Global adipic acid (ADA) demand is estimated at 2.3 million metric tons in 2012 and is growing at 3–5% per year. Nylon 66 accounts for about 85% of the total adipic acid demand. The other applications are polyurethanes (5%), adipic esters (4%), and others (6%). Major global producers of ADA include Invista, Ascend, Honeywell, BASF, Radici, China Shenma, and PetroChina. The average price has been $1,600/mt in 2012. High-purity fiber-grade adipic acid is used to make nylon 66, while lower purity adipic acid is used primarily to produce polyurethanes.
The purpose of this report is to evaluate the process engineering and corresponding economics for producing ADA from the conventional cyclohexane oxidation process, and compare the results to emerging bio-chemical routes for the purpose of determining 1) the competitive cost position of bio-routes compared to the conventional process, and 2) identifying the areas of bio-chemical processing in which meaningful technology advances can substantially improve cost competitiveness.
Recently, start-up companies such as Rennovia, Verdezyne, BioAmber, Celexion, and Genomatica have developed bio-based routes to produce adipic acid, aiming at creating 100% bio-based nylon; some have reached advanced pilot or demonstration scales. There are two basic motivations for considering alternative 'green' feedstock sources for making ADA: 1) in the long term, they could be less expensive to produce than conventional methods using crude oil derivative cyclohexane and 2) societal demands for producing industrial chemicals via 'sustainable' methods may create artificial incentives (green mandates, price subsidies, loan guarantees, government sponsored technology development) or technology-specific market demand that results in requirements for producing ADA from bio-chemical resources.
Adipic acid has traditionally been produced from various petroleum-based feedstocks (e.g., phenol, benzene, and cyclohexane), but shifts in the hydrocarbon market have resulted in the virtual elimination of phenol as a feedstock. In recent years, cyclohexane-based processes have accounted for about 93% of global production capacity. Two steps are involved in ADA production: 1) oxidation of cyclohexane to produce KA oil (cyclohexanone and cyclohexanol) and 2) nitric acid oxidation of KA oil to produce adipic acid.
This report reviews and compares the conventional DuPont/Invista cyclohexane-based process to bio-based processes developed by 1) Verdezyne using genetically modified enzymes to ferment glucose to adipic acid, and 2) Rennovia for using air oxidation to convert glucose to glucaric acid, followed by hydrodeoxygenation to convert glucaric acid to adipic acid.
We find that the Rennovia process has a high potential to be cost competitive with the conventional cyclohexane oxidation process, while the Verdezyne process has the potential to be cost competitive. The advantage of both bio-routes is their use of $300/mt glucose feedstock, compared to the conventional process using cyclohexane having a market price of $1,250/mt in 2012. However, significant challenges affect both alternative processes in their ability to achieve high feedstock selectivity and catalyst productivity (in the case of Rennovia), and high enzyme turnover rates and satisfactory kinetics for the Verdezyne enzyme fermentation route.