重质油在超临界水中的热裂化行为及动力学研究

发布时间：2018-06-03 12:29

本文选题：超临界水 + 重质油　；参考：《华东理工大学》2017年博士论文

【摘要】：重质油因其高粘性、高残炭和高杂原子含量对传统处理工艺的实施带来挑战。重质油所含沥青质是焦的直接前驱体,并富含金属和杂原子,同时也是重质油残炭的主要载体。水在其临界区域内良好的扩散与传质性能为超临界水(SCW)中的重质油改质提供了可能。据此,本文对重质油在SCW中的改质展开研究。论文采用反应动力学分析、分子动力学模拟和多种物理表征手段重点就沥青质在SCW中的反应行为进行考察。在此基础上,进一步分析了利用SCW热裂化工艺进行重质油脱残炭的可行性。实验结果表明,在高水油比、高水密度和强烈搅拌的介入下,SCW中的重质油热裂化能够转入拟均相相态中进行。在该相结构中,包括软沥青在内的轻组分溶解于SCW相,而沥青质则高度分散于水相中。无论是SCW相还是传统油相中的重质油热裂化,反应均遵循自由基烃反应机理。尽管如此,当裂化由传统油相转移至SCW相后,裂化所涉及的缩合和脱烷基类型反应都得到了本质的加速。根据反应动力学分析,油相和SCW相中的重质油热裂化都可以用拟平衡-自催化模型进行描述。随着反应温度的升高,软沥青缩合至沥青质和沥青质缩合至焦相继摆脱对于焦生成的自催化依赖。在高温下重质油的热裂化可以用仅考虑拟平衡约束的裂化集总模型进行描述。无论是以重质油还是以沥青质作为反应原料,在SCW环境和氮气环境下进行热裂化时最终得到的焦和液体收率基本相同。这意味着在具有工业可行性的水油比、反应温度和水密度条件下,SCW并不能作为重质油热裂化的有效氢供体。SCW介入的贡献主要体现在为反应提供了特殊的相结构以及溶剂环境。在SCW中沥青质的缩合较软沥青的缩合得到了不同程度的加速。基于COMPASS力场的分子动力学模拟表明,沥青质和SCW之间存在排斥作用。由此,SCW在沥青质周围形成空穴而非传统认为的簇近程溶剂结构。在稠环片段之间的π-π相互吸引、稠环芳烃与水分子之间的相互排斥以及SCW提供的良好扩散环境的促进下,沥青质在SCW中自发进行组装形成纳米团簇或者聚集体。聚集体形成的速率和规模在很大程度上取决于SCW密度,并且聚集体在结构上与沥青质缩合产物焦高度类似。对于分散在SCW中的沥青质团簇而言,其裂化机理和动力学受到溶剂环境供氢能力的影响。氢供体的存在能够有效封闭对于沥青质裂化具有关键作用的烃自由基。相应地,沥青质缩合至焦以及沥青质分解至软沥青的表观活化能都有所上升,并且其上升幅度与氢供体的浓度直接相关。在较低的反应温度下,少量氢供体的存在能够有效抑制沥青质的缩合与分解。随着反应温度的升高,沥青质裂化的引发效率得到本质提高。此时少量氢供体的存在对沥青质裂化的抑制作用被削弱。当沥青质的热裂化伴随着大量软沥青进行时,沥青质分解至软沥青这一集总反应可以被忽略。包括沥青质在内的重芳烃在SCW中的自组装效应,可以被用于重质油热裂化脱残炭。在高水油比和高水密度形成的拟均相框架下,主要包含沥青质和胶质的残炭虚拟组分的类焦自组装及后续缩合得到了促进。与此同时,轻质的非残炭组分的缩合得到抑制。在裂化反应初期,拟均相结构下得到的裂化液相产物具有残炭含量低、平均分子量低、H/C高和平均芳环数少的优势。
[Abstract]:Heavy oil has a high viscosity, high carbon residue and high impurity atoms. The asphaltenes contained in heavy oil are direct precursors of coke and are rich in metal and impurity atoms, and are also the main carrier of heavy oil residue. The good diffusion and mass transfer properties of water in its critical area are in supercritical water (SCW). The modification of heavy oil is possible. On this basis, this paper studies the modification of heavy oil in SCW. In this paper, the reaction kinetics analysis, molecular dynamics simulation and various physical characterization methods are used to investigate the reaction behavior of asphaltene in SCW. On this basis, the heavy oil is further analyzed by the use of SCW thermal cracking process. The experimental results show that heavy oil thermal cracking in SCW can be transferred into pseudo homogeneous phase under the intervention of high water to oil ratio, high water density and strong agitation. In this phase, the light components, including soft bitumen, are dissolved in the SCW phase and the asphaltenes are highly dispersed in the water phase. Both the SCW phase and the traditional oil are in the phase structure. The reaction mechanism of heavy oil thermal cracking in each phase follows the reaction mechanism of free radical hydrocarbon. However, when the cracking is transferred from the traditional oil phase to the SCW phase, the condensation and dealkylation type reactions involved in the cracking have been intrinsically accelerated. According to the kinetic analysis, the heavy oil thermal cracking in the oil and SCW phases can be used as a quasi equilibrium autocatalytic. The model is described. With the increase of reaction temperature, the condensation