Distillation equilibrium data

Chu, Getty, Brennecke, and Paul, Distillation Equilibrium Data, New York, 1950. 

Yu Chin, Distillation Equilibrium Data, 2nd Ed., Reinhold, New York 1956 Chu Wang, Levy and Paul, Vapour Liquid Equilibrium Data, Edwards, T. W., Ann Arbor, Mich. 1956... 

D15. We wish to batch distill 100 kmol of a mixture of n-butanol and water. The system consists of a batch still pot plus 1 equilibrium stage. The system is at one atmosphere. The feed is 48 mol% water and 52 mol% butanol. The distillate vapor is condensed and sent to a liquid-liquid settler. The water rich product (0.975 mole fraction water) is taken as the distillate product and the butanol rich layer (0.573 mole fraction water) is refluxed to the column. We desire a final still pot mole fraction of 0.08 water. Energy is added at a constant rate to the still pot thus, V = constant. Note that the distillate product is a constant mole fraction. The reflux ratio increases as the distillate vapor mole fraction decreases during the course of the batch distillation. Equilibrium data are given in Table 8-2. 

Prausnitz, J. M., and Eckert, C. A. Computer Calculations for Multicomponent Vapor-Liquid-Equilibria. Prentice Hall Inc. Englewood Cliffs N.J. 1967. Prausnitz, J. M., and Chueh, P. L. Computer Calculations for High-Pressure Vapor-Liquid-Equilibria. Prentice Hall Inc., Englewood Cliffs N.J. 1968. Chu, j. C. Distillation Equilibrium Data. Reinhold Publishing Corp., New York 1950. 

A typical apphcatiou of a simple batch still might be distillation of an ethanol-water mixture at 101.3 kPa (1 atm). The initial charge is 100 mol of ethanol at 18 mole percent, aud the mixture must be reduced to a maximum ethanol concentration in the stiU of 6 mole percent. By using equilibrium data interpolated from Table 13-1,... 

Commercial computer services are available to do rigorous distillation calculations. Perhaps the licensor will provide copies of rigorous computer runs to validate his balances. Alternately, the operating company can make such runs. For highly non-ideal systems, literature data for binary pairs may have to be sought. In some cases, laboratory equilibrium data may have to be obtained in-house or contracted out to one of several organizations or universities that are in this business. 

It is essential to calculate, predict or experimentally determine vapor-liquid equilibrium data in order to adequately perform distillation calculations. These data need to relate composition, temperature, and system pressure. 

Equilibrium data correlations can be extremely complex, especially when related to non-ideal multicomponent mixtures, and in order to handle such real life complex simulations, a commercial dynamic simulator with access to a physical property data-base often becomes essential. The approach in this text, is based, however, on the basic concepts of ideal behaviour, as expressed by Henry s law for gas absorption, the use of constant relative volatility values for distillation and constant distribution coeficients for solvent extraction. These have the advantage that they normally enable an explicit method of solution and avoid the more cumbersome iterative types of procedure, which would otherwise be required. Simulation examples in which more complex forms of equilibria are employed are STEAM and BUBBLE. 

Consider the accuracy of the equilibrium data required to calculate the number of equilibrium stages needed for the separation of a mixture of acetone and water by distillation (see Chapter 11, Example 11.2). Several investigators have published vapour-liquid equilibrium data for this system Othmer et al. (1952), York and Holmes (1942), Kojima et al. (1968), Reinders and De Minjer (1947). 

A binary mixture is to be separated by distillation into relatively pure products. Where in the distillation column is the vapor-liquid equilibrium data required at the highest accuracy ... 

An equimolar mixture of benzene and toluene is subjected to flash distillation at 100 kN/m2 in the separator. Using the equilibrium data given in Figure 11.9, determine the composition of the liquid... 

