Effects of hydrophilic groups of nonionic surfactants on the wettability of lignite surface: Molecular dynamics simulation and experimental study

• Published in: Fuel (Guildford) 2018-11, Vol.231, p.449-457
• Main Authors: Guo, Jianying, Zhang, Lei, Liu, Shengyu, Li, Bao
• Format: Article
• Language: English
• Subjects: Adsorption; Dynamic structural analysis; Ethers; Ethoxylated surfactant; Functional groups; Hydrophilicity; Hydrophobicity; Hydroxyl groups; Lignite; Moisture content; Molecular dynamics; Molecular dynamics simulation; Nonionic surfactants; Oxygen; Polarity; Pollutants; Simulation; Sugar-based surfactant; Surface chemistry; Surfactant adsorption; Surfactants; Water content; Wettability; Wettability modification
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2018.05.106

[Display omitted] •Wettability modification of lignite surface by nonionic surfactant was studied by MD.•Hydrophilic groups of nonionic surfactant affect adsorption strength and hydrophobic alteration.•C12E7 is better than C12G2 in strengthening hydrophobic of lignite surface. Abundant oxygen-containing functional groups make lignite high moisture content, which reduces the utilization efficiency of lignite. The decrease in hydrophilicity of lignite surface can be achieved by treating with surfactant. In the present work, two kinds of nonionic surfactants with different hydrophilic groups, n-dodecyl β-D-maltoside (C12G2) and dodecyl hepta glycol (C12E7), were selected to modify the wettability of lignite surface by molecular dynamics simulation. Because of the drastic differences in compositions and structure of their headgroups, different behaviors were observed. The adsorption results of simulation indicate that polyhydroxy surfactant, C12G2, adsorbs strongly on lignite surface as a comparison to the poly ether surfactant, C12E7. However, the extent of hydrophobicity of modified lignite surface by these surfactants is inconsistent with their adsorption capabilities. Compared to the raw lignite, the hydrophilicity of lignite significantly decreases by adsorption of C12E7, while the C12G2 makes the lignite even more hydrophilicity. The strong polar oxygen-containing functional groups of lignite surface are covered by ethers in C12E7 with weaker polarity, which weakens the interaction between water and lignite. The hydrophilicity of lignite adsorbed C12G2 is strengthened due to the increase in surface polarity by the introduction of polar hydroxyl groups. The results of simulations are in accord with the available experimental data.