Separation energy separating agent

The simple and complex distillation operations just described all have two things in common (1) both rectifying and stripping sections are providea so that a separation can be achieved between two components that are adjacent in volatility and (2) the separation is effected only by the addition and removal of energy and not by the addition of any mass separating agent (MSA) such as in liquid-liquid extraction. 

The topic covered in the 10 papers of the first section is commonly referred to as salt effect in vapor-liquid equilibrium and is potentially of great industrial importance. This salt effect leads to extractive distillation processes in which a dissolved salt replaces a liquid additive as the separating agent the replacement often results in a greatly improved separating ability and reduced energy requirements. Two papers in this volume, those by Sloan and by Vaillancourt, illustrate the use of such processing to concentrate nitric acid from its aqueous azeotrope. Nevertheless, the effect has not been exploited by industry to nearly the extent that would seem to be merited by its scientific promise. 

The use of a dissolved salt in place of a liquid component as the separating agent in extractive distillation has strong advantages in certain systems with respect to both increased separation efficiency and reduced energy requirements. A principal reason why such a technique has not undergone more intensive development or seen more than specialized industrial use is that the solution thermodynamics of salt effect in vapor-liquid equilibrium are complex, and are still not well understood. However, even small amounts of certain salts present in the liquid phase of certain systems can exert profound effects on equilibrium vapor composition, hence on relative volatility, and on azeotropic behavior. Also extractive and azeotropic distillation is not the only important application for the effects of salts on vapor-liquid equilibrium while used as examples, other potential applications of equal importance exist as well. 

Application of an energy-separating agent involves heat transfer and/ or shaft work to or from the mixture to be separated. Alternatively, vapour may be created from a liquid phase by reducing the pressure. 

Table 1 is a compilation of the more common industrial separation operations based on inter-phase mass transfer between two phases, either created by an energy-separating agent or added as a mass-separating agent. A more comprehensive table is given by Seader and Henley.1 In the following, the operations listed in Table 1 will be outlined briefly. The first two methods, distillation and absorption, will be discussed in more detail later. 

Table 1 Common separation operations based on phase creation or addition (MSA mass-separating agent ESA energy-separating agent)...

Since little is yet known about efficiency on the technical scale, future investigation should focus on (i) efficiency with respect to separation yield, energy demand and amount of mass separation agents required, (ii) long-term re-use options of auxiliary agents such as extractants or adsorbents and (iii) ease of scaling up. Furthermore, a crucial point for further development of regeneration will be to identify the pollutants that disturb the main process as well as their critical concentration levels in the electrodeposition process. 

Give examples of mass- and energy-separating agents. 

A separation involving an energy-separating agent (ESA) can involve input and removal steps, such as in distillation, where there is a reboiler for energy input and a condenser for energy removal. In other cases, such as evaporation, the vapor can be discharged without... 

While heat is the most common energy-separating agent used. Table 2.3 provides examples of separation processes using gravitational, electric and magnetic fields. 

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