Granular activated carbon hardness

Ignition Temperature of Granular Activated Carbon Carbon Tetrachloride Activity of Activated Carbon Ball-Pan Hardness of Activated Carbon... 

Most of the granular activated carbons u.sed in adsorber beds are produced from bituminous coal because their hardness, abrasion resistance, relatively high density, and pore size distributions render them suitable to withstand operating conditions and to adsorb the small organic molecules often present in drinking water. 

Other properties of activated carbons, however, may be even more important than their textural properties. One example is particle size. A classification of carbon axisorbents based on size divides them into Powdered Activated Carbons (PAC) or Granular Activated Carbons (GAC). For certain specific applications a choice must be made between PAC or GAC regardless of porous properties. For example, in order to clean up a gas stream in a fixed bed, a granular material must be used. Otherwise the pressure drop would be enormous. Furthermore, granular carbon must be dense, hard and with a low abrasion index. 

Investigations were carried out on commercially manufactured active carbons. Granular active carbons were obtained using following processes (AG) from hard coal at 1173-1227K, (RN) the same method of preparation as carbon AG, except in this case of peat at 1227K. 

In addition to surface area, pore size distribution, and surface chemistry, other important properties of commercial activated carbon products include pore volume, particle size distribution, apparent or bulk density, particle density, abrasion resistance, hardness, and ash content. The range of these and other properties is illustrated in Table 1 together with specific values for selected commercial grades of powdered, granular, and shaped activated carbon products used in Hquid- or gas-phase appHcations (19). 

For protection against toxic gases, activated carbon is supplied in granular form. Hardness of particles is essential to maintain a firmly packed bed in the canister and minimize dusting. Because of the small space available in the canister of a ga mask the adsorptive power must be concentrated in a small volume. The carbon, therefore, should be as dense as is consistent with high intrinsic adsorptive power. A rapid rate of adsorption is essential. 

Hardness Number 1) A measurement of the percentage of an activated carbon that survives impact and abrasion by standard size steel balls under prescribed conditions 2) The resistance of granular carbon to the degradation action of steel balls in a Ro-Tap machine under prescribed conditions. 

Activated carbon is available in various forms, ranging ftxim light and fluffy powder to hard, dense granules. Besides classification into granular (GAC) and powdered (PAC), commercially available activated carbons are further divided into grades based on adsorptive, physical and chemical properties [6, 18]. Commonly used tests for activated carbons ai e summarized in Table 2. 

Hardness and attrition Steam activated extrudated carbons in particular are very hard also compared to oxide carriers. Granular chemical activated carbons are much less hard. 

Hard coals (high-rank bituminous coals) are the preferred precursor in many countries, because they can be used both for production of inexpensive activated carbons, and also for the more expensive granular, hard carbons with well-developed porous structures. As-received coals have some porosity (which decreases with increasing rank of coal), and consequently further treatments are needed to increase the porosity. Low rank coals (peat, lignite, brown coal), which do not fuse on carbonization, are used to produce activated carbons with a wide pore-size distribution. The yield of activated carbons from coal is generally larger than for lignocellulosic materials, above 30 wt%. 

The gas-adsorptive properties of wood charcoal were recognized as early as 1773 by Scheele (Deitz, 1944) however, it was not until the middle of the nineteenth century that the property was utilized commercially. This application consisted of the use of charcoal air-filters in the ventilation and disinfection of sewers (Stenhousc, 1961). The next major step in the development of active carbon for gas ad.sorption occurred during World War I, when the use of poison gas by the Germans made it necessary to develop a hard, granular carbon for gas-mask use. 

Use a hard granular carbon that can withstand peptizing action Apply carbon in an admixture with another adsorbent such as magnesium silicate, bentonite, activated clay. In selecting an additional adsorbent it is necessary to consider whether the pH and other characteristics are compatible with the system being treated Conduct the adsorption in separate stages ... 

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