Separation process bulk liquid mixtures

The traditional application of adsorption in the process industries has been as a means of removing trace impurities from gas or liquid streams. Examples include the removal of H2S from hydrocarbon streams before processing, the drying and removal of C02 from natural gas, and the removal of organic compounds from waste water. In these examples the adsorbed component has little value and is generally not recovered. Such processes are generally referred to as purification processes, as distinct from bulk separations, in which a mixture is separated into two (or more) streams, each enriched in a valuable component, which is recovered. The application of adsorption to bulk separations is a more recent development that was stimulated to a significant extent by the rapid... 

Solute retention in reversed-phase HPLC is dependent on the different distribution coefficients established between a polar mobile and a nonpolar stationary phase by the peptidic components of a mixture. Although there are many similarities between reversed-phase HPLC separations of peptides and the classical liquid-liquid partition chromatographic methods, it is debatable whether the sorption process in reversed-phase HPLC arises due to partition or adsorption events, i.e., whether the nonpolar stationary phase functions as a bulk liquid or as an adsorptive monolayer. These aspects and the theoretical models for reversed-phase HPLC are discussed in a subsequent section. 

If one then fixes the thermodynamic state such that the bulk mixture is a gas [represented by in the inset in Fig, 4.15.(a)], confinement to a relatively wide pore (i.e., z — 12) may first cause capillary condensation to a mixed liquid mixture analogous to ordinary capillary condensation in pure fluids. If the fluid is confined to a narrower pore (z = 6), however, decomposition into A-rich and B-rieh liquid phases is triggered by confinement upon condensar tioii. Thus, by choosing an appropriate pore width, one can either promote condensation of a gas to a mixed liquid phase or, alternatively, initiate liquid liquid phase separation in the porous matrix where both processes are solely confinement-driven because the pore walls are nonselective for molecules of either species in our present model. 

Solid layer crystallization is a process in which the growth of a crystal layer takes place perpendicular to a cooled surface into the bulk of a melt (sophase change is used as the basis for the separation of the feed mixture. Such a phase separation is possible due to different equilibrium concentrations of the solid and liquid phases of the mixture (see Chapter 3). The driving force for the crystal growth is the temperature difference between the equilibrium temperature of the melt (the bulk) in front of the soUd layer and the temperature of the cooled surface (see Figure 15.2). 

The equilibrium distribution of a mixture of volatile liquids between a vapor phase and a liquid phase in a closed vessel was introduced in Sections 3.3.7.1 and 4.1.2 as the basis for tbe separation process of distillation. The preferential enrichment of the vapor phase with the more volatile species and the liquid phase with the less volatile species was illustrated in Section 4.1.2 for a variety of systems, along with the procedures for calculating the composition of each phase in a closed system. How chemical reactions in the liquid phase affect such vapor-liquid equilibrium was demonstrated in Section 5.2.I.2. In Section 6.3.2.1, open systems of flash vaporization and batch distillation in the context of bulk flow of the vapor and liquid phases parallel to the direction of the force were studied, and the separation achieved was quantified. The most common configuration of separation based on vapor-liquid equilibrium employs, however, a vertical column in which the vapor stream flows up and the liquid stream flows down. How the vapor and the liquid phases may contact each other was illustrated, for example, in Figure 2.1.2(b) for a... 

There are a number of phase equilibrium driven separation processes where the separation devices are such that crossflow of two bulk phases exists. Crossflow is utilized to enable continuous contacting between two immiscible phases, vapor and liquid, in an efficient fashion, as in a plate located in a distillation column. In chromatographic processes, crossflow of the solid adsorbent particles and the mobile fluid phase (liquid or gas) can lead to continuous separation of a multicomponent feed mixture introduced at one location of the mobile fluid (eluent) phase. We will illustrate first how crossflow of adsorbent particles or the adsorbent bed and the mobile fluid phase overcomes the batch nature of multicomponent separation in elution chromatography. Then we will focus on the cross-flow plate in a distillation column. 

I.2.I.4. Enantioselective Extractions Enantioselective iiquid-iiquid extraction (ELLE) is an implementation of the extraction of one enantiomer from a racemic mixture by the transfer between two liquid phases. Liquid-liquid extraction can be easily operated in a continuous counter-current mode to fractionate the racemate into its enantiomers, and this is a great advantage for the up-scaling. The possibility to operate at all scales, from laboratory separations to bulk processes in the chemical and pharmaceutical industries, makes this technology of a great interest to a... 

A packed-bed distillation column is used to adiabatically separate a mixture of methanol and water at a total pressure of 1 atm. Methanol—the more volatile of the two components—diffuses from the liquid phase toward the vapor phase, while water diffuses in the opposite direction. Assuming that the molar latent heat of vaporization is similar for the two components, this process is usually modeled as one of equimolar counterdiffusion. At a point in the column, the mass-transfer coefficient is estimated as 1.62 x 10-5 kmol/m2-s-kPa. The gas-phase methanol mole fraction at the interface is 0.707, while at the bulk of the gas it is 0.656. Estimate the methanol flux at that point. 

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