Effect of Benzene Ring Alkyl Chain Length on the Flotation Recovery of Coking Coal

The influence of the benzene ring substituent chain length on the flotation efficacy and fundamental mechanisms of coal slime was systematically examined via flotation tests, wrap angle measurements, density functional theory (DFT), and molecular dynamics simulation. Coal slime was from the Qipanjing Coal Preparation Plant, and two collectors: dimethyl phthalate (DMP) and diethyl phthalate (DEP) were used to assess the impact of molecular structure on the coal surface. The results indicated that at a collector dosage of 100 g/t, DEP attained a combustible recovery of 79.79%, markedly surpassing DMP's 39.75%. The wrap angle corroborated this trend, with DEP-treated particles displaying a wrap angle of 144°, in contrast to 131° for DMP, suggesting that DEP establishes a more persistent hydrophobic layer on the coal surface, thereby improving particle-bubble adhesion. Theoretical study elucidated the molecular foundation for this disparity: DFT results indicated that DEP possesses a reduced molecular polarity index (MPI), implying enhanced nonpolar traits favorable for hydrophobic interactions; molecular dynamics simulations revealed that DEP demonstrates a greater adsorption affinity and diminished molecular mobility and establishes a higher number of hydrogen bonds, alongside more negative interaction energy, signifying a more stable adsorption configuration. The chain length of substituents on the benzene ring is recognized as a crucial structural factor affecting collector efficacy. Extended chains augment the molecule's hydrophobicity and interfacial adsorption stability, resulting in enhanced flotation efficiency. This study offers theoretical insights and practical recommendations for the molecularly effective selection of high-performance flotation collectors.