# Carbon-Based Catalysts for Biodiesel Production--A Review
## 4 Economic and Operating Condition Assessment  
Table 7 compares the different CBAS catalysts discussed in terms of cost per kg, (the price given above does not represent bulk purchase prices and is for comparison purposes only) preparation conditions, operating conditions, reaction times, yield and reusability. Among the carbohydrate-derived catalysts, the carbonisation and sulphonation conditions are almost identical; carbonisation was carried out at between 400 and 450 \({}^{\circ}\)C for up to 15 h for all of the carbohydrate-derived catalysts. sulphonation conditions were typically 150-180 \({}^{\circ}\)C for 10-15 h with conc. H\({}_{2}\)SO\({}_{4}\) in the range of 10 cm\({}^{3}\) per gram of catalyst. In some cases, fuming sulphuric acid was used, giving an improved catalytic performance. The starch and glucose derived catalysts were relatively more economical than their sucrose and cellulose counterparts. The starch catalyst prepared by [PERSON] et al. [10] in particular shows excellent potential for commercial use. The catalytic activity of the starch catalyst is similar to that of concentrated H\({}_{2}\)SO\({}_{4}\) for both the esterification and transesterification reactions. The starch-derived carbohydrate achieved the highest conversion and highest rate of reaction of any of the carbohydrate catalysts produced. The reusability of the catalyst is key to its application in industry, as this will reduce production costs. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Catalyst** & \begin{tabular}{c} **Cost Per ks (9)** \\ **(Taken from Sigma Aldieck)** \\ \end{tabular}  & \ \begin{tabular}{c} **Carbonisation:** \\ **Temperature Time** \\ \end{tabular}  & **Sulphension Conditions** & **Reaction Conditions** &
\begin{tabular}{c} **Vide:  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Catalyst**} & **Cost Per kg (\(\mathbf{\Theta}\))** & **Carbonisation:** & **Subjunction Conditions** & **Reaction Conditions** & **Vield. Restriction** & **Reversibility** \\  & **(Linear from Sigma Aldrich)** & **Temperature Time** & & & & \\ \hline  & & & & & & \\ \multirow{3}{*}{Biochar A [21]} & \multirow{3}{*}{Waste wood} & 475\({}^{\circ}\)C & \multirow{3}{*}{Cenc. Its,SO\({}_{\mathrm{G}}\)} & \multirow{3}{*}{Reserification:} & \multirow{3}{*}{Reserification:} & \multirow{3}{*}{Reserification:} \\  & & & & & & \\ \cline{4-6}  & & & 150\({}^{\circ}\)C  
Biomass-derived catalysts have the advantage when it comes to economics, as the biochar is prepared from low-cost waste biomass feedstock. The catalyst synthesised from Calophyllum inophyllum seed cake by [PERSON] et al. [3] exhibited excellent catalytic properties and demonstrated reusability for three successive runs. The seed cake catalyst promotes a reduced raw material cost, whereas the starch catalyst exhibits greater reusability and the reaction takes place at milder conditions. Further investigation is required to determine the most economical catalyst. Of all the pyrolysis residue products that were investigated for their catalytic ability, the peanut shell biochar catalyst demonstrated the highest catalytic activity and the best reusability. The pyrolysis conditions used to produce this catalyst are mild in comparison with the other biochar catalysts discussed while the sulphonation conditions used are slightly harsher than those used in the starch or seed cake catalyst. Interestingly the ratio of concentrated H\({}_{2}\)SO\({}_{4}\) to catalyst is twenty times higher than that used for the starch and seed cake catalyst. It is not known whether this ratio is necessary or whether it was just decided arbitrarily, and this may be an important factor to consider in the cost of production if it is a requirement. The catalysts derived from pyrolysis products generally suffer with reusability issues when compared with carbohydrate-derived catalysts.