Synthesis And Application Of Dispersant Of Coal Water Slurry Based On Polycondensation Of Humic Acid

China is a coal-producing country. Direct combustion of coal has low efficiency and creats a great pollution. It is still a hot social problem that how to use coal resources efficiently and cleanly. The coal water slurry has the characteristics of mobility and stability, which results in high utilization rate of coal and less pollution. The non-toxic and environmental dispersants of coal water slurry plays very important role in the preparation of coal water slurry. Humic acid is a natural substance with a variety of active functional groups, and the advantages of cheap and environmental protection make it gradually become a research hotspot in the research field of dispersant of coal water slurry.Currently, the researches on the polycondensation modification of humic acid are still little, which mainly use the polycondensation with formaldehyde and sulfonated acetone. Though this modification method could improve the relative molecular mass and hydrophilicity of humic acid, it fails to enhance the adsorption performance of the modified dispersant. The adsorption between coal particles and dispersant just rely on the fused ring structures of humic acid. At the same time, if the hydrophilic property of dispersant is too strong, a thick hydration film could be formed on surface of coal, resulting in the reduction of free water in the system, which would produce a great impact on the apparent viscosity of coal water slurry.Based on the problems mentioned above, a novel monomer, the sodium p-aminobenzenesulfonate was introduced in this paper. The sodium p-aminobenzenesulfonate containing amino (-NH2) and sulfonic group (-SO3Na), has strong molecular polarity, which is easy to have hydroxymethylation with formaldehyde. Researches show that the dispersant with sodium p-aminobenzenesulfonate could obviously improve the electrostatic repulsion and steric hindrance. In addition, the adsorption capacity could be enhanced by increasing the adsorption site between dispersants and coal particles.In this paper, after the purification and sulfomethylation of humic acid, the sulfomethylated humic acid polycondensate (HBF) was synthetised through the reaction of sulfonated humic acid, sodium sulfanilate and formaldehyde. In order to further reduce the molecular rigidity of humic acid, sulfomethylated humic acid urea formaldehyde condensation polymer (HBUF) was synthetised through the reaction of sulfomethylated humic acid, sodium sulfanilate, urea and formaldehyde. The structures and thermal stability of HBF and HBUF were characterized by IR, TG, DSC and GPC. Compared with sulfonated humic acid-formaldehyde-sulfonated acetone polycondensate (SHA) and sulfonated humic acid-sulfonated acetone-urea-formaldehyde polycondensate (SHUA) respectively, these dispersants were applied in Binchang coal samples, and the properties of coal water slurry were discussed by apparent viscosity, rheological properties, adsorption capacity and stability. The experiment results show that coal water slurry possessed the good performance when the dosage of HBF dispersant was 0.5 wt%, and the apparent viscosity was 633 mPa·s. Then, the highest concentration of pulp was 67.7 wt%, the bleeding ratio was 4.65% after seven days and the maximum adsorption capacity was 3.91 mg/g. Coal water slurry possessed the good performance when the dosage of SHA dispersant was 0.3 wt%, and the apparent viscosity was 707 mPa·s. Then, the highest concentration of pulp was 66.8 wt%, the bleeding ratio was 5.29% after seven days and the maximum adsorption capacity was 3.55 mg/g. So, HBF had better property. Coal water slurry possessed the good performance when the dosage of HBUF dispersant was 0.45 wt%, and the apparent viscosity was 552 mPa-s. Then, the highest concentration of pulp was 68.2 wt%, the bleeding ratio was 4.41% after seven days and the maximum adsorption capacity was 4.09 mg/g. Coal water slurry possessed the good performance when the dosage of SHUA dispersant was 0.25 wt%, the apparent viscosity was 619.5 mPa·s. Then, the highest concentration of pulp was 67.4 wt%, the bleeding ratio was 4.85% after seven days and the maximum adsorption capacity was 3.86 mg/g. Thus, HBUF has better property.Finally, the coal water interfacial properties and adsorption mechanism were discussed. Results show that the aromatic structure of HBUF could closely combine with the coal when introducing sodium p-aminobenzenesulfonate. With the hydrophilic groups, the hydrophobic property of the coal particle surface is effectively weakened. The dispersant of HBUF could reduce the rigidity of humic acid when introducing urea. The molecular chain is easy to be folded to form a ring type adsorption, and the folded chain could expand the steric hindrance. And the stability of dispersion is better than that of HBF.