Reaction Kinetics And Hindered Diffusion Of Nickel Porphyrins Hydrodemetalation

The depletion of conventional crudes coupled with the increase of the fuel demand compel refiners to process increasing volumes of heavy crudes,which contain high contents of nickel and vanadium.About 50%of nickel compounds in vacuum residuum?VR?exists as metal porphyrin.In the hydrodemetalation?HDM?process,the deposition of metal and coke deactivates the catalysts,causing the reduction of HDM activity as well as the lifetime of catalysts.Metal porphyrin possesses generally large molecular size,leading to a hindered diffusion in the catalyst pores and thus the difficulty in contacting with the activated components of catalysts.To enhance the HDM activity,it is critical to conduct a systematic research on the reaction and diffusion behavior of nickel porphyrin with various catalysts of different pore sizes and structures.In this thesis,three different catalysts were used in HDM process.Two NiMo/SBA-15 catalyst possess distinct pore sizes but a close surface area and pore volume.In addition,a commercial catalysts?NiMo/?-Al₂O₃?was adopted.Two types of nickel porphyrin?Ni-TPP and Ni-OEP?were selected as model compounds.The reaction was then carried out by a micro high pressure fixed-bed reactor in order to obtain the kinetic data of Ni-TPP and Ni-OEP.Based on the experimental results,it was shown that hydrogenation of nickel porphyrin were substantially obstructed by diffusion in all three catalysts.The reaction of Ni-OEP is more active than the reaction of Ni-TPP.In addition,it has been revealed that NiMo/?-Al₂O₃ had significantly higher reaction activity than NiMo/SBA-15 in HDM reaction due to higher content of Lewis-acid.Therefore,NiMo/?-Al₂O₃ is more appropriate using as HDM catalysts.In the thesis,different types of novel analytical instruments were employed to investigate the transformation of Ni-TPP and Ni-OEP.High Performance Liquid Chromatography?HPLC?and Mass Spectrometry?MS?methods for both nickel porphyrins and their hydrogenation products were successfully established.In the HPLC results,the chromatographic peak for intermediate product Ni-TPPH₂ and Ni-OEPH₂ can be observed.It was further confirmed through mass spectrometry analysis by Orbitrap Fusion that there are Ni-TPPH₂ and Ni-OEPH₂ after hydrogenation.Moreover,the existence of Ni-TPPH₄ and Ni-OEPH₄ was also proven in the mass spectrogram of products,which were obtained by severer reaction condition.