Synthesis of cardanol grafted hydrophilic polymers and its mechanism of coal dust inhibition

Abstract

A novel hygroscopic sodium cardanol polyoxyethylene ether sulfate (SCPES) dust suppressant was synthesized via graft copolymerization, sulfonation, and alkalization reactions of cardanol and polyoxyethylene. The critical micelle concentration, chemical synthesis and wetting mechanism of SCPES were investigated using pyrene fluorescence spectroscopy, Fourier transform infrared spectroscopy, quantum chemistry and molecular dynamics software. SCPES was synthesized in three steps: first, the phenolic –OH of cardanol was de-H and grafted with polyoxyethylene to form cardanol polyoxyethylene ether (CPE); second, the H atom of CPE was replaced by the –SO3H of H2SO4 to generate cardanol polyoxyethylene ether sulfate (CPES); finally, the H+ of CPES was alkalized with the OH− of NaOH to form SCPES. It was found that the active centers of the three reactions were all at the O–H bond, the activation energies were 233.66, 85.99, and − 66.91 KJ/mol, and the final composite had distinct aromatic ether (Ar–O, R–O), S–O, and S = O infrared absorption peaks, proving that SCPES had been successfully prepared. 0.10 g/L and 0.25 g/L were the critical association concentration and critical micelle concentration of SCPES, and the surface tension and contact angle at the critical micelle concentration were 33.12 mN/m and 39.5°. Compared with the H2O-lignite system, the H2O-SCPES-lignite system exhibited an increase in the total number of hydrogen bonds from 2082 to 2136, a decrease in the interaction energies from − 13863.35 kcal/mol to − 17817.77 kcal/mol, and an increase in the diffusion coefficients of H2O molecules from 0.12 to 0.73. The results indicated that the long hydrophobic tail chain in the molecular structure of SCPES was entangled with the hydrophobic sites on the coal surface, acting as intermediate carriers between water and coal to improve the wettability of coal dust, and providing a new technical means for coal dust inhibition.