Investigation on selective separation of oxygen-containing compounds in lignite and sub-bitumite

Composition Distribution of the Thermal Soluble Organics from Naomaohu Lignite and Structural Characteristics of the Corresponding Insoluble Portions

“…In Figure 5 , the peak intensity of C 1s increases in the order of NL < NL CH-R < NL BE-R < NL EA-R , while the peak intensity of O 1s is exactly the opposite, aligning with the elemental analysis findings. According to references [ 4 , 15 , 17 , 24 , 25 ], the binding energies of C 1s at 284.0 eV, 285.6 eV, 287.3 eV and 288.7 eV correspond to C−C, C−H, C=O, and COO, respectively. Table 3 reveals that the dominant form of C 1s on the surface of the four samples is C−C, while O 1s is mainly in the form of C=O and C−O, primarily existing as phenols, alcohols, and esters.…”

“…The results of C 1s indicate that, compared to the original coal, the C=O content of NL decreased from 10.54% to 5.18%, 6.82%, and 5.67% after thermal dissolution with CH, BE, and EA, respectively, while the COO content increased from 4.01% to 4.59%, 4.20%, and 4.61%, respectively. This may be due to the destruction of oxygen bridges (such as C=O) in the coal sample during thermal dissolution in the presence of EA, leading to the formation of esters and carboxylic acid compounds [ 15 , 26 ]. Additionally, during the thermal dissolution processes with CH and BE at 300 °C, the capsule structure [ 27 ] in NL was disrupted, releasing some small OCOCs, with some C=O-containing compounds dissolving in CH and BE, while some COO-containing compounds were retained in the coal sample structure.…”

“…O 1s mainly exists in the form of C=O (531.1 eV), C−O (532.7 eV), and COO (534.5 eV) [ 4 , 15 , 17 , 24 , 25 ]. From Figure 5 and Table 3 , it can be observed that, compared to NL, the C=O content increased in NL CH-R , NL BE-R , and NL EA-R , while the C−O and COO contents relatively decreased.…”

“…The lowest C−O content was observed in NL CH-R (10.60%), indicating higher content in NL CH (as indicated by GC/MS, primarily existing in the form of aromatic alcohols, alkyl chain alcohols, and phenols). The COO content in NL EA-R decreased from 6.08% to 0.54%, which may be due to the reaction of carboxylic acid compounds in NL with EA during the thermal dissolution process, forming ethyl acetate and acetic acid [ 15 ], with possible reaction pathways, as outlined in Scheme 2 . In conclusion, the thermal dissolution treatment in the presence of CH, BE, and EA can break down and convert the oxygen-containing functional groups in NL into various forms of oxygen-containing compounds.…”

“…The results showed that, as a nucleophilic reagent, EA underwent esterification and ester exchange reactions during thermal dissolution, with EA and ethanol (produced from the reaction of EA with water in SL) significantly participating in the depolymerization of SL by attacking the C aryl , C acyl , and C alkyl structures in SL. Hao et al [ 15 ] conducted thermal dissolution of ZL and NL using ethanol, tetrahydrofuran, and ethyl acetate, and separated the thermal dissolution products into three fractions using column chromatography. The results indicated that ethanol exhibited good selectivity for phenols and esters, tetrahydrofuran released highly condensed polycyclic compounds from low-rank coal, and ethyl acetate showed strong selectivity for C=O in low-rank coal, releasing a significant amount of ester compounds during thermal dissolution.…”