Secrets of Wiped Film Distillation - Part 3

Secrets of Wiped Film Distillation - Part 3

Wiper Speed Doesn't Matter!!!!

Ok - that is a little bit of rage bait. However, in most cases, the exact speed of the wipers does not greatly influence the results of the distillation. Wiped film distillation has the big three major levers - Temperature, Feed Rate, and Vacuum. Minor adjustments to each of these results in significant changes in the results.

Wiper speed is a minor lever. It has an effect, but it is minor.

Basically, the wipers should be turned on and moving at a decent rate. I've seen wiper speeds used between 200 - 400 rpm. There is no major difference in results when the wipers are turned on in this range.

There are minor differences. The faster the wipers, the more distillate will collect. The operators at my last job would use the wipers to try to hit exact goals. If the target for a distillation was 20% distillate by weight, and they just measured 19.9% distillate; then they would use the wipers to try to land on 20.0%. They knew if they turned up the heat 1°C, they would overshoot. The wipers were used to try to super fine tune the distillation, mostly for fun and competitiveness.

However, turning the wipers ON - that is critical. If the wipers are off or are less than 60 rpm, the distillation will be majorly affected. There won't be enough wiping to make the thin film and there won't be time for all of the desired distillation to occur.

I've seen instances where a distillation is started and the results are about 40% less distillate than the day before. But everything is working - feed rate is great - temperature is good - vacuum is correct.

And then someone sees the wipers haven't been turned up. In this case, ineffective wiper speed makes a big difference. But overall, wiper speed is not really important. Just turn them on.