Experimental Study on Sorption and Desorption of Propylene on Polish Hard Coals

Abstract

Propylene is the unsaturated hydrocarbon emitted to the atmosphere of a coal mine in the process of coal selfheating. Its concentration in mine air is one of the indicators for the assessment of the development of the process of coal selfheating. Coal sorption capacities with respect to propylene may be the reason for the decrease in its concentration in mine air. This may affect the accuracy of the assessment of the self-heating process development, in particular, in the case of coals of considerable sorption capacities. The paper presents the results of coal sorption capacities with respect to propylene performed on 10 samples of bituminous coals acquired from operated coal seams. The sorption capacities of tested coal samples varied depending upon level of metamorphism, porosity, and chemical characteristics of a coal surface. The highest sorption capacities were reported for high-porosity coals of easily accessible pore structure, high specific surface area values, low level of metamorphism, and high oxygen content. The interactions between the electron-donor (and electron-acceptor) centers and π bond between the carbon atoms of the gaseous reactant probably play the most important role in the sorption of propylene on coals. Coals of low oxygen content, nonpolar surface structure, low porosity, and compact internal structure are characterized by low propylene sorption capacity. The results of the experimental study also indicate the partially irreversible character of the sorption process reflected in the open isotherm hysteresis. Some amount of propylene molecules remains in the coal structure, depending upon the coal properties and the experimental conditions applied.

Effect of Coal Grain Size on Sorption Capacity with Respect to Propylene and Acetylene

“…The lowest volumes of propylene were sorbed on coal samples 6 and 7, characterized by the lowest porosity and low micropore surface area (see Table 2). The grade of metamorphism [25][26][27], porosity, and chemical characteristics of coal surface [10,11] are the most important properties of coals in terms of their sorption characteristics. The increase in the grade of metamorphism and decrease in coal porosity resulted in the deterioration of sorption capacity of tested coals with respect to propylene.…”

“…The increase in the grade of metamorphism and decrease in coal porosity resulted in the deterioration of sorption capacity of tested coals with respect to propylene. The electrostatic interactions between oxygen-containing reactive centers on coal surface and π electrons of the double bonds between carbon atoms play also a significant role in sorption of unsaturated hydrocarbons on coals [9,10,28,29]. Coals of higher oxygen and moisture content, and therefore of higher number of reactive oxygen-containing groups, tended to sorb higher volumes of propylene.…”

“…This in turn causes the underestimation of the concentrations of gaseous indicators of the self-heating process and an incorrect assessment of the development of this process. The gases adsorbed on coal in the highest amounts include the unsaturated hydrocarbons-such as ethylene, propylene, and acetylene-which reduces their applicability in the assessment of the self-heating process progress [9][10][11]. This is particularly important in the case of coals with high sorption capacity, and with long distances between the self-heating center and the measurement point of concentrations of gaseous process indicators.…”

Energetic effects of adsorption of C6-C8hydrocarbons on hard coal samples of different metamorphism

“…Majority of sorption research on hard coal presented in literature is performed on powder samples or on samples of granulation not higher than 0,9mm. As a result of such drastic fragmentation lost of primary pore structure can be observed as well as lost of chemical character of outer coal grains surface, which can have influence on higher values of sorbed amount of gas/vapors [20,21]. In order to characterize the research material there were analysis carried out: porosimetry and densimetry analysis, helium density measurements.…”

“…The study found that the sorption isotherms of hydrocarbon vapors on hard coal in the investigated pressures ranges and temperatures were irreversible, in each of examined cases open hysteresis loop was easily visible (the predominance of sorption processes in the microporous coal structure) [20,21].…”