膜分散强化液相加氢反应过程中的介尺度机制及调控研究

The liquid-phase hydrogenation technology is very promising in producing clean oil-based products, which strongly depends on the highly efficient mass transfer of hydrogen into oil phase. In the project, the preparation of micrometer-sized bubbles using porous ceramic membranes is proposed for improving inter-phase mass transfer and enhancing liquid-phase hydrogenation reactions. Two key meso-scale structures exist in the membrane dispersion process, 1) the bubble swarm between single bubble and hydrogenation reactor and 2) the membrane distributor between membrane element and hydrogenation reactor. The project will focus on the two meso-scale issues, i.e. the flow-transport behaviors of bubble swarm and the design of membrane distributor. First, the hydrodynamic characteristics of bubble swarm will be studied to model gas-liquid interaction, mass transfer, bubble breakup and coalescence. The bubble-forming and bubble-flowing processes will be simulated to investigate the influence of membrane properties and operating parameters on gas dispersion. Second, the study will be carried out to obtain the influence of operating conditions on global dispersion performance of membrane distributor, and the membrane distributor will be simulated to study the influence of geometry of membrane element on gas dispersion, aiming at guiding the design and scale-up of membrane distributor. Third, the diesel hydrotreating will be studied to describe the reaction intensification by membrane dispersion, in order to obtain the influence of membrane properties and operating conditions on hydrogenation reactions. The hydrogen dispersion in diesel will be simulated to reveal the influence of membrane dispersion on the diesel hydrogenation. The project implementation would obtain some in-depth insights on mechanisms and manipulation of meso-scales in membrane dispersion process, which would provide theoretical basis and technical support for developing membrane dispersion technologies for different reaction systems.

液相加氢技术在清洁油品生产中具有广阔的应用前景，其关键在于氢气在油品中的高效传质。本项目提出采用多孔陶瓷膜制备微米级气泡，促进相间传质，强化液相加氢反应。膜分散强化液相加氢反应过程中存在两个关键介尺度问题：1）介于单气泡和加氢反应器之间的气泡群流动及传递行为；2）介于膜元件和加氢反应器之间的膜分布器设计。本项目针对这两个介尺度问题，研究膜分散过程中气泡群的流体力学特性，建立气泡群的作用力、传质、破碎及聚并模型，模拟气泡生成和流动过程，揭示膜材料性质及操作参数对气体分散的影响；研究膜分布器的宏观分散性能，获得不同操作条件对气液分散效果的影响规律，模拟预测膜元件构型对分散性能的影响，指导膜分布器的设计及放大；研究膜分散对柴油加氢反应的强化效应，模拟预测膜分布器内氢气在柴油中的分散效果。本项目将获得膜分散过程的介尺度机制及调控方法，为开发面向不同反应过程的膜分散技术提供理论参考和技术支撑。

膜分散技术具有高效的传质效率和良好的可控性，在多相催化反应过程中展示了优异的应用潜力。针对膜分散强化液相加氢过程中的介尺度问题，本项目开展了详细研究，主要进展有：. 1、揭示了膜分布器的结构及操作条件对气液分散性能的影响机制。设计了多通道陶瓷膜分布器，在并流鼓泡塔中制备大量微气泡。膜孔径越小越有利于气液传质。膜通道内错流速度是调控膜分散过程气泡大小分布的关键条件。粘度对气泡大小分布存在双重作用，气泡直径先减小后增大。随着表观气速的增大，气含率、相间面积、体积传质系数均增大，气泡大小分布变宽。与传统分布器相比，膜分散具有更高的气含率、体积传质系数和溶解氧浓度。. 2、建立了膜分散过程的介尺度模型及数值模拟方法，实现了对气液膜分散过程的准确计算。基于CFD模拟方法，使用OpenFOAM程序求解Navier-Stokes方程来计算多孔膜区域的渗透过程，发现Darcy定律可用于计算多孔膜内气体渗透。开发了相对渗透率模型及毛细管压力模型等介尺度模型，并耦合多相流模拟方法，对气液流动体系的气含率进行了准确计算。. 3、开发了一种基于多通道陶瓷膜强化气液分散的固定床反应器系统，强化了多相催化加氢反应性能，实现了稳定运行。在固定床反应器中研究了进料体积空速、氢气/甘油水溶液体积比、氢气压力、反应温度以及初始水含量等对Cu-ZnO催化甘油氢解制1,2-丙二醇性能的影响，发现操作条件显著影响甘油氢解性能，初始水含量的增加不利于甘油转化率和1,2-丙二醇选择性的提升。与传统进料相比，使用陶瓷膜分散氢气进料，形成了具有均一微泡且较高气含率的气液分散体系，氢气消耗量为传统进料的一半时，甘油转化率可以从84.9%提高到97.4%。该反应器连续运行52小时后，甘油转化率和1,2-丙二醇选择性分别达到92%和93%。. 以上研究过程中，在Ind. Eng. Chem. Res.等化工类期刊上发表SCI论文11篇，申请发明专利5件；参加了第10届全球华人化工会议、第10届亚太膜会议等；培养研究生7名。