Development of structured catalyst and reactor technologies for biomass conversion: Continuous production of sugar alcohols

Ali Najarnezhadmashhadi

Tutkimustuotos: VäitöskirjatyypitTohtorinväitöskirjaArtikkelikokoelma


Energy-efficient technologies have been an aspiration for chemical industries, especially the design of chemical reactors. Structured catalysts play an important role to achieve this purpose. Several types of structured catalysts have been invented and investigated in recent years, such as monoliths, fibers, solid foams as well as structures prepared by three-dimensional (3D) printing. Due to the fact that solid foam catalysts provide a high porosity (75-95%) and a high specific surface area, open cell foam catalyst packings have been investigated as an alternative for catalytically active reactor packings. Enhanced mass and heat transfer, suppressed pressure drop and high specific surface area are important positive features of the solid foam packings. Furthermore, the structures of pores and struts in open cell foams allow radial liquid flow and local vigorous turbulence which result in enhanced mass and heat transfer.

Development of a structured catalyst was performed successfully and ruthenium catalysts supported on carbon-coated aluminum foams (Ru/C) were prepared. First an active carbon support was prepared on open-cell aluminum foams. To incorporate a carbon layer into the aluminum foams, polymerization of furfuryl alcohol was carried out. The incorporation of ruthenium nanoparticles on the carbon coated aluminum foams was implemented by homogeneous deposition precipitation. Seven different characterization techniques such as SEM, TEM, XPS, TPR, ICP-MS, carbon monoxide chemisorption and nitrogen physisorption were applied on the solid catalysts.

The Ru/C foam catalysts were used in a continuously operating multiphase reactor set-up which had six tubular reactors working in parallel. Continuous hydrogenation of D-glucose, L arabinose and a binary mixture of L-arabinose and D-galactose were studied in the experimental setup. Through investigating different reaction parameters, the temperatures 100-110°C and the liquid flow rates 0.5-1 mL/min were found suitable for catalyst screening and activity testing. The experiments were carried out at 20 bar hydrogen pressure. The continuous hydrogenation experiments were successful, the reproducibility was good, and the foam catalysts were stable. High selectivities of the desired products, sugar alcohols and sugar alcohol mixtures were obtained.

A mathematical model for open foam catalyst structures was developed. It was based on the concept of axial dispersion as the prevailing flow pattern, on liquid-solid mass transfer effects and intrinsic kinetics on the active sites of the catalyst. Rate equations were presented for the hydrogenation of individual sugars and binary sugar mixtures on Ru/C catalysts and they were implemented in the mass transfer and flow models of the open foam catalyst. The flow pattern in the foam structure was confirmed with step change experiments with an inert tracer.

A kinetic model for sugar hydrogenation was fitted to the experimental data obtained from open foam ruthenium catalysts. The non-competitive adsorption model was used for the adsorption of sugars and hydrogen. The effect of external mass transfer was included in the IV model, because it is in practice impossible to completely eliminate the external mass transfer limitations in continuous operation of the shallow foam bed: in order to obtain a high enough liquid residence time, low liquid velocities were used.

Finally, a new advanced comprehensive and transient multiphase model for a trickle bed reactor with solid foam packings was developed where axial, radial and catalyst layer effects were combined. The unique feature of this model is that the gas, liquid and solid phase mass balances include most of the individual terms such as internal diffusion, gas-liquid and liquid solid mass transfer and intrinsic kinetics.

A very powerful software (gPROMS ModelBuilder) was used for the model development and implementation which provided rapid computations and parameter estimation results at a reasonable time. Parameter estimations for both models, including the activation energies and adsorption parameters were carried out. In all the cases, the confidence intervals of the parameters remained within 10% error, indicating a good accuracy of the parameters. To investigate the model performance, a sensitivity analysis was carried out and the effect of the kinetic parameters and the operation conditions on the arabinose and galactose conversions was studied in detail. The mathematical models developed and implemented in the present work are applicable for other three-phase research in continuous catalytic reactors with solid foam packings.
Painoksen ISBN978-952-12-4049-2
Sähköinen ISBN978-952-12-4050-8
TilaJulkaistu - 2021
OKM-julkaisutyyppiG5 Tohtorinväitöskirja (artikkeli)


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