Random column packing is the practice of packing a

distillation column A fractionating column or fractional column is an essential item used in the distillation of liquid mixtures to separate the mixture into its component parts, or fractions, based on the differences in volatilities. Fractionating columns are used in ...

with randomly fitting filtration material in order to optimize surface area over which

reactant In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

s 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 Countercurrent exchange is a mechanism occurring in nature and mimicked in industry and engineering, in which there is a crossover of some property, usually heat or some chemical, between two flowing bodies flowing in opposite directions to each ...

. 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 filtration, ...

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

surface area The surface area 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 definition of arc ...

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 highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular vol ...

stone and pieces of coke.

Applications

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

Distillation Distillation, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...

* Stripping * Carbon dioxide scrubbing *

Liquid%E2%80%93liquid extraction Liquid–liquid extraction (LLE), also known as solvent extraction and partitioning, is a method to separate compounds or metal complexes, based on their relative solubilities in two different immiscible liquids, usually water (polar) and an orga ...

Types

Raschig ring

The

Raschig ring Raschig rings are pieces of tube, approximately equal in length and diameter, used in large numbers as a packed bed within columns for distillations and other chemical engineering processes. They are usually ceramic, metal or glass and provide a la ...

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

invented in the early 20th century by German-born British chemist Rudolf Lessing (1878-1964) of

Mond Nickel Company The Mond Nickel Company Limited was a United Kingdom-based mining company, formed on September 20, 1900, licensed in Canada to carry on business in the province of Ontario, from October 16, 1900. The firm was founded by Ludwig Mond (1839-1909) to ...

. 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

. 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 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 it flows through the tube. The main de ...

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 The reaction rate or rate of reaction is the speed at which a chemical reaction takes place, defined as proportional to the increase in the concentration of a product per unit time and to the decrease in the concentration of a reactant per unit ...

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 Raschig rings are pieces of tube, approximately equal in length and diameter, used in large numbers as a packed bed within columns for distillations and other chemical engineering processes. They are usually ceramic, metal or glass and provide a l ...

was patented in 1974 by Polish chemical engineer from

Kraków Kraków (), or Cracow, is the second-largest and one of the oldest cities in Poland. Situated on the Vistula River in Lesser Poland Voivodeship, the city dates back to the seventh century. Kraków was the official capital of Poland until 1596 ...

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 of a material per unit of mass, (with units of m2/kg or m2/g) or solid or bulk volume (units of m2/m3 or m−1). It is a physical value that can be used to det ...

of filling ranges between 60 and 440 m²/m³.

Dixon ring

Dixon rings Dixon rings are a form of random packing used in chemical processing. They consist of a stainless steel mesh formed into a ring with a central divider, and are intended to be packed randomly into a packed column. Dixon rings provide a large surfa ...

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

stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...

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, or classical distillation, is the process of separation process, separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distilla ...

and scrubbing applications.

References

{{reflist Chemical process engineering