Relation Of Chemical Structure Of Comb-like Polycarboxylate Dispersant And Rheology Of Coal Water Slurry And Its Interac Mechanism With Coals

CWS technology is a clean use of coal liquefaction technology. Coal-waterslurry has the advantages of high combustion rate and low cost, and it is easy forit to achieve the environmental requirements of energy saving and emissionreduction, so it is a clean fuel to replace the oil. CWS is a two-phase crudedispersion system with solid and liquid. In order to make the slurry have goodfluidity, low viscosity to facilitate transport and also good stability to producelittle precipitate, the dispersing agent should be added to the coal slurry in thepreparation process. At present, the available industrial naphthalene sulfonatedispersant is easy to be affected by climate. When the climate is changing, theslurry stability of the naphthalene sulfonate dispersant cuts down, then theprecipitate with certain toxicity appears. In short, the production and the use of itare not conducive to environmental protection. So, we should find somereplacements. However, the coal-water slurry, prepared by humic acid, is notstable and the lignin dispersant has poor viscosity reducing effect. Bothdispersants have complex ingredients, which mean a lot of impurities. As a waterreducing agent of cement, polycarboxylic acid dispersant shows excellentperformance, and has a wide range of applications. Also, it has good dispersionproperty and slurry stability when used in coal-water slurry. It is a syntheticwater soluble polymer; its production and use do not result in the environmentalpollution. Moreover, polycarboxylic acid has clear components and flexiblestructures, so it could be designed and produced to adapt to a variety of CWSmade for various kinds of coals.At present, a systematic research about the molecule design, the preparationof polycarboxylic acid dispersant and the relationship between its structure and the CWS rheological properties is still blank. My work is about: design themolecular structures to prepare four categories, nine kinds of comb-likepolycarboxylic acid dispersants, based on the polyether macromonomer binarypolycarboxylic acid, the polyether macromonomer ternary polycarboxylic acid,polyester polycarboxylic acid and zwitterionic polycarboxylic acid, according tothe principle of free radical polymerization; systematically discuss the relativitybetween chemical structures of polycarboxylic acid dispersants and CWSrheological properties; reveal the acting mechanism of polycarboxylic aciddispersants and coal particles.This thesis designed and prepared binary polycarboxylic acid dispersantsbased on the polyether macromonomer. Methyl methacrylate (MAA), allylsulfonate (SAS), sodium styrene sulfonate (SSS) respectively, and allylpolyoxyethylene ether (APEG) macromonomer with different chain lengths(m=16,23,27,55) were used to copolymerize into three binary polycarboxylicacid dispersants, MAA-APEG, SAS-APEG and SSS-APEG. They had differentside chains. Using Fourier transform infrared spectroscopy (FT-IR), thepyrolysis-gas chromatography and mass spectrometry (Py-GCMS) and gelpermeation chromatography (GPC), the structures of the dispersing agents werecharacterized; using thermogravimetric （TGA） and differential scanningcalorimetry（DSC）, the thermal stabilities of the dispersants were tested. Theeffects on the viscosity of CWS from polymerization conditions were discussed.The optimal synthesizing conditions of the various dispersants were confirmedby univariate analysis. Dosage of k2S2O8as initiator for4%of the total mass ofmonomer, reaction temperature at80℃, reaction molar ratio of MAA, SAS, andSSS with APEG1:1,1:1and0.5:1respectively. And the preferred dispersantswere screened by comparing their dispersion performance. They were theMAA-APEG1200(m=27), the SAS-APEG1000(m=23), and theSSS-APEG1000(m=23). Besides, their slurrying stabilities were superior to theindustrial naphthalene sulfonate dispersing agent.Three ternary polycarboxylic acid dispersants (MAA-AM-APEG,MAA-SAS-APEG and SSS-AM-APEG) based on the polyether macromonomerwere prepared, using the two monomers of methacrylic acid, sodiumallylsulfonate, acrylamide, sodium styrene sulfonate and allyl polyoxyethylene ether (APEG) macromonomer with different chain lengths (m=16,23,27,55) tocopolymerize. They had different side chains. Using Fourier transform infraredspectroscopy (FT-IR), the pyrolysis-gas chromatography and mass spectrometry(Py-GCMS) and gel permeation chromatography (GPC), the structures of thedispersing agents were characterized; using thermogravimetric and differentialscanning calorimetry, the thermal stabilities of the dispersants were tested. Andeffects on the viscosity of CWS from polymerization conditions were discussed.Also, through univariate analysis, the optimal synthesizing conditions of thevarious dispersants were confirmed. They were: dosage of k2S2O8as initiatorfor2%of the total mass of monomer, reaction temperature at80℃, reactionmolar ratios of MAA-AM-APEG, MAA-SAS-APEG and SSS-AM-APEG2.5:1:1,2.0:1:1and0.5:1:1respectively. And the preferred dispersants werescreened by comparing their