| Coal gas has three properties of high-quality clean energy,main greenhouse gas and mine disaster gas,and its efficient extraction has significant significance to prevent coal and gas outburst and slow down greenhouse gas emissions.The extraction efficiency of coal gas largely depends on its dynamic characteristics of adsorption and desorption in coal seam.It is an effective method to improve the efficiency of coal gas extraction by using surfactants to change the pore structure of coal seam and improve the desorption ability of coal gas.At present,most of the research on surfactants focuses on wetting and dust suppression,and many surfactants have the characteristics of high toxicity and high residue,which is easy to cause environmental pollution.In this study,the environmental protection compound biosurfactants based on soybean protein was developed using Huainan Liuzhuang gas coal and Yunnan Yuwang anthracite as research objects.By using adsorption theory,functional density theory,fractal geometry,molecular dynamics and other theories,and using low-temperature liquid nitrogen adsorption,field emission scanning electron microscopy,Fourier infrared spectroscopy,XRD,Raman spectroscopy and low-field nuclear magnetic resonance,the effects of compound biosurfactants on the pore structure,functional groups and microcrystalline structure of coal are investigated.The evolution characteristics of coal methane desorption performance with pressure were analyzed,the evaluation model of coal physicochemical structure and methane desorption characteristics was established,and the promoting mechanism of coal methane desorption by modification of active agent was revealed.The main conclusions are as follows:(1)The effect of compound biosurfactants on the wettability of coal was studied.It was found from the sedimentation rate and sedimentation rate that the combination effect of modified soy protein isolate and rhamnose-lipids was the best.According to the adsorption capacity and water reabsorption rate of the compound active agent,it is found that the optimal concentration range is 0.25～3g/L.According to the sedimentation rate,surface tension and dynamic contact Angle,it is found that the compound 3:7 active agent has the best wettability,and the wettability is 5.96 times that of raw coal.The coal quality evaluation model was established by using the superstandard multiple method and the double weight superstandard weighting method,and it was proved that the compound biosurfactants treatment can effectively improve the coal quality.(2)The effect of compound biosurfactants on the pore structure of coal was revealed.The results show that the pore size distribution of the modified coal sample changes from2.91 nm to 28.54 nm.The number of micropores in gas coal showed a decreasing trend,and the proportion of large pores increased significantly,with the highest increase of66.41%.The pore shape changed from open pores at one end to open pores at both ends,which was conducive to the formation of more pores and mineral pores.The pore shape of the ink bottle in anthracite gradually widened,and the average pore diameter increased by 57.47% at the highest,which was inclined to the open pore shape with good air permeability,and the connectivity of more pores and micro-cracks was enhanced.Based on the fractal geometry theory,it is found that the surface roughness and structural complexity of coal are reduced and the Hurst index of coal is increased after treatment with compound biosurfactants,which proves that the pore connectivity of coal is enhanced under modification.(3)The influence mechanism of compound biosurfactants on the chemical structure characterization of coal was described.The modification results in the physical and chemical changes of coal samples.The aliphatic side chains and oxygen-containing functional groups of coal fall off and break,and shorter aliphatic hydrocarbons and cycloalkanes are produced.At the same time,through aromatization,the active agents involved in the reaction promote the structure of aliphatic hydrocarbons to form small aromatic rings.The partial network spacing of coal aromatic layer increases,the height and number of aromatic layer decrease,and the extension of aromatic layer decreases,which proves that the coal structure becomes looser.(4)The effect of compound biosurfactants on the desorption performance of coal methane was discussed.It is found that after the active agent treatment,the soluble organic matter in the coal sample dissolves,the total number of micropores decreases,the maximum adsorption capacity of coal methane decreases,the morphology of micropores changes,collapse or fuse into medium or large pores,which verifies that the compound active agent has the effect of pore expanding on the coal sample.Based on the molecular dynamics theory,it is found that the self-diffusion coefficient of methane treated with 3:7active agent is 1.77 times that of raw coal.The entropy weight TOPSIS model was established to evaluate the adsorption and desorption performance of coal,and it was verified that the desorption performance of coal treated with compound biosurfactants was generally better than that of raw coal,especially the comprehensive desorption index of coal sample treated with 3:7 was twice that of raw coal.Figure 【112】 Table 【50】 Reference 【132】... |
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