Isolation of Benzene, Toluene and Xylene Cont.....

Benzene toluene separation column:

•       Benzene-Toluene separator is binary distillation column produces pure aromatics. Low pressure steam is used as heating media for the reboiler. Pure benzene is obtained from top of the column and pure toluene from its bottom section. General column specification used in existing plant and may change to present optimum modification.

qTotal trays                    65 Bubble cap

qFeed tray                      30th

qPressure                      1.2 bars

qBenzene purity             99.97%

qToluene purity              99.95%

Isolation of Benzene, Toluene and Xylene Cont.....

Stripping column:

•       NFM and the dissolved aromatic solution obtained from the bottom of the extractive distillation column are fed to stripping column to recovery NFM for recycle. Column is operated along with aromatic column which operates at vacuum, pure aromatics are separated from the top and the NFM from the bottom. Heat of NFM is used to for the preheating the stream in heat exchanger system and returned to the extractive distillation column.

Equipment’s through which hot NFM is circulated:

qCenter re boiler on ED column

qReboiler on solvent recovery column.

qNFM re boiler on the stripper column

•         NFM is cooled by the trim cooler using solvent stream. Continuous reboilers are provided heat to the stripper column with BT vapours as heating medium. Solvent is removed by the reflux in the columns stripping section.
•        Total tray                                  30
•         Feed tray                                  5th
•         Top temperature                    56оC
•         Bottom temperature             119оC
•         Pressure                                 0.36 kg/cm3 vacuum

Isolation of Benzene, Toluene and Xylene Cont.....

Solvent recovery column:

•          To separate non-aromatics and residual carried over solvent contents, solvent recovery column is used. Top vapours of the extractive distillation column injected to the location below pall rings packing of the solvent recovery column.
•            N-formylmoropholine (NFM)  recovered at the bottom of the column is returned to the extractive distillation column. The purpose of the solvent recovery column is to eliminate the loss of NFM losses.
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•          The difference between normal distillation and extractive distillation column is based on phase separation in the separator at the bottom section. Non-aromatic compounds are separated to the bottom of the column with a two-phase product.

Following parameters are set during the process:

•Packing                         Pall rings

•Bottom pressure         0.25 kg/cm2

•Top pressure                0.2 kg/cm2

•Top temperature         100оC

•Bottom temperature    125оC