Heterogeneous acid catalysts based on sulfonated graphene like structures produced from bio-oil

In this work, bio-oil (BO) obtained from the flash pyrolysis of sugar cane straw was reacted with concentrated sulfuric acid (weight ratios H2SO4: BO of 1.8; 3.6; 9.2 and 18.4 at 120 °C for 2 h) to produce graphene-like structures containing -SO3H groups. RAMAN, FTIR, TG, potentiometric titrations and SEM suggests that the reaction of BO with H2SO4 starts with dehydration process, carbonization followed by sulfonation (Figure 1). A very intense G band in the Raman spectra suggested the formation of graphene structures with very few defects. The acidity strength of catalysts was potentiometrically measured with n-butylamine titration. All the materials presented strong acid sites (Ei >300 mV). The amount of acid sites was 0.02, 0.11, 0.26 and 0.30 mmol.g-1 for BS1.8, BS3.7, BS9.2 and BS18.4 samples, respectively. The esterification reactions of oleic acid with methanol were carried out at 100 °C during 3 h (oleic acid/methanol molar ratio 1:10, catalyst 7.5 %). Conversions of 90, 98, 100 and 100 %, were achieved, in the presence of BS1.8, BS3.7, BS9.2 or BS18.4, respectively. Thus, bio-oil sulfonation proved to be effective on carbonization and –SO3H groups’ formation, producing acid sites with sufficient acidity to convert fatty acids to esters.