What size molecular sieve is most suitable as a desiccant for methanol?

3A molecular sieve should be used to dry acetone, ethanol and methanol.

 

Molecular sieves are zeolite compounds that strongly adsorb water and have carefully controlled pore sizes. Although both the solvent and water are strongly adsorbed to the surface of the molecular sieve, the large surface area in the pores can only be approached by smaller water molecules, so they can be effectively removed from the solvent. Water (1.93A) will enter the 3A pore size, while acetone (3.08A) will be excluded. The water will be able to occupy a large surface area in the pores and thus be removed. If the solvent can also enter the pores, it will compete with water for surface area and will remove little or no water from the bulk solvent. Type 4A molecular sieve is not suitable for drying ethanol, methanol or acetone, because the pore size does not exclude these solvents.