Vacuum filtration

Vacuum filtration or suction filtration is a fast filtration technique used to separate solids from liquids using the difference of pressure between the flask and outside atmosphere as filtration force.

Setup

Equipment

• Aspirator or vacuum pump
• Vacuum flask with inlet tube (optional) or cold trap
• Rubber tubes
• Conical rubber seal
• Büchner flask
• Büchner funnel (fritted or perforated plate with filter paper) or Hirsch funnel

Operation

• Connect the vacuum filtering setup;
• Turn on the vacuum pump or open the water tap for the aspirator;
• Stir the suspension and then pour it in the Büchner funnel;
• Wash the flask/beaker with water/solvent, stir then pour it in the funnel, then repeat at least 3 times;
• The vacuum should continue until the last drop of solvent falls in the flask;
• Keep the vacuum on for a few minutes, to remove as much solvent as possible, and the solid becomes semi-dry;
• Turn off the vacuum pump and then remove the funnel to collect the suspension;

Tips

• If the solvent is extremely volatile or corrosive, use a vacuum flask with inlet tube or a cold trap to prevent the hazardous vapors from reaching the pump and damaging it;

Safety

Always inspect the glassware before working with vacuum for any defects/cracks, to prevent an implosion.

References

Relevant Sciencemadness threads

• Vacuum filtration without a vacuum flask.
• Vacuum Filtration