Preparation and esterification performance of sulfonated coal-based heterogeneous acid catalyst for methyl oleate production

A series of coal-based heterogeneous acid catalysts are prepared by partial carbonization followed by sulfonation approach and the performances in esterification for methyl oleate production are conducted. Characterization methods of XRD, N-2 adsorption-desorption, SEM, TG, FTIR, EDX, acid density tests and. Hammett indicator method are carried out to reveal the physical and chemical characteristics of the prepared catalysts. Catalyst with the highest acid density of 1.09 mmol g(-1) could be prepared under the condition of carbonization temperature at 350 degrees C for 2 h and sulfonation with concentrated sulfuric acid at 135 degrees C for 4 h. Acid value reduction of 97.29% on oleic acid through esterification with methanol, which is catalyzed by this coal-based heterogeneous acid, could be achieved under the optimized condition of 10 wt.% catalyst dosage, molar ratio of methanol/oleic acid of 10, reaction temperature at 67 degrees C and reaction duration of 4 h. Characterization results demonstrate that carbon in the catalyst, which is composed of aromatic carbon sheets with -COOH and -SO3H groups, is in amorphous structure and its acid strength is 3.3 < pK(a) < 0.8. Meanwhile, this catalyst could provide favorable thermal stability high to 220 degrees C and retain satisfactory catalytic activity after five cycles. In addition, catalytic capability could be reactivated with the acid value reduction efficiency of 95.30% after the fifth re-usage. (C) 2016 Elsevier Ltd. All rights reserved.