Synthesis, Characterization And Evalution Of Spinel Type Mixed Oxides As Environment Protection Additive For FCC Process

Fluid catalytic cracking (FCC) unit is one of the major emission sources of SO_x, NO_x and CO in the oil refineries. Sulfer and nitrogen oxides, kown as the acid rain precursors, are harmful to our environments. They may also cause serious corrosion to the equipments of FCC regenerating systems and have an important effect on the safety, reliability and lifetime of FCC units. The addition of suitable additive to the FCC units is considered to be the most practical and economical option to reduce SO_x, NO_x and CO emissions.MgAlCeFe spinel type mixed oxides are prepared by acid method, characterized by XRD, BET, FT-IR techniques and evaluated as SO_x transfer additive. The effect of active components and preparation methods on the structure and SO_x removal activity of the additive is discussed. Moreover, the performance of SO_x removal is investigated at different reaction conditions. The MgAl spinel type mixed oxide is proven to be an excellent material for SO_x transfer additive due to its SO_x adsorption activity and reducibility of the formed sulfates. Cerium is the main active component for the oxidation of SO₂ to SO₃. Ferrum plays an essential role in the regeneration step. The content of different active components in the additive has an optimal value due to their competitive and synergistic effect. The BET surface area, pore volume and pore diameter of the additive can be improved significantly through addition of macromolecular organic material PEG. The aditive shows optimum SO_x oxidation adsorption and regeneration performance after adding 10% PEG2000. Reaction temperature has no significant influence on the SO_x uptake capacity when the temperature changes between 650℃and 750℃. The additive exhibits better SO_x adsorption performance in the presence of oxygen and the activity is very sensitive to the changes of oxygen concentration. The reduction rate of the additive is strongly influenced by the reductive mediators and the regeneration of the sulfated additive is much more efficient with hydrogen. The stable and bulk sulfate species can only be decomposed at higher reduction temperature and the additive shows better regeneration performance.SFTS-1 SO_x transfer additive produced by spray drying technique has a good SO_x adsorption and regeneration performance. The additive is evaluated on the riser circulating fluidized bed unit and the results shows that more than 89% SO₂ is removed after adding 2.5% additive. The commercial test result shows that the utilization of SO_x transfer additive in the FCC unit can reduce the emissions of SO₂ in flue gas. When the additive makes up 2.5% of the catalyst inventory, the removal efficiency of SO2 reaches 64.4% and the additive exhibits high activity and stability. The addition of SO_x transfer additive to FCC system has no significant influence on the qualities of main products, production distribution and normal operation of the FCC units.The multi-functional additive which can remove SO_x, NO_x and CO is studied on the basis of SO_x transfer additive. Copper is proven to be an active component for NO reduction and CO oxidation and the additive shows optimal performance for simultaneous removal of SO_x, NO_x and CO by introducing 10% CuO to the SO_x transfer additive. The additive shows excellent hydrothermal stability and good resistence to SO₂ posioning. The relative content of oxygen and carbon monoxide has a great influence on the NO reduction activity. The additive shows high NO reduction activity when n(O₂)/n(CO)<0.5 and the activity declines greatly when n(O₂)/n(CO)>0.5. MgAl₂O₄-supported La_2-xSr_xCoO₄ mixed oxide catalyst has a good catalytic performance for NO reduction an CO oxidation and optimum catalytic activity could be obtained when x=0.8. But the catalytic activity is greatly decreased with exposure of the catalyst to atmosphere containing 0.02% SO2.