Vacuum Filtration

What is vacuum filtration?

Vacuum filtration (or suction filtration) is an indispensable technique for distillation, extraction, and purification. Compared with traditional, gravity-assisted filtration, adding a vacuum to your system greatly increases speed and efficiency in your laboratory. One of the most common uses is to separate a solid from a liquid.

The theory behind this powerful process is relatively straightforward, as we'll outline below.

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Vacuum Filtering Explained

We sell filtering products for labs large and small.

We’re pleased to bring you a wide selection of essential vacuum filtration supplies and equipment. We’ve taken care to source only the finest products available on the market, and where necessary, we created our own, American-made solutions and glassware.

Why do I need filtration?

Most, if not all labs use some sort of filtering process. And vacuums are an essential part of many purification systems. Without filtration products, achieving effective separation would be very difficult, if not impossible.

The diagram below shows one of the most common setups for filtering with a vacuum. We carry all of the products you see here. With these basic products in place, you are now able to start the filtering process.

A helpful diagram with associated products:

Vacuum Filtration Diagram

Qualitative filter paper has larger pores and filters faster than quantitative paper. The larger pores allow more material to get through.

Quantitative paper is the opposite: its smaller pores filter finer particles at the expense of filtration speed. Which one is the right choice for you depends on your application.

How does vacuum filtration work?

How does suction filtering work?
Once you have the proper equipment set up (more or less as pictured above), there are a few steps to take to ensure the process goes smoothly:

  • Insert the filter paper into the Büchner funnel. It should be as close to an exact fit as possible. If the paper’s diameter is too big, simply cut it to the appropriate shape using regular scissors.
  • Insert the rubber stopper into your filtering flask. The stopper should have a hole cut out of the center, so the funnel can fit snugly and securely inside without touching the walls of the glass.
  • Place the funnel inside the stopper. Or, put them together first and connect them to the flask as one unit.
  • Connect the tubing to the side spout. Connect the other end of the hose to your vacuum pump.
  • Thoroughly moisten the filter paper with the same solvent or liquid that forms the basis of the solution you are filtering. This step is critical, because it creates an air-tight seal between the filter paper and the funnel, preventing any unwanted contaminants from sliding through.
  • When everything is tightly connected, turn on your pump.
  • Pour the solution you wish to filter into the top of the funnel. 
  • Solids will be collected on top of the filter paper, and the filtered solvent will be captured in the filtering flask.
  • Repeat as necessary until the desired purity is achieved.

The vacuum creates a pressure differential.

As the directional arrow in the tubing shows, the vacuum is pulled through the tube, away from the Büchner Flask. This pulls the liquid or solvent down through the funnel at the top at a faster rate than gravity could alone.

The pressure of the suction also adheres the filter paper to the funnel on which it is resting, creating a tight seal that doesn’t allow unwanted particulate matter to slip through. This same force presses the funnel into the filter adapter, creating a tight seal that doesn’t allow particulate matter to sneak through.

As you can see, the process itself is fairly straightforward, and it’s highly effective!

A critical process for effective separation.

Effective Separation with Filter Pumps
Vacuum filtration works particularly well when separating fats or lipids, which are stuck or suspended in a solution and need to be removed. For example, the fats or lipids trapped in plant materials can be caught by well-chosen filter media.

Depending on what you are filtering, the residue left on the filter paper can either be discarded, reused, or processed again.

A filter will also catch other solid particulates, such as catalysts, salts, impurities, and any other unwanted solids.

Control multiple vacuum flows with a single pump.

Your valuable pumps are often at a premium in the laboratory. With our vacuum manifold kit, you can precisely control the amount of vacuum going out to multiple systems, all run by the same pump!

Some considerations:

Since the glass and products used will be subjected to pressure in vacuum filtration, make sure that the glass you use can withstand it. We recommend high quality, borosilicate glass for the task.

The filter paper itself will reduce the system flow rate, so vacuum (or suction) filtration is performed to increase the flow rate and reduce filtration time. Be advised that too strong of a vacuum can damage the paper or pull on it too strongly.

Hopefully, this handy guide gives you valuable insight into how to better make use of these techniques in your own laboratory.

Note: Depending on the substance you are trying to filter, a vacuum trap may be needed to reduce the chance of vapors reaching the vacuum pump, which could potentially damage it.