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It is simply a hypothetical equilibrium stage. However, the theoretical plate in packed beds, chromatography and other applications is defined as having a height. The empirical formula known as Van Winkle's Correlation can be used to predict the Murphree plate efficiency for distillation columns separating binary systems. [4]
Proper column packing is important for maximum resolution: An over-packed column can collapse the pores in the beads, resulting in a loss of resolution. An under-packed column can reduce the relative surface area of the stationary phase accessible to smaller species, resulting in those species spending less time trapped in pores.
For a packed column, the cross-sectional area of the column exit flow path is usually taken as 0.6 times the cross-sectional area of the column. Alternatively, the linear velocity can be taken as the ratio of the column length to the dead time. If the mobile phase is a gas, then the pressure correction must be applied.
A packed bed used to perform separation processes, such as absorption, stripping, and distillation is known as a packed column. [1] Columns used in certain types of chromatography consisting of a tube filled with packing material can also be called packed columns and their structure has similarities to packed beds.
A larger surface area allows more cycles, improving separation. This is the rationale for a Vigreux column or a packed fractionating column. Spinning band distillation achieves the same outcome by using a rotating band within the column to force the rising vapors and descending condensate into close contact, achieving equilibrium more quickly.
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.
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.
where: = (), = = (), is the modified Reynolds number, is the packed bed friction factor,; is the pressure drop across the bed,; is the length of the bed (not the column), is the equivalent spherical diameter of the packing,