Alumina gel

Fig. 3.35 Mercury porosimetry intrusion-extrusion plots of alumina gels prepared from solutions of aluminium monohydrate in A, propan-2-ol (2-5w/v%) B, propan-2-ol (4-9w/v%) C, 2-methylpropan-2-ol (4-9 w/v%) D, 2-methylpropan-2-ol (9-5 w/v%) E,butan-2-ol (9-5 w/v%). -------, ascending, intrusion curve -----, descending, extrusion curve.

Values of specific surface of alumina gels determined by nitrogen adsorption and by mercury porosimetry ... 

Gel-Based Activated Aluminas. Alumina gels can be formed by wet chemical reaction of soluble aluminum compounds. An example is rapid mixing of aluminum sulfate [17927-65-0], Al2(S0 2 XH20, and sodium aluminate [1302-42-7], NaA102, solutions to form pseudoboehmite and a... 

The terms gelatinous alumina or alumina gel covet a range of products in which coUoidal hydrated alumina is the predominant sohd phase. 

Gelatinous boehmite, called alumina gel in commeicial use, is used in the piepaiation of adsorbents, desiccants (qv), catalysts, and catalyst supports (see Catalysts, SUPPORTBd). A significant amount is used in pharmaceutical preparations. 

Gas Phase. The gas-phase methanol hydrochlorination process is used more in Europe and Japan than in the United States, though there is a considerable body of Hterature available. The process is typicaHy carried out as foHows vaporized methanol and hydrogen chloride, mixed in equimolar proportions, are preheated to 180—200°C. Reaction occurs on passage through a converter packed with 1.68—2.38 mm (8—12 mesh) alumina gel at ca 350°C. The product gas is cooled, water-scmbbed, and Hquefied. Conversions of over 95% of the methanol are commonly obtained. Garnma-alurnina has been used as a catalyst at 295—340°C to obtain 97.8% yields of methyl chloride (25). Other catalysts may be used, eg, cuprous or zinc chloride on active alumina, carbon, sHica, or pumice (26—30) sHica—aluminas (31,32) zeoHtes (33) attapulgus clay (34) or carbon (35,36). Space velocities of up to 300 h , with volumes of gas at STP per hour per volume catalyst space, are employed. 

Certain chemicals (sorbents) have the ability to absorb moisture from a gas they may be either solid or liquid. Performance of a chemical dehumidifi cation device depends on the sorbent used. The sorbent must t>e able to attract and remove the sorbate, such as water, from the gas stream, Stirbems absorb water on the surface of the material by adsorption or by chemically combining with water (absorption). If the unit is regenerative, the process is reversible, allowing water to be removed. This is achieved by a sorbent such as silica gel, alumina gel, activated alumina, lithium chloride salt, lithium chloride solution, glycol solution, or molecular sieves. In the case of nonregenerative equipment, hygroscopic salts such as calcium chloride, urea, or sodium chloride are used. 

The alumina gels, activated aluminas, and molecular sieves aic all chemically attacked by strong mineral acids and their adsorptive eapaetty... 

Pyridinium / -toluenesulfonate, 5°, 1 h." Similar selectivity can be achieved using a silica-alumina gel prepared by the solgel method. ... 

Many catalysts are used to effect the reaction, such as zinc chloride on pumice, cuprous chloride, and ignited alumina gel. The reaction conditions are 350°C at nearly atmospheric pressure. The yield is approximately 95%. 

Hirsch, D.E. Hopkins, R.C. Coleman, H.J. Cotton, F.O. Thompson, C.J. Separation of High-Boiling Petroleum Distillates Using Gradient Elution Through Dual-Packed (Silica Gel-Alumina Gel) Adsorption Columns, Anal. Chem. 1972, 44, 915. 

For most purposes, the correlations for jD presented in Tables 12.1 and 12.2 also suffice for estimating jH. There is, however, one additional correlation for fluidized beds that is worth noting. On the basis of data for the fluidization of 20 to 40 mesh silica and alumina gel particles in air at Reynolds number values (DpG/fi) ranging from 9 to 55, Kettenring et al. (92) suggest that... 

