Linear Alkyl benzene (LAB) is produced by the alkylation of benzene with olefins (assuming all dodecane). Raw maw materials: Kerosene and benzene.

The chemical plant design compromises of the Hydrodesulphurization, Pacol, Vapour recovery System, Alkylation reactor and liquid recovery system.

The liquid recovery System consists of benzene column and paraffin column to recycle benzene into the alkylation unit and paraffins back into the Pacol unit.

I need help with the detailed design of the benzene column. The feed stream into this unit is as follows;

Mol flow: 5284553 kmol/yr

Mole fractions:

Benzene- 0.69       Dodecane- 0.23          LAB- 0.08

Temperature: 135°C

Pressure: bubble point pressure at this temperature.

The benzene column as instructed by the design supervisor must contain 2 adiabatic flash columns and a stripping column towards the end to aim at getting all the benzene recycled back into the alkylation unit.

Mass and energy balances must be carried over each piece of equipment.

The methodology for flash calculations include specifying the exit temperature of the flash columns using the Rachford-Rice equation to find Top vapour flow, bottom liquid flow, temperature and compositions of the top and bottom.

Detailed sizing of the flash vessel is also required to get appropriate separation of vapour and liquid. In addition condenser duties must be found since the benzene needs to be recycled back into the alkylation unit as liquid.

The stripping column uses steam to strip the benzene. It is required to obtain the fluidization velocity of the column. Also the diameter and basic sizing of this column must be done.