Relationship Between The Solid Phase Form, Sulfur Distribution With COS Formation Over Mn-Based Metal Oxide Sorbents

Due to the high in precision and the wide in temperature range, the dry desulfurizations using metal oxide become one of the key technology in coal clean conversion and utilization. With further research and practice about metal oxide desulfurizations, the phenomenon of sulfur release (COS formation) is found during dry desulfurization. COS formation has a serious bad effect on the development of metal oxide desulfurization sorbents, and is also a poison for the catalysts used in downstream processes. Consequently, it is necessary to study the mechanism of COS formation in the desulfurization using metal oxide sorbents, and to obtain the method of decreasing the formation of COS at present.Because of the high activity and the fast reaction rate, the manganese oxide is widely used for H2S removal. However, the COS was formed during H2S removal while manganese oxide desulfurizers are applied in coal gas purification. In this paper, combined with the main research content of National Natural Science Foundation (20976116) and Basic Research project of Shanxi Province (2009011010-2), the manganese oxide was selected to be object of research. The rules of H2S removal and COS formation during desulfurizrion using manganese sorbents were investigated by the fixed bed reactor. Contacting with the result of XRD, XPS and EDS, the relationship between COS formation and the form and distribution of solid phase was discussed, and the mechanism of COS formation was deduced. The conclusions obtained are as follows:①Three different kind of MnOx sorbents were prepared by controlling the dropping velocity of precipitor, calcination temperature and reduction tempetature. Besed on the results of characterization by H2-TPR and CO-TPR, the reaction temperature for different MnOx sorbents were confirmed. The research plans on investigation properties of different MnOx sorbent were established under the condition of550℃in CO2+H2S+N2atomsphere, and250℃and550℃in CO+H2S+N2atomsphere, respectively.②The H2S removal and COS formation on three different kinds of MnOx sorbents were investigated in the fixed bed reactor at550℃in H2S+CO2+N2atomsphere. The sequence of the amount of COS formation over three MnOx samples is Mn3O4>Mn2O3>MnO, and the sequence of H2S penetration time is Mn3O4<Mn2O3<MnO, The larger non stoichiometry for manganese sulfide formed during desulfurization is, the more COS formaed. After the H2S breaks through, the COS concentration incresed with the H2S concentration increasing. The H2S removal and COS formation on three different kind of MnOx sorbents were investigated in the fixed bed reactor at250℃in H2S+CO+N2atomsphere. The amount of COS formation in the atmosphere containing CO is less than that in the atmosphere containing CO2. The COS was detected before the H2S penetrated for Mn2O3and MnO desulfurization sorbents at250℃. This phenomenon may be related to properties of the COS removal of MnOx.③The phases and surface components for sorbent located top, middle and bottom part of the penetrated and unpenetrated bed were characterized by XRD and XPS. The Mn2O3and Mn3O4were reduced by H2S during desulfurization. With the help of thermodynamic calculation and the mechanism analysis, it was pointed out that the active sulfur substance was formed not by oxidation-reduction reaction but by H2S decomposition catalysed by MnS. The COS was formed by the reaction between the active sulfur and CO or CO2.The MnS2was formed by the reaction of the unreacted sulfur and MnS. The MnS did not react with the CO or CO2. The result of EDS and FTIR showed that the chemical bond connecting the solid exterior with CO and that with CO2were different. The S element and O element were transferring in the solid phase. Then the intermediate over the solid phase was changed, and COS was formed.