Multi-stage extraction process

Details Multi-stage extraction process Multi-stage extraction process

1998-03-27

2000-11-07

Savage, Matthew O.

Liquid purification or separation

Processes

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

210511, 422256, B01D 1104, B01D 1200

Patent

active

061431788

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a process for multi-phase extraction in an extraction apparatus comprising a multiplicity of separating stages connected in series, wherein each stage comprises an extraction and a reextraction chamber, and wherein a raffinate phase is brought into contact with an extractant in the extraction chamber and the extractant is reextracted in contact with an extract phase in the reextraction chamber.
Extraction processes of this type are used in the chemical, hydrometallurgical and microbiological industries, and in other branches of industry, for the separation, concentration and purification of substances.
Single-stage apparatuses for carrying out three-phase liquid extraction processes are known in the form of a two-chamber system, wherein the two chambers are joined to each other at their upper parts or comprise a porous partition wall. The chambers are filled with a continuous phase through which two dispersed phases are passed which are insoluble in the continuous phase are passed in the form of droplets. A transfer of substances is thereby effected from one dispersed phase (the raffinate phase), through the continuous phase forming the extractant, into the other dispersed phase (the extract phase). This process is described, for example, in the journal "Theoretische Grundlagen der chemischen Technologie" 1984, Part 18, No. 6, pages 736-738).
Moreover, a three-phase extractor in which a first and a second chamber are filled with the continuous phase is known from Russian Patent Application No. 94-015776/26. The chambers have devices for the dispersion of the raffinate and extract phases, and are connected to each other by overflows for the circulation of the continuous phase. The overflows are constructed in the form of pipes which connect the upper and lower parts of each chamber to each other. The extractor is provided with connection pieces for the feeding and discharge of the raffinate and extract phases.
The raffinate phase and the extract phase are each broken down into droplets in the corresponding chamber, by means of a dispersing device. These droplets move through the continuous phase as a cluster of droplets. When the density differences between the raffinate phase, the extract phase and the continuous phase are appropriately selected and adjusted, continuous circulation through the top and bottom overflows is effected solely due to the density difference between the emulsions in the first and second chambers, so that a transfer occurs of the substance to be extracted from one chamber into the other, and thus from the disperse raffinate phase into the disperse extract phase, with the continuous phase functioning as the transport medium (carrier).
It is also known that a plurality of separating stages can be disposed in series in the extraction apparatus described above in order to increase the separation effect. In principle, various options are open for conveying the individual phases through the separating stages and for connecting the separating stages to each other.
The underlying object of the present invention is to improve the efficacy of a multi-stage extraction process by the optimum conveying of phases and the optimum coupling of separating stages. Of particular interest in this respect is the economic and efficient separation of systems of substances in which the distribution of the substance to be extracted between the individual phases is very low. When using conventional multi-stage extraction processes, separation problems such as these can only be solved with the aid of a very large number of separating stages, so that the process becomes uneconomic.
Starting from the process described at the outset, this object is achieved according to the invention by conveying the extractant in cross-flow to the extract and raffinate phases within the same separating stage in each case, whilst the raffinate and extract phases are conveyed through some or all of the separating stages in counter-current flow.
In the course of this process, the extractant can be caused t

REFERENCES:
patent: 4028462 (1977-06-01), Domic et al.
patent: 4111660 (1978-09-01), Kabasawa et al.
patent: 5575918 (1996-11-01), Virnig et al.

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