Centrifugation

Technology
Technology details
Name:	Centrifugation
Category:	Separation process
Feedstock:	all materials
Product:	separated products

Centrifugation is a mechanical separation process which involves the use of the centrifugal force to separate particles from a solution according to their size, shape, density, medium viscosity and rotor speed. The more dense components of the mixture migrate away from the axis of the centrifuge, while the less dense components of the mixture migrate towards the axis.. Next to the separation of solids from liquid, it is possible to obtain separation between two liquids of different densities as well, given that de density difference is large enough.

Feedstock

Laboratory centrifuge

Testtube with precipitate (pellet) and supernatant after centrifugation

Origin and composition

The centrifugation method is used to separate two miscible substances. The most common application is the separation of solids from highly concentrated suspensions, which is used in the treatment of sewage sludges for dewatering where less consistent sediment is produced. In the food industries, special centrifuges can process a continuous stream of particle-laden liquid.

Pre-treatment

For a centrifugation in general no specific pre-treatment is needed since it is used to separate different fraction within a process chain. Sometimes it is combined with other separation technologies like filtration.

Process and technologies

There is a correlation between the size and density of a particle and the rate that the particle separates from a heterogeneous mixture, when the only force applied is that of gravity. The larger the size and the larger the density of the particles, the faster they separate from the mixture. By applying a larger effective gravitational force to the mixture, like a centrifuge does, the separation of the particles is accelerated. This is ideal in industrial and lab settings because particles that would naturally separate over a long period of time can be separated in much less time.

The rate of centrifugation is specified by the angular velocity usually expressed as revolutions per minute (RPM), or acceleration expressed as g. The conversion factor between RPM and g depends on the radius of the centrifuge rotor. The particles' settling velocity in centrifugation is a function of their size and shape, centrifugal acceleration, the volume fraction of solids present, the density difference between the particle and the liquid, and the viscosity.

This sedimentation of particles can be explained by Stoke's law. The equation calculates the velocity of sedimentation utilizing five parameters.

From the Stokes equation five important behaviours of particles can be explained:

1. The rate of particle sedimentation is proportional to the particle size
2. The sedimentation rate is proportional to the difference in density between the particle and the medium.
3. The sedimentation rate is zero when the particle density is the same as the medium density.
4. The sedimentation rate decreases as the medium viscosity increases.
5. The sedimentation rate increases as the gravitational force increases.

Basket centrifugation

Basket centrifuges are often called centrifugal filters or clarifiers. The basket centrifuge uses centrifugal force to generate a pressure which forces the liquid through the caked solids, the filter cloth, the backing screen, and finally the basket perforations. The filter cloth retains the solid particles inside the rotating basket while the permeating liquid is continuously discharged.

Products

The remaining liquid that lies above the precipitate is called a supernatant or supernate. The precipitate and the supernatant can then be further processed or are the final product.

Post-treatment

The post-treatment of the precipitate and/or the supernatant is depending on the next steps within the production chain.

Technology providers

ABC

Centrifugation provider

General information
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Technology and process details
Technology name:		Technology category:	Pre-processing (Separation technologies), Post-processing (Separation technologies)
TRL:		Capacity:	l·h-1
Processable volume:	L	Relative centrifugal force:	g
Rotor type:		Temperature:	°C
		Other:
Feedstock and product details
Feedstock:		Product:

describe the company, here is an example

ABC was founded in 20... 12 by KNN and Syncom, in collaboration with the university of Groningen, Netherlands. The company is a technology provider developing chemical recycling technologies for different feedstocks including non-food bio- and plastics waste. In 2018 a pilot plant with the capability to process biomass and plastic waste was set up at the Zernike Advanced Processing (ZAP) Facility. The company is now focused on setting up their first commercial plant with a capacity of 20,000 to 30,000 tonnes. The investing phase B was recently completed, with the last investment phase in 2019 the financial requirements are fulfilled to complete the commercialisation activities to build the plant which is expected for 2023.

describe their technology, here is an example

The technology is based on an Integrated Cascading Catalytic Pyrolysis (ICCP) process, being able to produce aromatics including benzene, toluene, and xylene (BTX) as well as light olefins from low grade biomass and plastics waste. This technology utilises catalytic cracking in a two-step process at temperatures between 450- 850 °C. In the first step the feedstock material is vaporised via thermal cracking. The pyrolysis vapours are then directly passed into a second reactor in which they are converted into aromatics by utilising a zeolite catalyst which can be continuously regenerated. Finally, the products are separated from the gas via condensation. An ex situ approach of catalytic conversion has several advantages such as the protection of the catalyst from deactivation/degradation expanding its lifetime, a greater variety of feedstock, and a precise adjustment of process conditions (e.g. temperature, catalyst design, and Weight Hourly Space Velocity (WHSV) in each step for improved yields. In current pilot plant with 10 kg h-1 feed capacity for either waste plastics or biomass, final design details are established, which will be include in the running engineering activities for the commercial plant.

Open access pilot and demo facility providers

Pilots4U Database

Patents

Currently no patents have been identified.

References

• Centrifugation in Wikipedia
• Centrifuge in Wikipedia