Experimental Measurement of the Saddle Node Region in a Distillation Column Profile Map by Using a Batch Apparatus

• Published in: Chemical engineering research & design 2007, Vol.85 (1), p.24-30
• Main Authors: Modise, T., Kauchali, S., Hildebrandt, D., Glasser, D.
• Format: Article
• Language: English
• Subjects: Applied sciences; azeotropes; Chemical engineering; column profiles; distillate; Distillation; distillation boundary; Exact sciences and technology; pinch point curve
• ISSN: 0263-8762
• DOI: 10.1205/cherd06107

A simple theoretical method for the evaluation of the separation of mixtures using distillation columns operating at finite reflux, called column profile maps (CPMs), has been developed (Tapp et al., 2004). These CPMs are simply transforms of the residue curve maps (RCMs) and are used for sequencing and synthesis of distillation columns. Thus for example, the methanol, diethyl ether and benzene system has a low boiling azeotrope between methanol and benzene which appears as a saddle point in the RCM. As a result the RCM has two stable nodes and hence two distillation regions divided by a simple distillation boundary. It can be theoretically shown that the transformation of the CPM moves the saddle point that was on the boundary of the mass balance triangle in the RCM into the mass balance triangle of the CPM. Similarly the two stable nodes, corresponding to pure component nodes, in the RCM move out of the mass balance triangle of the CPM. The CPM of this system was experimentally evaluated to verify that a saddle point node does indeed occur inside the mass balance triangle. The experimental technique uses a semi-batch apparatus and measures the boiling liquid concentration in the still as a function of time (Modise et al., 2005). The importance of this is that concentration profiles achieved in the semi-batch still are essentially the same as those of a continuous distillation column section. The experimental measurements showed that there is indeed a saddle point in the CPM.