Solvent fractionation scheme

Figure 1. Solvent Fractionation Scheme Using Silicon Gel Column for Crude Oil and Shale Oil.

Extraction OF Tablets and Capsules Elaborate solvent fractionation schemes are not usually necessary for solid dosage preparations. Most drugs are soluble in methanol and most of the excipients are not therefore the preparation of a simple methanol extract is all that is required. However, if the methanol extract is too concentrated, the spot on the TLC plate will be overloaded and the resultant chromatogram will be useless. Any subsequent ultraviolet spectrophotometric examination of the extract may give specfra which are not on scale. This cannot always be avoided, but the following guide-lines have been found useful. 

The general solvent fractionation scheme and the composition and analysis of the coal liquid fractions were described previously (1,2). 

The solvent fractionation scheme for separating coal liquid products into flve fractions propane-soluble (oil) propane-insoluble and pentane-soluble (resin) pentane-insoluble and benzene-soluble (asphaltene) benzene-insoluble and carbon disulfide-soluble (carbene) and carbon disulfide-insoluble (carboid) was described previously (1,2). 

An important point that cannot be overly emphasized is that coal-derived asphaltenes and petroleum asphaltenes are considerably different materials. Other than the fact that they are derived using essentially the same solvent fractionation scheme, the two have little in comfnon. For example, asphaltenes from the liquefaction of coal are known to be much more highly aromatic (46) than asphaltenes from petroleum (47, 48). During the present investigation, it was determined that the ESR behavior of the two types of materials is also quite different. 

Our most recent work with B megapotamica has been with the isolation of large quantities of baccharinoids from a 1800 Kg collection. The workup of the crude extract (ca. 30 Kg of black tarry material) of this plant material was conducted by Dr. Fred Boettner of Polyscience, Inc. This near Herculean task required tremendous quantities of solvents, column packings and time to complete. An outline of the fractionation scheme is presented in Figure 2. Fractions F6-F11 contain a large number of baccharinoids. To date, we have characterized over twenty macrocyclic trichothecenes found in B mega-... 

These yields are also given on the basis of 100 g of original dry coal before fractionation. The bottom line of the table shows the mass of each fraction obtained from 100 g of dry coal. For every 100 g of original dry coal an additional 100 g of extraneous material was present. Elemental balances and other evidence (]J showed this to be made up almost entirely of phenol chemically combined with the coal material, with traces present of residual solvent associated with the fractions as a result of the coal preparation and fractionation scheme. Note that with fractions A and B no solid residue was obtained. 

The process is just like the solvent recovery scheme explained in Chapter 2. The IPA/acetone/water is fractionated with the acetone going overhead and the IPA/water coming out the bottom. The yield (the percent of the IPA that ends up as acetone) is 85-90%. 

Although the use of lignin as an additive to polyurethanes is not new (15-20), even the most judicious selection of lignin isolation or modification schemes has not allowed researchers to overcome the incorporation limit of 25 to 40 weight percent of lignin as an active component in polyurethanes. Solvent fractionation allows for the isolation of lignin fractions with well defined solubilities and functionalities (21,22). Both of these features are critical for the practical inclusion of lignin into liquid polyol systems. 

Chemical fractionation of whole products and by-products from synthetic fuel production affords a logical first step in the evaluation of these materials for biological activity and the subsequent prediction of health hazards. Aliphatic and aromatic hydrocarbons, along with smaller amounts of heteroatomic species, constitute the bulk of all crude product materials and define a primary class separation need. Subfractionation of these fractions can lead to identification of bioactive components, Aliphatics are separated from the entire sample by a simple liquid chromatographic elution scheme. Aromatic compounds can be isolated by a cyclo-hexane-dimethylsulfoxide solvent partitioning scheme, A Sephadex LH-20 gel separation scheme appears feasible for the fractionation of crude liquids into aliphatic-aromatic, lipophilic-hydrophilic, polymeric, and hydrogen bonding classes of compounds. 

Solvent Fractionation. To facilitate later structural analysis, we separated the coal into structural types by solvent fractionation. Some other workers using the phenol depolymerization method to solubilize coal have used gas chroma-tography/mass spectroscopy (GC/MS) techniques to identify individual compounds (11, 13). However, with material containing large amounts of phenol and other polar groups, elaborate preparation and separation schemes have to be used to avoid contamination of the chromatography columns. As the emphasis of the present work was on structural characterization of the whole coal rather than on detailed examination of small parts of it in order to elucidate the chemistry of the phenolation reaction, we used the relatively simple scheme shown in Figure 1. 

FIG. 15-9 Process concepts for single-solvent fractional extraction with extract reflux. The process flow sheet shown in Fig. 15-2 is an example of this general process scheme. 

A dual-solvent fractional extraction process can provide a powerful separation scheme, as indicated by the examples given above, and some authors suggest that fractional extraction is not utilized as much as it could be. In many cases, instead of using full fractional extraction, standard extraction is used to recover solute from a crude feed and if the solvent-to-feed ratio is less than 1.0, concentrate the solute in a smaller solutebearing stream. Another operation such as crystallization, adsorption, or process chromatography is then used downstream for solute purification. Perhaps fractional extraction schemes should be evaluated more often as an alternative processing scheme that may have advantages. 

A potential fourth type of fractional extraction operation involves the use of reflux at both ends of a dual-solvent process, i.e., reflux to the raffinate end of the process (the stripping section) as well as reflux to the extract end of the process (the washing section). The authors are not aware of a commercial apphcation of this kind however, Scheibel [Chem. Eng. Prog., 62(9), pp. 76-81 (1966)] discusses such a process scheme in light of several potential flow sheets. In the special case of single-solvent fractional extraction with extract reflux, Skelland [Ind. Eng. Chem., 53(10), pp. 799-800 (1961)] has pointed out that addition of raffinate reflux is not effective from a strictly thermodynamic point of view as it cannot reduce the required number of theoretical stages in this special case. 

Dual-Solvent Fractional Extraction As discussed in Commercial Process Schemes, under Introduction and Overview, fractional extraction often may be viewed as combining product purification with product recovery by adding a washing section to the stripping section of a standard extraction process. In the stripping section, the mass transfer we focus on is the transfer of the product solute from the wash solvent into the extraction solvent. If we assume dilute conditions and use shortcut calculations for illustration, the extraction factor is given by... 

Owing to the low temperature requirement, this type of method has not been extensively used or investigated for quantitative microanalysis. It should be noted, however, that the albumin separation is satisfactory even when the temperature during filtration rises as high as 7°C (PIO). Careful control at temperatures below zero is demanded for the ethanol fractionation scheme of Cohn et al. (C14). The higher dielectric constant of methanol undoubtedly renders the earlier method less sensitive to small changes in the many variables—temperature, molarity, pH of buffer, concentration of solvent and serum— and less likely to be adversely affected by albumin denaturation. ... 

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