Charcoal, general

Broadly speaking, the differences in effectiveness of palladium and platinum catalysts are very small the choice will generally be made on the basis of availability and current price of the two metals. Charcoal is a somewhat more efficient carrier than asbestos. 

Although the charcoal canisters are about 95% effective, fuel volatiUty still impacts the mass of vapors that break through the canister. Therefore, EPA mandated that starting in the summer of 1992, RVP levels be reduced below the levels specified in ASTM D4814. Class C regions, generally the northern part of the country, are limited to a maximum RVP of 62 kPa (9.0 psi) vs an ASTM limit of 79 kPa (11 psi), and the southern Class B regions are limited to a maximum RVP of 54 kPa (7.8 psi) vs 69 kPa (9.0 psi) for ASTM. 

The rationale for the development of such fibers is demonstrated by their appHcation in the medical field, notably hemoperfusion, where cartridges loaded with activated charcoal-filled hoUow fiber contact blood. Low molecular weight body wastes diffuse through the fiber walls and are absorbed in the fiber core. In such processes, the blood does not contact the active sorbent direcdy, but faces the nontoxic, blood compatible membrane (see Controlled RELEASE TECHNOLOGY, pharmaceutical). Other uses include waste industrial appHcations as general as chromates and phosphates and as specific as radioactive/nuclear materials. 

Wood is one of our most important renewable biomass resources. Unlike most biomass sources, wood is available year round and is more stable on storage than other agricultural residues. In the United States, wood residues from iadustrial by-products totaled 60.8 x 10 metric tons ia 1993 (73). Increasiagly, residues are iacorporated iato manufactured wood products and are used as a fuel, replacing petroleum, especially at wood-iadustry plants (73) some is converted to charcoal but most is used ia the pulp and paper iadustry. Residues are also available for manufacturiag chemicals, generally at a cost equivalent to their fuel value (see Fuels frombiomass Fuels fromwaste). 

Charcoal is generally satisfactorily activated by heating gently to red heat in a crucible or quartz beaker in a muffle furnace, finally allowing to cool under an inert atmosphere in a desiccator. Good commercial activated charcoal is made from wood, e.g. Norit (from Birch wood), Darco and Nuchar. If the cost is important then the cheaper animal charcoal (bone charcoal) can be used. However, this charcoal contains calcium phosphate and other calcium salts and cannot be used with acidic materials. In this case the charcoal is boiled with dilute hydrochloric acid (1 1 by volume) for 2-3h, diluted with distilled water and filtered through a fine grade paper on a Buchner flask, washed with distilled water until the filtrate is almost neutral, and dried first in air then in a vacuum, and activated as above. To improve the porosity, charcoal columns are usually prepared in admixture with diatomaceous earth. 

Because of their zwitterionic nature, amino acids are generally soluble in water. Their solubility in organic solvents rises as the fat-soluble portion of the molecule increases. The likeliest impurities are traces of salts, heavy metal ions, proteins and other amino acids. Purification of these is usually easy, by recrystallisation from water or ethanol/water mixtures. The amino acid is dissolved in the boiling solvent, decolorised if necessary by boiling with Ig of acid-washed charcoal/lOOg amino acid, then filtered hot, chilled, and set aside for several hours to crystallise. The crystals are filtered off, washed with ethanol, then ether, and dried. 

Charcoal Tubes Reference has been made earlier to adsorption, which is the property of some solid materials, such as activated charcoal, to physically retain solvent vapors on their surfaces. In environmental health testing, the adsorbed vapors are removed, generally with a solvent, in a laboratory. The solvent is then analyzed by physical methods (gas chromatography, etc.) to determine the individual compounds whose vapors, such as benzene, were present in the sampled air. Industrial atmospheric samples can be collected in small glass tubes (4 mm ID) packed with two sections of activated charcoal, separated and retained with fiberglass plugs. To obtain an air sample, the sealed ends of the tube are broken off, and air is drawn through the charcoal at the rate of 1 liter per minute by means... 

Charcoal Encyclopedia definitions and general information on adsorption. http //www.encvclopedia.com... 

The term porosity refers to the fraction of the medium that contains the voids. When a fluid is passed over the medium, the fraction of the medium (i.e., the pores) that contributes to the flow is referred to as the effective porosity of the media. In a general sense, porous media are classified as either unconsolidated and consolidated and/or as ordered and random. Examples of unconsolidated media are sand, glass beads, catalyst pellets, column packing materials, soil, gravel and packing such as charcoal. 

Acetylenes are most readily absorbed by CAA, and hence are generally removed in a prewash step. Strict control of the acetylene content of the recirculating solvent is necessary and a charcoal adsorbent bed is used to maintain the polymer content of the solution at low levels. 

Liquid-solid chromatography (LSC). This process, often termed adsorption chromatography, is based on interactions between the solute and fixed active sites on a finely divided solid adsorbent used as the stationary phase. The adsorbent, which may be packed in a column or spread on a plate, is generally a high surface area, active solid such as alumina, charcoal or silica gel, the last... 

MDHS 14 General method for the gravimetric determination of respirable and total dust MDHS 15 Carbon disulphide MDHS 16 Mercury vapour in air Laboratory method using hopcalite adsorbent tubes, and acid dissolution with cold vapour atomic absorption spectrometric analysis MDHS 17 Benzene in air Laboratory method using charcoal adsorbent tubes, solvent desorption and gas chromatography MDHS 18 Tetra alkyl lead compounds in air Continuous on-site monitoring method using PAC Check atomic absorption spirometry... 

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