Catalytic depolymerization of alkali lignin in subcritical water: influence of formic acid and Pd/C catalyst on the yields of liquid monomeric aromatic products

Abstract

Alkali lignin was subjected to depolymerization in subcritical water at 265 °C, 6.5 MPa for reaction times between 1–6 h in a batch reactor and in the presence of formic acid (FA) and Pd/C catalyst.

Influence of reaction conditions on the composition of liquid products from two-stage catalytic hydrothermal processing of lignin

“…In addition, Forchheim et al [21] found that the yields of catechol increased with increasing reaction temperature due to favourable reaction kinetics during non-catalytic lignin depolymerization in subcritical water. Onwudili and Williams [19] also reported significant formation of catechol and phenol from guaiacol.…”

“…The presence of some organic co-solvents and capping agents has been found to minimize heat-induced polymerization of lignin and its primary degradation products to form char. For instance, the addition of formic acid (FA) has been shown to influence the degradation pathway of lignin via hydrolysis of ether linkages, possible hydrogenolysis of C-C and C-O bonds, and hydrogenation of C=C bonds to produce a variety of compounds [19]. In recent work [19] carried out at 265 °C and 6.5MPa, lignin degraded to produce guaiacol as the dominant product in the absence of formic acid.…”

“…For instance, the addition of formic acid (FA) has been shown to influence the degradation pathway of lignin via hydrolysis of ether linkages, possible hydrogenolysis of C-C and C-O bonds, and hydrogenation of C=C bonds to produce a variety of compounds [19]. In recent work [19] carried out at 265 °C and 6.5MPa, lignin degraded to produce guaiacol as the dominant product in the absence of formic acid. However, in the presence of formic acid, the O-CH 3 bonds of the methoxy side groups were extensively hydrolysed, so that catechol became the dominant product.…”

“…The ability of formic acid to perform both roles could depend on its own reactivity under hydrothermal conditions and also on its concentration. It has been argued [19] that there might be a need to allow sufficient time for formic acid to act as a hydrolysing agent in order to achieve sufficient lignin depolymerization prior to acting a hydrogen-donor for hydrogenolysis or HDO of lignin products.…”

Supercritical water gasification of RDF and its components over RuO2/γ-Al2O3 catalyst: New insights into RuO2 catalytic reaction mechanisms

“…The gas products were analysed offline by a system of three gas chromatographs (GCs), with already published analytical conditions [20][21]. One of the GC was fitted with a 2 m x 2 mm Molecular Sieve column for the separation of hydrogen, oxygen, nitrogen and CO, which were detected by a thermal conductivity detector (TCD).…”