| In recent years,serious environmental pollution and energy shortage have generated a new energy revolution.As a cleaning method of coal utilization,coal water slurry has attracted the attention of domestic and foreign scholars.Lignite resources are rich in,especially in eastern Inner Mongolia where accounts for77.55%of the country's total lignite content.Lignite has characteristics like high water content,abundant oxygen-containing functional groups,and highly developed pore structures.Thus,lignite is difficult to prepare high-concentration coal water slurry.Therefore,it is very important to look for ways to solve these problems.In this paper,the technology combined thermal modification and surface chemical modification is used to increase the slurry concentration of lignite.According to the molecular structure and hydrophilic groups of Inner Mongolia coal,three types of cationic Gemini surfactants were designed and synthesized.Using n-propanol as the solvent,dodecyl-dimethyl-tertiary amine?12DMA?and1,3-dibromopropane or epichlorohydrin were synthesized by nucleophilic substitution reaction to synthesize the first type of cationic gemini surfactant with hydroxyl or a methylene as the spacer?SAA-1,SAA-2?.With the same synthesis reaction,12DMA or 16DMA and p-dibenzyl chloride as raw materials is used to synthesis cationic Gemini surfactant with p-xylylene dichloride as the spacer?Cn-B-Cn?.chelated Gemini surfactant?mDE-Si-mDE?surfactant was synthesized using 12DMA or 16DMA,KH540 and epichlorohydrin as raw materials.Their structures were confirmed by FT-IR and 1H NMR,respectively.The critical micelle concentration?cmc?,foaming properties,and emulsifying properties of the three types of surfactants were measured.Then,three kinds of cationic Gemini surfactants were applied to surface modification of Inner Mongolia coal.The wettability of raw and modified coal,and the adsorption properties of SAA,Cn-B-Cn and mDE-Si-mDE were analyzed.Firstly,The SAA was tested using a contact angle meter,a nano-particle surface potential analyzer,and an X-ray photoelectron spectrometer.The results showed that the effect of SAA is higher than that of monocationic cationic surfactant?CTAB?.The adsorption capacity of the SAA-2 was 2.95 mg/g,and the apparent viscosity was 723 mPa·s when the concentration of the slurry was57%.Besides,the contact angle increased 70.89°and the Zeta potential reached-37.4mV.Sharing the same positive adsorption sites of quaternary ammonium salt with SAA-2,the SAA-1 has additional adsorption stie of the hydroxyl group on the spacer,which could form hydrogen bond with oxygen functional groups on lignite surface.Thus,the adorption amount of SAA-1 is up to 3.17 mg/g.When the CWS concentration was 57%,the apparent viscosity was676 mPa·s and the contact angle increased 85.08°,the Zeta potential reached-49.6mV.The influence of SAA-1 and SAA-2 on the stability of CWS was studied by using Turbiscan Lab stability analyzer,indicated that slurry with SAA-1 is more than SAA-2.The influence of Cn-B-Cn on the slurry performance of coal water slurry was analyzed.The results showed that the surface contact angle increased from42.50°to 95.47°and the Zeta potential increased from-9.89 mV to 45.21mV.Cn-B-Cn can be adsorbed on the surface of coal particles by electrostatic interaction.With the carbon chain increase from C12-B-C12 to C16-B-C16,the adsorption film thickness on the surface of coal particles was increased from1.00nm to 1.48nm.The maximum concentration of coal water slurry is up to 60%with the addition of 1%C16-B-C16,Besides,performance on surface hydrophobic modification and slurribility of C16-B-C16 are better than C12-B-C12.The mechanism of interactions of mDE-Si-mDE on the surface of coal particles was analyzed.When the two kinds of mDE-Si-mDE were added at 2%,the contact angle was measured between the interface of coal and water or 300mg/L dispersant solution respectively.The equilibrium contact angle of16DE-Si-16DE is up to 104.57°or 71.46°and the 12DE-Si-12DE is 91.56°or 68.40°,both are larger than the contact angle?15.12°?of the dried coal.So the surface hydrophobicity of the coal particles is improved and the hydrophobic modification effect is successfully obtained.With zeta potential measurement,adsorption membrane thickness and other adsorption analysis,it can be concluded that mDE-Si-mDE is eventually adsorbed on the surface of coal particles by electrostatic adsorption,hydrogen bonding and metal ion complexation.When 16DE-Si-16DE is adsorbed on the surface of coal particles,Zeta potential is up to 37.9mV,and adsorption thickness is 4.00 nm which are both higher than that of 12DE-Si-12DE.This also verifies consistency with the contact angle test results.Through the pulping test of the coal samples adsorbed on mDE-Si-mDE,we found that the optimal dosages of 12DE-Si-12DE and16DE-Si-16DE are respectively 0.5%and 1%,when the slurry viscosity is the lowest.the maximum slurry concentration can be increased to more than 60%,which is 2%higher than the maximum coal slurry concentration of 57.8%of dried raw lignite. |
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