Filtration, Washing and Drying

Filtration, washing and drying remove undesired impurities. In our Al(OH)s example, sodium nitrate is washed away with water. Sometimes, ammonium hydroxide is added to expedite sodium removal. Subsequent air-and oven-drying removes most of the excess water and initiates the transformation of Al(OH)3 into alumina [AI2O3]. 

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A typical process for the preparation of a poly(methyl methacrylate) suspension polymer involves charging a mixture of 24.64 parts of methyl methacrylate and 0.25 parts of benzoyl peroxide to a rapidly stirred, 30°C solution of 0.42 parts of disodium phosphate, 0.02 parts of monosodium phosphate, and 0.74 parts of Cyanomer A-370 (polyacrylamide resin) in 73.93 parts of distilled water. The reaction mixture is heated under nitrogen to 75°C and is maintained at this temperature for three hours. After being cooled to room temperature, the polymer beads are isolated by filtration, washed, and dried (69). 

Diacetone-L-sorbose (DAS) is oxidized at elevated temperatures in dilute sodium hydroxide in the presence of a catalyst (nickel chloride for bleach or palladium on carbon for air) or by electrolytic methods. After completion of the reaction, the mixture is worked up by acidification to 2,3 4,6-bis-0-isoptopyhdene-2-oxo-L-gulonic acid (2,3 4,6-diacetone-2-keto-L-gulonic acid) (DAG), which is isolated through filtration, washing, and drying. With sodium hypochlorite/nickel chloride, the reported DAG yields ate >90% (65). The oxidation with air has been reported, and a practical process was developed with palladium—carbon or platinum—carbon as catalyst (66,67). The electrolytic oxidation with nickel salts as the catalyst has also... 

Palladiumdl) chloride-acetonitrile complex is formed by placing a.00 g of PdCl2 in 200 ml of acetonitrile and stirring for 2 days or refluxing for 3 hr. The complex (11.43 g, 97.8%) is collected by filtration, washed, and dried. 

According to the submitter, acidification of the combined sodium bicarbonate washings with 10% hydrochloric acid yields a colorless precipitate of 6,7-dimethoxy-3-methylindene-2-car-boxylic acid, which is collected by filtration, washed, and dried yield, 3.4-3.Q g. (14-16%) m.p. 216-218°. 

Design Example for a Batch Nutsche Filter Operation A batch Nutsche filter operates under constant pressure and maximum capacity with three stages filtration, washing and drying. The Nutsche filter with a 1 m filtration area operates under the following set of conditions ... 

The resistance of the filter plate is negligible. The problem is to determine the filtration, washing and drying times, the cake thickness, the volumes of filtrate, washing liquid and drying air. The solution to this design case is outlined below in steps. 

A solution of 1.5 grams of 17a-ethynyl estradiol in 50 cc of absolute ethanol is added slowly to a mixture of 3 grams of cyclopentyl bromide and 2 grams of potassium carbonate. This mixture is heated to reflux and stirred for 3 hours, then filtered. Most of the alcohol is eliminated by distillation and the resulting solution diluted with water, and cooled in an ice-bath. The product which precipitates Is collected by filtration, washed and dried. After recrystallization from methanol the 3-cyclopentyl ether of 17a-ethynyl estradiol shows a melting point of 107° to 108°C. 

Additional purification of the product and improvement of particle size and shape can be achieved by re-ciystallization. The process consists of sequential dissolutions of potassium heptafluorotantalate in appropriate solutions at increased temperatures, filtration of the solution to separate possible insoluble parts of the product and cooling of the filtrated solution at a certain rate. The precipitated crystals are filtrated, washed and dried to obtain the final product. Re-crystallization can be performed both after filtration of the preliminary precipitated salt or after drying if the quality of the product is not sufficient. HF solutions of low concentrations are usually used for re-ciystallization. In general, even water can be used as a solvent if the process is performed fast enough. Nevertheless, practical experience suggested the use of a 30—40% HF solution within the temperature interval of 80-25°C, and a cooling rate of about 8-10°C per hour. The above conditions enable to achieve an acceptable process yield and good performance of the product. 

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 most frequently used continuous drum type filters fall into the first category. These give maximum versatility, low cost per unit area, and also allow a wide variation of the respective time periods devoted to filtration, washing and drying. 

The precipitate was recovered by filtration, washed and dried to constant mass and was found to have a mass of 0-63 g. 

After 15 hours standing, 15.0-16.8 g. of crude o-carboxy-cinnamic acid may be recovered by filtration, washing, and drying. 

BSG was obtained from Sociedade Central de Cervejas (Vialonga, Portugal). The raw material was mixed with water at an 8 1 (w/w) liquid-to-solid ratio and pretreated in an autoclave (Uniclave 88, AJC, Lisbon, Portugal) for 1 h at 100°C for residual starch removal. The solid was separated by filtration, washed and dried at 50°C to reach a moisture below 10% (w/w) (2), homogenized to obtain a uniform lot, and stored in PA/PE vacuum-sealed bags. 

The mixture was heated to 90°C and filtered to remove slight persisting insolubles. The filtrate was acidified with acetic acid to bring the pH to about 5.5 and the precipitate formed was isolated by filtration, washed and dried to obtain 58 grams of 3-carboxy-4-hydroxy-8-trifluoromethylquinoline having a... 

Frequently, filtration, washing, and drying operations are integrated especially where noxious substances are being handled or when a crystal slurry of an API is being processed to a dry solid in a controlled environment room (CER). In the latter case, all types of combinations of filters and dryers are used (Figure 13). 

The optimum process for converting aqueous solutions of the sodium salt of R-aminoketone (X) to dilevalol DBTA salt resulted from a study of such parameters as reaction solvent, temperature, mole equivalents of sodium borohydride, mole equivalents of DBTA and crystallization conditions. The reduction process, which essentially yielded a 1 1 mixture of RR and SR compounds, was monitored by HPLC (Scheme 8). The plant equipment layout is shown in Figure 2. The process containment equipment (Krauss Mallei Titus system) used for the filtration, washing and drying steps is shown in Figure 3. 

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