LITMIR.BIZ

Scheme 4.3 Reaction scheme for glycerol acetalization with acetone [29].

Similarly, Chandrakala et al. have used sulfonic acid-modified heterogeneous carbon for the conversion of glycerol into TAG, a biofuel additive in two-step processes. The catalyst was synthesized by controlled carbonization and sulfonation of glycerol at 220 °C. The complete reaction scheme is shown in Scheme 4.4. The first step involves the esterification of glycerol in the presence of acetic acid and sulfonic acid functionalized heterogeneous carbon catalyst which was followed by acetylation of glycerol ester mixture with acetic anhydride using the same catalyst. The catalyst is reusable for up to five cycles without appreciable loss in its activity. The complete process is economically effective because of a highly stable and reusable carbon catalyst [30]. Higher esters (di- and tri-esters) of glycerol have a high boiling point, good miscibility with traditional fuel, and high octane and cetane numbers, so they are chosen as fuel components [31].

Sun et al. have explored the potential of rod-like carbon-based sulfonic acid-modified ionic liquids for selective glycerol esterification with the help of acetic acid or lauric acid into valuable products. The formation of catalyst takes place in two steps. The first step involves the hydrothermal treatment of glucose and cyanamide at 160 °C. In the second step, the hydrothermally synthesized nitrogen-enriched carbon nanorods undergo quaternary ammonization in the presence of 1,3-propanesultone and anion substitution with HSO₃CF₃. The final catalyst is labeled as [PrSO₃HN][SO₃CF₃]/C nanorods. The performance of the catalyst was evaluated for selective glycerol esterification using acetic acid and lauric acid. Glycerol in the presence of acetic acid leads to the formation of TAG and with lauric acid, MAG, and DAG was formed as shown in Figure 4.7. The catalyst [PrSO₃HN] [SO₃CF₃]/C nanorods show superior catalytic performance as compared to propylsulfonic acid-modified SBA-15, Amberlyst-15, p-toluenesulfonic acid, and [PrSO₃HN][SO₃CF₃] functionalized carbonaceous framework [32].

Table 4.3 Performance of different carbon catalysts for different valorization processes.