Reducing the dosage of the organic structure-directing agent in the crystallization of pure silica zeolite MFI (silicalite-1) for volatile organic compounds (VOCs) adsorption

Abstract

Pure silica zeolite MFI (silicalite-1) has been widely used in gas separation and volatile organic compounds (VOCs) adsorption. The molar ratio of tetrapropylammonium (TPA⁺) and SiO₂ (TPA⁺/SiO₂) included in the framework of silicalite-1 is 0.042. Reducing the utilization of TPA⁺ will not only benefit the environment but also reduce the cost of silicalite-1. Herein, we reported the synthesis of highly crystalline silicalite-1 from a reaction mixture with a TPA⁺/SiO₂ molar ratio of 0.035 and a seed loading of 5 wt% or 0.01 and a seed loading of 10 wt%. The investigation on the equilibrium and breakthrough adsorption of volatile organic compounds (VOCs) such as acetone and toluene on the resultant silicalite-1, activated carbon, and silicalite-1 seed showed that silicalite-1 synthesized with reduced TPA⁺ shows (1) a better performance on VOCs adsorption than activated carbon and (2) a higher adsorption efficiency of the micropore than that of the silicalite-1 seed. The replacement of the seed on TPA⁺ during the crystallization of silicalite-1 implies that silicalite-1 or other zeolites requiring an organic structure-directing agent (OSDA) might be synthesized in the absence of OSDA with an appropriate amount of seed.