Carbon black sulfur impurities

Typical applications in the chemical field (Beaver, op. cit.) include detarring of manufactured gas, removal of acid mist and impurities in contact sulfuric acid plants, recovery of phosphoric acid mists, removal of dusts in gases from roasters, sintering machines, calciners, cement and lime Idlns, blast furnaces, carbon-black furnaces, regenerators on fluid-catalyst units, chemical-recoveiy furnaces in soda and sulfate pulp mills, and gypsum kettles. Figure 17-74 shows a vertical-flow steel-plate-type precipitator similar to a type used for catalyst-dust collection in certain fluid-catalyst plants. 

As formed, carbon black is a fluffy powder possessing low density. The densification process involves the removal of occluded air by agitation and followed by dry or wet process pelletization. In both the dry and wet pelletization process, nearly spherical pellets or beads will form that are typically composed of >99% carbon black and trace impurities such as sulfur. Thus, carbon black is sold as a low density powder or as a pelleted form in pigmenting and other end uses. The choice of a fluffy or pelleted carbon black for dispersion in a given system depends upon the dispersion and handling equipment and end use. For example, pelleted carbon blacks are used most frequently in production of black masterbatch carbon black powders are typically used to tint chromatic compounds. 

Especially important is that carbon black possesses low levels of residual contaminants. Residual impurities alone within a carbon black can adversely affect an application s dispersion properties, processing, molded surface characteristics, and color. Impurities can be defined as moisture, residual carbonaceous residue, sulfur, and certain ionic species. 

Extensive efforts have been made to characterize the surface chemistry of carbon blacks. Although carbon blacks are nearly all carbon, impurities of oxygen, sulfur, nitrogen and small amounts of other elements are present. Most of the work has centered around the identification and quantification of oxygen containing... 

The data manipulation capabilities of the FTIR spectrometer can be used to quantitatively resolve the structural features which are superimposed upon the intrinsic absorption. The spectral features which exceed a baseline drawn between 1880 and 880 cm 1 in five independent preparation and measurement experiments are shown in Figure 4. The superposition of these five spectra illustrate both the reproducibility and the quantitative nature of this technique. The "resolved" spectra consist of three broad absorptions centered around 1725,1595 and 1245 cm1 and two superimposed sharp bands at 1135 and 1340 cm1. These latter peaks are characteristic of the particular type of carbon black and are presumably caused by impurities introduced in the manufacturing process. They may reflect the presence of residual sulfur compounds present in the form of sulfones or sulfonic esters in which the symmetric and antisymmetric stretching modes of the S02 vibrational modes occur in the range of 1140-1160 cm1 and 1300-1350 cm 1 [24], Note the absence of discemable bands above 1730 cm 1. This implies that these carbon blacks do not contain the lactone and cyclic anhydride functionalities observed on other carbon surfaces (see Figure 1) [17]. 

The resolved spectra of these carbon blacks are shown in Figure 15. The bands at 1725,1595 and 1245 cm 1 observed in Monarch 1300 are also present in the different carbon blacks, but in varying proportions. Note that the bands at 1595 and 1245 cm 1 are even present in the completely unoxidized Sterling MT black. This reinforces the proposal that these bands are associated with the bulk carbon black structure and are only enhanced by the presence of surface species. As mentioned above, the sharp bands at 1135 and 1340 cm 1 appear in some of the carbon blacks but not in others as might be expected from sulfur impurities introduced from different feed stocks. 

Metal impurities and anion impurities such as halogenides, sulfates, nitrates, and phosphates are the most important impurities that occur in carbon black and could have an influence on the electrochemical system. Besides, sulfur, inorganic residue of refractory material, coke particles, and organic molecules formed during the carbon black synthesis are possible contaminants in carbon blacks. 

Black Liquor Soap Acidulation. Only two-thirds of a typical black Hquor soap consists of the sodium salts of fatty acids and resin acids (rosin). These acids are layered in a Hquid crystal fashion. In between these layers is black Hquor at the concentration of the soap skimmer, with various impurities, such as sodium carbonate, sodium sulfide, sodium sulfate, sodium hydroxide, sodium Hgnate, and calcium salts. This makes up the remaining one-third of the soap. Cmde tall oil is generated by acidifying the black Hquor soap with 30% sulfuric acid to a pH of 3. This is usually done in a vessel at 95°C with 20—30 minutes of vigorous agitation. Caution should be taken to scmb the hydrogen sulfide from the exhaust gas. 

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