Zeolites are formed by crystallization at temperatures between 80 and 200 °C from aqueous alkaline solutions of silica and alumina gels in a process referred to as hydrothermal synthesis.15,19 A considerable amount is known about the mechanism of the crystallization process, however, no rational procedure, similar to organic synthetic procedures, to make a specifically designed zeolite topology is available. The products obtained are sensitive functions of the reaction conditions (composition of gel, reaction time, order of mixing, gel aging, etc.) and are kinetically controlled. Nevertheless, reproducible procedures have been devised to make bulk quantities of zeolites. Procedures for post-synthetic modifications have also been described.20 22... 

Alumina gel(s), 2 422, 427-428 drying of, 23 66-67, 78 Alumina hydrates, 2 421, 428 crystalline, 2 422-426 economic aspects, 2 432 gelatinous, 2 426-427 health and safety factors, 2 432 manufacture, 2 428-431 properties of normal coarse grade, 2 429t shipping and analysis, 2 431-432 uses of, 2 432 Alumina hydroxides economic aspects, 2 432 health and safety factors, 2 432 physical data, 2 423t uses of, 2 432... 

See also Ammonium compounds Anhydrous ammonia for activated alumina gel formation, 2 397... 

Yoldas, B. E. 1975. Alumina gels that form porous transparent AljOj. J. Mater. Science 10 1856-60. 

Separation of dibenzothiophene derivatives from petroleum oil fractions has been achieved by integrated approaches in which fractionating processes such as isothermal distillation, vacuum fractionation, and molecular distillation have been combined with spectroscopic methods including mass spectrometry and NMR spectroscopy. " Dibenzothiophenes have also been concentrated in sharp chromatographic fractions obtained, for example, by, alumina gel percolation, and have been detected by gas chromatography. Gas chromatography has also been used to... 

When cracking catalysts are prepared with a silica or silica-alumina gel base, the pore volume and average pore... 

SILICA ALUMINA GEL ACIDIC SURFACE FOR CRACKING LARGE MOLECULES... 

As our experimental work proceeded, I realized that we were dealing with a silica-alumina system (silica-alumina gel and platelet crystalline silica-alumina Kaolin) that should be similar to the alumina gel/alumina trihydrate crystal system of RD-150. It seemed possible to achieve a similar pore diameter spectrum structure here by judicious combination of crystals and gel. 

By achieving random dispersion of the Kaolin in the sodium silicate solution prior to formation of the silica-alumina gel, it was possible to disperse the clay crystals. They condensed somewhat perpendicular to each other and were bound together by silica-alumina gel. I therefore speculated that spray drying, during which the gel system contracts, might create a dual structure. An analogy would be a house built of cards (Kaolin), cemented together with silica-alumina gel. 

Kaolin had little or no cracking activity, and catalyst activity as tested in the laboratory was directly related to silica-alumina gel content. However, the catalyst performed much better in commercial tests than anticipated from laboratory testing. Undoubtedly, this open structure encountered much less severe conditions at the outer surface of the microsphere during regenerations and made internal catalytic surfaces more readily available. This first of the so-called "semisynthetics" was called Nalco 783, and the matrix is still used in many forms some 28 years later.(7,13) Today it is estimated that some 200,000 tons/yr. of kaolin clay is used for cracking catalyst manufacture as reported by Georgia Kaolin Corporation.(24) Figure 10 shows the pore volume distribution for Nalco 783 and two other commercial semisynthetics from that period. 

Silica-alumina gels containing 20-45% alumina provided the best combination of activity and activity stability. Therefore, we chose a gel with a composition in this range for binding the system together and as the matrix acidity ingredient. 

We explored various possibilities in our efforts to control nickel. Catalysts high in alumina content, especially if a separate inclusion of alumina gel is utilized, did seem to show some improvement. It also appears that in severe conditions such as in the RCC operation, nickel tends to agglomerate, this reducing exposed surface and possibly also embeds in the matrix or zeolite. 

Conformations and aggregate structures of sorbed natural organic matter on muscovite and hematite. Geochim. Cosmo-chim. Ada 65 1047-1057 Nanzyo, M. Watanabe,Y. (1981) Material balance associated with phosphate sorption by amorphous clays, silica-alumina gel and synthetic goethite. Soil Sd. Plant Nutr. 27 329-337... 

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