Process for high-pressure spray extraction of liquids

Details Process for high-pressure spray extraction of liquids Process for high-pressure spray extraction of liquids

1997-04-10

1999-01-05

Therkorn, Ernest G.

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

B01D 1104

Patent

active

058557865

DESCRIPTION:

BRIEF SUMMARY
REFERENCE TO RELATED APPLICATIONS

This application is a 371 of PCT/EP95/03950 filed Oct. 6, 1995.
The invention relates to a process for high-pressure spray extraction of liquid solutions and suspensions in the pressure range up to 1,000 bar by means of compressed gases such as CO.sub.2, propane, butane and mixtures thereof with and without entrainer additives such as: ethanol, propanol, methanol, acetone, water, methyl-ethyl-ketone, comprising liquid and gas mixing and mass transfer.
As is well known, the setting of an optimal dwell time is necessary for extraction processes. In discontinuous batch processes, this is produced by the period of extraction gas impact (DE 33 16 705 A1). As opposed to this, the process according to the invention allows the continuous guiding of the extraction gas while at the same time ensuring optimal dwell times for the liquid in this gas.
The use of alternating pressure impact for reducing the size of solids is known (DE 26 32 045 C2). With extraction procedures with compressed gases, however, the dispersion of a liquid must take place with as little pressure loss as possible because otherwise, the solubility of the gas decreases considerably and extraction becomes impossible. An alternating pressure impact would also be disadvantageous because the attainable drop ranges would then no longer be constant in time and product quality would thus be nonuniform. The technical problem of the invention is therefore to indicate a high-pressure spray extraction process in which a constant fine-dispersion of the liquid is achieved in a spraying device without alternating pressure impact and the optimal dwell time is set in an appropriate extraction geometry.
Unlike known nozzle extraction processes, in high-pressure spray extraction the charging does not take place in a mixing chamber, rather a distinction is made between a mixing zone and a charging zone adjoining it.
The spatial separation of the two process steps "mixing" and "charging" is advantageous physically speaking, because with a variable design of these two zones according to the invention formation can be set compared to known devices mixing zone can be given an adequate dwell time and geometrically optimized flight trajectories for the mass transfer (charging).
Compared to conventional spraying processes, high-pressure spray extraction offers the advantage that the prevailing process conditions have a positive effect on the spraying. The solubility of the gas in the liquid, substantially increased under pressure, leads to a considerable reduction in viscosity, in such a way that the liquid can be more easily dispersed into drops. But particularly the reduction of the interfacial tension between the phases to be mixed, noted as pressure increases, causes small drops to form (documentation: computer-assisted photographic image of two drops in supercritical carbon dioxide under different levels of pressure).
Furthermore, the mixing zone should be geometrically designed in such a way that due to an optimal pulse exchange, the high kinetic energy of the compressed gas is utilized to disperse the liquid into small drops. The spatial layout of the mixing zone for the spray extraction can be implemented as a two-substance nozzle with high-turbulent cross-flow or swirling flow of the gas as well as two single-substance nozzles (impact effect) directed toward each other. The use of a static mixer with subsequent unitary atomization of the gas and liquid is also conceivable.
The design of the charging zone is determined by the dwell time necessary for the mass transfer. A cylindrical design is sensible for relatively brief dwell times, e.g. for removing the oil from crude lecithin, because the mass transfer is completed before the sprayed particles hit the wall of the charging zone. There are greater transfer resistances for aqueous phases, such that the charging zone must allow longer dwell times without wall contact, e.g. a spherical or cut-off cone shape is advantageous for the separation of caffeine or nicotine from aqueous so

REFERENCES:
patent: 4367178 (1983-01-01), Heigel
patent: 4812233 (1989-03-01), Coenen
patent: 4828702 (1989-05-01), Coenen
patent: 5229000 (1993-07-01), Ben-Nasr
patent: 5258057 (1993-11-01), Baykut
patent: 5288511 (1994-02-01), Kazlas

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