Density functional study on the thermal stabilities of phenolic bio-oil compounds

Abstract

Pyrolysis of biomass provides a potential carbon-neutral route to fuels and precursor chemicals through the formation of bio-oil. Lignin accounts for up to 40% of the weight of biomass feedstocks and so the products of lignin deconstruction form a significant portion of the bio-oil. Understanding the thermal stability of bio-oil species is critical for predicting the relationship between product prevalence and pyrolysis temperature, which in turn will allow for greater control of the output of key products. In this work, density functional theory (DFT) was employed to assess the stabilities of key bio-oil compounds by calculating their bond dissociation enthalpies (BDEs). 140 individual bonds across twenty-seven common bio-oil compounds representing eight different bond types were assessed. It was found that the PW6B95 functional can be used as a reliable method for predicting pyrolysis product stability through calculation of functional group BDEs. This is mainly owing to its low mean unsigned error (MUE) (0.5 kcal mol-1 = 2.1 kJ mol-1) in predicting BDEs in a test set of six bonds, as well as correct treatment of aromatic substitution effects for phenolic derivatives. The assessment results reflected that the weakest bonds of phenolic bio-oil species were the O-Me and Ph-O bond of the methoxy groups and the O-H bond of hydroxy groups. The weak bond strength exhibited by methoxy group bonds correlates well with reduced presence of guaiacyl and syringyl type species following higher temperature pyrolysis. Conversely, the hydroxy Ph-O and propenyl Ph-C bonds exhibited high BDEs, which is in agreement with the persistent presence of phenol and styrene type species following high temperature pyrolysis.

Progress in Modeling of Biomass Fast Pyrolysis: A Review

“…The authors proposed dimer decomposition pathways in the presence of inorganic salts via C β –O homolytic and concerted cleavage based on the calculated PES. Shaw and Zhang used DFT calculations to assess the thermal stabilities and bond dissociation enthalpies for 27 common phenolic compounds found in bio-oil. The main findings included the relative bond strengths of various molecular fragments bound to the phenol ring, in part rationalizing low thermal stabilities of methoxy phenol compounds, such as guaiacol and syringol.…”

Plasma-Enabled Selective Synthesis of Biobased Phenolics from Lignin-Derived Feedstock

“…To summarize, the order of BDEs (H–PhOMe > Ph–OMe > PhOCH 2 –H > PhO–Me) in anisole reveals that the cleavage of the methyl group is prone to occur, which corresponds well with the distribution of liquid products. It is noteworthy that the above-mentioned findings that aryl C–O bonds (e.g., Ph–OH and Ph–OMe) are stronger than etheric C–O bonds (e.g., PhO–Me) were proved true regardless of the number or type of additional substituent groups. , …”

How Is Ultrasonic-Assisted CO2 EOR to Unlock Oils from Unconventional Reservoirs?

“…The functional groups in crude oil samples can be sensitively studied by Fourier transform infrared spectroscopy, and the relative concentration (ratio) of each functional group can be obtained by the relative quantitative calculation of aromatic rings, methylene and methyl according to the peak height or area. By comparing and analyzing the infrared spectra of crude oil before and after the reaction, the changes of various functional groups and their relative contents in the samples can be revealed [43,44].…”