不同煤级煤分级萃取后的XRD结构特征及其演化机理

基于溶剂萃取的方法,采用苯、CS2、丙酮以及THF等4种溶剂对褐煤、焦煤、低级无烟煤、中级无烟煤等进行分级超声萃取,并借助于X-射线衍射法,对原煤及其萃取物的微晶结构参数进行了测试。研究发现:①随着煤级的变化,溶剂的分级萃取率呈现相同的变化趋势,焦煤的萃取率最大,其次是褐煤,无烟煤萃取率最小;②4个煤样中,THF溶剂的可溶组分最多,其他3个溶剂的萃取率对比关系因煤级不同而略有差异,原因在于萃取率受到煤的显微组分和小分子化合物组成影响;③与原煤相比,萃余物的芳香层间距d002减小,而堆砌度Lc、延展度La均略增大,计算得到的芳香层片堆砌层数增多;④溶剂萃取条件下,煤的不同微晶结构参数的变化机理不同,表现为La主要与溶胀度有关,Lc受溶胀度和小分子相的溶出量有关,d002则是溶胀作用,小分子相溶出量以及溶剂分子的填充情况共同作用的结果;萃取后,芳香层片堆砌层数N的增加是由于Lc和d002变化后的计算效应引起的,而非事实上的增多。

Characteristics of XRD parameter for different ranks of coals under fractional extraction and its evolution mechanism

By means of the fractional ultrasonic-extraction mode，four different-rank coals，including lignite，coking coal，low- and mid-metamorphism anthracites were extracted by different solvent，and X-ray diffraction (XRD) was applied to investigate the microcrystalline structure parameters.The results reveal that，as the increase of coal metamorphism degree，the yields of fractional extraction show the similar trends，i.e.the extraction yield of coking coal is the largest，followed by the lignite and anthracites.For the four coals，the yield extracted by tetrahydrofuran(THF) is more than those by the other three solvents.The comparison of the extraction yields under the other three solvents，controlled by the maceral and chemical composition of coals，shows different trends.Further，the aromatic lamellae spacing (d002) of all residues is lesser than that of all raw coals，but the diameter (La) and the stack height（Lc）of aromatic layer appear slightly increasing trend.The research concludes that different microcrystalline structure parameters of coal have different evolution mechanism under fractionally extracted by solvents： La is affected by swelling degree of coal microscopic structure，Lc done by swelling degree and the amount of small molecular compounds dissolved out of coal body，and d002 comprehensive done by swelling degree，the amount of dissolved-off small molecular compounds and the hold-up solvent molecules.But the increase in stack layers N of aromatic layer is just because of the increase of calculation value obtained by the various aromatic lamellae spacing d002 and the stack height Lc rather than that in fact.