Liquid purification or separation – Liquid as separating medium
Patent
1987-04-02
1989-04-25
Spear, Frank
Liquid purification or separation
Liquid as separating medium
422260, 210634, B01D 1104
Patent
active
048245704
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for extracting constituents by supercritical fluids or pressurized liquids.
It more particularly applies to the extraction of the following organic constituents. lavender, Lavandin, rose, orange flower, jasmine, broom, camomile, mint, etc.,
It can also be used for partial water-alcohol separation and for the recovery of petroleum residues, e.g. for the separation of asphaltenes from heavy hydrocarbons using pentane and for the assisted recovery of deposits using methane, nitrogen or carbon dioxide gas.
Extraction processes using supercritical fluids or pressurized liquids consist of using a fluid under adequate pressure and temperature conditions to give said fluid an increased dissolving power compared with the constituents to be extracted. In the case of supercritical fluids, the pressure and temperature conditions are such that the pressure is above the critical pressure and the temperature above the critical temperature.
In the case of pressurized liquids, the pressure and temperature conditions are such that the pressure is above or below the critical pressure and the temperature below the critical temperature.
Throughout the remainder of the present text, the term "extraction fluid" will means that it is a supercritical fluid or pressurized liquid under the afformentioned temperature and pressure conditions.
The use of supercritical fluids offers certain advantages compared with pressurized liquids. Thus, supercritical fluids have a low viscosity and a high diffusivity, which leads to high extraction kinetics. However, pressurized liquids are sometimes of greater interest, because they generally give a more selective extraction and frequently lead to purer extracts. However, the extraction yields are generally lower.
Among the fluids which can be used under supercritical conditions or in the form of pressurized liquids, interest is attached to carbon dioxide gas, because it is non-toxic and causes no particular problems. Moreover, its critical temperature and pressure are not very high, because they respectively correspond to 31.degree. C. and 7.3 MPa. It is also of interest for application in the medical field, the agroalimentary field and the field of perfumes and cosmetics.
In order to carry out this type of extraction, the substance containing the constituents to be extracted is generally introduced into an extractor and in the latter is brought into contact with an extraction fluid raised to the desired temperature and pressure. On leaving the extractor, the extraction fluid consequently contains certain constituents and the latter are recovered by expansion of the fluid at atmospheric pressure, which makes it possible to collect the extraction fluid in gaseous form and to separate the extracted constituents in liquid form. On leaving the separator, the gaseous phase is then compressed and raised to the desired pressure, followed by cooling to the desired temperature and recycling in the extractor. In general, the liquid-gas separator is constituted by a cyclone and the gaseous phase leaving the latter may optionally be processed on several traps: active carbon, absorbing resins, etc. before being recycled into the extractor. This operating procedure is not very effective when the constituents to be extracted are highly volatile, because the latter cannot be easily collected in liquid form during the expansion of the extraction fluid at atmospheric pressure. Thus, during said expansion, the velocity of the fluid increases greatly and can, for example, pass from 1 cm/s to 250 cm/s on passing from a pressure of 15 MPa to 0.1 MPa. This velocity increase leads to the formation of very fine aerosols which cannot be separated in the cyclone separator and are consequently recycled or discharged with the gaseous effluence. To obviate this disadvantage, consideration has been given to the use of two-stage expansion. Firstly the fluid is expanded at a pressure intermediate between atmospheric pressure and the pressure used inthe extractor, followed by the separat
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patent: 3899398 (1975-08-01), Cole et al.
patent: 3969196 (1976-07-01), Zosiel
patent: 4402821 (1983-09-01), Yan
patent: 4406778 (1983-09-01), Borza et al.
patent: 4478705 (1984-10-01), Ganguli
Bethuel Louis
Carles Maurice
Neige Roger
Commissariat a l''Energie Atomique
Spear Frank
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