冷冻预处理对神府长焰煤萃取率的影响及机理研究

以神府长焰煤为研究对象,对其进行冷冻预处理,然后利用四氢呋喃对煤样进行索氏萃取,研究冷冻预处理的温度和时间对煤样萃取率的影响规律,获得冷冻预处理提高煤样萃取率的最优实验条件。通过分析冷冻预处理前后煤样的孔结构、表面形貌、萃取物的红外光谱和X射线光电子能谱,提出冷冻预处理提高煤样萃取率的机理。结果表明:冷冻预处理提高了煤样的萃取率,最优实验条件为温度-80℃、时间12h;在最优实验条件下,煤样的四氢呋喃萃取率由6.16%增加到7.67%,增加了24.68%;孔结构分析结果表明,与原煤相比,冷冻预处理后煤样的孔容、孔径和比表面积均增加,其中比表面积由6.77m²/g增加至7.21m²/g,增加了6.50%,孔容由0.011 mL/g增加至0.013mL/g,增加了18.18%,孔径由7.30nm增加到7.32nm,增加了0.27%;扫描电镜实验结果表明,与原煤相比,冷冻预处理后样品的表面粗糙度增加;红外光谱及X射线光电子能谱分析结果表明,冷冻预处理增加了萃取物中脂肪烃的含量,含C=C,C=O及C—O键的化合物含量减少。冷冻预处理提高煤样萃取率的机理为:冷冻预处理增大了煤样的孔容,对其进行溶剂萃取,有利于大分子骨架缝隙中独立存在的脂肪族低分子化合物的溶出。

Effects of Freezing Pretreatment on Extraction Ratio of Shenfu Long-flame Coal and Its Mechanism

Shenfu long-flame coal(SF)was selected as the research object,which was extracted by using the Soxhlet extraction method with tetrahydrofuran after freezing pretreatment.The effects of pretreatment temperature and time on the extraction rate were emphatically studied,and the optimum operating conditions for improving the extraction rate were obtained.The pore structure and surface morphology of coal samples before and after freezing pretreatment,as well as the Fourier transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS)spectra of the extracts,were analyzed in this study.Based on the above characterizations,a mechanism of freezing pretreatment to improve the extraction rate of coal was proposed.Experimental results show that the extraction ratio of coal can be effectively improved by the freezing pretreatment method,and a duration of 12hat the temperature of-80℃is the optimum experimental condition.Under this optimum condition,the extraction ratio is increased by 24.68%,from 6.16%to 7.67%.In addition,the pore volume,pore diameter,and specific surface area of the pretreated SF coal are all increased compared to that of raw coal samples.Specifically,the specific surface area increases by 6.50%,from 6.77m²/g to 7.21m²/g,the pore volume increases by 18.18%,from 0.011mL/g to 0.013mL/g and the pore size increases by 0.27%,from 7.30nm to 7.32nm.Meanwhile,the SEM testing results show that the surface roughness of the pretreated sample also increases compared to that of raw coal.Furthermore,the results of FTIR and XPS tests show that the freezing pretreatment can increase the content of aliphatic hydrocarbon,while reducingthecontentofC=C,C=O,and C O.Above all,the mechanism of freezing pretreatment to improve the extraction ratio of SF coal can be summarized as follows:freezing pretreatment increases the pore volume of coal,which is beneficial to the dissolution of low-molecular-weight aliphatic compounds during the solvent extraction process,which exist independently in the gap of the macromolecular framework.