Synthesis of SAPO-34 with the presence of additives and their catalytic performance in the transformation of chloromethane to olefins

Abstract

SAPO-34 molecular sieves were synthesized in the presence of soluble starch, sodium dodecyl sulfate and cetyltrimethylammonium bromide as the additives under hydrothermal conditions, and the differences stemmed from the additives among all obtained SAPO-34 samples were characterized by XRD, SEM, BET, NH3-TPD and TG. Compared with the conventional SAPO-34 sample, the SAPO-34 samples modified by sodium dodecyl sulfate and cetyltrimethylammonium bromide showed less crystalline order, enlarged mesopore volume and external surface area and a reduction in total acidity amounts. Meanwhile, the SAPO-34 modified by soluble starch exhibited more total acidity amounts than the conventional SAPO-34 samples. The SAPO-34 samples modified by sodium dodecyl sulfate and cetyltrimethylammonium bromide showed better catalytic stability and less carbon deposition than the conventional SAPO-34 catalyst in the conversion of chloromethane to olefins due to the reduction in total acid sites and the increasing mesopore volume. The overall results of this study demonstrate that it is an effective way to modify the SAPO-34 molecular sieve with sodium dodecyl sulfate and cetyltrimethylammonium bromide as the additives for improving the SAPO-34 catalyst stability in the transformation of chloromethane to olefins.