表面活性剂作用下煤体力学特性及改性规律

Mechanical properties and modification of coal under the action of surfactant

为了提高煤层润湿性,降低煤体结构致密性,减少或避免瓦斯事故发生,采用阴离子表面活性剂(SDS)改性煤体。以阜新长焰煤为研究对象,采用接触角实验和单轴压缩实验测定表面活性剂改性后煤样接触角、峰值强度、峰值应变和弹性模量等宏观物理力学特性随改性条件变化规律,采用X射线衍射(XRD)和傅里叶红外光谱(FTIR)实验测定表面活性剂改性后煤样矿物质组成和表面官能团等微观结构随改性条件变化规律,利用量子化学密度泛函理论探讨表面活性剂对煤体的改性规律,分析表面活性剂改性后煤体结构损伤过程。结果表明,当SDS溶液质量分数为0.5%、改性时间为48 h,改性温度为40℃时,煤体接触角达到最小,峰值强度和弹性模量降幅最大,峰值应变增幅最大。SDS溶液改性后,煤样中碳酸盐矿物含量减少,硅酸盐矿物含量增加,煤体的微晶结构完整性较差,煤分子内的官能团和各种桥键较为丰富,特别是脂肪类官能团较多,并且定向排列的有序性较低。基于量子化学密度泛函理论探讨了表面活性剂对煤体的改性规律,即表面活性剂通过静电作用力吸附在煤体上,在煤体表面发生化学反应,使煤体中有机矿物的官能团和化学键发生断裂,部分无机矿物发生溶解并分散,这也是煤体结构产生损伤的主要原因。煤表面的化学反应使煤体表面产生次生孔隙和裂隙,次生孔隙和裂隙相互连接形成裂纹,随着改性条件的变化,裂纹不断扩展延伸,直到裂纹贯穿整个煤体,导致煤体整体结构产生损伤,力学强度不断降低。

Anionic surfactant(SDS)was used to modify the coal to improve coal seam wettability,reduce the compactness of the coal structure,and reduce or avoid gas accidents.Fuxin Long flame coals were taking as the research object.The contact angle experiment and uniaxial compression experiments were carried out to determine the macrophysical and mechanical properties(such as contact angle,peak strength,peak strain and elastic modulus)of the coal sample after modification with different conditions.X-ray diffraction and Fourier infrared spectroscopy experiments were used to determine the changes of micro structure(such as mineral composition and surface functional groups)in the coal sample after modification with different conditions.The quantum chemical density functional theory was adopted to explore the modification of coal by surfactants,and to analyze the structure damage process of coal after SDS modification.The results show that when the mass concentration of SDS solution was 0.5%,the modification time was 48 h,and the modification temperature was 40℃,the contact angle of coal was the smallest,the peak strength and elastic modulus de-creased the most,and the peak strain increased the most.After the SDS solution was modified,the content of carbonate minerals in the coal sample decreased,and the content of silicate minerals increased.The micro crystalline structure integrity of coal was poor,the functional groups and various bridge bonds in coal mole-cules were rich,especially the fat functional groups were more,and the ordering order was lower.Based on the quantum chemical density functional theory,the modification of surfactant on coal was explored.In other words,the surfactant was adsorbed on the coal by electrostatic force,and the functional groups and chemical bonds of the organic minerals in the coal were broken,and some inorganic minerals were dissolved and dispersed.This was also the main cause of damage to the coal structure.The chemical reaction on the coal surface produced secondary pores and fissures,these secondary pores and fissures were interconnected to form cracks.With different modification conditions,the cracks continued to extend until the cracks penetrating the entire coal,which led to the overall coal structure damage,and the mechanical strength of coal continued to decrease.