Acrolein heterogeneous oxidation

Acrolein and Acrylic Acid. Acrolein and acrylic acid are manufactured by the direct catalytic air oxidation of propylene. In a related process called ammoxida-tion, heterogeneous oxidation of propylene by oxygen in the presence of ammonia yields acrylonitrile (see Section 9.5.3). Similar catalysts based mainly on metal oxides of Mo and Sb are used in all three transformations. A wide array of single-phase systems such as bismuth molybdate or uranyl antimonate and multicomponent catalysts, such as iron oxide-antimony oxide or bismuth oxide-molybdenum oxide with other metal ions (Ce, Co, Ni), may be employed.939 The first commercial process to produce acrolein through the oxidation of propylene, however, was developed by Shell applying cuprous oxide on Si-C catalyst in the presence of I2 promoter. 

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. 

Heterogeneous oxidative processes operate at high temperatures (250-450 6C) and are useful for the synthesis of acrolein and acrylic acid from propylene over bismuth molybdate catalysts, the synthesis of maleic and phthalic anhydrides from the oxidation of benzene (or C4 compounds) and naphthalene (or o-xylene) respectively over vanadium oxide,101 arid the synthesis of ethylene oxide from ethylene over silver catalysts.102... 

Other important uses of stannic oxide are as a putty powder for polishing marble, granite, glass, and plastic lenses and as a catalyst. The most widely used heterogeneous tin catalysts are those based on binary oxide systems with stannic oxide for use in organic oxidation reactions. The tin—antimony oxide system is particularly selective in the oxidation and ammoxidation of propylene to acrolein, acryHc acid, and acrylonitrile. Research has been conducted for many years on the catalytic properties of stannic oxide and its effectiveness in catalyzing the oxidation of carbon monoxide at below 150°C has been described (25). 

Attenlion should be drawn to ihe use of tin oxide systems as heterogeneous catalysts. The oldest and mosi extensively patented systems are the mixed lin-vanadium oxide catalysis for the oxidation of aromatic compounds such as benzene, toluene, xylenes and naphthalene in the. synthesis of organic acids and acid anhydride.s. More recenily mixed lin-aniimony oxides have been applied lo the selective oxidaiion and ammoxidaiion of propylene to acrolein, acrylic acid and acrylonilrile. 

Much work has been invested to reveal the mechanism by which propylene is catalytically oxidized to acrolein over the heterogeneous catalyst surface. Isotope labeling experiments by Sachtler and DeBoer revealed the presence of an allylic intermediate in the oxidation of propylene to acrolein over bismuth molybdate. In these experiments, propylene was tagged once at Ci, another time at C2 and the third time at C3. 

Although no direct evidence was available, Ben-Taarit et al. advanced a tentative mechanism for propylene oxidation [2]. As only heterogeneous or mixed oxides catalyze the formation of acrolein, the behavior of Cu+ y zeolite is similar to the heterogeneous case. On the contrary, on Rh +Y, acetone was selectively produced [2]. This is now in line with the behavior of Rh salts in... 

Oxo-metal complexes also intervene as active species in the heterogeneous gas-phase oxidation of hydrocarbons over metal oxide or mixed metal oxide catalysts at high temperatures. Characteristic examples are the bismuth molybdate-catalyzed oxidation of propene to acrolein and the V205-catalyzed oxidation of benzene to maleic anhydride (equations 17 and 18).SJ... 

Tin(IV) oxide is used in various heterogeneous catalyst mixtures, e.g. Sn02/V20s for oxidation of arenes to carboxylic acids and anhydrides, and Sn02/Sb20s for selective oxidation and ammoxidation of propylene to acrolein, acrylic acid, and acrylonitrile. 

Meth)acrylic acid and esters are large-volume industrial chemical intermediates for the production of co- and homopolymers. Acrylic acid (AA), with a worldwide production of approx. 1.5 X 10 t/a, finds its main use in the manufacture of superabsorbent polymers and various acrylate esters. The most important production process for AA involves the two-stage oxidation of propene (via acrolein) in the presence of a large excess of steam by heterogeneous catalysts. Selectivities to AA for the overall process reach 85-90% based on propene (cf. Chapter 1, Introduction). 

