Fetisov Evgenii O, Shah Mansi S, Knight Christopher, Tsapatsis Michael, Siepmann J Ilja
Department of Chemistry and Chemical Theory Center, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota, 55455, USA.
Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota, 55455, USA.
Chemphyschem. 2018 Feb 19;19(4):512-518. doi: 10.1002/cphc.201700993. Epub 2018 Jan 16.
Purifying sour natural gas streams containing hydrogen sulfide and carbon dioxide has been a long-standing environmental and economic challenge. In the presence of cation-exchanged zeolites, these two acid gases can react to form carbonyl sulfide and water (H S+CO ⇌H O+COS), but this reaction is rarely accounted for. In this work, we carry out reactive first-principles Monte Carlo (RxFPMC) simulations for mixtures of H S and CO in all-silica and Na-exchanged forms of zeolite beta to understand the governing principles driving the enhanced conversion. The RxFPMC simulations show that the presence of Na cations can change the equilibrium constant by several orders of magnitude compared to the gas phase or in all-silica beta. The shift in the reaction equilibrium is caused by very strong interactions of H O with Na that reduce the reaction enthalpy by about 20 kJ mol . The simulations also demonstrate that the siting of Al atoms in the framework plays an important role. The RxFPMC method presented here is applicable to any chemical conversion in any confined environment, where strong interactions of guest molecules with the host framework and high activation energies limit the use of other computational approaches to study reaction equilibria.
净化含有硫化氢和二氧化碳的酸性天然气流一直是一个长期存在的环境和经济挑战。在阳离子交换沸石存在的情况下，这两种酸性气体可以反应生成羰基硫和水（H₂S + CO₂ ⇌ H₂O + COS），但这个反应很少被考虑。在这项工作中，我们对全硅和钠交换形式的β沸石中H₂S和CO₂的混合物进行了反应性第一性原理蒙特卡罗（RxFPMC）模拟，以了解驱动转化率提高的主导原则。RxFPMC模拟表明，与气相或全硅β沸石相比，Na阳离子的存在可以使平衡常数改变几个数量级。反应平衡的移动是由H₂O与Na的非常强的相互作用引起的，这种相互作用使反应焓降低了约20 kJ·mol⁻¹。模拟还表明，骨架中Al原子的位置起着重要作用。这里提出的RxFPMC方法适用于任何受限环境中的任何化学转化，在这种环境中，客体分子与主体骨架的强相互作用和高活化能限制了使用其他计算方法来研究反应平衡。
