| Propylene oxide(PO) is an important propylene derivatives. Recently, a new process HPPO, which shows high environmental benefits and atom utilization, has been commercialized. But HPPO process need large amount of solvent, which causes PO solvolysis and large energy consumption for separation. Gas-phase epoxidation method can effectively avoid liquid solvent problems. Therefore, a gas-phase propylene epoxidation process G-HPPO was reported. In G-HPPO gaseous plasma H2O2directly react with propylene on the surface ofTS-1catalyst to produce PO. In this work, the influences of reaction conditions and catalytic activity on reaction efficiency were studied by optimizing reaction conditions and modifying TS-1catalyst. At the same time, the catalytic performance of TS-1involving different Ti species was also investigated.1, When the input power of the plasma unit reaches3.5W, the flow rates of H2, O2and propylene are170ml/min,8ml/min and18ml/min (the gaseous H2O2output in plasma unit is308mg/h), the epoxidation temperature is110℃and catalyst loading is0.2g, the propylene conversion and PO selectivity are13%and97%. PO productivity and H2O2utilization arel.9kg/(kg·h) and74%, respectively. When propylene flow rate is54ml/min, PO productivity and H2O2utilization can improved to2.4kg/(kg·h) and98.4%. More importantly, the activity of catalyst remains stable for more than600h. And the catalyst regeneration indicates that the absorption species could be burned by gaseous H2O2, which effectively avoids the inactivity of catalyst in G-HPPO process.2, Amorphous Ti species in titanium silicalite-1(TS-1) was investigated by UV Raman spectroscopy (UV Raman), UV-Vis diffuse reflectance spectroscopy (UV Vis). A peak at700cm-1in UV Raman, which is corresponding to the UV Vis band at260-280nm, is first assigned to symmetric vibration of hexacoordinated Ti-O-Ti linkages of amorphous Ti species. The existence of amorphous Ti species is the main reason to cause enhanced acidity and H2O2decomposition inTS-1.3, In order to improve the catalytic performance of TS-1, a small amount of sulfosalt impregnation can effectively reduce the negative effect of amorphous Ti species because of two reasons:(1) inhibiting the acidity of TS-1by metal cations, such as Na+or K+etc;(2) inactivating the ability of H2O2decomposition by formation of the Ti-O-S with anions SO42-.4, Hydrothermal treatment with TPAOH dilute solution can also reduce the negative effectof amorphous Ti species, then improve the catalytic performance of TS-1. The results of STEM, FT-IR, UV Vis and UV Raman show that TPAOH treatment could change TS-1crystal morphology, redistribute the Ti species in TS-1and modify the chemical micro- environmen of framework Ti. It showed that, TPAOH activation caused many intracrystalline voids, new crystal growth on the top of TS-1and the framework Ti enriched on the surface of TS-1. TPAOH activation also caused the blue shifting of peak at960cm-1(FT-IR and UV Raman spectrum), the red shifting of peak1125cm-1(UV Raman spectrum), as well as, new peak at850cm-1appearing in FT-IR and UV Raman spectrum of treatment TS-1. |
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