Adipic acid

Adipic acid is a white, crystalline solid. Chemically it is also called hex-anedioic acid (hexane-1,6-dioxic acid), which is a C6 straight-chain dicarbox-ylic acid. It is only slightly soluble in water but very soluble in alcohol and acetone.

The annual world production was about 3.8 Mio t in 2003 (EPA, 2005b). One-third is produced in the USA. It accounts for 90 percent of commercial nylon production which is further processed into fibers for applications in carpeting, automobile tire cord, and clothing. Furthermore adipic acid is used for plasti-cizers and lubricants components, and for making polyester polyols for poly-

urethane systems. Food grade adipic acid is used as a gelling aid, acidulant, leavening and buffering agent. Its derivates are used in making flavoring agents, internal plasticizers, pesticides, dyes, textile treatment agents, fungicides, and pharmaceuticals.

Commercial adipic acid is mostly produced from cyclohexane through a two-stage oxidation process. The first involves the catalytic reaction of cyclohex-ane with oxygen to produce a mixture of cyclohexanol and cyclohexanone. Afterwards, adipic acid is formed by another catalytic reaction of the mixture with nitric acid and air.

Due to the use of nitric acid in this process, N2O is generated at a rate of 0.333 t per ton of adipic acid. It is emitted by the waste gas stream. In modern plants the waste gas is treated by an abatement system which destroys pollutants by catalytic or by thermal reactions, with an efficiency of 95 and 98 percent, respectively. Due to the installation of these technologies in most plants, the N2O emissions from adipic acid production have been reduced by two-thirds since 1990. In 2000 the total emissions by adipic acid production were about 50 Mio t of N2O. Despite positive effects in reducing specific emissions by abatement technologies, a rise of the emissions by about one-third to about 67 Mio is envisaged due to rising worldwide production capacities. The current total emissions caused by adipic acid in the U.S. industry is about 5.7 Mio ton CO2-eq.

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