Solubility phenomena

The Important conclusion is that complex controlling processes can occur in solubility phenomena in mixed electrolyte solutions. This is especially true of surface coatings formed kinetically or by multistate thermodynamics and which prevent the aqueous solution from interaction with internal bulk phases. One should remember of course that, when the degree of supersaturation is large enough for bulk precipitation to occur, the kinetic and multiphase thermodynamic processes studied above will apply to the actual bulk phases. 

Alternatively, the structure-solubility relationship estimates solubility using equations that relate solubility to the molecular structures of solutes. The structure-solubility relationship is generally regarded as an empirical method. There is no doubt that an exact theoretical method is preferred over an empirical method forthe study of solubility phenomena. However, owing to the very complicated nature of molecular interactions and the various simpliLcations used in the development of mathematical models, exact thermodynamic approaches may not always provide accurate results without an extensive study of the compound of interest. At the present time, both theoretical and empirical approaches result in similar accuracy, and can be used equally well in the estimation of solubility. 

There are many aspects of solution chemistry. This is apparent from the wide range of topics which have been discussed during recent International Conferences on Solution Chemistry and International Symposia on Solubility Phenomena. The Wiley Series in Solution Chemistry was launched to fill the need to present authoritative, comprehensive and upto-date accounts of these many aspects. Internationally recognized experts from research or teaching institutions in various countries have been invited to contribute to the Series. 

Equilibria involving reductive dissolution reactions add to the complexity of mineral solubility phenomena in just the way that pE-pH diagrams are more complicated than ordinary predominance diagrams, like that in Fig. 3.7. The electron activity or pE value becomes one of the master variables whose influence on dissolution reactions must be evaluated in tandem with other intensive master variables, like pH or p(H4Si04). Moreover, the status of microbial catalysis under the suboxic conditions that facilitate changes in the oxidation states of transition metals has to be considered in formulating a thermodynamic description of reductive dissolution. This consideration is connected closely to the existence of labile organic matter and, in some cases, to the availability of photons.26... 

Solubility data of the dyestuffs are of interest for the optimization of this particular dyeing technique. Therefore an apparatus was developed for the determination of the solubilities in supercritical solvents at temperatures from 250 to 500 K and pressures up to 250 MPa according to the static analytical method [6, 7]. In particular, investigations on the solubility of some selected anthraquinone dyes in supercritical C02 and N20 and more recently of P-carotene in supercritical C02 and CC1F, were performed as a function of temperature and pressure (see section 4.). For the l,4-bis-(n-alkylamino)-9,10-anthraquinones the alkyl chains were systematically varied in the homologous series in order to study the effects of molecular size and polarity on the solubility phenomena [6-10]. 

Some of the historical perspective is extracted (no pun intended) from a previous paper of the author ( 1 ) and is expanded with a chronological development of solubility phenomena based upon an additional compilation of recent work on naphthalene-supercritical solvent systems. The new data on flavor extraction and fractionation point out the most unique feature of supercritical fluid solvents, viz., their often-demonstrated selective dissolving power properties, a selectivity that is achieved because the dissolving power of supercritical fluids is pressure-dependent and can, therefore, be adjusted. 

Similar solubility phenomena can also be observed for the resins. The sample for resin separation after removal of asphaltenes is normally applied as a solution in nC5. However, after the removal of the oil, the fractions obtained from the ion exchangers show a marked decline in solubility in the same solvent. Also, if resin separation is done by the SARA method, the tetrahydro-furan fraction is hardly soluble in nC5. This again shows the solubility criterion to be a function of several variables the removal of some of the solubilizing components of the resins renders the remainder insoluble. 

Rangel-Nafalle, Metzner and Wissbrun (8) reviewed studies on solubility phenomena in deforming solutions and developed an expression for stress-induced phase separation in polymer solutions. Other recent studies in this field were published by Wolf et al. (9-13) by Mazich and Carr (14) and by Vrahopoulou-Gilbert and McHugh (15). 

Application of cohesion energy parameters to interpreting surface phenomena requires additional caution. Steric hindrance and molecular orientation effects become very significant. The difference between the local cohesion energy parameter for one end of a molecule compared with the local cohesion parameter at the other end is often very large. For surface active agents it is customary to say that the one end is hydrophilic and the other end is very hydrophobic. For smaller molecules this difference from one end of the molecule to the other end may not affect interpretation of solubility phenomena, but can affect surface phenomena, for example. 

The first reports of solubility phenomena in supercritical fluids emphasized the pressure-dependent dissolution characteristics of high-pressure gases and liquids. But the authors of those early papers point out the potential application of using SCF solvents as media from which to nucleate solid materials. For example, Hannay and Hogarth write in the closing statements of their 1879 publication ... 

