The mutual transformation of hydrogen sulphide and carbonyl sulphide and its role for gas desulphurization processes with zeolitic molecular sieve sorbents

Understanding the Reactive Adsorption of H2S and CO2 in Sodium‐Exchanged Zeolites

“…Short exploratory simulations (2000 MC moves) at both 300 and 450 Kf or the 8:8H 2 S/CO 2 mixture in the all-silicaf orm of BEA do not yield any conversion.A lthough much longer simu-lations would undoubtedly encounter some reactive events, these exploratory simulations suggest that confinement in the BEA micropores is not sufficient to drive the reactionf orward and as tronger interaction betweent he products and the zeolite is required.T he lacko fa ppreciable conversion is consistent with experimental findings for other all-silicaz eolites. [10] Previously,t he effect of confinement on model chemical reactions was studied with standard RxMC simulations. Enhancements up to 40-foldw ere found for the NO dimerization reactioni n porousc arbon materials, [44,45] where the increased number density in the pore (compared to the bulk phase) leads to higherc onversion for this dimerization reaction with ad ecrease in the number of molecules in accord with Le Chatelier's principle.…”

“…This suggestst hat al arger local concentration of Na + cations helps in better product stabilization, and an increaseo ft he number of Na-Na pairs may contribute to the experimentally observed trend of higher conversion for lower Si/Al ratios. [10] Calculation of the internal reaction energies (see Ta ble 1) providest he thermodynamic reason for the large increase of K c and the relative temperaturei nsensitivity found in Na-BEA compared to the small effect of confinementi na ll-silica BEA. The reaction is strongly endothermic in the gas phase with DU = 29 kJ mol À1 ,b ut interactions of the products (see below) with Na-BEA reduce DU by more than 20 kJ mol À1 .T he small DU values of approximately 8a nd 5k Jmol À1 at T = 300 and 450 K, respectively,i nN a-BEA lead to strongly increased conversion andas mall temperature dependence.I nc ontrast, confinement in all-silica BEA reduces DU by less than 2k Jmol À1 .…”

“…[40] The predicted equilibrium constants of 2:0 Â 10 À7 (CP2K) and 1.0 10 À6 (all-electron) at T = 293 Ka re in good agreement with the experimental value of 1.4 10 À6 . [10] The simulated systems consist of one unit cell of all-silica BEA (with 64 SiO 2 formula units, 192 atoms) or of Na-exchanged BEA with Si/ Al ratio of 7:1( 56 Si, 8A l, 128 O, and 8N aa toms) and 48 guest atoms with the following three initial reactant ratios:4:12, 8:8, and 12:4 H 2 S/CO 2 molecules. The linear dimensions of BEA's tetragonal unit cell are 12.632 12.632 26.186 3 .T or educe the computational cost, the current simulations sample the classical partition function of the system (i.e.…”

“…rangesf rom am ere 10 À6 at 20 8Ct oa pproximately 10 À2 at 400 8C. [10] Thus, in the absence of any other agent or environment,c onversion to COS can essentially be arrested. However, it is known that adsorption in cation-exchanged zeolites can lead to significant conversion, [11] and also absorption in ionic liquids and deep eutectic solvents may potentially shiftt he equilibrium.…”

“…11 )a nd choice of operating conditions (to benefit from slower kinetics), to suppressC OS formation. [10,12,14] Since it is clear that confinement can influencet he reactione xtent, the opportunity exists to select different zeolite framework structures and to tune Si/Al ratio, Al siting, and cation chemistry to achieves our gass weeteningw ith minimal conversion to COS. To reach this goal, it is desirable to understand the governing reactive phenomena at atomic length scales in order to provide guidelines for aiding materials design.I nt his work, we use first principles simulations to study reactive mixtures of H 2 Sa nd CO 2 in the zeolite beta (BEA) with medium-sized 7 pores. [15] ComputationalDetails Recently,w ei ntroduced the reactive first-principles Monte Carlo (RxFPMC) method that can be applied to model reactive systems in highly non-ideal environments.…”