Acrylonitrile - Process
Chemistry
Researchers at the Standard Oil Company of Ohio (SOHIO) invented and developed the selective one-step vapour phase catalytic reaction of propylene with ammonia and air to yield acrylonitrile in the 1950s. This economical route to acrylonitrile is referred to as “ammoxidation of propylene” or the “SOHIO Process”. The chemical equation is as follows:
Feedstocks
The feedstocks for the SOHIO Process are propylene, ammonia, and air. Propylene and ammonia supply of adequate quantity and quality are the significant commercial issues relating to feedstocks.
Reaction
INEOS acrylonitrile technology utilizes its proven fluidized-bed reactor system. The feeds containing propylene, ammonia and air are introduced into the fluid-bed catalytic reactor which operates at 5-30 psig with a temperature range of 400 – 510 °C (750 – 950 °F). This exothermic reaction yields acrylonitrile, co-products, and valuable steam.
The most important issues in a fluid-bed design are obtaining and maintaining good catalyst/gas contact to achieve high yields. Obtaining good catalyst/gas contact is essential to achieve the best reactor performance. INEOS has refined these areas of fluid-bed technology through proper internal mechanical designs which mix reactants and maintain catalyst particle size distribution in the reactor’s catalyst bed. The learning of how to achieve and optimize these conditions through years of reactor design and catalyst development, as well as by operating commercial reactors for acrylonitrile production have resulted in extensive experience and understanding that make INEOS the leader in designing reactor/catalyst systems with better yields, fewer shutdowns, and fewer environmental problems than any other technology supplier. These well-proven designs, processes, and catalyst systems allow on-stream reliability factors of 98+%.
Recovery & Purification
The effluent vapour from the reactor is scrubbed to recover the organics. Non-condensables may be vented or incinerated depending on local regulations. Hydrogen cyanide, water, light-ends, and high-boiling impurities are separated from the crude acrylonitrile in a series of fractionation steps to produce acrylonitrile product that meets specification.
Co-Products
Hydrogen cyanide (HCN) may be recovered as a by-product of this process or incinerated. The SOHIO Process has become an important commercial source for HCN. In addition, ammonium sulphate rich streams may be processed to recover sulphuric acid or concentrated and purified for sale depending upon economic considerations.
Catalyst
The development and commercialization of the first fluid-bed catalyst system for the manufacture of acrylonitrile was completed in 1960. This catalytic ammoxidation process was truly revolutionary. Since the introduction of this technology, SOHIO and its successors have developed and commercialized numerous improved catalyst formulations. These catalyst improvements have improved yields and efficiencies versus each prior generation to continually lower the cost to manufacture acrylonitrile. INEOS continues to improve upon and benefit from this long and successful history of catalyst research and development. In fact, many of INEOS’ licensees have been able to achieve increased plant capacity through a simple catalyst change-out, without the need for reactor or other hardware modifications.
Acrylonitrile End Uses
The primary use for acrylonitrile is in the manufacture of polyacrylonitrile (PAN) for acrylic fibre, which finds extensive uses in apparel, household furnishings, and industrial markets and applications, such as carbon fibre. Other end-use markets such as nitrile rubber, styrene-acrylonitrile (SAN) copolymer and acrylonitrile-butadiene-styrene (ABS) terpolymers have extensive commercial and industrial applications as tough, durable synthetic rubbers and engineering plastics. Acrylonitrile is also used to manufacture adiponitrile, which is the feedstock used to make Nylon 6,6.
Safety, Health, Environmental Considerations
INEOS considers safety, health, and environmental (SHE) to be of the highest priority and we are committed to ensuring that best practices in SHE continue to be a key part of everything we do. A s such, our acrylonitrile plant designs, operations, and related work are thoroughly scrutinized to assure their safety and reliability. For over 45 years SOHIO Process plants designed under license have operated safely worldwide in a variety of conditions and environments.
We are also committed to an open discussion on all SHE issues. In particular, we work with companies around the world to progress the chemical industry’s commitment to Responsible Care, which involves the continuous improvement of our SHE performance and the open communication of that performance. We give high priority to safety in manufacturing, storage and handling operations, and devote considerable effort to monitoring these activities and minimizing risks. INEOS intends, therefore, to continuously improve our SHE performance and will be guided by the principles to provide safe operations, produce and market products which can be safely used, progressively improve our environmental performance, and respect the interests of our neighbours and the world community.
Not only do we support and participate in industry initiatives, we also take our own initiatives in areas where we have demonstrated strengths and expertise. INEOS shares information on process and mechanical safety issues with licensees when we become aware of these issues within our own plants or from within our broad licensee network.