Synthesis of 4-aminobenzenesulfonic acid functionalized carbon catalyst through diazonium salt reduction for biodiesel production

A series of carbon catalysts are synthesized through the arylation diazonium salt reduction approach from coal to catalyze esterification of oleic acid with methanol for biodiesel production. Under the activated carbon preparation temperature of 900 °C, mass ratio of 4-aminobenzenesulfonic acid to activated carbon of 6 and arylation temperature of 45 °C, the synthesized carbon catalyst gains the surface area and pore volume of 629.3 m2 g−1 and 0.29 cm−3 g−1, respectively. Besides, the carbon catalyst possesses abundant and strong active sites with the 4-sulfophenyl group density of 0.97 mmol g−1 and acid strength of 0.8 < pH < 3.3. Catalytic capability of the carbon catalyst, which is synthesized under the above optimized condition, in esterification is stronger than the commercial Amberlyst-15, where the maximum efficiency achieves 95.04% with the carbon catalyst added mass percentage of 12%, molar ratio of methanol to oleic acid of 10, esterification duration of 4 h and esterification temperature of 65 °C. Due to leaching of the 4-sulfophenyl groups, esterification efficiency declines to 77.63% for the fifth reused cycle of the carbon catalyst. Meanwhile, the regenerated carbon catalyst supplies the esterification efficiency of 86.05%. Chemical composition of the produced biodiesel is identical to pure methyl oleate and its fuel properties are in accordance with ASTM D 6751.