The snow and frost described are almost assuredly of different morphology, particle size, and size distribution than the starting material Hannay and Hogarth studied salts such as cobalt chloride and potassium iodide. Incidentally, the reference to the precipitation of the solid is not an Isolated report of nucleation from a supercritical fluid. For example, many other references to snow, fog, fumes, and crystals formed during depressurization of a solution of a solute in a supercritical fluid have been made by researchers studying supercritical fluid solubility phenomena. 

This patent is one that we have chosen to include for its historical and pedagogical value. Lorenz uses an extractor which is fed with gaseous solvent from the bottom and with feed at the top. The extract leaves at the top and the raffinate at the bottom. We present several statements that Lorenz writes about the workings of his gaseous solvent since these statements corroborate our statement solubility phenomena in supercritical fluids were not only known, but applied, many years ago. 

As we see again, the principles and applications of supercritical fluid solubility phenomena were quite well understood at the time of the filing of this patent, March 1936. 

Czubyrt, J. J., M. N. Meyers, and J. C. Giddings. 1970. Solubility phenomena in dense carbon dioxide in the range 270-1900 atmosphere. J. Phys. Chem. 74 4260. 

L.T. Guyseva and V.A. Khokhlov, Determination of Solubility Product for MgO in Molten KC1 Containing MgC12 by Electrochemical Method with the Oxygen Electrode (Fifth International Symposium on Solubility Phenomena, Moscow, Russia, 1992) p. 69. 

This chapter describes a recent and controversial period of supercritical fluid history, 1977-1987. An outline of the information to be covered in this chapter is given in Table I. The history of supercritical fluid solubility phenomena was summarized in an earlier paper (1). That paper reviewed the first literature report on the subject by Hannay and Hogarth in 1879 (2), the work of many researchers who investigated the phase behavior of various materials dissolved in supercritical fluids (3-5), and some process/product applications of supercritical fluid extraction (6-8). A quite detailed historical development, covering in depth the first score years after 1879, has been published elsewhere (9). 

The comparison between the two chain pairs is also consistent with the physical properties. Paramylon and amylose are known for their gel forming properties and their carbon reserve function in p1 ants.(13,69) Although (l- -3)-3-D-glucan also plays a structural rFTe when it occurs in the cell walls of yeast( ), it is probably more of a matrix substance than anything else. The ability to form multiple helices probably accounts for unusual solubility phenomena such as retrogradation( ) and irreversible gel formation on heating. (13)... 

Pervaporation, vapor permeation and gas permeation are very closely related processes. In aU three cases the driving force for the transport of matter through the membrane is a gradient in the chemical potential that can best be described by a gradient in partial vapor pressure of the components. The separation is governed by the physical-chemical affinity between the membrane material and the species to be passed through and thus by sorption and solubility phenomena. The transport through the membrane is affected by diffusion and the differences in the diffiisivities of the different components in the membrane can play an important role for the separation efficiency, too. All three processes are best described by the solution-diffusion mechanism , their main differences are determined by the phase state and the thermodynamic conditions of the feed mixture and the condensability of the permeate. 

FIGURE 5.1. The principle sources of surface charge in solids include (a) differential ion solubility phenomena, (h) direct ionization of surface groups, (c) isomorphous substitution of ions from solution, and (d) speciflc-ion adsorption from the solution phase (e) anisotropic crystal lattice structures. 

Solubility phenomena (i.e. dissolution and precipitation reactions) are the physicochemical basis of numerous biological processes. These include, for... 

All of these solubility phenomena are governed by the laws of thermodynamics and kinetics. The human body is essentially an isothermal system (a notable exception, related to gout, has been reported in the literature - see... 

Solubility phenomena between solid and aqueous phases are treated in the chapters Leaching from cementitious materials used in radioactive waste disposal sites by Kosuke Yokozeki, An evaluation of solubility limits on maximum uranium concentrations in groundwater by Teruki Iwatsuki and Randolf C. Arthur, and The solubility of hydroxyaluminosilicates and the biological availability of aluminium by Christopher Exley. 

Regarding the chapters not yet mentioned suffice it to say that this book altogether elucidates the interplay of solubility phenomena, thermodynamic concepts, and environmental problems. I congratulate the editor and the authors on this remarkable achievement in such a comparatively short time. 

The principal alms of the Solubility Data Project are the tabulation and evaluation of (a) solubilities as defined above b) the nature of the saturating phase. Thermodynamic analysis of solubility phenomena has two aims (a) to provide a rational basis for the construction of functions to represent solubility data (b) to enable thermodynamic quantities to be extracted from solubility data. Both these are difficult to achieve in many cases because of a lack of experimental or theoretical information concerning activity coefficients. Where thermodynamic quantities can be found, they are not evaluated critically, since this taslc would involve critical evaluation of a large body of data that is not directly relevant to solubility. The following is an outline of the principal thermodynamic relations encountered in discussions of solubility. For more extensive discussions md references, see books on thermodynamics, e.g., (5-12). 

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