Effective and regenerable Ag/4A zeolite nanocomposite for Hg0 removal from natural gas

Abstract

The silver loaded adsorbents has been demonstrated to be an exciting approach towards Hg0 removal from natural gas streams, its Hg0 removal efficiency and capacity is closely related to the valence state, particle size and dispersity of silver particles. This study focused on chemical reduction methods in aqueous solutions to synthesize Ag/4A zeolite, and the influences of ultrasonic and protective additives were investigated to reduce the size of silver particles. The characterization results showed that silver particles are loaded on the surface of 4A zeolite with highly dispersed elemental form, ultrasonic and addition of stearic acid as protective additives are the effective ways to produce small nano-scale silver particles close to 15 nm. Meanwhile, the silver particles on the surface of Ag/4A zeolite are the active sites for Hg0 adsorption which can react with Hg0 to form Ag-Hg amalgam alloy. The silver lattices disappeared from the outer boundary to the interior of the particles after Hg0 adsorption, which indicated that the Hg0 firstly reacts with the nano-scale silver on the surfaces and then gradually penetrates into the interior of silver particles. The Hg0 removal efficiency of prepared Ag/4A zeolite adsorbents was higher than 96% after 200 min adsorption at 30 °C, and adsorption capacity reached to 5.985 mg/g. Furthermore, the regeneration and reutilization results indicated that the Hg0 adsorption performance remained stable after 5 reuse cycles.