Filtration

Filtration is a type of process which separates solid particles and fluid from a mixture with the help of a filter medium that has a complex structure through which only the fluid can pass. Filtration is either a physical, biological or chemical operation. Solid particles that are oversize, cannot pass through the filter medium and the fluid that passes through is known as the filtrate. One problem that sometimes arises in the filtration is that oversize particles may form a filter cake on top of the filter that may block the filter lattice. This filter cake prevents the fluid phase from crossing the filter and is known as blinding.

What is Filtration?

Filtration is a process in which a filter medium is in use to separate solid particles from a liquid or gaseous mixture. The filter allows the fluid to pass through but holds the solid particles. Although filtration is an overused process but still the separation of solid and fluid is imperfect. This is because solids particles get contaminated with some fluid and filtrate also contain some fine particles.

Process Description

1) Filtration is in use to separate solid particles from a fluid in a suspension. This fluid can be a liquid, a gas or a supercritical fluid.

2) Filtration is an important part of chemistry as it deals with the separation of materials of different chemical composition. A solvent is taken into account which has the ability to dissolve one component, while not dissolving the other.

3) Filtration is widely in use as one of the key unit operations in the field of chemical engineering.

4) Filtration is different from sieving, although a filter is in use in both. In sieving, a single perforated layer (a sieve) is used for separation. In the filtration, a multilayer lattice retains those particles that are unable to pass through the barrier channels of the filter.

5) In the case of biological filters, oversize particulates are trapped and ingested and the resulting metabolites is usually released.

Methods of Filtration

A) Hot filtration as the name suggests, mainly is in use to separate solid particles from a hot solution. To prevent the formation of crystals in the funnel and to undergo effective hot filtration, the use of stemless filter funnel is effectively in use. Stemless filter funnel results in the decrease of the surface area of contact between the solution and the stem of the filter funnel. Thus, preventing the issue of re-crystallization of solid in the funnel.

B) In the cold filtration process, an ice bath helps to cool down the solution that’s going to be crystallized rather than leaving it out to cool it down slowly at room temperature.

C) The vacuum filtration process is applied for a small batch of solution in order to quickly dry out small crystals. This method requires a Büchner funnel.

Filter Media

In laboratories two main types of filter media are in use: one is a surface filter, a solid sieve which traps the solid particles, with or without the aid of filter paper (e.g. Belt filter, Büchner funnel,  Cross-flow filters). The second filter is the depth filter, which consists of a layer of granular material that retains the solid particles as it passes (e.g. sand filter). Filter media is usually cleaned by rinsing with solvents or detergents.

Uses of Filtration

• Belt filters to extract precious metals in mining.
• The coffee filter is in use to keep the coffee separate from the grounds.
• In furnaces, filtration prevents the furnace elements from fouling with particulates.
• Air filters help to remove airborne particulate matter in building ventilation systems and in many industrial processes.
• Oil filter is useful in the automobile industry, often as a canister or cartridge.

FAQs about Filtration

Q.1. What is a common issue for filtration in water treatment?

Answer – Dirty filter is a common issue for filtration in water treatment. Dirty filter chemicals and heavy metals find their way into drinking water. Different types of water filtering systems have their own requirements for maintaining the filter.

Q.2. What is the disadvantage of filtration?

Answer – The main disadvantages of barrier-based filtration are, replacement and disposal costs. When this type of filter gets blocked by waste particles, it needs to be replaced which is cost-effective.