Multicomponent chemical mixtures

The QCE model also allows numerical evaluation of the heat capacities, thermal coefficients, and compressibilities needed to construct the thermodynamic metric geometry. Unfortunately, the higher derivatives of Q that are needed to evaluate the QCE thermodynamic metric are subject to considerable errors, both from underlying theoretical approximations and from increasingly severe numerical errors in finite-difference evaluations. Significant improvements, including extension to multicomponent chemical mixtures and more accurate description of cluster-cluster interactions, are needed before QCE-like models can provide additional ab initio insights into the mysteries of nonideality in phase equilibria. 

Most chemical processes are dominated by the need to separate multicomponent chemical mixtures. In general, a number of separation steps must be employed, where each step separates between two components of the feed to that step. During process design, separation methods must be selected and sequenced for these steps. This chapter discusses some of the techniques for the synthesis of separation trains. More detailed treatments are given by Douglas (1995), Bamicki and Siirola (1997), and Doherty and Malone (2001). 

For a multicomponent chemical mixture being fed into a single-entry separator with only two product streams, existing methods of description involve amongst others separation factors for selected components. Some of these separation factors, namely a,>, (definition (1.6.6)), ay (definition (1.6.8)), etc., were introduced earlier with closed... 

Work in the area of simultaneous heat and mass transfer has centered on the solution of equations such as 1—18 for cases where the stmcture and properties of a soHd phase must also be considered, as in drying (qv) or adsorption (qv), or where a chemical reaction takes place. Drying simulation (45—47) and drying of foods (48,49) have been particularly active subjects. In the adsorption area the separation of multicomponent fluid mixtures is influenced by comparative rates of diffusion and by interface temperatures (50,51). In the area of reactor studies there has been much interest in monolithic and honeycomb catalytic reactions (52,53) (see Exhaust control, industrial). Eor these kinds of appHcations psychrometric charts for systems other than air—water would be useful. The constmction of such has been considered (54). 

Chemical-based products cover a broad spectrum of materials and forms, ranging from molecules to appliances. Table 16.1-1 shows the various product functional forms, along with examples in major application areas. Examples highlighted in italic are those discussed in this book. Most small molecules such as BTX (benzene-toluene-xyxlene) are sold to chemical and allied products industries while a limited number such as refrigerants and solvents are for sale in the consumer market. In contrast, multicomponent liquid mixtures such as liquid shampoo, semi-solids such as cream and paste, and structured solids such as controlled release herbicide are often sold directly to the consumers. Business-to-consumer sale is even more prevalent for ready-to-use devices and appliances such as diagnostic kits, drinking water filters and air cleaners. 

U.S. Patent 4,093,633 (1978)], and maximum-boiling azeotropes of hydrogen chloride-water and formic acid-water (Horsley, Azeotropic Data-III, American Chemical Society, Washington, 1983). Since distillation boundaries move with pressure-sensitive azeotropes, the pressureswing principle can also be used for overcoming distillation boundaries in multicomponent azeotropic mixtures. 

The present paper is devoted to the local composition of liquid mixtures calculated in the framework of the Kirkwood—Buff theory of solutions. A new method is suggested to calculate the excess (or deficit) number of various molecules around a selected (central) molecule in binary and multicomponent liquid mixtures in terms of measurable macroscopic thermodynamic quantities, such as the derivatives of the chemical potentials with respect to concentrations, the isothermal compressibility, and the partial molar volumes. This method accounts for an inaccessible volume due to the presence of a central molecule and is applied to binary and ternary mixtures. For the ideal binary mixture it is shown that because of the difference in the volumes of the pure components there is an excess (or deficit) number of different molecules around a central molecule. The excess (or deficit) becomes zero when the components of the ideal binary mixture have the same volume. The new method is also applied to methanol + water and 2-propanol -I- water mixtures. In the case of the 2-propanol + water mixture, the new method, in contrast to the other ones, indicates that clusters dominated by 2-propanol disappear at high alcohol mole fractions, in agreement with experimental observations. Finally, it is shown that the application of the new procedure to the ternary mixture water/protein/cosolvent at infinite dilution of the protein led to almost the same results as the methods involving a reference state. 

