Effect of lignite as support precursor on deep desulfurization performance of semicoke supported zinc oxide sorbent in hot coal gas

In this study, four different semicoke supported zinc oxide sorbents were prepared by combining high-pressure impregnation and heat treatment using four different lignites (Zhaotong, Xiaolongtan, Huolinhe, and Shengli districts) as precursors of supports and zinc nitrate as precursor of the active component. Their desulfurization performances were studied in a fixed-bed reactor at 400 °C in simulated coal gas. The physico-chemical properties of raw lignites were investigated using chemical titration, nitrogen adsorption and thermogravimetry (TG). The physico-chemical structures of sorbents were characterized by atomic absorption spectrometry (AAS), X-ray diffraction analysis (XRD), nitrogen adsorption, and scanning electron microscopy (SEM). The results indicate that the lignite as support precursor plays a critical role in the desulfurization performance of the sorbent. It affects the desulfurization activity of the prepared sorbent by influencing the loading content and utilization rate of the active component of the sorbent. The sorbent HPZn/C(Z) prepared using Zhaotong lignite presents the best desulfurization performance owing to its higher content and utilization rate of the active component, with a 13.74 h breakthrough time with the breakthrough sulfur capacity of 3.69 g sulfur/100 g sorbent. It is found that the loading content of the active component depends on the pore structure of the raw lignite, how its pore structure changes in high-pressure impregnation process and the content of oxygen-containing functional groups on its surface. The utilization rate of the active component is associated with the pore structure properties of the sorbent formed during heat treatment.