Synthesis Of Acrolein By Vapor-phase Glycerol Dehydration Over Supported Rare Earth Phosphates

With the growing shortage of fossil fuels, the energy crisis gradually becomes a crucial issue that has negative effect on human suivival and society development. Moreover, extensive use of fossil fuels leads to excessive discharge of pernicious gases such as SOX, NOX&CO2, which could cause severe environmental problems and threats to human survival and development like acid rain and the greenhouse effect. Being a renewable and green energy, biomass is not only abundant in the nature, but also environment friendly. Therefore, it has attracted much attention both from the academia and the industrial researchers. Synthesis of biodiesel by transeterification of fatty oils or vegetable oils with methanol is one of the successful examples in the utilization of biomass energy resources. In this context, the productivity of biodiesel around the world becomes larger and larger. Along with this process, unfortunately, a large volume of glycerol can be generated as byproduct, leading to market surplus for glycerol demand. Dehydration of glycerol to acrolein is considered to be an effective route to appreciate the economics of biodiesei. Acrolein is an important chemical intermediate, for example, the DL-methionine synthesis. It has been demonstrated that the glycerol dehydration reaction towards acrolein can proceed under the liquid phase, gas phase or sub-/supercritical water condition. The key factors that have decisive influence on the reaction selectivity include the microstructure of catalyst, acidity of the active component and redox site.The paper focuses on the catalyst of glycerol dehydration to acrolein under the gas phase as well as the process improvement, NdPO4/γ-Al2O3amorphous alloy catalysts were prepared by Nd2O3as precursor supported on γ-Al2O3. The effects of carrier and their pretreatment, load capacities, calcinations and solvents on the dehydration activity were investigated. The optimum carrier was γ-Al2O3with hydrothermal treatment, the optimal load capacity, and calcinations temperature were determined as7wt.%and500℃, methyl alcohol was the most suitable solvent of the reaction. XRD characterization and BET suggested that the catalyst possessed amorphous structure with high thermal stability and kept same structure active phase over the surface of γ-Al2O3were highly dispersed on the support. At the same time, we have optimized the reaction condition of glycerol dehydration to acrolein, Finally, we found the optimal reaction conditions were obtained as follows:liquid hourly space velocity9h-1, the content of glycerol0.10mol/L and temperature305℃. Under these conditions, the catalyst showed the optimal activity, the conversion of glycerol and the selectivity acrolein were maintained about98%and60%for a long time.We added new components such as hydrogen peroxide, CO2and acetic acid in order to change the performance of the catalyst. And we found that deposition burning online when added hydrogen peroxide, meanwhile, inhibit the production of coke to a certain extent, but at the same time make the products oxidation deeply lead to the low selectivity. By adding CO2or acetic acid in the feed to the benefit of regulate the atmosphere of acid-base in the reactor, and promote the dehydration reaction while produce a small amount of coke. Added CO2in the feel, the selectivity towards acrolein still remains about50%even after30h.