Another method suggested by the authors for predicting the solubility of gases and large molecules such as the proteins, drugs and other biomolecules in a mixed solvent is based on the Kirkwood-Buff theory of solutions [18]. This theory connects the macroscopic properties of solutions, such as the isothermal compressibility, the derivatives of the chemical potentials with respect to the concentration and the partial molar volumes to their microscopic characteristics in the form of spatial integrals involving the radial distribution function. This theory allowed one to extract some microscopic characteristics of mixtures from measurable thermodynamic quantities. The present authors employed the Kirkwood-Buff theory of solution to obtain expressions for the derivatives of the activity coefficients in ternary [19] and multicomponent [20] mixtures with respect to the mole fractions. These expressions for the derivatives of the activity coefficients were used to predict the solubilities of various solutes in aqueous mixed solvents, namely ... 

Livermore, A., Laing, D. G. 1998. "The Influence of Chemical Complexity on the Perception of Multicomponent Odor Mixtures." Perception and Pschophysics, 60 650-661. 

The kinetics of emulsion polymerization reactions are complex because of the numerous chemical and physical phenomena that can occur in the multicomponent, multiphase mixture. A large amount of literature exists on kinetics problems. The general references listed at the end of this chapter contain many important papers. The review paper by Ugelstad and Hansen (11) is a comprehensive treatment of batch kinetics. The purpose of the remainder of this chapter is to present the general kinetics problems and some of the published results. The reader should use the references cited earlier for a more detailed study. 

Step 12. Use the thermal energy and mass balances for multicomponent reactive mixtures to analyze diffusion and chemical reaction in nonisothermal catalytic pellets. 

Dejanovic, L, Matijasevicc, L.J., Halvorsen, I.J., et al. (2011) Designing four-product dividing wall columns for separation of a multicomponent aromatics mixture. Chemical Engineering Research and Design, 89, 1155-1167. 

When a multicomponent fluid mixture is nonideal, its separation by a sequence of ordinaiy distillation columns will not be technically and/or economically feasible if relative volatiK-ties between key components drop below 1.05 and, particularly, if azeotropes are formed. For such mixtures, separation is most commonly achieved by sequences comprised of ordinary distillation columns, enhanced distillation columns, and/or liquid-liquid extraction equipment. Membrane and adsorption separations can also be incorporated into separation sequences, but their use is much less common. Enhanced distillation operations include extractive distillation, homogeneous azeotropic distillation, heterogeneous azeotropic distillation, pressure-swing distillation, and reactive distillation. These operations are considered in detail in Perry s Chemical Engineers Handbook (Perry and Green, 1997) and by Seader... 

Engineering systems mainly involve a single-phase multicomponent fluid mixture with fluid friction, heat transfer, mass transfer, and a number of chemical reactions. A local thermodynamic state of the fluid is specified by two intensive parameters, for example, velocity of the fluid and the chemical composition in terms of component mass fractions. For a unique description of the system, balance equations must be derived for the mass, momentum, energy, and entropy. The balance equations, considered on a per unit volume basis. 

Distillation is still the most common unit operation to separate liquid mixtures in chemical and petroleum industry because the treatment of large product streams and high purities with a simple process design is possible. Despite of this the separation of azeotropic mixtures into pure components requires complex distillation steps and/or the use of an entrainer. Industrial applied processes are azeotropic, extractive or pressure swing distillation (Stichlmair and Fair, 1998). Another sophisticated method for the separation of binary or multicomponent azeotropic mixtures is the hybrid membrane process, consisting of a distillation column and a membrane unit. 

Keywords Mathematical modeling Numerical methods Plasma-chemical etching technology Multicomponent gas mixtures... 

Semi-continuous mixtures form a category in between the continuous chemical mixtures and the ordinary multicomponent mixtures. For example, solvents in a polymer solution or light hydrocarbons in a gas-condensate system can be described by discrete concentrations or mole fractions, whereas the continuous components are described by a density or distribution function approach as just outlined. For an introduction to such systems and the basics of calculation procedures needed to describe separation, consult Cotterman et al. (1985) and Cotterman and Prausnitz (1985). 

More recently, Solsvik and Jakobsen [140] performed a numerical study comparing several closures for mass diffusion fluxes of multicomponent gas mixtures the Wilke, Maxwell-Stefan, dusty gas, and Wilke-Bosanquet models, on the level of the single catalyst pellet and the impacts of the mass diffusion flux closures employed for the pellet, on the reactor performance. For this investigation, the methanol synthesis operated in a fixed packed bed reactor was the chemical process adopted. In the mathematical modeling study of a novel combined catalyst/sorbent pellet. Rout et al. [121] investigated the performance of the sorption-enhanced steam methane reforming (SE-SMR) process at the level of a single pellet. Different closures... 

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