Thermal, noncatalytic conversion of light olefins (C 2 = −C 4 =) was originally utilized in the production of motor fuels at several U.S. refineries in the 1920s to 1930s. However, the resulting fuels had relatively low octane number and required harsh operating conditions (T > 450 °C, P > 50 bar), ultimately leading to its succession by solid acid catalytic processes. Despite the early utilization of the thermal reaction, relatively little is known about the reaction products, kinetics, and initiation pathway under liquid-producing conditions. In this study, thermal ethylene oligomerization was investigated near industrial operating conditions, i.e, at temperatures between 300 and 500 °C and ethylene pressures from 1.5 to 43.5 bar. Nonoligomer products such as propylene and/or higher odd carbon products were significant at all reaction temperatures, pressures, and reaction extents. Methane and ethane were minor products (<1% each), even at ethylene conversions as high as 74%. The isomer distributions revealed a preference for linear, terminal C 4 and C 5 . The reaction order was found to be second-order with a temperature-dependent overall activation energy ranging from 39.4 to 58.3 kcal mol −1 . Four bimolecular initiation reaction steps for ethylene were calculated using DFT. Of these, simple H-transfer to yield vinyl and ethyl radicals was found to have a free energy activation energy barrier higher (about 10 kcal mol −1 ) than the other three initiation steps forming either cyclobutane, 1-butene, or tetramethylene. The importance of diradical species in generating free radicals during a two-phase initiation process was proposed. The reaction chemistry for ethylene, which has only strong, vinyl C−H bonds, starkly contrasted with propylene, which possesses weaker allylic C−H bonds and showed a preference for dimeric C 6 products over C 2 −C 8 nonoligomers. The resulting C 4 and C 5 nonoligomers from propylene contained more iso-olefins compared to linear C 4 and C 5 .

The construction of mechanistic models for the autoxidation of fatty acid or ester substrates found in oil paint binders is ac hallenging undertaking due to the complexity of the large crosslinked species that form, and the small molecules that volatilize. Building models that capture this product diversity are made possible by automating the process of network generation. This work presents am icrokinetic model for the autoxidation of ethyl linoleate catalyzedbycobalt(II) 2ethyl hexanoate.T he mechanism size was controlled by using ar ate-based criterion to include the most kinetically relevant reactions from among the millions of possible reactions generated. The resulting model was solved and compared to experimental metrics.Q uantities such as hexanal production and the consumption of unsaturated moieties were in good agreement with experiment. Finally,t he model was used to explore the effect of the catalyst concentration and temperature on key measurables.

Bifunctional catalysts are challenging to model because there are two active sites capable of unique intermediates and reaction types. Nevertheless, they are versatile catalysts because the relative number of both active sites can be tuned to alter rate and selectivity in response to variation in feed compositions. In this work, a microkinetic model of ethene oligomerization on a Ni−H-β zeolite catalyst was developed based on nickel and Brønsted acid reaction families, with kinetic parameters estimated using transition-state theory, Evans− Polanyi relationships, and thermodynamic data. Species lumping allowed for the formation of products of high molecular weight at high conversion to be captured in the model while avoiding network truncation effects. The reaction mechanism culminated in a complex model describing the formation of C2−C12 products that accurately predicted three published experimental investigations using Ni−H-β (10 unique experiments) up to about 30% conversion. The agreement between the experiment and model predictions demonstrates the model's broad applicability and robustness. Ni sites produce linear alkenes of even carbon number, while Brønsted acid sites catalyze further oligomerization, cracking, and isomerization to broaden the product distribution. The model was used to probe potential experimental conditions and catalyst properties, without extrapolation, allowing for a better understanding of the effect of common experimental parameters (space time, temperature, pressure, Ni wt %) on reaction flux and selectivity to desired products, demonstrating the model as a powerful tool in catalyst and process design.

Fast pyrolysis of lignocellulosic materials is a promising research area to produce renewable fuels and chemicals. Dehydration is known to be among the most important reaction families during cellulose pyrolysis; water is the most important product. Together with water, dehydration reactions also form a range of poorly known oligomer species of varying molecular sizes, often collected as part of the bio-oil water-soluble (WS) fraction. In this work, we used electronic structure calculations to evaluate the relative thermodynamic stabilities of several oligomer species from cellulose depolymerization intermediates undergoing three consecutive dehydration events. A library of the thermodynamically favored candidate molecular structures was compiled. Results revealed that most of the water molecules are eliminated from the non-reducing end, forming thermodynamically more stable conjugated compounds. This is consistent with results reported in literature where dehydration reactions occur preferably at the non-reducing ends of oligomers. The theoretical Fourier-Transform Infrared Spectroscopy and NMR spectra of these proposed sugar oligomers conform qualitatively to the experimental result of pyrolytic sugars. Understanding their chemical structure could help to develop rational strategies to mitigate coke formation as sugars are often blamed to cause coke formation during bio-oil refining. The estimated physical–chemical properties (boiling point, melting point, Gibbs free energy of formation, enthalpy of formation, and solubility parameters among others) are also fundamental to conducting first-principles engineering calculations to design and analyze new pyrolysis reactors and bio-oil up-grading units.

Pyrolytic lignin is a fraction of pyrolysis oil that contains a wide range of phenolic compounds that can be used as intermediates to produce fuels and chemicals. However, the characteristics of the raw lignin structure make it difficult to establish a pyrolysis mechanism and determine pyrolytic lignin structures. This study proposes dimer, trimer, and tetramer structures based on their relative thermodynamic stability for a hardwood lignin model in pyrolysis. Different configurations of oligomers were evaluated by varying the positions of the guaiacyl (G) and syringyl (S) units and the bonds βO4 and β5 in the hardwood model lignin through electronic structure calculations. The homolytic cleavage of βO4 bonds is assumed to occur and generate two free radical fragments. These can stabilize by taking hydrogen radicals that may be in solution during the intermediate liquid (pathway 1) formation before the thermal ejection. An alternative pathway (pathway 2) could occur when the radicals use intramolecular hydrogen, turning themselves into stable products. Subsequently, a demethylation reaction can take place, thus generating a methane molecule and new oligomeric lignin-derived molecules. The most probable resulting structures were studied. We used FTIR and NMR spectra of selected model compounds to evaluate our calculation approach. Thermophysical properties were calculated using group contribution methods. The results give insights into the lignin oligomer structures and how these molecules are formed. They also provide helpful information for the design of pyrolysis oil separation and upgrading equipment.