Heteroazeotrope
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A heteroazeotrope is an azeotrope where the vapour phase coexists with two liquid phases. Sketch of a T-x/y equilibrium curve of a typical heteroazeotropic mixture
Examples of heteroazeotropes
- Benzene - Water NBP 69.2 °C
- Dichloromethane - Water NBP 38.5 °C
- Butanol - Water NBP 93.5 °C
Continuous heteroazeotropic distillation
Heterogeneous distillation means that during the distillation the liquid phase of the mixture is immiscibility. In this case on the plates can be two liquid phases and the top vapour condesated splits two liquid phases, which can be separated in a decanter. The simplest case of continuous heteroazeotropic distillation is the separation of a binary heterogeneous azeotropic mixture. In this case the system contains two columns and a decanter. The fresh feed (A-B) be added into the first column. (The feed may also be added into the decanter directly or the into the second column depending on the composition of the mixture.) From the decanter the A-rich phase is withdrawn as reflux into the first column while the B-rich phase is withdrawn as reflux into the second column. This mean the first column produces "A" and the second column produces "B" as a bottoms product. In the industrial the butanol-water mixture is separated with this technique. Image:Conti hetero 1.png
At the previously case the binary system forms already heterogeneous azeotrope. The other application of the heteroazeotropic distillation, when binary system (A-B) forms homogeneous azeotrope and an entrainer or solvent is added to the mixture in order to form an heteroazeotrope with one or both of the components in order to help the separation of the original A-B mixture. The system became then ternary.
Batch heteroazeotropic distillation
Batch heteroazeotropic distillation is an efficient method for the separation of azeotropic and low relative volatility (low α) mixtures. A third component (entrainer, E) is added to the binary A-B mixture, which makes the separation of A and B possible. The entrainer forms a heteroazeotrope with at least one (and preferably with only one (selective entrainer)) of the original components. The main parts of the conventional batch distillation columns are the followings: - pot (inlude reboiler) - column - condenser to condesate the top vapour - product receivers - (entrianer fed) In case of the heteroazeotropic distillation the equipment is completed with a decanter, where the two liquid phases are splitted.
Three different cases are possible for the addition of the entrainer:
1, Batch Addition of the Entrainer: The total quantity of the entrainer is added to the charge before the start of the procedure.
2, Continuous Entrainer Feeding: The total quantity of the entrainer is introduced continuously to the column.
3, Mixed Addition of the Entrainer: The combination of the batch addition and continuous feeding of the entrainer. We added one part of the entrainer to the charge before the start of the distillation and the other part continuously during distillation.
In the last years the batch heteroazeotropic distillation comes into prominenece so several studies were published. The heteroazeotropic batch distillation was investigaed by feasibilty studies, rigorous simulation calculations and laboratory experiments. Feasibility analysis is conducted in Modla et al. [1][1] and Rodriguez-Donis et al. [1] for the separation of low-relative-volatility and azeotropic mixtures by heterogeneous batch distillation in a batch rectifier. Rodriguez-Donis et al. [1] were the first to provide the entrainer selection rules. The feasibility methods was extended and modified by Rodriguez-Donis et al., [1], Rodriguez-Donis et al., (2005), Skouras et al [1],[1] and Lang and Modla [1]. Varga [1]applied these feasibility studies in her thesis. Experimental result was published by Rodriguez-Donis et al. [1], Xu and Wand [1], Van Kaam [1] and others.
References
See also
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
