorptive Capacity: 35.8%

Used to Dry: Solids, Gases, Non-Polar Hydrocarbons, Organic Solvents

Typical Applications: Desiccators, Drying tube on AquaStar Titrators, Drying Tubes on Gas Chromatography Gases.

Regeneration: Affected at 120°C for 1 hour.

SILICA GEL

Silica gel is a highly porous drying agent. It has an outstanding capacity for adsorption. Silica gel is available in both indicating and non indicating form.

Characteristics:

High moisture loading capacity
Hardness and chemical resistance of the particles
Simplicity of regeneration
Used to Dry: Gases, Organic Liquids, Solids

Typical Applications: Desiccators, Used in packets to keep electronic parts dry

Regeneration: Capable by heating in an oven 100-250°C.

MOLECULAR SIEVES

Molecular Sieves are crystalline synthetic zeolites with crystal lattice structures that contain numerous cavities. A zeolite is a chemical structure with the formula Mo·AL₂O₃·xSiO₂·yH₂O where M is either K (Potassium), Na (Sodium), or Ca (Calcium). For example, the formula for Type 4A replaces M with Na for Sodium. Similarly, replacement of sodium ions in Type 4A with Calcium ions produces Type 5A. The cavities are connected by pores having exactly defined diameters (3,4,5,10 Angstroms according to the type of molecular sieve) which corresponds to the replacement ion diameter.

Depending upon the size of these pores, molecules may be readily adsorbed, slowly adsorbed, or completely excluded. Molecular Sieve can be used to separate a compound from another compound or as a drying agent to remove only water from the compound.

Used to Dry: Gases, Organic Liquids

ALUMINUM OXIDE

Aluminum oxide (alumina) can be used as a drying agent in addition to its use as a chromatography sorbent. Activated aluminas are physically and chemically stable with large surface areas. Although there are various types available, the best type to be used as a drying agent is active basic or neutral activity I aluminum oxide since this type contains the least amount of moisture.

Adsorptive Capacity: 10% for activated alumina

40% for Type H-151 activated alumina

Used to Dry: Liquids--Aromatic hydrocarbons, heavier alkanes, gasoline, kerosene, cyclohexane, propylene, ether, chloroform, pyridine, benzene.

Gases--Inert gases, air, saturated hydrocarbons, olefins, refrigerants, hydrogen sulfide, carbon dioxide.

Typical Application: Aluminum oxide is packed into glass columns. Solvent is allowed to flow through the columns.

Type H-151 Application: Excellent desiccant for high pressure applications due to its low resistance to fluid flow. Its high bulk density makes it the densest desiccant available.

Regeneration: Affected at 75°C for at least 1 hour.

DRIERITE® Drierite® is a desiccant made of anhydrous calcium sulfate. Water is absorbed by means of hydration. That means that anhydrous calcium sulfate salt (CASO₄) is converted to the hemihydrate form (CASO₄·1/2H₂O). Drierite has a neutral pH, is stable, and chemically inactive toward reagents other than water.

Absorptive Capacity: 6.6% for Liquids

10-14% for Gases

Used to Dry: Solids, Liquids, Organic Liquids, and Gases

Typical Applications: Laboratory Desiccators, Laboratory Gas Drying Tubes, used to maintain a dry atmosphere in several applications such as Aircraft Instrument Drying, Packaging and Shipping Desiccant.

Regeneration: Affected at 200-225°C for 1-2 hours

CALCIUM CHLORIDE For economic reasons, calcium chloride is very frequently used as a drying agent. It has a drying capacity of about 90%. It is suitable for drying ethers, many esters, hydrocarbons, halogenated hydrocarbons, and aromatics. It is not suitable for drying ammonia, amines, alcohols, phenols, and some esters and ketones because it will bind with these substances as well as water. Regenerate at 250°C for at least 1 hour.

CALCIUM OXIDE Calcium oxide is a basic drying agent which is generally used for dehydrating low boiling alcohols, ammonia, and amines. Since it is a basic drying agent, it is not suitable for drying acids or esters. Regenerate at 1000°C.

