Effect Of Hydrophobic Modification Of Xinjiang Lignite Surface And Dispersant Of Coal Water Slurry On The Properties Of Coal Slurry

Coal water slurry is a kind of coal-based fluid fuel with high efficiency,energy saving and environmental protection.It has become the main energy and important chemical fuel in China because of its high combustion efficiency and convenient transportation.However,with the rapid development of social economy,China’s demand for high rank coal is increasing,which leads to the phenomenon of insufficient supply of high rank coal.In contrast,the low rank coal with low metamorphic degree is rich,accounting for 46%of China’s coal resources.However,it is difficult to prepare high concentration CWS for low rank coal due to its high water content,developed pore structure and rich oxygen-containing groups.Therefore,the surface modification technology of low rank coal is an effective way to make rational use of low rank coal.In this paper,the surface hydrophobic modification of low rank coal makes it have strong hydrophobicity of high rank coal,and then different dispersants are used to prepare high concentration coal water slurry.In this paper,six modifiers were prepared by emulsifying Alkenyl succinic acid(ASA)and Alkyl ketene dimer(AKD)with cationic,anionic and nonionic surfactants.They were cation,anion,non-ionic silicone oil ASA modifier and cation,anion,non-ionic AKD modifier.Then six kinds of modified coal particles were obtained by coating six modifiers on the surface of dehydrated coal particles.The surface properties of coal particles before and after modification such as chemical composition,pore distribution,hydrophobic properties and Zeta potential were studied.Combined with the adsorption results of Naphthalene sulfonic acid sodium(NSF)and sodium polystyrene sulfonate(PSS)dispersant on the surface of coal particles before and after modification,the slurryability,rheology and stability of lignite coal water slurry were discussed.It is found that the surface of the modified coal particles have higher carbon content and lower oxygen content,while the pore structure of coal particles reduced,the contact angle of the coal-water interface increased,and the hydrophobicity of coal particles enhanced.The adsorption capacity of NSF dispersant on the surface of modified coal increases,which made the surface electronegativity of coal particles increased,and coal particles have better dispersion effect in water.The CWS prepared from ASA modified coal with PSS as dispersant has the characteristics of high concentration,low viscosity and high stability.The maximum concentration of CWS prepared by cationic ASA modified coal,anionic ASA modified coal and non-ionic ASA modified coal with PSS as dispersant increased from 57.5%of raw coal to 61.7%,61.8%and 62.9%respectively,and the water evolution rate of CWS decreased from 5.25%of raw coal to 2.5%,2.0%and 2.25%respectively.At the same time,The CWS prepared by modified coal particles changed from "shear thickening" swelling plastic fluid of raw coal to "shear thinning" pseudoplastic fluid.The specific surface area,pore volume and pore diameter of AKD modified coal reduced,the pore structure of coal surface blocked and physical adsorbed of AKD molecules on coal surface.XPS technology found that the relative content of C-O-H/C-O-C on the surface of coal particles decreased,while the relative content of C=O and O-C=O increased.Acid-base titration found that the content of phenolic hydroxyl on the surface of coal particles decreased.Physical adsorption and chemical adsorption increase the hydrophobicity of coal surface.The NSF and PSS are adsorbed by Langmuir monolayer on the surface of coal particles.The results of isothermal adsorption show that the saturated adsorption capacity of NSF and PSS dispersant on the surface of AKD modified coal is higher than that of raw coal.The results of adsorption kinetics show that the increase of concentration of NSF and PSS dispersant is conducive to the acceleration of adsorption rate.The results of adsorption thermodynamics show that the adsorption process of NSF and PSS on the surface of raw coal and microwave drying coal are spontaneous exothermic reaction.When the dosage of cationic AKD modifier,anionic AKD modifier and non-ionic AKD modifier is 1.5%,1%and 2%respectively,the apparent viscosity value of the slurry is the lowest,Among them,the CWS prepared by non-ionic AKD modified coal with PSS as dispersant has the best slurry forming performance,and the maximum slurry forming concentration is 64.2%;the CWS prepared by anionic AKD modified coal with PSS as dispersant has the best stability,and the slurry has no obvious water analysis.