煤焦油重组分沥青质性质分析及对加氢裂化生焦影响的推测

从中/低温煤焦油中切取重组分,提取了重组分C7-沥青质,并以此重组分为原料进行了高压釜加氢实验,通过1H-NMR、XRD、FT-IR、SEM、元素分析和相对分子量测定等手段对重组分沥青质结构参数、官能团、表观形态等方面进行了分析,并将其与加氢过程中生焦情况进行了关联。结果表明,C7-沥青质基本结构单元以稠环芳烃为中心,周围分布少而短的侧链,侧链以小于3个碳的短直链正构烷基为主,相对分子量小,芳香片层没有堆积结构。O是该沥青质中氢键主要来源,大多分布在环氧烷烃和醚类结构中,外围的O数量低,分子间氢键更难形成,结构单元之间缔合性弱,沉积聚合慢而均匀。沥青质中短侧链不易断裂,在反应过程中产生的稠环芳烃自由基少,缩合能力小,使该馏分油生焦能力低,具有较高的加氢潜质。

Properties of coal tar heavy fraction and its relevance to coking in hydrocracking

The hydrogenation experiment on the heavy fraction (>350 ℃) of medium/low temperature coal tar, prepared by vacuum distilling, was conducted in an autoclave, and the asphaltene was separated from heavy fraction with n-heptane solvent. The properties such as structure parameters, functional group and microstructure were analyzed by ¹H-NMR, XRD, FT-IR, SEM, ultimate analysis and average molecular weight determination (VPO). Moreover, the relevance of coking to C₇-asphaltene properties was discussed. The results show that C₇-asphaltene units are mainly composed of polycyclic aromatics linked in side with a few and short aliphatic chains (mainly n-alkane less than 3 C atoms). The asphaltene units have small average molecular weights and there is no aromatic sheet stacking structure existing. The propensity to aggregate for asphaltene units was weakened because O atoms in asphaltene are mainly distributed in epoxyalkane or ethers (C-O-C) and they are different from the petroleum asphaltene whose O atoms exist in the peripheral phenolic and alcoholic hydroxyl. So, the intermolecular hydrogen bond is more difficult to build. Furthermore, short chains are not easy to break and fewer polycyclic aromatic radicals are generated in the hydrocracking process, and the asphaltene has a lower coking potential.