Catalytic synthesis of benzoic esters with carbon-based solid acid from coal tar

A new carbon-based solid acid catalyst (C-SO₃H) was prepared by simultaneous crosslinking coal tar with benzaldehyde, hoist temperature-curing, sulphonation in sulfuric acid and was characterized by FT-IR, TG-DTG, XRD and neutralization potentiometric titration, and SEM techniques. The results indicated that there is the high density of SO₃H groups in forming amorphous coke consisting of polycyclic aromatic carbon sheets, and the acid value of catalyst was 3.01 mmol/g. The result of TGA indicated that carbon-based solid acid catalyst had considerable heat stability below 300°C.This new catalyst was used for preparation of benzoic esters, and the model esterification reaction of benzoic acid with butanol was systematic studied. The results showed that the best reaction conditions are as follows: catalyst dosage of 0.5g, n-butanol to benzoic acid mole ratio of 3.0:1, reaction time of 4h,and the esterification rate reached 99.2%, and it can be used for five times without loss of its activity. In summary, the advantage of the new carbon-based solid acid catalyst had the good reusability, non-causticity, less harmful to the environment, high catalytic activity and the product was separated easily.