Combustion acrylonitrile production

Fluidized beds are used for both catalytic and noncatalytic reactions. In the catalytic category, there are fluidized catalytic crackers of petroleum, acrylonitrile production from propylene and ammonia, and the chlorination of olefins to alkyl chlorides. Noncatalytic reactions include fluidized combustion of coal and calcination of lime. 

Acrylonitrile is combustible and ignites readily, producing toxic combustion products such as hydrogen cyanide, nitrogen oxides, and carbon monoxide. It forms explosive mixtures with air and must be handled in weU-ventilated areas and kept away from any source of ignition, since the vapor can spread to distant ignition sources and flash back. 

It has been estimated that over 100,000 workers are potentially exposed to acrylonitrile during production and use (NIOSH 1977, 1988). Occupational exposures include plastic and polymer manufacturers, polymer molders, polymer combustion workers, furniture makers, and manufacturers of fibers and synthetic rubber (EPA 1980a). Other populations who could have elevated exposure to acrylonitrile are residents in the vicinity of industrial sources or chemical waste sites. 

The fluidized-bed process for this reaction has several advantages over a fixed-bed process. First, the process is highly exothermic, and the selectivity to C3H3N is temperature dependent. The improved temperature control of the fluidized-bed operation enhances the selectivity to acrylonitrile, and substantially extends the life of the catalyst, which readily sinters at temperatures in excess of 800 K. Furthermore, since both the reactants and products are flammable in air, the use of a fluidized bed enables the moving particles to act to quench flames, preventing combustion and ensuring safe operation. 

The partial oxidation of olefins over a variety of mixed oxide catalysts is well known [ I ] and has been studied in great detail. For example, iron antimony oxide is known to be a selective catalyst for the partial oxidation of propene yielding acrolein [2-4] and of 1-butene yielding 1,3 butadiene and 2-butenal [5,6], The oxidation of paraffins, like propane, with this type of catalysts yields only the combustion products CO and CO2 [7]. Propane can however be selectively oxidised over this type of catalysts in the presence of ammonia to yield acrylonitrile [8],... 

The influence of ammonia on the partial (amm)oxidation of propene was studied over the iron antimony oxide catalyst (Sb/Fe = 2) at 375 °C (see Figure 5). The yield of the partial (amm)oxidation products acrylonitrile plus acrolein decreased with increasing ammonia partial pressure. The yield of the combustion products CO and CO2 first decreased and then increased with increasing ammonia partial pressure. The opposing trends for the yield of both product groups resulted in a complex behaviour of the conversion of propene as a function of the partial pressure of ammonia. The rate of formation of the partial (amm)oxidation products can be easily modelled as a surface reaction ocupying one or two active sites, and ammonia occupying one of the sites. 

The complex dependency of the yield of combustion products on the ammonia partial pressure indicates that various factors are influencing the rate of formation of this product class. If ammonia is only inhibiting the adsorption of propene, then the yield of combustion products is expected to follow the same trend as the yield of the partial (amm)oxidation products. Ammonia is not only consumed for the formation of acrylonitrile, but can also reduce the surface under the formation of e g. N2. This will change the degree of reduction of the surface, and hence the composition of the pool of oxygen species. If ammonia cannot... 

When polyacrylonitrile is burned, toxic gases are released. In fact, in airplane fires, more passengers die from inhalation of toxic fumes than from burns. Refer to Table 12.1 for the structure of acrylonitrile. What toxic gas would you predict to be the product of the combustion of these polymers ... 

EXPLOSION and FIRE CONCERNS noncombustible solid, but contact with water may release heat sufficient to ignite combustible materials NFPA rating Health 3, Flammability 0, Reactivity 1 can ignite or react violently with acetic acid, acetaldehyde, acetic anhydride, acrolein, acrylonitrile, allyl chloride, aluminum, chlorine trifluoride, chloroform and methanol, chlorohydrin, chlorosulfonic acid, 1,2-dichloroethylene, glyoxal, hydrogen chloride, hydrogen fluoride, hydroquinone, nitric acid, sulfuric acid, nitroethane, nitropropane, nitromethane, tetra-hydrofuran, water, zinc, and others reacts to form explosive products with ammonia and silver... 

Nitrile elastomers and PVC are considered to be harmless when used with good safety practices under normal operating conditions. Residual acrylonitrile monomers, free butadiene, and vinyl chloride monomer levels are limited and controlled by industrial and environment safety standards. Stabilization of nitrile needs to be adequate to prevent spontaneous combustion. Hazardous decomposition products include carbon monoxide, carbon dioxide, nitrogen compounds, hydrogen cyanide, hydrocarbons, vinyl chloride. 

Volatile products of combustion - CO, CO, cyanides, ammonia, acrylonitrile, styrene, nitrogen ... 

Addition of a base, such as ammonia, to propane-oxygen mixture (propane ammoxidation over Ga/H-ZSM-5) has a significant effect by enhancing the formation of valuable products (propene, acetonitrile, and acrylonitrile) over total combustion (Table 13.14) [105]. However, acetonitrile (C2 molecule) prevails over acrylonitrile (C3 molecule) in a similar manner as acetic prevails over acrylic acid in propane oxidation over HFGs. The increase in Si/Al ratio, meaning the reduction of the number of Brpnsted acid sites, benefits the selectivity to propene and acrylonitrile at the expense of acetonitrile. COx selectivities are not sensitive either to change in acidity or Ga content, which could suggest that those are... 

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