Drying refers to the process of removing water from any substance, even a liquid (which then becomes a "dry" liquid). Drying also applies to gases and solids.

The chemical industry uses drying in sectors ranging from agricultural products and fine chemicals through plastics and paints. Methods vary with material and application.

Gas drying
A popular form of gas drying is air drying. Dry gas is essential in chemical processing because it precludes ice from forming in instrument air lines. In the past, ice formation in instrumentation has caused plant shutdowns and emergency venting, both of which are very costly. The system operates under the principle of molecular diffusion. The wet compressed air flows through small, thin, hollow fibers made from polymers.

Solid drying
Drying may be defined as the vaporization and removal of water or other liquids from a solution, suspension, or other solid-liquid mixture to form a dry solid. It is a complicated process that involves simultaneous heat and mass transfer, accompanied by physicochemical transformations. Drying occurs as a result of the vaporization of liquid by supplying heat to wet feedstock, granules, filter cakes and so on. Based on the mechanism of heat transfer that is employed, drying is categorized into direct (convection), indirect or contact (conduction), radiant (radiation) and dielectric or microwave (radio frequency) drying.

Heat transfer and mass transfer are critical aspects in drying processes. Heat is transferred to the product to evaporate liquid, and mass is transferred as a vapor into the surrounding gas. The drying rate is determined by the set of factors that affect heat and mass transfer. Solids drying is generally understood to follow two distinct drying zones, known as the constant-rate period and the falling-rate period. The two zones are demarcated by a break point called the critical moisture content.

Chemical drying
Drying is the process of using evaporation to remove water from a solution, suspension, or other solid-liquid mixture. In addition to solids, the process can also be used to remove water from liquids or gases. Drying is used for many different industrial categories in chemical processing, including agricultural products, pharmaceuticals, plastics, and paints.

There are different types of drying. Those include:

1. Freeze: dehydration by means of freezing a material first, then lowering the pressure and adding heat to sublimate the ice.
2. Dielectric: using radiation or radio frequencies to transfer heat into materials to dry them internally.
3. Convective/direct: directly applying hot air onto the material and drying externally.
4. Contact/indirect: transferring heat through a wall or surface to dry the material.
5. Natural air: drying through unheated forced air.

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Industrial Chemistry
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