Hello dear researchers,
I am doing some experiments with the freeze-dryer at the moment and I am experiencing a temperature anomaly that I cannot explain.
I tried it with pure water, 1M sucrose in water and water+protein, same result for every sample.
The following happens:
I freeze the samples in glass vials at -70°C shelf temperature for 8 hours, and enable the vacuum at the 8:30h mark. As soon as the vacuum pump starts working, the temperatures of the samples start dropping. That is clear to me, because the sublimation removes heat from the samples.The thing that is not clear to me, is why the temperatures start rising pretty soon as the vacuum gets stronger, and even rise above the value they had before the vacuum was enabled.
There should also be a picture attached. The lines that make the curves are my sample temperatures, the pink line is the pressure and the red line is the shelf temperature. (the picture is zoomed in, the pink line actually starts dropping right where the temperatures start dropping!)
Im happy about any suggestion I can get! Thanks!
Hi,
Are you sure the red line (the lowest one) is the temp of the shelves? Isn't it the condensator temp? Usually during the process, the shelf temperature is kept higher than during freezing (depending on your sample, stability, etc).
While the samples are drying, it is normal that temperature tend to the temperature of the shelves (so the temp increases):
- When the process starts (when your samples contain water), the temperature of the samples is determined by the vacuum you put (according to the phase diagram of water).
- when your samples are totally dried (the lyophilisation process is finished), the sample temperatures correspond to the shelf temperature.
Do not hesitate of it is not clear,
Best
Rémi
Hi Ilja,
I agree with Rémi, that -70 °C is very unlikely the shelf temperatur, because in this case the heat flow should be in the direction of the heater.
During freezing you can get curves that are similar to your, due to the release of the phase transition. But these peaks are much smaller and the temperatur would go down finally.
Yours,
Harald
Hi Rémi Rosière ,
thank you for your answer.
The red line is the shelf temperature, it is set to -70°C. The ice condenser runs at -90°C.
What you say is also what I think should be happening in theory, but I wonder why it doesnt go that way in my process. The first problem is that the samples dont even reach the shelf temperature before the vacuum starts. The second problem is this weird anomaly shown in the screenshot. Is there any chance you could provide me a screenshot of a temperature curve to a lyophilisation process of yours, if you have access to a freeze-dryer?
Thanks!
Hello Harald Schuchmann, thank you for your answer. -70°C is definitely the shelf temperature, at least according to the sensor. The problem is that the samples are always 15-20K warmer than the shelf after turning on the vacuum and since I am also working with sucrose solutions, their temperature should not exceed -40°C, because I dont want to get near the collapse temperature. Although the shelf is at -70°C, the sublimation still progresses. I see it because a dry layer forms on top, and the samples with pure water disappear.