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The occurrence of metal ions in the form of inorganic minerals in coal is one of the main factors that affect the stability of surfactant foams. To explore the effect of metal ions in coal seams on the stability of anionic surfactant sodium dodecyl sulfate (SDS) foam, changes in the half-life of SDS foam under different base fluids were analyzed. The results showed that metal ions promoted the stability of SDS foam. When the Na + concentration in the base fluid increased from 20 to 40 mg/L, the foam half-life increased by 67 s. When the Mg 2+ concentration in the base fluid increased from 5 to 15 mg/L, the half-life of the foam increased by 148 s. The influence of divalent Mg 2+ was more pronounced than that of monovalent Na + . A two-phase molecular dynamics model at the foam interface was constructed in Materials Studio molecular dynamics simulation software. The diffusion characteristics of H 2 O molecules in the foam walls and the hydration of metal ions in the foam walls were used to investigate how metal ions affected the stability of SDS foam. It was revealed that metal ions inhibited the diffusion of water molecules in the foam wall, thereby improving the stability of the foam. The inhibitory force of divalent Mg 2+ was stronger than that of monovalent Na + .

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The threshold dilution ratio of acetaldehyde is much larger than those of other odor compounds generated during the spontaneous combustion process and so it is the most important odorant. Studying the mechanism by which acetaldehyde is generated can provide the necessary theoretical support for acetaldehyde-based odor analysis. In the present work, the release of acetaldehyde was monitored while heating lignite, long-flame coal, and coking coal specimens under either air or nitrogen. The data show that acetaldehyde was primarily produced by the oxidation of active sites in the coal rather than by the pyrolysis of oxygen-containing functional groups. Based on quantum chemistry and coal−oxygen reaction theory, the transition state approach was used to further study the formation of acetaldehyde during the low-temperature oxidation of coal. Using density functional theory, three different coal molecule structures were modeled and optimized structures for acetaldehyde formation and the energies, bond lengths, and virtual frequencies of each reaction stagnation point were obtained at the B3LYP-D3/6-311G** and M062X-D3/Def2-TZVP levels. The results indicate that the low-temperature oxidation of coal to generate acetaldehyde involves the capture of H atoms from aliphatic side chains to generate peroxy radicals. These radicals then attack unsaturated C atoms through complex inversions to generate peroxides. In the third step of this process, the O−O single bonds in the peroxides break in response to thermal energy to form carbonyl groups. Finally, specific C−C or C−O bonds on the aliphatic side chains are thermally cleaved to generate acetaldehyde.

Temperature changes in CO2 foam-fracturing construction can easily affect surfactant foam stability. To investigate the effect of temperature on the foam stability of different types of surfactants, this study measured the foam half-life and viscosity of four typical surfactants, CTAB, LAS-30, HSB1214, and TX-10, using a novel self-designed and built foam performance measurement device. The effects of temperature on foam half-life and viscosity were studied. The results show that as the temperature increased, the half-life shortened, and the viscosity of the liquid phase decreased, which led to a decrease in foam stability. Moreover, using Materials Studio, a type of molecular simulation software, an interfacial model of the foam film was constructed to calculate the IFE and the self-diffusion coefficient of water molecules at 300 ps after the equilibrium of the foam system to investigate the mechanism of temperature influence on the stability of the foam. The results show that, for CTAB, LAS-30, HSB1214, and TX-10, the temperature increases from 15 °C to 45 °C, the IFE is enhanced by −50.05%, −59.10%, −64.21%, and −44.26%, respectively, the interfacial system changes from a low-energy state to a high-energy state, and the interfacial stability decreases. Meanwhile, Dwater increased 1.10-fold, 0.78-fold, 1.43-fold, and 0.64-fold, respectively, which accelerated the diffusion and migration of water molecules, weakened the intermolecular forces, and accelerated the instability of the foam system.