Daimler-benz Ag

Mercedes-benz Aktiengesellschaft

Bernd-Uwe Kettemann

Michele Melchiorre

Karsten Lohr

Jorg Zurn

Michele Melciorre

The invention relates to a method for the recovery of secondary polyols from paint sludge coagulate, formed from paint overspray which has first been dewatered by mass action, by chemical treatment in a manner such that the recovered product can be reused in the manufacture of paints. According to the recovery method, the organic components contained in the paint coagulate are glycolytically split at an elevated temperature into reusable polyols. Preferably, a mixture of different glycols is used, preferably in an amount of about 20 to 50% by weight based on the dewatered paint coagulate. The addition of glycol dilutes the paint coagulate and makes it flowable. The water contained in the paint coagulate is evaporated and removed during the glycolytic splitting because of the increase in temperature. The impurities contained in the paint coagulate, such as pigments, coagulants or flocculants, can be comminuted and finely dispersed by intensive shearing of the paint coagulate. At the end of the process, these impurities can also be filtered out from the polyols formed.

Method for the recovery of secondary polyols from paint sludges

The invention comprises a process for recovering secondary polyols from polyadducts which contain nonglycolysable constituents. In the process, a precomminuted polyadduct starting material is pretreated with glycols in a shear reactor at elevated temperature and pressure, for a relatively short time period, the nonglycolysable constituent being further comminuted and dispersed and the polyadducts being preglycolyzed. The preproduct thus obtained is broken down in subsequent stir reactors at a somewhat elevated temperature and for longer times, first without the further addition of glycol, and then with further addition of glycol. From the secondary polyol finally obtained, a plastic can be produced which can be further processed to make plastic components.

Process for recovering secondary polyols from polyadducts mixed with

A process for stripping of used parts or reject parts, in particular of polycarbonate (PC) or of a polycarbonate blend, preferably with polybutylene terephthalate (PBT/PC), for the purpose of recycling the plastic. In this process the plastics parts are first mechanically comminuted to a pourable size and then are circulated together with anhydrous alkalified diethylene glycol or propylene glycol in a mass with mutual abrasion of the plastics chips at elevated temperatures of at least 50.degree. C., preferably from 80.degree. to 100.degree. C., until complete removal of the paint. Thereafter the stripped plastics chips are separated from the stripping agent, flushed and then dried. The quantity of glycol added corresponds to from 1 to 10% of the volume of the mass to be treated, so that the circulated parts are only wetted by the glycol, but with stripping agent being circulated continuously through the treatment space of the mass from a relatively large reservoir. The circulation of the mass of parts is preferably carried out in a closable free-fall or positive mixer or in a rotary tube mixer. During the abrasive circulation the plastics parts are preferably admixed with abrasive particles whose specific apparent density corresponds roughly to the specific apparent density of the plastics parts.

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Elchingen, Germany

Bernd-Uwe Kettemann