Study On Synthesis And Performance Of Polycarboxylate Dispersant For Low-Rank Coal Water Slurry

Coal is expected to remain the primary energy source in China for several decades,but direct combustion of coal results in the emission of large amounts of pollutants,which is in conflict with China’s current environmental policies.Coal water slurry(CWS)technology is a significant component of clean coal technology,offering high combustion efficiency,safety,and environmental standards.Therefore,enhancing the quality of CWS has significant environmental and economic value.Dispersants are one of the key technologies for high-performance CWS and a direct factor that affects coal slurry performance.Compared to naphthalene-based and lignin-based dispersants,polycarboxylate dispersant(PC)has the advantages of high efficiency,environmental friendliness,and the molecular structure is flexible and controllable.This paper focuses on the design and synthesis of efficient PC for low-rank coal and its dispersing mechanism through a combination of experimental and theoretical calculations,providing data and theoretical support for the widespread application of low-rank coal water slurry.Specifically,this study designed and synthesized three series of PC and explored the optimal synthesis conditions and action mechanisms of different PC series for low-rank coal of Shan coal.The adsorption behavior of PC was explained from a microscopic perspective using molecular dynamics simulation to obtain efficient PC for low-rank coal water slurry.1.A series of PC-2 was synthesized using acrylic acid(AA)and sodium styrene sulfonate(SSS)as raw materials,and the optimal synthesis conditions were determined to be a monomer ratio of n(AA): n(SSS)= 2:1,an initiator mass fraction of 4,and a reaction temperature of 85℃.The optimal dosage of PC-2 in Shan coal water slurry(CWS)was0.25%,which resulted in a maximum solid loading of 63.25%.Adsorption tests and Zeta potential measurements showed that the maximum adsorption capacity of PC-2 on the surface of Shan coal particles was 1.83 mg/g and the adsorption was monolayer adsorption mode,while the absolute Zeta potential increased to 65.3 m V,indicating that PC-2 had a good dispersion effect.The adsorption mechanism was microscopically explained by molecular dynamics(MD)simulation.2.A series of PC-3 was synthesized by introducing polyether chains(HPEG)into PC-2.The optimal synthesis conditions were a reaction temperature of 85℃,a monomer ratio of n(AA): n(SSS)= 2:1,an initiator mass fraction of 4 wt%,and an addition of HPEG-1000 at 20 wt% of the total raw materials.The maximum solid loading reached 64.2%when the PC-3 dosage was 0.5%.The maximum adsorption capacity of PC-3 on Shan coal particles was 1.54 mg/g,slightly lower than that of the binary PC,while the Zeta potential increased to 60.3 m V,which was consistent with the adsorption test results.Combining MD simulation with test results,it is revealed that the smaller adsorption capacity but better dispersion effect of PC-3 was mainly due to the steric hindrance of the adsorption space between the dispersant molecules caused by the polyether chains.This work showed that adding polyether chains to the PC structure can effectively improve the dispersant performance.3.A series of amphoteric PC-4 was synthesized by introducing cationic monomers containing quaternary ammonium ions based on PC-3.Cationic monomers used were allyl trimethyl ammonium chloride(ATAC)and hexyl trimethyl ammonium bromide(HTAB).The optimal synthesis conditions of amphoteric PC-4 were a reaction temperature of 85℃,a monomer ratio of n(AA): n(SSS)= 2:1,HPEG-1000 at 20 wt%,and a batch-wise addition of 2.5 g of HTAB with an initiator mass fraction of 4 wt%.The optimal dosage of PC-4 in Shan coal water slurry was 66.5%,and the maximum solid loading reached 0.5%.The experimental results show that PC-4 has a maximum adsorption capacity of 2.83mg/g on coal particles and an absolute Zeta potential increase to 59.4 m V,which is mainly attributed to the presence of quaternary ammonium ions in PC-4.MD simulation was used to simulate the adsorption process of PC-4 on coal particles,and the results showed that quaternary ammonium ions not only interacted with coal molecules through electrostatic interactions but also formed cation-π interactions with the aromatic rings in coal molecules,greatly enhancing the adsorption performance of PC-4.This work demonstrates that the type,proportion,and addition method of functional monomers can all affect the performance of PC,and quaternary ammonium ions can be used as anchoring groups to synthesize high-performance amphoteric PC.