Immiscible phase extractions

Extraction is a process for separating components in solution by their distribution between two immiscible phases. Such a process can also be called liquid extraction or solvent extraction. The former term may be confusing because it also applies to extraction by solid solvents. Since extraction involves the transfer of mass from one phase into a second immiscible phase, the process can be carried out in many ways. The simplest example involves the transfer of one component from a binary mixture into a second immiscible phase — extraction of an impurity from wastewater into an organic phase. In some cases, a chemical reaction can be used to enhance the transfer, e.g., the use of an aqueous caustic solution to remove phenolics from a hydrocarbon stream. 

Distribution of a Single Species between Immiscible Phases Extraction and Separation Processes... 

In a simple liquid-liquid extraction the solute is partitioned between two immiscible phases. In most cases one of the phases is aqueous, and the other phase is an organic solvent such as diethyl ether or chloroform. Because the phases are immiscible, they form two layers, with the denser phase on the bottom. The solute is initially present in one phase, but after extraction it is present in both phases. The efficiency of a liquid-liquid extraction is determined by the equilibrium constant for the solute s partitioning between the two phases. Extraction efficiency is also influenced by any secondary reactions involving the solute. Examples of secondary reactions include acid-base and complexation equilibria. 

To understand the fundamental principles of extraction, the various terms used for expressing the effectiveness of a separation must first be considered. For a solute A distributed between two immiscible phases a and b, the Nernst Distribution (or Partition) Law states that, provided its molecular state is the same in both liquids and that the temperature is constant ... 

In this case study, an enzymatic hydrolysis reaction, the racemic ibuprofen ester, i.e. (R)-and (S)-ibuprofen esters in equimolar mixture, undergoes a kinetic resolution in a biphasic enzymatic membrane reactor (EMR). In kinetic resolution, the two enantiomers react at different rates lipase originated from Candida rugosa shows a greater stereopreference towards the (S)-enantiomer. The membrane module consisted of multiple bundles of polymeric hydrophilic hollow fibre. The membrane separated the two immiscible phases, i.e. organic in the shell side and aqueous in the lumen. Racemic substrate in the organic phase reacted with immobilised enzyme on the membrane where the hydrolysis reaction took place, and the product (S)-ibuprofen acid was extracted into the aqueous phase. 

Many antibiotics have excellent solubihty in oiganic solvents and they are water immiscible. A multistage extraction separates the aqueous phase from the organic phase. Extraction can provide concentrated and purified products. 

Rhodium losses can also be reduced by using a two-phase system to separate the polyol products from the catalyst solution (64). In this modification the reaction is carried out in a production solvent (e.g., tetraglyme). In order to separate the products, water and an essentially water-immiscible organic extraction solvent (e.g., dichloromethane or chloroform) are added. The resulting two-phase system then consists of a water phase containing the alcohol products and an organic phase containing essentially all the rhodium complex. 

In order to extract acetic acid from a dilute aqueous solution with isopropyl ether, the two immiscible phases are passed countercurrently through a packed column 3 m in length and 75 mm in diameter. It is found that if 0.5 kg/m2 of the pure ether is used to extract 0.25 kg/m2s of 4.0 per cent acid by mass, then the ether phase leaves the column with a concentration of 1.0 per cent acid by mass. Calculate ... 

Consider a batch two-phase extraction system, with a single solute transferring from the feed phase into an immiscible solvent phase. The background to the problem is discussed in Section 3.3.1.1... 

Chemical separations are often either a question of equilibrium established in two immiscible phases across the contact between the two phases. In the case of true distillation, the equilibrium is established in the reflux process where the condensed material returning to the pot is in contact with the vapor rising from the pot. It is a gas-liquid interface. In an extraction, the equilibrium is established by motion of the solute molecules across the interface between the immiscible layers. It is a liquid-liquid, interface. If one adds a finely divided solid to a liquid phase and molecules are then distributed in equilibrium between the solid surface and the liquid, it is a liquid-solid interface (Table 1). 

A solid-liquid extraction is an extraction in which an analyte in a solid sample is extracted into a liquid solvent. A liquid-liquid extraction is an extraction in which an analyte dissolved in a liquid sample is extracted into a second liquid solvent that is immiscible with the first. A solid phase extraction is an extraction in which an analyte or its liquid solvent is extracted via contact with a solid material (sorbent) as the solution passes through a cartridge containing the sorbent. 

The phase transfer catalysis not only promotes the reactions between the reagents which are mutually insoluble in immiscible phases, but also offers a number of process advantages such as, increase in rate of reactions, increase in product specificity, lowering of energy requirement, use of inexpensive solvents and catalysts, extraction of cations or even neutral molecules from one phase to another etc. 

In order to extract acetic acid from dilute aqueous solution with isopropyl ether, the two immiscible phases are passed countercurrently through a packed column 3 m in length and 75 mm in diameter. 

Nondispersive solvent extraction is a novel configuration of the conventional solvent extraction process. The term nondispersive solvent extraction arises from the fact that instead of producing a drop dispersion of one phase in the other, the phases are contacted using porous membrane modules. The module membrane separates two of the immiscible phases, one of which impregnates the membrane, thus bringing the liquid-liquid interface to one side of the membrane. This process differs from the supported liquid membrane in that the liquid impregnating the membrane is also the bulk phase at one side of the porous membrane, thus reducing the number of liquid-liquid interfaces between the bulk phases to just one. 

Table 4.2 summarises a selection of solvent pairs that are sufficiently immiscible to form biphasic mixtures suitable for LLE. Klick used LLE as one step in a method to measure an epoxide degradant of a pharmaceutical [12]. In an application of SEC to environmental analysis, LLE was found to give higher extraction efficiencies than solid-phase extraction (SPE - see below) [29]. 

Rate of protein transfer to or from a reverse micellar phase and factors affecting the rate are important for the practical applications of RME for the extraction and purification of proteins/enzymes and for scale-up. The mechanism of protein exchange between two immiscible phases (Fig. 2) can be divided into three steps [36] the diffusion of protein from bulk aqueous solution to the interface, the formation of a protein-containing micelle at the interface, and the diffusion of a protein-containing micelle in to the organic phase. The reverse steps are applicable for back transfer with the coalescence of protein-filled RM with the interface to release the protein. The overall mass transfer rate during an extraction processes will depend on which of these steps is rate limiting. 

Difficult separations can often be effected by liquid-liquid solvent extraction, which depends on differences in the distribution of solute species between two immiscible or partially immiscible phases.4,9 For a solute species A, this distribution is governed by the Nemst partition law... 

Ci = concentration of solute in first of two immiscible phases C2 = concentration of solute in second of two immiscible phases F = composition of feed to solvent extraction operation VGC = viscosity gravity constant... 

To understand any extraction technique it is first necessary to discuss some underlying principles that govern all extraction procedures. The chemical properties of the analyte are important to an extraction, as are the properties of the liquid medium in which it is dissolved and the gaseous, liquid, supercritical fluid, or solid extractant used to effect a separation. Of all the relevant solute properties, five chemical properties are fundamental to understanding extraction theory vapor pressure, solubility, molecular weight, hydrophobicity, and acid dissociation. These essential properties determine the transport of chemicals in the human body, the transport of chemicals in the air water-soil environmental compartments, and the transport between immiscible phases during analytical extraction. 

Extraction or separation of dissolved chemical component X from liquid phase A is accomplished by bringing the liquid solution of X into contact with a second phase, B, given that phases A and B are immiscible. Phase B may be a solid, liquid, gas, or supercritical fluid. A distribution of the com-... 

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