重油在催化剂中的有效扩散系数及扩散受阻因子

摘要

通过对大港减压渣油超临界萃取(SFEF)窄馏分在FCC催化剂与SiO2模型催化剂中有效扩散系数的研究,得到了催化剂孔径对有效扩散系数的影响和催化剂的扩散受阻因子.结果表明,SFEF窄馏分在FCC催化剂中的扩散受阻因子均小于1,为受限扩散,在大孔FCC催化剂中的扩散受阻因子是参比催化剂中的2～3倍.当扩散分子直径小于1.8 nm时,SFEF窄馏分在孔径大于5.6 nm的SiO2模型催化剂中的扩散受阻因子均大于1；当扩散分子直径大于1.8 nm时,SFEF窄馏分在孔径为5.6～7.9 nm的模型催化剂中的扩散为受限扩散.SiO2模型催化剂的曲折因子为2.87,在经验值范围内.当平均孔径相近时,SFEF窄馏分在模型催化剂中的有效扩散系数比大孔FCC催化剂中大两个数量级,说明有效扩散系数不仅与扩散分子直径与催化剂孔径的比值λ有关,还与催化剂的孔结构密切相关,仅用λ来关联扩散受限程度是不准确的.采用SiO2模型催化剂研究有效扩散系数与孔径的关系更为准确合理.%Through the measured effective diffusion coefficient of Dagang vacuum residue supercritical fluid extraction and fractionation (SFEF) fractions in FCC catalysts and SiO2 model catalysts the restricted diffusion factor was calculated. The restricted diffusion factor in FCC catalysts is less than 1 and it is 2~3times larger in large pore catalyst than in the conventional FCC catalyst. The results show that the diffusion of SFEF fractions in the two FCC catalysts is restricted by the pore. When the average molecular diameter is less than 1. 8 nm, the diffusion of SFEF fractions in SiO2 model catalyst which average pore diameter bigger than 5. 6 nm is unrestricted. The diffusion is restricted in the catalyst pores of less than 8 nm for SFEF fractions which diameter more than 1. 8 nm. The tortuosity factor of SiO2 model catalyst was obtained to be 2. 87, within the range of empirical value. The effective diffusion coefficient of the SFEF fractions in SiO2 model catalyst was two orders of magnitude bigger than that in FCC catalyst with the same average pore diameter. It indicates that besides the ratio of molecular diameter to the pore diameter A, the effective diffusion coefficient is also closely related to the pore structure of catalyst. Because SiO2 model catalyst has uniform pore size, the diffusion coefficient can be precisely correlated with pore size of catalyst, so it is a good model material for catalyst internal diffusion investigation.