Proposal for the introduction of the concept of multiplicity of solutions in steady-state distillation problems in the syllabus of separation processes |
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| Affiliation: | 1. Department of Process Engineering, Faculty of Engineering, Stellenbosch University, Banghoek Road, Stellenbosch, South Africa;2. SARChI Work-Integrated Learning Research Unit, Cape Peninsula University of Technology, South Africa;1. Department of Chemical Engineering, School of Engineering, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain;2. Department of Chemical and Biomolecular Engineering, School of Engineering, Universidad de Cantabria, E-39005 Santander, Spain;3. Department of Chemical and Environmental Engineering, School of Engineering and Architecture (EINA), Universidad de Zaragoza, E-50018 Zaragoza, Spain;4. Department of Chemical Engineering, Universidad de Huelva, Huelva, Spain;5. Department of Chemical Engineering, Faculty of Science, Universidad Autónoma de Madrid, Madrid, Spain;6. IQS School of Engineering, Universitat Ramon Llull, Barcelona, Spain;7. Department of Chemical Engineering, Universitat Politècnica de València, E-03801 Alcoy, Spain;1. Department of Chemical Engineering, UNTAG University in Semarang, Bendhan Dhuwur Campus, Semarang 50233, Indonesia;2. Mechanical Engineering Graduate Program, DIPONEGORO University, Tembalang Campus, Semarang 50275, Indonesia;3. Chemical Engineering Vocational School, DIPONEGORO University, Tembalang Campus, Semarang 50275, Indonesia |
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| Abstract: | The existence of multiplicity in steady-state separation problems based on the use of equilibrium stage cascades has been known since the second half of the 20th century. Nevertheless, there are few textbooks -among those usually accessible to Chemical Engineering students- explaining this behavior and even when it is considered it is not deeply treated. In this work, we propose a distillation problem whose resolution allows the instructor the opportunity to introduce some specific characteristics and behavior that may otherwise pass unnoticed. Thus, the simulation of a column for the heterogeneous azeotropic distillation of ethanol using benzene as an entrainer is suggested, and the results obtained do not seem to be compatible with the distillation boundaries of the ternary system. The apparent contradictions can be explained by means of the representation of mass balances on the residue curve map, and allow the students to actually understand the requirements for the feasibility of the separation. The obtainment of two different solutions depending on the initial composition profiles used for starting the calculations allows the instructor to introduce the steady-state multiplicity concept. Errors associated with bad checking of the thermodynamic model are also pointed out. |
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| Keywords: | Azeotropic distillation Multiplicity Residue curve maps Steady-state Thermodynamic model |
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