Integrierte Vermeidung und Verminderung der Umweltverschmutzung

2.1.2.4.3 Description of techniques, methods and equipment
Chapter 2
In forming or moulding, the material is in a viscous form and is fed into the appropriate mould.
As the moulding process progresses, the material becomes firmer and solidifies up to the point
that it becomes a fixed shape.
Extruding is a continuous process of shaping. The material is kneaded under high pressure and
pressed continuously through openings of the required shape. In cooking extruders, the material
is also heat-treated or cooked, to solubilise starches. Extruders can contain one or two screws.
The rotation of the screws transports and mixes the material and produces pressure build-up.
2.1.3 Separation techniques (C)
2.1.3.1 Extraction (C.1)
2.1.3.1.1 Objective
The objective of extraction is to recover valuable soluble components from raw materials by
primarily dissolving them in a liquid solvent, so that the components can be separated and
recovered later from the liquid. It is not always the objective to recover one particular
compound in pure form from a raw material, i.e. sometimes extraction is intended to separate all
of the soluble compounds from the residue; an example of this is the extraction of coffee.
2.1.3.1.2 Field of application
Extraction is widely applied in the FDM sector. For example, in the extraction of sugar from
sugar beets or sugar cane, oil from oilseeds and from virgin pomace, coffee extract from coffee
beans, caffeine from coffee beans and various other compounds such as proteins, pectins,
vitamins, pigments, essential oils, aroma compounds and flavour compounds from many
different materials.
2.1.3.1.3 Description of techniques, methods and equipment
Extraction works according to the principle that soluble components can be separated from
insoluble or less soluble components by dissolving them in a suitable solvent. Raw materials
that are suitable for extraction may contain either solids only, solids and a solution, or solids and
a liquid. Solid/liquid extraction is sometimes called leaching. When the soluble component is
incorporated in a liquid, the extraction may be applied to recover the valuable soluble
component. Commonly, the extract is the product or intermediate product and the residue is a
waste or by-product. The efficiency of the extraction process depends on the selectivity of the
solvent. Common solvents include water, organic solvents such as hexane, methylene chloride,
ethyl acetate and alcohol. Supercritical CO2 is used in coffee extraction.
Raw materials are usually pretreated to ensure efficient extraction of the desired compounds.
For example, sugar beets and sugar cane are cut into thin slices, nuts and seeds are ground or
flaked, coffee beans are roasted and ground, and tea leaves are dried and ground.
The simplest extraction method is a repeated extraction with fresh solvent called lateral flow
extraction. However, this is rarely used because of the costs of the solvent and because it results
in a very low concentration extract. The most common method used is countercurrent
extraction, either in a batch or continuous process. Batch wise countercurrent extraction is
normally only used for the processing of small amounts of material. In continuously operating
extractors, the solid material and the solvent flow countercurrently. One difficulty with
extraction is the recovery of the extracted material from the solvent. This can be carried out by
evaporation, crystallisation, distillation or steam stripping.
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