The hydrothermal transformation of solid geopolymers into zeolites

This study confirms the existence of several-nanometer ordered structures in amorphous geopolymers by HRTEM and SAED. To obtain low-ratio Si/Al geopolymers and to overcome the disadvantages posed by the use of impure raw materials, an amorphous Al2O3-SiO2 powder is first prepared using a sol-gel method in accordance with specific chemical compositions. The composition of the Al2O3-2SiO(2)-Na2O geopolymer is designed according to the NaA zeolite composition (Si/Al/Na atom ratio is 1:1:1), and the expected NaA zeolites are obtained from the Al2O3-2SiO(2)-Na2O geopolymer using a hydrothermal reaction. This process can be used to transform geopolymers into zeolites and provides a new preparation method for the self-supporting NaA zeolite membrane. The preliminary separation resulted in alcohol dehydration and shows that ethanol solutions can be powerfully dehydrated by pervaporation. A feed containing 90 wt.% ethanol at 20 degrees C and achieving a water flux of 2.67 kg m(-2) h(-1) with a separation factor H2O/EtOH approximate to 200 is found. (C) 2012 Elsevier Inc. All rights reserved.