Solubility and Solution Equilibria in Crystallization

However, often the phase diagrams required are not known in particular for new substances in the fine chemical and pharmaceutical fields. Even more hard to find are ternary solubility phase diagrams that describe equilibria of two substances in a solvent such as the target compound and an impurity in a solvent of choice or the two enantiomers of a chiral system in a solvent. Often one faces a lack of consistent solubility data for the substance of interest. Experimental determination of solubilities is a tedious and time-consuming work and requires a sufficient amount of substance that is often not available in an early stage of development. Also, usually a combination of different analytical techniques is necessary to obtain both the solubility and the identity of the solid phase in equilibrium. 

Crystallization Basic Concepts and Industrial Applications, First Edition. Edited by Wol ang Beckmann. 

Feasibility of crystallization-based recovery of a target compound (separation, purification)  

Which purity Miscibility in solid state (solid solutions) 

How Derivation of the crystallization procedure, quantification, and process design 

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The relationship between. Keu and a, for carbamazepine co-crystals in aqueous solutions with different pH values and in several organie solvents is shown in Figure 11.16. The data points represent. Keu values and solubilities obtained from measured eutectic solution concentrations of eo-crystal components according to equations (11.40) and (11.42). Co-crystal stoichiometric solubilities increase relative to drug solubility as the [eo-former]eu increases relative to the [drugjeu- Other eo-crystal stoichiometries and solution equilibria are presented in the original publication. ... 

Although aqueous hydrolytic equilibria such as equation (1) provide an overall framework for the discussion of isopolyanions, several species have been synthesized in nonaqueous media, and are unstable in water. Other isopolyanions that are crystallized from aqueous solution, may be incongruently soluble and have polymeric structures. It will, however, prove to be convenient to treat all isopolyanions as though they were derived by equation (1), and characterize each by its acidity , Z (=p/q). Note that Z for a specific anion is not necessarily equal to the value of p/q for the solution from which the anion was crystallized.10... 

The effect of neutral salts (e.g., NaCl) on the composition of borates precipitated from, or in equilibrium with, aqueous solutions doubtless arises from a reduction in water activity, metal borate complexation, and a shift in polyborate equilibria (Sections IV,A, B). The "indifferent or inert component method has frequently been used for the synthesis of borates. Potassium and sodium chlorides can be used to enhance the precipitation of specific nickel (48), aluminum (51), iron (49), and magnesium (151) borates. In the K20-B203-H20 system at 25°C (248), the presence of potassium chloride results in a reduced boric acid crystallization curve, lower borate solubilities, lower pH, and an extended B203 K20 range over which the pentaborate crystallizes. 

Hypothetical projections of the solidus surfaces of the Sc-M-C (M=Zr, Hf, V, Nb, Ta) phase diagrams are proposed in a paper of Velikanova et al. (1989). A complete miscibility of the binary carbides ScCi- and MCi- (M=Zr, Hf, V, Nb, Ta) crystallizing in the NaCl type structure, and the absence of ternary compounds in each of these ternary systems is predicted. However, these data need to be confirmed experimentally. Recently Ilyenko et al. (1996) reported the existence of continuous solid solutions between ScCi x and MC] x (M=Zr, Hf), and accordingty these solid solutions are in equilibria with all the phases of the solidus surface. The same authors reported that the VCi x binary carbidedissolves at least 15at.% Sc while the V solubility in ScC x is at least 17at.%. These data reject the earlier prediction of a complete miscibility of the NaCl-t5q)e binary carbides in the system Sc-V-C. However, no figures of the phase equilibria are presented in the brief communication of Ilyenko et al. 

Co-crystal solubility in micellar solutions has been described by the equilibria between the co-crystal phase and its components in the aqueous and micellar environments. We first present a simplified model that assumes nonionizing solution conditions and negligible co-former partitioning into the micelle, as illustrated in Figure 11.7. 

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