Poly(sodium styrene sulfonate)-Grafted SiO2 Nanoparticle: Synthesis and Use as a Water-Insoluble Dispersant for Coal Water Slurry

This study introduces a novel water-insoluble dispersant for coal water slurry (CWS), namely, a poly(sodium styrene sulfonate)-<i>grafted</i> SiO₂ nanoparticle (SiO₂-<i>g</i>-PSSNa). SiO₂-<i>g</i>-PSSNa was synthesized by combining the surface acylation reaction with surface-initiated atom transfer radical polymerization (SI-ATRP). Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS), energy dispersive spectrometer (EDS), nuclear magnetic resonance spectroscopy (NMR) and thermogravimetric analysis (TGA) verified that SiO₂-<i>g</i>-PSSNa with the desired structure was successfully obtained. Afterwards, the performance of SiO₂-<i>g</i>-PSSNa as a dispersant in CWS preparation was evaluated. The results indicated that the optimal dosage of SiO₂-<i>g</i>-PSSNa was 0.3%. Compared to the famous commercial products, PSSNa and lignosulfonate (LS), SiO₂-<i>g</i>-PSSNa exhibits improved viscosity reduction performance. When SiO₂-<i>g</i>-PSSNa was used as the dispersant, the maximum coal loading of CWS was 64.2%, which was higher than LS (63.4%) and PSSNa (63.9%). All CWSs obtained in this study were pseudoplastic fluids and more consistent with the Herschel-Bulkley rheological model. The turbiscan stability index (TSI) of CWS prepared with SiO₂-<i>g</i>-PSSNa was 0.05, which was significantly lower than CWSs obtained from PSSNa (0.30) and LS (0.36). Therefore, SiO₂-<i>g</i>-PSSNa also exhibits excellent stability performance. This result was confirmed by rod penetration tests. The underlying mechanism was also clarified by various measurements, such as contact angle, zeta potential, EDS and low-field nuclear magnetic resonance spectra (low-field NMR). The results reveal that SiO₂-<i>g</i>-PSSNa can adsorbed onto the coal surface. SiO₂-<i>g</i>-PSSNa possesses a special branched structure, which bears a higher charge density as compared to linear ones with approximate chemical composition. As a result, coal particles adsorbed with SiO₂-<i>g</i>-PSSNa exhibit more electronegativity. With the enhancement of the electrostatic repulsive between coal particles, the apparent viscosity was lowered and the static stability was improved. This study demonstrated that solubility in water is not an essential factor in engineering the dispersant. Densely charged groups are probably more important.