The Study On Reduction And Regeneration Process Of NiO/ZnO-TiO₂ Desulfurization Adsorbent

The increasing requirements of sulfur emission standards have led to the trend of low sulfidation of fuel oil,and promotes the global continuous exploration of new deep desulfurization processes.Adsorption desulfurization has the characteristics of simple process flow,low equipment investment and low operation cost.The reduction and regeneration of adsorbent is an important part of the adsorption desulfurization process.In this paper,NiO/ZnO-TiO₂adsorbents were prepared by kneading method.Used FCC light gasoline as raw material,the effect of reducing conditions on the adsorption desulfurization performance of the adsorbent was investigated on a fixed-bed device,and the influence of the regeneration conditions on the regeneration performance of the adsorbent was also investigated.NiO/ZnO-TiO₂ adsorbents were characterized by XRD,mercury intrusion,H₂-TPR.The reasons for the deactivation of the adsorbent and the causes of the decreased activity of the regenerated adsorbent have been analyzed.The main conclusions are as follows:（1）Taking NiO/ZnO-TiO₂ desulfurization adsorbent obtained under optimal preparation conditions as the research object,it was found that reduction is beneficial to improve the desulfurization performance of the NiO/ZnO-TiO₂ adsorbent.The optimal reduction conditions for the adsorbent are:reduction temperature is 350℃,reduction pressure is 0.3 MPa,hydrogen space velocity is 1500 h^-1 and reduction time is 2 h.The adsorbent reduced under this reduction condition has better desulfurization performance,can reduce the catalytic cracking light gasoline with a sulfur content of 500μg/g to below 5μg/g.The penetrating sulfur capacity of the adsorbent is 7.17%（71.7 mg S/g adsorbent）.According to the characterization,it is found that a higher reduction temperature is beneficial to the formation of Ni-Zn alloy that is detrimental to the desulfurization activity of the adsorbent.When the reduction temperature is 350℃,the NiO component is more fully reduced than at 300℃,has a larger specific surface area than the adsorbent reduced at 400℃and 450℃,and no Ni-Zn alloy is formed,so it has the best adsorption desulfurization activity.（2）XRD and mercury intrusion characterization results of NiO/ZnO-TiO₂adsorbents before and after deactivation show that the main reasons for the deactivation of the adsorbent are as follows:the sulfur storage capacity of the adsorbent will decrease due to the sulfide of ZnO and Ni components in the adsorbent.In addition,as the adsorption desulfurization reaction proceeds,the proportion of 10-25 nm pores in the adsorbent decreases,and the specific surface area decreases.It has an adverse effect on the desulfurization activity of the adsorbent.（3）The investigation results of NiO/ZnO-TiO₂ adsorbents regeneration process show that the suitable regeneration conditions for deactivated adsorbent are as follows:regeneration temperature is 400℃,regeneration pressure is 0.4 MPa,regeneration space velocity is 2000 h^-1,regeneration oxygen concentration is 0.3v%-2v%.According to the characterization analysis,the loss of active Ni and ZnO components in the adsorbent,the formation of by-product Zn₃O（SO₄）₂ and decrease in specific surface area are the main reasons that the desulfurization activity of the regenerated adsorbent cannot be restored to the fresh adsorbent.