of soft bitumen to asphaltene and asphaltene condenses to the autocatalytic dependence of coke formation. The thermal cracking of heavy oil at high temperature can be described by a lumped lumped model, which only considers the quasi equilibrium constraint. In SCW environment and nitrogen environment, the final coke and liquid yield is basically the same. This means that under the industrial feasibility of water and oil ratio, reaction temperature and water density, the contribution of SCW to the effective hydrogen donor.SCW intervention of heavy oil thermal cracking is mainly reflected in the special phase for the reaction. Structure and solvent environment. The condensation of asphaltenes in SCW is accelerated in varying degrees. The molecular dynamics simulation based on the COMPASS force field shows that there is an exclusion between asphaltenes and SCW. Thus, the SCW is formed around the asphaltenes rather than the traditionally recognized close range solvent structure. With the mutual attraction of pi - pi, the mutual exclusion between the polycyclic aromatic hydrocarbons and water molecules and the favorable diffusion environment provided by the SCW, the asphaltenes are spontaneously assembled in SCW to form nanoclusters or aggregates. The rate and scale of the formation of aggregates depends largely on the SCW density, and the aggregates are structurally related to the shrinkage of the asphalts. For the asphaltene clusters dispersed in SCW, the cracking mechanism and dynamics are affected by the hydrogen supply capacity of the solvent environment. The existence of the hydrogen donor can effectively seal the hydrocarbon radicals that have a key role in the asphaltene cracking. Accordingly, the asphaltenes are condensed to the coke and the asphaltene decomposition to the soft bitumen. At lower reaction temperature, the presence of a small amount of hydrogen donor can effectively inhibit the condensation and decomposition of asphaltenes. With the increase of the reaction temperature, the initiation efficiency of the asphaltene cracking is improved. At this time a small amount of hydrogen donor exists on the asphalt. The inhibitory effect of mass cracking is weakened. When asphaltene thermal cracking is accompanied by a large number of soft bitumen, the total reaction of asphaltene decomposition to soft bitumen can be ignored. The self assembly effect of heavy aromatic hydrocarbons, including asphaltenes, in SCW, can be used for heavy oil thermal cracking and deresidual carbon. At the same time, the coke self assembly and subsequent condensation of the virtual components including the asphaltene and the colloid are promoted. At the same time, the condensation of the light non residual carbon components is suppressed. In the early stage of the cracking reaction, the products of the liquid phase obtained under the pseudo homogeneous structure have low carbon residue, low average molecular weight, high H/C and average. The advantage of few aromatic rings.
【学位授予单位】：华东理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TE621

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