## 4 Discussion and Conclusions  
The results of the present work clearly indicate the presence of multiple components in the biomass chars. The relation of such components with lignocellulosic constituents of biomass (lignin, cellulose and hemicelluloses) and the impact of biomass components on tar composition are now open to discussion. In a parallel work [22], where similar experimental procedures were applied to lignin, cellulose and hemicelluloses, a complex picture emerged. Fast pyrolysis of hemicellulose and cellulose produced light tars mainly made of anhydrous monosaccharides, while light tar from lignin pyrolysis included also important amounts of oxo-aromatics and PAHs. High molecular weight species were recovered in heavy tar produced at a high temperature from lignin and cellulose. Char was produced only from lignin. Its reactivity was rather low, with DTG peaks above 700 K. The least reactive char was produced at 2073 K in N\({}_{2}\). Results of the three biomasses investigated in the present work are summarized in Table 3. Results from [22] on the individual biomass components are summarized in Table 4. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Atmosphere** & **T (K)** & \begin{tabular}{c} **Light Tar** \\ **(GC-MS)** \\ \end{tabular} & \begin{tabular}{c} **Heavy Tar** \\ **(SEC)** \\ \end{tabular} & \begin{tabular}{c} **Char** \\ **DTG Peaks (K)** \\ \end{tabular} \\ \hline \multicolumn{5}{c}{_Walnut Shells_} \\ \hline N\({}_{2}\) & 1573 & \begin{tabular}{c} Anhydrous monosaccharides: 40\% \\ \end{tabular} & None & 720 \\ \hline CO\({}_{2}\) & 1573 & \begin{tabular}{c} Alphributes: 10\% \\ Light PAHs: 10\% \\ \end{tabular} & 650; 710 \\ \hline N\({}_{2}\) & 2073 & \
\begin{tabular}{c} Heavy PAHs: 60\% \\ Light PAHs: 30\% \\ Anhydrous monosaccharides: 5\% \\ Oxo-aromatics: 5\% \\ \end{tabular} & 820 \\ \hline CO\({}_{2}\) & 2073 &
\begin{tabular}{c} Light PAHs: 55\% \\ Oxo-aromatics: 20\% \\ Heavy PAHs: 15\% \\ \end{tabular} & (higher MW) & 760 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of results for walnut shells, pinewood and straw. The analysis of pyrolysis products from pyrolysis of WS, PW and ST is often not consistent with the results obtained for single lignocellulosic components in [22], as summarized in the following points:  
* In ref. [22], anhydrous monosaccharides were found to dominate tar from cellulose and hemicellulose. At odds, in the present work, anhydrous monosaccharides are scarce in ST, the biomass with the highest content of cellulose and hemicelluloses, and most abundant in tar from WS, the biomass with the largest fraction of lignin. * In ref. [22], PAHs were found to be the most abundant species in tar from lignin pyrolysis, especially in CO\({}_{2}\)-rich atmospheres. Consistently, in the present work, PAHs are present in tars from all the examined biomasses but are particularly abundant in WS tar. * In ref. [22], heavy tars were obtained from pyrolysis of both cellulose and lignin at high temperature. Consistently in the present work, they are produced from pyrolysis of all the examined biomasses at high temperature. * In [22], cellulose and hemicelluloses did not produce relevant char residues, while lignin did. Its char appeared to be constituted by one or two components. Differently, all the biomasses investigated in the present work produced char. Chars were quite different from each other in terms of combustion reactivity and appeared to be constituted by several components. After heat treatment in N\({}_{2}\) at 1573 K, the most reactive char was the one from ST, followed by WS and PW. However, the char of WS, the biomass with larger lignin content, appeared the most similar to the char produced from lignin in [22]. * In [22], lignin char had DTG combustion peaks in the range of 700-770 K. More severe heat treatment resulted in higher peak temperature values (lower combustion reactivity) and a higher degree of structural order/thermal annealing of the char.