Filtration, Drying, Milling

Finishing not only improves the application properties of a pigment, such as hue, tinctorial strength, brilliance, transparency/hiding power, dispersibility, and flow behavior, but also considerably enhances its lightfastness and weatherfastness and its solvent and migration resistance. 

Following manufacture and possibly further processing, the pigment is separated from the suspension and dried. Both processes can be carried out either continuously or by batch operation, depending on the tonnage of the product. 

Plate-and-frame filter presses are particularly suited to batch operations. Modern frames are made of polymers (mainly polypropylene), which have replaced wood as a building material. Large amounts of products, on the other hand, are filtered routinely via continuous-belt filters or rotary drum-type filters. Following the filtration step, inorganic salts are removed by washing with water. 

In a spray dryer, the aqueous pigment paste passes through a rotating disk or nozzle into a cone-shaped spray chamber fed with hot air. The dried pigment powder trickles through a grate at the bottom. 

Before being milled on an industrial scale, each pigment has to pass a test concerning its sensitivity to dust explosion. There are standardized milling regulations for each hazardous class. 

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This type of pigment is the precipitate formed when molybdic oxide is dissolved in aqueous sodium hydroxide with the addition of sodium chromate. The resulting mixture is reacted with a solution of lead nitrate. The precipitate formed is further processed through filtration, washing, drying, milling, and packaging. 

The reaction of zinc oxide, hydrochloric acid, sodium dichromate, and potassium chloride produced zinc yellow as a precipitate, which is a complex compound of zinc, potassium, and chromium. The complex compound is further subjected to filtration, washing, drying, milling, and packaging for use. 

According to the ICH guidance document, introducing an intermediate (key or final) or API that does not conform to standards or specifications back into the process by repeating a crystallization step or other physical manipulation (i.e., distillation, filtration, chromatography, milling, and drying) that is part of the... 

Wet ball-milling is faster than dry-milling and facilitates the separation of the milling media from the charge. Its disadvantage is that the liquid must be removed, which is most economically achieved by filtration, but any soluble constituent will be removed with the liquid. If this is undesirable the alternative is to evaporate the liquid which can be effected by spray-drying if the liquid is water. Evaporation can also take place in shallow trays in ovens in this case soluble material may appear as a skin on the surface and heavy coarse particles may settle out. 

Composition of the adhesive One part spray-dried, milled sulfite liquor containing ca. 20% sugar and 1.5 parts concentrated culture filtrate of Trametes versicolor (grown on 0.1% organosolv lignin in a 25 L fermenter), containing 420 U/mL phenoloxidase activity. 

This pigment, also called zinc yellow, is produced by reacting an aqueous slurry of zinc oxide or hydroxide with dissolved chromate ions, followed by neutralization, or by precipitation of dissolved zinc salts with dissolved chromate salts, followed by washing, filtration, drying, and milling processes [5.56]. Previously zinc yellow used to hold a major share of the anticorrosive pigment market... 

The manufacturer of filter aids produces filter aid grades in a wide range of particle sizes to meet practically any industrial filtration requirement. The relative flow rates of these grades are determined by a standard filtration test and are shown in Fig. 4. Typical properties of some commercial filter aids are shown in Tables 1-3. Filter Cel, the finest grade, shown in Fig. 4, giving the highest clarity and lowest flow rate, is a natural diatomite, which has been selectively quarried, dried, milled, and air-classified. To make coarser, faster flow rate filter aids, Filter-Cel is calcined and air-classified. These straight... 

Identification of Processing Equipment Requirements. When transferring processes from pilot to commercial-scale operations, a comparative analysis is usually made between the equipment used in the pilot operation with the proposed commercial facility. Process flow diagrams (PFDs) that include material balances from pilot plant experiments can facilitate this analysis. Specifications and requirements for agitation, filtration, drying, and milling devices are established based on experimental results that support these specifications and are documented. 

PHYSICAL MANIPULATION A process other than a chemical reaction that may change the purity or the physical properties of the material, including but not limited to crystallization, recrystallization, gel filtration, chromatography, milling, drying, or blending. 

APl/polymer solution Antisolvent Precipitation Filtration Washing Drying Milling... 

Preparation of the alcohol insoluble solids (AIS) The content of the can was drained and the carrot cubes were immediately frozen in hquid nitrogen, freeze-dried and milled. Carrot powder (ca. 10 g) was mixed with 200 ml 80% ethanol previously heated to 60°C. After filtration the residue was extracted with ethanol until the filtrate was colorless (5 times) and gave negative reaction with phenol-sulfuric acid test (Dubois et al., 1956). 

The solid azo pigment is then separated by filtration, washed, and dried immediately. It is also possible to reslurry the pigment presscake in another agitation vessel in order to prepare it for thermal aftertreatment. Milling follows drying. 

The synthetic route may be exemplified by the preparation of a tetra-chloroisoindolinone pigment. A mixture of one mole of 1,4-diaminobenzene in o-dichlorobenzene with a solution of two moles of 3,3,4,5,6,7-hexachloroisoindoline-1-one in o-dichlorobenzene is heated to 160 to 170°C for 3 hours. Closed filtration equipment is used to filter the hot product, which is then washed with o-dichlorobenzene and alcohol, dried, and milled. The resulting product is a reddish yellow pigment with the structure 45 ... 

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