Desiccants can be divided into acidic, alkaline and neutral desiccants according to their chemical properties.
Acidic desiccants: This type of desiccants is usually suitable for drying acidic materials. Common acidic desiccants include phosphorus pentoxide, anhydrous calcium chloride and concentrated sulfuric acid. Phosphorus pentoxide has strong dehydration ability and is suitable for drying reagents such as ethers, hydrocarbons, and halogenated alkanes; anhydrous calcium chloride has strong water absorption capacity, but is not suitable for drying alcohols, amines, ketones, etc.; concentrated sulfuric acid is often used for drying gases such as inert gases and hydrogen chloride, but is highly corrosive.
Alkaline desiccants: Suitable for drying alkaline materials. Common alkaline desiccants include solid potassium hydroxide, solid sodium hydroxide, anhydrous potassium carbonate and calcium oxide. These substances have strong hygroscopicity and are often used to dry organic alkaline liquid reagents, but their corrosiveness and exothermic effect should be noted when using them.
Neutral desiccants: It has a wide range of uses and high safety. Common neutral desiccants include anhydrous sodium sulfate and anhydrous magnesium sulfate. Anhydrous sodium sulfate absorbs a large amount of water, but the water absorption effect is slow; anhydrous magnesium sulfate absorbs water quickly and efficiently, and is suitable for drying dichloromethane extracts.
In addition, desiccants can be divided into two categories according to their adsorption methods: physical adsorption and chemical adsorption. Physical adsorption desiccants such as silica gel, alumina gel, molecular sieves, etc., adsorb water molecules by physical means; chemical adsorption desiccants include acidic, alkaline and neutral desiccants, which absorb water through chemical reactions.
