Dehydration and Purification of Spent Tetra Hydro Furan Solvent

Tetra Hydro Furan (THF), a critical solvent in pharmaceutical industry, gets diluted with water and contaminated with impurities during the course of the reaction. Dehydration and purification of the THF allows reuse of this spent THF at the cost of extra energy and chemical consumption. But this recycling is rendered economically striking due to the fact that there is a large difference in the market price of Fresh THF and the realizable salvage value of spent THF.

Though economically attractive dehydration and purification of THF is uncommon because of the following characteristics of THF and issues with the process:

1. THF forms azeotropic mixture with water; this restrict the purity of product THF during dehydration
2. THF reacts readily with oxygen (from air) to form peroxides which are unstable and decompose in stages into high boiling organic acids
3. Further, the formation of these peroxides have caused violent explosions during past attempts of dehydration of THF

The process developed by Ingenero provides a safe, efficient and economic process, first for dehydration of THF to reduce its water content to the required specifications and subsequently for removal of other impurities in order to enable its reuse as a solvent.

The newly developed dehydration process comprises addition of an alkali such as potassium hydroxide or sodium hydroxide to wet THF solution, separation of the solution into an aqueous phase and an organic phase, removal of the aqueous phase, and subjection of the organic phase to molecular sieve adsorption in order to obtain THF with moisture content of less than 0.05 % wt. The process for separating organic impurities, if any, present in wet THF comprises of a batch distillation wherein low boiling impurities are removed as a first cut and pure THF is obtained as second cut, while removing high boiling impurities in the form of residue.

Although these individual unit operations are widely practiced in the chemical process industry, their combination coupled with use of stabilizers for enhancing safety makes this process a unique one and to the best of our knowledge and belief, this combination is not being practiced anywhere.  Ingenero’s THF process has been tested out and is operating successfully on a commercial scale at one of India’s largest pharmaceutical company facilities.

THF is a moderately polar solvent that can dissolve a wide range of non-polar and polar chemical compounds. With global annual production of 200 million kilograms, this water-miscible ether is mainly used solvent for polymerization and pharmaceuticals. The present invention can be applied to most of the applications of THF in pharmaceuticals that, today, require a significant addition of fresh THF stock due to loss of purity.