Separation of CO2 and N2 with a lithium-modified silicalite-1 zeolite membrane

Abstract

Carbon dioxide capture and storage is gaining attention as a strategy to abate greenhouse gas emissions. However, currently available commercial processes to remove CO2 from flue gas streams, mainly from N2 are costly and energy intensive. A silicalite-1 membrane was prepared on a porous alumina support using hydrothermal synthesis. The resulting silicalite-1 membranes were modified using Li solutions in order to achieve better CO2 separation. SEM micrographs exhibited a thin, uniform and compact silicalite-1 film well adhered to the alumina support. Crystallinity of the membrane was confirmed by XRD. CO2 and N2 permeation experiments were carried out in a stainless steel module. CO2 single gas permeation was measured through a silicalite-1 membrane from room temperature to 400°C, having a 25psi pressure on the feed side. The resulting CO2 permeance measurements indicated molecular sieving as the principal transport mechanism for the unmodified silicalite-1 membrane, whereas surface diffusion is the principal transport mechanism for lithium-modified silicalite-1 membranes. The separation between CO2 and N2 takes place due to preferential CO2 adsorption and diffusion, which in turn hinders N2 permeation through the silicalite-1 pore network. A CO2/N2 separation factor up to 6 at 25psi and 400°C was obtained using the silicalite-1 modified membrane, whereas this was 1.46 using the unmodified silicalite-1 membrane.