Structure and CO₂ Gasification Reactivity of Char Derived through Pressured Hydropyrolysis from Low-Rank Coal

Abstract

Chinese long flame coal named Naomaohu was pyrolyzed at 600 °C under hydrogen pressures of 0.1–3.0 MPa. The resultant chars were gasified at 900 °C under carbon dioxide to illustrate the correlations between structure and reactivity of pyrolyzed chars. For comparison, experiments under the same conditions in the nitrogen atmosphere were also conducted. The char yield decreased markedly with increasing hydrogen pressure, whereas the char yield under nitrogen stayed constant regardless of nitrogen pressure, being certainly larger than that of hydropyrolysis. The structure of chars was analyzed by Raman spectroscopy and X-ray diffraction, which informed that more content of larger aromatic sheets and higher graphitic order was found, respectively, in the char pyrolyzed under higher pressures. Hydropyrolysis certainly led to more content of larger aromatic sheets and higher graphitic order in its char than those of chars pyrolyzed under the nitrogen atmosphere. The gasification reactivity of hydropyrolyzed char decreased with the increase of hydrogen pressure, indicating that the higher graphitic order and more content of larger aromatic sheets in char are related to the lower char gasification reactivity. Higher hydrogen pressure in the pyrolysis can enhance the hydrocracking of the reactive char components, decreasing yield, and gasification reactivity of the chars. The intrinsic structure features of raw char obtained at 600 °C have good correlations with its CO2 gasification reactivity at 900 °C. The successive combination of hydropyrolysis and CO2 gasification has been promised to provide an effective conversion scheme of the low-rank coals. The most efficient balance of hydropyrolysis and gasification conversions can be designed or higher reactivity of hydropyrolyzed char can be explored.

Effect of Pyrolysis Atmosphere on the Gasification of Waste Tire Char

“…Higher reactive chars are characterized by larger porosity and surface area and have a higher quantity of active sites [29]. The number of active sites is strongly dependent upon porosity or surface area as they are associated with edges or defects on the surface [30,31]. The higher reactivity of chars obtained during pyrolysis in CO 2 atmosphere can by caused by the inclusion of oxygen and elevated total surface area, leading to the formation of new pores or the closing of pores opened by CO 2 [32,33].…”

CO2 Gasification Reactivity and Syngas Production of Greek Lignite Coal and Ex-Situ Produced Chars under Non-Isothermal and Isothermal Conditions: Structure-Performance Relationships

“…The 002 plane corresponds to the cross-section plane, from which the interlayer distance (d002) between the aromatic ring layers can be derived, while the 100 plane corresponds to the parallel plane of the aromatic ring layers. Moreover, the 002 band reflects the distance between the aromatic ring layers [48,49]. On the left side of the 002 peak the γ-band appears, ascribed to the aliphatic side chains connected to the edge of aromatic rings from which the packing distance of saturated structures can be derived [50].…”

Transformation of alkali and alkaline earth metals during the preparation of activated carbon from Zhundong high-alkali coal

“…4(a). The GRAMS/32 AI soware was used to deconvolute the Raman spectra into 10 Gaussian bands, 21,22 and the assignments of these bands represented specic structures, which had been recorded in previous work, 23 and the variations of I D /I G under different activation conditions are shown in Fig. 4(b).…”