Chemical fractionation methods solvent extraction

The simplest approach to the collection and subdivision of organic materials in seawater is to use some physical or chemical means of removing one fraction from solution or suspension. The techniques vary, from simple filtration to collect particulate matter, to chemical methods, such as solvent extraction and coprecipitation. With each of these methods, the analyst must know the efficiency of collection and exactly which fraction is being collected. Very often the fraction is defined by the method of collection two methods... 

There are several processes for commercial thorium production from monazite sand. They are mostly modifications of the acid or caustic digestion process. Such processes involve converting monazite to salts of different anions by combination of various chemical treatments, recovery of the thorium salt by solvent extraction, fractional crystallization, or precipitation methods. Finally, metalhc thorium is prepared by chemical reduction or electrolysis. Two such industrial processes are outlined briefly below. 

The most common method for the separation and concentration of flavor chemicals before chromatography is solvent extraction. If the aroma active components in a sample are less than a microgram/liter then solvent extraction followed by fractional distillation can be used to concentrate the analytes above 1 4g/liter. This is done for two reasons (1) to remove the odorants from some of the interfering substances and nonvolatiles, and (2) to concentrate the sample for greater sensitivity. The choice of solvent(s) depends on a number of issues, but similar results can be obtained with many solvents. Table Gl.1.2 lists a number of solvents, their polarity, and physical properties. Pentane is the least polar and ethyl acetate the most. The sample must be an aqueous or dilute sample, dissolved or slurried into water to a final concentration of 80% to 90% water. Dilute aqueous samples will present the greatest polarity difference between the solvent and the sample, driving more volatiles into the extracting solvent. 

Lavoisier s quantitative method was crucial to the creation and to the success of the chemical revolution. Chemistry, however, is a science of qualities as well as of quantities. Chemical analysis has to be qualitative as well as quantitative. Chemists need to know what substances they are dealing with, as well as how much of each of those substances is present. Lavoisier recognized the importance of traditional operations for separating substances that were mixed rather than combined, including solvent extraction, crystallization, and fractional distillation (where substances with different boiling points are distilled at those different temperatures from a mixture). 

The PLC-8 fractionation method is shown to be an appropriate procedure for analyzing the effects of temperature, solvent density and addition of cosolvents on the characteristics of the extracts, allowing the maximization of specific chemical fractions. 

In summary, the results from this and other studies (30, 31, 32) unambiguously demonstrate that simple solvent extraction of coal liquids does not yield chemically well-defined fractions. Consequently, detailed molecular analysis is a prerequisite for an in-depth analysis/prediction of the production and/or upgrading of coal liquids and for the correct evaluation of process effectiveness. In addition, implementation of routine process control/monitoring schemes employing fractions obtained from separation of products/reactants necessarily requires calibration by detailed molecular analysis. Finally, the separation method(s) should produce fractions possessing chemical significance. 

The classical chemical methods to separate lanthanoids were based upon the redox behavior of Ce, Sm, Eu, and Yb , Other classical methods (fractional crystallization) are essentially physical processes. Cerium is oxidized to the 4-I- state and separated from the 3+ rare earths by solvent extraction, iodate precipitation, or selective hydrolysis or precipitation of basic Ce(IV) compounds in weakly acidic solution. Europium is reduced and maintained in H2O as Eu " by Zn amalgam and precipitated as EUSO4. Sm and Yb are extracted from H2O by reduction into dilute Na or Li amalgam. 

One important trend in the food industry is the increased demand for natural food ingredients free of chemicals. Therefore, special attention has been paid to alternative processes directed toward extraction solvents and techniques with both GRAS and GMP labels (Ibanez et al., 1999). Supercritical C02-extraction (SFC C02) has been used (Weinreich, 1989 Nguyen et al., 1991 Nguyen et al., 1994 Ibanez et al., 1999). Tena et al. (1997) noted that extracts from rosemary obtained by SFC C02 (35 bar at 100°C) were the cleanest extracts and provided the highest recovery of carnosic acid compared to solvent extracts (acetone, hexane, dichlor-methane and methanol) after bleaching with active carbon. Bicchi et al. (2000) reported a fractionated SFC C02 method to selectively isolate carnosol and carnosic acid at 250 atm and 60°C in the second fraction. The authors used 5% methanol to modify the dissolution power of SFC C02. 