dispersion performance. They were theMAA-AM-APEG1000（m=23）, the MAA-SAS-APEG1000（m=23）and theSSS-AM-APEG1000（m=23）. Besides, their slurrying stabilities were superior tothe industrial naphthalene sulfonate dispersing agent.Methacrylic acid, sodium styrene sulfonate and alternatively itaconic acidpolyethylene glycol ester, IAPEG （m=5,9,14,18,23,45） and maleic acidpolyethylene glycol ester, MaPEG（m=9,14,18,23,45）were copolymerized intotwo ternary polycarboxylic acid dispersants with different side chains,MAA-IAPEG-SSS and MAA-MaPEG-SSS. Using Fourier transform infraredspectroscopy (FT-IR), the pyrolysis-gas chromatography and mass spectrometry(Py-GCMS) and gel permeation chromatography (GPC), the structures of thedispersing agents were characterized; using thermogravimetric and differentialscanning calorimetry, the thermal stabilities of the dispersants were tested. Andeffects on the viscosity of CWS from polymerization conditions were discussed.Also, through univariate analysis, the optimal synthesizing conditions of the twodispersants were confirmed. For MAA-IAPEG-SSS, the conditions were:reaction molar ratio of methacrylic acid, maleic acid polyethylene glycol esterand sodium styrene sulfonate3:1.5:1, dosage of k2S2O8as initiator for2%ofthe total mass of monomer, reaction temperature at76℃, dropping time2hours,reactive time totally5hours. And preferred dispersants were screened bycomparing their dispersion performances. They were the MAA-IAPEG600-SSS （m=14）, the MAA-MaPEG800-SSS（m=18）and the SSS-AM-APEG1000（m=23）. In all, their slurrying stabilities were better than the industrialnaphthalene sulfonate dispersing agent.On the basis of previous research, amphiprotic polycarboxylic aciddispersing agent (SSS-DMC-AAPEG) with quaternary ammonium cations,carboxyl group and sulfobenzoic acid group was prepared, using cationicmonomer methyl acrylic acid ethyltrimethyl chloride ammonium(DMC), sodiumstyrene sulfonate and polyester monomer esterified by polyethylene glycol andacrylic acid. Using Fourier transform infrared spectroscopy (FT-IR), thepyrolysis-gas chromatography and mass spectrometry (Py-GCMS) and gelpermeation chromatography (GPC), the structures of the dispersing agents werecharacterized; using thermogravimetric and differential scanning calorimetry, thethermal stabilities of the dispersants were tested. And effects on the viscosity ofCWS from polymerization conditions were discussed. Also, through univariateanalysis, the optimal synthesizing conditions of the amphiprotic poly carboxylicacid dispersing agent were confirmed. They were: reaction molar ratio of sodiumstyrene sulfonate and polyester monomer1:1, dosage of cationic monomer DMCfor5%of the total mass of sodium styrene sulfonate and polyester monomer,dosage of ammonia sulfate and sodium sulfite (molar ratio4:1) as initiator for8%of the total mass of monomer, reaction temperature at80℃. The stability ofCWS (concentration65%)produced by Amphiprotic poly carboxylic aciddispersing agents was better than that(concentration63%) made by naphthalenesulfonate dispersants. Also the former has lower water separating rate. And itsstability reached to grade one; its dynamic and static stabilities were fine. Whenits additive amount ran up to0.5%, the highest concentration of CWS was72%.According to the experimental results, adaptive properties of polycarboxylicacid dispersants to different coals were studied. It indicated thatSSS-DMC-AAPEG1000, MAA-IAPEG600-SSS, SSS-AM-APEG1000andMAA-SAS-APEG1000were suitable for shenfu coal to prepare CWS; whileSSS-DMC-AAPEG1000, SSS-AM-APEG1000, MAA-IAPEG600-SSS,MAA-AM-APEG1000and MAA-MaPEG800-SSS were suitable for binchangcoal. There were three models used to fit the CWS rheological curve ofpolycarboxylic acid dispersants. It showed that the Bingham model was much suited to the CWS rheological curve fitting. The model equation was τ=τ0+μγ;fitting correlation coefficient R2was0.9993.Through surface contact angle, zeta potential analyzer, adsorption quality ofdispersant on coal and scanning electron microscope, tests of coal surfacewettability improvement from dispersants, Zeta potential of coal surface,adsorption of dispersants on coal surface were made; interactions betweendispersants and coal particles were studied. The research indicated that themolecular structure of comb-like polycarboxylic acid dispersants improvedactions of the water-coal interface. The molecular structures of the dispersants(main chain length, the type of side groups and side chain length) affected thestable systematic adsorption–dispersion status with the CWS. Coal adsorbedcomb-like polycarboxylic acid dispersants to form special micelle structure. Andcomb-like polycarboxylic acid dispersants on the dispersion of coal had dualroles, namely electrostatic repulsion and sterical hindrance, providing theoreticalguidance for new dispersants applied for actual production. The structures ofcomb-like polycarboxylic acid dispersants were flexible. And the molecularstructures of comb-like polycarboxylic acid dispersants could be changedaccording to characteristics of different coals to produce dispersants of lowdosage, high performance and strong adaptation.