A review of adiponitrile industrial production processes and associated atom economies

Adiponitrile (ADN) is an important raw material in the chemical industry, and is primarily used in the synthesis of 1,6- hexamethylenediamine (HMDA), a component of nylon 6,6. In present-day China, the technology required for the synthesis of ADN has been monopolized by several foreign corporations, including BASF, Invista, Asha and Solutia, which has hampered the development of a domestic nylon 6,6 industry. Based on this scenario, it is anticipated that the ADN market patterns in China will remain unchanged for a significant time span, suggesting that the domestic ADN industry will face long-term challenges. There are three main methods of producing ADN: electrolytic hydrodimerization of acrylonitrile, hydrocyanation of 1,3-butadiene and catalytic dehydration of adipic acid and ammonia. In the case of the electrohydrodimerization process, earlier versions employed the diaphragm method. Considering acrylonitrile do not participate in the anodic reaction, process improvements have removed the need for a diaphragm, thus allowing a simplified, one-step reaction process. However, the electrohydrodimerization method still consumes large amounts of electric energy, and the associated reaction parameters, such as the acrylonitrile concentration, electrolyte pH, current density and electrolyte flow rate, must be strictly controlled, as they may potentially affect both the selectivity and yield of the reaction. The dehydration process is typically conducted in either the liquid or vapor phase, and has the advantages of requiring minimal investment and equipment. However, the atom economy associated with this process is unsatisfactory as a result of the high reaction temperature and uncontrollable side reactions. The hydrocyanation process is comparatively superior, with the advantages of low raw-material costs, reduced energy consumption, short process flows and higher atom economy. However, the raw material hydrogen cyanide is highly toxic and its use involves significant risk, thus requiring extremely rigorous control of production equipment, operating conditions and process management practices. This paper presents an analysis of the specific technical aspects, reaction mechanisms and atom efficiencies of these different processes. The review presented herein concludes that the development of greener processes and autonomous technologies to produce ADN in place of traditional methods would be of significant benefit to the nylon 6,6 industry in China