Analysis of Porous Structure Parameters of Biomass Chars Versus Bituminous Coal and Lignite Carbonized at High Pressure and Temperature—A Chemometric Study

Abstract

Abstract:The characteristics of the porous structure of carbonized materials affect their physical properties, such as density or strength, their sorption capacity, and their reactivity in thermochemical processing, determining both their applicability as fuels or sorbents and their efficiency in various processes. The porous structure of chars is shaped by the combined effects of physical and chemical properties of a carbonaceous material and the operating parameters applied in the carbonization process. In the study presented, the experimental dataset covering parameters of various fuels, ranging from biomass through lignite to bituminous coal, and chars produced at 1273 K and under the pressure of 1, 2, 3, and 4 MPa was analyzed with the application of the advanced method of data exploration. The principal component analysis showed that the sample of the highest coal rank was characterized by lower values of parameters reflecting the development of the porous structure of chars. A negative correlation was also observed between the carbon content in a fuel and the evolution of the porous structure of chars at high pressure. The highest total pore volume of chars produced under 1 and 3 MPa and the highest micropore surface area under 3 MPa were reported for a carbonized fuel sample of the highest moisture content.

Porous Structure Properties of Andropogon gerardi Derived Carbon Materials

“…Further increase in pressure to 4 MPa resulted in a decrease in the specific surface area and the total pore volume of about 19 and 23%, respectively, when compared to the maximum values reported for 3 MPa chars. This effect is in line with previous observations made for other precursors, including coal [ 15 , 16 , 17 , 18 ] and biomass [ 20 ], though the opposite tendency of the surface area of biomass-derived carbon materials to decrease with pressure has also been reported [ 19 ].…”

“…The slight decrease in the development of porous structure under the pressure of 4 MPa reflected in the decreased specific surface area and the total pore volume, as well as micropore area and volume, may also be the effect of merging of previously melted particles under the increased external stress. The pressure of 3 MPa may, therefore, be considered as the threshold value under the experimental conditions applied, exceeding which would result in the counteracting effects of the pressure on the porous structure development with the release of moisture and volatiles ( Table 1 ) as well as swelling behavior of the carbonized material [ 18 , 19 , 20 ]. If the target is to receive a carbon material with the largest volume of narrow micropores, then the value of 2 MPa can be considered optimal on the basis of the carbon dioxide isotherm data ( Table 2 ).…”

“…Clearly, the application of pressure itself is not sufficient to provide materials of the specific surface area and total pore volume comparable with commercial activated carbons or the materials after a complex cycle of physical and chemical activation of most suitable precursors [ 6 , 8 , 12 , 14 ]. Nevertheless, its application was proved to produce wood- and grass-derived materials with porous structures that are more developed than those obtained by the chemical activation of waste biomass, e.g., rice husk [ 9 , 20 ].The relatively low heating rates applied in this study also resulted in higher values of the specific surface area (of 40%) and micropore area (of 60%) than previously observed for pine-derived carbon materials produced under 2 MPa with high heating rates of 500 °C/min [ 19 ]. This implies that low heating rates are more applicable in tailoring the porous structure of carbon materials for high microporosity.…”

“…However, reports on the effects of pressure on the development of the porous structure of carbon materials are limited and concern mostly the characterization of coal chars’ behavior, including their reactivity, in gasification and combustion processes [ 15 , 16 , 17 , 18 ]. The studies presenting the effect of pressure on the development of biomass-derived carbon material porosity are even more scarce [ 19 , 20 ]. The pressures range applied in previous studies is also quite narrow and relatively low (0.5–2.5 MPa) [ 15 , 19 ], while the heating rates are high (of a few hundred °C per minute), representing the conditions of gasification reactors.…”

Contribution of Minerals in Different Occurrence Forms to PM10 Emissions during the Combustion of Pulverized Zhundong Coal

“…Each mode has a different mechanism of formation, namely: ultrafine mode PM is formed by the vaporization and condensation of minerals [11,12], coarse mode PM is the result of mineral coalescence of char [12,13], and the central mode PM is affected by multiple mechanisms [14]. The release of volatiles forms a large number of pores in the char [15,16], and the fragmentation of char caused by these pores during combustion is an important factor affecting the central mode PM. PM 10 was transformed during coal combustion from minerals that mainly contain K, Na, Ca, Mg, Fe, Si, and Al.…”