RESUMO
Sequential extract residues (R i , i = 1, 2, 3, 4, and 5) were obtained from Hefeng acid-washing coal (HFAC) by petroleum ether, carbon disulfide, methanol, acetone, and isometric carbon disulfide/acetone mixture, sequentially. Pyrolysis behavior of the residues was determined using thermogravimetry analysis. The Coats-Redfern method with different reaction orders was used to analyze the pyrolysis kinetic of each sample, and the kinetic parameters, including correlation coefficient (R 2), activation energy (E), and pre-exponential factor (A), were calculated. Results showed that the weight loss of extract residues was higher than HFAC, and pyrolysis behavior varies greatly for residues, which is related to the unstable structure after extraction. From conversion-temperature (α-T) curves, the pyrolysis process was divided into three stages: low-temperature stage (150-350 °C), medium-temperature stage (350-550 °C), and high-temperature stage (550-950 °C). The medium-temperature stage made great contribution to the process of pyrolysis, which was dominated by depolymerization and decomposition reaction. The relationship between kinetic parameters and reaction order showed that the swelling effect is an important reason for the discrepancy of E for each sample in the process of pyrolysis.
RESUMO
Taking five coal samples (FCSs) in Xinjiang as the research object, characterizations such as proximate analysis, ultimate analysis, Fourier transform infrared (FTIR), and thermogravimetry-differential thermal analysis (TG-DTG) were carried out. The Coats-Redfern model was used to simulate pyrolysis kinetics of FCSs under different reaction orders (ROs). The results showed that except for HSBC, the R 2 of the other four coal samples are all higher than 0.9, which showed a good correlation effect. FCSs present similar reaction activation energy in the same RO and temperature range. Results of FTIR showed that the hydroxyl groups of FCSs, in the range of 3100-3600 cm-1, were mainly self-associated hydroxyl hydrogen bonds and hydroxyl π bonds, and they occupied over 63%. Among them, the pyrolysis characteristic index (D) of XBC was 4.139 × 10-6, higher than those of other samples, and it showed good pyrolysis performance. Moreover, by reducing the temperature range appropriately, the fitting results showed a better correlation effect.
RESUMO
N-methyl-2-pyrrolidone (NMP), pyridine (Py), tetrahydrofuran (THF), and tetralin (THN) were used to swell Hefeng acid-washed bituminous coal (HBCAC). The swelling effect on HBCAC by each solvent is different, among which NMP presented well swelling performance, with a swelling degree of 2.11. FTIR results showed that acid washing and swelling processes presented a marginal effect on HBC, and there was no damage to the macromolecule structure of the coal. TG-DTG profiles of the swollen coals illustrated that the total weight loss of each sample was lower than that of the acid-washing one, while the temperature of the maximum weight loss rate peak was almost unchanged, around 445 °C. Extract yield by methanol followed the order of HBCAC > HBC > HBCAC-NMP (swelled by NMP), showing that acid washing promoted the methanol extraction process, with a higher extract yield of 3.21%, which is twice that of HBC (1.66%).
RESUMO
The direct regio- and enantioselective C6 functionalization of 2,3-disubstituted indoles with azadienes has been developed using chiral phosphoric acid as catalyst, providing a convenient approach to synthesize the optically active heterotriarylmethanes with excellent yields, broad substrate scope, and up to 98% ee. Mechanistic studies revealed that N-alkylation of 2,3-disubstituted indoles with azadienes would be reversible, and enantioselective C6 functionalization could be enabled.