Secrets of Wiped Film Distillation - Part 7

Secrets of Wiped Film Distillation - Part 7

Faster is better

One thing that I learned early on about wiped film stills is their incredible capacity to distill material. I came from a world of distillation that utilized short path glassware setups, reactors, fractional systems and rotovaps to distill. And the resounding issue was distillations were slow. When distilling out of a reactor, it would take a long time to distill a large amount of material.

When moving to wiped film stills, I was surprised how quickly a small still like a 6" diameter system could distill a whole drum of material.

One mistake many operators make on their wiped film still is run it too slow. Let's say you have a mixture that is 40% volatile and 60% not volatile, the goal of the pass would be to remove the volatiles. Some may send the material through at a low feed rate to "make sure" they got all the volatiles. However, these machines are so efficient, that is not necessary.

When using a low feed rate, all that is accomplished is a waste of the potential of the equipment. As the material travels down the wall, the volatile component vaporizes. If the feed rate is too slow, the volatile component will be fully removed after only traveling a small portion of the length of the wall. All this does is increase the time that the remaining material is being heated.

This is a waste of capacity. The bottom half of the still is very capable of stripping the volatiles. So, the feed rate should be increased to take advantage of that capacity, and the productivity of the unit will be increased.

Your manufacturer should provide a typical feed rate range. I am also available to discuss this, should you desire some input into feed rates.