The global growth in biodiesel production over the past decade has led to the availability of significant quantities of glycerol as a byproduct of the triglyceride transesterification process. Glycerol is a versatile feedstock for producing chemicals such as propylene glycol and epichlorohydrin. Another attractive application of glycerol is to convert it into cyclic acetals via direct condensation with aldehydes and ketones or transacetalization with another acetal compound. The product, glycerol acetal, can be used as fuel additives to improve viscosity and cold properties of biodiesel, and alleviate the pollution problems by reducing particulate emissions from fuel combustion.In this work, glycerol acetal was synthesized via the acid-catalyzed reaction of glycerol with acetaldehyde or 1,1-diethoxyethane. Results show that at 25°C, the reaction gives nearly theoretical yield in 2 h if 1,1-diethoxyethane is used as the acetal forming reagent. The kinetics of this reaction was then investigated in batch reactors. The effect of solvent, reactant molar ratio, catalyst loading, and temperature were examined. A second order kinetic model is proposed to describe this reaction, and rate constants, activation energies, and equilibrium constants have been calculated based on the experimental results. The product from glycerol transacetalization is a mixture of four glycerol acetal isomers. In the presence of acid catalyst, the isomers interconvert to form an equilibrated mixture with the same composition. Vacuum distillation was carried out to separate the four acetals into their purified forms. Result show that the cis-5-hydroxy-2-methyl-1,3- dioxane (1) is the most volatile isomer among the four. When the distillation is carried out in the presence of an acid catalyst to promote interconversion, isomer (1) is obtained as a nearly pure distillate stream. This is further adapted to a continuous reactive distillation which produced 90-96% isomer (1) in a lab scale column. With the availability of pure isomer (1), new synthesis pathways are developed to obtain valuable chemicals such as 1,3-propanediol and 1,3-dihydroxyacetone. For instance, by oxidizing the remaining free hydroxyl group in isomer (1) and hydrolyzing the corresponding ketone product, the tanning ingredient 1,3-dihydroxyacetone can be produced. The novelty and advantage of this method is that the cyclic acetal structure in isomer (1) blocks the primary hydroxyl groups of glycerol, thus can ensure a good selectivity of secondary alcohol oxidation and eliminate the byproduct generated from primary alcohol reaction. To assess the feasibility of this concept, oxidation of isomer (1) to the corresponding ketone product was investigated using a variety of oxidants. Results show that a ruthenium tetroxide-based catalyst has the highest efficiency. Based on the experimental results obtained in this study, a novel process to convert glycerol to the desired acetal (1) and then to 1,3-dihydroxyacetone is presented.
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