Drying of catalysts

It is well known that microwave drying of many solid materials is a very efficient and widely used process even on an industrial scale [3] it is also an attractive means of drying of heterogeneous catalysts. Microwave drying of catalysts and supported sorbents has several advantages ... 

Removal of diluent Drying of catalyst residue Purification and new drying of diluent Waste-water treatment Drying of polymer... 

The vanadium pentoxide catalyst Is prepared as follows Suspend 5 g. of pure ammonium vanadate in 50 ml. of water and add slowly 7 5 ml. of pure concentrated hydrochloric acid. Allow the reddish-brown, semi-colloidal precipitate to settle (preferably overnight), decant the supernatant solution, and wash the precipitate several times by decantation. Finally, suspend the precipitate in 76 ml. of water and allow it to stand for 3 days. This treatment renders the precipitate granular and easy to 6lter. Filter the precipitate with suction, wash it several times with cold 5 p>er cent, sodium chloride solution to remove hydrochloric acid. Dry the product at 120° for 12 hours, grind it in a mortar to a fine powder, and heat again at 120° for 12 hours. The yield of catalyst is about 3 - 5 g. 

Endo-exo product mixtures were isolated using the following procedure. A solution of cyclopentadiene (concentration 2-10" M in water and 0.4 M in oiganic solvents) and the dienophile (concentration 1-5 mM) in the appropriate solvent, eventually containing a 0.01 M concentration of catalyst, was stirred at 25 C until the UV-absorption of the dienophile had disappeared. The reaction mixture (diluted with water in the case of the organic solvents) was extracted with ether. The ether layer was washed with water and dried over sodium sulfate. After the evaporation of the ether the... 

Polymerization. Thermal polymerization or curing of an ink film at elevated temperatures can foUow many different chemical paths. Condensation and cross-linking reactions may be accompHshed with or without the use of catalysts. However, this method of drying generally has not been widely used for printing inks, except those used for metal and glass decoration, and some clear coatings. 

Some slurry processes use continuous stirred tank reactors and relatively heavy solvents (57) these ate employed by such companies as Hoechst, Montedison, Mitsubishi, Dow, and Nissan. In the Hoechst process (Eig. 4), hexane is used as the diluent. Reactors usually operate at 80—90°C and a total pressure of 1—3 MPa (10—30 psi). The solvent, ethylene, catalyst components, and hydrogen are all continuously fed into the reactor. The residence time of catalyst particles in the reactor is two to three hours. The polymer slurry may be transferred into a smaller reactor for post-polymerization. In most cases, molecular weight of polymer is controlled by the addition of hydrogen to both reactors. After the slurry exits the second reactor, the total charge is separated by a centrifuge into a Hquid stream and soHd polymer. The solvent is then steam-stripped from wet polymer, purified, and returned to the main reactor the wet polymer is dried and pelletized. Variations of this process are widely used throughout the world. 

Dry reduced nickel catalyst protected by fat is the most common catalyst for the hydrogenation of fatty acids. The composition of this type of catalyst is about 25% nickel, 25% inert carrier, and 50% soHd fat. Manufacturers of this catalyst include Calsicat (Mallinckrodt), Harshaw (Engelhard), United Catalysts (Sud Chemie), and Unichema. Other catalysts that stiH have some place in fatty acid hydrogenation are so-called wet reduced nickel catalysts (formate catalysts), Raney nickel catalysts, and precious metal catalysts, primarily palladium on carbon. The spent nickel catalysts are usually sent to a broker who seUs them for recovery of nickel value. Spent palladium catalysts are usually returned to the catalyst suppHer for credit of palladium value. 

Two or more soHd catalyst components can be mixed to produce a composite that functions as a supported catalyst. The ingredients may be mixed as wet or dry powders and pressed into tablets, roUed into spheres, or pelletized, and then activated. The promoted potassium ferrite catalysts used to dehydrogenate ethylbenzene in the manufacture of styrene or to dehydrogenate butanes in the manufacture of butenes are examples of catalysts manufactured by pelletization and calcination of physically mixed soHd components. In this case a potassium salt, iron oxide, and other ingredients are mixed, extmded, and calcined to produce the iron oxide-supported potassium ferrite catalyst. 

The paper-impregnation drying oven exhausts contain high concentrations (10—20% LEL) of alcohols and some resin monomer. Vinyl resins and melamine resins, which sometimes also contain organic phosphate fire retardants, may be used for air filters. The organic phosphates could shorten catalyst life depending on the mechanism of reduction of catalyst activity. Mild acid leaching removes iron and phosphoms from partially deactivated catalyst and has restored activity in at least one known case. 

The catalyst is previously prepared in an apparatus for catalytic hydrogenation, in which are placed 0.5 g. of palladous chloride, 3.0 g. of Norite, and 20 ml. of distilled water. The bottle is swept out with hydrogen and then shaken with hydrogen for 2-3 hours at 2-3 atmospheres (40 lb.) pressure. The palladium on carbon is collected on a Biichner funnel, washed with five 50-ml. portions of distilled water, then with five 50-ml. portions of 95% ethanol, and finally twice with ether. Upon drying, about 3 g. of the catalyst is obtained. It is stored in a vacuum desiccator over solid sodium hydroxide. If the reduction of the chloro-lepidine does not proceed normally, the used catalyst should be removed by suction filtration and a fresh 3-g. portion of catalyst added. Failure of the reduction step is usually due to an inactive catalyst or to impurities in the acetic acid or chlorolepidine. The palladium catalysts, prepared as described elsewhere in this volume, are presumably also satisfactory for the reduction of 2-chlorolepidine (p. 77). 

In the manufacturing of USY catalyst, the zeolite, clay, and binder are slurried together. If the binder is not active, an alumina component having catalytic properties may also be added. The well-mixed slurry solution is then fed to a spray dryer. The function of a spray dryer is to form microspheres by evaporating the slurry solution, through the use of atomizers, in the presence of hot air. The type of spray dr er and the drying conditions determine the size and distribution of catalyst particles. 

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