Research On Deep Desulfurization And Regeneration Performance Of The Adsorbents For Ultra-deep Reactive Adsorption Desulfurization Of Diesel Fuel

Reactive adsorption desulfurization (RADS) has become one of important means for producing clean diesel fuels whose sulfur content is less than 10μg/g because of its high desulfurization rate, simple operation, low investment cost and no pollution, etc.Effect of Ni-ZnO/Al2O3-SiO2 adsorbent compositions and preparation conditions on its desulfurization performance was investigated using a fixed bed reactor in this paper. The optimal sorbent composition was as follows:22.98% Ni,57.44% ZnO,10.68% SiO2,8.9% Al2O3; the optimized preparation conditions were as follows:adding Na2CO3 as the precipitating agent to 0.2 mol/L metallic ions solution at 20℃, then aging at a temperature of 20℃for 6 h. The sorbent comprising the optimal sorbent composition and prepared under optimized preparation conditions could possess a breakthrough adsorption capacity of 38.4 mg/g. On the foundation of characterizations for the fresh and used sorbents, it was discovered that formation of ZnS and coke, sintering of the active and support ingredients and reduction in the surface area and pore volumes were all the important factors leading to deactivation of the Ni/ZnO-Al2O3-SiO2 adsorbent in the fixed bed reactor.Regeneration performance of the sorbent formed under optimal conditions was evaluated in the fixed bed reactor, it was found that the spent sorbent regenerated at 460～525℃for 2～4 h could only regain partial desulfurization ability. So many measures, which included changing the regeneration conditions (regeneration temperature and time), altering preparation conditions (precipitation methods and calcination temperature), lowering desulfurization temperature and changing regeneration reactors (inside and outside regeneration), were taken to regenerate the used sorbent completely in the study, but it didn't work well. It was disclosed that sintering of NiO and ZnO grains and residual surface coke were responsible for the failure of sorbent regeneration through various characterizations. It was selected that doping of CaO not only increased the sorbent desulfurization capacity but also improved its regeneration performance, which was due to the fact that incorporation of CaO reduced the interaction between the active component and the carrier and enhanced sorbent resistance to sintering of the NiO and ZnO particles. Finally the CaO/Ni/ZnO-Al2O3-SiO2 adsorbent was regenerated completely by reducing the PAHs level in the diesel feed and applying an innovative regeneration process.