What is Vacuum Filtration?

Core Concepts

Filtration is an everyday technique used to separate solid particles from a liquid or sometimes gases. Among the various different methods of filtration, vacuum filtration stands out as a fast and simplistic process. In this article, we will explore what vacuum filtration is, its basic principles, equipment required, and some real-life applications.

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What’s special about Vacuum Filtration?

Vacuum filtration is a filtration technique used to separate a solid from a liquid. Separation is accomplished by creating a pressure differential between the two sides of a filter paper or membrane surface. The pressure difference is achieved by using a vacuum pump to remove air from the receiving chamber below the filter paper. As the liquid passes through the filter paper, the solid particles get trapped on the paper’s surface. The remaining liquid will remain at the bottom of the collecting flask or be transferred to another larger waste container.

The efficiency of any filtration can be manipulated by 2 different variables. First, the pressure difference between the 2 chambers of a filter paper or membrane can be changed. Second, the pore size of the specific filter piece used can be modified. Most regular filtrations rely on gravity to create the pressure difference needed to separate substances. However, in vacuum filtration, the pressure difference is created by the vacuum pump that is attached to the specialized vacuum flask. The pump is attached to the flask through tubing. The vacuum pump exponentially decreases the amount of time it takes to run a sample. It also allows for the filtration of more murky or concentrated samples that gravity filtration would not work with.

The pore size of a filter paper or membrane surface will change the speed of analysis, and also determines the size of solid substances that are allowed to be passed through. Both of these factors are instrumental to getting any filtration method tailored. So it is important to experiment with filter pore size and vacuum strength to get the best possible results.

vacuum filtration setup

Standard Equipment Used

The equipment needed for vacuum filtration is relatively simple and readily available in almost any lab:

  • Buchner Funnel: A specialized funnel designed with a flat perforated plate at the bottom to hold the filter paper or membrane. This is usually paired with a rubber ring or septum when placed on the vacuum flask. The rubber ring is in order to prevent glass from shattering when using the vacuum.
  • Filter Paper or Membrane Surface: The filter medium placed inside the Buchner funnel, which traps the solid particles while allowing the liquid to pass through. The size of the pores in the medium determine what solid particles will pass through and what will stay behind.
  • Vacuum or Filtration Flask: A flask that has a tube opening meant to be connected to a vacuum pump. Th pump generates the pressure difference required for filtration.
  • Vacuum Source: A pump or device that removes air or gas from the vacuum flask. This creates the pressure differential necessary for vacuum filtration.
  • Rubber Tubing and Adapters: These are used connect the vacuum sources to the vacuum flasks.

In some setups, there are specialized pumps that are already built into the collecting chamber or what would be the vacuum flask. These setups have detachable plastic beakers that are used to mainly filter water samples. The collected water will be transferred to a larger waste container that is also connected to the vacuum source.

Other real life applications don’t always use the standard setup of equipment used in the lab. However, they still rely on the 2 main variables of filtration across 2 different chambers.

Real-Life Applications of Vacuum Filtration

While the principles explained may depict the use of vacuum filtration to be a technique only used in the lab, there are also a few different applications that are used in every day activities you might have not yet thought of:

  • Sample Purification: Scientists use vacuum filtration in laboratories to isolate and purify solid compounds from a mixture or extract a solid from a liquid solvent. It is a great way to dry a solid sample before or after also baking it in an oven. In environmental studies, vacuum filtration helps analyze water samples to determine pollutants or suspended particles.
  • Cleaning vacuums: The vacuums we use everyday are a prime example of vacuum filtration, just without water. The vacuum itself is the collecting chamber that produces its own vacuum source, and the outside solid particles are technically in a gaseous matrix when passing through the filter in the vacuum, instead of the commonly associated liquid matrix.
  • Coffee makers: When brewing coffee, the machine uses vacuum filtration in order to press out the filtered coffee liquid from the mixture of hot water and coffee beans.
  • Textile manufacturing: The fabric industry uses vacuum filtration to separate different fiber thread sizes for a uniform arrangement. Collecting excess dyes from fabrics that have been stained also uses vacuum filtration. This prevents excess dyes from setting into fibers and not creating a uniform color.