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Research on the Mechanisms of Sulfur Poisoning with Copper-based Catalyst

Author: Liu
Tutor: NingPing
School: Kunming University of Science and Technology
Course: Environmental Engineering
Keywords: low temperature water-shift reaction CuO-ZnO-Al2O3catalyst sulfur-poisoning thermodynamics XPS XRD
CLC: X701
Type: Master's thesis
Year: 2013
Downloads: 38
Quote: 0
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Abstract

In recent years, the synthesis of CO industry product by industrial emissions containing CO has seized more attention from researchers. Especially, the research of feed gas of water-gas shift reaction such as coke oven gas, yellow phosphorus tail gas, sealed calcium carbide furnace exhaust, as well as oxygen-enriched blast furnace gas and other industrial emissions of CO-rich gas has become an important issue for waste recycling. However, such an industrial waste gas not only has sufficient CO to meet the water-gas shift reaction, but also contains the impurities such as the polymorphous sulfur compounds that tend to make the shift catalysts poisoning.Iron-based catalyst, copper-based catalyst and sulfur-tolerant shift catalyst are the catalysts commonly used for CO water-gas shift reaction. Due to the lower operating temperature (423.15K～573.15K) and the higher activity and selectivity, copper-based catalyst is an ideal catalyst for CO water-gas shift reaction. Though copper-based catalyst has high activity, but it is sensitive to impurities and easy poisoning inactivation. Catalyst poisoning has a serious impact on the performance of the catalyst. So the research of poisoning mechanism of catalyst and morphological changes of the active component after poisoning have the guidance for the regeneration of catalyst poisoned. This article is focused on the problem that sulfur-containing compounds-COS, CS2, SO2, H2S which leaded to copper-based catalyst poisoning and the mechanism of sulfur poisoning and poisoning product of CuO-ZnO-Al2O3shift catalyst. The similarities and differences of mechanism of various forms of sulfur compounds resulting in CuO-ZnO-Al2O3catalyst poisoning, as well as the changes of chemical composition of catalyst active component, have been comprehensively analyzed too. In this paper, a theoretical basis for the CuO-ZnO-Al2O3catalyst regeneration is also provided. The conclusions are as follows:(1) Thermodynamics of poisoning on copper-based catalyst for low temperature water-shift reaction with sulfurous gases were calculated according to thermodynamic calculation methods. In the condition of low temperature water-shift reaction (423.15K-573.15K), the possible chemical reactions and products in the process of the copper-based catalyst poisoned by COS, CS2, H2S and SO2were analyzed by the thermodynamics of heterogeneous reactions. The results showed that the most easily products were Cu2S and CuS followed by COS and H2S participating in poisoning reactions. When CS2and SO2participated in poisoning reactions, the products were more complex, which CUCO3and CUSO4were generated at the same time. Based on the thermodynamic analysis, the toxicities for the low temperature water-gas shift catalyst were in the order of: CS2> SO2> COS> H2S.(2) Compulsory sulfur poisoning experiments conducted on CuO-ZnO-Al2O3catalyst. By monitoring the conversion rate of CuO-ZnO-Al2O3catalyst in poisoning process, the conversion rate changes over time was obtained. A same trend was presented by COS and H2S. Conversion rate of them declined sharply because of the toxic gases passed into the subsequent, then slowed down on plurality of buffer platforms, and finally stabilized at a lower level. As a consequence, it was a long period for the catalyst to lose their activity with these two gases. Yet, with the addition of CS2and SO2, the conversion rate decreased rapidly, followed by a sharp decline after a buffer platform, slowed down after reached a certain level and a buffer platform appeared again, stabilized at a lower level at last. The process of the loss on activity of the catalyst was decelerated by these two gases.(3) The results of CuO-ZnO-Al2O3catalyst sulfur poisoning samples of XRD demonstrated that:The production of COS poisoning was CuS、Cu8S5(3Cu2S-2CuS), the production of CS2poisoning was CuCO3and the production of H2S poisoning was CuS, Cu8S5(3Cu2S-2CuS). This was basically consistent with the thermodynamic calculation results. But due to the reaction kinetics of the adsorption process, the thermodynamic calculations of the reaction would be different.(4) XPS characterization results of CuO-ZnO-Al2O3catalyst sulfur poisoning samples showed that the toxic product of COS are CuS、Cu2S、CuSO4、ZnS, and the toxic product of CS2are CuS、Cu2S、CuCO3、ZnS. While, the toxic product of SO2and H2S are CuS、 CuSO4、ZnS、Zn(OH)2and CuS、Cu2S、CuSO4、ZnS, respectively.(5) SEM characterization results of CuO-ZnO-Al2O3catalyst sulfur poisoning samples indicated that due to the change of the product on the surface of the catalysts before and after deactivation, there are some differences between the surface morphology before and after the catalyst poisoning.

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