Multicomponent steam distillation

Steam distillation is a process whereby organic liquids may be separated at temperatures sufficiently low to prevent their thermal decomposition or whereby azeotropes may be broken. Fats or perfume production are examples of applications of this technique. The vapour-liquid equilibria of the three-phase system is simplified by the usual assumption of complete immiscibility of the liquid phases and the validity of the Raoult and Dalton laws. Systems containing more than one volatile component are characterised by complex dynamics (e.g., boiling point is not constant). 

Steam distillation is normally carried out as a semi-batch process whereby the organic mixture is charged into the still and steam is bubbled through continuously, as depicted in Fig. 3.64. 

As discussed, modelled and simulated by Prenosil (1976), the dynamics of the process bring in the question of steam consumption, steam flow rate, starting time of the distillation, and shut-down time when the desired degree of separation has been reached. The modelling of steam distillation often involves the following assumptions. 

1) Ideal behaviour of all components in pure state or mixture. 

3) Zero temperature gradients in the bulk phases (ideal mixing in the boiler). 

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Prenosil, J. E. (1976) Multicomponent Steam Distillation A Comparison between Digital Simulation and Experiment. Chem. Eng. J., 12, 59-68. 

Multicomponent steam distillation is illustrated in simulation example STEAM. 

Steam Distillation—Continuous Flash, Multicomponent or Binary... 

Batch with Constant Reflux Ratio, 48 Batch with Variable Reflux Rate Rectification, 50 Example 8-14 Batch Distillation, Constant Reflux Following the Procedure of Block, 51 Example 8-15 Vapor Boil-up Rate for Fixed Trays, 53 Example 8-16 Binary Batch Differential Distillation, 54 Example 8-17 Multicomponent Batch Distillation, 55 Steam Distillation, 57 Example 8-18 Multicomponent Steam Flash, 59 Example 8-18 Continuous Steam Flash Separation Process — Separation of Non-Volatile Component from Organics, 61 Example 8-20 Open Steam Stripping of Heavy Absorber Rich Oil of Light Hydrocarbon Content, 62 Distillation with Heat Balance,... 

STEAM - Multicomponent, Semi>Batch Steam Distillation... 

Bioremediation of Soil Particles 591 Spouted Bed Reactor Mixing Model 390 Steady-State, Two-Pass Heat Exchanger 515 Multicomponent, Semi-Batch Steam Distillation 508 Space-Time-Yield and Safety in a Semi-Continuous Reactor 365... 

The methods of steam distillation have been summarized by Bernhauer [13] and Thormann [14]. A detailed discussion of practical and theoretical aspects of steam distillation as illustrated by the distillation of essential oils is given by von Weber [15], Rigamonti [16] developed a nomogram which can be used to calculate the steam requirements for various enrichments. Prenosil [16a] compared theoretical and experimental steam distillation data for multicomponent mixtures. He modified the calculating method by introducing a value for evaporation efficiency. Steam distillation can also be carried out in thin-film apparatus. Berkes etal. [16 b] give a description of the material transfer conditions of a steam distillation performed in such apparatus in terms of the balance equations. 

Van Winkle (VI) derives equations for steam distillation where an appreciable amount of a nonvolatile component is present with the high-boiling component. This involves a three-component system. He also considers other cases for binary batch, continuous, and multicomponent batch steam distillation. 

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. 

Uses of Oldershaw columns to less conventional systems and applications were described by Fair, Reeves, and Seibert [Topical Conference on Distillation, AIChE Spring Meeting, New Orleans, p. 27 (March 10-14, 2002)]. The applications described include scale-up in the absence of good VLE, steam stripping efficiencies, individual component efficiencies in multicomponent distillation, determining component behavior in azeotropic separation, and foam testing. 

When operation is under vacuum, however, the performance of the reboiler is sensitive to changes in the liquid driving head, especially in the distillation of multicomponent mixtures. The optimum liquid level for vacuum service is midway between the tube sheets, with about 50 percent of the liquid vaporized per pass. For usual applications with saturated steam on the shell side the heat flux can be estimated from Figure 15.13, which is based on BWG 14 stainless-steel... 

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