## 2 Biofuels Classification
### Second-Generation Biofuels
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Characteristics**} & \multirow{2}{*}{**Biodiesel**} & \multicolumn{6}{c}{**Vegetable Oils**} & \multicolumn{2}{c}{**Biotechnol**} & \multicolumn{2}{c}{**Bio-ETBE**} \\ \cline{3-10}  & & \multicolumn{2}{c}{**Sunflower**} & \multicolumn{2}{c}{**Rapeseed**} & \multicolumn{2}{c}{**Soybean**} & \multicolumn{2}{c}{**Palm**} & \\ \hline
**LHV (MJ kg\({}^{-1}\))** & 37 & 39.6 & 37.4 & 36.8 & 36.5 & 27 & 36 \\
**Oxygen content (\% weight)** & 11 & 10 & 10.4 & 10.3 & 11.5 & 35 & 16 \\
**Iodine number** & 108.7 & 110-143 & 94-120 & 117-143 & 35-61 & - & - \\
**Cetane number** & 56 & 37 & 32-37.6 & 36-39 & 38-42 & 27 & - \\
**Octane number** & - & - & - & - & - & 113 & 110 \\
**Flash point C\({}^{\circ}\)** & 160 & 274 & 246 & 254 & - & 13 & - \\
**Cloud point C\({}^{\circ}\)** & \(-\)2 & 7.2 & -3.9 & -3.9 & - & - & - \\
**Point of flow C\({}^{\circ}\)** & \(-\)9 & \(-\)15.0 & \(-\)31.7 & \(-\)12.2 & - & - & - \\
**Viscosity (cS0)** & 5.1 (20 \({}^{\circ}\)C) & 37.1 (38 \({}^{\circ}\)C) & 37 (38 \({}^{\circ}\)C) & 28.5–32.6 (38 \({}^{\circ}\)C) & 8.3 (38 \({}^{\circ}\)C) & 0.5 (20 \({}^{\circ}\)C) & \\
**State** & Liquid & Liquid & Liquid & Liquid & Liquid & Liquid & Liquid & Liquid \\
**Appearance** & Limpid & Limpid & Limpid & Limpid & Limpid & Limpid & Limpid \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physico-chemical characteristics of first-generation biofuels (adapted from [11] LHV: lower heating value; Bio-ETBE: bioethyl tert-butyl ether. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Characteristics**} & \multirow{2}{*}{**Biopsies**} & \multirow{2}{*}{
\begin{tabular}{c} **Bio** \\ **Hydrogen** \\ \end{tabular} } & \multicolumn{6}{c}{**Syngas**} & \multirow{2}{*}{**Bio-Oil**} & \multirow{2}{*}{**Biotechnol**} & \multirow{2}{*}{**Bio-DME**} & \multirow{2}{*}{**Bio-MTBE**} & \multirow{2}{*}{**Biobethanol**} & \multirow{2}{*}{**FT-Diesel**} \\ \cline{3-10}  & & & & & & & & & & \\ \cline{3-10}  & & & & & & & & & & \\ \hline
**LHV (MJ kg\({}^{-1}\))** & 23.3 & 10.05 & 42 & 10 & 12 & 18.5 & 19.5 & 28.3 & 35 & 36 & 42.9 \\
**Oxygen (\% weight)** & traces & & - & 45 & 34.7 & 35 & 18 & 22 & \\ Methane (\% weight) & 65 & & 2-4 & 4-6 & 124 & - & - & - & - & - \\ CO\({}_{2}\) (\% weight) & 40 & & 14-17 & 25-29 & 17-19 & - & - & - & - & - \\ HiS (\% weight) & 0.1 & & & & - & - & - & - & - & - \\ Cetane number & - & - & 02-1 & 0.7 & 2.5 & 10 & 5 & 57 & - & 17 & 74 \\ Octane number & - & 130 & - & - & - & 104.3 & - & 110 & 87 & \\
**Boiling temperature C\({}^{\circ}\)** & & \(-\)252 & & - & - & 65 & \(-\)23 & 55 & 118 & \\
**Flash point C\({}^{\circ}\)** & - & 585 & & - & - & 464 & 292 & - & 35 & 315 \\
**State** & Gaseous & Gaseous & Gaseous & Liquid & Liquid & Gaseous & Liquid & Liquid & Liquid \\
**Appearance** & Gaseous & Gaseous & & Limpid & Limpid & Gaseous & Limpid & Limpid & Limpid \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Physico-chemical characteristics of second-generation biofuels (modified from [11] LHV: lower heating value; Bio-DME: biodimethyl ether; Bio-MTBE: biomethyl tert-butyl ether; FT-Diesel.