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Gas-Phase Epoxidation Of Propylene With Hydrogen Peroxide Over Titanium Silicalite Catalyst

Posted on:2010-06-15Degree:MasterType:Thesis
Country:ChinaCandidate:W D YuFull Text:PDF
GTID:2121360275458242Subject:Industrial Catalysis
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In this article, the experiments were conducted in a small fixed-bed reactor equipped with an on-line chromatography. The first part of this work was devoted to the interaction between TS-1 and H2O2 solution, which was investigated by purging H2O2 dipped TS-1 with hydrogen or propylene. Departure from this, the second part of this paper was carried out to address the direct gas-phase epoxidation of propylene with hydrogen peroxide over TS-1 under continuous feeding of both propylene and hydrogen peroxide. Epoxidation conditions including reaction temperature, space velocity of propylene, concentration of H2O2, and catalyst were studied. The following results and conclusions were gained:1. Being purged by dry hydrogen, H2O2 dipped on TS-1 decomposed even at very mild temperature. In fact, the H2O2 was completely consumed when enough time of purging was given. By comparing with the H2O2 decomposition in liquid-phase, we found that H2O2 decomposed more easily in the gas-phase condition. During propylene purging the same sample, the epoxidation of propylene was seen occurred simultaneously with the decomposition of H2O2. The increases of the propylene purging rate and the purging temperature can effectively suppress the decomposition of H2O2, and thereby improve the selectivity of epoxidation.2. Washing the H2O2 dipped TS-1 sample with different volumes of deioned water led to the decrease of the DRUV-Vis absorption in 386 nm region which is related to H2O2, and the decrease of PO formation rate. The water washing experiments and the experiments of re-impregnating the released TS-1 with washing liquor demonstrated that the interaction of H2O2 with TS-1 is reversible.3. Direct gas-phase epoxidation of propylene with hydrogen peroxide under the continuous feeding mode showed that, (1) the direct epoxidation of propylene with hydrogen peroxide vapor over cheap TS-1 catalysts took place effectively under the gas-phase conditions; (2) in the gas-phase epoxidation of propylene, the decomposition of H2O2 is a major competitive side-reaction to the propylene epoxidation. This side-reaction can be effectively depressed by decreasing the amount of non-framework titanium in TS-1 (TS-10→TS-11→S-12), elevating reaction temperature, and increasing the propylene/hydrogen peroxide ratio; (3) when TS-12, which had the lowest content of non-framework titanium, was employed as the catalyst of epxidation of propylene and the optimal conditions were used (reaction temperature 95℃, space velocity of propylene 2.81 h-1, concentration of H2O2 8.82 mol/L, molar ratio of propylene to H2O2 3.65/1, mass of TS-12 0.8 g), about 15% propylene conversion, more than 95% propylene oxide selectivity and about 559 mgPOh-1(gcat)-1 yield were reached. The H2O2 utilization of this reaction was approximately 60%, comparable to the reported result.
Keywords/Search Tags:Gas-phase Epoxidation, Propylene, Hydrogen Peroxide, Titanium Silicalite, H2O2 Utilization
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