Production Of Acrolein From Selective Catalytic Dehydration Of Glycerol

In research and production of bio diesel oil,the application of major glycerol byproduct attracts great attention.The VPO type catalyst was found to be effective for selective catalytic dehydration of glycerol to acrolein in recent years.However,the VPO catalyst system is highly complicated,and its structure and performance is multiply affected by a variety of factors.Thus to develop highly efficient yet stable catalyst is the key issue for the selective dehydration of glycerol,especially for scale-up practice.In the present thesis,we synthesized different VPO catalysts by changing the preparation conditions,in order to accomplish the promising VPO catalysts and to figure out the structure-performance relationship.Based on the systematic characterization and activity evaluation,the following conclusions are obtained:（1）In fabrication of VPO catalyst,the adoption of the mixed solvent of isobutanol and benzoic alcohol showed better result than the application of single benzoic alcohol.Introduction of PEG additive to the preparation medium and activation of VPO precursor in the atmosphere of butane-air mixture can further enhance the derived VPO catalyst performance.It was found that acrolein yield of 94.5%can be obtained over the as-synthesized VPO catalyst under the following conditions:an aqueous glycerol solution feed with glycerol weight percentage of 36.5%,liquid hourly space velocity of 4 h^-1,and a reaction temperature of 320℃.（2）Within an extended period of reaction（50 h）at 300℃,the conversion of glycerol declines slowly.During the first 20 hours,the acrolein yield decreases continuously;while in the the following 30 hours,it nearly retains a value of approximately 60%.（3）The characterization results revealed that the alcohol composition of preparation medium and the addition of PEG component show notable impact on the crystallinity and morphology of VPO catalyst,the reactivity of lattice oxygen,and the surface V⁵⁺/V⁴⁺ ratio.The use of PEG additive can not only modify the crystallinity of both the precursor and the activated samples,but also enhance the reactivity of lattice oxygen.And the adoption of mixed alcohols as the preparation medium showed similar effect.Raman spectroscopy investigation indicates the presence of V⁵⁺ specimen（the VOPO₄ in different forms）and particularly the reduction of its content during a continuous reaction running.XPS study not only reveals the surface elemental concentration and the oxidation states of V species of the fresh catalysts,but also the changes in surface states of the used ones,especially the significant decrease in V⁵⁺/V⁴⁺ ratio and the deposition of surface carbon species.The latter aspects may account for the observed catalyst deactivation.The curve fitting results of V2p3/2 peaks of different catalysts suggest association between superior activity and suitable surface V⁵⁺/V⁴⁺ ratio of catalyst.