Propylene ammoxidation over

Table II. Catalytic Activity for Propylene Ammoxidation Over Bismuth-Iron Molybdate...

Processes rendered obsolete by the propylene ammoxidation process (51) include the ethylene cyanohydrin process (52—54) practiced commercially by American Cyanamid and Union Carbide in the United States and by I. G. Farben in Germany. The process involved the production of ethylene cyanohydrin by the base-cataly2ed addition of HCN to ethylene oxide in the liquid phase at about 60°C. A typical base catalyst used in this step was diethylamine. This was followed by liquid-phase or vapor-phase dehydration of the cyanohydrin. The Hquid-phase dehydration was performed at about 200°C using alkah metal or alkaline earth metal salts of organic acids, primarily formates and magnesium carbonate. Vapor-phase dehydration was accomphshed over alumina at about 250°C. 

Acrylonitrile is produced commercially by the process of propylene ammoxidation, in which propylene, ammonia and air are reacted in a fluidized bed in the presence of a catalyst (EPA 1984, 1985a). Production in the United States has increased gradually over the past 20 years from 304,300 kkgain 1967 (Cogswell 1984) to 1,112,754 kkg in 1987 (USITC 1988). 

It was argued that the mechanism of ammoxidation over this catalyst was different from other metal oxides, because propylene was not observed to be an... 

Aykan (35) reported that ammoxidation of propylene occurred over a silica-supported bismuth molybdate catalyst in the absence of gas-phase oxygen, although the catalytic activity decreased rapidly with increasing catalyst reduction. The reduction process was followed by X-ray and it was found that phase changes which occurred in the catalyst and the decrease in catalytic activity corresponded quantitatively to the depletion of lattice oxygen. 

The main route to ACRN is the one-step propylene ammoxidation process. In this process propylene, ammonia and air reacted in a fluidized bed reactor to produce ACRN with acetonitrile and hydrogen cyanide as by-products. New technology based on propane ammoxidation has been developed by BP, Mitsubishi (in conjunction with BOC) and Asahi Kasei with claims of a 30% production cost advantage over the propylene route276. However no plans have been announced to build a propane-based plant as of first quarter 2004 297. 

In fact, over the last 30 years, the market as well as the supply situation for formic acid has been very dynamic. It has been affected by the development of several other major technologies. The commercialization of acetic acid by the carbonylation of methanol and the development of the Propylene ammoxidation process for acrylonitrile which replaced the cyanohydrin process both had a large impact on formic acid. 

Fig. 2. Mechanism of selective propylene ammoxidation to acrylonitrile over a bismuth molybdate catalyst. Reprinted from Ref. (56), Copyright (1984), with permission from Academic Press, Inc.

Alcohol ammoxidation provides an option to augment the production of HCN and/or acetonitrile in a propylene ammoxidation process for producing acrylonitrile (103). This is accomplished by co-feeding alcohol or alcohol mixtures with propylene over conventional molybdate or antimonate ammoxidation catalysts under typical process conditions for propylene ammoxidation. 

The two reaction steps can occur over a single ammoxidation catalyst tailored for propylene ammoxidation, or the two steps can be separated in two reactors. In the case of the latter, the first reactor uses an acidic alcohol dehydration catalyst with the resulting propylene containing product sent to a second reactor containing a conventional propylene ammoxidation catalyst (104). 

Fundamental studies of the mechanism of propane ammoxidation over Mo-V-Nb-0 based catalysts show that the mechanism is the same as earlier studies foimd for other propane ammoxidation catalysts, notably those based on V-Sb-O (see above). Isotope labeling studies using C-labeled propane show that the reaction proceeds through propylene as the only intermediate (156). There is no dimerization or skeletal rearrangement of C3 moities rather intermediate propylene is converted directly to acrylonitrile. Also pulse reaction studies show that the reaction occurs by a redox process wherein lattice oxygens are used in the... 

It is an alternative to acetonitrile produced as a coproduct of the commercial propylene ammoxidation process for the manufacture of acrylonitrile (see above). Acetonitrile is used primarily in the pharmaceutical industry as a solvent in drug synthesis. Ethane ammoxidation has several potential advantages over coproduct acetonitrile. 

