Random column packing is the practice of packing a distillation column with randomly fitting filtration material in order to optimize surface area over which reactants can interact while minimizing the complexity of construction of such columns. Random column packing is an alternative to structured column packing.

Packed columns

Packed columns utilizing filter media for chemical exchange are the most common devices used in the chemical industry for reactant contact optimization. Packed columns are used in a range of industries to allow intimate contact between two immiscible/partly immiscible fluids, which can be liquid/gas or liquid/liquid. The fluids are passed through a column in a countercurrent flow. In the column it is important to maintain an effective

mass transfer Mass transfer is the net movement of mass from one location (usually meaning stream, phase, fraction, or component) to another. Mass transfer occurs in many processes, such as absorption, evaporation, drying, precipitation, membrane filtra ...

, so it is essential that a packing is selected which will support a large

surface area The surface area (symbol ''A'') of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the d ...

for

History

Random packing was used as early as 1820. Originally the packing material consisted of glass spheres, however in 1850 they were replaced by a more porous

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of extremely vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicula ...

stone and pieces of coke.

Applications

Random packed columns are used in a variety of applications, including: *

Distillation Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixt ...

* Stripping * Carbon dioxide scrubbing *

Liquid%E2%80%93liquid extraction Liquid–liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds or metal complexes, based on their relative solubility, solubilities in two different Miscibility, immiscible liquids, usually wate ...

Types

Raschig ring

The Raschig ring is a piece of tube, invented circa 1914, that is used in large numbers in a packing column. Raschig rings are usually made of ceramic or metals, and they provide a large

within the column, allowing for interaction between liquid and gas vapors.

Lessing ring

Lessing rings are a type of random packing similar to the Raschig ring invented in the early 20th century by German-born British chemist Rudolf Lessing (1878-1964) of Mond Nickel Company. Originally wrapped from steel strips according to his 1919 patent, now they are made of ceramic. Lessing rings have partitions insides which increase the

and enhance

efficiency. Lessing rings have a high density and an excellent heat and acid resistance. Lessing rings withstand corrosion and are used in regenerative oxide systems and transfer systems.

Pall ring

Pall rings are the most common form of random packing. They are similar to Lessing rings and were developed from the Raschig ring. Pall rings have similar cylindrical dimensions but has rows of windows which increase performance by increasing the

. They are suited for low

pressure drop Pressure drop (often abbreviated as "dP" or "ΔP") is defined as the difference in total pressure between two points of a fluid carrying network. A pressure drop occurs when frictional forces, caused by the resistance to flow, act on a fluid as i ...

and high capacity applications. They have a degree of randomness and a relatively high liquid hold up, promoting a high absorption, especially when the rate of reaction is slow. The cross structure of the Pall ring makes it mechanically robust and suitable for use in deep packed beds.

Białecki ring

The Bialecki ring was patented in 1974 by Polish chemical engineer from

Kraków , officially the Royal Capital City of Kraków, is the List of cities and towns in Poland, second-largest and one of the oldest cities in Poland. Situated on the Vistula River in Lesser Poland Voivodeship, the city has a population of 804,237 ...

Zbigniew Białecki rings are an improved version of Raschig rings. The rings may be injection moulded of plastics or press-formed from metal sheet without welding.

Specific surface area Specific surface area (SSA) is a property of solids defined as the total surface area (SA) of a material per unit mass, (with units of m2/kg or m2/g). Alternatively, it may be defined as SA per solid or bulk volume (units of m2/m3 or m−1). I ...

of filling ranges between 60 and 440 m²/m³.

Dixon ring

Dixon rings have a similar design to Lessing rings. They are made of

stainless steel Stainless steel, also known as inox, corrosion-resistant steel (CRES), or rustless steel, is an iron-based alloy that contains chromium, making it resistant to rust and corrosion. Stainless steel's resistance to corrosion comes from its chromi ...

mesh, giving Dixon rings a low pressure drop and after pre-wetting. Dixon rings have a very large

, which increases the rate of

. Dixon rings have a large liquid hold up, a low pressure drop and a large surface area, and have a high mass transfer rate. Dixon rings are used for laboratory

distillation Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixt ...

and scrubbing applications.

References

{{reflist Chemical process engineering