In this study, a practical strategy to develop a microkinetic model for methanol synthesis from syngas over a Cu-based catalyst is described. The comprehensive model consists of forward and backward reactions of 28 possible elementary-step reactions for CO and CO 2 hydrogenation and the water−gas shift reaction. A combination of ab initio density functional theory (DFT) and semiempirical unity bond index−quadratic exponential (UBI-QEP) methods was used to determine the heat of adsorption and activation energies. DFT calculations confirmed that formate (HCOO**) adsorbs in a bidentate fashion and provided the enthalpies and adsorption energies of gas and surface intermediates for subsequent UBI-QEP calculations. The pre-exponential factors were estimated from the order of magnitude of the transition state theory as the initial values and by fitting the experimental data, thus reducing the computational load by not calculating the vibrational frequencies and partition functions for translational, rotational, and vibrational motions. For the reactor model, partial equilibrium ratios were used to reduce the stiffness of the microkinetic model. The most plausible reaction pathways were suggested by considering relatively fast step reactions, while the surface reaction of H 3 CO* and H* was found to be the rate-determining step by the degree of rate control. The developed model was also used to evaluate the effects of the temperature, pressure, and H 2 fraction in the feed on the methanol synthesis rate to elucidate the suitable operating conditions. The model effectiveness was validated by comparison with other reported works. The proposed approach can be further exploited for the efficient development of other microkinetic models.

No abstract

In this paper, we present a multicompartment model of an ethylene–vinyl acetate autoclave reactor including the mixing effects of the stirring device analyzed using computational fluid dynamics; the model is simplified by cell aggregation, and the polymerization kinetics is modeled with the method of moments. The proposed model has been verified through comparison of the predicted product properties and locally distributed temperatures with those from an industrial plant. The proposed model, which is capable of simulating a complex system with low computational load, can be applied to maintain consistent product quality, prevent undesired thermal runaway, and optimize the conversion and production rates.

No abstract

Dimethyl ether (DME) is an environmentally friendly fuel and economical compound that can be synthesized through methanol (MeOH) dehydration or direct synthesis from syngas via the water-gas shift reaction. Catalysts such as CZA for syngas conversion to MeOH and zeolites or γ-Al2O3 for MeOH dehydration are necessary for these reactions. A hybrid catalyst, CZA/FER, can be used to directly convert syngas into DME via MeOH. While previous studies have developed kinetic models for these catalytic reaction systems using lumped or microkinetic models, differences in describing elementary reactions have led to variations in detail. In this study, we developed a microkinetic model for DME synthesis from syngas via MeOH over a CZA/FER hybrid bifunctional catalyst. We considered detailed reaction rates and site fractions to determine the dominance of DME synthesis path between the associative and dissociative paths. The model is based on a two-site fraction model for each catalyst, with 28 reactions over CZA and nine reactions over FER. Reaction parameters were determined using transition state theory (TST) and the UBI-QEP method for CZA and the second-order Møller-Plesset perturbation theory (MP2) for FER The pre-exponential factors of Arrhenius rate constants were estimated with experimental data at 250 ℃, which supported the model's accuracy. Our results showed that the associative pathway is dominant for DME synthesis over a CZA/FER hybrid catalyst, which differs from our previous research on microkinetic modeling for MeOH dehydration to DME over a FER zeolite. We also suggest an operating condition range for converting CO2 in the feed. We compare the relative reaction rates of elementary reactions and site fractions in each catalyst to enhance the understanding of the catalytic reaction system.