Activated alumina desiccant

F-200 ActivatedMlumina forMdsorption Applications, Product Data, Alcoa Chemicals Division, Aluminum Company of America, Pittsburgh, Pa., 1985. R. D. Woosley, "Activated Alumina Desiccants," in L. D. Hart, ed.. Alumina Chemicals Science and Technology Handbook, American Ceramic Society, Westerville, Ohio, 1990. 

Two air dryers contained activated alumina desiccant, and moist compressed air was routed through one dryer until it was ready to be regenerated. The moist air was then switched to the companion dryer, and the spent dryer was heated by internal steam coils until it achieved a certain temperature. The moisture was drawn out of the hot dryer by the blower. However, the blower was sucking in ambient air from a very humid environment. [6] (See Figure 2-19.)... 

Trade Publication (F35-14480), Choosing an Alcoa Activated Alumina Desiccant Basics of Dehydration Design, Alcoa, Pittsburgh, Pennsylvania, U.S.A., 15219. 

The first commercially available activated alumina was a granular material designated F-1 by the manufacturer, the Aluminum Company of America (Alcoa). This material was introduced in the 1930s and was an important solid desiccant for several decades. A spherical form of activated alumina, H-I5I Alumina Gel, was later introduced by Alcoa and proved quite successful. Production of H-151 by Alcoa ceased in 1985, and it was replaced by newer spherical products such as H-152 and F-200. The granular F-l is still available, but is not considered to be an important solid desiccant for gas dehydration (Woosley, 1990). Both granular and spherical activated alumina desiccants have been introduced by other manufacturers and several of these are listed in Table 12-4. 

Goodboy and Fleming (1984) point out that the term alumina is a misused expression for aluminum oxides and hydroxides that exist in at least flve thermodynamically stable phases and many more metastable transition forms. The commercial activated alumina desiccants arc generally manufactured by a process involving the following. steps (Woo.sley, 1990) ... 

The chemical analysis and physical properties of a typical activated alumina desiccant are given in Table 12-5. The data are for a spherical product, A-201, produced by LaRochc Chemicals (LaRoche is the successor company to Kaiser Chemicals, which produced the activated alumina products prior to mid-1988). 

Table 12-4 Properties of Commercial Activated Alumina Desiccants ...

Woosley, R. D., 1990, Activated Alumina Desiccants, in Alumina Chemicals, Science and Technology Handbook, L. D. Harte, editor. The American Ceramic Soc., Inc., West-eville, OH. 

Aluminium oxide. The commercial material, activated alumina, is made from aluminium hydroxide it will absorb 15-20 per cent, of its weight of water, can be re-activated by heating at 175° for about seven hours, and does not appreciably deteriorate with repeated use. Its main application is as a drying agent for desiccators. 

Desiccants. A soHd desiccant is simply an adsorbent which has a high affinity and capacity for adsorption of moisture so that it can be used for selective adsorption of moisture from a gas (or Hquid) stream. The main requkements for an efficient desiccant are therefore a highly polar surface and a high specific area (small pores). The most widely used desiccants (qv) are siHca gel, activated alumina, and the aluminum rich zeoHtes (4A or 13X). The equiHbrium adsorption isotherms for moisture on these materials have characteristically different shapes (Fig. 3), making them suitable for different appHcations. 

By-product water formed in the methanation reactions is condensed by either refrigeration or compression and cooling. The remaining product gas, principally methane, is compressed to desired pipeline pressures of 3.4—6.9 MPa (500—1000 psi). Einal traces of water are absorbed on siHca gel or molecular sieves, or removed by a drying agent such as sulfuric acid, H2SO4. Other desiccants maybe used, such as activated alumina, diethylene glycol, or concentrated solutions of calcium chloride (see Desiccants). 

Activated alumina is a relatively innocuous material from a health and safety standpoint. It is nonflammable and nontoxic. Fine dusts can cause eye irritation and there is some record of lung damage because of inhalation of activated alumina dust mixed with siUca [7631-86-9] and iron oxide [1317-61 -9] (30). Normal precautions associated with handling of nuisance dusts should be taken. Activated alumina is normally shipped in moisture-proof containers (bags, dmms, sling bins) because of its strong desiccating action. 

Usually best choice for desiccation of gases (<3% water) such as argon, helium, hydrogen, chlorine, hydrogen chloride, sulfur dioxide, ammonia, air, and chemical classes such as aliphatics, aromatics, halogenated compounds, oxygenated compounds (siUca gel, zeoHtes, activated alumina all alternatives some regenerable, some not). 

Desiccants Used in Static Drying. The most commonly used desiccants are discussed in this section activated alumina, siUca gel, and molecular sieves, which are discussed later under dynamic, sohd drying agents, are also widely used in static or batch-drying situations. 

