## 3 Results and Discussion
### Energy Content
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{2}{c}{**Phenolic**} & \multicolumn{2}{c}{**C-OP**} & \multicolumn{2}{c}{**L-OP**} & \multicolumn{2}{c}{**P-OP**} \\ \cline{3-8} \multicolumn{2}{c}{**Compound**} & \multicolumn{2}{c}{**OM 1**} & \multicolumn{2}{c}{**OM 2**} & \multicolumn{2}{c}{**OM 1**} & \multicolumn{2}{c}{**OM 2**} & \multicolumn{2}{c}{**OM 1**} & \multicolumn{2}{c}{**OM 2**} \\ \hline \multirow{2}{*}{**Hydroxyprosional**} & Free & 207.08 \(\pm\) 13.95\({}^{\mathrm{c}}\) & 173.67 \(\pm\) 13.68\({}^{\mathrm{c}}\) & 573.43 \(\pm\) 59.62\({}^{\mathrm{a}}\) & 504.73 \(\pm\) 27.67\({}^{\mathrm{b}}\) & 81.62 \(\pm\) 20.98\({}^{\mathrm{d}}\) & 26.54 \(\pm\) 8.35\({}^{\mathrm{e}}\) \\  & Bound & 17.35 \(\pm\) 6.03\({}^{\mathrm{c}}\) & 16.44 \(\pm\) 4.70\({}^{\mathrm{c}}\) & 78.51 \(\pm\) 8.70\({}^{\mathrm{a}}\) & 15.99 \(\pm\) 1.53\({}^{\mathrm{c}}\) & 43.14 \(\pm\) 9.85\({}^{\mathrm{b}}\) & 11.93 \(\pm\) 3.69\({}^{\mathrm{c}}\) \\ \hline \multirow{2}{*}{**Tynosol**} & Free & 51.21 \(\pm\) 3.01\({}^{\mathrm{b}}\) & 65.89 \(\pm\) 6.91\({}^{\mathrm{a}}\) & ND & ND & ND & 35.48 \(\pm\) 1.87\({}^{\mathrm{c}}\) & 20.75 \(\pm\) 3.48\({}^{\mathrm{d}}\) \\ \hline \multirow{2}{*}{**Protocatechic acid**} & Bound & 10.30 \(\pm\) 1.17\({}^{\mathrm{b}}\) & 8.38 \(\pm\) 1.02\({}^{\mathrm{b}}\) & ND & ND & 15.73 \(\pm\) 1.32\({}^{\mathrm{a}}\) & 10.09 \(\pm\) 1.03\({}^{\mathrm{b}}\) \\  & Free & 21.92 \(\pm\) 1.71\({}^{\mathrm{a}}\) & 8.79 \(\pm\) 1.25\({}^{\mathrm{a}}\) & 23.63 \(\pm\) 3.10\({}^{\mathrm{a}}\) & 15.14 \(\pm\) 0.85\({}^{\mathrm{b}}\) & 14.01 \(\pm\) 0.58\({}^{\mathrm{b}}\) & 0.51 \(\pm\) 0.12\({}^{\mathrm{d}}\) \\  & Bound & 25.15 \(\pm\) 2.15\({}^{\mathrm{b}}\) & 16.61 \(\pm\) 2.35\({}^{\mathrm{d}}\) & 40.71 \(\pm\) 5.23\({}^{\mathrm{a}}\) & 23.10 \The values of HHV, moisture and pH were measured to support the stones fraction application as solid biofuel. Besides, its character, being free of impurities (oil and low-weight particles), guarantees a better and safer combustion performance for this olive pomace fraction. In the future, other compounds of stones (ash, chlorine, nitrogen, potassium, magnesium and phosphorus) need to be quantified in order to ensure its quality as a solid biofuel [12], as well as the possible use of binders and additives to improve the stability and the combustion characteristics of the stones fraction [68]. Evaluation of the Fractionation Valorisation Approach for Olive Pomace in the Centre Region of Portugal: Case Study  
The present fractionation process has the potential to be a promising strategy for the whole valorisation of crude olive pomace at a large scale, due to being cheaper and more efficient regarding water and energy usage. To demonstrate the potential of the fractionation process proposed, we have considered the situation in the centre region of Portugal (third major olive oil producer region in Portugal), which represented around 15% of the national olive oil production in 2018 [35]. According to data from Instituto Nacional de Estatistica (INE) [35], the production of olives used for olive oil extraction was of 62,280 tonnes in the centre region. It is estimated that approximately 35-40 kg of olive pomace is produced per 100 kg of olives [64], or, according to data of the most significant world producing regions of olive products (Andalusia), it represents approximately 65% of the initial weight [13]. So, at least 21,978 tonnes of crude olive pomace was generated in 2018, only in the centre region of Portugal. Assuming the recovery of 80% of crude olive pomace through the selective collection in the centre region of Portugal, over 17,500 tonnes of crude olive pomace could be used to produce, on average: (1) 460 tonnes of enriched phenolic-mineral-sugar extract (liquid fraction) with a very significant recovery of hydroxytyrosol (\(\sim\)53%), (2) 3440 tonnes of antioxidant fibre powder (pulp fraction) and also (3) 1200 tonnes of stones fraction with an HHV of about 19 MJ/kg that could be applied as solid biofuel (Figure 4).