extractive distillation

[sattu]

hi,
i am using benzene as an entrainer for separating a
solution of dimethyl formamide and water, the two being
miscible in each other.boiling point of dimethyl formamide is 124degree celsius.can someone please explain me the
equilibria,liquid-liquid and l-v, in this process.where
can i find data on ternary heterogenous azeotropes

 

[25362]

From books: BP of DMF is 153^oC, not 124 ^oC. The water-benzene azeotrope boils at 69.25^oC with 8.83% mass water. I didn't find azeotropes containing DMF. However, a good source would be Lange's Handbook of Chemistry (McGraw-Hill). See also Perry VI, section 13, for the subject of ternary azeotropes. Good luck.

 

[sattu]

thank u 25362.when i add benzene to a DMF-water system
i will get two immiscible layers.one is the DMF-benzene solution,other is the DMF-water solution,a heterogenous
azeotrope.can i make my calculations taking the vapour
pressures of the two layers based on roults law .for that i need to know the compositions of the two phases which depends on the solubility of benzene in both components.
is it the right way to proceed.can u advice m on that

 

[25362]

Do you know for sure there is a ternary azeotrope with DMF, benzene and water ?

The presence of two liquid phases doesn't necessarily mean there is a ternary azeotrope.

Depending on their concentration, benzene and water may boil away as a binary (heterogeneous) azeotrope leaving behind the high boiling DMF.

 

[DickRussell]

Raoult's Law cannot be applied here, because the system is highly non-ideal. It is this nonideality that leads to the immiscibility. If the system were close to ideal, there would be only one liquid phase. If you find some ternary VLE data, regressed to fit the NRTL or UNIQUAC model for liquid activity coefficients, then the separation for other compositions can be predicted. A process simulator can do those calculations for you.

 

[sattu]

hi 25362,
thank u for that information.it is a hetrogenous
azeotrope with benzene and DMF forming one liquid phase
and DMF-water the other phase.now treating it as a heterogenous azeotrope dmf-benzene phase exerts it own
vapour pressure and viceversa with the other phase.can
the concentrations of the individual components in vapour
phase be calculated treating the two phases as binary solutions and the whole system as a heterogenous azeotorpe

 

[Velterop]

Maybe it is somewhat out of the scope of this discussion, but DMF and water can be readily separated by pervaporation.Take a look at

http://www.pervatech.com