Activated carbon iodine number

Portions of this test are adapted from ASTM D 4607-94(1999)— Standard Test Method for Determination of Iodine Number of Activated Carbon. The original ASTM method is available in its entirety from ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428 phone 610-832-9585 fax 610-832-9555 email service astm.org website . 

Calculation The capacity of a carbon for any adsorbate depends on the concentration of the adsorbate. The concentrations of the standard iodine solution and filtrate must be known to determine an appropriate carbon weight to produce final concentrations agreeing with the definition of iodine number. The amount of sample to be used in the determination is governed by the activity of the sample. If filtrate normalities (C) are not within the range of 0.008 N to 0.040 N, repeat the procedure using different sample weights. 

However, the usual tests for characterizing active carbon — such as the phenol number, the surface area (BET 2)> tl tannin index or the iodine index — are inadequate for evaluating the potential removal of the humic substances by the carbon. Moreover the resulting adsorption may differ according to the source and previous treatment of those substances and the characteristics of the feed water used. 

The iodine number of activated carbon was determined in the beginning of the experiment, as well as at particular stages of column functioning, just before changing the column operating mode. 

Six common isotherm shapes are shown in Figure 14.4. In fact, those are the classic isotherm types suggested by Brunauer et al. (1940). Each can be represented by numerous empirical equations, some of which are discussed later. The inherent shapes or types arise from the pore structure of the adsorbent, the nature of the forces between the adsorbent surface and adsorbate, and the dependence on concentration. Besides isotherms, other properties are related to adsorption capacity, especially surface area and pore size distribution. Some other properties are application oriented, such as CTC (carbon tetrachloride) index, iodine number, methylene blue factor, and molasses number, all defined in Table 14.1. They are frequently employed to describe activated carbons. 

The Iodine Number relates to the ability of activated carbon to adsorb low molecular weight substances (micropores have an effective radius of less than 2.0 pm). 

The charcoal is moderately active even without further steam activation. The surface area was determined by the iodine number method (456 mg Vg). Steam activation converted the initial charcoal product to a higher-surface-area activated carbon with the iodine number 540 mg t/g, but with loss of about half of the carbon. The initial charcoal should be adequate for a number of decolorizing and other aqueous treatments. 

The liquid-phase materials are usually characterized by sorption tests using phenol, iodine, or "molasses number." The vapor-phase activated carbons are usually characKiized by carbon tetrachloride or benzene adsorption tests. The adsorption capacity and the bulk density define the volumetric treatii capability of the material. 

Iodine Number The iodine number is defined as the amount of iodine (in milligrams) adsorbed by powdered carbon (per gram) from 0.02 N iodine aqueous solution (ASTM D4607-94). Iodine is in the form of I2, with a very small amount of Ib anion. A typical iodine number for activated carbon is 900, with values > 1000 for better grades of carbon. The iodine number has been roughly correlated to the surface area of pores >10 A diameter. It is regarded approximately as the total pore volume. 

J. There are separate tests for the capacity of activated carbon used in water service to hold impurities. They are known as the Iodine Number test (ASTM D4607-94) and the Molasses Number test (no ASTM test). 

Another potential application of the packed fluidized bed is in the regeneration of spent activated carbon after its use in municipal waste water treatments and in the removal of odors from waste gases (Kato et al. 1980). The adsorption capacity of the regenerated catalyst as measured by the iodine number was found to agree well with the values predicted by the model described above. 

Iodine adsorption it is a simple and quick test, giving an indication of the internal surface area of the carbon in many activated carbons the iodine number (expressed as milligrams of iodine per gram of carbon) is close to the Brunauer-Emmett-Teller (BET) surface area. In this method, the activated carbon is boiled with 5% HCl and, after cooling, a 0.1N iodine solution is added and shaken for 30 s after filtration, the filtrate is titrated with O.IN sodium thiosulfate solution, with starch as indicator. The standard used is AWWA B600-78 (see Section 8.1.2). 

Pore volumes of carbons are typically of the order of 0.3 cm /g. Porosities are commonly quoted on the basis of adsorption with species such as iodine, methylene blue, benzene, carbon tetrachloride, phenol or molasses. The quantities of these substances adsorbed under different conditions give rise to parameters such as the Iodine Number, etc. Iodine, methylene blue and molasses numbers are correlated with pores in excess of 1.0,1.S and 2.8 nm, respectively. Other relevant properties of activated carbons include the kindling point (which should be over STO C to prevent excessive oxidation in the gas phase during regeneration), the ash content, the ash composition, and the pH when the carbon is in contact with water. Some typical properties of activated carbons are shown in Table 2.2. 

The Iranian team of Esfandiari and coworkers has also investigated activated carbon production from PET [83]. Carbon dioxide activation was used and the effects of variables such as temperature, heating rate, flow rate, and duration of heat treatments were investigated. It was observed that the most influential parameters are the activation time, activation temperature, and carbonization time. At the expense of further bum-off, the iodine number of the sample was seen to increase with elongation of the activation time. The experimental values for the iodine number were in good agreement with those obtained by the Taguchi optimization model [84]. 

Finally, the brominations of mesitylene, 1,2,4,5-tetramethyl- and pentamethyl-benzene in chloroform (which is more polar than carbon tetrachloride) are first-order in bromine and iodine monobromide318, so that this is entirely consistent with the pattern developed above, i.e. the more polar the solvent and the more reactive the compound, the fewer the number of molecules of iodine monobromide that are involved in the rate-determining step. Measurements of rates between 25 and 42 °C revealed no significant trend owing to the variability of the rate coefficients determined at any temperature, but even so it is clear that there is no appreciable activation energy for these compounds, and there may have been temperature inversion for some of them. 

Lord and Pritchard34 found that when the iodinolysis of dimethylmercury was carried out with rigorous exclusion of light, the reaction was first-order in dimethylmercury and first-order in iodine. Activation energies and rate coefficients for iodinolysis of dimethylmercury in a number of solvents were determined. For solvent carbon tetrachloride, the second-order rate coefficient at 28 °C was found to be 0.073 l.mole-1.min-1 and Ea = 7.7 kcal.mole-1. The corresponding values of Razuvaev and Savitskii33 are k2 = 0.11 l.moIe-1.min-1 and Ea = 9.5 kcal. mole-1. ... 

The difficulty in dealing with solvent influences on reaction rates is that the free energy of activation, AG, depends not only on the free energy of the transition state but also on the free energy of the initial state. It is therefore of considerable interest to dissect solvent influences on AG into initial-state and transition-state contributions. As far as electrophilic substitution at saturated carbon is concerned, the only cases for which such a dissection has been carried out are (a) for the substitution of tetraalkyltins by mercuric chloride in the methanol-water solvent system (see page 79), and (b) for the iododemetallation of tetraalkylleads in a number of solvents (see p. 173). Data on the latter reaction (6) are more useful from the point of view of the correlation of transition-state effects with solvent properties, and in Table 13 are listed values of AG (Tr), the free energy of transfer (on the mole fraction scale) of the tetraalkyllead/iodine transition states from methanol to other solvents. 

This review deals only with the heterogeneous oxidation of-carbon monoxide by solid materials which show some catalytic activity or a fast surface reaction. It does not include purely stoichiometric reagents used in detection and analysis, such as iodine pentoxide, mercuric oxide, palladium salts activated by molybdenum salts, or liquid-gas systems. A review of such agents has recently been presented elsewhere (11). Furthermore, no attempt has been made to provide complete coverage of the numerous patents in this field, although a number of the more important ones are mentioned. 

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