Catalyst Poisoning Mechanism And Resistance Of Carbonyl Sulfide In CO Shifting Process

With the production of calcium carbide, the high volume fraction of CO(>85%) has been emissioned to environment and burned directly. The pollution can be reduced by achieving recycling if the synthesis gas (H2 and CO2) could be derived through the transformation reaction of CO. However, the impurities in cleaning calcium carbide furnace gas such as sulfur, phosphorus, arsenic, and so on, limit the possibility of the gas as carbon-chemical products. What's more, the catalyst poisoning mechanism is unclear so far. Based on the thermodynamic analysis, experiment and XRD and XPS characterization analysis, the poisoning mechanism, poisoning behavior of catalyst with existing COS, poisoning characteristics under furnace gas of calcium carbide and regeneration of poisoned catalyst is studied. The major results are showed as follows:(1) The influence of catalyst particle size, COS concentration and feed gas concentrations during the catalyst poisoning process was studied. The results showed that with the increasing concentration of COS, the poisoning intent of the catalyst is deeper and the shift ratio is lower. And when the catalyst particle size increases, the poisoning phenomenon is more significant and the final shift ratio is smaller. The experiments of space velocity indicated that the influence of space velocity is inconspicuous with the low concentrations of COS. But in the condition of high concentration of COS, the shift ratio significantly falls with the increasing of space velocity.(2) The investigation was carried out under the furnace gas of calcium carbide; the different conditions such as N2, CO2 and H2 were researched. It was proved that the CO shift ratio suddenly dropped and then kept on a low level under N2 which is showed the similar poisoning characteristics with merely COS, it maybe due to that N2 is diluting agent. The effect of CO2 and H2, which is the resultants of CO shift reaction, not only lead to decrease CO shift ratio but also influence the stability. The effect of the furnace gas of calcium carbide is the same as CO2 and H2.(3) Using thermodynamics software HSC Chemistry 5.0 and its database software, based on the principle of Gibbs free energy minimum, we inferred theoretically that the compounds, spontaneity and reaction competitive force may produced during the poisoning process of the active constituent Fe3O4 of high concentration CO shift catalyst on the condition of the carbide furnace gas. The main reaction is observed which is following: 4.5COS(g)+Fe3O4+9.25O2(g)=1.5Fe2(SO4)3+4.5CO2(g), which is most possibly to occur spontaneously. And the eventual production is FeSO4,Fe7S8 and FeS,which lead to catalyst deactivation and poisoning.(4) Comparing the reduced and poisoned samples of catalyst through the XRD and XPS characterization analysis, the poisoning process is included two aspects:the active catalyst has been changed to FeS and the coke on the surface of catalyst covers part of the active center.(5) Regeneration of poisoned catalyst is unavoidable. For partly poisoned catalyst, the activity could be recovered though purging by N2 due to the poisoned resultant is unstable. But the completed poisoned catalyst was irreversible with the generation being FeS. The catalytic activity can be recovered after reacting under condition of O2 to regenerate Fe3O4 with part of Fe2O3.