# Carbon-Based Catalysts for Biodiesel Production--A Review
## 3 Biomass Precursors
The yield of the three catalysts carbonised at three different temperatures can be seen in the Figure 11. The catalyst carbonised at 675 \({}^{\circ}\)C gave the highest yield of 18.9 wt.%, and this catalyst provided the right balance between high surface area and high acid site density. A high pressure (P) and temperature (T) transesterification reaction was carried out at 150 \({}^{\circ}\)C and 1.52 MPa. The reaction was carried out for 3 h and the yield was 44%, which is a marked improvement over the previous result presented in Figure 11. Upon evaluation of the reusability of the catalyst, it was found that the catalyst retained little to no activity (0.9 wt.%) after the first run, and this was due to acid site leaching. [PERSON] and [PERSON] [58] completed a further investigation using the biochar carbonised at 675 \({}^{\circ}\)C, where an improvement in the reusability of the catalyst was observed. The catalyst was prepared in a  
Figure 11: Transesterification yield of biochar catalyst. \begin{table}
\begin{tabular}{l c c c c c c c c c} \hline \hline \multirow{3}{*}{**Catalyst**} & \multirow{3}{*}{\begin{tabular}{c} **Carbonisation** \\ **Temperature** \\ **\end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} **HCI** \\ **Treatment** \\ **\end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} **Surface** \\ **Area** \\ **(SA) before** \\ **Subplanation** \\ **m\({}^{2}\)/g** \\ **m\({}^{2}\)/g** \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} **Decrease in** \\ **SA after** \\ **Sulphation** \\ **m\({}^{2}\)/g** \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} **Pore Size** \\ **before** \\ **Sulphation** \\ **m\({}^{2}\)/g** \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} **Total Pore** \\ **Volume** \\ **after** \\ **Subplanation** \\ **m\({}^{3}\)/g** \\ \end{tabular} } \\ \hline \begin{tabular}{l} Biochar \\ [57] \\ [57] \\ [57] \\ [58] \\ [59] \\ \end{tabular} & 450 & No & 204 & 1.9 & 99 & 2.6 & - & 0.01 & 2.6 \\ \begin{tabular}{l} Biochar \\ [57] \\ [57] \\ [58] \\ [59] \\ \end{tabular} & 675 & No & 668 & 640 & 4 & 2.2 & 2.2 & 0.35 & 1.2 \\ \begin{tabular}{l} Biochar \\ [57] \\ [58] \\ [59] \\ \end{tabular} & 875 & No & 1469 & 1411 & 4 & 2.2 & 2.2 & 0.71 & 0.5 \\ \
\begin{tabular}{l} Biochar \\ [58] \\ [59] \\ \end{tabular} & 675 & Yes & 990 & 949 & 4 & 3.2 & 3.2 & 0.85 & 2.0 \\
\begin{tabular}{l} Peant \\ shell \\ [59] \\ \end{tabular} & 450 & No & - & 12 & - & - & 39.3 & - & 6.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Catalyst characterisation results for the various biochar catalysts. similar way to method B described previously with the addition of one extra step--before sulphonation, the catalyst was treated with 0.1 M HCl. Catalyst characterisation results can be found in Table 5.  
A high pressure and temperature transesterification reaction was carried out at 150 \({}^{\circ}\)C and 1.5 MPa. The yield achieved was 48 wt.% presented in Figure 11, which is very promising for biodiesel production. The reaction yield only decreased by 8 wt.% upon reuse of the catalyst. This is a substantial improvement in the reusability compared with previous biochar catalysts. [PERSON] et al. [59] produced a biochar-derived catalyst that was superior to all other catalysts discussed in terms of yield and reusability. Waste peanut shells were used as a biomass feedstock for a biochar catalyst. The waste peanut shells were carbonised at 450 \({}^{\circ}\)C and sulphonated with conc. H\({}_{2}\)SO\({}_{4}\). Table 5 contains catalyst characterisation data. The transesterification of cottonseed oil was used to assess the catalytic performance of the peanut shell catalyst. The optimum reaction conditions were determined to be as follows; methanol: oil molar ratio of 9:1, and a reaction temperature of 85 \({}^{\circ}\)C. Under the stated reaction conditions, a yield of 90% was achieved. The catalyst showed good stability. However, a gradual loss in activity was observed, following five runs the catalyst still maintained approx. 50% of its activity (Figure 9).