Sustainable Synthesis of ZSM-5 Zeolite from Rice Husk Ash Without Addition of Solvents

The development of sustainable and environmentally friendly techniques for synthesizing zeolites has attracted much attention, as the use of solvents in the hydrothermal synthesis of zeolites is a major obstacle for realizing green and sustainable synthesis ways. As a solid waste, it still has a challenge for zeolites synthesis from rice husk ash by solvent-free method to increase its recovery rate and economic value. Our approach focused on reutilization of rice husk ash by converting it to ZSM-5 zeolite without employing solvents. The influence of TPABr/SiO2, Na2CO3·10H2O/SiO2 and synthesis time on ZSM-5 crystal growth and ZSM-5 zeolite properties were evaluated by various analytical methods. The results suggested that the optimal conditions of TPABr/SiO2, Na2CO3·10H2O/SiO2 and synthesis time for the ZSM-5 synthesis were 0.125, 0.3 and 72 h, respectively. Base on the optimal synthesis condition, the recovery rate of Si and Al were 98%, which were 70% compared with that of hydrothermal method. The synthesis process was solid phase conversion, Na2CO3·10H2O played key role in promoting hydrolysis and condensation of Si–O–Si and Si–O–Al bonds during synthesis process. The resultant ZSM-5 zeolite exhibited well-defined crystallinity and porosity, ZSM-5 aggregate particles possessed micro-/meso-porous structures. The BET surface area of synthetic ZSM-5 zeolite was 304 m2/g, comparable to hydrothermal synthetic ZSM-5 zeolite (320 m2/g). Overall, proposed synthetic route provides novel green alternative for the recovery of rice husk ash, further mitigating the environmental and health care concerns.