重质油分子化学组成结构及其扩散和反应行为研究

The worldwide crude oils available are becoming heavier. At the same time, the demand for high-quality transportation fuels has continuously increased. As a result, effective conversion of heavier crude oils to clean fuels has become one of the most critical issues in the petroleum processing industry. Residue hydrotreating is expected to contribute in a decisive way to worldwide new demands for fuels with improved quality. It is well-known that the size of most heavy crudes is comparable to the average pore diameters of typical hydrotreating catalysts. This causes hindered diffusion to occur during such catalytic conversion process. Resistance to diffusion would significantly reduce the effectiveness of the catalysts and the overall reaction rate. Large pores can provide better access to active sites within the catalyst. However, the reaction rate decreases with increasing pore diameter because the area of the reacting surface decreases. Therefore, the study on diffusion behavior of heavy petroleum is crucial to the design of efficient catalysts and the effective utilization of the feedstocks. .This project performs a detailed elemental composition analysis of heavy crudes on sulfur, nickel and vanadium compounds and their enriched fractions. Several model compounds containing these three contaminants are chosen for diffusion study. The diffusion behavior of the model compounds through membranes and catalysts under ambient and hydrotreating conditions is obtained by diffusion cell and fixed-bed reactor, respectively. Therefore, hindered diffusivity models of them are developed. By comparison, quantitative structure/diffusivity correlation models for these contaminant compounds can be developed. The enriched fractions containing sulfur, nickel and vanadium compounds are separated from heavy crudes. These fractions are subjected to diffusivity experiments by the same methods as above. A detailed analysis of both the enriched fractions and the corresponding products is obtained using the advanced Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) technique. Similarly, quantitative structure/diffusivity correlation models for the enriched fractions are developed. And it can play a critical role during the development, optimization, and selection of hydrotreating catalysts.

常规原油的锐减和清洁油品的强劲需求促进了重质油的开发利用。重质油富含S、N、O等杂原子及镍、钒等金属化合物，且分子尺寸大，其催化转化不仅受反应本身影响，重质油大分子在催化剂孔道内的扩散也不容忽视。本项目借助傅里叶变换离子回旋共振质谱等多种分析手段，从分子水平对重质油中硫、镍和钒化合物的分子组成结构进行表征，确定代表性模型化合物和重质油特征馏分，研究它们在非反应条件下通过有机膜孔和加氢反应条件下通过加氢催化剂孔道的扩散行为，并通过对比建立重质油杂原子化合物在催化剂孔道中的受阻扩散关联模型。结合对重质油特征馏分及其加氢反应产物的组成鉴定和定量分析，建立重质油分子及其缔合体在加氢反应条件下通过催化剂孔道的受阻扩散关联模型，从分子层次研究重质油杂原子的催化转化规律，从而为新型催化剂设计和反应器优化提供理论依据。

重质油的高效催化加氢是解决当前劣质重油增加和清洁油品需求强劲这一矛盾的关键。重油和加氢催化剂组成的高度复杂性造成扩散和反应动力学相关研究极具挑战。基于此，本课题优选适宜的模型化合物，适当分离渣油得到富集组分，并合成出介孔催化剂，以降低体系的复杂性，并应用隔膜池和固定床微反装置系统研究了模型化合物以及渣油杂原子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；溶质的扩散受到分子构型的显著影响，化合物构型偏离球状越大，相同无因次尺寸下的受阻扩散因子越小，致使扩散受阻程度加剧。（2）渣油硫化物和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）模型硫化物和渣油硫化物富集组分反应条件下在催化剂中的扩散受阻更加严重，产物的逆向扩散对反应物向内扩散产生阻滞作用，致使其扩散受阻加剧。（4）渣油中硫醚类、噻吩类和极性组分等硫化物富集组分反应活性存在较大差异，从而造成其扩散对HDS反应的影响程度不尽相同。噻吩组分的本征活性最高，扩散传质对HDS的影响最大；硫醚组分的本征反应活性有所降低，HDS过程扩散的影响有所缓解；极性组分的本征反应活性大幅降低，其加氢脱硫过程中内扩散的影响最低。（5）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。（6）渣油四个SFEF窄馏分基本不存在缔合现象，可溶质和沥青质存在一定程度的缔合，而且沥青质展现出更强的缔合能力。