Desiccant can be divided into three categories: acidic desiccant, alkaline desiccant and neutral desiccant.
Acidic desiccant: This type of desiccant is usually suitable for drying acidic materials. Common acidic desiccant include phosphorus pentoxide, anhydrous calcium chloride and concentrated sulfuric acid. Phosphorus pentoxide has a strong dehydrating ability and is often used for drying ethers, hydrocarbons, halogenated alkanes, etc.; anhydrous calcium chloride has a large water absorption capacity, but is not suitable for drying alcohols, amines, ketones, etc.; concentrated sulfuric acid is often used for drying inert gases, hydrogen chloride, etc., but is highly corrosive.
Alkaline desiccant: Suitable for drying alkaline materials. Common alkaline desiccants include solid potassium hydroxide, solid sodium hydroxide, anhydrous potassium carbonate, calcium oxide and barium oxide. These desiccants are highly alkaline and hygroscopic and are often used for drying organic alkaline liquid reagents. However, barium oxide has a certain toxicity and should be avoided as much as possible in pharmaceutical processes.
Neutral desiccant: This type of desiccant has a wide range of uses and is relatively safe. Common neutral desiccants include anhydrous sodium sulfate and anhydrous magnesium sulfate. Anhydrous sodium sulfate absorbs water slowly and easily clumps, but it is cheap and often used in laboratories; anhydrous magnesium sulfate absorbs water quickly and efficiently, and is suitable for drying dichloromethane extracts.
