Paints, Pigments, Coatings - Liquid Filtration
Pigment processing typically involves a chemical reaction to precipitate metal oxides from solvent slurries. The resulting precipitate then must be separated from the slurry in a solid/liquid separation. The cake left on the filter is actually the product and this cake is typically washed to remove all traces of the solvent mother liquor. The mother liquor, because it is a solvent, is expensive to replace and/or dispose of, so it is also important that the filtrate be relatively clear for reuse. The most common type of liquid/solid separation (filter) used in this application is a recessed chamber filter press, very often fitted with the diaphragm squeeze option.
Some specialty pigments, especially titanium dioxide and kaolin clay utilize large rotary drum vacuum filters to separate aqueous based slurries where mother liquor concerns are less. Menardi has supplied the high tech woven fabrics typically used on the filter presses and the specially treated felts typically used on the rotary drum vacuum filters:
Common problems that have been solved with our solution-oriented products:
- Plugging of filter cloths resulting in short filter life
- Poor cake release
- Low throughputs
- Chemical attack
- Marginal temperature levels and spikes
Menardi products and services that have solved such problems include:
- Latest Generation woven fabrics
- Mikrotex®; ePTFE membrane laminated to woven and felt substrates
- Micro denier felts
- Dual density felts
- Oleophobic bath treated felts
Example Applications
A pigment processor was using monofilament/multifilament woven polypropylene fabric in his recessed chamber filter press to insure effective removal of the fine particle phase of the precipitate. Such tight filtration minimized product loss through the liquid/solid separation and also minimized further filtration of the mother liquor for reuse. The problem was that the multifilament fibers readily plugged resulting in short filter life and difficulty drying the cake during the latter stages of the filter life cycle.
Menardi recommended an engineered monofilament/monofilament fabric that filtered as effectively as the monofilament/multifilament fabric, but did not plug as readily. The result was longer cloth life, better cake release, and effective drying much longer into the fabric life cycle.
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