[jbrown144]

What is the best process to remove water vapour before cryogenic distillation?

The process is producing bio-hydrogen from 2-stage combined fermentation. Before the separation of hydrogen from carbon dioxide, the water vapour needs to be removed to prevent freezing.

[Arkcon]

There are a number of drying agents available, you just have to know how much moisture there is, to be sure you have enough, and change it before you need to.  However, since you're using cryo, perhaps a simple cold trap to condense the water is within your means?

[Enthalpy]

A difficulty could be that bio processes are meant to create abundent and cheap products. Not quite sure that a drying agent would be cheap enough. At least, it should be recycled by the hydrogen producer, through simple means.

A few special places to collect the condensation water before freezing look more promising. Though, some vapour will remain at 0°C, which will make frost at lower temperatures. So maybe:
- Use a drying agent only there, once most vapour has already condensed
- Let vapour make frost at an acceptable special place, and from time to time, blow reversed warmer air to sublimate the frost.
- Other gasses than water vapour will make ice before 20K! Like methane, carbon dioxide, nitrogen, oxygen, argon... Will you remove each one separately? Or can you design a cold machine that survives some ice of varied nature, which you can filter out of the liquid hydrogen?

[sorbead]

A process by which a vapor side product stream is taken from the bottom section of a cryogenic distillation column, such as a propane or ethane recovery column, which process optionally employs a nonpolar liquid additive for use in the separation of acid gases from a hydrocarbon feed stream. The withdrawal of the vapor side stream prevents the build-up of water in the column which would ordinarily lead to free-water formation or the formation of solid hydrates in the cryogenic distillation column.