Effect of impregnation methods on sorbents made from lignite for desulfurization at middle temperature

With lignite after vacuum drying as the raw material, a series of Zn-based sorbents were prepared by static impregnation, ultrasonic-assisted impregnation, bubbling-assisted impregnation and high-pressure impregnation. The physical properties and the desulfurization performances of Zn-based sorbents were studied systematically by XRD, BET, AAS characterization techniques and the fixed-bed desulfurization evaluation apparatus. The sorbents obtained by high-pressure impregnation method have a larger specific surface area, pore volume and pore diameter comparing with other methods, which is conducive to the sulfidation reaction of hydrogen sulfide gas in the sorbent. The effects of pressure during the high-pressure impregnation and concentration of Zn(NO3)2 precursor solution on the sorbents properties and desulfurization behavior were investigated. The higher the impregnation pressure and the concentration of impregnation solution are, the greater the amount of the active components are uploaded. However, overhigh impregnation pressure can cause collapse and blocking of the carrier pore. The optimal operating condition of high-pressure impregnation method for preparing the sorbents was the impregnation pressure of 20 atm and the solution concentration of 41%. Under that condition, the sorbent had the best desulfurization ability with a sulfur capacity of 13.94 gS/100 gsorbent and a breakthrough time of 54 h. Its desulfurization precision and efficiency of removing H2S before sorbent breakthrough from the middle temperature gases of 400 °C can reach <5 ppm and >99%, respectively. Sorbents could be regenerated under the condition of 1 vol% O2, 20 vol% H2O, 0.5 vol%NH3, and N2 balance gas. The regenerated sorbent could be used for repeated absorption of H2S with a slight decrease in desulfurization effect.