Selecting an Extraction Solvent

Choose a solvent to treat a waste water stream saturated with butanoic acid, C4Hg02, at a concentration of 0.64 mol/L. The foUowing are some useful data for butanoic acid  

You are aware that methyl isobutyl ketone is used to extract salicylic acids from wastewaters (see Applications section). Salicylic acid is an aromatic carboxylic acid however, butanoic acid is an aliphatic acid. So the question becomes if a ketone (an H-acceptor) would still be a good choice for the extraction of an aliphatic acid. 

calculate the distribution coefficients for the four representative solvents octanol, hexadecane, diethylether, and chloroform. 

There is no single parameter model for calculating the diethylether and chloroform distribution coefficients, so you need to use the multiple parameter model given in Eq. (2) and Tables 1-3. 

Solvent Extraction Performance in Organic Chemicals Industry (Ethylene Oxychlorination Subcategory) Using Extractor (Multistage Extractor and Stripper) and Solvent (Paraffin) 

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Extraction/deproteinization has been performed by either vortexing liquid samples or homogenizing semisolid samples with acetonitrile (227, 382, 383, 386-392), methanol (14, 393-395), methanol/water mixtures (396-401), ethyl acetate (384,402-406), dichloromethane (379,380,407), and acetone (408,409). Nonpolar organic solvents, such as isooctane (410, 411) and toluene (407), have also been reported to work extremely well for extracting salinomycin and dimetridazole from chicken tissues, respectively. Sample extraction with these nonpolar solvents yields a cleaner extract and an easier workup than extraction with commonly used polar solvents. However, selecting an extraction solvent is critical in establishing an analytical method because it is closely related to the cleanup systems. 

Another consideration when selecting an extraction solvent is its density [41]. Solvents that are more dense than water will form the lower layer of the pair when mixed together, while solvents that are less dense than water will form the upper layer or float on water. For example, ethyl ether has a density of 0.7133 g/mL at 20°C and would constitute the upper phase when combined with water, which has a density of 0.9982 g/mL at that temperature. On the other hand, the density of chloroform is 1.4892 at 20°C. Therefore, water would form the top layer in a water chloroform solvent pair. 

Although solvents may form two visibly distinct phases when mixed together, they are often somewhat soluble in each other and will, in fact, become mutually saturated when mixed with each other. Data on the solubility of various solvents in water (Table 2.2) and on the solubility of water in other solvents (Table 2.3) should be consulted when selecting an extraction solvent pair. For example, 1.6% of the solvent dichloromethane (or methylene chloride) is soluble in water. Conversely, water is 0.24% soluble in dichloromethane. According to Table 2.3, when the phases are separated for recovery of the extracted analyte, the organic solvent layer will contain water. Similarly, according to Table 2.2, after extraction the depleted aqueous phase will be saturated with organic solvent and may pose a disposal problem. (Author s note I previously recounted [43] my LLE experience with disposal of extracted aqueous samples that were cleaned of pesticide residues but saturated with diethyl ether. Diethyl ether is 6.89% soluble in water at 20° C.)... 

Research on solvents for extraction has been carried out for more than 150 years and has intensified sinee the first patent was issued to Deiss of France in 1855. " In the early effort of selecting an extraction solvent, the availability, operation safety, extraetion efficiency, product quality and cost were the major concerns. In reeent deeades, toxieity,... 

The separation of components by liquid-liquid extraction depends primarily on the thermodynamic equilibrium partition of those components between the two liquid phases. Knowledge of these partition relationships is essential for selecting the ratio or extraction solvent to feed that enters an extraction process and for evaluating the mass-transfer rates or theoretical stage efficiencies achieved in process equipment. Since two liquid phases that are immiscible are used, the thermodynamic equilibrium involves considerable evaluation of nonideal solutions. In the simplest case a feed solvent F contains a solute that is to be transferred into an extraction solvent S. 

Reactive distillation is one of the classic techniques of process intensification. This combination of reaction and distillation was first developed by Eastman Kodak under the 1984 patent in which methyl acetate was produced from methanol and acetic acid. One of the key elements of the design is to use the acetic acid as both a reactant and an extraction solvent within the system, thereby breaking the azeotrope that exists within the system. Likewise, the addition of the catalyst to the system allowed sufficient residence time such that high yields could be obtained, making the process commercially viable. Other examples in which reactive distillation may enhance selectivity include those of serial reactions, in which the intermediate is the desired product, and the reaction and separation rates can be systematically controlled to optimize the yield of the desired intermediate. ... 

The most critical decision to be made is the choice of the best solvent to facilitate extraction of the drug residue while minimizing interference. A review of available solubility, logP, and pK /pKb data for the marker residue can become an important first step in the selection of the best extraction solvents to try. A selected list of solvents from the literature methods include individual solvents (n-hexane, " dichloromethane, ethyl acetate, acetone, acetonitrile, methanol, and water ) mixtures of solvents (dichloromethane-methanol-acetic acid, isooctane-ethyl acetate, methanol-water, and acetonitrile-water ), and aqueous buffer solutions (phosphate and sodium sulfate ). Hexane is a very nonpolar solvent and could be chosen as an extraction solvent if the analyte is also very nonpolar. For example, Serrano et al used n-hexane to extract the very nonpolar polychlorinated biphenyls (PCBs) from fat, liver, and kidney of whale. One advantage of using n-hexane as an extraction solvent for fat tissue is that the fat itself will be completely dissolved, but this will necessitate an additional cleanup step to remove the substantial fat matrix. The choice of chlorinated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride should be avoided owing to safety and environmental concerns with these solvents. Diethyl ether and ethyl acetate are other relatively nonpolar solvents that are appropriate for extraction of nonpolar analytes. Diethyl ether or ethyl acetate may also be combined with hexane (or other hydrocarbon solvent) to create an extraction solvent that has a polarity intermediate between the two solvents. For example, Gerhardt et a/. used a combination of isooctane and ethyl acetate for the extraction of several ionophores from various animal tissues. 

