渣油镍、钒化合物加氢脱金属反应机理和扩散行为的研究

The depletion of conventional crudes coupled with the increase of the fuel demand compel refiners to process increasing volumes of heavy crudes, which contain high contents of nickel and vanadium. These two metallic compounds are the most abundant and troublesome contaminants in petroleum residue. They deposit and deactivate catalysts in resid hydroprocessing and catalytic cracking. As a result, removal of nickel and vanadium compounds is crucial to the following processes of effective conversion of residuum oils. Hydrometallation results from chemical transformation of the metal-bearing compounds on the catalyst surface coupled with diffusional transport to the active sites. A better understanding of kinetics concerning HDM of metallic petroleum constituents is very important to improving and developing catalysts. And the diffusion behavior of residue plays a significant role in hydrodemetallation due to the size of reactant molecules is comparable to the pore size of typical hydrotreating catalysts. Hydrodemetallation mechanism and diffusivity of nickel and vanadium compounds in catalyst are two challenging subjects due to the lack of in-depth understanding of the chemistry of these metal compounds. This project performs diffusivity and hydrodemetalation on nickel and vanadium compounds in residue. The hydrodemetalation mechanism and diffusivity in commercial catalysts can be obtained by analyzing composition of samples using the advanced FT-ICR MS technique coupled with HPLC method. The results will provide a better understanding of the diffusion and reaction of metal-bearing compounds in the hydrodemetallation process, which in turn could lead to the design of more efficient catalysts and the more effective utilization of the feedstocks.

重质油是全球未来重要的石油资源。镍、钒化合物是重质油加工中危害最大的两种金属化合物，它们的有效脱除是改善重质油加工性能的最有效方法。但由于对镍、钒化合物的分子组成缺乏深入认识，其加氢脱金属反应机理及其在催化剂孔道中的扩散行为目前仍是学术难题。本项目将傅里叶变换离子回旋共振质谱这一先进技术与高效液相色谱分离手段相结合，从分子水平对镍、钒卟啉化合物和渣油金属镍、钒化合物的加氢反应中间产物和扩散实验样品进行深入研究，揭示镍、钒化合物的加氢脱金属反应机理及其在催化剂孔道中的扩散行为，并通过不同浓度溶液的实验获得镍、钒化合物的缔合信息以及缔合对反应和扩散影响的新认识，从而为加氢处理工艺开发和催化剂设计取得突破提供重要理论指导。

常规原油的锐减和清洁油品需求的强劲促进了重质油的高效转化。金属化合物的有效脱除是重质油后续高效转化的关键，镍钒化合物的组成结构及其在孔道中的扩散和加氢反应动力学行为的深入认识将会为催化剂和工艺设计提供指导。基于此，本课题将委内瑞拉渣油进行分离得到钒化物富集组分，并应用隔膜池和固定床微反装置系统研究了金属模型化合物以及渣油钒化物富集组分的受阻扩散和加氢反应行为，主要取得了如下成果：（1）溶质在有机膜孔中的扩散主要受分子尺寸和孔径大小两个因素决定，随着溶质尺寸的增大和孔径的降低，其有效扩散系数和受阻扩散因子逐渐降低，表明扩散受到的阻力逐渐增大；卟啉镍钒的受阻扩散程度明显高于富勒烯，其盘状刚性结构是扩散受阻程度加剧的主要原因。（2）溶剂萃取结合柱色谱分离可实现对渣油钒化物进行有效分离，各个组分的紫外可见光谱和高分辨质谱结果存在明显差异，表明组分间结构明显不同。渣油钒化物富集组分相对于其模型化合物在有机膜孔中受到更加严重的扩散阻力，渣油物料体系的复杂程度加剧和稠环结构更加偏离球形是其主要原因。（3）应用质谱获得两种卟啉镍化物加氢中间产物的直接证据，丰富了对它们加氢反应路径的深入认识；两种卟啉镍化物显示出较高的加氢活性，其加氢过程受到内扩散的显著影响，且镍卟啉在介孔硅基催化剂中的扩散系数明显高于商业氧化铝催化剂，前者均一的孔径结构是扩散改善的主要原因。（4）渣油钒化物富集组分的加氢反应性能存在较大差异，造成其扩散对HDV反应的影响程度不尽相同。卟啉钒组分反应活性高，在缓和条件下具有较高的加氢脱钒率；“非卟啉”钒组分的加氢反应活性明显低于卟啉组分，缔合体或螯合体的组成结构致使其较低的反应性能。（5）渣油整体则展现出比两个钒化物富集组分都低的HDV活性，渣油中的氮化物和稠环芳烃等极性较大组分对其影响的结果。