Microfluidic reactor development for isothermal kinetic measurements of sugar hydrolysis and global kinetics determination by the model-fitting approach†

In this study, a novel method was developed to understand the liquid-state reactions occurring inside the intermediate liquid component (ILC) during biomass fast pyrolysis. A new experimental setup using a heated 300 μm inner diameter capillary microchannel with flow visualization was designed to study isothermal kinetics and reaction mechanisms of liquid-state sugar hydrolysis reactions. Heat- and flow patterns were investigated to confirm the intrinsic character of the kinetic measurements. Following the conventional dimensional analysis, observations with a high-speed camera and computational fluid dynamics modelling (CFD) in COMSOL Multiphysics® were used to confirm the hydrodynamic slug-flow pattern and the scale function of the temperature. The microfluidic reactor can operate within a temperature range of 453–533 K, up to 7 MPa, and a residence time within the hot section of 5 to 80 s, which is controlled by the volumetric flow rate. The novelty of this reactor is that under the specified operating conditions and residence times, it can provide isothermal measurements of intrinsic reaction kinetics, which have never been reported for hydrolysis systems. After hydrolysis in the microfluidic reactor, liquid samples were analysed off-line through HPLC to determine the sugar conversion and product yields. A fitting kinetic approach was developed to treat the kinetic data and extract intrinsic kinetic parameters describing sugar hydrolysis, key reactions occurring in the softening phase of biomass fast pyrolysis that are too often overlooked. It is proposed to integrate this experimental kinetic information into complete biomass fast pyrolysis models to take into consideration the solvent-like reactional environment.