# Single-Stage Fractionation of Vine Shoots Using Microwave Heating
## 3 Results and Discussion
### Fractionation  
Treatments performed in media containing water/1-butanol mixtures enable the selective separation of hemicelluloses in the aqueous phase and lignin in the organic one [19; 20; 21; 24]. Additionally, the organic phase can be processed to recover the organic solvent to separate the lignin as a solid material for further valorization [37]. Figure 4 shows the results achieved in fractionation treatments performed at different temperatures in terms of the variables %SY, %C, %Hr and %D defined above. As a general trend, %SY decreased steadily with temperature, from more than 80% at 145 \({}^{\circ}\)C to 42.7% at the highest temperature assayed, mainly due to the solubilization of hemicelluloses and lignin. %Hr was near 100 at 190 \({}^{\circ}\)C, although significant hemicellulose solubilization (74.5%) was reached at 175 \({}^{\circ}\)C. At the mildest temperature assayed, %Hr hardly reached 13%. Similarly, %D increased with temperature, reaching values of 36% and 54.3% at 175 and 190 \({}^{\circ}\)C, respectively. The cellulose content of the solids from fractionation (measured by %C) increased with temperature due to the lower susceptibility of this fraction to hydrolysis reactions. Figure 4: Solid yield (%SY), percentage of cellulose in the processed solid (%C), percentage of hemicellulose removal (%H\({}_{r}\)) and percentage of delibification (%D) achieved in fractionation treatments performed at diverse temperatures. Figure 3: Average composition of water-extracted vine shoots, expressed as g of component per 100 g oven-dried material. The highest value of %C (71%) was reached at the highest temperature assayed. The type of effects achieved by the treatments were in the range reported for vine shoot fractionation using other processing methods. [PERSON] et al. [4] employed a two-stage method for vine shoot utilization: in the first step, the substrate was treated with dilute sulfuric acid at 120 \({}^{\circ}\)C for 30 min to dissolve 68.7% of the hemicellulose fraction, achieving a solid containing 75% cellulose with poor susceptibility to enzymatic hydrolysis. Obtaining a suitable hydrolysis substrate required a further treatment with 2% NaOH at 100 \({}^{\circ}\)C, conditions under which an almost complete conversion was obtained, no matter of the high lignin content (31.9%) of the material. [PERSON] et al. [17] also needed two chemical treatments for achieving a complete fractionation vine shoots: the first step, conducted to remove hemicellulose, corresponded to a hydrothermal reaction conducted at 201 \({}^{\circ}\)C; whereas the second one consisted of a treatment with 8% NaOH at 124 \({}^{\circ}\)C, which provided a solid containing 55.4% cellulose and 33.8% lignin. [PERSON] et al. [38] subjected vine shoots to one-stage processing in alkaline media (containing NaOH or mixtures of Na\({}_{2}\)S and NaOH) or organic solvents (ethanol or ethylene-glycol), looking for cellulose-enriched solids. In this study, the utilization of hemicellulose was not considered. The cellulose and lignin contents of the treated solids were as follows (method/cellulose wt%/l lignin wt%: NaOH/70.00/24.07; Na\({}_{2}\)S + NaOH/73.74/17.18; ethanol/53.70/31.92; ethylene glycol/60.22/35.26). Concerning the solubilization of hemicellulose, Table 1 shows the effects of the fractionation treatment on the composition of the hemicellulose-derived compounds present in the aqueous phase. The NVC fraction, calculated as the joint contribution of OS, acetyl groups (AG), monosaccharides and ONVC, increased with temperature up to 175 \({}^{\circ}\)C, and then decreased, which is ascribed to the generation of volatile compounds (such as acetic acid and furans) from their respective non-volatile precursors.