especially the consolidated bioprocessing, chemistry, and physical base pretreatment and their importance in the valorization of lignocellulosic biomass conversion.

Alili, A.S., Siddiquee, M.N., de Klerk, A., 2020. Origin of free radical persistence in asphaltenes: Cage effect and steric protection. Energy &Fuels 34, 348-359.

https://doi.org/10.1021/acs.energyfuels.9b03836 Heavier petroleum fractions contain persistent free radicals, and the highest concentration of persistent free radicals is usually found in asphaltenes. The origin of free radical persistence was studied. The potential influence of exposure to air, free radical caging, and steric protection was evaluated. The free radical content of asphaltenes diluted in toluene remained constant to within 5% over a period of 465 h under both nitrogen and air atmospheres. The persistent free radicals were accessible for reaction in dilute solution. Caging of free radicals due to high viscosity could not explain the observations. Caging of free radicals due to molecular-level aggregation was possible, but explaining all of the observations in terms of the cage effect became tenuous. The asphaltenes appeared unencumbered by steric constraints compared to 9,10-dihydroanthracene during hydrogen transfer reactions, which made it unlikely that steric protection was a major contributor to the persistence of free radicals. The asphaltenes were reactive at 250 °C, both for self-reaction and for conversion of various model molecules (1,2- dihydronaphthalene, α -methylstyrene, 2,4,6-trimethylstyrene, 1,1-diphenylethylene, trans-1,2- diphenylethylene, triphenylethylene, tetraphenylethylene, and 9,10-dihydroanthracene). An alternative explanation for the origin of free radical persistence was forwarded. It was considered unlikely that individual free radical species could remain as persistent free radicals over geologic time but also be reactive. The observed persistence of fre e radicals could be explained in terms of a dynamic 'equilibrium' of free radical pairs, which is a self-stabilizing process that gives the impression of free radical persistence. Dynamic formation and destruction of free radicals through addition and decomposition reactions of radical pairs average out on the macroscopic scale to create the impression of persistent free radicals. Any individual species does not remain persistent beyond what one would expect from a reactive persistent free radical.

Alshareef, A.H., 2020. Asphaltenes: Definition, properties, and reactions of model compounds. Energy &Fuels 34, 16-30.

https://doi.org/10.1021/acs.energyfuels.9b03291 The simple definition of asphaltenes - the material that dissolves in aromatic solvents and precipitates in normal alkanes - proved to be not very defining at all. The nature of this material, how it formed, what its key properties are, and how it behaves under thermal or catalytic reaction conditions has extensively evolved over decades of continuous research and debate. One of the main sources of the debate was the apparent conflicting findings between numerous analytical studies and thermal reaction studies of asphaltenes and their model compounds. Similar to the blind men describing different parts of an elephant, many studies were describing some aspect of the material as it is observed but not realizing the existence of a 'larger' object, and even the observations were very subjective to how asphaltenes were precipitated and analyzed and how data was generated and interpreted. In this paper, a brief summary is given on how asphaltenes are defined, how they form, and the current consensus on their properties, and finally a focus on thermal behavior, as observed from thermal studies on asphaltenes and their model compounds. The collective knowledge from analytical and thermal studies on the asphaltenes and various model compounds helped settle most of the debate on the notoriously complex material named asphaltenes.

Amaral, M.S.S., Nolvachai, Y., Marriott, P.J., 2020. Comprehensive two-dimensional gas chromatography advances in technology and applications - biennial update. Analytical Chemistry 92, 85-104.

https://doi.org/10.1021/acs.analchem.9b05412 Apart from the pure methodological process of implementing a comprehensive two-dimensional gas chromatography (GC×GC) method, surely it is the excitement engendered by a well-designed separation that