Random column packing

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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.

Contents

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, so it is essential that a packing is selected which will support a large surface area for mass transfer. [1]

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 stone and pieces of coke.

Applications

This shows a photo of Raschig rings RaschigRings005.JPG
This shows a photo of Raschig rings
Pall rings (beige and large white) and Bialecki rings (others) Pall rings (2) and Bialecki rings (6).jpg
Pall rings (beige and large white) and Białecki rings (others)
Dixon rings Lots of Dixon rings.jpg
Dixon rings

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

Types

Raschig ring

The Raschig ring is a piece of tube, invented circa 1914, [2] that is used in large numbers in a packing column. Raschig rings are usually made of ceramic or metals, and they provide a large surface area 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. [3] Originally wrapped from steel strips according to his 1919 patent, [4] now they are made of ceramic. Lessing rings have partitions insides which increase the surface area and enhance mass transfer 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 surface area. They are suited for low pressure drop 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 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 of filling ranges between 60 and 440 m2/m3. [5]

Dixon ring

Dixon rings have a similar design to Lessing rings. They are made of stainless steel mesh, giving Dixon rings a low pressure drop and after pre-wetting. Dixon rings have a very large surface area, which increases the rate of mass transfer. 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 and scrubbing applications.

Related Research Articles

<span class="mw-page-title-main">Distillation</span> Method of separating mixtures

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 mixture and the condensation of the vapors in a still.

Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. It uses distillation to fractionate. Generally the component parts have boiling points that differ by less than 25 °C (45 °F) from each other under a pressure of one atmosphere. If the difference in boiling points is greater than 25 °C, a simple distillation is typically used.

<span class="mw-page-title-main">Raschig ring</span>

A Raschig ring is a piece 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 large surface area within the volume of the column for interaction between liquid and gas vapours.

<span class="mw-page-title-main">Fractionating column</span> Equipment to separate liquids by distillation

A fractionating column or fractional column is equipment used in the distillation of liquid mixtures to separate the mixture into its component parts, or fractions, based on their differences in volatility. Fractionating columns are used in small-scale laboratory distillations as well as large-scale industrial distillations.

Chemical kinetics, also known as reaction kinetics, is the branch of physical chemistry that is concerned with understanding the rates of chemical reactions. It is different from chemical thermodynamics, which deals with the direction in which a reaction occurs but in itself tells nothing about its rate. Chemical kinetics includes investigations of how experimental conditions influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition states, as well as the construction of mathematical models that also can describe the characteristics of a chemical reaction.

<span class="mw-page-title-main">Vacuum distillation</span> Low-pressure and low-temperature distillation method

Vacuum distillation or distillation under reduced pressure is a type of distillation performed under reduced pressure, which allows the purification of compounds not readily distilled at ambient pressures or simply to save time or energy. This technique separates compounds based on differences in their boiling points. This technique is used when the boiling point of the desired compound is difficult to achieve or will cause the compound to decompose. Reduced pressures decrease the boiling point of compounds. The reduction in boiling point can be calculated using a temperature-pressure nomograph using the Clausius–Clapeyron relation.

<span class="mw-page-title-main">Continuous distillation</span> Form of distillation

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<span class="mw-page-title-main">Packed bed</span> A hollow object filled with material that does not fully obstruct fluid flow

In chemical processing, a packed bed is a hollow tube, pipe, or other vessel that is filled with a packing material. The packed bed can be randomly filled with small objects like Raschig rings or else it can be a specifically designed structured packing. Packed beds may also contain catalyst particles or adsorbents such as zeolite pellets, granular activated carbon, etc.

<span class="mw-page-title-main">Structured packing</span>

The term structured packing refers to a range of specially designed materials for use in absorption and distillation columns and chemical reactors. Structured packings typically consist of thin corrugated metal plates or gauzes arranged in a way that force fluids to take complicated paths through the column, thereby creating a large surface area for contact between different phases.

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<span class="mw-page-title-main">Air stripping</span>

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<span class="mw-page-title-main">Reflux</span> Condensation of vapors and their return to where they originated

Reflux is a technique involving the condensation of vapors and the return of this condensate to the system from which it originated. It is used in industrial and laboratory distillations. It is also used in chemistry to supply energy to reactions over a long period of time.

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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 surface area and low pressure drop while maintaining a high mass transfer rate, making them useful for distillations and many other applications.

References

  1. Perry's_Chemical_Engineers'_Handbook
  2. Raschig USA. "Metal Random Packings: Brief Summary of Design History" (PDF). Raschig USA.
  3. Raine, A. H. (1965). "Obituary". Proceedings of the Society for Analytical Chemistry. 2 (2): 26. doi:10.1039/SA9650200026.
  4. GB 139880A
  5. "Stainless Białecki Ring". ZPWK.