Liquid-phase epoxidation

Liquid-Phase Epoxidation with Hydroperoxides. Molybdenum, vanadium, and tungsten have been proposed as Hquid-phase catalysts for the oxidation of the ethylene by hydroperoxides to ethylene oxide (205). tert- uty hydroperoxide is the preferred oxidant. The process is similar to the arsenic-catalyzed route, and iacludes the use of organometaUic complexes. 

The latest industrial strides in PO synthesis are liquid phase epoxidation of propylene with H2O2 over TS... 

Hydronium ion, 14 23 Hydroperoxidates, 18 411 Hydroperoxide process, for propylene oxide manufacture, 20 798, 801-806 Hydroperoxides, 14 281, 290-291 18 427-436 alkylation of, 18 445 a-oxygen-substituted, 18 448-460 chemical properties of, 18 430 433 decomposition of, 14 279 18 431-432 liquid-phase epoxidation with, 10 656 physical properties of, 18 427-430 preparation by autoxidation, 18 434 synthesis of, 18 433-435 Hydrophile-lipophile balance system,... 

The epoxidation of propene is analogous to that of ethylene catalyzed by silver. However, the selectivity is much lower. Due to the pronounced oxidation sensitivity of the allyl CH3-group, excessive combustion occurs as a side reaction. The heterogeneous process has no practical significance, therefore, as it has to compete with a highly selective liquid phase epoxidation process. 

In the present work the synthesis of highly dispersed niobium or titanium containing mesoporous molecular sieves catalyst by direct grafting of different niobium and titanium compounds is reported. Grafting is achieved by anchoring the desired compounds on the surface hydroxyl groups located on the inner and outer surface of siliceous MCM-41 and MCM-48 mesoporous molecular sieves. Catalytic activity was evaluated in the liquid phase epoxidation of a-pinene with hydrogen peroxide as oxidant and the results are compared with widely studied titanium silicalites. The emphasis is directed mainly on catalytic applications of niobium or titanium anchored material to add a more detailed view on their structural physicochemical properties. 

In concomitance with the displacement observed by i.r., an evolution of the catalytic activity has been observed while studying the liquid-phase epoxidation of cyclohexene in the presence of (EGDA)- Mo(VI), freshly prepared or after four months of conditioning at room temperature under inert atmosphere. As usual, the appearance of epoxide was followed by gas chromatographic analyses or by direct titration of oxirane oxygen and the disappearance of hydroperoxide was monitored by iodometric titration. In figure we report concentration-time for typical runs in ethylbenzene at 80°C obtained with the experimental procedure already described (ref. 9). It may be seen that with a freshly prepared catalyst an induction period is observed which lowers the initial catalytic activity. Our modified Michaelis-Menten type model equation (ref. 9) cannot adequately fit the kinetic curves obtained due to the absence of kinetic parameters which account for the apparent initial induction period (see Figure). 

Co2 + -exchanged faujasite zeolite is a unique heterogeneous catalyst for liquid-phase epoxidation using 02 [45]. This catalyst is active only for styrene, and the conversion and yield of styrene oxide were 65 and 45%, respectively. The TON, based on Co ions, reached 12. The Co2+ ions, located in supercages, are thought to cause activation of 02 for epoxidation. 

Thus, there may be an unlimited increase in selectivity by the elimination of free-radical intermediates. For example, selectivity of liquid-phase epoxidation with organic hydroperoxides depends on two factors [3] ... 

HETEROGENEOUS Mo(Vl) CATALYSTS FOR LIQUID-PHASE EPOXIDATION EVALUATION OF THE DEACTIVATION PATTERNS... 

Besides hydrogen, other reductants for O2 in the liquid-phase epoxidation of propene include carbon monoxide, aldehydes, alcohols and other organic compounds. The reaction proceeds very efficiently with methanol as the reductant, in the presence of Pd and the Ti-Al-MCM-22 catalyst or Pd and peroxo-polyoxometalate catalysts the latter have been intercalated inside layered double hydroxides to make them heterogeneous [29e,h]. A propene conversion of 47%, with 91.5% selectivity for PO, was obtained at 80°C [29h]. 

Key Words Propylene, Propylene oxide. Liquid-phase epoxidation, Semibatch reactor. Supercritical CO2, Gas-phase epoxidation, Pd/TS-1 catalyst, Au/Ti02 catalyst, Au/Ti-Si02 catalyst, Ag catalyst, Mesoporous... 

The liquid-phase epoxidation of propylene with O2-H2 mixtures was first reported by Sato and Miyake of Tosoh Corp., who used BuOH as a solvent and Pd as the catalytic metal [10]. In liquid-phase epoxidation, TS-1 is usually used as a catalyst support for Pd because it exhibits the best performance for the epoxidation of propylene with H2O2 [13]. When the reaction is conducted at temperatures below 323 K, the selectivity to PO is above 90%, whereas the conversion of propylene is not sufficiently high and below 4%. 

The introduction of microporous and mesoporous supports with well-dispersed Ti has allowed for some detailed kinetic studies into the PO and water generation mechanisms primarily as a result of the outstanding stability of catalysts prepared from these materials. Prior to the synthesis of stable catalysts, a number of reaction mechanisms were proposed based on observed trends in reactivity, DPT calculations [63,64,76,78], and analogs to liquid-phase epoxidation reactions over Ti-based catalysts [14,15,89] rather than kinetic analysis. The first proposed mechanisms were constructed for the Au/Ti02 and Au/Ti02/Si02 system. 

Polyimide particulates carrying a functional group have been prepared by non-aqueous suspension polycondensation. Molybdenum(VI) complex has been supported on a functional polyimide bead and used as a catalyst in the liquid-phase epoxidation of cyclohexene with tert-butylhydroperoxide (TBHP), as oxygen source. The polyimide-supported Mo catalyst was highly active and selective, and has been recycled 10 times vrith no detectable loss of Mo from the support. 

In this review we shall focus on the use of heterogeneous catalysts for the liquid phase epoxidation of olefins with alkyl hydroperoxides or hydrogen peroxide. The latter is generally the oxidant of choice for fine-chemicals production owing to a better availability and lower price. Emphasis is placed on methods with a broad scope in organic synthesis. 

By using differently functionalized polymeric siqiports conventional Mo( T) catalysts have been successfully heterogenized and tested in liquid phase epoxidation of cyclohexene. 

Liquid-phase epoxidation. Epoxides are produced in liquid-phase reactions of olefins with hydroperoxides in the presence of (soluble or insoluble) compounds of molybdenum, tungsten or vanadium. 

The catalytic properties of post-synthesized PS-Ti-MWW were compared with directly hydrothermally synthesized HTS-Ti-MWW and TS-1 in the epoxidation of 1-hexene with H2O2 (Figure 4.8). For reasonable comparison, the reactions were carried out in the most suitable solvents for the two titanosilicates - in acetonitrile for Ti-MWW and in methanol for TS-1. HTS-Ti-MWW showed much higher intrinsic adivity than TS-1 for 1-hexene. PS-Ti-MWW further proved to be about twice as adive as HTS-Ti-MWW. The efficiency of H2O2 utilization was also very high on PS-Ti-MWW. Thus, in terms of the activity, epoxide selectivity and H2O2 efficiency, PS-Ti-MWW has so far been a most effident heterogeneous catalyst for liquid-phase epoxidation of linear alkenes. 

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