# Carbon-Based Catalysts for Biodiesel Production--A Review
## 3 Biomass Precursors  
The conversion of biomass to effective and value-added catalytic material for biodiesel production makes use of a readily available and renewable feedstock that would usually be disposed of. The development of sulphonated carbon catalysts derived from waste biomass such as seed cake, nut husks and pyrolysis by-products will be the subject of this section. [PERSON] et al. [3] generated a sulphonated catalyst from the seed cake of Calophyllum Inophyllum (more commonly known as polanga). Polanga, an inedible tropical seed, was incompletely carbonised at 400 \({}^{\circ}\)C and the resulting powder was then sulphonated with concentrated H2 SO4. SEM analysis of the material revealed large grains with irregular shapes and rough edges. The carbon was determined to be amorphous comprised of aromatic sheets in random orientation. A one-step production of biodiesel (simultaneous esterification and transesterification) from polanga oil (15% FFA) was used to evaluate the catalytic ability of the sulphonated seed cake catalyst. The seed cake derived catalyst achieved a biodiesel yield of 99%. The reusability of the catalyst was also evaluated, as presented in Figure 9. For three consecutive uses, the catalyst retained good reusability after the third use the catalytic activity began to decrease substantially. As observed by some researchers, a combination of sulphur leaching [48] and catalyst poisoning by glycol [3] is believed to be responsible for the loss of activity. Figure 8: Acid content of D-glucose catalyst carbonised at different temperatures. Vegetable oil and petroleum oil asphalt is another form of biomass that has received attention for its potential catalytic ability for biodiesel production. [PERSON] et al. [49] prepared two solid acid catalysts by sulphonating vegetable and petroleum oil asphalt that was carbonised at 500-700 \({}^{\circ}\)C. Following sulphonation the vegetable oil asphalt derived catalyst was found to have a loose irregular structure of large pores, conversely the petroleum asphalt catalyst exhibited little to no pores. The reason for the difference in morphology is believed to be due to the composition of the petroleum oil, consisting of the heaviest hydrocarbon non-metallic elements, which lead to a high degree of graphitisation following carbonisation, whereas vegetable oil asphalt is comprised of mainly straight chain aliphatic hydrocarbon polymers leading to a much lower level of graphitisation. The acid site density and the average pore size are presented in Table 3. The sulphur content and pore size of the vegetable oil asphalt derived catalyst were substantially higher than that of the petroleum oil asphalt. The attachment of SO3H groups to non-graphitic carbon is more favourable than graphitic carbon leading to a higher acid site density. As well as a higher acid site density, the sulphonated vegetable oil asphalt exhibited a larger average pore volume than the petroleum oil catalyst allowing the reactants easier access to acid sites. Both the vegetable oil asphalt and the petroleum oil asphalt catalysts were assessed for their esterification and transesterification ability using a model waste oil (50% cottonseed oil and 50% oleic acid). A combined esterification and transesterification process was used with a catalyst loading of 0.3 wt.% and a molar ratio of methanol: oil of 20:9. The esterification was carried out at 140 \({}^{\circ}\)C for 2 h, and following the esterification, the FAME and water formed in the first step were removed, fresh methanol was re-added to the reaction and the transesterification reaction was carried out at 220 \({}^{\circ}\)C for 3 h. The esterification and transesterification conversion are presented in Figure 10. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Catalyst** & **Sulphur wt.\%** & **Average Pore Size nm** \\ \hline Vegetable oil asphalt & 7.1 & 43.9 \\ Petroleum oil asphalt & 3.6 & 2.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Sulphur content of oil asphalt catalysts.