# Influence of Hydrothermal Carbonization on Catalytic Fast Pyrolysis of Agricultural Biomass
## 4 Conclusions  
In general, hydrothermal carbonization influences subsequent fast pyrolysis in a couple of ways: firstly, a positive influence is the decrease in oxygen content as a result of HTC; this causes the presence of fewer oxygen-containing compounds in the pyrolysis oil, which are responsible for the poor characteristics of the pyrolysis oil as a liquid fuel.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \(\mathbf{R}^{2}\) & \(\mathbf{\mathit{E_{a}}}\) & \(\mathbf{ln\,A}\) & \(\mathbf{A}\) \\ \cline{2-6}  & & **kJ/mol** & **1/s** & **1/s** & **1/min** \\ \hline Miscanthus (Raw) & 0.9454 & 70.25 & 10.619 & 4.09 \(\times\) 10\({}^{4}\) & 6.82 \(\times\) 10\({}^{2}\) \\ \hline Miscanthus + 10\% CaO & 0.9909 & 86.75 & 13.594 & 8.01 \(\times\) 10\({}^{5}\) & 1.34 \(\times\) 10\({}^{4}\) \\ Miscanthus + 20\% CaO & 0.9717 & 74.48 & 11.774 & 1.30 \(\times\) 10\({}^{5}\) & 2.16 \(\times\) 10\({}^{3}\) \\ \hline HTC Miscanthus 180 \({}^{\circ}\)C & 0.9452 & 88.83 & 14.064 & 1.28 \(\times\) 10\({}^{6}\) & 2.14 \(\times\) 10\({}^{4}\) \\ HTC Miscanthus 200 \({}^{\circ}\)C & 0.9399 & 101.10 & 16.087 & 9.69 \(\times\) 10\({}^{6}\) & 1.62 \(\times\) 10\({}^{5}\) \\ HTC Miscanthus 220 \({}^{\circ}\)C & 0.9530 & 91.33 & 14.556 & 2.10 \(\times\) 10\({}^{6}\) & 3.49 \(\times\) 10\({}^{4}\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Activation energy and pre-exponential (frequency) factor for fast pyrolysis of Miscanthus.  
Secondly, a part of inorganics is removed since an ash yield smaller than 1.0 is typically achieved, even for low residence times in HTC. This is important mainly due to the potentially detrimental influence of inorganics on the combustion properties of the solid residues (char), which is necessary for generating the heat required for fast pyrolysis. In many fast pyrolysis units, such combustion is performed in a fluidized bed, where agglomeration of the bed could be an important issue. Furthermore, improved grindability should be named as an important factor in favor of HTC as a pretreatment method for fast pyrolysis. However, this comes at a price of smaller quantities of volatiles available for pyrolysis, as a part of volatile matter is removed during HTC. An increase in activation energy of pyrolysis has been observed as a consequence of HTC treatment. Activation energy also decreased with an increasing share of the CaO catalyst. Further research should involve confirmation of the positive effects of HTC and addition of the catalyst on the properties of pyrolysis oil.  
Conceptualization: E.B., A.P., P.O. and G.B.; methodology: A.B., E.B. and P.O.; validation: H.P.-K., K.M. and A.A.; formal analysis: L.N. and A.B.; investigation: L.N., K.M. and M.W.; resources: E.B., A.P. and G.B.; data curation: K.M.; writing--original draft preparation: L.N., V., C.A.-B. and M.W.; writing--review and editing: [PERSON], [PERSON] and [PERSON]; visualization: [PERSON]; supervision: [PERSON], [PERSON], [PERSON], P.O. and [PERSON]; project administration: [PERSON], A.P., K.M. and [PERSON]; funding acquisition: L.N. All authors have read and agreed to the published version of the manuscript.  
Financial support of this work from the National Science Centre, Poland--project no. 2019/33/N/ST8/02641, is gratefully acknowledged.  
Not applicable.  
The authors declare no conflict of interest.