de - Beste verfügbare Techniken (BVT) - Umweltbundesamt

Chapter 2
2.3.2.2 Liquid-solid separation
Liquid-solid separation is used, e.g. for the separation of a precipitated product, catalyst, solid
impurities. The spectrum of the available and used equipment is wide and includes decanters,
decanter centrifuges, sieves, sand filters, rotary drum filters, band filters, plate filters, Nutsche
filters, membrane systems, centrifuges.
The environmental issues are linked to the properties of the liquid. The main aspects
are:
- VOCs from vents
- organic or aqueous mother liquors or washes.
These are usually treated by applying recovery or abatement techniques.
2.3.2.3 Distillation
Distillation is carried out to separate or purify volatile components from less volatile
components. A distillation unit always consists of a means of heating the feed, the column or
the vapour line (with many alternatives of packing to achieve specific results) and a heat-
exchanger to condense the vapours.
The main environmental issues are:
- energy efficiency (efficient design, insulation, heating, cooling)
- emissions to air from the condenser vent in case of atmospheric distillations
- waste streams (which can be re-used or recovered, or disposed of)
- wastes from cleaning.
2.3.2.4 Liquid-liquid extraction
Liquid-liquid extraction or solvent extraction is a separation process which is based on the
different distribution of the components to be separated between two liquid phases.
Liquid-liquid extraction is primarily applied where direct separation methods such as distillation
and crystallisation cannot be used or are too costly. Liquid-liquid extraction is also used when
the components to be separated are heat sensitive (e.g. antibiotics) or relatively non-volatile.
Extraction apparatus can be classified into countercurrent columns, centrifugal extractors, and
mixer-settlers. In a simple case, even a stirred tank may be applicable. All industrial equipment
designs use the principle of dispersing one of the two liquids into the other in order to enlarge
the contact area for mass transfer.
The main environmental issues are linked to the properties of the liquids:
- VOCs from vents
- organic or aqueous mother liquors.
These are usually treated by applying recovery or abatement techniques.
26 Dezember 2005 OFC_BREF