HI Riven,
Thank s for your reply.I think my question needs more explanation. As you said, the usual way to separate formic acid from water is extractive distillation but in my project amount of mixture is low and I like to investigate other ways.
First of all, I compared azeotropic data from page 1233 perry s hand book with different property methods data to select best of them that is UNIQUAC.
As you know, in maximum boiling azeotrop mixture , we can take azeotrope point from the bottom of batch distillation , my feed is about 2000 lit per batch with 60
% formic acid and I need formic acid 85% , as x-y diagrams show with increase pressure formic acid concentration in azeotrope point moves higher for example at 1 atm , formic acid mass frac = 0.63 and at 3 atm mass frac = 0.838 ,and I want to take formic acid 83% ( it depends on pressure) from bottom of batch tower at 3 atm or higher and I m not sure about that can I decrease amount of formic acid in distillate or not? . Because it s a hard distillation and k value is low and because of similarity between some properties of water and formic, there is not any third component to break the azeotrope and also any pressure.
Another problem I will have if I use this method, is material selection and corrosion of formic because of temperature increment that I think it has comprehensive affect on project cost.
As you suggest, another way to avoid temperature increment , in first step I can take formic acid in azeotrope point at 2 atm from bottom and in second step , separate mixture at vaccum pressure and take formic from top, but in simulation (at vacuum) when I use mixture with 70% formic ,separation is not good but with 80% formic it s better and it s make me to use 2 atm pressure in first step.
Edited by behnam, 19 May 2010 - 01:52 PM.