Experimental Study On Preparation Of Coal Dust Suppressant By Carbon-Fixing Microalgae Oil Extraction

As the most abundant fossil energy on the earth,coal is an important support for global economic and social development.China has long used coal as the main production and consumption energy,and a large amount of dust will be produced in various processes of coal production.Dust not only often induces occupational diseases such as pneumoconiosis,but also causes disasters such as explosions,which restricts the safe,efficient and green mining of coal mines.Adding dust suppressant to reduce the surface tension of liquid and improve the wettability of dust is one of the important means of wet dust removal technology,which is widely used in the practice of mine dust pollution control.Traditional dust suppressants are mostly chemical dust suppressants.The preparation process is complex and the cost is high.There are problems such as weak interface performance,poor dust suppression effect and poor environmental compatibility under hard water conditions.Therefore,based on the idea of efficient utilization of carbon-fixing microalgae oil,this thesis oposes a new method for preparing coal dust suppressant using microalgae oil as biomass raw material,and studies this by theoretical analysis,experimental research and performance test.The main work and results are as follows:The relationship between microalgae culture and carbon fixation and the factors affecting the relative extraction rate of microalgae oil were studied.There is a linear relationship between the concentration of chlorella and the absorbance,and the absorbance can directly reflect the growth of chlorella.The effect of CO₂ on the growth of Chlorella showed a trend of promoting first and then inhibiting with the increase of gas concentration,and 20%CO₂ had a significant inhibitory effect on the growth of Chlorella.With the increase of CO₂ concentration,the removal rate of CO₂ by Chlorella increased first and then decreased,and 10%CO₂ was the best concentration for Chlorella.The quadratic polynomial regression equation of solvent ratio（A）,liquid-solid ratio（B）and extraction time（C）was obtained by single factor experiment and response surface optimization.The regression model R_Adj²=0.9443,and the fitting effect was good.The primary and secondary order of each factor affecting the extraction rate of microalgae oil was extraction time>liquid-solid ratio>solvent ratio.The optimum conditions for the relative extraction rate of microalgae oil were as follows:solvent ratio 2.04:1,liquid-solid ratio 4:1,extraction time 4h,and the response value was 89.2%.Through gas chromatography analysis,the proportion of saturated fatty acids in microalgae oil was 50.19%,and the proportion of unsaturated fatty acids was49.81%.The method and material of bio-based coal dust suppressant synthesized by microalgae oil were developed.A green and efficient coal dust suppressant was developed by methyl esterification and amidation reaction with microalgae oil as raw material,and its hard water resistance was studied.The reaction product MODS was determined to be an amide coal dust suppressant by FTIR analysis.The results of hard water resistance test showed that the average calcium ion tolerance CIS of MODS was1271.28 mg·L^-1,which had good hard water resistance and could be applied to hard water environment.The interfacial properties of MODS increased with the increase of mass concentration,and the surface tension remained at 31.95 m N·m^-1.Under the condition of hard water,the surface tension of microalgae oil-based coal dust suppressant MODS remained at 31.8-33 m N·m^-1 when the temperature,p H and salinity changed greatly（temperature≤60°C,p H 2-13,Na Cl mass fraction≤43%）,and the interface performance was relatively stable,showing good environmental tolerance.The wetting and dust suppression performance of microalgae oil-based coal dust suppressant MODS was clarified.The SEM images show that the wetting effect of MODS on coal samples is better than that of the commonly used anionic surfactant SDBS,and the liquid film formed on the surface of coal samples is denser and more uniform.The contact angle test results show that MODS can improve the wettability of coal.The dynamic contact angles of SDBS and MODS solutions with the surface of coal samples at 60 s are 26.78°and 13.41°,respectively,which are 34.05%and 66.48%lower than the initial state,respectively.The wetting effect of MODS on coal is significant.FTIR test results show that the content of hydrophilic functional groups in coal samples increases and the content of hydrophobic functional groups decreases after MODS treatment,which further reveals the mechanism of MODS on coal chemical structure from the micro level.The results of sedimentation experiments showed that the sedimentation time of dust in MODS solution was less affected by the change of water hardness.It remained basically unchanged in the range of 0-400 mg·L^-1 hard water,and the maximum rise rate was only 38.02%in the range of 400-1000 mg·L^-1.The sedimentation time of dust in MODS solution was less than that of SDBS solution at the same concentration,and MODS showed better wettability.The results of dust reduction experiments show that with the increase of the concentration of MODS and SDBS,the dust reduction effect of dust with different particle sizes is improved.The dust reduction efficiency of MODS solution is higher than that of SDBS solution at the same concentration,and the dust reduction effect is more significant.