Carbon, activated properties

Although various carbonaceous sources can be used, petroleum cokes were preferred because of their low ash contents and generally higher yields of active carbon. The cokes were obtained from various sources and with widely varying properties. Sulfur contents ranged from 2.0 to 6.0 wt.% metals, primarily nickel and vanadium, from 500 ppm to 5,000 ppm volatile matter, from 11% to 20%. The coke quality within these ranges did not appear to affect active carbon properties. However, somewhat lower active carbon yields were noted with the higher volatile matter cokes (58-62 wt% vs. 

The usability of waste carbon deposits was demonstrated for preparation of active adsorbents with both zeolite and active carbon properties. 

Adsorption of NOM onto activated carbon has been found to be influenced by a number of physicochemical properties such as e.g. pH value, NOM initial concentration, type and molecular size distribution of NOM, ionic strength, and water temperature (Lee et al., 1981 Cornel et al., 1986 Fettig and Sontheimer, 1987 Summers and Roberts, 1988 Johannsen et al., 1991 Kilduff et al., 1996 Bjelopavlic et al., 1999). Besides physicochemical characteristics of the process water adsorption is also dependent on properties of the activated carbon as e.g. pore volume, pore size distribution (Lee et al., 1981 Bjelopavlic et al., 1999 Ebie et al., 2001) surface area accessible for adsorption and surface functional groups as e.g. carboxyl, hydroxyl and carbonyl groups (Cookson, 1980). Adsorption of organic micro-pollutants is also affected by water and activated carbon properties. 

The distribution of the active phase through the activated carbon particles and the dimensions of metal(compounds) are determined by activated carbon properties in relation to the chosen preparation method. Important activated carbon quality criteria are ... 

Cabrera-Codony A, Montes-Moran MA, Sanchez-Polo M, Martin MJ, Gonzalez-Olmos R (2014) Biogas upgrading optimal activated carbon properties for Siloxane removal. Environ Sci Technol 48 7187-7195... 

Activated carbons contain chemisorbed oxygen in varying amounts unless special cate is taken to eliminate it. Desired adsorption properties often depend upon the amount and type of chemisorbed oxygen species on the surface. Therefore, the adsorption properties of an activated carbon adsorbent depend on its prior temperature and oxygen-exposure history. In contrast, molecular sieve 2eohtes and other oxide adsorbents are not affected by oxidi2ing or reducing conditions. 

Physical Properties. Physical properties of importance include particle size, density, volume fraction of intraparticle and extraparticle voids when packed into adsorbent beds, strength, attrition resistance, and dustiness. These properties can be varied intentionally to tailor adsorbents to specific apphcations (See Adsorption liquid separation Aluminum compounds, aluminum oxide (alumna) Carbon, activated carbon Ion exchange Molecular sieves and Silicon compounds, synthetic inorganic silicates). 

Traditional adsorbents such as sihca [7631 -86-9] Si02 activated alumina [1318-23-6] AI2O2 and activated carbon [7440-44-0], C, exhibit large surface areas and micropore volumes. The surface chemical properties of these adsorbents make them potentially useful for separations by molecular class. However, the micropore size distribution is fairly broad for these materials (45). This characteristic makes them unsuitable for use in separations in which steric hindrance can potentially be exploited (see Aluminum compounds, aluminum oxide (ALUMINA) Silicon compounds, synthetic inorganic silicates). 

Other techniques include oxidative, steam atmosphere (33), and molten salt (34) pyrolyses. In a partial-air atmosphere, mbber pyrolysis is an exothermic reaction. The reaction rate and ratio of pyrolytic filler to ok products are controlled by the oxygen flow rate. Pyrolysis in a steam atmosphere gives a cleaner char with a greater surface area than char pyroly2ed in an inert atmosphere however, the physical properties of the cured compounded mbber are inferior. Because of the greater surface area, this pyrolytic filler could be used as activated carbon, but production costs are prohibitive. Molten salt baths produce pyroly2ed char and ok products from tine chips. The product characteristics and quantities depend on the salt used. Recovery of char from the molten salt is difficult. 

Many attempts have been made to reduce the ammoniacal and sulfurous odor of the standard thioglycolate formulations. As the cosmetics market is very sensitive to the presence of impurities, odor, and color, various treatments of purification have been claimed to improve the olfactory properties of thioglycolic acid and its salts, such as distillation (33), stabilization against the formation of H2S using active ingredients (34), extraction with solvents (35), active carbon (36), and chelate resin treatments (37). 

The stmcture of activated carbon is best described as a twisted network of defective carbon layer planes, cross-linked by aHphatic bridging groups (6). X-ray diffraction patterns of activated carbon reveal that it is nongraphitic, remaining amorphous because the randomly cross-linked network inhibits reordering of the stmcture even when heated to 3000°C (7). This property of activated carbon contributes to its most unique feature, namely, the highly developed and accessible internal pore stmcture. The surface area, dimensions, and distribution of the pores depend on the precursor and on the conditions of carbonization and activation. Pore sizes are classified (8) by the International Union of Pure and AppHed Chemistry (lUPAC) as micropores (pore width <2 nm), mesopores (pore width 2—50 nm), and macropores (pore width >50 nm) (see Adsorption). 

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). 

Table 1. Properties of Selected U.S. Activated Carbon Products ...

Specifications. Activated carbon producers furnish product bulletins that Hst specifications, usually expressed as a maximum or minimum value, and typical properties for each grade produced. Standards helpful in setting purchasing specifications for granular and powdered activated carbon products have been pubHshed (33,34). 

Source references for frequentiy used test procedures for determining properties of activated carbon are shown in Table 4. A primary source is the Jinnual Book ofyimerican Societyfor Testing and Materials (ASTM) Standards (61). Other usehil sources of standards and test procedures include manufacturers of activated carbon products, the American Water Works Association (AWWA) (33,34), and the Department of Defense (54). 

Catalysis. Catalytic properties of the activated carbon surface are useful in both inorganic and organic synthesis. For example, the fumigant sulfuryl fluoride is made by reaction of sulfur dioxide with hydrogen fluoride and fluorine over activated carbon (114). Activated carbon also catalyzes the addition of halogens across a carbon—carbon double bond in the production of a variety of organic haUdes (85) and is used in the production of phosgene... 

M. Smisek and S. Cemy, Active Carbon—Manufacture, Properties, and Applications, Elsevier Publishing Co., New York, 1970, pp. 290—294. 

The classifications in Table 16-3 are intended only as a rough guide. For example, a carbon molecular sieve is truly amorphous but has been manufactured to have certain structural, rate-selective properties. Similarly, the extent of hydrophobicity of an activated carbon will depend on its ash content and its level of surface oxidation. 

Lin, R. Y. and Economy, J., Preparation and properties of activated carbon fibers derived from phenolic resin precursor, Appl. Polym. Symp., 1973, 21, 143 152. 

The activated carbon materials are produced by either thermal or chemical activation as granular, powdered, or shaped products. In addition to the form of the activated carbon, the final product can differ in both particle size and pore structure. The properties of the activated carbon will determine the type of application for which the carbon will be used. 

Properties of activated carbons produced by Westvaco for automotive applications are presented in Table 5. 

Table 4. Properties of selected activated carbon products. Reprinted from [11], copyright (c) 1992 John Willey Sons, Inc., with permission.

Smisek M. and Cemy S., Active Carbon - Manufacture, Properties and Applications, Elsevier, Amsterdam - London - New York, 1970. 

---