摘要
积炭是分子筛催化剂失活的主要原因。目前,有关ZSM-5积炭的研究报道还不多,且多采用甲醇汽油化的反应作探针。我们利用甲苯乙基化反应研究ZSM-5分子筛的积炭,得到了一些有意义的结果。 NaZSM-5分子筛用NH<sub>4</sub>NO<sub>3</sub>进行交换,灼烧成氢型HZSM-5。镁改性采用浸渍法,改性后的样品记为MgHZSM-5。乙基化反应在小型积分反应器上进行。
The coking over HZSM-5 zeolite and magnesium modified zeolite MgH-ZSM-5 in the alkylation of toluene with ethanol was systematically examined. Due to the reducing of the pore size and the decreasing of Bronsted acid sites especially on the external crystalline surfaces by Mg modification, the rate of coke formation on MgHZSM-5 is lower than that on HZSM-5, and also the coke content of the former is smaller than that of the latter. For HZSM-5, coke deposits mainly on the external crystalline surface, the Bronsted acid sites and the external surface Lewis acid sites are reduced to a large extent with the coke deposit. But for MgHZSM-5, coke deposits chiefly within the pore and causes the decrease of Bronsted acid sites and the internal surface Lewis acid sites. It is demonstrated that the Lewis acid sites participate the coke formation in the presence of Bronsted acid sites. From the data of specific surface area and pore volume,it is concluded that the blockage of MgHZSM-5 by coke is moke serious than that of HZSM-5, and thus the deactivation of MgHZSM-5 is faster.
