Study of structural features in Pittsburgh bituminous, Illinois #6 bituminous, rawhide sub-bituminous, and Texas lignite

[摘要] Studies of the slow pyrolysis of coals using matrix-isolation Fourier-transform infrared spectroscopy (MI-FTIR) and electron spin resonance (MI-ESR) have given insight to coal structures. Evolution of light carbonyl compounds below 250$spcirc$C and dealkylation reactions to form light hydrocarbons occurred from 150-400$spcirc$C. CH$sb4$ evolution continued to 800$spcirc$C. Hydroxyl group decomposition evolved H$sb2$O from 150$spcirc$C to 700$spcirc$C. Tar evolution began at 150$spcirc$C with maximum production from 300-600$spcirc$C. H$sb2$S evolved with the tar fraction at 300-500$spcirc$C. CS$sb2$ evolved from 800-1200$spcirc$C. SO$sb2$ from sulfate decomposition was most notable for Pittsburgh and Illinois #6, less so the lower range coals. Nitrogen pyrolysis products were NH$sb3$ at 300-700$spcirc$C and HCN at 3500-800$spcirc$C. C$sb2$H$sb2$ was formed from 950-1400$spcirc$C. Kaolinite reduction yielded SiO, Al$sb2$O, and aluminum atoms complexed with CO at 1150-1500$spcirc$C. Two distinct hydroxyl groups at 3626 cm$sp{-1}$ and 3581 cm$sp{-1}$ were detected in a N$sb2$ matrix for tars evolved from 300-600$spcirc$C. These groups were identified as phenolic hydroxyls and were most prevalent in Pittsburgh and Illinois #6. O-methylation of the carboxyl, aliphatic and phenolic hydroxyl groups in coal changed the pyrolysis behavior. Esters, aromatic ethers, and aliphatic ethers were observed in FTIR spectra of KBr methylated (CD$sb3$I) coals. Pittsburgh and Illinois #6 contained phenolic-OH groups with some COOH groups and fewer aliphatic-OH groups. Rawhide and Texas Lignite contained more phenolic-OH than COOH and aliphatic-OH. Methanol and formaldehyde were produced from ester and aliphatic ether decomposition whereas methane and carbon monoxide evolved from aromatic ethers. MI-ESR studies indicated peroxy radicals in evolved tars which can be attributed to surface peroxides. Pittsburgh and Illinois #6 tars displayed two radicals, one with average g values of 2.0366, 2.0071 and 2.0014 and the other 2.0302, 2.0098 and 2.0014. MI-FTIR studies showed a marked influence on the pyrolysis behavior of Pittsburgh for CaO and to a lesser extent MgO. The phenolic hydroxyl at 3626 cm$sp{-1}$ was decreased when Pittsburgh was pyrolyzed with CaO and a large amount of water preceded the tar evolution. For all additives tar was evolved at higher temperatures indicating their ability to change the mechanism of tar evolution.

[发布机构] Rice University