How Inter‐ and Intramolecular Reactions Dominate the Formation of Products in Lignin Pyrolysis

Abstract

One of the key challenges in renewable chemical production is the conversion of lignin, especially by fast pyrolysis. The complexity of the lignin pyrolysis process has hindered the elucidation of the mechanism, inhibiting further industrial implementation. By combining pyrolysis of model compounds (4-phenoxyphenol and 2-methoxy-phenoxybenzene) with lignin bond characteristics both under vacuum and under realistic pressure conditions, the roles of inter- and intramolecular reactions were established. On the one hand, the stable 4-O-5 ether bond enables, without breaking, C-C bond formation and even directly forms naphthalene depending on the position and type of the substituent. p-Benzoquinone intermediates, on the other hand, are highly unstable at ambient pressure and directly decompose into coke and carbon monoxide. The system pressure (radical concentration) plays a crucial role in the dominant reaction mechanism by initiating intramolecular reactions, interfering with intramolecular reactions. H-transfer and recombination reactions suppress the decarbonylation of phenoxy radicals, thus yielding a very different product distribution.

Catalytic Fast Pyrolysis of Lignin Isolated by Hybrid Organosolv—Steam Explosion Pretreatment of Hardwood and Softwood Biomass for the Production of Phenolics and Aromatics

“…There are several studies available in the literature that have focused on the fast pyrolysis of model lignin compounds, including dimers/oligomers containing β-and α-ether, β-aryl, and other representative bonds in the structure of lignin, as well as in situ spectroscopic investigations that aim to identify the formation of reactive intermediates [109][110][111][112][113]. The reported results and related discussion provide valuable insight but are highly dependent on the type of model compound and A similar superior behavior of hierarchical ZSM-5 zeolites was also observed in our previous work on the catalytic fast pyrolysis of kraft spruce lignin [43].…”

Lignin‐g‐poly(acrylamide)‐g‐poly(diallyldimethyl‐ ammonium chloride): Synthesis, Characterization and Applications

“…By subtracting the nitrogen content of the copolymer associated with DADMAC from the overall nitrogen content of the copolymer,t he nitrogen content of AM portion of the copolymer was determined [Eq. (4). The grafting ratio of acrylamide was then calculated using Equation (5): [22,60] Overall nitrogen ðmmol g -1 Þ¼…”

“…The reactions were monitored by 1 HNMR and the integrated area under the resonances originating from the allyl groups in both acrylamide and DADMAC monomers between 5-6 ppm were considered for copolymerization analysis. These values were then compared with the integrated area of an internal standard trimethylsilyl propionic acid-d. [4] The consumption of monomer was then plotted against time and the slope was taken as the rate of copolymerization (k). Plotting ln k versus 1/T (K), as traight line was achieved with the slope representing the apparent activation energy of the copolymers.…”

“…It currently represents 30 % of all non‐fossil organic carbon on earth and its availability would exceed by 20 billion tons each year . Despite an estimated 50 million tons of lignin extracted annually, only 2 % of lignin is converted into value‐added commodities including dispersants, adhesives, and surfactants . In addition to the high abundance, lignin has many desirable physiochemical characteristics including a large number of functional groups.…”

“…[3] Despite an estimated 50 million tons of lignin extracted annually,only 2% of lignin is converted into value-added commoditiesi ncluding dispersants, adhesives, and surfactants. [3,4] In addition to the high abundance, lignin has many desirable physiochemical characteristics including al arge number of functional groups. As lignin has such aw idev ariety of reactive units arising from its monomer-ic structure including phenol,e ther,c arboxylic acid, and ÀOH functional groups, [5] one can render lignin functionalized for specific applications,s uch as flocculants, [6] dispersants, [7,8] binders, [9,10] adhesives, [11] hydrogels, [12] and composites.…”