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Separation of Ternary Heteroazeotropic Mixtures in a Closed Multivessel Batch Distillation Column

N T N U. International Conference on Distillation & Absorption 30 September - 2 October 2002, Baden - Baden, Germany. Separation of Ternary Heteroazeotropic Mixtures in a Closed Multivessel Batch Distillation Column. Stathis Skouras and Sigurd Skogestad. N T N U.

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Separation of Ternary Heteroazeotropic Mixtures in a Closed Multivessel Batch Distillation Column

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  1. N T N U International Conference on Distillation & Absorption 30 September - 2 October 2002, Baden - Baden, Germany Separation of Ternary Heteroazeotropic Mixtures in a Closed Multivessel Batch Distillation Column Stathis Skouras and Sigurd Skogestad

  2. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden Presentation Outline • Project objective • The multivessel batch column • The model • Simulation results • System 1: Serafimov’s topological class 1.0-2 • System 2: Serafimov’s topological class 1.0-1a • Discussion • Conclusions • Future plans

  3. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden Project Objective • Is it feasible to separate heteroazeotropic mixtures in the closed multivessel batch column? • What kind of heteroazeotropes can be separated in the novel column?

  4. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden The Multivessel Batch Column Characteristics: • Batch column • 2 sections and 3 vessels • Closed (total reflux) operation • Vapor bypass configuration • Indirect level control in the vessels with TCs Why multivessel column? • Simple to operate. No off-cut fractions. Column ‘runs by itself’ • Ternary mixtures separated simultaneously in one closed operation. Final products accumulated in the 3 vessels • Energy (time) savings due to the multieffect nature of the operation.

  5. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden The Model • Staged column model, 25 stages in each section • No vapor holdup - constant liquid holdup • Constant vapor flows - liquid flows from the T-controllers • Perfect mixing and equilibrium at all stages • Ideal vapor phase • VLE from UNIQUAC • LLE from experimental data • Atmospheric pressure P = 1.013 bar • Simulations performed in MATLAB

  6. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden System 1:Serafimov’s topological class 1.0-2 DISTILLATION LINES MAP • One binary heteroazeotrope • One distillation boundary (unstable separatrix) • Two distillation regions • Final products in the vessels depend on the feed The problem Not all 3 original components can be recovered by simple distillation The idea The boundary is crossed by decantation and all 3 original components are recovered in a distillation-decanter hybrid

  7. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden Simulations Step 1: Built up the composition profile • FeedF in the left feed region • Methanol in the top (unstable node) • Heteroazeotrope in the middle (saddle) • 1-Butanol in the bottom vessel (stable node)

  8. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden Simulations Step 2: Decant-Reflux the organic phase • Decanter at the middle of the column (internal) • Split the heteroazeotrope in the decanter • Reflux the organic phase in the column • Direct level control in the decanter

  9. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden System 2: Serafimov’s topological class 1.0-1a DISTILLATION LINES MAP • One binary heteroazeotrope • No distillation boundary • Final products in the vessels depend on the feed The problem Separation stops because of the heteroazotrope accumulation in the top The idea The liquid-liquid split is used to overcome the azeotropic composition, thus enhancing the separation of the original mixture

  10. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden Simulations Step 1: Built-up the composition profile • Feed F in the upper feed region • Heteroazeotrope in the top (unstable node) • Ethyl Acetate (EtAc) in the middle (saddle) • Acetic Acid (AcAc) in the bottom (stable node)

  11. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden Simulations Step 2: Decant-Reflux the organic phase • Decanter at the top of the column • Split the heteroazeotrope in the decanter • Reflux the organic phase in the column • Direct level control in the decanter

  12. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden Discussion • A combination of the closed multivessel batch column with a decanter was proposed for the separation of ternary heteroazeotropes • Separation of two classes of heteroazeotropes was studied. Both of them can be separated in the novel column • The decanter can be placed either in the middle (internal) or in the top of the column, according to the nature (class) of the mixture • Part of the separation is accomplished by distillation, while the liquid-liquid split in the decanter is used for crossing the distillation boundary and overcoming the azeotropic composition • Final products accumulated in the vessels at the end of the process • The novel process is simple, there is no need for off-cut fractions and the column runs almost ‘by itself’

  13. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden Conclusions • Separation of heteroazeotropic mixtures is feasible in a closed multivessel batch distillation decanter hybrid • Systems belonging to Serafimov’s topological classes 1.0-2 and 1.0-1a can be separated in the proposed novel process

  14. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden Future Plans • Which other azeotropic classes can be separated in the proposed column? • System Water-Acetic Acid-Butyl Acetate belongs to Serafimov’s class 1.0-1b. Can it be separated? • Experimental verification of our simulation results • Energy (time) savings of the proposed process compared to conventional batch configurations e.g. batch rectifier?

  15. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden Serafimov’s classification • Serafimov’s work back in the late 60’s in USSR • 26 classes of feasible topological structures of VLE diagrams • Results presented again in 1996: • Serafimov, L.A., (1996). “Thermodynamic and Topological Analysis of Liquid-Vapor Phase Equilibrium Diagram and Problems of Rectification of Multicomponent Mixtures”, Book: Mathematical Methods in Contemporary Chemistry, S.I. Kuchanov (Ed.) Gordon and breach Publishers, Amsterdam, 557-605 • More material: • PhD thesis (2000) by E. K. Hilmen., Chapter 3 • Available at: www.chembio.ntnu.no/users/skoge/publications/thesis/2000/hilmen

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