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The Influence of Dispersant Structure on the Adsorption of Coal-water Interface

Author: Wang
Tutor: QiuXueQing
School: South China University of Technology
Course: Applied Chemistry
Keywords: Coal-water slurry dispersant Molecular weight Sulfonation degrees Rheology Adsorption performance
CLC: TQ531
Type: Master's thesis
Year: 2010
Downloads: 362
Quote: 2
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Abstract

Coal-water slurry (CWS) technology was began to developed instead of petroleum in the 1970s. It not only keeps the original chemical and physical properties of coal , but also has similar liquidity and stability as petroleum, so CWS has strong practicability and popularize value. Dispersant is the key facter of CWS properties. It can change the nature of coal by the interaction between the main structure, substitutional group, molecular weight, sulphonated degree and coal particles, which leads to good rheological properties. Shenhua coal is a kind of low-rank coal, so it has high water and oxygen content, which results to bad performance. Therefore, the study of dispersing mechanism between dispersant structure and low-rank coal will have important significance for synthesis of high performanc dispersant and CWS development.In the paper, by sulfonation and fasculation reaction, aliphatic sulfonate (SAF) and sodium lignin sulfonate (GCL3S) were prepared as dispersants. These addiitives with different molecular and sulfonation degree were used as diapersants in CWS. Apparent viscosity and rheological behavior represent the properties of CWS. The mechanism of adsorption performance was discussed in the dissertation, including sterically hindered, static repulsion and wettability. Based on the theoretic study, sodium tripolyphosphate (P) was used as accessory ingredient compounding with different molecular structure dispersants to study the properties of CWS.Firstly, SAF with different molecular weight, sulfonation degree and ultrafiltration were made to study adsorption properties. The study finds that, suitable molecular weight (Mw 31800 ~ 36800) and sulfonated degree (1.53~1.64 mmol/g) can improve the dispersion of CWS. The adsorption isotherm of SAF on Shenhua coal is fit to Langmuir single molecule layer absorption. Through the analysis of thermodynamics, adsorption is a processes of spontaneous system, and exothermic reaction with entropy increased. Temperature has little effect on SAF with different degrees of sulphonation. Zeta potential test shows that, good dispersion viscosity-reduced SAF has higher Zeta potential absolute value on coal particles. Contact angle was measured between dispersant solution and coal particles, which indicates that good wetting ability can lead to good dispersion viscosity-reduced ability. For ultrafiltration SAF, the study found that the highest fraction (intercept molecular weight more than 50000) SAF has significant better viscosity-reduced ability than FDN. The adsorption tests conclude that the higher fraction is, the less adsorption quantity is, which is less than FDN. Thermodynamic analysis shows that temperature can improve the adsorption of lower fraction SAF (intercept molecular weight less than 2500), but inhibit adsorption of higher fraction SAF(intercept molecular weight more than 50000). The higher Zeta potential absolute value is, the better viscosity-reduced ability is, so is wettability.Sodium lignin sulfonate (GCL3S) was developed to be a kind of efficient CWS dispersant by chemical modification , it can not only increase the added value of lignin which came from paper-making waste, but also can reduce the cost of dispersants. Different molecular weight and different degree of sulphonated GCL3S dispersants were used to make the pulp. The study finds that appropriate molecular weight (inherent viscosity 11.86 mL/g, Mw 45396) and lower sulfonated degree (1.35 mmol/g) can improve their dispersing ability. Langmuir isotherm of GCL3S is similar with the single molecule layer absorption type. Along with the increase of GCL3S molecular weight, the adsorption quantity gradually reduce, but negative charge increases on the coal surface. Thermodynamic analysis results show that temperature has little effect on lower molecular weight(inherent viscosity 5.57 mL/g,Mw 17463) and lower degree of sulphonation (1.23 mmol/g) GCL3S, but can boost the higher ones(inherent viscosity 12.38~23.9 mL/g,Mw 57478~58483, 1.72~2.06 mmol/g). Parameters of thermodynamic functions illustrate that adsorption process is an exothermic reaction with entropy increased. Better wettability still leads to better pulp performance.In this study, sodium tripolyph-osphate was compounded with several different molecular structure dispersants to study the pulp performance. Sodium tripolyphosphate can reduce the dispersion viscosity-reduced ability of lower molecular weight SAF(inherent viscosity 5.21~7.03 mL/g,Mw 20800~31800), but has opposite influence on the highter ones(inherent viscosity 10.87~19.70 mL/g,Mw 36800~38100). In adsorption tests, adsorption isotherm do not fit Langmuir single molecule layer absorption any more. Sodium tripolyph-osphate significantly reduces SAF adsorption, even displayed negative adsorption. Meanwhile, it reduces the coal surface negative charge. Sodium tripolyph-osphate is advangtage for viscosity-reduced ability of medium sulfonation degree SAF(1.64 mmol/g). Adsorption quantity reduces, but little change in Zeta potential. Sodium tripolyph-osphate against dispersion viscosity of highest fraction SAF(intercept molecular more than 50000) dispersion viscosity. The adsorption quantity decreases obviously, when Zeta potential shows sharp fluctuation.Sodium tripolyph-osphate compounded with GCL3S(inherent viscosity 5.21~23.90 mL/g,Mw 17463~57478) shows a better dispersing ability. It can promote the adsorption of lower molecular weight GCL3S(inherent viscosity 5.57~6.47 mL/g,Mw 17463~27676), inhibit the adsorption of higher molecular weight dispersants. Zeta potential absolute value reduces sharply. For different degrees of sulphonated GCL3S, after adding sodium tripolyph-osphate, slurry changes from "shear thickened" dilatant fluid to "shear thinning" pseudoplastic fluid. Sodium tripolyph-osphate compounded with lower degrees of sulphonated (1.23 mmol/g) GCL3S acts as promotion to CWS properties, and it can raise Zeta potential absolute value at the same time, but suppresses the performance of the slurries formulated from higher sulphonated degrees (1.35~2.06 mmol/g)GCL3S.

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