关键词: 不同煤种, 复合表面活性剂, 官能团, 润湿性, 分子动力学模拟

Abstract:

Adding wetting agent to water is an effective method to improve the wetting effect of coal bed water injection. Taking coal samples with different degrees of metamorphism as the research object, a combination of macroscopic experiments, mesoscopic experiments and microscopic molecular dynamics simulations was used to explore the effects of compound surfactants on the wettability of different coal types. Firstly, surface tension and contact angle experiments were used to evaluate the effects of different compounding ratios of surfactants on the wettability of the three coal samples from a macroscopic point of view and to determine the optimal compounding method. The results showed that the best wetting effect was achieved when sodium laureth sulfate (SLES) and aliphatic alcohol ethoxylate (AEO-9) was compounded at a mass ratio of 3∶2. Secondly, mesoscopic experiments such as scanning electron microscopy and Fourier transform infrared spectroscopy were used to further investigate the wettability and adsorption capacity of the composite surfactants on different coal samples. The results indicated that after treatment with the composite solution, agglomerated bulk coal particles would be formed on the coal surface and the cracks between the coal particles were conducive to the penetration of the aqueous solution to wet the coal seam. At the same time, the total content of hydrophobic groups in coal molecules was significantly reduced, the content of hydrophilic functional groups was significantly increased and the aggregation ability between coal particles was enhanced, which was conducive to dust deposition. Finally, the wetting synergistic mechanism of composite surfactants on different systems was analyzed from the perspective of microscopic molecular simulation. The results showed that the composite surfactant molecules can be well adsorbed on the surface of coal molecules, promote the movement of a large number of water molecules to the coal surface, improve the interaction energy at the interface between coal and water, enhance the thickness of the water molecule layer on the coal surface and increase the diffusion coefficient of water molecules. The research results were of great significance to improve the wettability of coal.

Key words: different coal types, complex surfactants, functional groups, wettability, molecular dynamics simulation