# Eco Valorization of _Eucalyptus globulus_ Bark and Branches through Liquefaction
## 3 Results and Discussion
### Liquefaction Optimization  
The most important parameter in the liquefaction reaction is the catalyst in use, which allows the reaction to be developed at lower temperatures and pressures than non-catalyzed liquefaction. Catalyst promotes both the degradation of cellular macromolecular compounds and their reactions with the liquid medium, favoring their dissolution. In this work, sulfuric acid was used as an acid catalyst and potassium hydroxide as a basic catalyst. Figure 2 shows the liquefaction yields for the bark (a) and branches (b) in both alkaline and acid media. The results show that the acid catalyzed process led to higher liquefaction yields than for the base-catalyzed one for both bark and branches. The best liquefaction yield for bark in acid medium was around 60% for 60 min reaction time, while in basic medium, the highest yield of about 50% was obtained at 120 min reaction time. In relation to branches, the results were different since liquefaction percentage was higher with 61.7% for acid medium obtained at 60 min and 53.2% for basic medium at the same time. Alkaline medium is generally favorable for banks with high suberin content since it is known that suberin can be depolymerized by alkaline-catalyzed treatment in alcohol media as highlighted previously [18; 32; 50]. For instance, [PERSON] et al. [50] reported a liquefaction yield of around 60% for KOH and 30% for sulfuric acid catalyzed liquefaction of _Pseudotsuga menizeizeizi_ bark, which is a bark with high suberin content. The lower liquefaction yield obtained here for basic catalysis is probably due to the very low suberin content of eucalyptt bark (<1%, [15]). Similar results were reported previously by other researchers [67; 68]. Figure 3 presents the variation of the liquefaction yield in relation to the size of the particles. Results show that the particle size has no significant influence on the liquefaction yield and for the samples of bark and branches a similar yield of 61.6% and 56.0%, respectively, could be achieved using fractions of <80 mesh. The size of the samples is generally important when the chemical composition of the various fractions is very different, which happens, for example, in the bark of _Pseudotsuga menizeisi_, which has a higher cork content in the larger particles than in the smaller ones. Results presented by [PERSON] et al. [63] show that the chemical composition of fine (F, <0.180 mm), medium (M, 0.250-0.450 mm),  
and coarse (C, \(>\)2 mm) fractions differs mostly in the extractive content and there is only a smaller percentage of lignin and therefore higher holocellose content in the coarse fraction. That work demonstrated that, theoretically, the coarse bark fraction would be more easily liquefied than the fine fraction by looking only at the chemical composition. However, in finer fractions, the reaction should be faster due to the better accessibility of the chemicals to the material. This equilibrium might justify the results presented in Figure 3, because there is a slightly higher liquefaction yield in the coarse (\(<\)40 mesh) fraction, decreasing further for the 60-80 mesh fraction, and increasing for the fine (\(<\)80) fraction. The best temperature to achieve the highest liquefaction was studied for 60 min reaction time. Figure 4 shows the liquefaction yields for reaction temperatures between 140 \({}^{\circ}\)C and 200 \({}^{\circ}\)C for both bark and branches. The best liquefaction yields were obtained for the bark at 180 \({}^{\circ}\)C (61.6%) and for the branches at 160 \({}^{\circ}\)C (62.2%). The different results between bark and branches can be attributed to the somewhat different chemical composition of both forest wastes. The poorer results obtained at 200 \({}^{\circ}\)C are probably due to some condensation reactions between the liquefaction products. Similar results were reported previously for the liquefaction of cork [69]. According to [PERSON] and [PERSON] [70], re-condensation happens at higher temperatures when both the cellulose and the lignin are liquefied.