Fractional liquid extraction

The above process is repeated ten times, the broths obtained are combined, the pH is adjusted to 6, the combined broths are filtered, and the resulting filtrate is extracted countercurrently at the rate of 128 gallons per hour with about the same rate of butanol, in a 12" diameter by 11 ft. high Karr extraction column. A water backwash of 0.2 times the butanol rate is employed at the top of the extraction column to minimize the carry-over of water soluble components. The butanol extract is concentrated to approximately a 5% solution which comprises the feed to the center of a 3" diameter by 20 ft. high Karr fractional liquid extraction column. This column is operated at a water to butanol ratio of about 10 to 1, and the butanol extract contains the product. The butanol extract is concentrated by evaporation to a solution or paste containing about 5 to about 20% ent solids then about 25 to about 50 volumes of n-hexane are added, and the resulting slurry filtered. The precipitated product is then vacuum-dried to give a solid compound. 

A method for overcoming the relatively high attraction of a solvent to water in liquid/liquid extraction is to employ a pair of extraction solvents, one with a very strong affinity to water and the other with a great affinity to the solvent being separated from water, a technique known as fractional liquid extraction (FLE). 

Liquid-liquid and liquid-solid equilibria also find industrial applications in liquid-liquid extraction and fractional crystallization operations. 

Progress of a liquid-liquid extraction using two identical extractions of a sample (initial phase) with fresh portions of the extracting phase. All numbers are fractions of solute in the phases A = analyte, I = interferent. 

Let s assume that the solute to be separated is present in an aqueous phase of 1 M HCl and that the organic phase is benzene. Because benzene has the smaller density, it is the upper phase, and 1 M HCl is the lower phase. To begin the countercurrent extraction the aqueous sample containing the solute is placed in tube 0 along with a portion of benzene. As shown in figure A6.1a, initially all the solute is present in phase Lq. After extracting (figure A6.1b), a fraction p of the solute is present in phase Uq, and a fraction q is in phase Lq. This completes step 0 of the countercurrent extraction. Thus far there is no difference between a simple liquid-liquid extraction and a countercurrent extraction. 

The feed to a liquid-liquid extraction process is the solution that contains the components to be separated. The major liquid component in the feed can be referred to as the feed solvent. Minor components in solution are often referred to as solutes. The extraction solvent, or just plain solvent, is the immiscible liquid added to a process for the purpose of extracting a solute or solutes from the feed. The extraction-solvent phase leaving a liquid-liquid contactor is called the extract. The raffinate is the liquid phase left from the feed after being contacted by the second phase. A wash solvent is a hquid added to a liquid-liquid fractionation process to wash or enrich the purity of a solute in the extract phase. 

Fraetionation dissoeiation extraetion involves both the chemical reaction and the fractionation scheme for the separation of components by their difference in dissociation constants as described by Colby [in Hanson (ed.). Recent Advances in Liquid-Liquid Extraction, Pergamon, New York, 1971, chap. 4]. 

Refinery product separation falls into a number of common classes namely Main fractionators gas plants classical distillation, extraction (liquid-liquid), precipitation (solvent deasphalting), solid facilitated (Parex(TM), PSA), and Membrane (PRSIM(TM)). This list has been ordered from most common to least common. Main fractionators are required in every refinery. Nearly every refinery has some type of gas plant. Most refineries have classical distillation columns. Liquid-liquid extraction is in a few places. Precipitation, solid facilitated and membrane separations are used in specific applications. 

The principal components of the cut are butene-1, butene-2, isobutylene and butadiene-1,3. Methyl, ethyl, and vinyl acetylenes, butane and butadiene-1,2 are present in small quantities. Butadiene is recovered from the C4 fraction by extraction with cuprous ammonium acetate (CAA) solution, or by extractive distillation with aqueous acetonitrile (ACN). The former process is a liquid-liquid separation, and the latter a vapor-liquid separation. Both take advantage of differences in structure and reactivity of the various C4 components to bring about the desired separation. 

Nonselective membranes can assist enantioselective processes, providing essential nonchiral separation characteristics and thus making a chiral separation based on enantioselectivity outside the membrane technically and economically feasible. For this purpose several configurations can be applied (i) liquid-liquid extraction based on hollow-fiber membrane fractionation (ii) liquid- membrane fractionation and (iii) micellar-enhanced ultrafiltration (MEUF). 

Two main schemes exist for the separation and purification of tantalum and niobium using liquid-liquid extraction. The first is based on the collective extraction of tantalum and niobium from an initial solution into an organic phase so as to separate them from impurities that remain in the aqueous media, the raffinate. The separation of tantalum and niobium is subsequently performed by fractional stripping into two different aqueous solutions. In this case, stripping of niobium is performed using relatively weak acids prior to the stripping of tantalum. Fig. 125 presents a flow chart of the process. 

In processing, it is frequently necessary to separate a mixture into its components and, in a physical process, differences in a particular property are exploited as the basis for the separation process. Thus, fractional distillation depends on differences in volatility. gas absorption on differences in solubility of the gases in a selective absorbent and, similarly, liquid-liquid extraction is based on on the selectivity of an immiscible liquid solvent for one of the constituents. The rate at which the process takes place is dependent both on the driving force (concentration difference) and on the mass transfer resistance. In most of these applications, mass transfer takes place across a phase boundary where the concentrations on either side of the interface are related by the phase equilibrium relationship. Where a chemical reaction takes place during the course of the mass transfer process, the overall transfer rate depends on both the chemical kinetics of the reaction and on the mass transfer resistance, and it is important to understand the relative significance of these two factors in any practical application. 