Acrylonitrile is currently the second largest outlet for propylene (after polypropylene). It is used as a monomer for synthetic fibers and acrylic plastics (thermoplastics and food packaging mainly), AS (acrylonitrile-styrene) resins, and ABS (aerylonitrile-butadiene-styrene) thermoplastics, as well as in the synthesis of acrylamide, adiponitrile, and nitrile elastomers. The manufacture of acrylonitrile is exclusively based on the one-step propylene ammoxidation process. Originally developed by Sohio, Standard Oil Company (now part of BP America), the conventional method used since 1957 employs a fluidized-bed reactor and multicomponent catalysts based on Mo-containing mixed-metal oxides. Over the years, the industrial... 

Burrington, J. D., Kartisek, T, and Grasselli, R. Surface intermediates in selective propylene oxidation and ammoxidation over heterogeneous molybdate and anti-monate catalysts. J Cato/ 87, 363-380 (1984). 

Fig. 3. Mechanism of selective ammoxidation and oxidation of propylene over antimonate catalysts (31).

Oxidation Catalysis. The multiple oxidation states available in molybdenum oxide species make these exceUent catalysts in oxidation reactions. The oxidation of methanol (qv) to formaldehyde (qv) is generally carried out commercially on mixed ferric molybdate—molybdenum trioxide catalysts. The oxidation of propylene (qv) to acrolein (77) and the ammoxidation of propylene to acrylonitrile (qv) (78) are each carried out over bismuth—molybdenum oxide catalyst systems. The latter (Sohio) process produces in excess of 3.6 x 10 t/yr of acrylonitrile, which finds use in the production of fibers (qv), elastomers (qv), and water-soluble polymers. 

The surface transformations of propylene, allyl alcohol and acrylic acid in the presence or absence of NHs over V-antimonate catalysts were studied by IR spectroscopy. The results show the existence of various possible pathways of surface transformation in the mechanism of propane ammoxidation, depending on the reaction condition and the surface coverage with chemisorbed NH3. A surface reaction network is proposed and used to explain the catalytic behavior observed in flow reactor conditions. 

Fig. 2. Mechanism of selective ammoxidation of propylene to acrylonitrile over bismuth molybdate catalyst by Burrington et at. (19).

ACRYLONITRILE. [CAS 107-13-1], Today over 90% of the approximately 4,000.000 metric tons of acrylonitrile (also called aciylic acid nitrile, propylene nitrile, vinyl cyanide, and propenoic acid nitrile) produced worldwide each year use the Soldo-developed ammoxidation process. Acrylonitrile is among the top 50 chemicals producedin the United States as aresult of the tremendous growth m its use as a starting material for a wide range of chemical and polymer products. Acrylic fibers remain the largest use of acrylonitrile other significant uses are in resins and nitrile elastomers and as an intermediate in the production of adiponitnle and acrylamide. 

Fig. 27. Correlation between quadrupole splitting and selectivity to acrylonitrile in the ammoxidation of propylene over mixed iron oxides. Filled symbols, C02 open symbols, CH2CHCN. Figure according to Skalkina et al. (202).

The creation of selective catalysts for such complex reactions seems to be an especially difficult problem. Nevertheless, surprisingly, selective catalysts have been developed for complex reactions, which can be exemplified by the oxidation and ammoxidation of propylene, oxidation of butene and even butane to maleic anhydride (which requires seven oxygen atoms). Such reactions are usually performed over V and Mo oxide systems [4, 6, 8-10]. High selectivity of these systems is presumably provided by a special structure of the catalyst surface that allows control... 

Selective Oxidation and Ammoxidation of Propylene by Heterogeneous Catalysis Robert K. Grasselli and James D. Burrington Mechanism of Hydrocarbon Synthesis over Fischer-Tropsch Catalysts P. Biloen and W. M. H. Sachtler Surface Reactions and Selectivity in Electrocatalysis... 

Cerium also has minor uses in other commercial catalysts [17]. The dominant catalyst for the production of styrene from ethylbenzene is an alkali-promoted iron-oxide based material. The addition of a few percent of cerium oxide to this system improves activity for styrene formation. The ammoxidation of propylene to produce acrylonitrile is carried out over catalytically active complex molybdates. Cerium, a component of several patented compositions [18], supports the chemical reaction. 

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