Template-free ZSM-5 membrane preparation on alumina support by secondary hydrothermal synthesis

Abstract

Zeolite membranes stand out for presenting molecular sized uniform pores. The current work aimed to optimize supported template-free ZSM-5 zeolite membrane preparation by evaluating the effect of two parameters: successive synthesis cycles of the zeolitic film and aging time of the synthesis solution. The zeolitic film synthesis was carried out by secondary hydrothermal treatment using α-alumina tubes as support, commercial zeolite as seeds and SiO2: 0.3 Na2O: 0.01 Al2O3: 114 H2O as molar composition of the synthesis solution. The aging time tested for the dissolution of silicon and aluminum was 30, 60, 120 or 180 ​min; whilst for the silicon and aluminum mix was 60 or 15 ​min. Hydrothermal synthesis was performed at 180 ​°C for 24 ​h. This procedure was executed 1, 2 or 4 times. One synthesis cycle was already capable of producing a homogeneous zeolitic film on the support with crystal interconnection. This finding was corroborated by gas permeation tests, in which the membrane did not show any apparent defects. The aging time had an effect on the type of zeolite formed. Only the aging time conditions of 180 and 60 ​min and 180 and 15 ​min prompted the exclusive formation of zeolite ZSM-5.