Low-temperature pyrolysis offers a potential way of upgrading lignite and producing chars to replace thermal or pulverized coal injection (PCI) coals in combustion or being used as inert components in a blend for coking. In this study, the characteristics of chars from low-temperature pyrolysis of two lignite coals have been investigated. The changes in char morphology and chemical structures were investigated using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The combustion reactivity of chars was analyzed in a thermogravimetric analyer (TGA) using non-isothermal techniques. The results show that chars from low-temperature pyrolysis of lignite coal below 450 °C were more reactive than higher temperature chars. Higher reactivity of low-temperature chars was attributed to the higher concentration of active sites and lower degree of structural order compared to that of high-temperature chars. Indonesian (YN) lignite showed a higher weight loss rate compared to Hulunbeier (HL) coal, which was attributed to a higher concentration of liptinite and vitrinite in YN coal. FTIR analysis indicated that the aliphatic structures and oxygen-containing functional groups decreased with an increasing pyrolysis temperature. The intensity of tightly bound cyclic OH tetramers and OH−ether O hydrogen bonds were higher than other hydrogen bonds in the 3700−3600 cm −1 region of infrared (IR) spectra. The density of alkyl chains and crosslinking reactions affected the yield of tar. The aromaticity of char increased with an increasing pyrolysis temperature. The abundance of CO and COOH structures decreased drastically with increasing temperature. A lower concentration of active sites on high-temperature chars resulted in lower combustion reactivity compared to low-temperature chars. The C−O and C C groups decreased as the temperature increased possibly because of the aromatic condensation. The extent of aromatic substitution decreased up to 650 °C. At temperatures above 650 °C, the degree of aromaticity was strengthened and larger condensed aromatic nuclei were formed. Brunauer−Emmett−Teller (BET) surface area analysis revealed that high-temperature chars have significantly higher surface area compared to chars produced at low temperatures. However, the concentration of active sites was lower in high-temperature chars. Therefore, it can be concluded that diffusion was the main reaction mechanism in high-temperature chars.

Combustion of coal gangue is extensively used for power generation in China. In this paper, pyrolysis and combustion characteristics of a low-rank coal gangue have been investigated under oxy-fuel (O 2 /CO 2 ) and air (N 2 /O 2 ) conditions using a drop tube furnace and thermogravimetric analysis. Pyrolysis experiments were carried out in N 2 and CO 2 environments, which are the main diluting gases of air and oxy-fuel environments, respectively. The burnout and yields of volatile matter were analyzed during DTF experiments. At lower temperatures, the weight loss rate of coal gangue during pyrolysis in N 2 was higher than that in CO 2 . However, further weight loss took place in CO 2 atmosphere at temperatures above 800 °C due to CO 2 gasification of chars. The thermogravimetric analysis (TGA) results confirmed that the pyrolysis in CO 2 environment can be divided into three stages: moisture release, devolatilization, and char gasification by CO 2 in a higher temperature zone. Combustion experiments were carried out in four different atmospheres: air, an oxygen-enriched air environment (30% O 2 −70% N 2 and 40% O 2 −60% N 2 ), an oxy-fuel environment (21% O 2 −79% CO 2 ), and an oxygen-enriched oxy-fuel environment (30% O 2 −70% CO 2 and 40% O 2 −60% CO 2 ). Coal gangue reactivity under oxy-fuel conditions differed from that under air combustion conditions. The combustion rate of coal gangue increased with increasing O 2 concentration while the ignition and burnout points shifted to lower temperatures and complete combustion was achieved at lower temperatures and shorter times. Comparison of the combustion performance of coal gangue in N 2 /O 2 and CO 2 /O 2 environments for equivalent O 2 concentrations indicated that the combustion characteristics of coal gangue in a CO 2 /O 2 environment were similar to those in a N 2 /O 2 environment at 21 vol % O 2 oxygen concentrations. However, increasing O 2 partial pressures resulted in a higher combustion rate under oxy-fuel conditions. Kinetic constants for the samples were calculated by using the isoconventional method. The activation energy decreased with increasing O 2 partial pressure under oxy-fuel combustion conditions and reached lower values compared to air combustion cases. The mineral matter reactions during coal gangue combustion were investigated by means of XRD analysis. During combustion at 1200 °C, mineral phases in coal gangue were transformed to ash comprised of kaolinite, quartz, mullite, magnetite, hematite, and anhydrite.

Cubosomes with surface cross-linked chitosan exhibit anti-digestion effect, sustained drug release behavior, and significantly enhanced oral bioavailability of vinpocetine.

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