渣油热反应体系中第二液相的形成机制

FORMATION MECHANISMS OF SECOND LIQUID PHASES IN THERMAL REACTION SYSTEMS OF VACUUM RESIDUA

在渣油热反应体系中，随着热处理时间的延长，用光学显微镜从渣油反应样品中依次观察到了片状／不规则状物理第二液相，少数圆球状化学物理第二液相和大量不规则状化学第二液相。对第二液相相分离点时渣油热反应体系物理化学状态的考察指出：物理第二液相是渣油原始体系中的沥青质胶质重组分混合胶团破坏后，丧失胶质组分保护的原生沥青质组分通过物理聚集过程形成的，其形貌特征源于原生沥青质组分的分形聚集过程和热力学成长过程；在化学物理第二液相相分离点，丧失胶质组分保护的原生沥青质发生分子内桥键和脂肪侧链断裂，形成平面性较高的稠环芳香性分子，它们在适宜的体系流动性条件下经有序聚集成长为具有最低能量构型的球形态；随着反应程度加深，原生沥青质特别是原生胶质的自由基反应经诱导期后速度剧增，导致体系中在短时间内产生大量次生沥青质，它们经由动力学成长形成不规则状化学第二液相。

In the thermal reaction systems of vacuum residua, some sparsely scattered planar and irregular entities and spheroids as well as aggregated irregular bodies densely distributed in the bulk phase of the sample come in sequence into the optical microscopic view in the sampled reacting vacuum residue with the elapse of the heat treatment time Previously these three categories of neophases were temporarily named as the physical, chemiphysical and chemical second liquid phase based on the limited preliminary analyses of their solubility class, compositions and structures In the present study, electronic transmission microscope observations of the physical structures of Shengli vacuum residue and chemical characterization of the nheptane insolubles and toluene solubles at onset points of the second liquid phases were examined and discussed, and accordingly, schematic routes which might account for both the inception of the second liquid phases and their growth into different morphologies were formulated At the onset point of the physical second liquid phase, the protoasphaltenes, which is from the partial or complete breakdown of the mixed asphaltenesheav ier resins micella due to thermomotions of molecules, dilution and agitation in the thermal reaction systems of vacuum residue, goes first through the kinetic growth and then through the thermodynamic growth to form, respectively, the fractal and the regularly shaped phase separation entities At the onset point of the chemiphysical second liquid phase, no any mixed micelle of asphaltenes or heavy resins coherent of the physical structure of the original vacuum residua is found Molecules of the protoasphlatenes unprotected by the heavy resins undergo the breakage fo intramolecular bridge bonds and the scissoring of the aliphatic sidechains, resulting in the formation of polycyclic aromatics with plane configurations With appropriate system fluidity, the embyroic polyaromatics molecules aggregate orderly, driven by the principle of minimum energy, into the spheroid chemical second liquid phase At the onset point of the chemical second liquid phase, the mixed micelle of asphaltenes and heavy resins in the original vacuum residua can not be seen anywhere in terms of the physical structure of reacting vacuum residua The radical propagation of the protoasphaltenes and in particular the resins accelerates automatically after the induction period, and neoasphaltenes are generated in a great quantity within a very short period These neoasphaltenes go via kinetic growth forming the irregular chemical second liquid phase