Water content in IPA is 1.7%. I want to decrease it to less than 0.5%. I have tried simple distillation and also distillation using an entertainer such as ethylene glycol. No positive results were observed.
Secondly, One anomaly observed during distillation of the first cut which we discard is having water content - 3.4% and 1st main fraction - 3%. I do not understand how this water content increased to 3% from 1.7%.
You most likely have an azeotrope. Have you considered different types of entrainers? Consider this document: Article Different extractive distillation processes for isopropanol ...
To the second question: I am not sure, but looking at the atmospheric boiling points, I would say IPA is more volatile, and thus gets distilled faster. To answer this question properly, you might need to make a mass balance to the system, check a Txy diagram at the temperature you achieve during the first cut, and see if the values are that unreasonable.
Paul Shain , yes sir, I used activated molecular sieve of 5 wt% and added in the IPA solution. kept it overnight. Found water content decrease from 1.7% to 1.1%. Further I distilled it in lab scale and found the first fraction of IPA distilled has water content - 4%, Second Fraction - 1.6% and third fraction - 0.7%.
I think they use concentrated sulphuric acid to dehydrate ethanol once it as reached the distillation limiting value Solvent Recycling and Azeotropes (solvent--recycling.com) 5% water.
Never done it, but water and concentrated sulphuric are very exothermic, so great care will be needed.
Some people use anhydrous salts to remove traces of water, not sure that would work or silica gel - it is self indicating so you would 4know when it is saturated.
You can see and follow Following Ref:
J Am Oil Chem Soc (2018) 95: 753–765.
You will see there about the "Salting out" effect in distillation.
I. Benzene can be selected as entrainer for the dehydration of (wet) isopropanol by heteroazeotropic distillation. The liquid―liquid equilibrium ternary diagram for the isopropanol―water―benzene system presents a miscibility gap between two isopropanol bearing phases (one chiefly bearing the water; other chiefly bearing the benzene); cf.:
Article Optimization study on the azeotropic distillation process fo...
Article Liquid–Liquid Equilibrium Data for the Ternary Systems of Wa...
Article A Study of Solutions of Isopropyl Alcohol in Benzene, in Wat...
Article IUPAC-NIST solubility data series 69. Ternary alcohol-hydroc...
II. Toluene can also be selected as entrainer for the dehydration of (wet) isopropanol by heteroazeotropic distillation; cf.: https://doi.org/10.3303/CET1869073
III. The water-isopropyl alcohol azeotropic mixture of boiling point 80.37 °C, with 87.7 wt% (91 vol%) isopropyl alcohol, can be substantially dried with CaO (200 g/dm3), preferably while refluxing a few hours. After that, distilling (rather than filtering) would be advisable.
IV. To dry isopropyl alcohol you could also consider Linde type 5A molecular sieves.
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