The curious behavior of homogeneous azeotropic distillation—implications for entrainer selection

-This paper provides a feasibility study of azeotropic mixture separation based on a topological analysis combining thermodynamic knowledge of residue curve maps, univolatility and unidistribution curves, and extractive profiles. Thermodynamic topological features related to process operations for typical ternary diagram classes 1.0-2 are, for the first time, discussed. Separating acetone/chloroform is presented as an illustrative example; different entrainers are investigated: several heavy ones, a light one, and water, covering the Serafimov classes 1.0-2, 1.0-1a and 3.1-4, respectively. The general feasibility criterion that was previously established for ternary mixtures including only one azeotrope (1.0-1a or 1.0-2) is now, for the first time, extended to that including three azeotropes (class 3.1-4).

Section: Introductionmentioning

confidence: 99%

Thermodynamic Topological Analysis of Extractive Distillation of Maximum Boiling Azeotropes

Shen

Benyounes

Song

2015

“…After studying more than 400 couples of azeotrope -entrainer systems, Laroche et al (1992) concluded that: (1) light entrainers, even though rare in industrial practice, could be as common as heavy entrainers theoretically since it is as easy to find a potential light entrainer as a heavy one; (2) light entrainers often represent the only viable alternative when a heavy entrainer cannot be used; and (3) light entrainers can perform as well or better than heavy entrainers.…”

Section: State Of the Art With Light Entrainermentioning

confidence: 99%

Conceptual Design of Non-Ideal Mixture Separation With Light Entrainers

Shen

Benyounes

Dong

et al. 2016

-A method is proposed to study the separation of minimum-, maximum-boiling azeotropic, and low volatility mixtures with a light entrainer, to investigate feasible regions of the key operating parameters reboil ratio (S) and entrainer -feed flowrate ratio (F E /F) for continuous processes. The thermodynamic topological predictions are carried out for 1.0-2, 1.0-1a, and 0.0-1 Serafimov's class diagrams. It relies upon the knowledge of residue curve maps, along with the univolatility line, and it enables the prediction of possible products at the bottom of the column and limiting values of F E /F. The profiles of the stripping, extractive, and rectifying sections are calculated by equations considering S and F E /F, and they bring information about the location of singular points and possible composition profile separatrices that could impair process feasibility. Providing specified product composition and recovery, the approximate calculations are compared with rigorous simulations of extractive distillation processes. Separating non-ideal mixtures using a light entrainer provides more opportunities for the case when it is not easy to find an appropriate heavy or intermediate entrainer.

“…Figure 6(a) shows that, as the distance between the two feed stages increases, the purity of the distillate decreases; furthermore, it shows that the best separation between stages is one, but also that the best thing to do is to refrain from performing the flow split, since this will cause a decrease in the purity of ethanol being produced. The theory indicates that the distance between the two feed stages must be as large as possible, so that the solvent is present throughout most of the column at the concentration to break the azeotrope (Laroche et al, 1992;Knapp et al, 1994). But also a rectifying section is required in order to obtain ethanol, so it is not recommended to set the feed at the top (Rodriguez-Donis et al, 2009).…”

Section: Effect Of the Separating Agent Feed Stage And Flow Splitmentioning

confidence: 99%

Simulation of ethanol extractive distillation with mixed glycols as separating agent

Gil

García

Rodríguez

2014

-Extractive distillation is an alternative for ethanol dehydration processes that has been shown to be more effective than azeotropic distillation and, in close proximity, to be very competitive against the process that uses adsorption with molecular sieves. Glycols have been shown to be the most effective solvents in extractive distillation, mainly ethylene glycol and glycerol. In this work, an extractive distillation column was simulated with the Aspen Plus software platform, using the RadFrac module for distillation columns, to investigate the effect on the separation of the ethylene glycol-glycerol mixture composition, the separating agent feed stages, the separating agent split stream feed, and the azeotropic feed temperature. The NRTL model was used to calculate the phase equilibrium of these strongly polar mixtures. A rigorous simulation of the extractive distillation column finally established was also performed, including a secondary recovery column for the mixture of solvents and a recycle loop, to simulate an industrially relevant situation. This simulation allowed establishing the complete parameters to dehydrate ethanol: the optimal stage for separating agent feed is stage 4; the most adequate composition for the glycols mixture is 60 mol% ethylene glycol and 40 mol% glycerol. Finally, energetically efficient operating conditions for each one of the columns were established through a preliminary pinch analysis.