• Khyati Jain

    The extractive distillation unit of this cyclohexane production plant consists of two distillation columns (Figure 10), which we can easily classify as direct sequence columns. The first column acts as an extractive column where the solvent is introduced at the second stage of the column, so that it will be present throughout the column and exits with the bottoms. As were stated above, the solvent alters the natural volatility of the binary mixture by forming hydrogen bonds with benzene and allowing it to be recovered as the bottom product.

    The bottom product of the first column will then fed to the second column, i.e. the solvent recovery column, to undergo the normal distillation to separate both the components for further usage, i.e. benzene being recycled to the reactor for further conversion while solvent to the first column for reuse. The main operation parameter of the distillation unit is shown in Table below

    Unit Operationand Stream

    Description

    Operating Parameters

     

    Distillation Column

     

    T-20

    First column (extractive column)

    Operating pressure: 150 kPa

    Number of trays: 45

    Solvent (str. 27) feed tray: 2Feed (str. 47) tray = 28

    T-21

    Second column (solvent recovery column)

    Operating pressure: 105 kPa

    Number of trays: 20Feed stream: 10

     

    Heat Exchanger

     

    X-22

    Cool down the solvent for recycling

    Outlet temperature: 80 °C

     

    Pump

     

    P-23

    Pump the solvent for recycling

    Outlet pressure: 150 kPa

     

    Stream

     

    Stream 27

    Solvent stream of 1,2-propanediol

    Molar flow rate: 3600 kgmol/h

    Stream 47

    Feed stream

    Molar flow rate: 355.43 kgmol/h

    Stream 28

    Product stream of Column T-20 distillate

    (cyclohexane)

    Molar flow rate: 158.75 kgmol/hwith a purity of 99.3%

    Stream 29

    Benzene solvent stream of bottom productfrom column T-20, fed to solvent recovery

    column T-21

    Molar flow rate: 3795.5 kgmol/hwith a purity of 94.8%

    Stream 30

    Product stream of column T-21 distillate

    (benzene) for recycle

    Molar flow rate: 223.91 kgmol/hwith a purity of 84.96% benzene

    Stream 31

    Solvent stream of bottom product fromcolumn T-21 (solvent) for recycle

    Molar flow rate: 3571.6 kgmol/hwith a purity of 99.87% solvent

    22.jpg

                                                                                                 Figure 10: Extractive Distillation Unit for Cyclohexane Production Plant

     

    22.jpg

    Figure 11: Distillation Ternary Diagram for the Extractive Distillation Unit

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