Extension of Thermodynamic Insights on Batch Extractive Distillation to Continuous Operation. 1. Azeotropic Mixtures with a Heavy Entrainer

Abstract

We have studied the batch and continuous extractive distillation of minimum-and maximum-boiling azeotropic mixtures with a heavy entrainer. These systems exhibit class 1.0-1a and 1.0-2 ternary diagrams, each with two subcases depending on the location of the univolatility line. The feasible product and feasible ranges of the operating parameters reflux ratio (R) and entrainer/feed flow rate ratio for continuous (F E /F) and batch (F E /V) operation were assessed. Class 1.0-1a processes allow the recovery of only one product because of the location of the univolatility line above a minimum value of the entrainer/feed flow rate ratio for both batch and continuous processes. A minimum reflux ratio R also exists. For an identical target purity, the minimum feed ratio is higher for the continuous process than for the batch process, for the continuous process where stricter feasible conditions arise because the composition profile of the stripping section must intersect that of the extractive section. Class 1.0-2 mixtures allow either A or B to be obtained as a product, depending on the feed location. Then, the univolatility line location sets limiting values for either the maximum or minimum of the feed ratio F E /F. Again, the feasible range of operating parameters for the continuous process is smaller than that for the batch process. Entrainer comparison in terms of minimum reflux ratio and minimum entrainer/feed ratio is enabled by the proposed methodology.

Thermodynamic Topological Analysis of Extractive Distillation of Maximum Boiling Azeotropes

“…The separation of the maximum-boiling mixture acetone/chloroform with the proposed solvents exhibit class 1.0-1a, 1.0-2, and 3.1-4. The thermodynamic insights published in previous work (Shen et al, 2013a;Benyounes et al, 2014;Benyahia et al, 2014;Lelkes et al, 2002;Lang et al, 1999;Rodriguez-Donis et al, 2012;Shen et al, Gerbaud, 2013b) and validated for the 1.0-1a and 1.0-2 ternary mixture class are applied here, and the general feasibility criterion 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).…”

“…A heavy entrainer E has a boiling temperature higher than A and B; an intermediate entrainer E has a boiling temperature between the A and B; a light entrainer E has a boiling temperature lower than A and B. In industry, the extractive distillation entrainer is usually chosen as heavy (high boiling) component mixtures (Luyben and Chien, 2010;Lang et al, 1994;Rodriguez-Donis, 2009;Shen 2012;Shen et al, 2013a;Benyounes et al, 2014;Benyahia et al, 2014). Theoretically, any candidate entrainer satisfying the feasibility and optimal criteria can be used, no matter whether it is a heavy, light, or intermediate entrainer.…”

Conceptual Design of Non-Ideal Mixture Separation With Light Entrainers

“…Laroche et al (1991) investigated the use of heavy, intermediate, and light boiling entrainers to separate minimumboiling azeotropes. In a batch operation, a recently published paper reviewed the use of these three kinds of entrainers to separate maximum-boiling azeotropes and low relative volatility mixtures (Rodriguez-Donis et al, 2009a,b;Rodriguez-Donis et al, 2012a,b;Shen et al, 2013aShen et al, ,b,2015. However, Rodriguez-Donis et al (2012a) mainly focused on thermodynamic topological insight of how knowledge of the location of univolatility lines and residue curve analysis help in assessing the feasibility of batch extractive distillation.…”

Extractive Distillation Process Optimisation of the 1.0-1a Class System, Acetone - methanol with Water

“…Hot topics of extractive distillation are focused on two main issues: entrainer selection and process optimisation. The entrainer selection issue for the separation of all non-ideal zeotropic or azeotropic mixtures with heavy, light or intermediate entrainer, and how it sets the attainable products and process configuration is now well understood, though the combined analysis of residue curve maps and univolatility curve location (Shen et al, 2012). Here we focus on the most frequent case, the separation of a minimum boiling azeotrope acetone -methanol with a heavy entrainer water, corresponding to the (1.0-1a) extractive class separation (Rodriguez-Donis et al, 2009).…”