Research On Reactive Adsorption Desulfurization Over A Ni/ZnO Adsorbent

Reactive adsoption desulfurization (RADS) is an effective method for deep desulfurization because it combines the advantages of the HDS and adsorption.Ni/ZnO adsorbent was prepared by homogeneous precipitation using urea hydrolysis and was applied for reaction adsorption deep desulfurization of gasoline. Reactive adsorption desulfurization (RADS) of model gasoline, FCC and commercial gasoline over Ni/ZnO adsorbent was evaluated in a fixed-bed system at hydrogen atmosphere. The adsorbents were characterized by N2adsorption-desorption, X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR) and scanning electron microscope (SEM). Also, the support modification and the adsorption mechanism have been studied. The main and important results are as follows:The adsorbents were prepared by homogeneous precipition. The calcining procedure for prepared adsorbent is170℃for2hours,250℃for2hours, and450℃for5hours. The dosage of the surfactant is20g and the optimal molar ratio of Zn:Ni is5.The optimum conditions were673K,1.0MPa and liquid hourly space velocity (LHSV) of60h-1, and V (H2):V (feed)(volume of H2at standard state) volume ratio of300. Under the optimum conditions, ultralow sulfur gasoline could be produced and the breakthrough sulfur capacity of the adsorbent was230.4and169.8mg-s/g-sorb for the model gasoline A and B, respectively.The reaction adsorption mechanism for thiophene was proposed. It can be predicted that three possible reactions exist in the desulfurization process. First, thiophene continually approaches the surface of the adsorbent and adsorbs onto the active Ni atoms to form S-Ni bonds. This weakens the S-C bond leading to the cleavage of that bond and the formation of butene and NiSx. Next, NiSx reacts with H2to form H2S, which is rapidly adsorbed by ZnO resulting in the generation of a ZnS layer on the surface of Ni/ZnO. Finally, the Ni is regenerated and again participates in the reactive adsorption.Reactive adsorption desulfurization (RADS) experiments were conducted over four different metal oxide supports (Al2O3-, SiO2-, TiO2-and ZrO2-) at the same reaction conditions. The adsorbents were characterized by N2adsorption-desorption, X-ray diffraction (XRD), and temperature programmed reduction (TPR), in order to find out the influence of physical characteristics and surface chemistry on the desulfurization performance. It was found that coexisting olefins in gasoline had an inhibiting effect on the desulfurization performance of the adsorbent. The desulfurization performance of all the four adsorbents decreased in the following order:Ni/ZnO-TiO2> Ni/ZnO-ZrO2> Ni/ZnO-SiO2> Ni/ZnO-Al2O3. Ni/ZnO-TiO2adsorbent has the best desulfurization performance with a breakthrough sulfur capacity117.3mg-s/g-sorb.