Characterization of Pore Structure of Turkish Coals

Abstract

Pore structure of coal has a great influence on its behavior during mining, preparation, and utilization. Characterization of the pore structure of twelve Turkish coals from different geographic locations and with carbon contents varying between 61 and 84% (on dry ash-free basis) was carried out using different techniques. The volume and area of macropores were determined by mercury intrusion porosimetry. Mesopore volumes and areas were determined by N2 gas adsorption at 77 K using the Barrett−Joyner−Halenda (BJH) method. Brunauer−Emmet−Teller (BET) areas were calculated using the same data. Micropore volumes and areas were determined by the application of the Dubinin−Radushkevich (DR) equation to the CO2 adsorption data at 298 K. True and apparent densities of coals were measured by helium and mercury displacement. Pore size distributions were evaluated using data thus obtained. Small-angle X-ray scattering (SAXS) technique was also employed to determine the surface area of some samples. The highest BET surface area, 34 m2/g, was found for Tunçbilek coal which has a significant mesoporous volume; while the corresponding values for the rest of the coals were less than 7 m2/g. DR surface areas which varied in the range 19−115 m2/g were larger than BET areas indicating molecular sieve character of coals. SAXS areas were larger than DR areas for some coals which can be explained by the presence of closed pores in these samples. For some coals having relatively small porosities, SAXS areas were found to be smaller than DR areas which is attributed to the inability of the method to distinguish ultramicropores of molecular dimensions which are probably accessible to CO2 molecules. SAXS surface area of Illinois No. 6 coal and a synthetic char (Spherocarb) were also measured and the values found agreed well with the ones given in the literature.

Coal gasification in CO2 atmosphere and its kinetics since 1948: A brief review

“…The figure shows that at 875 C, the variation of reactivity with conversion profiles for all lignite samples has similar trends; it first increases up to a certain conversion, which is different for each lignite sample, then decreases with a further increase in the conversion. The authors explained the reactivity with conversion data of different ranks of coal using the results from a previous study which involved several texture characterization techniques [17] and demonstrated that lignite samples under study possessed micropores of molecular dimensions and that SAXS (Small Angle X-ray Scattering) measurement and carbon dioxide adsorption data indicated that some of these pores were closed and some were opened to larger mesopores and macropores with restricted passages [18]. It is observed that in the initial stages of the gasification disorganized carbon from tars are removed resulting in the opening of inaccessible porosity and then an increase in all sizes of pores which enhance reactivity until up to a certain conversion.…”

A review of coal properties pertinent to carbon dioxide sequestration in coal seams: with special reference to Victorian brown coals

“…However, water sorption and X-ray scattering (SAXS) methods are currently used to measure the surface area of coal (Senel et al 2001) due to high accuracy. The variation of coal physical properties with carbon content or rank is shown in Fig.…”

Physical and chemical properties of selected Turkish lignites and their pyrolysis and gasification rates determined by thermogravimetric analysis

“…Turkey has considerable amount of coal reserves of which lignites constitutes major portion with a reserve of 8.05 Â 10 6 tonnes [26,27] and mainly utilized conventionally for power production and heating purposes.…”

“…The present study was undertaken to provide information on pyrolysis and gasification rates of lignite samples representative of four important lignite deposits in Turkey. A detailed study on the textural properties of Turkish coals including the samples used in this study was published previously [26].…”