Action of solvents on coal at low temperatures

The dual role of oxygen functions in coal pretreatment and liquefaction: Crosslinking and cleavage reactions

“…The dissolution of coals in the aqueous alkaline solutions may be due to the breaking of ester bonds in coal, i.e., RCOOR' + OH- RCOO-+ R'OH. This coal dissolution mechanism was also proposed by other workers [6]. The solubility of coal in alkaline solutions varies with the cations contained in the solution.…”

“…Ca++ ions can act as cross-links between two acid groups of different coal fragments [6], whereas K+ can only interact with one acidic site. The results also show that the barium solution extracted more coal than the calcium solution.…”

Effect of Various Experimental Parameters on the Swelling and Supercritical Extraction Properties of Lignite

“…In various investigations, EDA is considered to be a specific solvent for coal owing to its ability to disrupt specific interactions in coal such as the H-bonds (Suuberg et al, 1994;Larsen and Lee, 1985;Brenner, 1983). Van Bodegom et al (1984) reported similar results and adduced that the strong bases such as EDA are good solvents for lignites. The swelling of coal in polar solvents such as pyridine, NMP, etc.…”

Fluorescent carbon nano dots from lignite: unveiling the impeccable evidence for quantum confinement

“…3 3 In our case, the considerable decrease in the swelling ratio (∼50%) is due to the presence of large excess of water and hence the dissolution process strongly depends on temperature. 4 On refluxing in 5% EDA solution, the cross linking hydrogen bonds and the ester covalent bridges were cleaved (to form primary amide) results in a dark brown solution. The TEM image ( Figure S2a) of this raw solution shows the existence of both the layered structure of unreacted coal and carbon particles of nano to micro dimensions.…”

“…Rather than burning coal for power generation converting them into environmentally clean products is the need of the hour. 2,3 Coal has a complex structure, comprised of islands of sp 2 carbon domains of variable size (earlier it was referred as micelles) 4 which are linked together in a three dimensional network of covalent bridges like methylenic, ethylenic, esters, ethers, epoxides and non-covalent interactions which includes hydrogen bonding and pi-pi interactions. 5,6 Hence, exfoliating these aromatic islands from this cross linked macromolecules require a reactive solvent such as ethylenediamine (EDA), N-methyl-2-pyrrolidone (NMP).…”