不同体积分数THF萃取后焦煤的GC/MS和FTIR分析

GC/MS and FTIR Analysis of Coking Coal Extracted with Different Volume Fractions of THF

以山西古交焦煤为实验用样,采用不同体积分数的四氢呋喃(THF)溶剂进行萃取,计算得到溶剂萃取率,并分别对萃取物的化合物组成和萃余物的主要官能团进行气相色谱-质谱联用(GC/MS)和傅立叶变换红外光谱(FTIR)分析。结果表明:萃取率随着THF体积分数的增加呈现增大的趋势,随着萃取时间的增加和萃取温度的升高,分别呈现倒“∽”波动和倒“V”型的变化趋势;焦煤的THF萃取物主要为脂肪烃、芳香烃和含杂原子有机化合物等,其中芳香烃相对含量最小,含杂原子有机化合物相对含量最大,且多为含氧化合物。进一步发现,随着THF体积分数的增加,萃取物的脂肪烃含量先增大后减小,而杂原子化合物含量呈现相反的变化规律,芳香烃则仅在THF纯溶剂萃取作用下能检测到。25℃萃取物中的酯类、醛类和羧酸类等含氧化合物较多,45℃萃取物中醇类化合物明显增多。此外,水溶剂的存在有利于醇类和酸类低分子化合物的溶出。从焦煤及其各萃余物中的官能团分布来看,100%THF萃余物中脂肪烃含量最高,富氢指数I1达到3.24;脂肪链结构参数I4随THF体积分数的增大呈先增大后减小的趋势,且在100%THF萃取时最小,为2.59;相比于芳香结构的化合物,脂肪族化合物相对溶出更多,是萃余物芳构化程度I2计算值增大的原因。而受杂原子化合物中含氧低分子化合物溶出影响,萃余煤含氧指数I3在不同体积分数的THF萃取后表现出先增大再减小的特征。研究认为,尽管萃取过程中水不占据主导地位,但在一定程度上会影响THF溶剂的萃取化合物类型及抑制其萃取能力。

The present study took coking coal collected from Gujiao,Shanxi province as an experimental sample,using different volume fractions of tetrahydrofuran(THF)extraction.The solvent extraction yields were calculated,and the chemical composition of extracts and main functional groups of residues were analyzed by using gas chromatography-mass spectrometry(GC-MS)and Fourier transform infrared spectroscopy(FTIR).Research results show that the extraction yield presents an increasing trend with the increasing volume fraction of THF.With the increasing extraction time and temperature,the extraction yield presents an inverted“∽”fluctuation and an inverted“V”trend,respectively.The extracts of coking coal are mainly composed of aliphatic hydrocarbons,aromatic hydrocarbons and heteroatom-containing compounds.Among them,the aromatic hydrocarbons account for the smallest proportion,while the heteroatom-containing compounds,especially oxygen-containing compounds account for the largest proportion.The further analysis find that,with the increasing volume fraction of THF,the aliphatic hydrocarbon content of the extract increases first and then decreases,while the heteroatom-containing compounds show an opposite pattern,and the aromatic hydrocarbons are only detected under 100%THF extraction.The 25℃extract contains more oxygen-containing compounds such as esters,aldehydes,and carboxylic acids,while the 45℃extract contains more alcohol compounds.In addition,it can be seen that the water-based solvent is conducive to the dissolution of the alcohols and acid low molecular weight compounds.In terms of the distribution of the functional groups in coking coal and its residues,the content of the aliphatic hydrocarbons in 100%THF residues is the highest,with the hydrogen index I1 correspending to 3.24,and the aliphatic chain structure parameter I4 first increasing,and then decreasing with the increasing volume fraction of THF,and it is the smallest at 100%THF,which is 2.59;compared with the aromatic compounds,more aliphatic compounds are dissolved,which is the reason for the increase in the aromatic degree I2.Affected by the dissolution of oxygen-containing low molecular weight compounds in heteroatom compounds,the oxygen index I3 of residues shows the characteristics of first increasing and then decreasing after extraction with different volume fractions of THF.Therefore,although water does not dominate the extraction process,it affects the type of soluble compounds and inhibits the solvent extraction ability to a certain extent.