Screening of metal oxides and metal sulfides as sorbents for elemental mercury at elevated temperatures

详细信息	查看全文 | 推荐本文 |

• 作者：David J. Couling ; Hoang V. Nguyen ; William H. Green ; ^{whgreen@mit.edu}
• 关键词：Coal gasification ; Mercury ; Adsorption ; Computational chemistry
• 刊名：Fuel
• 出版年：2012
• 期刊代码：33_00162361
• 类别：ce
• 出版时间：July, 2012
• 卷：97
• 期：Complete
• 页码：783-795
• 文件大小：1189 K

摘要

A technical challenge for the implementation of Integrated Gasification Combined Cycle (IGCC) coal power plants is determining a method to efficiently capture the pollutants present in coal-derived syngas. One such method is to capture the pollutants at elevated temperatures to decrease the parasitic energy costs associated with their capture. Elemental Hg is difficult to capture because it is present in low concentrations and is relatively inert. In order to overcome technical and economic impediments to investigating potential materials experimentally, here we present an alternative approach in which we screen these materials using density functional theory. We compute the thermochemistry for 23 materials reacting with Hg to evaluate their efficacy for Hg capture. We also compute the thermochemistry of these materials reacting with H₂, a major component of syngas. Using these calculations we were able to obtain estimates for the thermochemistry of 21 metal oxide and metal sulfide compounds, 17 of them containing Hg, where no experimental data are available. We predict several sorbent materials such as BaO₂, CrO₂, and Na₂O₂ to be effective for Hg capture at elevated temperatures but unusable in syngas because of their reactivity with H₂. These materials may instead be effective for Hg capture from flue gas. We also predict that the selectivity of K₂S₂ for Hg over H₂ is favorable, even at the IGCC conditions. Finally, we experimentally evaluate the Hg adsorption ability of K₂S₂, BaO₂, and CrO₂ in order to test the theoretical predictions. CrO₂ was also evaluated for its potential to H₂ reduction. CrO₂ is shown to be an effective high-temperature sorbent for Hg in an inert carrier gas but is not stable in H₂ streams, which agrees well with our theoretical calculations.