Raschig ring

Raschig rings are a form of random packing and are used in commercial fractional distillation columns to reduce pressure loss (versus using trays), while maintaining good efficiency and economy. Typically the change in pressure (also called "delta p") is lower than in the case of trays but slightly higher than for structured packing. Raschig rings are named after the German chemist Friedrich August Fritz Raschig.

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Raschig rings are small tube cuttings providing a surface for (re)evaporation of the most volatile part in the refluxing distillate, typically 10 mm in diameter and 12 mm long. These can be made from metal, glass, or can be ceramic. Raschig rings made of copper tube cuttings are superior at fractionating volatile hydrocarbons (or ethanol) mixed with water.

Due to recent advancements in structured packing the technical window where application of random packing is optimum is reduced significantly. Use typically limited to columns of very small diameter where structured packing is more difficult to fit in and the disadvantages of a lower efficiency and hence taller column have less economic impact.

Raschig rings made from borosilicate glass are sometimes employed in the handling of nuclear materials, where they are used inside vessels and tanks containing solutions of fissile material, for example solutions of enriched uranyl nitrate, acting as neutron absorbers and preventing a potential criticality accident.

See also

• Fractionating column