Process-design intensification – direct synthesis of adipic acid in flow
I. Vural Gürsel, Q. Wang, T. Noël, V. Hessel
Eindhoven University of Technology (TU/e), Micro Flow Chemistry & Process Technology, Dep. Chem. Eng. and Chem., Den Dolech 2, 5600 MB Eindhoven, The Netherlands; tel: +31(0)40 247 3108, fax: +31(0)40 244 6653, e-mail: I.Vural@tue.nl.
The use of microreactors for faster and eco-efficient process development and design as the third intensification field in Novel Process Windows will be demonstrated at the example of adipic acid production used for Nylon 6,6 manufacture. This goes beyond the first transport intensification field which refers to the high mass/heat transfer capability of microreactors and the second chemical intensification field which refers to using highly intensified and typically harsh process conditions [1-3]. Currently operating commercial production processes for adipic acid are carried out in two stages. The first step involves the production of KA Oil (a mixture of cyclohexanone, the ketone and cyclohexanol, the alcohol component) and the second stage is its subsequent oxidation to adipic acid with an excess of strong nitric acid in the presence of copper and vanadium catalysts. Only 3-8 % conversion of cyclohexane is obtained in the first step. Recycling of the large amount of cyclohexane unreacted and separation of cyclohexanol and cyclohexanone from cyclohexane present major problems. In the second step the highly corrosive nature of nitric acid and the nitrous oxide gas produced create reactor material issues and serious environmental problems . Research effort has thus been concentrated to search for an economically viable, practical (single stage, without high amount of recycle) process avoiding use of nitric acid. Recently, direct oxidation of cyclohexene to adipic acid with 30% hydrogen peroxide (H2O2) over Na2WO2 and [CH3(n-C8H17)3N]HSO4 as a phase-transfer catalyst (PTC) has been reported (see Figure...
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