extraction

[thubelihle]

Hi. Was wondering how do we determine number of stages and minimum solvent for an extractor since there no shortcut methods for an extraction unit like for distillation. I am trying to solve the question from the ChemSep book, which is as follows: An equimolar mixture of n-pentane (1) and benzene (2), at a total flow rate of 100 mol/s is to be separated by liquid-liquid extraction. This operation might be carried out in equipment very much like distillation columns except that there is no reboiler or condenser. Our extractor is to operate at 50oC. It is required to recover 99.98% of the benzene. Further the purity of the extract is to be such that not more than 2.5 mole % n-pentane can be present in the extract product. The solvent is sulfolane. Determine the solvent flow rate and the number of equilibrium stages required to achieve the recovery and purity targets specified above. Assume that the optimum design corresponds to the use of the lowest possible solvent to feed ratio for a specified number of stages. My plan was to use an infinite number of stages, say 1000 and determine the minimum flowrate, but this is also required as an input in Chemsep. l am now lost. Thanks for your help.

[hkooijman]

There are short-cut methods for LL extraction, see Perry's handbook of Chemical Engineering, chapter 15 (7th Ed.). I suggest you to look there.

[thubelihle]

Thank you l will take a look. l meant there are no such shortcut methods incorporated in simulations packages, l guess one has to first do hand calculations as a starting point.