磷改性MCM-22分子筛上苯与1-十二烯烷基化合成十二烷基苯

Synthesis of Dodecylbenzene with Benzene and 1-Dodecene over MCM-22 Zeolite Modified with Phosphorus

采用浸渍法制备了一系列用于苯和1-十二烯烷基化合成十二烷基苯的磷改性MCM-22分子筛,以X射线衍射(XRD)和固体27Al3、1P核磁共振,N2吸附,氨程序升温脱附(NH3-TPD),热重(TG)和红外光谱(FT-IR)等表征技术,结合固定床连续流动反应器中的性能评价,较为系统地研究了磷改性对MCM-22分子筛的结构、表面酸性及其烷基化催化性能的影响.结果表明,用磷改性MCM-22分子筛虽然不会影响分子筛的晶体结构,但是会破坏分子筛上的Si-O-Al键,使部分四配位铝转化为六配位铝.由于聚合态的磷酸盐可能与Al发生键合,多聚态磷酸盐数量随着磷含量的增加而增多,从而改变了分子筛的孔道大小和酸性,使得强酸减少,弱酸增多,酸强度降低,总酸量和B酸中心数随着磷含量的增加呈现先增后减的规律,L酸减少.适当的磷含量有利于提高MCM-22分子筛对苯与1-十二烯烷基化反应的催化选择性和稳定性,改性磷含量为0.5%左右时产物2-十二烷基苯收率最高.

A series of MCM-22 zeolite catalysts modified with phosphorus were prepared by incipient wetness impregnation. The effects of phosphorus on the structure and acidity of the MCM-22 were studied using X-ray powder diffraction, solid-state 27A1 and 31p nuclear magnetic resonance, N2 adsorption, temperature-programmed desorption of ammonia, thermogravimetry and IR spectroscopy of adsorbed pyridine. The alkylation of benzene with l-dodeeene to form dodecylbenzene was evaluated in a fixed-bed reactor. The results showed that the crystal structure was intact after modification, but there was partial breaking of the Al-O-Si bonds, and some tetrahedral aluminum was eonverted to octahedral aluminum. The formation of aluminum phosphate species and polyphosphate chains led to changes in the pore size and acidity. With an increase in the phosphorus content, the quantity of weak acid sites increased gradually, and the quantity of strong acid sites decreased. The quantities of the total acid sites and Bronsted acid sites increased initially and then decreased, and the quantity of Lewis acid sites decreased. A proper phosphorus content can improve the selectivity for 2-dodecylbenzene and the catalytic stability of the MCM-22 catalyst for the alkylation of benzene with 1-dodecene. For the MCM-22 modified with 0.5 % of phosphorous, the maximum yield of 2-dodecylbenzene was obtained.