Classifying – separating – and assorting solids – Precedent preparation of items or materials to facilitate... – Sorting special items or sorting by methods and apparatus...
Patent
1993-04-09
1994-10-25
Dayoan, D. Glenn
Classifying, separating, and assorting solids
Precedent preparation of items or materials to facilitate...
Sorting special items or sorting by methods and apparatus...
209173, 2091274, 209 11, B07C 502
Patent
active
053581199
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for the separation of plastic particles of a plastic mixture of plastics of a chemically different type which partly have an overlapping and partly a different density range, e.g. polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC).
2. The Prior Art
Such different types of plastic occur as waste, for example when different one-way bottles are mixed. For example, still waters are predominantly filled in 1.5-liter PVC-bottles, whereas other beverages are sold in so-called PET-bottles. In Western Europe alone, 1.4 billion PET-bottles are manufactured annually. The bottles have, as a rule, a polyethylene screw cap, whereby the PET-bottles may have a bottom part made of polyethylene as well. Direct recycling of the mixed bottle plastics is not possible because PET melts only at 260.degree. C., whereas PVC decomposes with separation of HCl already above the softening temperature of 160.degree. C. There are, therefore, no appreciable recycling possibilities, so that the waste plastics have not been collected heretofore but eliminated via the household refuse, i.e., they are finally incinerated or deposited.
Furthermore, it is not possible, as a rule, to achieve any profits for mixed PVC-containing plastics. The fact is rather that the reuser frequently demands a credit that is oriented on the dumping costs saved.
As opposed to the above, there is a market for purely sorted recycling plastics since long, whereby the prices are oriented on the prices for new material. Up to 60% of the new material is achieved for recycling material depending on the quality. Thus there is much interest in processes for the separation of mixed plastics.
The processes known from the state of the art for the separation of plastic particles of plastics of a chemically different type operate with plants separating according to the density, for example hydrocyclones. Said process, however, fails in connection with plastics that are in the same density range such as, for example, PET (density about 1.37 to 1.38 g/cm.sup.3) and PVC (density about 1.38 g/cm.sup.3). However, the separation of polyethylene (PE) from the other two plastic types PET and PVC is possible because of the different density of 0.95 g/cm.sup.3. The separation of plastics that are in the same density range can be carried out, for example electrostatically.
It is known from DE-PS 30 35 649 to separate plastics electrostatically in a free-fall separator.
However, it has been found that in the separation of a plastic mixture with three or four different types of plastics, thus for example PE, PET, PS and PVC with one of said processes, a large quantity of medium material is collected, or that the deposits on the respective electrode have only an insufficient degree of purity. Furthermore, the medium material has a high component of at least one of the plastics used.
SUMMARY OF THE INVENTION
The invention, therefore, has the object of creating a process of the type specified at the beginning in which several components of a plastic mixture even of similar or the same densities can be safely separated from one another. This object is achieved in that the separation takes place in at least two steps, whereby in a first step, the plastic particles having a different density range are separated from each other, and whereby in a second step, the plastic particles with the same density range are separated. In this connection, the plastic particles are advantageously separated in the first step according to the principle of density separation, whereby the density of the separation liquid is selected in such a way that it falls in the field of the greatest density difference between the individual plastic types of the plastic mixture; advantageously, the density of the separation liquid is adjusted in this connection between 1.0 and 1.3 g/cm.sup.3. The density separation can take place in this connection by means of a hydro
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Geisler Iring
Hollstein Axel
Kleine-Kleffmann Ulrich
Neitzel Ulrich
Stahl Ingo
Dayoan D. Glenn
Kali und Salz Aktiengesellschaft
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