1. Chemical drying: This method involves passing ammonia gas through a desiccant, such as calcium chloride or sodium hydroxide, which absorbs moisture from the gas.

2. Physical drying: This method involves cooling ammonia gas below its dew point, causing the water vapor to condense and separate from the gas.

3. Membrane drying: This method uses a semipermeable membrane to separate water vapor from ammonia gas. The membrane allows water vapor to pass through but blocks the passage of ammonia.

4. Molecular sieve drying: This method uses a molecular sieve, which is a porous material with small pores that trap water molecules but allow ammonia molecules to pass through.

The choice of drying method depends on the specific requirements of the process.