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

2. Presentation Outline ØProject objective ØThe multivessel batch column ØThe model ØSimulation results System 1: Serafimov’s topological class 1.0-2 System 2: Serafimov’s topological class 1.0-1a ØDiscussion ØConclusions ØFuture plans N T N U International Conference on Distillation & Absorption 2002, Baden-Baden

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

4. The Multivessel Batch Column Characteristics: ØBatch column Ø2 sections and 3 vessels ØClosed (total reflux) operation ØVapor bypass configuration ØIndirect level control in the vessels with TCs Why multivessel column? ØSimple to operate. No off-cut fractions. Column ‘runs by itself’ ØTernary mixtures separated simultaneously in one closed operation. Final products accumulated in the 3 vessels ØEnergy (time) savings due to the multieffect nature of the operation. N T N U International Conference on Distillation & Absorption 2002, Baden-Baden

5. The Model ØStaged column model, 25 stages in each section ØNo vapor holdup - constant liquid holdup ØConstant vapor flows - liquid flows from the T-controllers ØPerfect mixing and equilibrium at all stages Ideal vapor phase VLE from UNIQUAC LLE from experimental data ØAtmospheric pressure P = 1.013 bar ØSimulations performed in MATLAB N T N U International Conference on Distillation & Absorption 2002, Baden-Baden

6. System 1: Serafimov’s topological class 1.0-2 DISTILLATION LINES MAP ØOne binary heteroazeotrope ØOne distillation boundary (unstable separatrix) ØTwo distillation regions ØFinal 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 N T N U International Conference on Distillation & Absorption 2002, Baden-Baden

7. Simulations Step 1: Built up the composition profile ØFeed F in the left feed region ØMethanol in the top (unstable node) ØHeteroazeotrope in the middle (saddle) Ø1-Butanol in the bottom vessel (stable node) N T N U International Conference on Distillation & Absorption 2002, Baden-Baden

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

9. System 2: Serafimov’s topological class 1.0-1a DISTILLATION LINES MAP ØOne binary heteroazeotrope ØNo distillation boundary ØFinal products in the vessels depend on the feed N T N U International Conference on Distillation & Absorption 2002, Baden-Baden 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. Simulations Step 1: Built-up the composition profile ØFeed F in the upper feed region ØHeteroazeotrope in the top (unstable node) ØEthyl Acetate (EtAc) in the middle (saddle) ØAcetic Acid (AcAc) in the bottom (stable node) N T N U International Conference on Distillation & Absorption 2002, Baden-Baden

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

12. Discussion ØA combination of the closed multivessel batch column with a decanter was proposed for the separation of ternary heteroazeotropes ØSeparation of two classes of heteroazeotropes was studied. Both of them can be separated in the novel column ØThe decanter can be placed either in the middle (internal) or in the top of the column, according to the nature (class) of the mixture ØPart 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 ØFinal products accumulated in the vessels at the end of the process ØThe novel process is simple, there is no need for off-cut fractions and the column runs almost ‘by itself’ N T N U International Conference on Distillation & Absorption 2002, Baden-Baden

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

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

15. Serafimov’s classification ØSerafimov’s work back in the late 60’s in USSR Ø26 classes of feasible topological structures of VLE diagrams ØResults 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 ØMore material: PhD thesis (2000) by E. K. Hilmen., Chapter 3 Available at: www.chembio.ntnu.no/users/skoge/publications/thesis/2000/hilmen N T N U International Conference on Distillation & Absorption 2002, Baden-Baden