The theoretical treatment which has been developed in Sections 10.2-10.4 relates to mass transfer within a single phase in which no discontinuities exist. In many important applications of mass transfer, however, material is transferred across a phase boundary. Thus, in distillation a vapour and liquid are brought into contact in the fractionating column and the more volatile material is transferred from the liquid to the vapour while the less volatile constituent is transferred in the opposite direction this is an example of equimolecular counterdiffusion. In gas absorption, the soluble gas diffuses to the surface, dissolves in the liquid, and then passes into the bulk of the liquid, and the carrier gas is not transferred. In both of these examples, one phase is a liquid and the other a gas. In liquid -liquid extraction however, a solute is transferred from one liquid solvent to another across a phase boundary, and in the dissolution of a crystal the solute is transferred from a solid to a liquid. 

Liquid-liquid extraction (also called solvent extraction) is the transfer of a substance (a consolute) dissolved in one liquid to a second liquid (the solvent) that is immiscible with the first liquid or miscible to a very limited degree. This operation is commonly used in fine chemicals manufacture (I) to wash out impurities from a contaminated solution to a solvent in order to obtain a pure solution (raffinate) from which the pure substance will be isolated, and (2) to pull out a desired substance from a contaminated liquid into the solvent leaving impurities in the first liquid. The former operation is typically employed when an organic phase is to be depleted from impurities which are soluble in acidic, alkaline, or neutral aqueous solutions Water or a diluted aqueous solution is then used as the solvent. The pure raffinate is then appropriately processed (e.g. by distillation) to isolate the desired consolute. In the latter version of extraction impurities remain in the first phase. The extract that has become rich in the desired consolute is then appropriately processed to isolate the consolute. Extraction can also be used to fractionate multiple consolutes. 

Temperature-Controlled Residuiun Oil Supercritical Extraction (ROSE) The Kerr-McCee ROSE process has been used worldwide for over two decades to remove asphaltenes from oil. The extraction step uses a hquid solvent that is recovered at supercritical conditions to save energy as shown in Fig. 20-21. The residuum is contacted with butane or pentane to precipitate the heavy asphaltene fraction. The extract is then passed through a series of heaters, where it goes from the liquid state to a lower-density SCF state. Because the entire process is carried out at conditions near the critical point, a relatively small temperature change is required to produce a fairly large density change. After the light oils have been removed, the solvent is cooled back to the liquid state and recycled. 

In the UV filter analyses, clear extracts were obtained which did not need any further time- and labor-consuming cleanup when using PLE with in-cell purification. In contrast, a thorough purification procedure was required for the cleanup of the extracts obtained by solid-liquid extraction. Columns packed with silica gel (previously activated) in hexane having Na2S04 at the top of the column were employed for the purification of the extracts. The two first fractions obtained with 20 mL of hexane and 20 mL of hexane/diethyl ether (9/1, v/v) were discarded and 4-MBC, EHMC, and OC were collected with 50 mL of hexane/diethyl ether (9/1, v/v). OT was recovered with 70 mL of hexane/diethyl ether (3/2, v/v). 

CAA [Cuprous ammonium acetate] A general process for separating alkenes, di-alkenes, and alkynes from each other by extraction of their cuprous complexes from aqueous cuprous ammonium acetate into an organic solvent. Exxon used it for separating C4 fractions containing low concentrations of butadiene. The liquid-liquid extraction processes for butadiene have all been replaced by extractive distillation processes. 

Electrofining A process for purifying petroleum fractions by extracting them with various liquid reagents and then assisting their separation by means of an electric field. Developed by the Petreco Division of Petrolite Corporation, and first operated in California in 1951. 

LEDA [Low energy de-asphalting] A process for removing the asphalt fraction from petroleum residues by liquid-liquid extraction in a special rotating disc contactor. The extractant is a C3-C6 aliphatic hydrocarbon or a mixture of such hydrocarbons. Developed in 1955 by Foster Wheeler USA Corporation and still widely used 42 units were operating in 1996. 

Sulfolane A process for removing aromatic hydrocarbons from petroleum fractions by liquid-liquid extraction using sulfolane (tetramethylene sulfone tetrahydrothiophene-1,1-dioxide) at approximately 190°C. Developed by Shell Development Company in 1959 and first commercialized in 1962 now licensed through UOP. It replaced the Udex process. Sulfolane is used for another purpose in the Sulfinol process. 

A plug-flow, liquid-liquid, extraction column is represented in Fig. 4.19. For convenience, it is assumed that the column operates under low concentration conditions, such that the aqueous and organic flow rates, L and G, respectively are constant. At low concentration, mole fraction x and y are identical to mole ratios X and Y, which are retained here in the notation for convenience. This however leads to a more complex formulation than when concentration quantities are used, as in the example AXDISP. 

This model of liquid extraction is symmetrical to fractional crystallization and has attracted renewed interest after the demonstration by Johnson et al. (1990) that REE distributions in abyssal peridotite clinopyroxene cannot be accounted for by equilibrium melting processes. The solid is supposed to maintain its chemical homogeneity while liquid is continuously extracted. Only the last drop of liquid is supposed to be in equilibrium with the residue. 

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