| It is urgent to develop new recyclable energy sources to meet the gradually reducing of the energy sources. The biodiesel has been receiving more and more interesting for it is environment friendly, recyclable and has excellent performance compared to the traditional energy sources. The transesterification with methanol of triglycerides extracted from oilseeds yields so-called biodiesel , a clean biofuel. Since this reaction yields up to 14wt.-% glycerol as by-product, it's necessary to find some effect way to absorb it. Since glycerol is already a highly functionalized molecule, an advantageous outlet would be to use it as feedstock for the production of valuable oxygenates, such as dihydroxyacetone, which is an important intermediate compound in chemical synthesis and is applied widely in the cosmetic industry and medicine industry due to its skin pigmentation property.Activated carbon supported Pt-based catalysts has been broadly applied in the oxidation of alcohols with the environment friendly molecular oxygen as oxidant. But the platinum give the rate of oxidation of a primary alcohol function higher than that of a secondary alcohol, when associating platinum with p-electron metals such as bismuth, the selectivity towards the oxidation of the secondary alcohol function can be greatly improved. Besides, Au and Ag apply in the oxidation of alcohol widely. Based on these knowledge, we systematically studied the reaction of selective oxidation of glycerol to dihydroxyacetone with activated carbon supported Pt-based catalysts improved by Bi, Au and Ag. The results of the conversion of glycerol and the yield of DHA are better than that of the literatures. We also studied the separation of DHA from the reactants and got satisfying results. The results we got list below:In the first chapter, we reviewed the application of various catalysts in the oxidation of alcohols and various possible mechanisms and the development of the reaction of selective oxidation of glycerol to dihydroxyacetone.In the second chapter, we investigated the effect of activated carbon supported Pt-based catalysts with various promoters on the oxidation of glycerol to dihydroxyacetone , the effect of reaction conditions on the reaction and the possible mechanism of the reaction. It was found that the conversion of glycerol and the selectivity of dihydroxyacetone improved after the loading of Bi on supported Pt, and the 9% Pt-5% Bi gave by far the best results: the conversion of glycerol is 81.69% , the selectivity of dihydroxyacetone reached 40.24% and dihydroxyacetone yielded 32.87% when the reaction was operated at 55℃for 8 hours with the air flux 1200ml/min; given the other conditions unchanged, the conversion of glycerol is 100% and the selectivity and the yield of dihydroxyacetone both are up to 50.05%, which is much higher than the literature of yield 34%. The reaction may follow the dehydrogenation mechanism, the role of molecular oxygen may due to its oxidizing the H anion removed from the C-H bond.In the third chapter, we characterized the various catalysts we prepared, it was found that PtBi2 existed on the support and the BET surface area of the activated carbon reduced remarkably; The mesopore volume increased after activation by CeO2 and the promoting effect of CeO2 on the development of mesopore is significantly at lower temperature (680℃) but less effective at higher temperature. The dispersion of the catalysts varied randomly and the best catalyst gave the lower dispersion thus it was concluded that the proper dispersion gave the best performance of the catalyst.In the forth chapter, the separation and purification of dihydroxyacetone(DHA) from the partial oxidation product of glycerol by PUROLITE PCR (Ca) ion exchange resin were investigated. It was found that the dynamic permeable adsorption capacity and adsorption velocity of dihydroxyacetone on ion exchange resin were larger than those of glycerol, and the separation efficiency could generally be enhanced with the increase of the ratio of column height to diameter (H/D), decreased with the increase of the temperature, the loading quantity and the flowing velocity. Under the typical separation operating condition, the content of dihydroxyacetone could reach 90.8% from 17.4%, and the average separation yield was about 76.0%. |
