SCFE PROCESS DESCRIPTION

In the supercritical fluid extraction (SCFE) process, extraction is carried out by a solvent above its critical pressure and temperature. In this case the solvent used is carbon dioxide (Co₂) and extraction is carried out at pressures between 100 to 350 or 500 bar and temperatures between 35 - 60 0C. A brief description of the SCFE process is given below.

The commercial scale SCFE plant has three extractors, two separators, one Co₂ hold-up tank and heat exchangers (see enclosed flow diagram). The extraction process works in a closed loop with constant circulation of Co₂ in the system. It is a semi-batch operation with typical batch time of 2 to 4 hours. Co₂ is liquefied and fed to the hold-up tank through a heat exchanger (Condenser). Liquid Co₂ is then fed to the high-pressure metering pump, through a heat exchanger (sub-cooler) to ensure supply of Co₂ in liquid form. The high-pressure liquid from the pump discharge (350 / 500 bar max.) is then heated in a heat exchanger (pre-heater) to achieve supercritical temperature. The entrainer pump can be used for dosing a small quantity of other solvents such as water, ethanol etc. in to the Co₂ stream, if desired. This supercritical fluid then flows through the extractors. The solid material to be extracted is held in these extractors with help of perforated baskets for easy handling. Extractors are equipped with specially designed quick acting closures for easy and fast opening of extractors. At any given time only two extractors operate in series mode, while the third extractor is out of cycle for change of feed. When any of the two operating extractors need feed change, it is taken out of process and replaced by the third extractor having fresh feed. This sequencing continues to minimise the downtime required for feed change. The supercritical Co₂ with dissolved extract then flows to separators.

In the separators, lower temperature and pressure conditions are maintained for recovery of the extract from the Co₂ stream. Thus with proper selection of conditions, fractionation of extract can be achieved by using two separators operating in series. Separator-1 is maintained at supercritical conditions (40-60 0C, 120 bar max.), where typically high molecular weight components of the extract precipitate. Whereas in separator-2 sub-critical conditions are maintained for complete recovery of any extract from Co₂ stream. The Co₂ vapour leaving separator-2 is condensed and fed back to Co₂ hold-up tank.

When the solid feed in the extractor needs replacement or when plant is to be shut down, respective vessels are depressurised to atmospheric pressure. In doing so maximum possible Co₂ is fed back to Co₂ hold-up tank through Co₂ depressurising line. Co₂ from each vessel can be transferred till the pressures become equal to that of the hold-up tank. Remaining Co₂ is then vented off to the atmosphere.

Courtesy : Printed with permission from Dept. of Chemical Engineering, IIT, MUMBAI

For any information / Co₂ requirements, contact :

SICGIL INDIA LIMITED
VI Floor, Dhun Building, # 84, (Old No. 827), Anna Salai, Chennai-600 002.
Phone : 91 - 044 - 2852 1644 / 2852 1467 / 2852 0657 / 2852 0870
Fax : 91 - 044 - 2852 1249, E-mail : sicgil@vsnl.com, vijay@sicgil.com,

Contact Persons
V.N.Vijay Kumar		Phono No: 044 39850715/728
Ruqshad Dadabhoy

_____________________________________________________________________
At : Bangalore, Chennai, Cochin, Coimbatore, Goa, Hyderabad, Indore, Kakinada, Kolkata, Madurai, Mumbai, Surat, Tuticorin, Vadodara, Vizag.