Preparation Of Lactic Acid From Glycerol Catalyzed By Zirconia Supported Copper And PtAu

Lactic acid has broad applications in the food and pharmaceutical industries, and it is also a raw material for the preparation of polylactide prepolymer. The current commercial process for the production of lactic acid involves the fermentation of various carbohydrates. However, this process suffers from low efficiency. Hence, alterative catalytic processes for the production of lactic acid by using byproduct glycerol from biodiesel production are highly desirable.In thesis, zirconia-supported copper oxide catalysts with various compositions were prepared by the deposition precipitation method, co-precipitation method and impregnation method. PtAu/ZrO₂ bimetallic catalysts were prepared by sol-gel method and impregnation method, using PtAu as the active component. Prepared catalysts were used for the conversion of glycerol to lactic acid and characterized by atomic absorption spectroscopy, N₂ physical adsorption, temperature programmed reduction, powder X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscope.The CuO/ZrO₂ catalysts were evaluated for the conversion of glycerol to lactic acid in aqueous solution in the presence of a base and under an inert atmosphere. The conversion of glycerol catalyzed by various CuO/ZrO₂ catalysts, we also examined the effect of reaction temperature, reaction time, reaction pressure and glycerol concentration. The results showed that CuO/ZrO₂ with 30% Cu loading exhibited the highest activity for the conversion of glycerol. Under optimum conditions,100% glycerol conversion and 94.6% selectivity for lactic acid were obtained over 30%CuO/ZrO₂ when reacting 10 mL of glycerol solution （1.4 M）, using 0.2 g catalyst in the presence of NaOH （1:1 NaOH/glycerol molar ratio） at 180℃ and 1.4 MPa N₂ for 8 h. The CuO/ZrO₂ catalyst was shown to be reusable, albeit with a gradual loss in activity during successive batch runs. The accumulation and growth of crystalline CuO occurred during recycling, decreasing the catalytic activity. A reaction mechanism using CuO/ZrO₂ catalysts for the conversion of glycerol is proposed through changing inert atmosphere and substrates as well. The reaction process involves the initial dehydrogenation of glycerol to glyceraldehyde and dehydration of glyceraldehyde to pyruvaldehyde, an intermediate that can be converted via a Cannizzaro reaction to lactic acid.The partical size in PtAu/ZrO₂ catalysts were 2～3 nm. The effects of different PtAu ratio and various reaction temperatures on the yield of lactic acid were investigated. The highest selectivity for lactic acid could reach to 93.7% with 89.9% conversion of glycerol when reacting 10 mL of glycerol solution （1.1 M）, using 0.132 g catalys tin the presence of NaOH （1:1 NaOH/glycerol molar ratio） at 160℃ and 1.4 MPa N₂ for 6 h. Moreover, the reusability of the catalysts were characterized by atomic absorption spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscope. The reasons for the deactivation of the catalyst could be due to the combination of the aggregation and leaching of the metal particles.