Separation Power with Multiple Stages

The separation power in a distillation column can be defined by the ratio of light key to heavy key component in the distillate divided by the ratio of these components in the bottoms (Equation 3.2)  

For example, a distillation column running at total reflux that achieves the equivalent of four theoretical stages of 

The Fenske equation gives the minimum number of theoretical stages required to achieve a desired separation power at total reflux for a constant relative volatility (Equation 3.3)  

In the control of distillation columns, the distillate composition is often close to 100% light component 1, and the bottoms is close to 100% heavy component 2, so the key impurity separation power can be calculated for control purposes from Equation 3.4. 

In other words, the key impurity separation power is indicated by the reduction of heavy key impurity from the distillate and the reduction of light key impurity from the bottoms. The maximum separation power that a distillation tower can achieve would be at total reflux, that is, total boilup and reflux with zero feed rate. One rule of thumb for an economical design of a distillation column is to use 2.0 times the minimum number of theoretical stages. This generally coincides with a design for about 1.3 to 1.5 times the minimum 

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Electrospray mass spectrometry has developed into a well-established method of wide scope and potential over the past 15 years. The softness of electrospray ionization has made this technique an indispensable tool for biochemical and biomedical research. Electrospray ionization has revolutionized the analysis of labile biopolymers, with applications ranging from the analysis of DNA, RNA, oligonucleotides, proteins as well as glycoproteins to carbohydrates, lipids, gly-colipids, and lipopolysaccharides, often in combination with state-of-the-art separation techniques like liquid chromatography or capillary electrophoresis [1,2]. Beyond mere analytical applications, electrospray ionization mass spectrometry (ESMS) has proven to be a powerful tool for collision-induced dissociation (CID) and multiple-stage mass spectrometric (MSn) analysis, and - beyond the elucidation of primary structures - even for the study of noncovalent macromolecular complexes [3]. 

This unit can simulate any type of separation processes, as distillation, absorption, stripping, or extraction columns, modelled as cascade of counter-current equilibrium stages. The model Radfrac in Aspen Plus is particular powerful. It is first built on the inside-out algorithm that increased dramatically the robustness in simulating distillation-based operations (Boston, 1980). Columns with multiple feeds, side streams products, stage heaters or coolers, can be treated, as illustrated in Fig. 3.13. The following capabilities are generally available ... 

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