Batch Distillation

Batch Distillation

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Batch Distillation

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1. Batch Distillation Pharmaceutical API Process Development and Design

3. Distillation Used for separating a mixture of two or more liquids Takes advantage of the differences in volatilities (vapor pressure) For a binary mixture,

4. VLE Curve and BP/DP Curves

5. Homogeneous Azeotropes

6. Homogeneous Azeotropes

7. Heterogeneous Azeotropes

8. Thermo Properties Calculations Important properties of pure components, mixtures Vapor liquid equilibria Y-X diagrams, T-X, T-Y diagrams Existence of multiple liquid phases Commercial packages Part of process simulators Activity++, PPDS etc Helps you identify distillation boundaries

9. Rayleigh Distillation

10. Rayleigh Distillation (Contd) For binary mixture when ?ij is constant

11. Batch Evaporation

12. Batch Evaporation Example

13. Batch Distillation Preferred method for separation when Feed quantities are small Feed composition varies widely Product purity specification change with time High purity streams are required Product tracking is important Feed has solids

14. Batch Distillation Advantages Advantages Flexible Accurate implementation of recipe specific to a given mixture Several components separated using one column Requires least amount of capital

15. Conventional Batch Distillation Column

16. Column Configurations

17. Column Configurations

18. Dual Column Configuration Side stream from the main column fed to a second column Can be used for mixtures with 3 or more components Take advantage of the build up of medium volatile component in the column Eliminate slop cut Reduce cycle time, energy consumption

19. Column Operation Start-up period Vapor boilup rate policy Constant vapor boilup rate Constant condenser vapor load Constant distillate rate Constant reboiler duty Product period: Reflux ratio policy Shutdown period

20. Column Operation Operate under total reflux until the column reaches steady state (L / V = 1, R = ? ) Change reflux ratio to the desired value Collect distillate in accumulator End the ?cut? when certain criteria are satisfied Duration Condenser composition Accumulator composition, amount Reboiler composition, amount

21. Effect of Reflux Ratio Increasing reflux ratio Improves separation Increases cycle time Increases energy consumption Profile optimization Trade-off between cycle time and value of recovered material Maximize profit

22. Staged Separation

23. Packed Columns HETP ? Height equivalent to one theoretical plate Characteristic of packing Number of plates = packed bed height/HETP

24. Simulation of Batch Distillation Simulation of startup period Simulation of product period Column model Examples Benzene?toluene Benzene?toluene?ortho-xylene Acetone?chloroform

25. Simulation of Start-up Period Dynamics of column during start-up are very difficult to model Rigorous model of tray hydraulics Rigorous model of heating column internals Typical simulation of start-up period Run column under total reflux until column reaches steady state At the beginning, assume that liquid compositions on plates and in the condenser are same as feed composition

26. Simulation of Product Period Total condenser without sub-cooling Perfect mixing of liquid and vapor on plates Negligible heat losses Condenser material balance

27. Column Model Mass balance equations on plate j

28. Column Model (Contd) Enthalpy balance equations on plate j

29. Solution of Dynamic Model Vapor boilup rate from plate 1 is constant Quasi steady-state approximation During a small time interval, plate temperature, K values, vapor and liquid flowrates remain constant Solve the set of ODEs numerically up to the next update interval After each update interval, recompute bubble point, K values, plate enthalpies Vapor compositions Reboiler composition from mass balance Liquid and vapor flowrates from enthalpy derivatives

30. Benzene?Toluene Distillation Equimolar mixture of Benzene and Toluene 8000 liters charge Vapor boilup rate 20 kmol/hr Number of plates = 20 Plate holdup 4 liters Condenser holdup 180 liters Recover 99% mole fr Benzene and Toluene Simulated using BDIST-SimOpt Uses Activity++ physical properties package

34. Benzene?Toluene?O-Xylene

35. Acetone?Chloroform

37. Use of Simulation in Batch Distillation Synthesis of operating recipe and rapid characterization of batch distillations Accurate determination of operating and design parameters of a batch column Use in column operation to determine cut amounts and switching policy for each batch

38. Role of Simulation in Column Operation

39. Problems Related to Batch Distillation Design of a batch column Operating policy determination for individual column batches Design and operation issues are interdependent

40. Design of Batch Columns Main design parameters Number of stages Vapor boilup rate Diameter Still capacity (batch size) Reboiler and condenser size heat transfer areas Single separation duty Multiple separation duties

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