The technical term for what a "catch can" does is coalesce. The function is to remove liquids saturated into a flow of a gas.
Air Compressor systems have various methods to coalesce as do aircraft air conditioning/pressurization systems.
The simplest form of a coalescing device is an expansion type that allows the saturated gas to cool and slow. This allows the liquid vapor to form into droplets that stick to the chamber walls. These types are commonly seen for air compressor systems, with a clear bowl and drain valve. They are effective, but leave room for improvement.
When you add a type of baffle or labyrinth path for the gas to the above chamber, it increases the efficiency in removing liquid. The changes in direction allow inertia to force contact of droplets, formed from expansion, with the chamber walls. Centrifugal separators also rely on the inertia of the droplets to go to the outer wall because they are heavier than the gas. Centrifugal designs are difficult to make efficient with low flow rates.
Filter type coalescing systems are most often a combination of the above designs. They are almost always combined with expansion types. In many cases, labyrinth design is combined in at least a minimal way. Large airplanes use a type of filter, along with an expansion chamber to coalesce water out cabin air before it is sent to the cabin. The filter is simply a surface for the liquid droplets to adhere to. In these airplane a/c systems, it is a fabric stretched over a conical screen, in a larger cylindrical chamber (can). You often see a filter added to those "water separators " in compressor lines. This is not really for particulate removal, although it will do that. It is to provide more surface for droplets to adhere (coalesce).
The liquid in a crankcase vent flow will contain a significant amount of water vapor along with the oil vapor . This is condensation formed during cooling in the crankcase.