The effect of microreactor geometry on performance

The objective of this paper is to understand how microreactor geometry affects performance. In particular, the performance of posted and channel microreactors is compared for a simple test reaction 2 NH₃ → N₂ + 3 H₂. We find that geometry plays an important role in performance. For example at a temperature of 550 C and a residence time of 0.2 seconds, a posted reactor gives about 50% conversion while a straight channel reactor gives 98% conversion. Experimentally, the conversion in the posted reactor is as expected for a CSTR, while the conversion in the channel reactor is as expected for a PFR. Flow visualization using smoke to image the flow shows little backmixing in the channel reactor, while the posted reactor shows considerable mixing. RTD measurements show a narrow residence time distribution for the channel reactor. In contrast, the posted reactor shows a broad residence time distribution with many fluctuations. This result suggests that the presence of posts can induce considerable backmixing in a microreactor, even though the flow is laminar.