Molecular Structure Control Of Alkali Lignin-naphthalene Type Coal-water-slurry Dispersants And Dispersion Mechnism

The existing coal water slurry(CWS)dispersants have problems of poor suitability and low dispersion performance on low rank coals.Therefore,the development of low-cost and high performance dispersants has broad market prospects and scientific significance.In this work,JC was taken as a low-rank coal to explore the slurriability with modified alkali lignin(AL)and naphthalene sulfonate formaldehyde condensates(NSFCs),respectively.The AL was chemically modified to investigate the effect of molecular weight and the numbers of hydrophilic groups on its dispersion properties.The synthesis of NSFC was optimized on the products'distribution and dispersion performance.Moreover,molecular dynamics(MD)simulations were performed to study the adsorption behavior of NSFC on the JC surface and at the JC/water interface.Research results were summarized blow:The moisture and volatile content of JC was reduced via pyrolysis modification,otherwise,the semi-coke had a low content of oxygen functional group,which determined the hydrophilicity of the semi-coke.The semi-coke had more abundant of pore structure.These were the main reasons that caused the constant viscosity concentration of JC increased from 65.2%to 69.6%.The mixture of semi-coke and JC had a superior performance on the slurriablity compared to that of JC.The concentration and rheological characteristics of the mixed sample were mainly affected by the slurriability of the semi-coke.Epichlorohydrin(EPI)was used as a cross-linking agent between?-cyclodextrin(?-CD)and AL molecular.The molecular weights and the numbers of hydrophilic hydroxyl groups of modified AL(?-CD-AL)were increased.?-CD-ALs used as CWS dispersants were good at reducing the viscosity and improving the slurry stability.The maximum adsorption capacity of AL and?-CD-AL4 on JC particles was 7.22 and 4.82 mg/g,respectively.Although the adsorption capacity decreased,the constant viscosity concentration increased from 57.2%to 58.7%.The zeta potential provided by?-CD-AL4was about 2 m V higher than that of AL.The number of?-CD grafted on AL structure significantly affect the performance of?-CD-AL.Due to combined effects of electrical repulsion and steric hindrance from?-CD in alkali enviroment,the absolute value of Zeta potential increased and the slurry stability improved with the increasing of?-CD's content.The maximum yield of 2-naphthalene sulfonate acid(2-NSA)was obtained under the mole ratio of naphthalene to concentrated sulfuric acid at 1:1.15,the reaction temperature of 160°C and the reaction time of 3 h.When the reaction temperature reached115°C with the reaction time of 60 min,and the mole ratio of naphthalene to water at1:2.3,the hydrolysis conversion yield of 1-naphthalene sulfonate acid(1-NSA)reached the maximum value.The 2-NSA was totally polymerized with formaldehyde under the reaction conditions of acidity at 30%,the reaction temperature of 105°C,and the mole ratio of naphthalene to formaldehyde at 1:1.However,the 1-NSA was prone to excessive condensation and coking while the acidity was atover 40%.Due to the???interaction between the aromatic ring of NSFC and the surface of JC,the adsorption configuration of NSFC made the hydrophilic sulfonic group facing to the water,forming a single layer physical adsorption on the JC surface,which enhanced the hydrophilicity of the coal surface.The HPLC analysis illustrated that NSFC had differences in the degree of sulfonation and molecular weight.It was concluded that the NSFC with a high degree of sulfonation and a linear structure had a better performance on viscosity reduce,and was conducive to improving the slurry's stability from the results of CWS preparation experiment.Otherwise,the branched NSFC was prone to reducing the surface tension of water.The JC molecular model was constructed based on the structural information with ACD/Chemsket software.The accuracy of the molecular structural model and the bulk model were validated by comparison with the 13C NMR and density results,respectively.The results of MD simulation showed that the NSFC had a strong steric hinerance effect,a lower diffusion coefficient and a loose adsorption on JC with the increase of polymerization degree.The adsorption thickness between NSFC-2 and JC surface was the closest.The MD calculated the absorption of NSFC-5 at the JC/H₂O interface.The results suggested that NSFCs had unique performance with regard to viscosity reduction,which was attributed to the increased ratio of free water confirmed by the density profiles.The NSFC-5 increased the diffusion coefficient of water molecules in the system,caused some bounded water originally existing in JC's internal voids to free,which was the key reason for the viscosity reduction.