Synthesis of binderless zeolite X microspheres and their CO2 adsorption properties

Abstract

Binderless zeolite NaX microspheres were readily prepared by using chitosan-assisted synthesis. The synthesis was conducted by hydrothermal treatment of silica/chitosan hybrid microspheres formed from a silica sol–chitosan mixture solution in a sodium aluminate alkaline solution, followed by calcination to remove the chitosan. The obtained microspheres are composed of compactly packed and intergrown octahedral particles with a particle size of ca. 500–750nm, and exhibit an uniform particle size of ca. 1.3mm, medium crashing strength and a surface area of 931m2/g that is greater than that of the conventionally prepared zeolite X powders. CO2, CH4 and N2 adsorption under both ambient and elevated pressures to 1000kPa at 298K on the binderless NaX microspheres and Ca2+ and K+-exchanged ones were measured. Separation of CO2/CH4 and CO2/N2 mixtures on the CaX microspheres in breakthrough experiments was performed. The binderless NaX microspheres have larger CO2 adsorption capacity than reported zeolite X powders and the binderless CaX and KX microspheres. The CaX microspheres have the highest ideal separation factors for CO2 from CH4 and N2 under mild conditions. The separation factors of CO2/N2 and CO2/CH4 mixtures on CaX microspheres are 79 and 12, respectively.