Synthesis of NaA zeolite membrane by microwave heating

The synthesis of NaA zeolite membrane on a porous alpha -Al2O3 support by m icrowave heating (MH) was investigated. The formation of a NaA zeolite memb rane was drastically promoted by MH. The synthesis time was reduced from 3 h for conventional heating (CH) to 15 min for MH. Surface seeding cannot on ly promote the formation of NaA zeolite on the support, but also inhibit th e transformation of NaA zeolite into other types of zeolites. The thickness of the NaA zeolite membrane synthesized by MH was about 4 mum, thinner tha n that of NaA zeolite membrane synthesized by CH. The permeance of NaA zeol ite membrane synthesized by MH was four times higher than that of the NaA z eolite membrane synthesized by CH, while their permselectivities were compa rable. Multi-stage synthesis resulted in the transformation of NaA zeolite into other types of zeolites, and the perfection of the as-synthesized memb rane decreased. The formation mechanism of NaA zeolite membrane on the porous alpha -Al2O3 support by MH was proposed. The promotion effect on the formation of NaA ze olite membrane by MH can be divided into two parts: the "thermal effect" an d the "microwave effect". The formation of a homogeneous and thin NaA zeoli te membrane resulted from both the "thermal effect" and the "microwave effe ct", while the fast formation of NaA zeolite membrane was mainly caused by the "microwave effect". (C) 2001 Elsevier Science B.V. All rights reserved.