Silica gel alumina

A typical example, from the extensive study by Kamakin on an alumina-silica gel, is shown in Fig. 3.32. When the mercury pressure was reduced to 1 atm at the end of the first cycle, 27 per cent of the intruded mercury was retained by the sample a second intrusion run followed a different path from the first, whereas the second extrusion curve agreed closely with the first. Change in f re structure of the kind described above could perhaps account for the difference between the two intrusion curves, but could not explain the reproducibility of the remainder of the loop. There is no doubt that hysteresis can exist in the absence of structural change. 

Fig. 332 Mercury penetration in alumina-silica gel (Kamakin" ). O, penetration A, retraction , re-penetration A. renewed retraction. (After...

Weigh about 80 g of the adsorbant (alumina, silica gel, etc. ) for a typical 15 X %-in. column, into either a large beaker or a large screw-cap bottle. 

A thin layer of adsorbent is applied to a support that may be a sheet of glass, metal, or plastic (Figure 13.4, D). Adsorbents are typically alumina, silica gel, or cellulose and may be mixed with gypsum to aid in adhering to the support. They may also include a fluorescent indicator that aids in visualization once the plate is developed. These adsorbents may also have hydrocarbons attached to them such that reverse-phase TLC can be carried out. 

Millson [113] investigated components of sewage sludge and found elementary sulphur in the hydrocarbon fractions eluted from liquid adsorption columns. By using a solid adsorbent such as alumina, silica gel, or Florisil, and heptane as eluent, the sulphur could be separated from weakly adsorbed hydrocarbons, e.g. squalene or biphenyl, but not from more strongly adsorbed hydrocarbons such as phenyldodecane. 

Several classes of solids have commonly been used for surface organic chemistry including aluminas, silica gels and clays. Zinc oxide (ZnO) is certainly one of the most interesting of these solids because it has surface properties that suggest that a very rich organic chemistry may occur there. 

Cholesterol can be extracted more effectively from beef tallow with the addition of adsorbents such as activated alumina, silica gel or molecular sieve to the extraction chamber, but flavor constituents are removed as well. 

Charcoal Molecular sieve Porous polymer Alumina Silica gel... 

However, a larger portion of materials which may be of concern as trace components will not be extractable or generally soluble in aqueous systems. This presents the necessity to concentrate components contained in organic solvents. When the organic solution is too complex, or the components sought are too volatile to allow concentration simply by evaporation, then more complex means must be pursued. Under these circumstances, liquid column processes are again commonly used. Alumina, silica gel,... 

The position of each component of a mixture is quantified by calculating the distance traveled by the component relative to the distance traveled by the solvent. This is called relative mobility and symbolized by Rf. In Figure 3.2D, the R values for components B and C are calculated. The Rf for a substance is a constant for a certain set of experimental conditions. However, it varies with solvent, type of stationary support (paper, alumina, silica gel), temperature, humidity, and other environmental factors. R values are always reported along with solvent and temperature. 

Thin-layer chromatography is now more widely used than paper chromatography. In addition to its greater resolving power, TLC is faster and plates are available with several sorbents (cellulose, alumina, silica gel). 

Adsorbing materials come in various forms and sizes. The most suitable forms are dry powders or a slurry form of the material in an aqueous buffer or organic solvent. Alumina, silica gel, and fluorisil do not normally need special pretreatment. The size of particles in an adsorbing material is de-... 

A variety of adsorbents, such as alumina, silica gel, Florisil, and various activated carbons, have been employed for carbamate residue cleanup (43). Liquid chromatography on alumina (44-46), silica gel (14), or Florisil (47) has also been used as a cleanup step. 

Microwave heating has proven to be of benefit particularly for reactions under dry media (e.g., solvent-free conditions) in open vessel systems (i.e., in the absence of a solvent, on solid support with or without catalysts) [4]. Reactions under dry conditions were originally developed in the late 1980 s [51], but solventless systems under microwave conditions offer several additional advantages. The absence of solvent reduces the risk of explosions when the reaction takes place in a closed vessel. Moreover, aprotic dipolar solvents with high boiling points are expensive and difficult to remove from the reaction mixtures. During microwave induction of reactions under dry conditions, the reactants adsorbed on the surface of alumina, silica gel, clay, and other mineral supports absorb microwaves whereas the support does not, and transmission of microwaves is not restricted. Moreover, microwaves can interact directly with reagents and, therefore, can more efficiently drive chemical reactions. The possible accelerations of such reactions are expected... 

In open-column liquid chromatography, the test sample is added to the top of a column packed with adsorbent material (e.g. alumina, silica gel, polymer gel or fine-particle substrate coated with an organic compound). Differential movement... 

Water, soil, sediment, fly ash, fuel oil, sludge, still bottoms, fish, adipose Addition of 13C-labeled standards followed by solvent extraction (exact method depends on matrix), acid-base washing treatment, solvent exchange, and cleanup using alumina, silica gel, and activated carbon, addition of Relabeled internal standards. HRGC/HRMS (MIM) (EPA Method 8290) 10 ppq for water to 1 ppt for other matrices (depending on complexity) No data EPA 1994c... 

Organochlorine -insecticides Clean up of water with deactivated alumina silica gel and Florasil prior to GLC [359]... 

Since adsorption is essentially a surface phenomenon, a practical adsorbent must have a high specific surface area, which means small diameter pores. Conventional adsorbents such as porous alumina, silica gel, and activated carbon have relatively wide pore size distributions, spanning the entire range from a few angstroms to perhaps 1 /xm. For convenience the pores are sometimes divided into three classes ... 

Conjugated dienes have been polymerised using supported half-sandwich metallocene catalysts. For instance, catalysts derived by supporting CpTiCl3 on alumina-silica gels, containing—0-Ti(Cp)Cl2 species, displayed activity in isoprene polymerisation without the addition of any other activator. Depending on the alumina-silica gel composition, the kind of polymerisation medium and the temperature, these catalysts exhibited various activities and selectivities polyisoprenes with a predominant 3,4 structure and mixed 1,2/ trans-1,4 structure were obtained [118,119],... 

This chapter discusses the fundamental principles for designing nanoporous adsorbents and recent progress in new sorbent materials. For sorbent design, detail discussion is given on both fundamental interaction forces and the effects of pore size and geometry on adsorption. A summary discussion is made on recent progress on the following types of materials as sorbents activated carbon, activated alumina, silica gel, MCM-41, zeolites, n -complexation sorbents, carbon nano tubes, heteropoly compounds, and pillared clays. 2001 Academic Press. 

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