Synthesis of binderless zeolite X microspheres and their CO2 adsorption properties

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. 500-750 nm, and exhibit an uniform particle size of ca. 1.3 mm, medium crashing strength and a surface area of 931 m(2)/g that is greater than that of the conventionally prepared zeolite X powders. CO2, CH4 and N-2 adsorption under both ambient and elevated pressures to 1000 kPa at 298 K on the binderless NaX microspheres and Ca2+ and Kr+-exchanged ones were measured. Separation of CO2/CH4 and CO2/N-2 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 N-2 under mild conditions. The separation factors of CO2/N-2 and CO2/CH4 mixtures on CaX microspheres are 79 and 12, respectively. (C) 2013 Elsevier B.V. All rights reserved.