Hydrothermal Liquefaction of Lignin

Abstract

The majority of platform chemicals are currently provided through crude oil processes. Nevertheless, the substitution of the crude oil with biomass should be the ecological aim. Lignin, an aromatic macromolecule, may play an important role in that exchange, as it is the only bio based source of aromatic compounds. For instance, it could be a source of bifunctional aromatic molecules, like the monocyclic compounds catechol or guaiacol, or bifunctional oligomers. However, no process for the production of aromatics from lignin in technical scale has been established until now. Hence, the focus of this work is to clarify the chemical degradation mechanism under hydrothermal conditions, to liquefy lignin delivering high functional molecules and to increase the yield and selectivity of the cleavage towards bifunctional molecules like catechol. The combination of fast hydrolysis, thermal degradation reactions and hydrogenation drives the hydrothermal liquefaction; this gives the possibility to narrow down the product spectrum in comparison to other "dry" cleavage methods, towards a higher yield of e.g. catechols.

Techno-economic Assessment of Integrated Hydrothermal Liquefaction and Combined Heat and Power Production from Lignocellulose Residues

“…Both compounds are lignin derivatives, where seven out of the top ten compounds are intermediates from lignin degradation mechanisms. This falls in line with reports in literature of phenolic and aromatic structures resistance for further degradation in non-catalytic conditions after the initiation of lignin hydrolysis reactions by subcritical water [52]. Cellulose and hemi-cellulose originated compounds were present at smaller quantities compared to their lignin counterparts.…”

Sub- and Supercritical Water Liquefaction of Kraft Lignin and Black Liquor Derived Lignin

“…The temperature and pressure of HTL are key process parameters because they affect reaction condition, such as density and the amounts of ionic compounds. In addition, the reaction temperature also influences certain reaction mechanisms and the kinetics of various competing reactions; subcritical water properties prefer ionic reactions, whereas gas-like density in a supercritical water condition favors radical reactions [22,107,117]. However, it is possible to enhance ionic reactions under supercritical conditions by increasing the fluid density [118].…”

Hydrothermal Depolymerization of Biorefinery Lignin-Rich Streams: Influence of Reaction Conditions and Catalytic Additives on the Organic Monomers Yields in Biocrude and Aqueous Phase

“…Lignin is one of the main constituents of lignocellulosic biomass, and making up to 15-35 wt. % of the total organic matter weight, carrying also the highest specific energy content compared to cellulose and hemicellulose [1][2][3]. The global amount of lignin estimated in the Earth's surface is 300 billion tons and annually increases by around 20 billion tons [4].…”