Ammoxidation propylene

Most, if not all, of the acetonitrile that was produced commercially in the United States in 1995 was isolated as a by-product from the manufacture of acrylonitrile by propylene ammoxidation. The amount of acetonitrile produced in an acrylonitrile plant depends on the ammoxidation catalyst that is used, but the ratio of acetonitrile acrylonitrile usually is ca 2—3 100. The acetonitrile is recovered as the water azeotrope, dried, and purified by distillation (28). U.S. capacity (1994) is ca 23,000 t/yr. 

Acrylonitrile is produced in commercial quantities almost exclusively by the vapor-phase catalytic propylene ammoxidation process developed by Sohio... 

Fig. 1. Process flow diagram of the commercial propylene ammoxidation process for acrylonitrile. BFW, boiler feed water.

The active site on the surface of selective propylene ammoxidation catalyst contains three critical functionalities associated with the specific metal components of the catalyst (37—39) an a-H abstraction component such as Sb ", or Te" " an olefin chemisorption and oxygen or nitrogen insertion component such as Mo " or and a redox couple such as Fe " /Fe " or Ce " /Ce" " to enhance transfer of lattice oxygen between the bulk and surface... 

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. 

Because of the large price differential between propane and propylene, which has ranged from 155/t to 355 /1 between 1987 and 1989, a propane-based process may have the economic potential to displace propylene ammoxidation technology eventually. Methane, ethane, and butane, which are also less expensive than propylene, and acetonitrile have been disclosed as starting materials for acrylonitrile synthesis in several catalytic process schemes (66,67). 

Mixed Metal Oxides and Propylene Ammoxidation. The best catalysts for partial oxidation are metal oxides, usually mixed metal oxides. For example, phosphoms—vanadium oxides are used commercially for oxidation of / -butane to give maleic anhydride, and oxides of bismuth and molybdenum with other components are used commercially for oxidation of propylene to give acrolein or acrylonitrile. 

The full cost of acrylonitrile manufacture based on methane was about 22)4/lb in 1960 (allowing 15% return). But the marginal cost—with no capital charges or overheads—was only 7 /lb. The full cost of propylene ammoxidation (with 15% return) was about 13-16ff/lb according to location. Thus, as soon as it was clear that ammoxidation was likely to... 

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

Acrylonitrile produced industrially via propylene ammoxidation contains trace amounts of benzene. When using Pseudonocardia thermophila JCM3095 or Rhodococcus rhodochrous J-1 as microbial NHase catalyst for conversion of acrylonitrile to acrylamide, concentrations of benzene of <4 ppm produced a significant increase in the reaction rate [16]. Maintaining the concentration of HCN and oxazole at <5 ppm and <10 ppm respectively produced high-quality acrylamide suitable for polymerization. 

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). 

Processes based on propane ammoxidation to manufacture acrylonitrile have also been developed,915 966 and BP has announced commercialization.966 Dehydrogenation at high reaction temperature (485-520°C), which is about 100°C higher than for propylene ammoxidation, results in the formation of propylene, which subsequently undergoes normal ammoxidation. Despite higher investments and the markedly lower selectivity (30-40%), the process can be economical because of the price difference between propylene and propane.966 Better selectivites can be achieved at lower (40-60%) conversions. 

Most, if not all, of the acetonitrile produced commercially in the United States recently was isolated as a by-product from the manufacture of acrylonitrile by propylene ammoxidation. The acetonitrile is recovered as the water azeotrope, dried, and purified by distillation. 

Chen BH, Dai QL, Lu DW. Development and modeling of a loop fluidized-bed reactor with baffle for propylene ammoxidation. Chem Eng Sci 1996 51 2983. 

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. 

The very high exothermal reaction of propylene ammoxidation develops a large amount of heat, in this case 61.5 MW or 15.35 GJ/t. Up to 30% can be exported on site, depending on the technology [21]. For assessing the opportunities for... 

Hydrogen cyanide (HCN) is a widely used high-volume raw and intermediate material in the world chemical industry. For the last several decades it has been increasingly supplied as a by-product of propylene ammoxidation—by... 

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