Abstract Inhibition of coke formation in cracking of distillation residues, such as the vacuum residue (VR), has attracted extensive attention for the development of better technologies. However, the radical coking mechanism was seldom studied in the past. This work studies coking and radical concentration during cracking of two VRs and their SARA fractions in sealed micro-reactors at 400, 420, 440 and 460 °C and elaborates the results with respect to the chemical composition of the starting materials and the kinetics of radicals formation. It is found that most of the radicals in VR locates mainly in the asphaltene fraction (Asp). The agglomeration of Asp to coke at low temperatures does not involve significant change in radical concentration. The coke yield includes that formed from the agglomeration of Asp and that from the condensation of radical fragments generated in cracking of all the fractions. The coke itself also undergoes cracking and condensation, resulting in a higher radical concentration and a lower coke yield. The interactions between the Asp and other SARA fractions are relatively large in coke formation by agglomeration, but relatively small in cracking and condensation due to limited amounts of small radicals or hydrogen radicals from the cracking of other fractions. The VR with a higher Asp fraction and richer poly-aromatic structures (QD-VR) is higher in radical generation and lower in activation energy.

中文翻译：

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两种减压渣油及其 SARA 馏分热裂解过程中的自由基和焦化行为

摘要 在减压渣油 (VR) 等蒸馏渣油裂解过程中抑制焦炭的形成已引起广泛关注，以开发更好的技术。然而，过去很少研究自由基焦化机理。这项工作研究了在 400、420、440 和 460 °C 下密封微反应器中两种 VR 及其 SARA 馏分在裂解过程中的结焦和自由基浓度，并详细阐述了有关起始材料化学成分和自由基动力学的结果形成。发现VR中的大部分自由基主要位于沥青质部分（Asp）中。Asp 在低温下聚集成焦炭不涉及自由基浓度的显着变化。焦炭产率包括由Asp 的附聚形成的焦炭产率和由所有馏分裂解产生的自由基碎片的缩合形成的焦炭产率。焦炭本身也会发生裂化和缩合，导致较高的自由基浓度和较低的焦炭产率。Asp 和其他 SARA 馏分之间的相互作用在通过附聚形成焦炭时相对较大，但由于来自其他馏分裂化的小自由基或氢自由基的数量有限，因此在裂化和冷凝中相对较小。具有更高 Asp 分数和更丰富的多芳烃结构 (QD-VR) 的 VR 自由基生成更高，活化能更低。导致较高的自由基浓度和较低的焦炭产率。Asp 和其他 SARA 馏分之间的相互作用在通过附聚形成焦炭时相对较大，但由于来自其他馏分裂化的小自由基或氢自由基的数量有限，因此在裂化和冷凝中相对较小。具有更高 Asp 分数和更丰富的多芳烃结构 (QD-VR) 的 VR 自由基生成更高，活化能更低。导致较高的自由基浓度和较低的焦炭产率。Asp 和其他 SARA 馏分之间的相互作用在通过附聚形成焦炭时相对较大，但由于来自其他馏分裂解的小自由基或氢自由基的数量有限，因此在裂解和冷凝中相对较小。具有更高 Asp 分数和更丰富的多芳烃结构 (QD-VR) 的 VR 自由基生成更高，活化能更低。