Liquid purification or separation – Processes – Separating
Patent
1987-01-08
1987-12-08
Sever, Frank
Liquid purification or separation
Processes
Separating
210789, B01D 17038
Patent
active
047117290
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the recovery of valuable substances from lacquer sludge which, in addition to solvent, vehicle and adjuvants, contains up to 50% by volume solids in the form of inorganic and/or organic pigments and/or fillers. Such lacquer sludge is collected in great amounts in painting operations in lacquering plants in the form of so-called overspray. In the Federal Republic of Germany alone, the amount of overspray comes to approximately 150,000 tons annually.
The lacquer sludge collected in painting operations has, on the average, about the same composition as the lacquer used. Accordingly, it consists of up to about 33% vehicles (film-forming substances such as cellulose nitrate, vinyl chloride-vinyl acetate copolymer, unsaturated polyester resin, epoxide resin etc.), 27% solvents (low-, medium or high-boiling organic substances such as, for example, benzene, xylene, carbon tetrachloride, alcohol etc.), 26% pigments (finely ground organic or inorganic solids dispersed in the lacquer, which provide the lacquer with color, covering power and often also with stability), and 14% dyestuffs and fillers (for example heavy spar, chalk, kaolin etc.), as well as adjuvants (substances that enhance the properties of the lacquer with respect to processibility and stability).
As the disposal of such lacquer sludge in special waste dumps is expensive (about 400.00 German marks per ton) and the incineration of lacquer sludge poses problems due to the toxic exhaust gases and dusts released during such incineration, the search for suitable recycling methods has been on for some time now. Such a method is disclosed, for example by the Japanese published patent disclosure No. Sho 55-8810, from which it is known to dry the lacquer sludge at 100.degree. to 250.degree. C., recover the volatile components released in such drying step, and to grind the remaining solid mass to a granulate which, for example, can be used as an aggregate in the production of concrete. However, the value of the recovered solvent and granulate is so low that the proceeds cannot cover the additional cost of the recycling process.
If a lacquering plant is continuously operating using one and the same type of lacquer all the time in one color, it is, of course, possible to leave the overspray in the processible condition and to collect it by suitable means, dilute it with solvents and to use it again in the lacquering plant. Of course, this is not possible in lacquering plants with a changing color program, which means in the greater number of practical cases of application, as the overspray leads to a mixture of colors which, as a rule, makes reuse impossible.
Thus the objective of the invention is to recover from the lacquer sludge valuable substances with a high resale value, in particular the expensive vehicle (film-forming substances).
This objective is accomplished by the present invention, which proposes that the kinematic viscosity of the lacquer sludge is reduced to less than 100 cSt by adding to the sludge up to 50% by volume solvent and/or by heating it up to 60.degree. C., and that the content of solids of the liquefied lacquer sludge is reduced to less than 3% by volume first in a decanting centrifuge with a centrifugal acceleration of up to 4,000 g, and subsequently in a centrifugal separator with a centrifugal acceleration of up to 14,000 g.
Although the lacquer, when produced, is compounded in such a way that the solids will not sedimentate, or do so only with difficulty, it was surprisingly found that the solids, that is, primarily the pigments, which are contained in the lacquer sludge in great amounts, can be largely removed from the lacquer sludge by relatively simple mechanical separation methods if the viscosity is reduced to a certain level and a two-stage separation process is used with certain sedimentation centrifuges, in which process especially the inorganic pigments are separated in the first stage at lower centrifugal acceleration, and the remaining pigments, which are predominantly organic, are s
REFERENCES:
patent: 2704779 (1955-03-01), Apgar
patent: 3994943 (1976-11-01), Gibble et al.
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