If, for example, a mixture of ethanol and water is distilled, the concentration of the alcohol steadily increases until it reaches 96 per cent by mass, when the composition of the vapour equals that of the liquid, and no further enrichment occurs. This mixture is called an azeotrope, and it cannot be separated by straightforward distillation. Such a condition is shown in the y — x curves of Fig. 11.4 where it is seen that the equilibrium curve crosses the diagonal, indicating the existence of an azeotrope. A large number of azeotropic mixtures have been found, some of which are of great industrial importance, such as water-nitric acid, water-hydrochloric acid, and water-alcohols. The problem of non-ideality is discussed in Section 11.2.4 where the determination of the equilibrium data is considered. When the activity coefficient is greater than unity, giving a positive deviation from Raoult s law, the molecules of the components in the system repel each... 

Figure 4. Equilibrium Data for Light Lubricating Oil Distillate from California Wax-Free Crude in Aqueous Phenol...

The calculational base consists of equilibrium relations and material and energy balances. Equilibrium data for many binary systems are available as tabulations of x vs. y at constant temperature or pressure or in graphical form as on Figure 13.4. Often they can be extended to other pressures or temperatures or expressed in mathematical form as explained in Section 13.1. Sources of equilibrium data are listed in the references. Graphical calculation of distillation problems often is the most convenient... 

Distillation of Ammonium Bicarbonate Solutions. Vapor-liquid equilibrium data for ammonium bicarbonate solutions at the boil are apparently not available in the literature. The data in the literature, however, do indicate that when the temperature of such a solution is increased, or the pressure on it decreased, the gas that is evolved is predominantly carbon dioxide. Thus, it appears that such a distillation would be two consecutive processes first, a steam stripping of the carbon dioxide in the solution, followed by a distillation of ammonia from an ammonia-water mixture containing perhaps some carbon dioxide. Possibly the ammonia, carbon dioxide, and water in the distillate product would recombine completely in the condenser to form an ammonium bicarbonate solution. Perhaps an absorption tower would be necessary to effect the recombination. 

Reflux Rate. The optimum reflux rate for a distillation column depends on the value of energy, but is generally between 1.05 times and 1.25 times the reflux rate, which could be used with infinite trays. At this level, excess reflux is a secondary contributor to column inefficiency. However, when designing to this tolerance, correct vapor—liquid equilibrium data and adequate controls are essential. 

The adsorbent used in this study is Filtrasorb 400 activated carbon obtained from Calgon Corporation, Pittsburg, Pennsylvania. The adsorbent was sieved and the size fraction 30/35 mesh -particles passing 30 mesh sieve and retained on a 35 mesh sieve -was used in all rate studies. Adsorption equilibrium is independent of particle size, and equilibrium data were obtained with both 30/35 and 60/100 mesh size fractions. The carbon was washed in distilled water to remove fines and leachable material and dried to constant weight at 105°C prior to use. 

Fractional distillation and crystallization were the separation methods used in earlier studies of redistribution reactions. Quantitative equilibrium data were obtained first by Calingaert over a quarter of a century ago from an equilibrated mixture of tetraethyllead and tetramethyllead. Fractional distillation showed that, in addition to the starting materials, all three of the expected redistribution products were found in amounts corresponding to random interchange of methyl and ethyl groups on lead. 

For the synthesis of heterogeneous batch distillation the liquid-liquid envelope at the decanter temperature is considered in addition to the residue curve map. Therefore, the binary interaction parameters used in predicting liquid-liquid equilibrium are estimated from binary heterogeneous azeotrope or liquid-liquid equilibrium data [8,10], Table 3 shows the calculated purity of original components in each phase split at 25 °C for all heterogeneous azeotropes reported in Table 1. The thermodynamic models and binary coefficients used in the calculation of the liquid-liquid-vapour equilibrium, liquid-liquid equilibrium at 25 °C and the separatrices are reported in Table 2. 

As for distillation, the thermodynamic data form the basis for the design for absorption and the absorption equilibrium data can be found either tabulated, from correlations or from commercial software. Again, good data is vital to ensure good design. 

Figure 4.7 shows the simulated instant distillate composition profiles by Mujtaba and by that of Nad and Spiegel using nonideal phase equilibrium models. The figure also includes experimentally obtained instant distillate composition data and the adjusted reflux ratio profiles used by Nad and Spiegel and Mujtaba. 

---