# Eco Valorization of _Eucalyptus globulus_ Bark and Branches through Liquefaction
###### Abstract
In another study, it is concluded that by applying pre-treatment, in a biorefinery context, _Eucalyptus globulus_ stumps (with 11.9% extractives and 22.2% Klason lignin) could be successfully delignified and, therefore, used for the production of cellulosic pulp [17]. Regarding the chemical composition of _Eucalyptus globulus_ stumps, it was found that the amount of ash in piled industrial stumps (19.2%) is much higher than in fresh stumps (3.5%) and that the extractive content is different in fresh stumps (7.5%) and on stacked stumps (4.1%) [16]. Recently, a study on the structural composition of lignin from _Eucalyptus globulus_ bark revealed a H:G:S ratio of 1:26:73 [18]. This study also showed some structural units (\(p\)-counaric acid, coniferylic acid, and sinapylic acid) in addition to the three main groups mentioned above. The identification of the components present in the extractives have also motivated several studies. Recently, 202 compounds were found in the lipophilic fraction of _Eucalyptus globulus_, of which, 189 were fully identified [19]. The most studied hydrothermal liquefaction takes places at high temperatures (200-370 \({}^{\circ}\)C) and pressures (4-20 MPa). However, at these temperatures and pressures, the obtained liquid has very small molecules and is mainly produced as a source for liquid fuels [20]. In the last few years, special attention has been given to liquefaction at lower temperatures and pressures where the resulting liquid has higher molecules than can easily be repolymerized into value added material. Since lignocellulosic materials are the most abundant natural material, many studies on their liquefaction from agricultural or forest residues have been done, such as wheat straw [21], corn stover [22; 23; 24; 25], soybean straw [26], cotton stalks [27; 28], olive pits [29], pine bark [30; 31], _Quercus cerris_ bark [32], cork [33], microalgae [34], lignin from enzymatic hydrolysis [35] and pure cellulose [36], pine wood sawdust [37], almond husk [38], rice husk [24; 39], apricot stone [40], peanut shell [41], walnut shells [42], agricultural residues (rice straw, wheat straw, corn stover, and oilseed rape straw) [24], wheat straw [43], corn husks [44]; digested sewage sludge, hemp stalk hurd, and sugar beet pulp [45] were reported. The growing interest in the study of liquefaction of agroforest residues is due to these processes allowing the manufacture of value-added products similar to those traditionally made from petroleum. This is just one more path to substitute petroleum-based products, similar to what's been done with liquid and solid biofuels [1]. In biomass liquefaction at relatively low temperatures and pressure, the most used solvents are phenol [46], ethylene glycol (EG) [23; 47], polyethylene glycol (PEG) [27], and glycerol [20; 26; 36]. The function of the solvent in liquefaction is to dissolve the liquefaction products and prevent them from re-polymerization [20]. In the absence of a catalyst, liquefaction conditions require high pressure and temperatures (300-500 \({}^{\circ}\)C). In contrast, in the presence of a suitable catalyst, and at atmospheric pressure, the temperature range required for liquefaction of biomass is around 180 \({}^{\circ}\)C [46]. Both basic and acid catalysts can be involved in liquefaction reactions. The most used acid catalysts are organic acids, such as oxalic acid, \(p\)-toluenesulfonic and methanesulfonic acids, and inorganic acids, such as hydrochloric, sulfuric, or phosphoric acids [48; 49]. Sulfuric acid was identified as the acid with the best catalytic efficiency [20]. The most common basic catalysts are potassium hydroxide [50] and sodium hydroxide [51]. The liquefaction of lignocellulosic materials comprises a complex set of reactions involving the three components of the plant cell wall: lignin, hemicellulose, and cellulose. Such reactions are basically of three types: esterification, etherification of cellulose, or lignin derivatives and different degradation reactions of biomass [22].