Bismuth Molybdate Catalysts. The Raman spectra of the bismuth molybdates, with Bi/Mo stoichiometric ratios between 0.67 and 14, have been examined using the FLS approach (see Section 3.2). " The bismuth molybdates fall into an unusual class of compounds, the ternary bismuth oxide systems Bi-M-0 (where M = Mo, W, V, Nb, and Ta) which exhibit a variety of interesting physical and chemical properties. Of commercial importance, the bismuth molybdates are heterogeneous catalysts for selective oxidations and ammoxidations (the Sohio process), for example, propylene ( 311 ) to acrolein (C3H4O) by oxidation or to acrylonitrile (C3H3N) by arrunoxidation. ... 

It was substituted by the new process of oxidation of propylene to acrylic add via acrolein using heterogeneous Bi-molybdate based catalysts followed by acid-catalyzed reaction of acrolein with the alcohol ... 

H. Redlingshofer, O. Krocher, W. Bock, K. Huthmacher, G. Emig, Catalytic wall reactor as a tool for isothermal investigations in the heterogeneously catalyzed oxidation of propene to acrolein, Ind. Eng. Chem. Res. 41 (2002) 1445. 

The modern beginning of the heterogeneous catalytic oxidation of olefins to aldehydes may be taken as the discovery of the oxidation of propylene to acrolein over cuprous oxide by Hearne and Adams (5 ). This reaction has been carried to commercial operation by Shell Chemical Company. More recently, the use of bismuth phosphomolybdate has been demonstrated for the oxidation of propylene to acrolein by Veatch and co-workers (88), and, in the presence of ammonia, to acrylonitrile by Idol (89). It was also shown, by Heame and Furman (90), that diolefins could be made from C4 and higher olefins by oxidative dehydrogenation over a bismuth molybdate catalyst. From these beginnings, information on olefin oxidation has increased very rapidly, both in journal and patent literature. We shall make no attempt to review the large number of patents that have issued, but shall limit ourselves mainly to journal literature. 

Shell catalysts consist of an compact inert support, usually in sphere or ring form, and a thin active shell that encloses it [4]. Since the active shell has a thickness of only 0.1-0.3 mm, the diffusion paths for the reactants are short. There are many heterogeneously catalyzed reactions in which it would be advantageous to eliminate the role of pore difiusion. This is particularly important in selective oxidation reactions, in which further reactions of intermediate products can drastically lower the selectivity. An example is acrolein synthesis two catalysts with the same active mass but different shell thicknesses differed greatly in selectivity at the high conversions desired in industry (Fig. 6-5). Therefore, if acrolein synthesis is to be operated economically, the shell thickness must be optimized. 

Among such oxidations, note that liquid-phase oxidations of solid paraffins in the presence of heterogeneous and colloidal forms of manganese are accompanied by a substantial increase (compared with homogeneous catalysis) in acid yield [3]. The effectiveness of n-paraffin oxidations by Co(III) macrocomplexes is high, but the selectivity is low the ratio between fatty acids, esters, ketones and alcohols is 3 3 3 1. Liquid-phase oxidations of paraffins proceed in the presence of Cu(II) and Mn(II) complexes boimd with copolymers of vinyl ether, P-pinene and maleic anhydride (Amberlite IRS-50) [130]. Oxidations of both linear and cyclic olefins have been studied more intensively. Oxidations of linear olefins proceed by a free-radical mechanism the accumulation of epoxides, ROOH, RCHO, ketones and RCOOH in the course of the reaction testifies to the chain character of these reactions. The main requirement for these processes is selectivity non-catalytic oxidation of propylene (at 423 K) results in the formation of more than 20 products. Acrylic acid is obtained by oxidation of propylene (in water at 338 K) in the presence of catalyst by two steps at first to acrolein, then to the acid with a selectivity up to 91%. Oxidation of ethylene by oxygen at 383 K in acetic acid in... 

Andrushkevich, T. (1993). Heterogeneous Catalytic-Oxidation of Acrolein to Acrylic-Acid Mechanism and Catalysts, Catal. Rev., 35, pp. 213-259. 

Example 9.2-4 Discovery of new heterogeneous catalysts for the selective oxidation of propane to acrolein (Oh et al., 2007). 

---