Liquid purification or separation – Processes – Chromatography
Patent
1993-12-27
1995-06-06
Therkorn, Ernest G.
Liquid purification or separation
Processes
Chromatography
2101982, B01D 1508
Patent
active
054220076
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns an apparatus and an industrial process for fractionation of component mixtures, preferably liquids, but also solids or gases, the eluent being either at a supercritical pressure, that is a fluid in a supercritical state or a subcritical liquid, or in the gaseous state in the form of a compressed gas.
It must be remembered that chromatography is based on the following principle: a fluid mixture whose components need to be separated is passed through a generally cylindrical container, the column, which contains a packing of a fluid-permeable porous solid, the stationary phase. The packing is constituted, for example, by a gel or aggregate of powdered particles; the fluid crossing it is constituted either by the fluid mixture whose constituents need to be separated, or by a mixture dissolved in a fluid solvent, the eluent. The rate of passage of the different constituents through the permeable solid depends on the physico-chemical characteristics of the different constituents, resulting in the constituents leaving the column successively and selectively. Certain constituents tend to be strongly retained by the solid mass and are thus more retarded, others are only slightly retarded and pass through rapidly with the eluent.
Materials occur in three states: solid, liquid and gas. Temperature and/or pressure can be varied to pass from one state to another. There is a point beyond which a material can pass from the liquid to the gaseous or vapour state without boiling, or vice versa by condensing, in continuous fashion: this point is known as the critical point.
It is known that a fluid in a supercritical state, that is a state characterised either by a pressure and temperature respectively greater than the critical temperature and pressure in the case of a pure material, or by a representative point (pressure, temperature) situated above the envelope of critical points on a (pressure, temperature) graph in the case of a mixture, produces a far higher solvating power in many substances compared to that observed in the same fluid as a compressed gas; similarly for subcritical liquids, that is in a state characterised either by a pressure above the critical pressure and by a temperature lower than the critical temperature in the case of a pure material, or by a pressure above the critical pressures and a temperature lower than the critical temperatures of the components in the case of a mixture.
Large and modifiable variations in solvating power are exploited in numerous processes for removal (solid/fluid), fractionation (liquid/fluid), analytical or preparative chromatography, material production (ceramics, polymers . . . ); chemical or biochemical reactions are also carried out in such solvents.
One of the main advantages of processes employing fluids at supercritical pressures resides in the ease of separation of solvent (the fluid) from the extracts and solutes, as described in numerous publications and, for certain important aspects of carrying out the processes, in French patent FR-A-2 584 618.
Interesting properties of these fluids have long been used in elution chromatography, either in analysis or for industrial production in accordance with a process described in French patent FR-A-2 527 934. These fluids have also been used as desorption solvents for compounds retained on absorbants, as described in several United States patents (U.S. Pat. Nos. 4,061,551, 4,124,528, 4,147,624).
Numerous studies of elution chromatography using supercritical fluids or subcritical liquids have shown a surprising behaviour in these fluids, in particular the large dependence of the retention factor (and thus retention time) on the bulk density and temperature of the eluent fluid. This property will be widely exploited in the apparatus and process described in the present invention. In addition, whilst perfect gases (that is primarily gases at low pressures and temperatures much higher than their boiling point at the pressure under consideration) have a retention factor which is independent of pr
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Hotier Gerard
Nicoud Roger
Perrut Michel
Institut Francais du Petrole & Separex
Therkorn Ernest G.
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