Technology Profile: Production of Adipic Acid

Adipic acid (hexanedioic acid; Figure 1) is among the most important aliphatic dicarboxylic acids, with about 2.5 billion kg produced annually. It is isolated as odorless, colorless crystals with an acidic taste. Adipic acid undergoes the reactions of carboxylic acids, reacting at one or both carboxylic acid groups to form salts, esters, amides, nitriles and so on. Because of the bifunctional nature of this acid (Figure 1), it is used in a number of industrial polymerization processes. Figure 1. Adipic acid is an industrially important 6-carbon dicarboxylic acid[/caption] Most adipic acid is used captively by the producer in the manufacture of nylon-6,6 polyamide, prepared by reaction of adipic acid with 1,6-hexanediamine. Adipic acid is also used for a wide range of applications, including: conversion to esters; in placticizers, lubricants and polyurethane resins; as an acidulant for gelatins and jams; as a food additive for buffering or neutralizing; to make insect repellent; as a starch crosslinking agent; and as an intermediate for paints. Commercial production of adipic acid has been predominantly based on cyclohexane and, to a lesser extent, phenol. In light of shifts in hydrocarbon pricing, alternative adipic acid production…