Silica gel, activation

Distd, then repeatedly fractionally crystd by partial freezing. Immediately before use, the material was passed through a column containing Woelm silica gel (activity I) and Woelm alumina (neutral) in separate layers. 

New, unused columns were used to minimize the memory effects known not only with silica gel active packings, but also with PS/DVB materials (13). One single column of each kind (7.5, 7.8, 8, or 10 mm in diameter and 250 or 300 mm in length) was used in each series of experiments. 

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... 

Packing materials for column chromatography. Adequate cleanup can be achieved with alumina instead of silica gel. Activated carbon is not suitable for sample cleanup of ripe orange and leaf. 

Dimethylbutane [79-29-8] M 86.2, b 58.0 , d 1.375, n 1.37231. Distd from sodium, passed through a column of silica gel (activated by heating in nitrogen to 350° before use) to remove unsaturated impurities, and again distd from sodium. Also distilled azeotropically with MeOH, then washed with water, dried and redistd. 

MeOH addition, filtration. SPE on silica gel activated with hexane and elution with MeOH. 

GC column molecular sieve 5A, 13X Chromosorb 102 (80/100 mesh), Carboxen 1004, Haye Sep Q, Carbosieve, Carbosphere, silica gel, activated alumina, or any other equivalent material. Fused silica nonpolar capillary column may be used for low sample volume. 

Fig. 1. Pore-size distribution for activated carbon, silica gel, activated alumina, two molecular-sieve carbons, and zeolite 5A (Yang, 1997).

Abstract. Structural and adsorption characteristics of various adsorbents such as fumed silicas, silica gels, activated carbons and carbon/silicas were analyzed. The adsorption of a variety of compounds reveals the effects of adsorbent grain size, specific surface area, pore volume, pore size distribution, surface chemistry, conditions of adsorbent synthesis and pre-treatment. Both dynamic (nonequilibrium) and static (equilibrium) adsorption conditions are addressed. 

Keywords fumed oxides silica gels activated carbons carbon-mineral adsorbents toxic and narcotic compounds explosives dynamic and static adsorption... 

Thiohydantoins of amino acids Silica gel, activated at 100°C for 1 h (1) n-Heptane-l-butanol-anhydrous formic acid (10 7 3) (2) Chloroform-95% ethanol-acetic acid (100 50 15) 17... 

The attachment of particular solute molecules to the surface of the particulate sorption packing material can be achieved by a number of different methods, which are outside the scope of this paper. There are a large number of different sorption materials and complex physical and chemical interactions which must be considered. The most common sorption materials are activated carbon, silica gel, activated alumina, molecular sieves, and ion exchange resins. This chapter deals with the industrial aspects of handling these materials and operating process-scale equipment, but does not look at the choice of sorption material for a particular process. 

A1203 activated by heating to about 200 C in a current of air or carbon dioxide, is the most, widely used absorbent. Other adsorbents used are silica gel (activated in the same manner as alumina), magnesium oxide, magnesium carbonate, calcium carbonate, calcium sulphate, barium carbonate, charocal, sucrose, talc, starch, cellulose and Fuller s earth. The inorganic adsorbents are usually heated to 200-220 C before use. 

Gas phase adsorption on solids (silica gels, activated charcoal, synthetic zeolites, molecular sieves) is also practised industrially. It is more suitable for the purihcation of effluents that display some complexity of composition. Its effectiveness depends on many parameters, particularly the volatility and polarity of the feedstock components. 

Desiccants. A solid 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 liquid) stream. The main requirements for an efficient desiccant are therefore a highly polar surface and a high specific area (small pores). The most widely used desiccants (qv) are silica gel, activated alumina, and the aluminum rich zeolites (4A or 13X). The equilibrium adsorption isotliemis for moisture on these materials have characteristically different shapes (Fig. 3), making them suitable for different applications. 

Amorphous silica gel, activated alumina, activated carbon, and molecular sieve carbons. 

Moderately polar crystalline molecular sieves with low aluminum and low cation contents, silica gel, activated alumina., activated carbons with highly oxidiz... 

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