Critical Reflux, Parametric Sensitivity, and Hysteresis in Azeotropic Distillation of Isopropyl Alcohol + Water + Cyclohexane

Abstract

In this work, the characteristics of heterogeneous azeotropic distillation of isopropyl alcohol (IPA) + water (H2O) with cyclohexane (CyH) as an entrainer were investigated. Critical reflux, parametric sensitivity, and hysteresis were found by theoretical analysis and supported by experiment using a laboratory-scale sieve plate distillation column. At each given reflux rate, there are two branches of stable steady states as reboiler duty varies, one with desirable purity and another with almost no separation. The highest attainable purity is achieved at a specific reboiler duty. Beyond this duty there is a catastrophic loss in IPA purity. At higher refluxes, the temperature profiles of the column with highest attainable purity pass around the IPA + CyH azeotrope. A plateau at 69.3 °C characterizes this type of profile. There is little change of highest attainable IPA purity as reflux varies. When reflux is reduced below a critical value, the temperature profile of the column with highest attainable purity passes around the IPA + H2O azeotrope. The highest attainable IPA purity decreases substantially as reflux is reduced. The critical reflux represents an operating state that achieves high IPA purity with minimum energy consumption. Furthermore, at a given pair of reflux and reboiler duty, the steady-state temperature profile that achieves good separation is not unique. The exact position of the temperature front can be fixed at any position inside the column using a cyclic series of step changes in reboiler duty. This hysteresis phenomenon is attributable to changes in entrainer inventory inside the column.

Heat pump assisted reactive and azeotropic distillations in dividing wall columns

“…13. NRTL model is used to describe the non-ideality of the liquid phase, and the related parameters are obtained from Wang et al [21]. The thermodynamically equivalent model of the ADWC developed by the Aspen Plus is shown is Fig.…”

Separation of the Mixture 2-Propanol + Water by Heterogeneous Azeotropic Distillation with Isooctane as an Entrainer

“…Several studies have been published on the subject of HAD, with particular reference to advantages and disadvantages, heterogeneous phase diagrams, residue curve maps and column sequencing [12,[14][15][16][17][18][19][20]. Furthermore, the optimization, dynamics and control of the process configuration have been addressed [21][22][23][24][25][26].…”

“…Further studies on the subject of 2-propanol dehydration processes with cyclohexane or benzene as an entrainer have been published [15,21,22,26,30,40]. In addition, DIPE can be envisaged as a possible entrainer [30], while other studies are related to the potentiality of using isooctane for the separation of 2-propanol + water mixtures [41,42], analysing phase equilibria.…”

“…It is also important to highlight that the use of isooctane as an entrainer can be extremely beneficial in the case of 2-propanol dehydration: traces of such an entrainer do not pose a problem within the recovered dehydrated alcoholic product with a view to its subsequent use as a fuel. [27] New simulation method for three-phase distillation using a modified phase-stability analysis Luyben [24] Process simulation Pienaar [30] Process simulation cyclohexane Gomis et al [45] VLE and VLLE data toluene Gomis et al [62] VLE and VLLE data Zhao et al [31] Process simulation isooctane or 2,2,4-trimethylpentane Cairns and Furzer [27] New simulation method for three-phase distillation using a modified phase-stability analysis Font et al [28] VLE and VLLE data Simulation method 1 Wang et al [26] Experiment using a laboratory-scale sieve plate distillation column; dynamic simulation Chien et al [21] Dynamics and control of a HAD column…”

Experimental Validation of Model-Based Control Strategies for Multicomponent Azeotropic Distillation

“…For these reason, in order to isolate two pure components which lie in two different distillation regions, it is necessary to have two different feed compositions (one from each of the two regions) and two distillation columns (Doherty and Caldarola 1985). Published experimental work on azeotropic distillation has often analyzed the behavior of the azeotropic distillation systems in laboratory scale sieve columns (Baur, et al, 1999;Müller and Marquardt, 1997;Springer and Krishna, 2001;Wang, et al, 1998); in addition, some experimental studies (Chien, et al, 2000) have also implemented different control strategies using temperature as the controlled variable. This work presents the results from experimental validation of dynamic models of an azeotropic distillation system of methanol, normal pentane and cyclohexane.…”