| Polycarboxylate is a synthetic water-soluble polymers,whose structure is flexible, controllable, designable. Its various structures adapt to different coals, thus to obtain highly enriched Coal Water Slurry(CWS). The polycarboxylate used for different coal CWS, whose performance is better than the current industrialization lignin and naphthalene-based dispersant. Currently, empirical and semi-empirical approach still is common study way of molecular structure of dispersants match coal. The study of mechanism of dispersion and coal is only a conjecture and hypothesis. Especially, the research of adsorption is less and not fine. It isn’t systematicly studied and clearly stated for Polycarboxylate to correlation between adsorption behavior and rheological properties on CWS.In the paper, different long side chain polycarboxylate dispersants were synthesized by free radical copolymerization, and studied the adsorption behavior of coal/water interface and aggregation state, as well as rheological properties of Binchang coal. Analysis of the relationship adsorption-dispersionrheology, in order to discuss polycarboxylate dispersion mechanism on coal particle.Comb-like copolymer dispersants with different side chain lengths n ranging from 8~23 were synthesized using esterified macromer of methoxypolyethyleneglycol(MPEG)-acrylic acid(AA), AA and styrene sulfonic sodium(SSS). The molecular structure of the dispersant was analyzed by 1H NMR, FT-IR and GPC. The carboxyl and sulfonic acid group content of the dispersant were tested titration, in order to analyze structural characteristics of different side chain length of the dispersant. Thermal properties of dispersants were studied by TG and DSC. The polycarboxylate dispersants used for Binchang, Shenhua and Huolinhe coal was to investigate the optimum dosage, the maximum plasma concentration and stability, and compare with traditional naphthalene.The results showed: the relative molecular mass of the polymer(Mw) within 2 ~5×104, the molecular weight distribution index Mw/Mn= 2.50~2.91. Molecular structural features: The characteristics of PC350 and PC500 were the main chain of the long, short side chain and high anion group; the characteristics of PC750 and PC1000 were the short main chain, long side chain and poor anion group. And they had good thermodynamic performance to can meet the needs of CWS. Slurry tests show: for Binchang coal, PC dispersant have better dispersibility and stability than conventional naphthalene-based. Dispersion properties of PC500 was the best in the four long side chain polycarboxylate dispersant, when optimum amount was 0.4%, viscosity was 526.4mPa.s, liquidity was Class A, CWS maximum concentration could reach 68% and stability was improved greatly. Different kinds of CWS: Binchang>Shenhua>Huolinhe, optimum amount was 0.4%, 0.6% and 0.6% individually. The maximum concentration: 68%, 67% and 48.5% respectively.In addition, dispersant adsorption kinetics and thermodynamics performance were studied on coal surface, and its rheological properties were studied at different temperatures and content. The relationship was researched between polycarboxylate’s side chain and rheology, as well as it was analyzed that polycarboxylate adsorption on coal/water interface by TEM, SEM, Zeta, contact angle and XPS, in order to explain the dispersion mechanism of comb type polycarboxylate.The results showed that PC Binchang CWS exhibited "shear thinning" rheological properties, and were suitable for Herschel-Bulkley rheological model. PC500’s, which had long main chain, short side chain, rheological properties was better, apparent viscosity was the lowest. Temperature increased, the CWS’s fluidity index n increased, liquidity enhanced, apparent viscosity decreased; Increasing the dosage of dispersant, coal water slurry remained pseudoplastic fluid, yield stress τ0 also reduced from 46.4Pa to 19.9Pa, the apparent viscosity decreased first and then increased. In a certain range of dosage, with increasing the amount of, rheological model changed from Herschel-Bulkley model to Bingham. The adsorption results showed: Isotherm experiments showed PC dispersants was monolayer adsorption on coal particle surface, belong to Langmuir adsorption model, the saturated adsorption amount: PC500> PC350>PC750>PC1000, PC500’s adsorption density was maximum on Binchang coal’s suface, 0.6375mg/m2. Adsorption kinetics showed pseudosecond adsorption rate equation could better describe the dispersant adsorption kinetics on the surface of Binchang coal. Adsorption thermodynamics showed within a certain temperature, the increase of temperature was advantageous to the saturated adsorption amount; △Had adsorption enthalpy was negative, dispersant adsorption was an exothermic process on the coal’s suface. Dispersants were not uniform on the coal surface adsorption by TEM. XPS, Zeta, and the contact angle showed the thickness of the adsorbed dispersant: PC500>PC1000>PC750>PC350, PC500 adsorption layer thickness was maximum, 4.20 nm. PC dispersants had improved the coal surface electrostatic to charge from-11.2mV to-41.5mV. And PC had good hydrophilic modification for Binchang coal. Through the analysis, it was showed that the proper length of the side chain of PC played the steric hindrance and electrostatic repulsion to disperse CWS by balancing adsorption thickness and Zeta potential. Meanwhile, the adsorption density had great influence on adsorption thickness and zeta potential; The analysis of thermodynamic stability, The right length of the side chain of PC could reduce Gibbs of CWS to weaken "aggregation" among the coal particles while improving dispersibility of CWS. |
PDF Full Text Request