Calcined rare-earth-exchanged

In the early 70 s, FCC formulations containing 10-40% CREY (calcined rare-earth exchanged Y zeolites) were widely employed because these catalysts offered improved chemical as well as thermal and hydrothermal stability over FCC compositions containing equivalent amounts of (low sodium) HY crystals (23-25). The... 

In REHY and in calcined rare earths exchanged Y-zeolites (CREY) containing about 7.6% CeA, 4.0% La203, 2.8% Nd203 and 0.9 Pr203 crystals, it is believed that Ce+4 ions, present as an oxycerium complex, undergo a redox reaction with oxyvanadyl cations (VO+2) and form a stable orthovanadate (74) ... 

In a new, environmentally acceptable NCL process developed by Rajappa and collaborates (Deshmukh et al., 1990a,b,c,d Reddy et al., 1993), nitro-methane (10) is condensed with A -methylcarbonimidodithioic ester (11) in the presence of rare-earth-exchanged NaY zeolite to give (12) which then is easily converted to (13). The yields are good, and the catalyst can be recycled after calcination. A plausible mechanism for reaction 6.7 has been proposed (Bhawal et al., 1994). It is expected that this new ecofriendly process will soon be taken up by industry. 

Insoluble silica residues are removed by filtration. The solution now contains beryllium, iron, yttrium, and the rare earths. The solution is treated with oxalic acid to precipitate yttrium and the rare earths. The precipitate is calcined at 800°C to form rare earth oxides. The oxide mixture is dissolved in an acid from which yttrium and the rare earths are separated by the ion-exchange as above. Caustic fusion may be carried out instead of acid digestion to open the ore. Under this condition sihca converts to sodium sihcate and is leached with water. The insoluble residue containing rare earths and yttrium is dissolved in an acid. The acid solution is fed to an ion exchange system for separating thuhum from other rare earths. 

Infrared spectral studies of rare earth (RE) ion-exchanged faujasites have been reported by Rabo et al. (214), Christner et al. (217), Ward (211, 212), and Bolton (218). Distinct hydroxyl absorption bands are observed at 3740, 3640, and 3522 cm-1 after calcination at temperatures in the range of 340° to 450°C. As previously discussed, the hydroxyl groups at 3740 cm-1 are attributed to silanol groups either located at lattice termination sites or arising from amorphous silica associated with the structure. The hydroxyl groups that form the 3522 cm-1 band are nonacidic to pyridine or piperidine and are thought to be associated with the rare earth cations. 

Components of fluidized cracking catalysts (FCC), such as an aluminosilicate gel and a rare-earth (RE) exchanged zeolite Y, have been contaminated with vanadyl naphthenate and the V thus deposited passivated with organotin complexes. Luminescence, electron paramagnetic resonance (EPR) and Mossbauer spectroscopy have been used to monitor V-support interactions. Luminescence results have indicated that the naphthenate decomposes during calcination in air with generation of (V 0)+i ions. After steam-aging, V Og and REVO- formation occurred. In the presence of Sn, Tormation Of vanadium-tin oxide species enhance the zeolite stability in the presence of V-contaminants. 

Materials Used. The NaY zeolite and an ion-exchanged form of it, SK-500, were supplied by Union Carbide Corp., Linde Division, in the form of uncalcined powder. The SK-500 (Lot Number 12506-39) is a rare earth-ammonium exchanged type Y zeolite and had not been activated previously or calcined in its preparation. The calculated unit cell formula was... 

The hydrogen form was obtained by calcining the ammonium form at 427°C in air. The latter was prepared by ion-exchanging NaY with NH4NO3 solutions, using conventional techniques. Rare earth chlorides (99.9% ) were obtained from the American Potash and Chemical Corp. to prepare the various rare earth forms from NaY. ThY was prepared using Th(N03)4. 

A commercial digestion process is currently in use for the extraction of REE, including yttrium from monazite. The process is based on the application of caustic soda, and one of the products is REE hydroxide. The rare earths are leached from bastnaesite with hydrochloric acid (or sulfuric acid), followed by calcination at >600°C they are then treated with 16 M nitric acid (Kirk-Othmer 1999). Yttrium is produced as pure silver metal, both on the laboratory and industrial scale, by molten salt electrolysis and metallothermic reduction of the fluoride, oxide, or chloride with calcium following an enrichment process, after separation by fractionated crystallization, ion exchange... 

The first generation of zeolite FCC catalyst involved the use of zeolite Y exchanged with trivalent rare earth ions and was activated by calcination according to Eq. 3. 

The major industrial producers of rare earths recover individual rare earths from monazite, bastnasite, euxenite, and other rare earth containing raw material, through a series of unit operations. These unit operations include leaching with an appropriate lixiviant, separation and concentration by solvent extraction and/or ion exchange, precipitation as an oxalate and calcination to produce the individual oxide. Solvent extraction technology is the most efficient and economical separation method presently available. 

The zeolite is synthesized in its Na-form, which is a nonactive material, since acidic sites (Broensted acid sites) responsible for the formation of carbocations and hence cracking reactions are not present. Thus, the NaY zeoUte must undergo ion exchange with ammonium (or rare earth ions) to prepare the ammonium/RE form of the zeolite which will generate the acidic form HY upon calcination. 

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