Optimized Preparation of Algal Carbon-Based Solid Acid Catalysts and their Esterification Performance
摘要
In this study, two carbonaceous solid acid catalysts are prepared from marine biomass (Sargassum and Enteromorpha) by phosphoric acid impregnation-pyrolytic carbonization-sulfuric acid functionalization. The effect of carbonization temperature (250, 350 and 450 °C) on the performance of the carbonaceous acid catalysts is studied. Furthermore, multiple test techniques are used to characterize the algal catalysts and their performance in the esterification of oleic acid (OA) and methanol (MeOH) to produce biodiesel is evaluated. The results show that carbonization temperature has a significant effect on the sulfonic acid density and activity of the catalysts. At 250 °C, the Sargassum- and Enteromorpha-based catalysts reach sulfonic acid densities of 1.27 and 0.95 mmol/g, respectively. Under the conditions of a molar ratio of MeOH to OA of 12, a catalyst dosage of 9 wt%, a reaction temperature of 64 °C and a reaction duration of 120 min, the OA conversion of the two catalysts reaches 95.6% and 92.5%, respectively. Compared with raw algal biomass, the chemical composition and morphological characteristics of the Sargassum- and Enteromorpha-based catalysts change significantly. The catalysts show the characteristics of amorphous materials, with –SO3H groups on the surface, and have good thermal stability up to 200 °C. However, due to the different structural and elemental content characteristics of Sargassum and Enteromorpha materials, the Sargassum-based catalyst shows enhanced catalytic performance in esterification.