Permeation

Permeation (Latin permeare, penetrate, go through, walk through ') is the process in which a substance (permeate) penetrates or travels through a solid. The driving force is a concentration or pressure gradient. Permeability is tested by permeation.

• 6.1 with gases
• 6.2 with liquids
• 6.3 in hydrogeology

Description of the process

Without external influences, the permeate always moves in the direction of lower concentration or the lower partial pressure. The permeation proceeds in three steps:

Related terms

• Permeate a substance which passes through a solid ( permeate )
• Permeability: degree of permeability of a solid, a measure of the permeation through the substance. This property is affected by both the nature of the permeate, as well as pressure, temperature, thickness of the solid and the area size.
• Semipermeability: property of a substance to be permeable to some permeates and impermeable to others.
• Permeation measurement: Measurement method for the quantification of the permeability of a substance ( for a given permeate)

Historical

Abbé Jean- Antoine Nollet ( Physicist, 1700-1770 )

Jean -Antoine Nollet wanted to finish wine air-tight, locked to the container with a pig's bladder and dipped it additionally in a water bath. By the time he realized that the bubble arched more and more to the outside. When he finally aufstach, a lot of pressure discharged. Out of curiosity, he turned to the experimental setup, filled into the container of water and dipped it in wine. As expected, he observed now a similar curvature of the pig's bladder into the interior of the container. These experimental results are the first scientific mentions a kind of permeation ( this would later be called semi-permeability ).

Thomas Graham (chemist, 1805-1869 )

Thomas Graham showed the dependence of gas diffusion from the molar composition of experimental. He is the founder of Graham 's Law, which thus is directly related.

Richard Barrer (1910-1996)

Richard Barrer laid the foundations for today's metrology. He used the first modern scientific methods to investigate the permeation. He laid the foundation for today's essential in process chemistry permeation. According to him, the Barrer is named, a unit for the gas permeability of thin materials.

Permeation in everyday life

In daily life, there are numerous situations in which permeation plays an essential role:

• Packaging: Packaging should either be completely sealed (eg for chocolate or beer) or selectively permeable (eg for oxygen in strawberries). Therefore, the knowledge of the permeability, or even the precise rate of permeation is essential.
• Auto tires: The pressure in car tires should be as slow decline. Therefore, it is interesting to know which gas permeates the slowest through a hoop.
• Insulating materials: For thermal insulation, for example, the water vapor permeability of the materials is important. The insulation of submarine cables must protect the conductor from corrosion.
• Fuel System: The fulfillment of legal requirements in the automotive industry, such as the regulations of CARB (California Air Resource Board ) for Low Emission Vehicle LEV requires impermeable barrier materials for fuel lines and tanks.
• Seepage of water

Permeation in the membrane technology

In the membrane permeate technology is a central concept. It called for liquid filtration, freed by the filtration of eg bacteria, hardness minerals or heavy metals in fluid or gas filtration, the purified or depleted gas. The in filtration retained by the membrane materials are retentate (from the Latin retentare = hold back, hold fast ) or concentrate called. Membrane filtration systems are used for example in the food industry and waste water treatment or gas separations for use.

Permeation

Films and membranes can be checked both with any gases and liquids of any kind on their permeability.

With gases

The measurement techniques for gas all include a central module that is shared by the membrane under test: On the " feed - side ", the measuring cell is overflowed with the test gas, the rest of the retentate is derived. The arrived on the other hand the amount of gas (permeate) is led by the purge gas to a detector, where the concentration is measured. The graph on the right represents this dimly the example of a cell for films dar. upper and lower part of the cell surround the centered membrane. An O-ring, which rests on the specimen, seals the interface. This type of cell is usually made of metal such as stainless steel.

If the permeation tubes to be measured, the cell must have a different geometry, such as in the photo on the right, similar to a Liebig condenser. Here, the inner white tube is filled with a gas or a liquid, and the permeate is collected in the space between the specimen and the glass panel where it is fed from a carrier gas, which flows from the bottom upward through this intermediate space to an analysis unit. There, the amount of the permeated substance is determined. The gas permeability is expressed in units of Barrer.

With liquids

Analogous to the permeation of gases is determined in the membrane technique of so-called water value. It is used to characterize the performance of a liquid filtration device and is expressed in l / (m² · h · bar).

In hydrogeology

This laboratory test is used to calculate the permeability coefficient and is useful for the assessment of groundwater recharge rate and the spring discharge. It is based on Henry Darcy and follows the law named after him:

With:

• Density Meter
• Thermodynamics
• Solid State Physics
• Membrane Technology
• Measure of process engineering