2- and 3-Stage temperature ramping for the direct synthesis of adipic acid in micro-flow packed-bed reactors

Abstract

The synthesis of adipic acid from cyclohexene and hydrogen peroxide was investigated in micro-flowpacked-bed reactors. The isolated yield of adipic acid increases with increasing residence time inmicro-flow packed-bed reactors. The addition of phosphoric acid cannot effectively improve the isolatedyield of adipic acid though it is generally known to reduce the decomposition of H2O2. Then, differenttemperatures were tested along the reactor length, since the adipic acid synthesis is known to consistof 6 elementary reactions with different temperature needs. For experiments with 2-stage temperatureramping, 70°C and 100°C, respectively, are the optimal temperatures for the first stage and second stagereactor, which lead to 63% isolated yield of adipic acid. Furthermore, 3-stage temperature rampingimproves the yield of adipic acid to 66%. Multi-injection of hydrogen peroxide at different stages doesnot lead to a further increase in adipic acid yield. Although high temperatures are used in this transfor-mation, the in-line recording of temperature profiles along the flow axis shows that safe operation for thisexothermic reaction can be realized in the micro-flow packed-bed reactors. Notably, the space–timeyields in micro-flow packed-bed reactors are more than one order of magnitude higher than thoseobtained in batch reactors.