The capacity of siUca gel is shown in Figures 9a and 9b, and the shape of the isotherm is similar to activated alumina. At saturation (pjp° = 1-0), sihca gel, which takes up 40 kg H2O /100 kg of adsorbent, has the highest capacity of the desiccants shown. However, some high capacity siUca gels tend to shatter in the presence of Hquid water. When Hquid water may be present, a lower capacity, water-resistant siUca gel must be used. 

H2O/100 kg of adsorbent. At equilibrium and at a given adsorbed water content, the dew point that can be obtained in the treated fluid is a function only of the adsorbent temperature. The slopes of the isosteres indicate that the capacity of molecular sieves is less temperature sensitive than that of siUca gel or activated alumina. In another type of isostere plot, the natural logarithm of the vapor pressure of water in equiUbrium with the desiccant is plotted against the reciprocal of absolute temperature. The slopes of these isosteres are proportional to the isosteric heats of adsorption of water on the desiccant (see... 

Market Data. The largest U.S. manufacturer of molecular sieves for adsorbent and desiccant use is UOP, which has a production capacity of 18—20 million kg/year. W.R. Grace and Zeochem have about 7 and 2 million kg/year capacity, respectively (55). W.R. Grace is the largest producer of siUca gel desiccants. Activated alumina for use as adsorbent and desiccant is produced by LaRoche Chemicals (formerly Kaiser) and by Aluminum Company of America. About one-third of the U.S. supply of activated alumina adsorbent and desiccant is imported by Rhc ne-Poulenc. 

Desiccant grade activated alumina is a highly porous form of aluminium oxide. It has the appearance of white chalky beads. Standard stock sizes have 2 - 5 mm or 5 - 8 mm. beads. An adsorbent from liquids and gases it is supplied usually in bulk packs. 

Activated alumina Hydrated aluminum oxide, a granular desiccant activated at high temperature that absorbs moisture and gases. 

Adsorption is the property of certain extremely porous materials to hold vapors in the pores until the desiccant is either heated or exposed to a drier gas. The material is a solid at all times and operates alternately through drying and reactivation cycles with no change in composition. Adsorbing materials in principal use are activated Alumina and silica gel. Molecular sieves are also used. Atmospheric dew points of minus 1000°F are readily obtained using adsorption. 

Desiccating agents used in corrosion prevention must be cheap, easy to handle and non-corrosive. These requirements rule out many of the familiar laboratory desiccants, and in practice the most common packaging desiccants are silica gel, activated alumina and quicklime (calcium oxide). Activated... 

Silica gel and activated alumina present few practical problems. They are easily reactivated after use by heating in a ventilated oven, to 130-300°C for silica gel, and 150-700°C for activated alumina. British standard specifications have been published for desiccants for packaging which regulate the contents of soluble chloride and sulphate, dust content and absorptive capacity. 

Activated Alumina for Use as a Desiccant for Packages, BS 2 541 1960, British Standards Institution, London... 

Desiccant. A substance with large surface area per pound that will adsorb or absorb water vapor from the air. Popular desiccants are activated alumina, calcium chloride, silica gel, and zinc chloride. 

All zeolites have a highly hydrophilic surface and are very efficient desiccants. Contrary to other nonzeolitic desiccants such as silica gel and activated alumina, zeolite adsorbents have type I adsorption isotherms for water—i.e., a high water adsorption capacity at a low concentration of water. To obtain extremely dry gases and liquids, therefore, zeolite adsorbents are strongly preferred over amorphous desiccants. The 3A mo-... 

The name activated alumina is generally applied to an adsorbent alumina (usually an industrial product) prepared by the heat treatment of some form of hydrated alumina (i.e. a crystalline hydroxide, oxide-hydroxide or hydrous alumina gel). It has been known for many years that certain forms of activated alumina can be used as powerful desiccants or for the recovery of various vapours. It was apparent at an early stage that the adsorbent activity was dependent on the conditions of heat treatment. For example, in 1934 Bayley reported that the adsorption of H2S by a commercial sample of activated alumina was affected by prior heating of the adsorbent at different temperatures, the maximum uptake being obtained after heat treatment at SS0°C. During an investigation of the catalytic dehydration of alcohols, Alekseevskii (1930) found that a calcination temperature of c. 400°C was required to optimize the adsorption of the alcohol reactants, whereas calcination at 600°C was preferable for the adsorption of the olefine products. 

The grade of alumina is important. With an ordinary grade of desiccator alumina, the checkers were unable to obtain the yields stated. The alumina employed successfully was Alorco activated alumina, from the Aluminum Ore Company, East St. Louis, Illinois. The catalyst darkens in use, but it can be kept in a clean and active condition by the following treatment after each run, or at least after two or three runs, the tube is heated to 420-470°, and a slow stream of air is drawn through it until the alumina is white (two to five hours). 

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