CALCIUM SULFATE Calcium sulfate is a neutral drying agent that is prepared by heating gypsum to 130-160°C. The drying agent can be used up to 100°C. The disadvantage is its low capacity for water uptake, less than 6.6% by weight. Calcium Sulfate is suitable for drying almost all liquids and gases, in particular when azeotropically eliminating liquids such as acetaldehyde, alcohols, or formic acid. Regeneration is best carried out at 190-230°C.

COPPER (II) SULFATE Copper (II) sulfate is used as a drying agent to take up 5 moles of water to form copper (II) sulfate 5-hydrate. The drying agent turns blue in the presence of water. The reaction serves at the same time as a method of detecting water in organic liquids.

MAGNESIUM OXIDE Magnesium oxide is a basic drying agent comparable to calcium oxide but less effective. It is used to dry alcohols, hydrocarbons, and basic liquids. Regenerate at 800°C.

POTASSIUM CARBONATE Potassium carbonate is a deliquescent drying agent which may be regenerated by heating at 158°C. It is suitable for drying liquids such as amines, nitriles, chlorinated hydrocarbons, and acetone.

SODIUM SULFATE Sodium sulfate is a neutral drying agent which is suitable for drying sensitive compounds such as fatty acids, aldehydes, ketones, alkyl and aryl halides.

TRACEPUR® sodium sulfate is used to remove residual water from extraction solvents without adding interfering contaminants. Contaminants will interfere with accurate results and will result in sample reruns.

TRACEPUR® anhydrous sodium sulfate is tested under similar conditions found in EPA procedures for Priority Pollutants. Chromatograms show reagent blank with capillary gas chromatography after heat treatment of the sodium sulfate at 400°C for 4 hours in accord with EPA procedure. Total concentration of all peaks detected by electron capture (ECD) is 1.3 ppt.

ALUMINUM, CALCIUM, & MAGNESIUM Aluminum, calcium, and magnesium are all used in a similar manner for drying alcohols. Both aluminum and magnesium must be activated before use as a drying agent. Aluminum is activated with iodine or mercury (II) salts. Magnesium is activated best with iodine. The drying process includes the formation of insoluble metal hydroxides, then metal alcoholates which are insoluble in alcohol. Distillation must then be performed after drying.

CALCIUM HYDRIDE Calcium hydride is a highly active drying agent which does not decrease in activity during the drying process. Hydrogen is formed during the reaction with water. It is used to dry gases and organic solvents.

POTASSIUM HYDROXIDE & SODIUM HYDROXIDE Potassium hydroxide and sodium hydroxide are basic drying agents which cannot be regenerated. They are generally used for drying basic liquids such as amines. They are also used to adsorb acidic vapors. Potassium hydroxide is a more effective drying agent than sodium hydroxide.

SODIUM Sodium metal is used for drying ethers, saturated, and aromatic hydrocarbons and tertiary amines. It is used in the form of sodium wire, which is prepared directly prior to use using a sodium press or as finely distributed sodium. Since sodium reacts explosively with water, extreme caution is required when handling sodium.

SICAPENT® & PHOSPHORUS PENTOXIDE SICAPENT® is a phosphorus pentoxide drying agent for desiccators. SICAPENT consists of 25% support material and 75% phosphorus pentoxide. Phosphorus pentoxide is one of the most active drying agents for drying gases and some liquids such as saturated and aromatic hydrocarbons, anhydrides, nitriles, alkyl and aryl halides and carbon disulfide. The disadvantage of phosphorus pentoxide alone is that its deliquescent nature allows it to form a syrupy layer over unconsumed phosphorus pentoxide powder. This layer retards diffusion and adheres strongly to the walls of the drying vessels. The advantage of using SICAPENT is that even after absorbing 100% of its own weight, it still remains free-flowing. The addition of an indicator makes it possible to determine the degree of water uptake visually. The color changes are listed in the chart below.

SICAPENT® SX0137

PHOSPHORUS PENTOXIDE Powder

PX1040-1 500 G

SULFURIC ACID & SICACIDE Sulfuric acid and Sicacide behave very similarly as drying agents. Sicacide is a drying agent composed of 75% sulfuric acid on a solid support which makes handling the sulfuric acid more safe. It is used to dry inert gases and gases such as hydrogen chloride, chlorine, carbon monoxide, sulfur dioxide, and hydrocarbons. It is also suitable for use in desiccators. Like SICAPENT, Sicacide remains free-flowing particles even after 100% of its weight in water uptake.