Preparation And Catalytic Performance Of Sulfonated Carbon-Based Solid Acid

At present, one of the most widely used acid catalysts in the biodiesel synthesis is concentrated sulfuric acid, its main shortcomings are difficulty in separation of product and catalyst, strong corrosion to reaction device and environmental pollution. To solve the above problems, solid acid catalysts were introduced to substitute homogeneous catalysts, such as molecular sieve, ion exchange resin and super-acid etc. Although those catalysts solved the above problems, they are exposed of obvious shortcomings in use, such as high cost, low catalytic activity and low stability. At present, raw materials for biodiesel preparation were inedible fatty oil or waste edible oil. With the limit of catalyst, those raw materials must be pre-esterified, that is, to esterify the high content free fatty acid. Thus it will increase the cost as well as prolong the production time, which will not conductive to the biodiesel promotion. Therefore, investigation on preparation and application of a novel and cheap biodiesel solid acid catalyst were of great realistic meaning and practical value.This thesis took rich resources and renewable corn stalk as raw material, carbon-based solid acid catalyst was prepared by carbonization-sulfonation method. Effects of preparation parameters on catalytic properties were discussed. Results indicated that carbonation and sulfonation temperature, carbonation and sulfonation time had significant effects on catalytic activity of carbon-solid acid catalyst. The optimum conditions were obtained as follows: carbonation temperature 300~400℃, carbonation time 10h, sulfonation temperature 140~160℃, sulfonation time 7h.Fourier transformation infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy analysis (XPS) and acid density were taken to characterize carbon-based solid acid catalyst. The result showed that sulfuric acid group (-SO3H) content in the optimal condition catalyst reached as high as 13.9%. X-ray diffraction (XRD) and scanning electron microscopy (SEM) showed that solid acid catalyst had amorphous carbon structure, and porous carbon particles were flake or layered. The specific surface area was 140 m2/g, showed that catalyst is porous structure. Thermo-gravimetric analysis (TGA) result showed that carbon-based solid acid catalyst has good thermal stability under 260℃.The results indicated that solid acid catalyst made from corn stalk can be reused 8 times in esterification. The catalytic activity decreased rapidly after 8 times, and the solid acid catalyst can be regenerated after sulfonation, which has close acid density and catalytic activity with new catalyst.The effect on esterification of oleic acid and ethanol with various factors were studied through single factor experiment and orthogonal experiment, and optimum conditions were obtained as follows: catalyst dosage 8%, reaction time 10h, ethanol-acid molar ratio 6:1, and reaction temperature 90℃.Compare catalytic activity and acid density of catalysts made from D-glucose, sucrose, starch and corn stalk. Results indicated that the activity and acid density had the same sequence: corn stalk>D-glucose>sucrose>starch. There was a positive correlation between catalytic activity and acid density.