Kinetic Modeling of Hydrogen Abstractions Involving Sulfur Radicals

Abstract

One of the requisites for the development of detailed reaction networks is the availability of accurate kinetic data. Group additivity based models linking the Arrhenius parameters to structural characteristics of the transition state have proven to be a valuable tool to obtain those data. In this work, group additivity values are presented to allow a broad range of CH and SH hydrogen abstraction reactions by S radicals to be modeled. Rate coefficients in the temperature range from 300 to 1500 K are obtained by using the CBS-QB3 method in the high-pressure limit and are corrected for tunneling and anharmonicity of rotation about the transitional bond. A total of 149 reactions are studied. From these reactions, a total of 52 group additivity values and 35 resonance corrections are derived. The general applicability of the group additivity method is demonstrated for a test set containing 25 reactions. At 300 K, rate coefficients are on average reproduced within a factor of 2.8. The mean absolute deviations on the Arrhenius parameters are 2 kJ mol(-1) for the activation energy and 0.38 for log A in which A is the pre-exponential factor.

Group Additive Kinetics for Hydrogen Transfer Between Oxygenates

“…Sabbe et al 30 proposed the fourth-order polynomial of eq 5, with temperaturedependent coefficients for calculating tunneling coefficients for hydrogen abstractions with transition states of the C--H--C type, based on the group additively calculated activation energy of the exothermic direction for the particular reaction. Similar fourthorder polynomial equations were found to provide tunneling coefficients for hydrogen abstractions of the S--H--C and S--H--S type 32 and also the H--H--C type. 28 The parameters A, B, and C in eq 5 for the above-mentioned tunneling equations are summarized in Table 1.…”

Detailed kinetic model for hexyl sulfide pyrolysis and its desulfurization by supercritical water

“…High accuracy calculations are already available for many hydrocarbons and small molecules. 47 More recently, a detailed database for the thermochemistry and kinetics of sulfur compounds was developed by Vandeputte et al [33][34][35][36][37] The sulfur database was then extended to include reactions and thermochemistry estimations for compounds containing both sulfur and oxygen, particularly for use in high-temperature models involving chemical reactions of sulfur compounds and water. 38 Collectively, these data provide reasonably accurate rate estimations (within an order of magnitude) for a variety of reactions that are potentially relevant in our system, including the usual free radical reactions as well as more specific reaction types, such as the addition of water or hydrogen sulfide to a double-bond, ipso-additions to sulfides, and intra-hydrogen abstractions in organosulfur compounds (for a full list of reaction types in the RMG database, see the work by Gao et al).…”

“…The accuracy of a desulfurization model requires accurate thermo-chemical and detailed rate information for sulfur compounds. Vandeputte et al [33][34][35][36][37] developed a detailed database for the thermochemistry and kinetics of sulfur compounds. Class et al later extended the database to include reactions and thermochemistry estimations for compounds including both sulfur and oxygen, particularly for use in high-temperature models involving sulfur compounds and water.…”

Symmetry calculation for molecules and transition states

“…The algorithm could be used in chemical engineering applications such as the automated construction of detailed kinetic models of complex chemical processes [15] in which thermochemical properties of hundreds of species and the rate coefficients of thousands of reactions need to be evaluated. [44,[49][50][51][52][53][54][55] However, group contribution methods cannot determine nonlocal properties such as symmetry and, hence, Benson's group additivity always needs to be complemented with a procedure to account for symmetry contributions. [44,[49][50][51][52][53][54][55] However, group contribution methods cannot determine nonlocal properties such as symmetry and, hence, Benson's group additivity always needs to be complemented with a procedure to account for symmetry contributions.…”

“…In this type of application, group contribution methods such as Benson group additivity [47] are frequently used to provide fast estimates of thermochemical properties [47,48] or rate coefficients. [44,[49][50][51][52][53][54][55] However, group contribution methods cannot determine nonlocal properties such as symmetry and, hence, Benson's group additivity always needs to be complemented with a procedure to account for symmetry contributions. Moreover, obtaining information on the degree of symmetry, expressed by the symmetry number could also be useful in the selection of suitable candidates for pharmacophore identification or docking algorithms.…”