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Extraction
Liquid – Liquid Extraction
Solid – Liquid Extraction
High Pressure Extraction

Lecturer: Thomas Gamse
ao.Univ.Prof.Dipl.-Ing.Dr.techn.

Department of Chemical Engineering and Environmental Technology
Graz University of Technology
Inffeldgasse 25, A-8010 Graz

Tel.: ++43 316 873 7477
Fax: ++43 316 873 7472
email: Thomas.Gamse@TUGraz.at

Extraction, Lecturer: Dr. Gamse

-1-

EXTRACTION
1. Introduction
Extraction is the withdrawing of a active agent or a waste substance from a solid or
liquid mixture with a liquid solvent. The solvent is not or only partial miscible with the
solid or the liquid. By intensive contact the active agent transfers from the solid or
liquid mixture (raffinate) into the solvent (extract). After mixing the two phases are
separated which happens either by gravity or centrifugal forces.
For recovery of the solvent and to get the active agent in pure form a further
separation process is necessary (rectification or re-extraction)

Depending on the phases following types of extraction exist:
• Solid – liquid extraction
• Liquid – liquid extraction
The gas – liquid extraction is called absorption.

The main area of extraction is for hydrometallic processes, for pharmaceutical
industry (producing active agents), for petroleum industry (production of monomers
and aromates) and for cleaning of waste water to separate solved compounds.

1.1. Selection of the solvent
The solvent for extraction has to withdraw the active agent from a mixture.
• selectivity: Only the active agent has to be extracted and no further
substances which means that a high selectivity is required.
• capacity: To reduce the amount of necessary solvent the capacity of the
solvent has to be high.
• miscibility: To achieve simple regeneration of the solvent the miscibility of
solvent and primary solvent has to be low.
• difference in density: After extraction the two phases have to be separated
in a separator and for this a high difference in density is positive.
• optimal surface tension: σ low -> low amount of energy for dispersing
required; if surface tension < 1 mN/m stable emulsions are produced. σ >

Extraction, Lecturer: Dr. Gamse

-2-

50 mN/m -> high amount of energy for dispersing and high tendency to
coalesce
• recovery: The solvent has to be separated from the extract phase easily to
produce solvent free active agents.
• corrosion: If the solvent is corrosive prices for construction increase
• low price
• no or low toxicity
• flame temperature: 25 °C ...
Extraction
Liquid – Liquid Extraction
Solid – Liquid Extraction
High Pressure Extraction
Lecturer: Thomas Gamse
ao.Univ.Prof.Dipl.-Ing.Dr.techn.
Department of Chemical Engineering and Environmental Technology
Graz University of Technology
Inffeldgasse 25, A-8010 Graz
Tel.: ++43 316 873 7477
Fax: ++43 316 873 7472
email: Thomas.Gamse@TUGraz.at
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