Degassing Deep Dive - Part 1

Degassing Deep Dive - Part 1

Why is degassing necessary?

Degassing is the act of removing trace super-volatile material from your feed material before performing a wiped film distillation. This is probably the most important part of performing an efficient wiped film distillation. Here are three reasons why degassing is a critical step prior to wiped film distillation.

1. Vacuum level fluctuations

When a feed material contains trace volatiles, it will manifest more and more as the distillation continues. The volatile material will instantly vaporize upon entering the environment of the still. As the run continues, the vacuum level will get worse and worse.

This typically is only seen on the vacuum gauge if the vacuum gauge is placed between the still body and the cold trap. Many manufacturers place the vacuum gauge after the cold trap, and the cold trap condenses the volatile component. This gives a false appearance of a good vacuum level - but the distillate amounts will be less than desired because the vacuum level is actually poor. If your distillation starts out really well, and then you need to add heat to maintain the distillate amount - very possibly you need to degas your feed.

2. Damage to vacuum systems

If you are pulling high vacuum on feed that contains trace super-volatiles, it is very likely that the volatiles will get past the cold trap and end up in your vacuum pump. Then they can corrode, burn, polymerize or do unspeakable things inside of your vacuum pump. If you find your pumps seizing up on a regular basis, you probably need to degas your feed.

3. Inconsistent results

Feed that contains super-volatiles will give very inconsistent results batch to batch. Most likely this feed was prepared in a rotovap or a reactor. Sometimes it might be 1% solvent remaining, another time it might be 4%.

Each time you try to distill this, without handling the super-volatiles first, it will behave differently. One time it might foam and cause feed material to spit over to the distillate side. Another time it might just need more heat than it ever has before. A third time, your vacuum pump might start exhausting a mist. For these reasons, super-volatiles must be removed by degassing prior to starting the high vacuum distillation.

In the next post I will share a practical way to perform a degas pass on a wiped film still.