Research On The Resourceization Technology Of Petroleum Refinery Spent Hydrodesulphurization(HDS) Catalysts

In the petroleum refining process,HDS catalysts are used to remove impurities such as S,N and metals from crude oil to obtain a cleaner petroleum product.These catalysts are eventually turned into spent catalysts after several cycles of use due to loss of active metals,carbon deposition and sintering of the catalyst structure.The spent catalysts usually contain some crude oil and heavy metals.On the one hand,it has been classified as hazardous waste by the Ministry of Environmental Protection of China due to its harmful effects on the environment.On the other hand the abundant oil(20-60%)and valuable metal content(grade is much higher than the original ore)make it a high quality secondary resource.Therefore,resourceful recycling of crude oil and valuable metals from spent HDS catalysts not only alleviates the increasing lack of resources,but also prevents environmental pollution,which has important environmental and economic significance.In this paper,novel technologies for the resource recovery of oily spent catalysts are explored to address the issues of low utilization efficiency of oil resources,low quality of recovered oil,and poor selectivity of metal leaching during the process of spent catalyst resourceization.Firstly,the crude oil in the spent catalyst is rapidly recovered by solvent extraction,followed by improving the washing efficiency of the washing solution for crude oil through the addition of solvent to the aqueous surfactant solution.The roasted spent HDS catalyst ash is then utilized as a pyrolysis catalyst to enhance the quality of pyrolysis oil during the pyrolysis of oily spent HDS catalyst.Finally,a Pyro-hydrometallurgical process is employed for the recovery of valuable metals from de-oiled spent HDS catalysts,utilizing organic acids and ammonium hydroxide for selective leaching of metals.The key research findings are summarized as follows:(1)A solvent extraction method was used to recover crude oil from spent HDS catalysts in a rapid and efficient manner.Four solvents with different polarities(pxylene,acetone,dichloromethane and hexane)were used to investigate the desorption of oil from the spent catalyst by the solvents.The crude oil and solvents in the oilcontaining washing solution were also separated and recovered,and the solvent recycling washing performance was evaluated.The results showed that p-xylene,due to the high similarity with crude oil molecular structure in terms of polarity and aromaticity,had the best removal effect on crude oil in spent catalysts,which could exceed 94%in 2 min.The solvent was recycled 10 times and still achieved 93%removal of crude oil from the spent catalyst.Compared with crude oil,the recovered oil has less viscosity,ash and residual carbon and higher heat of combustion,making it easier to be refined and recovered.Comparison of SEM,EDX,FT-IR and CA of the catalysts before and after oil removal showed that p-xylene could effectively remove oil from the spent HDS catalyst.The strong interaction formed by the hydrogen bonds between crude oil molecules and particles is an important reason why the oil removal efficiency cannot be increased further.After solvent washing of the catalyst,the metals loaded on Al2O3 in the catalyst were exposed,which would facilitate the subsequent chemical recovery of valuable metals.(2)The solubilization ability of surfactants was improved by adding solvents to the aqueous surfactant solution to further enhance the oil removal efficiency of the washing solution for crude oil.Six types of surfactants and solvents were employed for optimization,and established an optimal mixture of surfactant and solvent for the removal of crude oil from the contaminated catalyst.It was found that Brij-58 with the lowest surfactant CMC,highest interfacial activity and high hydrophobicity had the highest removal efficiency(67.65%)of the spent catalyst crude oil.The Brij-58/oxylene mixd system had higher oil removal efficiency than the single washing solution.The crude oil removal rate of the contaminated HDS catalyst exceeded 95%at a higher mass ratio of o-xylene.The added solvent played a positive role in the formation of micelles and the desorption of oil from the crude oil contaminated catalyst surface.The result is that the presence of the solvent affects the properties of the surfactant itself or of the bulk phase,such as decreasing the CMC of the surfactant,increasing the number of micelles,and increasing the micelle kernel volume,thus improving the oil removal efficiency of the mixed system.(3)To address the oil quality problems caused by the high content of heteroatoms and recombinant fractions in the recovered crude oil,catalytic pyrolysis was selected and roasted spent HDS catalyst ash(sHDSc-A)was used for the first time to catalytically pyrolyze the oily spent HDS catalyst to improve the yield and quality of the pyrolyzed oil.The results showed that sHDSc-A promoted the decomposition of coke in oily spent HDS catalyst,resulting in the recovery of more oil and gas.Meanwhile,sHDSc-A significantly improved the quality of the pyrolysis oil.It increased the saturation of the pyrolysis oil from 59.39%to 74.25%and the H/C ratio from 1.62 to 1.72;increased the content of C11-C22 from 41.97%to 61.99%;and decreased the migration of N,S and O from the spent catalyst to the pyrolysis oil.The promotion of sHDSc-A in the pyrolysis process is attributed to the catalytic effect of the metal oxides in sHDSc-A.Among them,Al2O3 and Fe2O3 can promote decarboxylation of carboxylic acids and reduce O mobility,while MoO3 and Fe2O3 play a significant role in reducing coke and increasing pyrolysis oil.NiO can also promote methane vapor reforming,and thus increase the production of H2 in pyrolysis gas(4)The objective of this study was to increase the selectivity of the metal leaching process while minimizing the damage to the alumina carriers during the process.To achieve this goal,organic oxalic acid was used to selectively dissolve Mo,V,and Ni in the spent HDS catalyst.Various organic acids were compared for their ability to leach metals from the spent catalyst,and the acid that exhibited the most effective overall leaching was selected.Subsequently,the effects of key leaching parameters,including acid concentration,temperature,and S/L,on metal leaching were investigated.Kinetic fitting was utilized to analyze the leaching mechanism.The results showed that oxalic acid had the greatest leaching ability for Mo and V,followed by citric acid,tartaric acid,malonic acid,acetic acid,and formic acid.The different solubilities of oxalic acid and the complexes formed by various metals were used to achieve a leaching rate of 93.07%for Mo,86.64%for V,and 74.21%for Ni from the spent catalysts,while limiting the destruction of catalyst carriers(leaching rate of Al<1%).The correlation coefficients(R2>0.98),activation energies(23.95 kJ/mole for V and 30.66 kJ/mole for Mo),and n values(0.32±0.02 for Mo and 0.20±0.06 for V)showed that Mo and V followed the Avrami dissolution reaction model,with V leaching controlled by diffusion mode and Mo leaching controlled by diffusion and chemical reaction mixture control.The article addresses the challenges in recycling oily spent HDS catalysts and proposes a two-step recovery process involving oil removal and calcination-acid leaching.The calcination process enhances the effectiveness of catalysts in metal leaching and also endows them with properties that catalyze the pyrolysis of oily spent catalysts to improve the quality of pyrolysis oil.The"waste-to-waste" strategy is implemented to achieve self-circulation of oily spent HDS catalysts and establish a preliminary method system for high-value energy recovery and waste utilization.This approach provides a theoretical basis for technological innovation in spent catalyst treatment plants.