Research On The Cu/ZnO Adsorbent For Reactive Adsorption Desulfurization

With the increasing of the environmental proctection and promulgated legislation,the sulfur content and the olefin content have been restrict rigorously.Althought the content of sulfur and olefin could easily reach the requirement during the traditional process,resuting in the loss of octane number.For ultra-deep desulfurization without the loss of octane number for gasoline,design and preparation of technology and catalysts with high activity and selectivity are arguably the most important.Therefore,in this work,a novel copper-based catalyst for FCC gasoline by reactive adsorption desulfurization(RADS)coupling isomerization process was investigated,and designed of catalysts and catalytic mechanism are also explored to establish the industries.The aim of the dissertation is to research the parameter of thermodynamic for optimizing of RADS process.It is found that,the enthalpy changed of thiophene and olefins reactions are all of exothermic reactions,which increasing the temperatures are benefical for negative direction between 250 ^oC and 450 ^oC.In the high temperature stage,the Gibbs free energies of thiophene desulfurization reactions and aromatic hydrogenation reactions are greater than zero,which can not proceed spontaneously.In constract,the Gibbs free energies of olefins hydrogenation reacitons are below zero,which can proceed easily.The results show that the reactions are limited by the thermodynamic.The DFT results show that the S atom of thiophene molecules is located over the surface of Cu(111)upon adsorption(Cu-S),an elongation of the C-S bonds steer fracture.The process tends to the hydrogenolysis desulfurization route.The adsorption energies of thiophene and olefin are-1.23 e V and-1.00e V,respectively.Therefore,the thiophene molecules and olefin molecules are competed each other while adsorbing.The desulfurization stability was investigated by the pilot fixed-bed reactor.The results show that the Cu/ZnO adsorbents has high activity and the adsorbent amounts of sulfur were 290.0 mg/g.Especially,Ni-based adsorbents have less olefins saturation and the loss of octane number.The desulfurization activity of adsorbents with different copper loading amounts was investigated.The results show that the copper loading reached 6 wt.%at the temperature of375 ^oC is the optimized condition for achieving the aim of ultra-deep desulfurization.The calculated apparent activation energy of thiphene and olefins show that the activity of Cu-based catalysts depended mainly on the dispersion of Cu.The small size Cu particles were more active than large ones.For the low loading content,although the particle size and dispersion is small and homogenous,the number of Cu particle is the limited,leading to not enough active sites to reach the ultra-deep desulfurization.However,for the 8 wt.%Cu/ZnO catalyst,the Cu particles are reunited,leading the high of apparent activation energy.The desulfurization activity and selective hydrogenation of Cu/ZnO adsorbents on the different polarity ratios of ZnO as supports was investigated in reactive adsorption desulfurization.The ZnO particles were synthesized by the hydrothermal process and Cu O/ZnO adsorbents were synthesized by incipient impregnation method.The ZnO surface area was adjusted by the calcination temperature of ZnO precursors.Meanwhile,the polarity ratio was controlled by the concentration of P₁₂₃.The high dispersion and small copper particles depend on the higher surface area of ZnO,leading to a higher desulfurization activity of Cu/ZnO adsorbents.The high dispersion of copper particles provides the more reactive activity sites and in favor of transforming the ZnO to Zn S.Moreover,decreasing the polarity ratio of ZnO supports could offer the more selective sites at the polar facet in RADS.To design and research the effect of pore structure,the ordered mesoporous Cu-ZnO-Al₂O₃ adsorbents were synthesized and carried out by model gasoline in the fixed-bed reactor to compare with the common Cu/ZnO-Al₂O₃ adsorbent.The results show that the ordered mesoporous Cu-ZnO-Al₂O₃ adsorbents own the large sulfur capacity(49.4mg/g)and the common Cu/ZnO-Al₂O₃ adsorbent presents the low sulfur capacity,which the sulfur capacity is 13.5 mg/g.In the RADS system,the well-dispersed ZnO in the ordered mesoporous could facilitate the sulfidation of ZnO by H₂S with weakly metal-support interaction.This process is of benefit for maintaining the initial state of the active metal of Cu and improving the ZnO conversion,which can maintain the good active and long periods of RADS process.And the ordered mesoporous structure should inhibit the string of Cu particles to improve the desulfurization activities and stability.To solve the olefin saturation problem in the RADS process,SAPO-11 was used as modifier,and investigated the desulfurization activity and the composition of hydrocarbon by FCC gasoline.The results show that both of adsorbents have good activity,which the sulfur contents are below 10?g/g.The olefins contents decreased at 14.73 wt.%and 15.07 wt.%,respectivity.The liquid yields are 98.5%and 97.9%,respectivity.The loss of octane number are 3.4 units and 0.8 units,respectivity.The coupling mechanism of isomerization was investigated by hexane-1 as model.The results show that the hexane-1 occurs the location isomerism of double bond and skeletal isomerism by SAPO-11,and inhibits the olefins hydrogenation.Therefore,the coupling adsorbents could avoid the loss of octane number.