| Coal is one of the most important energy sources in our country,but the harmful substances produced by the direct combustion of coal will cause environmental pollution.As a clean and efficient coal-based slurry fuel,coal water slurry(CWS)is the main component of clean coal technology,which can effectively alleviate the contradiction between environmental pollution and sustainable development.Dispersant of CWS is the key to produce high quality CWS.Compared with lignin-based,naphthalene-based,humic acid-based and other dispersants,polycarboxylate dispersants have the advantages of high efficiency,environmental protection,and the molecular structure and molecular weight design can according to the requirements of coal structural characteristics,so they are widely used in the preparation of CWS.At present,anionic polycarboxylate CWS dispersants are mostly used in industrial production.However,a large number of studies have found that the dispersion and viscosity reduction effect of amphoteric polycarboxylate dispersants were better than that of anionic type,and their pulping performance were significantly improved.In this paper,3 series and 10 kinds of amphoteric polycarboxylate dispersants with different structures were prepared by means of free radical polymerization reaction of aqueous solution,and the mechanism of action between dispersant and coal particle surface was discussed to improve the performance of low-rank coal slurry.Through the comparison of experimental results,suitable functional monomers were selected,and then the better performance polycarboxylate brine coal slurry dispersant was obtained.First of all,allyl alcohol polyoxyethylene ether 500(APEG-500),sodium styrene sulfonate(SSS),carboxylic acid monomer(acrylic acid or itaconic acid),dimethyl diallyl chlorination ammonium(DMDAAC)were used as raw materials to synthesized two kinds of amphoteric CWS dispersants PASAD and PASID with different carboxylic acid monomers,and dispersant PASD without carboxylic acid monomers.The single factor experiment method was used to optimize the synthesis conditions of the dispersant,the performance of three dispersants were compared by the CWS viscosity test,adsorption performance test,zeta potential and other tests.The experimental results show that the three amphoteric dispersants have better dispersion effect and better pulping performance than the traditional anionic polycarboxylate dispersants,and the prepared slurry is pseudoplastic fluid.The PASID with double carboxyl group has the best performance,making the maximum slurry concentration of Yulin coal reach 66.5%,the zeta potential of the coal particle surface drops from-20.8 mV to-32.4 mV,and the saturated adsorption capacity of the coal particle to the dispersant is 3.23 mg/g,the thickness of the adsorption layer can reach 2.56 nm,the wettability of coal particles is much better,and the stability of the slurry is significantly improve,indicating that the double carboxyl group can improve the performance of the dispersant better than that of single carboxyl group.Secondly,the cationic monomer DMB containing a benzene ring structure was generated by the nucleophilic substitution reaction using benzyl chloride and dimethylaminoethyl methacrylate(DM).Then DMB,amide monomer,sodium styrene sulfonate(SSS),etc.were used as raw materials to polymerized two double comb type amphoteric CWS dispersants PHASD and PHNSD with different amide groups.The results show that when the amount of dispersant is 0.5%,PHNSD containing N-methylolacrylamide can make the maximum slurry concentration of Yulin coal reach 66.1%,and the dispersion and viscosity reduction effect are significantly better than that of PHASD.The adsorption performance test shows that the thickness of the adsorption layer of PHNSD on the surface of coal particles reach 1.91 nm,and the saturated adsorption capacity is 2.71 mg/g,both of which are greater than that of PHASD.In addition,PHNSD can reduce the contact angle of the coal-water interface from 80° to 32°,which significantly improves the wettability of the coal particle surface;and the slurry prepared by PHNSD has a 7-day water separation rate of 3.9%,and the instability coefficient is only 0.15,which means it has a good slurry stability.Finally,two kinds of amphoteric monomers,DMSB and DMCB,were prepared by quaternization,and their structure were characterized.And then 5 kinds of different cationic type amphoteric polycarboxylate dispersants were synthesized by polymerization reaction using sodium styrene sulfonate(SSS),acrylic acid(AA)and 5 kinds of cationic monomers,the cationic monomers are DMSB,DMCB,DMB,methacryloyl ethoxy ammonium chloride(DMC)and dimethyl diallyl ammonium chloride(DMDAAC).The tests show that when the monomer molar ratio of AA/SSS are 1:1,the mass fraction of DMC,DMB and DMD are 6%,and when the mass fraction of DMSB and DMCB is 8%,the corresponding dispersant had the best performance.From the comparison,it is found that the performance of the amphoteric dispersant containing DMCB and DMSB are significantly better than that of the other three dispersants.which could increase the maximum slurry concentration of Yulin coal to 66.64%and 66.89%,respectively,the saturated adsorption capacity and adsorption layer thickness on the surface of coal particles are 2.86 mg/g,3.03 mg/g and 3.32 nm and 3.75 nm,respectively,which make the zeta value on the surface of coal particles change greatly,and the stability of the slurry are better,and the mechanism of action between different cationic monomer dispersants and coal particle surface are further explored.Considering the above comparison,when synthesizing amphoteric CWS dispersant,the priority selection order of cationic monomer is:DMSB>DMCB>DMB>DMDAAC>DMC. |
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