In photocatalytic experiments, vacuum extraction is a common pretreatment step. However, many researchers have experienced the troublesome phenomenon of solution “bumping” — when the reaction liquid boils violently and splashes out. This not only causes catalyst loss but can also contaminate optical windows, block gas lines, and seriously affect both experimental accuracy and equipment longevity.
Why does bumping easily occur during vacuum extraction? The key lies in the sudden pressure drop. When system pressure decreases rapidly, dissolved gases in the solution escape quickly, forming large quantities of bubbles and triggering violent boiling. Under negative pressure, this phenomenon becomes even more intense and likely to cause bumping.
So, is there an effective way to mitigate or even prevent bumping? The answer is yes. The following experimentally verified methods can significantly improve operational stability:
01 Pre-cooling
Before vacuum extraction, start the chiller to bring the system temperature below 10 °C. Low temperature can significantly suppress vigorous boiling.
02 Stirring Assistance
Place a stir bar in the reaction liquid and turn on magnetic stirring. The vortex created helps break up large bubbles and promotes smooth gas release.
03 Controlled Pumping Speed
Adjust the valve opening to control the vacuum rate and avoid rapid pressure drops that trigger bumping.
04 Intermittent Pumping
If bumping occurs, stop the vacuum process and let the system rest under low pressure for about 10 minutes. This allows dissolved gases to escape slowly. When vacuuming is resumed, bumping will be greatly reduced.
01 Turn on stirring and cool the system to below 10 °C;
02 Ensure that valves B, E, D are in system circulation mode, C1 and C2 in pipeline circulation mode, and C3 in circulation pressure mode;
03 Start the vacuum pump and slowly turn valve D toward vacuum mode;
04 Once the system pressure stabilizes, gently turn valve C2 to the system circulation position;
05 If the reaction liquid produces excessive bubbles, return valve C2 or switch to pipeline circulation and let it rest for 2–3 minutes;
06 After the solution stabilizes, slowly rotate valve C2 back to system circulation. If bumping reappears, repeat the previous step as needed;
07 Once bumping has stopped, sequentially turn each valve to complete the vacuum operation.
01 Similarly, begin by cooling and stirring;
02 Confirm that the valve positions are correct: D valve in system circulation, C1 and C2 in pipeline circulation;
03 Start the vacuum pump and slowly turn valve D toward vacuum mode;
04 Once system pressure stabilizes, gently rotate valve C1 to system circulation mode;
05 If excessive bubbling occurs, return valve C1 or switch to pipeline circulation and let it rest for 2–3 minutes;
06 After stabilization, rotate valve C1 back to system circulation. If bumping occurs again, repeat the previous step as needed;
07 When bumping ceases, turn the valves in order to complete the vacuum extraction process.
Summary
Bumping is common but not inevitable. By combining cooling, stirring, controlled pumping, and intermittent extraction — and by familiarizing yourself with the valve operation logic of each specific instrument — you can ensure both experimental safety and data reliability, while improving overall efficiency.
We hope this practical guide helps you stay free from bumping issues and achieve smoother experiments!