All in all, the spectrophotometric methods for the measurement of SFs in various samples are a rapid and simple way to get a value for the total SFs. However, they do not provide any information on the sterol composition (molecular species of different sterols) found in a sample, which may be of biological significance. The spectrophotometric detemination works best on oil samples, where the extraction of SFs and the challenges caused by the selection of an extraction solvent are omitted Extraction . 

Even though a high excess of butadiene was applied in the two-phase reaction the primary octadienylamine was the main product. The low solubility of the monooctadienylamines in water prevents the consecutive reaction to secondary octadienylamines. If an excess of ammonia is applied and CH2CI2 is used as an extraction solvent, the selectivity to primary octadienylamines can be as high as 98-99%, illustrating the industrial potential of this reaction. 

The data indicate that dicyanobutane discriminates on the basis of degree of unsaturation and relatively little on other structural effects in hydrocarbons. The volatility of hydrocarbons is reduced in the order of the number of double bonds and cyclic structure. Thus, it would be possible to separate monoolefins from paraffins, diolefins from monoolefins, naphthenes from paraffins, and aromatics from olefins, naphthenes, and saturates by using dicyanobutane as an extractive solvent with mixtures having selected boiling ranges. 

Other monohydric alcohols listed in Tables 1.1-1 A but not mentioned thus far are used as chemical intermediates to prepare specialty ester and amine derivatives. These solvents may be latent or active solvents in certain adhesive, coating, or lacquer formulations or act as an extraction solvent. The desired evaporation rate of the adhesive or coating formulation will often determine which alcohol is selected. 

Another important application of ethyl lactate is related with the edible oil industry, taking advantage of the partial liquid-liquid miscibility that present the mixtures of ethyl lactate with different lipid type substances. This property could be exploited to develop new separation processes, similar to those mentioned in this chapter, namely the recovery of squalene from olive oil deodorized distillates and the extraction of tocopherols from olive oil. In both applications, the yield and separation factors obtained indicate good selectivity of using ethyl lactate as an extractive solvent, and demonstrate the viability of developing liquid-liquid countercurrent process using green ethyl lactate solvent in edible oil industrial applications. 

Solvent power characterizes the miscibility of solute and solvent. This concept covers two types of uses dissolving a solid or reducing the viscosity of a liquid. The solvent power should be as high as possible. However, a solvent used as an extractant should also be selective, i.e., extract certain substances preferentially from the feed being treated. 

Solvent deasphalting. This is an extraction of the heaviest fractions of a vacuum residue or heavy distillate. The extract is used to produce the bitumen. The separation is based on the precipitation of asphaltenes and the dissolution of the oil in an alkane solvent. The solvents employed are butane or propane or a butane-propane mixture. By selecting the proper feedstock and by controlling the deasphalting parameters, notably temperature and pressure, it is possible to obtain different grades of bitumen by this process. 

Selection of solvents. The choice of solvent will naturally depend in the first place upon the solubility relations of the substance. If this is already in solution, for example, as an extract, it is usually evaporated to dryness under reduced pressure and then dissolved in a suitable medium the solution must be dilute since crystallisation in the column must be avoided. The solvents generally employed possess boiling points between 40° and 85°. The most widely used medium is light petroleum (b.p. not above 80°) others are cycZohexane, carbon disulphide, benzene, chloroform, carbon tetrachloride, methylene chloride, ethyl acetate, ethyl alcohol, acetone, ether and acetic acid. 

Dual solvent fractional extraction (Fig. 7b) makes use of the selectivity of two solvents (A and B) with respect to consolute components C and D, as defined in equation 7. The two solvents enter the extractor at opposite ends of the cascade and the two consolute components enter at some point within the cascade. Solvent recovery is usually an important feature of dual solvent fractional extraction and provision may also be made for reflux of part of the product streams containing C or D. Simplified graphical and analytical procedures for calculation of stages for dual solvent extraction are available (5) for the cases where is constant and the two solvents A and B are not significantly miscible. In general, the accurate calculation of stages is time-consuming (28) but a computer technique has been developed (56). 

Solvent extraction—purification of wet-process phosphoric acid is based on preferential extraction of H PO by an organic solvent vs the cationic impurities present in the acid. Because selectivity of acid over anionic impurities is usually not sufficient, precipitation or evaporation steps are included in the purification process for removal. Cmde wet-process acid is typically concentrated and clarified prior to extraction to remove post-precipitated sludge and improve partition of the acid into the solvent. Concentration also partially eliminates fluoride by evaporation of HF and/or SiF. Chemical precipitation of sulfate (as Ba or Ca salts), fluorosiUcates (as Na salt), and arsenic (as sulfides) may also be used as a prepurification step preceding solvent extraction. 

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