Solvent extraction relationships

Solvent Extraction Relationships. In a solvent extraction system, the two phases are immiscible, but under proper conditions phase-transfer of one or more species can occur across the organic/aqueous interface. Expansion of the interface by gentle agitation of the vessel containing the two phases allows phase equilibrium to be attained quickly, usually in 1 to 2 minutes. In such an extraction system, the distribution of a metal, M, between the two phases at equilibrium is described by a distribution coefficient, Dj, where [M] represents the concentration of the metal. 

Solvent extraction removes harmful constituents such as heavy aromatic compounds from lubricating oils to improve the viscosity-temperature relationship. The usual solvents for extracting lubricating oil are phenol and furfural. 

Essentially, extraction of an analyte from one phase into a second phase is dependent upon two main factors solubility and equilibrium. The principle by which solvent extraction is successful is that like dissolves like . To identify which solvent performs best in which system, a number of chemical properties must be considered to determine the efficiency and success of an extraction [77]. Separation of a solute from solid, liquid or gaseous sample by using a suitable solvent is reliant upon the relationship described by Nemst s distribution or partition law. The traditional distribution or partition coefficient is defined as Kn = Cs/C, where Cs is the concentration of the solute in the solid and Ci is the species concentration in the liquid. A small Kd value stands for a more powerful solvent which is more likely to accumulate the target analyte. The shape of the partition isotherm can be used to deduce the behaviour of the solute in the extracting solvent. In theory, partitioning of the analyte between polymer and solvent prevents complete extraction. However, as the quantity of extracting solvent is much larger than that of the polymeric material, and the partition coefficients usually favour the solvent, in practice at equilibrium very low levels in the polymer will result. 

Materials. Samples of dewatered crude oils were obtained from the Athabasca oil sands of the McMurray formation by extraction using the commercial hot water process (Suncor Inc.) the Bl uesky-Bu11 head formation at Peace River, Alberta by solvent extraction of produced fluids the Clearwater formation at Cold Lake, Alberta by solvent extraction of core material and the Karamay formation in Xing-Jiang, China. A summary of the physical and chemical properties of the crude oils, including chemical composition, and density-temperature and viscosity-temperature relationships, is given in Table I. 

The standard molar Gibbs energy of transfer of CA is the sum v AG°(C) -i-v AtG°(A), where the charges of the cation C and anion A " and the designation of the direction of transfer, (aq org), have been omitted. The values for the cation and anion may be obtained from tables [5-7], which generally deal with solvents org that are miscible with water and not with those used in solvent extraction. However, AtG°(C) depends primarily on the (3 solvatochromic parameter of the solvent and AtG°(A) on its a parameter, and these can be estimated from family relationships also for the latter kind of solvents. 

This chapter provides the groundwork of solution chemistry that is relevant to solvent extraction. Some of the concepts are rather elementary, but are necessary for the comprehension of the rather complicated relationships encountered when the solubilities of organic solutes or electrolytes in water or in nonaqueous solvents are considered. They are also relevant in the context of complex and adduct formation in aqueous solutions, dealt with in Chapter 3 and of the distribution of solutes of diverse kinds between aqueous and immiscible organic phases dealt with in Chapter 4. 

The amount of a solute that can be introduced into a solvent depends on its solubility, be it a gas (section 2.7.1), a solid nonelectrolyte (section 2.7.2), or an electrolyte (section 2.7.3). Ternary systems, which are the basic form of solvent extraction systems (a solute and two immiscible solvents), have then-own characteristic solubility relationships (section 2.8.1). 

We have hitherto dealt with the complexation thermodynamics in the homogeneous solutions. However, the above interpretation based on the linear enthalpy-entropy relationship may be extended to the complexation behavior in the solvent extraction of aqueous metal salts with ionophores in organic solvent. 

By using experimentally obtained data for 1 mM salicylic acid, a plot of reciprocal analytical signal versus reciprocal a, yielded a linear relationship for the pH range 1.65-3.01. This result supported the solvent extraction model. The corresponding estimate of capacity ratio and distribution coefficient using this treatment was 8.5. 

Testing with a Gieseler plastometer (ASTM D-2639) gives a semiquantitative measurement of the plastic property, or apparent melting of coal when heated under prescribed conditions in the absence of air. The chemical nature of the constituents that account for a coal s plastic properties is not known. The material thought to be responsible for the plastic properties of coal has been removed from coal successfully by solvent extraction, leaving a nonplastic residue. Such residue has been rendered plastic by returning to it the extracts obtained by the solvent extraction. No definite relationship has been established between the amount of extract and the plastic properties of the coal. 

C Quantitative Structure-Property Relationships in Solvent Extraction and Complexation of Metals... 

The inner sphere and outer sphere character was also ascertained in the case of halates and chloroacetates of lanthanides by calorimetry and solvent extraction techniques. Another aspect of the study is to ascertain the relationship between pKa and inner and outer sphere character [30]. 

Flash and Fire Point. Flash point is the temperature at which the volatile products are evolved at such a rate that they are capable of being ignited but not supporting combustion. At the fire point, the accumulated breakdown products are capable of supporting a flame on their own. A crude cottonseed oil with a fatty acid content of 1.8% was found to have a flash point of 560°F or 293.3°C. Solvent-extracted oils can have a low flash point because of a solvent residue. A flash point analysis would identify this crude oil deficiency to prevent an accidental fire or explosion in an atmosphere that was not explosion proof. Crude vegetable oil shipments received with a flash point below 250°F are rejectable by most trading rules. Figure 1 shows the relationship between free fatty acid content, smoke, flash, and fire points of processed cottonseed and peanut oils. 

A number of papers have looked at the development of relationships between base stock composition as measured by NMR and either physi-cal/chemical properties or their performance.22 27 Most of this work has been focused on group II and III base stocks, with less or little attention paid to solvent extracted ones. These have all relied on various techniques to simplify the spectra and the assignments of peaks and make peak integration more reliable. These have many acronyms,23 for example, GASPE (gates spin echo), PCSE (proton coupled spin echo), INEPT (insensitive nuclei enhancement by polarization transfer), DEPT (distortionless enhancement by polarization), QUAT (quaternary-only carbon spectra), 2D COSY (two-dimensional homo-nuclear spectroscopy), and HETCOR (heteronuclear shift correlated spectroscopy)]. Table 4.10 provides an example of some of the chemical shift data generated26 and employed in this type of work, and Adhvaryu et al.25 were able to develop the correlations between base stock properties and carbon types in Table 4.11, whose main features correspond to intuition (e.g., the values of API and aniline points are both decreased by aromatic carbon and increased by the... 

Studies on the relationship between composition and the resistance of base stocks to oxidation started many years ago when solvent extracted stocks were the only ones available. World War II made this an area of particular importance and intensified the effort. Many of the significant early studies date from this period. 

Von Fuchs and Diamond (Shell Oil) pursued these results further by examining the effects of increasing the content of the aromatics on base stock oxidation rates.15 They undertook this study because of the increasing realization that while solvent extraction technology improved lubricant performance, overextraction of the base stock could make it less resistant to oxidation because of removal of the autoretardant components. Since extraction removed aromatics and nitrogen and sulfur compounds, a relationship between these levels and oxidation stability seemed likely. 

Examination of the relationship of the level of B[a]P to that of other individual PAHs in the various CSCs from the solvent-extracted tobaccos or from the component- spiked tobaccos confirmed what was already obvious from other literature data B[a]P is not a valid indicator for either total PAHs or other individnal PAHs with fewer than fonr fnsed rings, with fonr fnsed rings, or with more than fonr fnsed rings. 

---