Boleslav Taraba

Reversible and irreversible interaction of oxygen with coal using pulse flow calorimetry

Abstract The effects of temperature, time, particle size and coal moisture content on heats of reversibly and irreversibly sorbed oxygen were studied separately using pulse flow calorimetry. The results of measurements performed on seven coal samples, ranging from subbituminous to low volatile bituminous, show that in coals of low porosity (open porosity less than ≈8%), the particle size affects the heat of the apparent physical adsorption of oxygen much more than that of chemical sorption. However, in two samples of high porosity (open porosity 25 and 28%), the heats of both physically and chemically sorbed oxygen were found to be independent of particle size. The heat of reversibly sorbed oxygen decreased with increase in moisture content, while the heat of irreversibly sorbed oxygen remained constant and even increased in highly hydrophilic samples. Comparison of coal surfaces occupied by adsorbed molecules of oxygen and coal surfaces occupied by a nitrogen monolayer (BET) shows that at ambient temperature, oxygen is able to penetrate even into those micropores of coal which are inaccessible to N 2 at −196 °C.

Differentiation of thermal effects during low temperature oxidation of coal

Abstract The heat evolution during the low temperature oxidation of coals ranging from lignite to anthracite was measured by means of four independent methods: adibatic, pulse flow microcalorimetric, differential microcalorimetric, and gas chromatographic. The last one was used to determine the heat evolved during physical adsorption of oxygen on the coal surface. The heat of this sort has been found to represent values from 0.16 to 0.6 J ml−1 O2 according to coal rank. On the other hand, the chemical reaction releases 11–12 J ml−1 O2 and is the same for lignite and brown coals at ordinary temperatures as for bituminous coals at elevated temperatures (60–80 °C). The heat of chemical interaction varies at a temperature range 30–40 °C between 3 and 5 J ml−1 O2 for high rank bituminous coals and 7 and 10 J ml−1 O2 for bituminous coals with volatile matter greater than 28 wt%. The highest thermal effect (up to 25 J ml−1 O2 is related to existing active sites on the coal surface and therefore is observable only for extremely clean surfaces or at higher initial temperatures of oxidation.

Immobilization of Heavy Metals and Phenol on Altered Bituminous Coals

Abstract This article evaluates adsorption ability of the altered bituminous coals to remove heavy metals and/or phenol from aqueous solutions. As for heavy metals, copper (II), cadmium (II) and lead (II) cations were used. In addition to phenol, cyclohexanol and 2-cyclohexen-1-ol were also examined. Adsorption experiments were conducted in the batch mode at room temperature and at pH 3 and 5. To characterize the texture of coal samples, adsorption isotherms of nitrogen at −196°C, enthalpies of the immersion in water, and pH values in aqueous dispersions were measured. Coal hydrogen aromaticities were evaluated from the infrared spectrometric examinations (DRIFTS). Based on the investigations performed, cation exchange was confirmed as the principal mechanism to immobilize heavy metallic ions on coals. However, apart from carboxylic groups, other functionalities (hydroxyl groups) were found to be involved in the adsorption process. During adsorption of phenol, π-π interactions between π-electrons of phenol and aromatic rings of coal proved to play the important role; however, no distinct correlation between adsorption capacities for phenol and hydrogen aromaticities of the coal was found. Probable involvement of oxygenated surface groups in the immobilization of phenol on coal was deduced. As a result, for waste water treatment, oxidative altered bituminous coal can be recommended as a suitable precursor, with the largest immobilization capacities both for metallic ions and phenol, as found in the studied samples.

Adsorption of the SDS on Coal

Simultaneous measurements of the sodium dodecyl sulphate (SDS) adsorption on coal and zeta potential determination of the (adsorption) suspensions were carried out. Three samples of sub-bituminous, bituminous and oxidative altered bituminous coal were investigated. The adsorption isotherms were found to be of typical Langmuir type, values of the SDS adsorption capacities have been calculated. Shape of the adsorption isotherms was correlated with zeta potential values of the suspensions in (adsorption) equilibrium. The results indicate that adsorption of SDS on coal is going mainly through hydrophobic interactions between the surfactant molecules and the coal surface.

Immobilization of Heavy Metal Ions on Coals and Carbons

Adsorption of heavy metals from the aqueous phase is a very important and attractive separation techniques because of its ease and the ease in the recovery of the loaded adsorbent. For treatment of waste as well as drinking water, activated carbons are widely used (Machida et al., 2005; Guo et al., 2010). Due to an increasing demand on thorough purification of water, there is a great need to search for cheaper and more effective adsorbents. Thus, alternative resources for manufacturing affordable activated carbons are extensively examined (e.g. Guo et al., 2010; Qiu et al., 2008; Giraldo-Gutierrez & MorenoPirajan, 2008). Simultaneously, natural coals are investigated as economically accessible and efficient adsorbents to remove heavy metals (Kuhr et al., 1997; Zeledon-Toruno et al., 2005; Mohan & Chander, 2006). Radovic et al. (2001) published a principal comprehensive review of the adsorption from aqueous solutions on carbons with incredible 777 references. Their analytical survey covers adsorption of both organic and inorganic compounds (including heavy metals) and, certainly, it remains a basic source of information on the topics. This chapter is concerned with the immobilization of heavy metals on carbonaceous surfaces, and, it attempts to compare adsorption behaviour of activated carbons with that of natural coals. Here, references published in the last decade are mainly reported, the literature findings being immediately confronted with experimental data as obtained from laboratory examinations of two natural coals. First, a brief insight into adsorption kinetics is given, followed by a survey of models to describe adsorption at equilibrium. The issue of thermodynamics of heavy metals adsorption follows. Finally, the possible immobilization mechanisms of heavy metals on carbons/coals are carefully considered and discussed.

Mechanical decarbonylation of coal

Abstract Desorption, oxidation and mechanically activated decarbonylation of coal were examined as possible sources of carbon monoxide emitted from coal during the grinding process. The effects of grinding time, temperature, coal pretreatment and coal rank on CO emission as well as adsorptive capacity of coal for carbon monoxide were investigated for 12 coal samples. Mechanical decarbonylation of coal was found to be the most probable source of CO evolved from coal in milling under inert conditions. During milling under oxygen, however, some of the CO emission originates from coal oxidation.

REVERSIBLE AND IRREVERSIBLE INTERACTION OF OXYGEN WITH COAL OF VARIOUS RANK

Publisher Summary This chapter describes the effect of coal rank on reversible and irreversible oxygen sorption separately, using the pulse-flow calorimetric method. In a study described in the chapter, 50 coal samples ranging from lignite to anthracite were investigated. Grain size of 0.06–0.14 mm was prepared from a lump of fresh coal. The maximum time of exposure of the sample to air during crushing and screening was ∼30 min. Samples were examined in both wet and dry states. Drying pretreatment was performed in flow of argon at 90°C and/or 60°C. The chapter presents some experimental data obtained from measurements with wet coals. Calorimetric investigation of heats of irreversibly and reversibly sorbed oxygen on set of coals of various rank showed that there are coal types for which one or another sort of oxygen interaction quite prevails. For subbituminous coals and lignites, irreversible oxygen sorption dominates, reversible sorption being negligible.