Pyrolysis reactions of various lignin model dimers

Lignin pyrolysis reactions

“…1 Thermogravimetric analysis of milled wood lignin isolated from Japanese cedar (Cryptmeria japonica) [9] understanding the pyrolytic reactions of lignins. Hence, various model dimers including β-ether [20,27,28,34,[40][41][42][43][44][45][46][47][48][49][50][51][52][53], α-ether [20,30,34,45,47,49,51,54], β-aryl [20,31,32,47,54], β-β [33], and biphenyl [20,47,54] types, trimers [34,49,51] and oligomers/polymers such as dehydrogenative polymerization products of cinnamyl alcohols [35] and β-ether type polymers [55][56][57] have been used in pyrolysis studies. Phenolic (Ph) and non-phenolic (Non-Ph) model compounds are commonly used to represent the ends and repeating units of lignin macromolecules, respectively.…”

“…Early studies conducted by the Domburg group [54,58] reported the thermal stability of various model compounds, which were representative of the linkages between phenylpropane-units and side-chains. Analyses of the pyrolysis products of dimers along with NMR analysis of the pyrolyzed lignins revealed that α-and β-ether bonds are readily cleaved during the primary pyrolysis stage; however, condensed (C−C) type linkages are stable during depolymerization of lignin macromolecules [13,20,47]. The Ph β-aryl type dimers give stilbenes selectively, but this reaction does not lead to depolymerization of lignins [20,47].…”

“…Analyses of the pyrolysis products of dimers along with NMR analysis of the pyrolyzed lignins revealed that α-and β-ether bonds are readily cleaved during the primary pyrolysis stage; however, condensed (C−C) type linkages are stable during depolymerization of lignin macromolecules [13,20,47]. The Ph β-aryl type dimers give stilbenes selectively, but this reaction does not lead to depolymerization of lignins [20,47]. Normally, Ph dimers are more reactive than corresponding Non-Ph ones [20,40,41,47,49,53].…”

“…The Ph β-aryl type dimers give stilbenes selectively, but this reaction does not lead to depolymerization of lignins [20,47]. Normally, Ph dimers are more reactive than corresponding Non-Ph ones [20,40,41,47,49,53]. Compared with hardwood lignins, softwood lignins contain a greater proportion of condensed type linkages.…”

Relationships between Biomass Composition and Liquid Products Formed via Pyrolysis

“…As waste products are often selected as biofuel feedstocks, it is also relevant to note that lignin derived from other monolignols such as caffeyl alcohol and 5-hydroxyconiferyl have been found in the seedcoat of both monocots and dicots . Lignin structural heterogeneity and various types of incorporated groups can lead to a variety of different depolymerization reactions during pyrolysis (Kawamoto et al, 2007). Often traceable to the corresponding bio-oil components, the three major lignin units differ in the degree of methoxylation of their carbon ring.…”