Continuous Production of Formic Acid from Biomass in a Three-Phase Liquid–Liquid–Gas Reaction Process

Abstract

In this contribution, we present for the first time a continuous production of formic acid under industrially relevant conditions using real biomass as a feedstock. A scale up to 2 L of reaction volume including product separation and catalyst recycling in an automated continuous miniplant has been realized and demonstrated for 670 h time-on-stream using sucrose as a feedstock with space-time yields of 1.1 gFA L–1 h–1, a turnover number (TON) of 840, and an average turnover frequency (TOF) of 1.3 h–1. Very remarkably, by performing a sensitivity analysis, a maximum space-time yield of 1.7 gFA L–1 h–1 was achieved. Moreover, we could demonstrate that oxygen pressures of only 0.5 bar are sufficient for complete catalyst reoxidation in our miniplant. This shows great potential for simply using air as the oxidant in a large-scale application. Very importantly, an experiment with molasses as the substrate showed the use of a technically relevant biomass for a long-term economic application of the continuous OxFA process. By using optimized conditions from the sensitivity analysis, a total amount of 1.2 g h–1 of formic acid could be continuously produced by our miniplant.