Oxidation of propene

Methyloxirane is an important building block for the manufacture of polyurethane, of various organic intermediates and solvents7-13 (Section 14.3.6). It is currently made in one of two ways (i) the chlorohy-drin process and (ii) the hydroperoxide process.7-10,12 The former is not environmentally friendly, due to the formation of calcium chloride and 

As with so many other gold-catalysed reactions, the particle size is important it has been claimed9,20 that only hemispherical particles between 2 and 10 nm in size are suitable and early work recommended 2.3 nm particles as the best.16 The deposition-precipitation (DP) method is favoured because of the intimate contact between metal and support that it gives. Particles smaller than 2 nm appear to shift the reaction mode towards formation of propane,7,9,10,15 which is clearly a waste of both propene and 

Hydrogen can of course also be lost if it is oxidised to water instead of the hydrogen peroxide that is needed for epoxidation. Its consumption can be lowered by 90% and selectivity raised to 97% at 1.7% conversion by admixing Au/Ti-MCM-41 with caesium chloride,23 but it is unclear how it acts. Water has however been found to decrease the rate of deactivation of Au/Ti02.24 25 

While these considerations are of great importance, it is first necessary to form the methyloxirane. Investigation of a number of titanium-containing 

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CH2 CH CH0. a colourless, volatile liquid, with characteristic odour. The vapour is poisonous, and intensely irritating to eyes and nose b.p. 53"C. It is prepared by the distillation of a mixture of glycerin, potassium sulphate and potassium hydrogen sulphate. It is manufactured by direct oxidation of propene or cross-condensation of ethanal with meth-anal. 

Recently (79MI50500) Sharpless and coworkers have shown that r-butyl hydroperoxide (TBHP) epoxidations, catalyzed by molybdenum or vanadium compounds, offer advantages over peroxy acids with regard to safety, cost and, sometimes, selectivity, e.g. Scheme 73, although this is not always the case (Scheme 74). The oxidation of propene by 1-phenylethyl hydroperoxide is an important industrial route to methyloxirane (propylene oxide) (79MI5501). 

Currently, the main route to acrylic acid is the oxidation of propene (Chapter 8). 

Transition metal oxides or their combinations with metal oxides from the lower row 5 a elements were found to be effective catalysts for the oxidation of propene to acrolein. Examples of commercially used catalysts are supported CuO (used in the Shell process) and Bi203/Mo03 (used in the Sohio process). In both processes, the reaction is carried out at temperature and pressure ranges of 300-360°C and 1-2 atmospheres. In the Sohio process, a mixture of propylene, air, and steam is introduced to the reactor. The hot effluent is quenched to cool the product mixture and to remove the gases. Acrylic acid, a by-product from the oxidation reaction, is separated in a stripping tower where the acrolein-acetaldehyde mixture enters as an overhead stream. Acrolein is then separated from acetaldehyde in a solvent extraction tower. Finally, acrolein is distilled and the solvent recycled. 

The oxidation of propene on Pt/YSZ was studied28 at temperatures 350° to 500°C. Figure 8.19 shows SEMs of the porous Pt/YSZ film which has a surface area corresponding to a reactive oxygen uptake NG=6.8-10 7 mol O. 

Oxidation of propene labelled with C(CH3-CH- CH2) yields acraldehyde (88 %), acetone (10 %) and propanal (2 %). The labelled acraldehyde consists... 

Propene is an intermediate utilized in the chemical and pharmaceutical industries. The partial oxidation of propene on cuprous oxide (CU2O) yields acrolein as a thermodynamically imstable intermediate, and hence has to be performed under kinetically controlled conditions [37]. Thus in principle it is a good test reaction for micro reactors. The aim is to maximize acrolein selectivity while reducing the other by-products CO, CO2 and H2O. Propene may also react directly to give these products. The key to promoting the partial oxidation at the expense of the total oxidation is to use the CU2O phase and avoid having the CuO phase. 

Beneficial Micro Reactor Properties for the Oxidation of Propene to Acrolein... 

Oxidation of Propene over AuPt Si02 and Pt/Si02... 

There are a few examples of 02 oxidations catalyzed by zeolite-encapsulated complexes. Encapsulated CoPc was active in the oxidation of propene to aldehyde, whereas the free complex was inactive.76 A triple catalytic system, Pd(OAc)2, benzoquinone, and a metal macrocycle, was used to oxidize alk-enes with molecular oxygen at room temperature.77,78 Zeolite-encapsulated FePc79-81 and CoSalophen80,82 complexes were used as oxygen-activating catalysts. 

