Abstract:

Y molecular sieves of high n(SiO₂)/n(Al₂O₃) ratio were prepared by the seeding method, and then different crystal size(515mn、317nm、220nm) Y molecular sieves were synthesized by changing the aging temperature of the seeding gel. The prepared Y molecular sieves with different crystal sizes and amorphous silica-alumina were mixed as supports, and the loaded NiW/(Y+ASA) hydrocracking catalysts were prepared by the incipient impregnation method. The physicochemical properties of the Y molecular sieves with different crystal sizes and corresponding catalysts were analyzed by scanning electron morphology(SEM), X-ray diffraction(XRD), N₂ sorption-desorption, and NH₃ temperature-programmed desorption(NH₃-TPD). The active metals morphology, dispersion, and sulfation of the catalysts were characterized by H₂ temperature-programmed reduction (H₂-TPR), transmission electron microscopy(TEM), X-ray photoelectron spectroscopy(XPS), and other characterization methods. The results showed that the external specific surface area and pore size increased with the decrease of Y molecular sieves grain size. Meanwhile, as the n(SiO₂)/n(Al₂O₃) ratio increases, the weak and medium acid acidity decreases, and the number of acid decreases. The results of hydrocracking of n-hexadecane showed that the reduction of Y molecular sieve crystal size was beneficial to improve the yield and selectivity of the middle distillate products (C₈—C₁₂). Since the small crystal size of Y molecular sieve can reduce the residence time of reactant molecules in the pore channel and improve the accessibility to the active phase on the catalyst surface, over cracking can be avoided and higher yields of middle distillates can be obtained. Therefore, the highest yield of C₈—C₁₂ products was obtained for the Y zeolite catalyst NiW/(Y₃+ASA) with a crystal size of 220nm.

Key words: molecular sieves, crystal size, catalyst, hydrogenation, middle distillate selectivity

摘要：

采用晶种导向剂法制备高硅Y分子筛，并通过调变晶种导向剂的陈化温度制得了不同晶粒尺寸（515mn、317nm、220nm）的Y分子筛。将制备的不同晶粒尺寸的Y分子筛和无定型硅铝混合作为载体，采用等体积共浸渍法制备了负载型NiW/(Y+ASA)加氢裂化催化剂。采用扫描电子显微镜（SEM）、X射线衍射（XRD）、N₂吸附脱附、氨气程序升温脱附（NH₃-TPD）、氢气程序升温还原（H₂-TPR）、透射电子显微镜（TEM）和X射线光电子能谱（XPS）等表征手段分析了不同晶粒尺寸的Y分子筛及相应催化剂的理化性质。结果表明，随着Y分子筛晶粒尺寸的减小，外比表面积和孔径增大。同时，Y分子筛的n(SiO₂)/n(Al₂O₃)增大，弱酸和中强酸酸性减弱，酸量减少。催化剂对正十六烷的加氢裂化反应结果表明，Y分子筛晶粒尺寸的减小有利于提高中间馏分产物（C₈~C₁₂）的收率及选择性，即缩短反应物分子在Y分子筛孔道中的停留时间、提高与催化剂表面活性相的可接近性，可避免过度裂化，提高中间馏分产物的收率。因此晶粒尺寸为220nm的Y分子筛催化剂NiW/(Y₃+ASA)的C₈~C₁₂产物收率最高。

关键词: 分子筛, 晶粒尺寸, 催化剂, 加氢, 中油选择性