(736c) Model-Based Equipment Design for the Biphasic Production of 5-Hydroxymethylfurfural in a Tubular Reactor

The acid catalyzed dehydration of fructose to 5-hydroxymethylfurfural (5-HMF) in aqueous solutions suffers from low yields and carbon efficiency due to formation of undesired by-products, namely humines. A promising approach to overcome this drawback is the in-situ extraction of 5-HMF into an organic phase, leading to a significant suppression of humine formation^1,2.

On a technical scale, the concept of in-situ extraction can be realized in a biphasic countercurrent tubular reactor. In this reactor, the reaction takes place in a continuous aqueous phase with simultaneous extraction of 5-HMF into an organic phase dispersed as droplets. To facilitate the rational design of such an in-situ extraction process, we derive a dynamic reactor model containing both, reaction and extraction, as an integrated process in a biphasic system. This approach enables the time resolved simulation of the production process in a countercurrent tubular reactor. From this comprehensive description of the process as a function of space and time, we identify relevant process parameters and evaluate the potential of different solvents according to their thermo physical properties.

The biphasic reactor is modeled by a system of coupled partial differential equations (PDE) taking into account the intrinsic reaction kinetics, fluid dynamics and mass transfer. A model for the intrinsic reaction kinetics for the acid catalyzed dehydration of fructose to 5-HMF is obtained from single-phase experiments. We describe the fluid transport of the continuous phase by a convective term with the additional consideration of axial back mixing. For the description of the fluid transport of the disperse phase, we assume stationary swarm sedimentation of monodisperse droplets. Validated models for extraction columns allow us to describe single-drop mass transfer. The specific area for mass transfer is determined from the liquid hold-up in a range of technical relevant operation. The numerical solution of the PDE is obtained in less than 5 sec, thus allowing the determination of an optimized window of operation based on solvent properties and reaction conditions.

The in-situ extraction of 5-HMF increases the overall reaction yield (Y) to 69 mol% compared to single phase operation (56 mol%)³. The maximum space-time yield (STY) from simulation is 0.3 kgm^-3s^-1 which is significantly higher compared to the literature value for single-phase operation (0.18 kgm^-3s^-1)³. Moreover, solvent properties strongly influence the dynamics of mass transfer in the biphasic reactor. At high reaction rates, solvents with low viscosity can compensate for lower partition coefficients due to higher mass transfer rates. At low reaction rates, solvents with higher density are favored in order to provide a sufficient residence time for mass transfer into the disperse phase. The combination of Y and STY as an objective function allows for the optimization of the economic cost of the production process.

(1) Saha, B.; Abu-Omar, M. M. Advances in 5-hydroxymethylfurfural production from biomass in biphasic solvents. Green Chem 2014, 16, 24–38.

(2) Delidovich, I.; Leonhard, K.; Palkovits, R. Cellulose and hemicellulose valorisation: an integrated challenge of catalysis and reaction engineering. Energy Environ. Sci. 2014, 7, 2803.

(3) Fachri, B. A.; Abdilla, R. M.; Bovenkamp, Henk H. van de; Rasrendra, C. B.; Heeres, H. J. Experimental and Kinetic Modeling Studies on the Sulfuric Acid Catalyzed Conversion of D -Fructose to 5-Hydroxymethylfurfural and Levulinic Acid in Water. ACS Sustainable Chem. Eng. 2015, 3, 3024–3034