In an experiment (Williams, 1996) to evaluate a catalyst for the selective oxidation of propene (C3H6) to various products, 1 g of catalyst was placed in a plug-flow reactor operated at 450°C and 1 bar. The feed consisted of propene and air (21 mole % 02,79% N2 (inert)). GC analysis of the inlet and outlet gas gave the following results, the outlet being on a water-free basis (H20 is formed in the oxidation) ... 

Structure Sensitivity in Selective Oxidation of Propene over CU2O Surfaces... 

The oxidation of propene to acrolein has been one of the most studied selective oxidation reaction. The catalysts used are usually pure bismuth molybdates owing to the fact that these phases are present in industrial catalysts and that they exhibit rather good catalytic properties (1). However the industrial catalysts also contain bivalent cation molybdates like cobalt, iron and nickel molybdates, the presence of which improves both the activity and the selectivity of the catdysts (2,3). This improvement of performances for a mixture of phases with respect to each phase component, designated synergy effect, has recently been attributed to a support effect of the bivalent cation molybdate on the bismuth molybdate (4) or to a synergy effect due to remote control (5) or to more or less strong interaction between phases (6). However, this was proposed only in view of kinetic data obtained on a prepared supported catalyst. 

Selective oxidation of propene to acrolein was carried out in a dynamic differential microreactor containing 40 to 60 mg of catalyst as described previously (12). Reaction conditions were as follows propene/02/N2 (diluting gas) = 1/1.69/5 total flow rate 7.2 dm. h-i total pressure 10 Pa and reaction temperature 380 °C. 

Feo.67Coo.33Mo04 is in the p form). The oxidation of propene was conducted at 380°C under the conditions given in the experimental section. The products of the reaction were in all cases exclusively acrolein (ACRO) and CO2. 

An intermediate proposed to occur during the ammonoxidation of propene and that would correspond to the intermediate B suggested for the oxidation of propene is B as shown in Scheme 1. Compounds designed to model these intermediates structurally or functionally should contain a 7r-allyl-molybdenum group covalently bound to an imido ligand as a minimum requirement, ideally an 0x0 ligand should be bound in addition. 

The oxidation of olefins has also been investigated on a-Mo03 supported on carbon the mild oxidation of propene into acrolein takes place mainly on the (100) face of a-Mo03 while total oxidation occurs on the (010) face (425fg). Similar results have been obtained for the oxidative dehydrogenation of 1-butene into butadiene (425h). 

The oxidation of propene to propene oxide is considered an essential practice in industrial chemistry [1]. Haruta et al. showed that this process can be led by heterogeneous catalysis with gold supported over titania [15, 16]. Another goal in the gold catalysis sequence is the selective oxidation of some alcohols and carbohydrates with molecular oxygen, as studied by Prati and Rossi [17]. 

The oxidation of propene to propene oxide, a strategic compound in the manufacture of polyurethane and polyols, displays very low selectivity with many catalysts, unlike the epoxidation of ethane, whose selectivity may be as high as 90% when a supported Ag catalyst is used [235]. Lambert et al. recently showed that selectivities of about 50% can be achieved at 0.25% conversion by supported catalysts, although selectivity declines when the conversion increases [236]. 

Propene to acrolein. Hildenbrand and Lintz87,88 have used solid electrolyte potentiometry to study the effect of the phase composition of a copper oxide catalyst on the selectivity and yield of acrolein during the partial oxidation of propene in the temperature range of 420-510°C. Potentiometric techniques were used to determine the catalyst oxygen activity, and hence the stable copper phase, under working conditions. Hildenbrand and Lintz used kinetic measurements to confirm that the thermodynamically stable phase had been formed (it is known that propene is totally oxidised over CuO but partially oxidised over ). 

In another example13 the oxidation of propene is carried out with an electrolyte consisting of dichloromcthane containing 0.2 M tetrabutylammonium tetrafluoroborate and 2 % acetic acid. The potential of the platinum anode is controlled at 3.05 V versus aqueous SCE. The two major products are 3-acetoxyprop-1-ene (20%) and l-acetoxy-2-fluoropropane (30%). 

The oxidation of propene is at present the most extensively studied gas phase heterogeneous oxidation process. The selective production of acrolein over cuprous oxide has been known for a very long time. However, the discovery of bismuth molybdates as highly active and selective catalysts for the oxidation to acrolein, and particularly the ammoxidation to acrylonitrile, has opened a new era in oxidation catalysis. 

The oxidation of propene to acrolein has received much attention for several reasons. Firstly, the process is of industrial importance in itself, and it is also a suitable model reaction for the even more important, but at the same time more complicated, ammoxidation. Secondly, propene oxidation is, in many aspects, representative of that of a class of olefins which possesses allylic methyl groups. Last, but not least, the allylic oxidation is a very successful example of selective catalysis, for which several effective metal oxide systems have been discovered. The subject has therefore attracted much interest from the fundamental point of view. 

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