Solvent selection chapter

This type of solvent selection problem can be formulated and solved as a Computer Aided Molecular Design (CAMD) problem [22], Application of this method for solvent selection and design is highlighted in chapter 14 and is not discussed in detail in this chapter. The ProCAMD software [23], which is based on a hybrid CAMD method can be used to solve solvent selection problems of this type. 

When a non-aqueous solvent is to be used for a given purpose, a suitable one must be selected from the infinite number available. This is not easy, however, unless there are suitable guidelines available on how to select solvents. In order to make solvent selection easier, it is useful to classify solvents according to their properties. The properties of solvents and solvent dassification have been dealt with in detail in the literature [1, 2]. In this chapter, these problems are briefly discussed in Sections 1.1 and 1.2, and then the influences of solvent properties on reactions of electrochemical importance are outlined in Section 1.3. 

Solvent selection depends largely on the nature of the analytes and the matrix. Although the discussions in Chapter 2 can be used as a guideline to account for the solvent-analyte interactions, the matrix effects are often unpredictable. There is no single solvent that works universally for all analytes and all matrices. Sometimes, a mixture of water-miscible solvents (such as acetone) with nonmiscible ones (such as hexane or methylene chloride) are used. The water-miscible solvents can penetrate the layer of moisture on the surface of the solid particles, facilitating the extraction of hydrophilic organics. The hydrophobic solvents then extract organic compounds of like polarity. For instance, hexane is efficient in the extraction of nonpolar analytes, and methylene chloride extracts the polar ones. 

Solvent extraction has long been established as a basic unit operation for chemical separations. Chapter 7 summarizes the effects of temperature, pH, ion pairs, and solvent selection on solvent extraction for biomolecules. Solvent extraction of fermentation products such as alcohols, aliphatic carboxylic acids, amino acids, and antibiotics are discussed. Enhanced solvent extraction using reversed micelles and electrical fields are also discussed. Solvent-extraction equipment and operational considerations are adequately covered in this chapter. 

Often solvents are selected or avoided due to the extent of water miscibility. Solvents with low water solubility readily afford phase separations when extracts are washed with aqueous solutions, and minimal loss of the product to the spent aqueous phase occurs. Product may be lost to the aqueous phase when extracting solutions of solvents with high water solubility. To minimize such losses it may be necessary to partially concentrate the solution before extraction or to dilute with large volumes of water and water-immiscible solvents (see Chapter 10). 

Solvent selection is usually very important in preparing both high-quality product and the desired crystal form. Details may be found in Chapter 11. 

Tremendous improvements in yields can be realized by selecting the most appropriate solvent (see Chapter 4). Extensive examination of solvents was undertaken... 

This is not an example of solvent selection. It is given to show a selection of co-substrates from subgroups in the determination of the scope of a reaction, viz, amine variation in the Willgerodt-Kindler reaction. The general features of this reaction were discussed in Chapter 6. 

In this chapter, the effects of these thermodynamic, kinetic, and molecular recognition phenomena on crystallization and the role of solvent in these processes will be described. The role of solvent on crystallization, polymorphic outcome, and phase transformations will also be discussed. Experimental approaches for polymorph screening will be presented with an emphasis on the important considerations and strategies for solvent selection. 

High-solids coatings of the solvent type have been discussed in other sections of this chapter. This field is active, but greatest emphasis appears to be focused on the resin component of high-solids solvent coatings. Nevertheless, proper solvent selection can materially help in the quest for high-solids coatings based on solvents. 

Table 7.23 presents generic heuristics for sequencing the separation of liquid mixtures. More rules, specific for the separations of zeotropic mixtures by distillation, will be shown later. The separation for azeotropic mixtures is treated in Chapter 9, although the emphasis is on the solvent selection and not on the number of splits. 

It is easy to forget that solvents are chemicals and can react with other paint ingredients. For stability in the can, this is undesirable. Examples of the influence of chemical reactivity on solvent selection are given in Chapters 14 and 15. 

As discussed in the chapter on solvent power, most concepts are related historically to paint application, either as diluents or solvents for natural binders, synthetic resins and polymers. At first the requirements tended to be rather low, both in solvent power and sophistication. However, with the broadening of the spectrum of binders and application techniques the criteria for solvent selection became sharper and the formulations more complex. 

The science of solvent selection has not yet developed to the state where a simple set of rules or a selection flowchart can be provided to give an optimum choice. This chapter seeks to address the principles involved in determining the performance of the solvent at the reaction stage. It will provide an outline of the properties of solvents relevant to the solvation of solutes and reactive intermediates, and show how these relate to reaction rate and selectivity. Solvent-dependent regioselectivity effects are due to selective solvation of incipient reactive sites on a multidentate reactant, and some general predictive principles are available. An outline of the scope and mechanistic principles of two-phase reaction systems is presented, and their potential for providing simpler solvent recycle is emphasised. An alternative approach to easier solvent recovery via the use of volatile inorganic solvents is also discussed. 

The increasing diversity in the applications of liquid extraction has led to a correspondingly diverse proliferation of extraction devices that continue to be developed. This chapter focuses on those fundamental principles of diiiusion, mass transfer, phase equilibrium, and solvent selection that provide a unifying basis for the entire operation. Design procedures for both stagewise and differential contactors alM receive considemtion, including packed and perforated plate columns and mixer-settlers. Some mechanically aided columns are discussed and an attempt is made to conqiare the performance of various equipment tteigns. 

The solvent selected for a particular reaction should not cause any environmental pollution and health hazard. The use of liquid or supercritical liquid CO2 should be explored. If possible, the reaction should be carried out in aqueous phase or without the use a of solvent (solventless reactions). A better method is to carry out reactions in the solid phase (for details see Chapter 13). 

In a final section of this chapter, we look at the use of other solvents beside water. The purpose is to see the effect of solvent selection on dynamic controUabihty. 

The solvent used in the discussions presented so far in this chapter was water. In this section we look at the possibility of using other solvents. Solvent selection is critical to the successful design and operation of extractive distillation systems. Different solvents affect the phase equilibrium in different ways. 

In this chapter, the use of extractive distillation has been illustrated using the acetone-methanol system as a numerical example. Steady-state and dynamic comparisons have been presented between extractive distillation and a pressure-swing distillation, with and without heat integration. In addition, the effect of solvent selection on dynamic controllability has been investigated. 

Solvents of n ons for light scattmng measurements are mostly multicomponent. An error in M, due to the optical effed of selective sorption, may be avoided by using the refractive index increment measured under the condition of dialyas equilibrium between the solution of nylon in a pven mixed solvent and the mixed solvent (See Chapter 6). 

---