Lignite specific surfaces

The total x-ray specific surfaces of Beulah lignite determined at the University of North Dakota and the University of Missouri agree within the estimated uncertainty. For the specific surfaces of the macropores and the transitional pores, the agreement, though still within the estimate uncertainty, is not so close. This greater difference may be a result of the fact that the scattering curves from the Universities of North Dakota and Missouri were determined by fits of Equation (3) with n = 2 and n = 1,... 

The transitional-pore specific surfaces listed in Table 1 for all of the subbltumlnous coals except PSOC 138 are about 3 to 8 times as large as the corresponding macropore specific surfaces. The ratio of the area associated with the transitional pores to that for the macropores is large enough in these subbltumlnous coals that at least a trace of an Inflection can be seen on careful examination of the scattering curves. On the other hand, for the subbltumlnous Coal 138 and for the lignites, the specific surfaces of the macropores and the transitional pores are more nearly equal, and no inflection is evident in the scattering curves. 

If our suggestion that Equation (4) approximates the pore-dimension distribution in lignites is correct, there is no unique way to classify the pores as macropores, transitional pores, and micropores, at least for pores smaller than about 3000 A. Instead, there is a continuous distribution of the pore dimensions from about 4 A to at least 3,000 A. However, the fact that the pore classes may not be uniquely defined does not invalidate the alternative and essentially equivalent analysis of the data in which we employed Equation (3) to determine the x-ray specific surface. 

Hydro Darco 3000 (see also HD 3000), Raw Material Lignite Properties BET specific surface area 600-650 m7g, mean particle diameter... 

Despite a significantly lower adsorption capacity of activated carbons for the removal of SOj and NO from flue gases in comparison with the VOC removal capacity, there are many processes in which they (or activated cokes) are applied for purification of industrial fumes [171-174] from coal fired power plants and waste incinerators. Activated coke is a carbonaceous adsorbent manufactured from lignites or hard coals. Typically, the specific surface areas of commercially available activated cokes are relatively low (up to 400 m g" ) and the pore volumes are only up to ca. 0.25 cm g Depending on the material origin and the manufacturing process, either adsorptive or catalytic characteristics may play a dominant role in the removal of contaminants on this adsorbent. The majority of activated cokes is used for the removal of SO and dioxins fiom waste and flue gases. 

For all fluid-dynamic calculations, it is advisable to correct the Sauter diameter by the sphericity yielding the representative diameter based on equivalent specific surface area d. Equation (3.70) assumes a constant sphericity for all size fractions. For pulverized bituminous coal (<100 pm) sphericities between 0.73 and 0.78 are reported while for coarse bituminous coals (4-22.4 mm) somewhat lower values of 0.66-0.71 occur. For lignite fibers (xylite), sphericity may decrease to 0.38 [114,115]. 

Lignite GAC This presents a total surface area of 650 m2/g and an apparent density of 0.50 g/cm3, approximately. It is usually used for liquid-phase adsorption, and specifically, in decolorizing applications because it has a higher percentage of meso (transitional) and macro pores than bituminous GAC, and therefore is appropriate for larger molecules. 

To achieve a significant adsorptive capacity an adsorbent must have a high specific area, which implies a highly porous structure with very small micropores. Such microporous solids can be produced in several different ways. Adsorbents such as silica gel and activated alumina are made by precipitation of colloidal particles, followed by dehydration. Carbon adsorbents are prepared by controlled burn-out of carbonaceous materials such as coal, lignite, and coconut shells. The crystalline adsorbents (zeolite and zeolite analogues are different in that the dimensions of the micropores are determined by the crystal structure and there is therefore virtually no distribution of micropore size. Although structurally very different from the crystalline adsorbents, carbon molecular sieves also have a very narrow distribution of pore size. The adsorptive properties depend on the pore size and the pore size distribution as well as on the nature of the solid surface. 

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