Metal-oxide adsorbents

Release of and regeneration of the metal oxide adsorbent in the stripper. 

The H2S comes out with the reactor products, goes through the product-recovery system of the FCCU, and eventually goes to a Claus plant for sulfur recovery. The metal oxide adsorbent recirculates with the spent cracking catalyst back to the regenerator for the next SO adsorption cycle. 

A sohd solution of a pure magnesium aluminate spiael (MgAl20 with MgO is an effective metal oxide adsorbent (43). Such a soHd solution (Mg2A10 ) does not destroy the spiael framework the MgO adsorbs SO and the adsorption activity of the dispersed MgO ia the spiael is much greater than that of pure MgO itself (43). 

Metal Oxide - Since metals are less electrophilic than silicon, metal oxide adsorbents show even stronger selectivity for polar molecules than do siliceous materials. The most commonly used metal oxide adsorbent is activated alumina, used primarily for gas drying. Occasionally, metal oxides find applications in specific chemisorption systems. For example, several processes are under development utilizing lime or limestone for removal of sulfur oxides from flue gases. Activated aluminas have surface areas in the range of 200 to 1,000 ftVft Average pore diameters range from about 30 to 80 A. 

As already mentioned, the electronic interactions involved at the metal oxide-adsorbate interface have not been studied nearly as extensively as, for example, metal surfaces. Some notable experimental progress has, however, taken place in the last few years, see e.g. [101, 102], and some relevant theoretical models have recently been proposed [103, 104, 105, 106, 107, 108]. However, little is known about the perhaps single most important factor determining the interaction the electronic coupling strength between the excited adsorbate levels and the metal oxide conduction band. 

Novel Supported Metal Oxide Adsorbents and Catalysts Prepared from Polynuclear Metal Complexes... 

Suzuki, A., Seki, H., and Maruyama, H., An equilibrium study of adsorption of divalent metal ions onto a metal oxide adsorbent, J. Chem. Eng. Jpn, TI, 505, 1994. 

The aim of this work was to develop and present a new method for the synthes selective platinum catalysts for the hydrogenation of unsaturated aldehydes to unsatui alcohols. The method of preparation presented above makes it possible to obtain cata possessing polar platinum surface, due to the presence of active centers near the intei metal - partially reduced transition metal oxide. This transition metal oxide adsorb carbonyl oxygen atom whereas adjacent platinum atom interacts with carbonyl ca atom. In such a situation, the C=C bond is quite far from the surface so its adsorption i favored. There are also some additional parameters which should be taken consideration. The first is the size of platinum crystallites located on the catalyst sur Large platinum crystallites cause planar adsorption of aldehyde molecule in such adsorption of both double bonds is highly probable. It is known that a more sur... 

The second approach involves gas-phase desulfurization of reformate in the fuel processor using a metal oxide adsorbent, typically ZnO, to remove H2S. Gas-phase desulfurization requires that the reforming catalyst be sulfur tolerant at least to the concentration of sulfur present in the fuel. 

The simplest version of the iron (III) coagulation-microflltration process is by nature more complex and costly than the simplest versions of the ion-exchange and metal-oxide adsorbent processes. Furthermore, as is the case with the MOA processes, high feed pH, and the presence of signiflcant silica, phosphate, and fluoride concentrations will decrease the arsenic-removal efficiency of the C-MF process. Nevertheless, C-MF is attractive for arsenic removal because of lower chemical consumption and less waste production. 

The granular metal-oxide adsorbents discussed in this chapter are activated alumina (AAl), modified activated aluminas, iron-oxide-coated sand (IOCS), granular ferric hydroxide (GFH or GEH), and proprietary filter media such as ADI. Although they differ in physical appearance, they all involve hydrous oxides of iron or aluminum that remove arsenic by a process of ligand exchange. Generally, they are employed in packed beds or small filters containing 28 X 48 mesh (0.6-... 

The expected influence of silica on other metal oxide adsorbents, such as granular ferric hydroxide, is similar to its negative effect on alumina. Phosphate and fluoride are other strong ligands commonly found in groundwater that exhibit a negative influence similar to that of silicate on the arsenic capacity of alumina and GFH (5,12). Thus, the concentrations of these ions must be known before a reasonable estimate of arsenic capacity can be made. 

Before the development of reversed-phase bonded phases, normal-phase chromatography was the most popular separation technique. It relies on the interaction of analytes with polar functional groups on the surfooe of the stationary phase, which is strongest when nonpolar solvents are used as mobile phase. Previously, it was also called adsorption chromatography. However, the technique has expanded from the exclusive application of metal oxide adsorbents such as silica and alumina as stationary phases to the use of polar bonded phases. Thus the name adsorption chromatography has become too narrow. 

In a number of instances adsorption of polar compounds from dilute solutions passes through a region in which the surface is covered by a closely packed monolayer of the polar solute. The author discovered in 1966 that most non-porous metal oxides adsorb preferentially n-butanol from n-heptane with the formation of such a monolayer. The integral heat produced during the formation of the monolayer correlated very well with the specific areas of the metal oxides measured by the BET(Na) method [26], The specific surface areas of these solids could be effectively measured by a single point method, in which a sample of the solid immersed in n-heptane was flooded with a 2 gl > solution of n-butanol producing a heat of n-heptane displacement which was proportional to the total surface area of the sample. 

Silicates, titanium oxide, zirconium oxide, zirconium sulfate, and other metal oxides adsorb water, and therefore incorporation of a few percent of silicates or other metal oxides in polysulfonated membranes improved their performance at elevated temperatures and low relative humidity (e.g., [124,125]). 

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