Event-based description of chemical kinetics by probability of states and entropy

• Applicant: Dr. Markus Seifert
• Subject Area: Technical Chemistry
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 507997100

Current model descriptions of complex kinetics in chemistry focus on the temporal change of state values, e.g. concentration. During transfer from nano- to macro-scale models, challenges occur, e.g. the modelled vs real concentration of fluid molecules (pressure gap), the behavior of real matter vs model fluids (materials gap), and the complexity, heterogeneity and imperfection of real feeds, catalysts and physical reactors (complexity gap). Beside this, the time-scale of molecular and macroscopic processes differs and a chronologic description of local molecular reactions over macroscopic systems is often misleading (time gap).Despite recent single-event approaches for complex surface kinetics, chemical reactions in a stationary continuous reactor could also be considered as states rather than processes. Thus, reaction networks become multidimensional state variables, which can reduce the number of parameters. The main objective in this project is the implementation of such a probability-based description of the industrially relevant ethanol dehydration (ED) and ethanol-to-olefins (ETO) reaction networks as demonstration.In case of a clever choice of basic events and parameters (complexity gap) benefits arise: (i) a focus to the local environment of the event (no materials / pressure gap), (ii) the substitution of the counter “time” by a physically more precise “event” (no time gap) and (iii) the description of the network kinetics by a finite number of basic reactions (=states). Moreover, the state’s probabilities and associated noise from experimental setup, thermal fluctuation and transport are connected to a state- and noise-derived entropy as marker from Gibbs theory.The work program is split into a full characterization of commercial catalyst materials (SAPO-34, ZSM-5), catalytic testing, the model implementation and finally the evaluation of setup-derived noise (NA1), thermal-derived noise (NA2) and dissipation of conversion probabilites (NA3). Beside solid-state characterization, catalytic testing in a continuous mode with GC-FID, GC-TCD and GC-MS analysis helps to quantify noise and sensitivity of setup parameter control (T, p, residence time). The new kinetic approach is adapted to ED and ETO tests incl. matrix operations, numerical integration and Runge-Kutta method for diff. equations. Changing probabilities and their noise (NA1+NA2+NA3) for varying reaction parameters are discussed and compared to qualitative structure-performance relations to reveal dependencies of macroscopic product distribution to microscopic reactions.The quantification of noise within the product distribution on macroscopic level does not only help to give the complex kinetics a thermodynamic frame but it also potentially supports economic considerations in hydrocarbon production.

• DFG Programme: Research Grants