Catalytic Effect Of Molybdenum-doped Akaganeite Nano-particles On The Viscosity Reduction Of Shengli Extra Heavy Crude Oil

Heavy oil,one of the low-grade oil resources,has attracted a great attention with the gradual decline of conventional petroleum resources.Heavy oil is plentiful and accounts for 70%of global oil reserves.At present,the exploitation of heavy oil is increasing,but the recovery rate is low.One of the most important methods of heavy oil recovery is thermal recovery,which bases the characteristics that the viscosity of oil decreases with the increase of temperature.Catalyst can effectively reduce the activation energy of hydrothermal cracking reaction to reduce the temperature of the cracking reaction.Therefore,the catalytic viscosity reduction can promote the degradation of heavy components of heavy oil,thus upgrading the heavy crude oil.In this paper,the molybdenum-doped?-FeOOH nano-rods were prepared by allowing hydrous ferric chloride hexahydrate?FeCl₃·6H₂O?aqueous solution to react with ammonium heptamolybdate(?NH₄?₆Mo₇O₂₄·4H₂O)aqueous solution via a hydrothermal method.The as-prepared nano-particles were characterized by means of XRD,FTIR,TEM,SEM,XPS,and thermal analysis.The catalytic performance of molybdenum-doped?-FeOOH on the viscosity reduction of heavy crude oil was investigated.The mechanism of viscosity reduction was explored by analyzing the results of four-component separation,elemental analysis,and ¹H NMR.The main research contents and results are as follows:1.Preparation and characterization of molybdenum-doped?-FeOOH nano-particles and its catalytic viscosity-reducing effect on heavy oilMolybdenum-doped akaganeite nano-rods were prepared by one step facile synthesis.According to the results of XRD and FTIR,the formation of akaganeite depends on the molar ratio of hexaammonium molybdate to ferric chloride hexahydrate.The catalytic performance of molybdenum-doped?-FeOOH on the viscosity reduction of Shengli Oilfield extra heavy crude oil?175000 mPa s at 50?C?was evaluated by measuring the viscosity reduction rates of the molybdenum-doped akaganeite nano-rods and other products.The catalytic temperature,reacton time,and content of catalyst are 200?,24h,and 0.2 wt%,respectively.Of the catalysts,Mo1Fe50 has the highest activity of 28.2%.Mo1Fe50 were further characterized by SEM mapping,XPS,XRD,and thermal analysis.The results exhibited that Mo element was well distributed in the?-FeOOH particles with a form of MoO₃ and its chemical formulation should be FeMo_0.14O_1.42?OH?.The nano-rods can effectively increase the viscosity reduction rate of Shengli Oilfield extra heavy crude oil to 72.7%combined with tetralin.At last,the contents of C,H,S,N and ¹H NMR of the four-componet in the heavy oil were investigated before and after reaction.The mechanism were presumed to be that the catalyst can promote the breaking of C-S bond and the tetrline suppress the re-polymerziation of the small molecules.2.Effect of catalyst's surface modification,reaction temperature,and oil to water ratio on the viscosity reduction of heavy oilA series of catalysts were obtained by modifying Mo1Fe50 with 1,1,1,3,3,3-Hexamethyldisilazane?HMDS?.The successful modification of HMDS was confirmed by XRD and FT-IR.Then,the catalytic activity of catalyst was evaluated by the viscosity-reduction reaction of heavy oil.CTAB was as the co-surfactant,the ratio of oil to water of 70:30,the reaction temperature was 200°C,and the reaction time was 24 h.The results show that Mo1Fe50@HMDS-1-15 has the highest the viscosity reduction rate of38.8%.elemental alalysis result indicates that the removal rates of S of the asphalten and heavy component are 79.9%and 27.6%,respectively catalyzed by Mo1Fe50@HMDS-1-15,while the removal rates are75.1%and 26.6%,respectively catalyzed by Mo1Fe50@HMDS-1-1.These indicate that modified catalysts can obviously promote the breaking of C-S bond.¹H NMR result indicates that Mo1Fe50@HMDS-1-15 has no effect on the polycondensation of aromatic compounds,but Mo1Fe50@HMDS-1-1 can accelerate the decomposition of aromatic condensation polymer.The effect of reaction temperature on the viscosity reduction rate of extra heavy oil was investigated under a constant pressure of 3 MPa and an oil to water ratio of 70:30.The results indicate that the viscosity reduction rate increases with increasing the temperature whether adding catalyst or not.In comparaton,adding catalyst can further increase the viscosity reduction rate,which reaches to 64.88%at 280°C.Then the effect of oil-to-water-ratio on the viscosity reduction rate of extra heavy oil was investigated under a constant pressure of 3 MPa and a temperature of 280°C.The results indicate that the viscosity reduction rate increases with increasing the temperature without the presence of the catalyst but it reaches a peak with the presence of the catalyst.The viscosity reduction rate reaches to 69.26%at 280°C and an oil to water ratio of 70:30.After analysizing the contents of C,H,S,N and ¹H NMR results of the four-componet in the heavy oil,we presumed the mechanism of viscosity reduction is that the catalyst can promote the breaking of C-S bond and water provides active hydrogen at high temperature to accelerate the de-polymeration of macromolecules and inhibit the re-polymerization of small molecules.