Adipic acid is an important intermediate product for polyamide 6.6 (Nylon), but is also a precursor for thermoplastic polyurethanes and other elastomers, flexible or rigid foams. Industrially, adipic acid is obtained today from a cyclohexanone/cyclohexanol mixture in a multi-stage process. When treated with nitric acid, which has first been diluted accordingly, the mixture oxidises in the presence of catalysts (acids) to form a suspension of raw adipic acid. This produces nitrogen oxides (e.g. nitrogen monoxide (NO), nitrogen dioxide (NO₂) and dinitrogen monoxide (N₂=), as well as possibly carbon monoxide and carbon dioxide.
These nitrogen oxides are separated in a different step and recycled in the nitric acid cycle. Then the crystallised adipic acid is separated. Part of the bittern from the adipic acid crystallisation is discharged from the process to prevent byproducts from accumulating and to achieve greater efficiency. The final process stages involve concentrating, crystallising/separating, purifying, cooling and drying the adipic acid produced, which at the end will be a white powder in the form of monoclinic crystals.

Costs are key when it comes to manufacturing fine chemicals on a large scale and the demand for cost-effective and efficient synthesis routes is thus high. The aim is to achieve a high yield of adipic acid, sustainable use of raw materials and energy sources as well as recovery of the basic substances in their entirety. This requires optimisation of both the chemical reactions and the process technology. KROHNE can offer a wide range of innovative, state-of-the-art measuring technology in this respect. This includes, for example, 3-path ultrasonic flowmeters based on the transit time difference principle which can identify changes in the process/contamination of the liquids via the sound velocity. Coriolis mass flowmeters are ideal for challenging process tasks and are available in four materials (titanium, stainless steel, Hastelloy® C, tantalum) to meet every requirement. Our electromagnetic flowmeters can also come fitted with an optional measuring tube made of high-tech ceramic for very aggressive liquids such as nitric acid and are extremely durable, thus saving staff resources and money.