The BP (Sohio) process to produce acrylonitrile involves the catalytic oxidative reaction of propylene with ammonia in the vapor phase. Approximately stoichiometric amounts of propylene and ammonia, combined with air, are passed through the reactor in a single pass operation with a residence time of just a few seconds. 
The reaction is highly exothermic and the heat of reaction is generally used to make high pressure steam utilized downstream in separation and purification operations. The main by-products produced are hydrogen cyanide, used primarily in the manufacture of methyl methacrylate, and acetonitrile, used as an industrial solvent. Unreacted ammonia in the reactor effluent is neutralized with sulfuric acid. The resulting ammonium sulfate can be recovered for use as a fertilizer. In an effort to achieve even lower production costs, much research has been performed by several companies worldwide involving propane ammoxidation. In 1998, six patents were issued to Mitsubishi Chemical Corp. These patents deal with gas phase catalytic oxidation of propane with ammonia, i.e., ammoxidation reaction, in the presence of oxide catalyst systems. Air is used as the oxidant in the Mitsubishi ammoxidation process: 
The reaction temperature is from 340 to 480°C. Other products formed during the reaction include HCN, acetonitrile, CO, CO2 and C3H6. With air as the source of oxygen, the process suggests a high propane conversion on a once-through basis to minimize equipment size and capital cost. The Mitsubishi process has a high conversion of propane and a modest selectivity to acrylonitrile. Standard Oil Company (BP) has patents that describe conditions suitable for either a recycle process at low propane conversion and oxygen as oxidant source or a once-through process using air as oxidant. The once-through conditions feature high propane conversion with small amounts of propylene and acrylic acid by-products. For the recycle design, propylene production is high enough to necessitate recycle for propylene ammoxidation to improve overall yield. BP has patented a process for the recovery and recycle of excess ammonia from the propane ammoxidation reactor that would reduce ammonia consumption, further improving the economics. The process involves the following steps:
- Quenching the reactor effluent with an aqueous ammonium phosphate solution of which the ratio of ammonium ions to phosphate ions is between 0.7 and 1.3, with the ammonia absorbed to form a second solution stronger in ammonium ions.
- Heating the second solution to an elevated temperature to reduce the amount of ammonium ions present in the second solution back to the same level as the first solution and generate an ammonia vapor stream
- Recycling the ammonia vapor back to the ammoxidation reactor
This new report from Chem Systems compares the production economics of conventional propylene ammoxidation to developing propane ammoxidation under several scenarios (once-through, propane recycle, and ammonia recycle cases). | 
