US EPA

1632704 

Journal Article 

Critical reflux, parametric sensitivity, and hysteresis in azeotropic distillation of isopropyl alcohol plus water plus cyclohexane 

Wang, CJ; Wong, DSH; Chien, IL; Shih, RF; Liu, WT; Tsai, CS 

1998 

Yes 

Industrial and Engineering Chemistry Research
ISSN: 0888-5885
EISSN: 1520-5045 

37 

7 

2835-2843 

English 

10.1021/ie970855t 

WOS:000074704500031 

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 degrees 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.