基于热解中间体结构识别的油页岩有机质热转化基础研究

The comprehensive utilization of oil shale by pyrolysis as the core technology to produce oil and gas can significantly improve the energy efficiency. An accurate understanding of the microscopic feature and mechanism of chemical reactions is the scientific foundation to solve the problems existing in the pyrolysis process of oil shale, such as low oil yields and too many heavy species. Therefore, this project will make the structure identification of pyrolysis intermediate as a breakthrough to investigate the pyrolysis process of oil shale by combining experimental and theoretical approaches. This project is mainly focused on the formation mechanism of the intermediate and the relationship between the structural feature and reactivity of the intermediate. The reaction mechanism can be revealed by the pyrolysis intermediate connecting oil shale organic matter and product. Then the method for optimizing the distribution of products will be explored by controlling the characteristic of intermediate. The structures of intermediate and product are constructed by computer-aided molecular design method. Furthermore, macromolecular structures which are close to the true nature of oil shale organic matter are inferred based on the structural information of intermediate and product. Reactive molecular dynamics modeling approach is then used to explore the process of oil shale pyrolysis, which can track the generation and reactivity of free radical intermediate to reveal the bond breaking rule and the formation pathway of oil and gas. A study of the reaction mechanism for the pyrolysis process will provide a reliable theoretical guidance not only for designing the regulation method of pyrolysis process, but also for controlling the yield of heavy oil.

油页岩通过以热解炼制油气为核心的综合利用可显著提高能源利用效率。正确认识热解过程的微观化学反应机理是解决目前油页岩热解工艺中存在的油收率低且重质组分多等问题的科学基础。本项目以热解中间体的结构识别为突破口，拟在实验与理论计算两个层面上研究油页岩的热解过程，重点分析中间体的生成规律及结构与反应性的关系，揭示以热解中间体连接油页岩有机质与产物的反应机理，并探索通过中间体的调控优化产物分布的方法。基于油页岩有机质及其热解中间体、产物的结构分析，利用计算机辅助分子设计方法构建中间体及产物的分子结构，进而反演出接近真实油页岩有机质的大分子键合模型。采用反应分子动力学方法模拟热解反应过程，追踪中间体的产生及其二次反应特点，并揭示有机质断键规律及油气产物形成路径。本项目关于热解反应机理的研究可为油页岩热解过程调控方法的设计以及调控重质组分的产率提供可靠的理论指导。

油页岩的综合开发利用对于我国的能源安全起到了重要的保障。通过热解技术制备高品质油气可显著提高能源的利用效率，是油页岩综合利用的核心。深入认识油页岩热解中化学反应的微观机理，对于理解热解过程调控的本质，实现产物的定向可控具有重要的意义。鉴于此，本项目以油页岩有机质热解中间体的结构识别为核心，建立了实验与分子模拟结合的研究方法，解析了热解中间体的结构特征，构建了油页岩有机质大分子模型，研究了热解过程中有机质大分子的断键，中间产物的形成与反应过程，产物分布及影响因素，并探索了外加多种氢源以及矿物质对热解过程和产物分布的影响规律。实验研究表明，油页岩热解中间产物在一定温度下（最快产油速率阶段）能够生成并且稳定存在，且随着温度的升高，热解中间体的轻组分增加，进一步裂解产物以脂肪烃为主，芳香烃主要以单环化合物的形式存在，且支链较短。结合热解产物及有机质碳结构和官能团的分析结果，构建了龙口油页岩油母质大分子模型。通过反应分子动力学方法模拟了油母质在不同温度下的直接热解和加氢热解，结果表明氢的加入促进油母质的初始断键反应，提高了轻质油组分的产率，同时加氢热解有助于产生水分子，辅助硫向气体转移，促进了热解中间产物向油转化过程的脱硫作用。甲醇存在下的油母质热解过程模拟结果表明，相比于直接热解，甲醇在较低温度下能够产生多种自由基，参与了油母质中弱共价键的断裂反应，促进了重质页岩油中间体的生成。随着温度不断升高，更多的甲醇与油母质热解中间体发生反应，阻止了大自由基碎片之间的结合，促进了重质油组分向轻质油的转化。蒙脱石参与油页岩有机质热解过程的模拟结果表明，二者之间以范德华相互作用为主，蒙脱石促进了有机质的热解反应在更低的温度下发生，对长链烷基的裂解起到促进作用，提高油气收率。本项目的研究成果为油页岩热解过程调控奠定了理论基础。