Degassing Deep Dive - Part 3

Degassing Deep Dive: Post 3

Degas Pass effectiveness

The number one complaint I get when I encourage customers to run a degas pass is the time it takes to do one. They don't want to "waste" a pass on a degas pass. It doubles the time it takes to get to their product and they don't see the point.

Instead, they use other technologies to "dry" the feed prior to the still.

But these other technologies are incredibly ineffective. In a later post, I will demonstrate why even 0.2 wt% solvent/water can cause a MAJOR problem in a wiped film distillation.

In this post, I want to share the expected effectiveness of three different technologies.

Technology 1 - Reactor

One option is to strip off solvent/water directly out of the reactor. This is the least effective method. Reactors are large vessels, and when the solvent wt% gets low, it struggles to get out of the liquid, up out of the headspace and travel all the way to the condenser.

Typical results: 1 - 5 wt% super-volatiles remaining.

Technology 2 - Rotovap

A rotovap works in a very similar manner to a reactor. But the volume is much less, and therefore the solvents sometimes can escape the liquid better than a reactor. The path of travel to the condenser is shorter, and they can be more effective.

Typical results: 0.2 - 2 wt% super volatiles remaining.

Technology 3 - Wiped Film Still

Using a wiped film still to remove trace super-volatiles is the most effective way to prepare a feed for distillation. Trace for this discussion means up to 5 wt% super-volatiles. If you have more than that, you may need to do a pass to remove bulk solvent, and then a degas pass.

Typical results: 10 ppm - 0.05 wt% super-volatiles remaining

The reason the wiped film still is more effective than the other two methods is the feed material is spread into a super thin, highly agitated film. The super-volatiles see the heat on the wall and instantly vaporize. If an internal condenser is used, they are immediately stripped from the vapor phase and not given any opportunity to reabsorb.

The degas pass is the correct method to prepare your feed material for distillation and will avoid all the problems mentioned in post 1 in this series.