Table 30-1 lists a variety of separation methods that are in common use, including (1) chemical or electrolytic precipitation, (2) distillation, (3) solvent extraction, (4) ion exchange, (5) chromatography, (6) electrophoresis, and (7) field-flow fractionation. The first four are discussed in Sections 30A through 30E of this chapter. An introduction to chromatography is presented in Section 30F. Chapters 31 and 32 deal with gas and liquid chromatography, respectively, while Chapter 33 deals with electrophoresis, field-flow fractionation, and other separation methods. 

Methods of separation of hydrocarbons became more diversified. Fractional distillation was improved by the use of azeotropic and extractive distillation. Continuous adsorption on solids such as active charcoal or silica gel was established. Liquid-hquid solvent extraction, already used in petroleum refining, was adapted to the concentration and purification of some of the raw materials for petroleum chemicals finally, the formation of physical complexes, the so-called clathrate compounds, which permit separation of hydrocarbons of different shapes, is being developed as a new separation method, now known as extractive crystalhzation. 

Chemical purity. Chemical purity is the fraction of a radiopharmaceutical in the form of the desired chemical molecule whether all of it is radiolabeled or not. The presence of extraneous stable atoms may cause adverse reactions and is not desirable in a PET radiopharmaceutical. These impurities arise from the incomplete synthesis, addition of extraneous ingredients during the synthesis, and so on. Chemical methods such as the spectrophotometric method, ion exchange, solvent extractions, chromatography, etc. are applied to measure the level of these chemical impurities. Again, these tests can be performed a priori in many dry runs and thus the level of chemical impurities can be established, prior to human administration. 

Processes available for the extraction of natural organics from waters include vacuum distillation, freeze-drying, freeze concentration, co-precipitation, ultrafiltration, reverse osmosis (RO), solvent extraction, sorption, anion exchange, and non-ionic macroporous sorbents (Aiken (1985)). Many of these methods include chemical treatment that may alter the HS characteristics. In this section, the most common methods for the processing of large samples will be described. An important issue in NOM extraction is the recovety of organics. Minimising the loss of certain fractions, such as small compounds which are difficult to treat, is also important. 

Certain lipid classes (e.g., FA and hydrocarbons) can be fractionated from lipid extracts according to their differing solubilities in solvent systems, particularly following chemical reactions to release ester-linked FA from complex lipids. However, for the separation of complex lipid classes and/or individual components within lipid classes, chromatographic techniques afford robust and reliable methods. Column chromatography is useful for the collection of lipid fractions retained in solvent for further analysis while TLC yields separations more suited to the analytical identification of lipids. 

This means that the element of interest can be determined simply by measuring the radioactivity. The substoichiometric determination procedure consists of three steps radioisotopic labelling of the element of interest, reproducible separation of a fraction of the element of interest, and measurement of the radioactivity of the separated portion. In the first step, it is necessary to achieve an isotopic equilibrium between the element of interest and the added radioisotope. The x)nd step, known as substoichiometric separation, is the most important one. The absolute amount of the separated portions is not of concern a constant amount of the element of interest must be sejmrated with high reproducibility. The substoichiometric se mration is usually made by an appropriate chemical separation method. In solvent extraction, for example, this is made by adding a substoichiometric amount of reagent Miich is less than... 

In the early years, most of the crude tall oil was burned for the fuel value and as a method of disposal. But because it was recognized early that CTO was a potential source of fatty acids and rosin, numerous processes including acid refining, solvent extraction, adsorption, selective chemical transformations, and, particularly, distillation were developed to upgrade CTO. Although the distillation processes provided useful products, it was not until 1949 that production of high quality tall oil fatty acids and tall oil rosins by fractional distillation was commercially realized. Virtually all tall oil is now being fractionated. 

Probably the most important chemical procedure in the determination of the rare earths is the determination of total rare earths in some matrix which usually involves the precipitation of the rare earth oxalates and ignition to the oxides, R2O3. This procedure also serves to separate the rare earth group from other elements present in solution prior to the determination of the individual rare earths by other methods such as flame emission spectrometry. Chemical methods can also be employed to separate the light rare earth fraction from the heavy rare earth fraction with minimum difficulty. Chemical methods such as solvent extraction are also quite useful in the preconcentration of the rare earths where they are present at extremely low concentrations prior to their determination by other methods. 

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