Ratebased Models

Although the widely used equilibrium-stage models for distillation, described above, have proved to be quite adequate for binary and close-boiling, ideal and near-ideal multicomponent vapor-liquid mixtures, their deficiencies for general multicomponent mixtures have long been recognized. Even Murphree Ind. Eng. Chem., 17, 747-750 and 960-964 (1925) , who formulated the widely used plate efficiencies that carry his name, pointed out clearly their deficiencies for multicomponent mixtures and when...

100

FIG. 13-75 Number of theoretical stages versus solvent-to-feed ratio for extractive distillation. (a) Close-boiling vinyl acetate-ethyl acetate system with phenol solvent. (b) Azeotropic acetone-methanol system with water solvent. no longer be achieved and the distillate purity actually decreases for a given number of stages LaRoche et al., AIChE J., 38, 1309 (1992) . The difference between Rmin and Rmax increases as the S F ratio increases. Large amounts of reflux lowers the solvent...

Phase Equilibrium Data

For a binary mixture, pressure and temperature fix the equilibrium vapor and liquid compositions. Thus, experimental data are frequently presented in the form of tables of vapor mole fraction y and liquid mole fraction x for one constituent over a range of temperature T for a fixed pressure P or over a range of pressure for a fixed temperature. A compilation of such data, mainly at a pressure of 101.3 kPa (1 atm, 1.013 bar), for binary systems (mainly nonideal) is given in Table 13-1. More...

Extractive Distillation

Introduction Extractive distillation is a partial vaporization process in the presence of a miscible, high-boiling, non-volatile massseparation agent, normally called the solvent, which is added to an azeotropic or nonazeotropic feed mixture to alter the volatilities of the key components without the formation of any additional azeotropes. Extractive distillation is used throughout the petrochemical- and chemical-processing industries for the separation of close-boiling, pinched, or azeotropic...

Applications Of Rcm And

Rcm Curve Distillation

Residue curve maps and distillation region diagrams are very powerful tools for understanding all types of batch and continuous distillation operations, particularly when combined with other information such as liquid-liquid binodal curves. Applications include 1. System visualization. Location of distillation boundaries, azeotropes, distillation regions, feasible products, and liquid-liquid regions. 2. Evaluation of laboratory data. Location and confirmation of saddle ternary azeotropes and a...

Graphical Kvalue Correlations

As discussed in Sec. 4, the K value of a species is a complex function of temperature, pressure, and equilibrium vapor- and liquid-phase compositions. However, for mixtures of compounds of similar molecular structure and size, the K value depends mainly on temperature and pressure. For example, several major graphical K-value correlations are available for light-hydrocarbon systems. The easiest to use are the DePriester charts Chem. Eng. Prog. Symp. Ser. 7, 49, 1 1953 , which cover 12...

Reactive Distillation

Introduction Reactive distillation is a unit operation in which chemical reaction and distillative separation are carried out simultaneously within a fractional distillation apparatus. Reactive distillation may be advantageous for liquid-phase reaction systems when the reaction must be carried out with a large excess of one or more of the reac-tants, when a reaction can be driven to completion by removal of one or more of the products as they are formed, or when the product recovery or...

Insideout Methods

The BP, SR, and SC methods described above expend a large percentage of their computational effort during each iteration in the calculation of K values, enthalpies, and derivatives thereof. An algorithm designed to significantly reduce that effort was developed by Boston and Sullivan Can. J. Chem. Engr., 52, 52 1974 . The MESH equations are solved in an inner loop using simple, approximate equations for K values and enthalpies. The empirical constants in these equations are determined and...

Thielegeddes Stagebystage Method For Simple Distillation

Prior to the availability of digital computers, the most widely used manual methods for rigorous calculations of simple distillation were those of Lewis and Matheson LM Ind. Eng. Chem., 24, 496 1932 and Thiele and Geddes TG Ind. Eng. Chem., 25, 290 1933 , in which the equilibrium-stage equations are solved one by one by using tearing techniques. The former is a design method, in which the number of stages is determined for a specified split between two key components. Thus, it is a rigorous...

Design Procedures

Two general procedures are available for designing fractionators that process petroleum, synthetic crude oils, and complex mixtures. The first, which was originally developed for crude units by Packie Trans. Am. Inst. Chem. Eng. J., 37, 51 1941 , extended to main fractionators by Houghland, Lemieux, and Schreiner Proc. API, sec. III, Refining, 385 1954 , and further elaborated and described in great detail by Watkins op. cit. , utilizes material and energy balances, with empirical correlations...

Rigorous Methods For Multicomponent Distillationtype Separations

Thiele-Geddes Stage-by-Stage Method for Simple Distillation 13-40 Example 3 Calculation of TG Equation-Tearing Procedures Using the Tridiagonal-Matrix Tridiagonal-Matrix BP Method for Example 4 Calculation of the BP Certain portions of this section draw heavily on the work of Buford D. Smith, editor of this section in the fifth edition. SR Method for Absorption and Example 5 Calculation of the SR Simultaneous-Correction Naphtali-Sandholm SC Example 6 Calculation of Naphtali-Sandholm SC Method...