Fast pyrolysis of lignocellulosic biomass is considered to be a promising thermochemical route for the production of drop‐in fuels and valuable chemicals. During the past decades, a comprehensive understanding of feedstock structure, fast pyrolysis kinetics, product distribution, and transport effects that govern the process has allowed to design better pyrolysis reactors and/or catalysts. A variety of lignocellulosic biomass feedstocks, like corn stover, pinewood, poplar, and model compounds like glucose, xylan, monolignols have been utilized to study the thermal decomposition at or close to fast pyrolysis conditions. Significant progress has been made in understanding the kinetics by developing unique setups such as drop‐tube, PHASR, and micropyrolyzer reactors in combination with the use of advanced analytical techniques such as comprehensive gas and liquid chromatography (GC, LC) with time‐of‐flight mass spectrometer (TOF‐MS). This has led to initial intrinsic kinetic models for biomass and its main components, namely cellulose, hemicellulose, and lignin, validated using experimental setups where the effects of heat and mass transfer on the performance of the process, expressed using Biot and pyrolysis numbers, are adequately negligible. Yet, not all aspects of fast pyrolysis kinetics of biomass components are equally well understood. The use of time‐resolved or multiplexed experimental techniques can further improve our understanding of reaction intermediates and their corresponding kinetic mechanisms. The novel experimental data combined with first principles based multiscale models can reshape biomass pyrolysis models and transform biomass fast pyrolysis to a more selective and energy efficient process. This article is categorized under: Energy and Climate > Climate and Environment Energy Research & Innovation > Science and Materials Bioenergy > Science and Materials

Kinetics of cellulose acid hydrolysis is reported to be very different under dilute acid–high temperature and concentrated acid–low temperature conditions due to the heterogeneous and homogeneous nature of the reactions, respectively. This work aims at unifying the kinetics of cellulose deconstruction by developing a mechanistic model that includes formation and decomposition of glucose and cellulo-oligomers under extremely low (0.07%) to high (70%) acid concentrations and high (225 °C) to low (25 °C) temperatures. A continuous distribution kinetic model that includes (i) random mid-chain and specific end-chain scission of cellulose to form cellulo-oligomers and glucose; (ii) specific scission of cellulo-oligomers to form glucose, cellobiose, cellotriose, cellotetraose, and cellopentaose; and (iii) degradation of glucose was developed. The model predicted reasonably well the experimental data of concentration of cellulose, glucose, and other oligomers obtained from different studies in a broad range of acid concentrations and temperatures. The effects of initial concentration and degree of polymerization on cellulose conversion and glucose yield were evaluated using this model. Moreover, the model also predicted various reported physical effects on cellulose deconstruction and, importantly, manifested its applicability for cellulose hydrolysis in lignocellulosic biomasses like walnut green skin and yellow poplar wood.

Pyrolysis of polyolefins has been proposed as a potential resource recovery strategy by converting macromolecules into valuable fuels and chemicals. Due to variations in possible backbone structures, chain-length distributions, and arrangements of pendant groups, their decomposition behavior via pyrolysis can be complex. In the present work, a review of historical data and empirical models for two distinct polyolefins, polyethylene (PE) and polypropylene (PP), is provided followed by a comparison to recent mechanistic models. The characteristic sigmoidal behavior of linear polymer decomposition is captured with global, lumped-species, and mechanistic models of high-density polyethylene. The PE model was extended to simulate PP using the same reaction families and reaction family parameters, but with distinct rate coefficients that accounted for the difference in the structure of PP with its pendant methyl groups compared to PE as manifested through heats of reaction embedded in the Evans−Polanyi relationship, E a = E 0 + γ×ΔH reacn . The change in structure and its associated kinetic parameters resulted in no sigmoidal conversion, consistent with experimental reports for atactic PP. This suggests that mechanistic modeling could be an important complement to global model studies to understand when other effects are at play in the pyrolytic decomposition of polymers such as PP.

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Genetic engineering is a powerful tool to steer bio-oil composition towards the production of speciality chemicals such as guaiacols, syringols, phenols, and vanillin through well-defined biomass feedstocks. Our previous work demonstrated the effects of lignin biosynthesis gene modification on the pyrolysis vapour compositions obtained from wood derived from greenhouse-grown poplars. In this study, field-grown poplars downregulated in the genes encoding CINNAMYL ALCOHOL DEHYDROGENASE ( CAD ), CAFFEIC ACID O-METHYLTRANSFERASE ( COMT ) and CAFFEOYL-CoA O-METHYLTRANSFERASE ( CCoAOMT ), and their corresponding wild type were pyrolysed in a Py-GC/MS. This work aims at capturing the effects of downregulation of the three enzymes on bio-oil composition using principal component analysis (PCA). 3,5-methoxytoluene, vanillin, coniferyl alcohol, 4-vinyl guaiacol, syringol, syringaldehyde, and guaiacol are the determining factors in the PCA analysis that are the substantially affected by COMT , CAD and CCoAOMT enzyme downregulation. COMT and CAD downregulated transgenic lines proved to be statistically different from the wild type because of a substantial difference in S and G lignin units. The s CAD line lead to a significant drop (nearly 51%) in S-lignin derived compounds, while CCoAOMT downregulation affected the least (7–11%). Further, removal of extractives via pretreatment enhanced the statistical differences among the CAD transgenic lines and its wild type. On the other hand, COMT downregulation caused 2-fold reduction in S-derived compounds compared to G-derived compounds. This study manifests the applicability of PCA analysis in tracking the biological changes in biomass (poplar in this case) and their effects on pyrolysis-oil compositions.

A kinetic Monte Carlo model of polyurethane polymerization which explicitly tracks the polymer sequences is developed and shared. This model is benchmarked against theoretical and experimental polyurethane data and used to investigate the effect on oligomer distributions of unequal reactivity of the first and second isocyanate to react. The reverse reactions using thermodynamic consistency are then added to the framework, and analogous to the addition polymerization concept of ceiling temperature, equilibrium chain length distributions at various temperatures are calculated. For a mixture of three monomers AA, BB, and CC, where BB and CC do not react with one another, are present in stoichiometric proportions, and have different enthalpies of reaction with AA, an odd-even effect emerges. Odd length chains are more likely than even length chains for temperatures at which BB and CC have significantly different equilibrium conversions. The concept of ceiling temperature that is typically cited for addition polymers is extended here to provide a measure of conditions under which depolymerization for recycling is favored.