Preparation And Properties Of Coal Water Slurry Dispersant Based On Starch Graft Copolymers By HRP-catalyzed System

In recent years,the clean coal-water slurry（CWS）is concerned because of the increasingly serious energy and environmental problems,which is important in a country with rich coal and lacked oil.The dispersant plays an important roal in making high quality CWS.Currently,the requirements for dispersant are not only achieving high performance,but also being in line with the concept of green.Starch is a renewable natural product that is cheap and easily degradable.The horseradish perox idase（HRP）is a kind of biological enzyme with special catalytic performance,which can initiate the graft of functional monomer on starch.In order to meet the current development demands,starch and HRP are used to prepare dispersants.In this paper,two kinds of CWS dispersant SHA（St-HBS-AM）and SHN（St-HBS-NaAA）were synthesized by using starch（St）as main materials,sodium 4-hydroxybenzenesulfonate（HBS）,acrylamide（AM）and sodium acrylate（NaAA）as monomers,and HRP/H2O2/ACAC as catalyst.The solid content,monomer conversion,grafting rate,grafting efficiency and molecular weight of the dispersant were determined.The polymers were characterized by Fourier transform infrared spectrometer（FTIR）and nuclear magnetic resonance hydrogen spectrum（1H NMR）.The thermal properties of the dispersants were studied by thermo gravimetric（TG）and differential scanning calorimetry（DSC）.Firstly,the dispersants were applied to Bin Chang coal and the synthetic process of the dispersant was optimized with the apparent viscosity of CWS as the measure.The optimum conditions are as follows: the amount of starch is 25%,HBS:AM（NaAA）is 3:1.The results show that SHA has better performances than SHN,such as the viscosity,stability and maximum concentration.Then,the metal ions of Bin Chang coal were eluted using CH₃COONH₄,CH₃ COOH and NaOH solutions.And CWS was made by using SHA with good performance.Compared with the original coal,the slurry formation of the coal is improved obviously when the soluble metal ions are disposed by different solutions,and the effect is CH₃COONH₄>Na OH>CH₃COOH.The effects of different conditions on the apparent viscosity,maximum concentration,stability,Zeta potential,adsorption capacity and the thickness of the adsorbed film were investigated by changing the concentration,temperature and the final pH value.The results show that the slurry formation is the best when the temperature is 40 ℃,the concentration of the solution is 1 mol·L-1 and the pH is 7.The Zeta potential decreases and the adsorption capacity of the dispersant and the thickness of the adsorbed film increase with the decrease of the content of soluble metal ions,and the change of the three indexes is beneficial to improve of the performances of CWS.Finally,the SHA and the NSF dispersants were applied to Xinjiang coal.It is found that concentrated（67%）apparent viscosity using SHA is 667 mPa·s,the bleeding ratio is 3.6% and the maximum concentration is 68%.However,indexes are 365 mPa·s,6.93% and 70%,separately when using NSF.Compared with NSF,the CWS using SHA has higher apparent viscosity,lower maximum slurry concentration and better stability.Therefore,the two dispersants were combined to be applied to the coal.The effects of the ratio（NSF:SHA）and the dosage amount on the apparent viscosity,stability and the maximum concentration were studied.The performance of CWS is the best when the ratio is 1:2 and the dosage is 0.5%,and the stability is the same as SHA used alone.In addition,the maximum concentration is 70%,which is the same as that of NSF used alone.Meanwhile,the soluble metal ions of Xinjiang coal were treated with CH₃COONH₄ and NaOH.The results show that both of the methods can improve the slurryability,but for Xinjiang coal,combined dispersant is more useful.The mechanism was explained by discussing the adsorption film thickness of the coal particle in different cases.