A countercurrent microflow strategy for simultaneous high selectivity and conversion in aromatic nitration

TL;DR

A new microflow strategy improves both conversion and selectivity in aromatic nitration, solving a long-standing trade-off issue.

Contribution

A two-stage countercurrent microflow strategy is introduced to simultaneously enhance conversion and selectivity in aromatic nitration.

Findings

The countercurrent microflow strategy increases spatiotemporal conversion rate by over five times compared to single-stage co-current microflow.

The inhibition mechanism of over-nitration is identified, involving in situ H2O reducing nitroaromatic dissolution.

The microflow strategy achieves high conversion and selectivity without trade-offs across various aromatic substrates.

Abstract

Aromatic nitration, a hazardously complex process, poses serious risks. A major challenge for the reaction is the trade-off effect between spatiotemporal conversion rate and selectivity, particularly the over-nitration side reactions that have plagued the field for nearly 200 years. We propose a countercurrent microflow mode between two microreactors, which boosts spatiotemporal conversion rate by over five times compared to the normal single-stage co-current microflow mode, and two orders of magnitude compared to traditional batch reactors. Meanwhile, we identify an inhibition mechanism of over-nitration. The generated H2O in the main reaction can in situ reduce the dissolution of nitroaromatics in the aqueous phase and effectively prevent over-nitration. Through synergistic control of both kinetics and thermodynamics in the microreaction process, high spatiotemporal conversion and selectivity are achieved simultaneously, overcoming the trade-off effect. Furthermore, we demonstrate the broad applicability of the microflow strategy across various aromatic nitration processes.

Aromatic nitration faces a trade-off effect between conversion and selectivity. Here, the authors develop a two-stage countercurrent microflow strategy that regulates reaction kinetics and thermodynamics, simultaneously achieving high conversion and selectivity across multiple aromatic substrates.

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