Treatment Of Titanium Silicalite-1 As Catalyst For The Epoxidation Of Propylene

Propylene oxide?PO?is one of the most important basic organic chemial materials,which is the third kind of propylene derivatives,second to polypropylene and acrylonitrile.Currently,the main industrial production method of propylene oxide is chlorohydrin process,which brings out serious environmental pollution of large quantities of solid waste and waste water.It no longer meets the basic requirement of environmental protection.While,Titanium silicalite?TS-1?catalyzed epoxidation of propylene to propylene oxide?HPPO process?has the advantages of mild reaction conditions,high atom utilization,green non-pollution,etc.,which is gradually applied in chemical industrial production.The process is the development direction of industrial production of propylene oxide.Although the HPPO process has been widely used in industry,the catalyst of the reaction still need to be improved further because they deactivate fast and should be regenerated frequently.The purpose of this work is to improve the catalytic stability of TS-1 zeolite in HPPO process through post-treatment modification.Firstly,the effect of mixed alkaline?TPAOH+NaOH?treatment on the catalytic properties and catalytic performance in the epoxidation of propylene were totally investigated.The results showed that the addition of NaOH in the treatment solution could further improve the catalytic stability.With increasing NaOH concentration,the relative crystallinity and the framework titanium decreased to some extent,while the mesopore volume,mesopore diameter,and extra-framework titanium increased significantly.The increase of mesopore volume may be the main reason for the improvement of catalytic performance.Secondly,the effect of treatment with TPAOH and?NH₄?₂CO₃ on the catalytic properties and the catalytic performance in propylene epoxidation were investigated.The results showed that the treatment with the mixture of TPAOH and?NH₄?₂CO₃could reduce the content of extra-framework titanium,leading to the improvement of catalytic stability.As a possible reason,the addition of?NH₄?₂CO₃ slowed down the recrystallization rate,making the incorporation rate of dissolved Ti into the framework match well with recrystallization rate,then the content of extra-framework titanium could be reduced effectively.