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Mathematical modelling of transient states of continuous stirred tank reactors was considered for the case of homogeneous liquid-phase reactions. A simple and very precise kinetic measurement strategy was proposed: registration of the reactor temperature during the start-up of the reaction process. The dynamic reactor model consisted of mass and energy balances written in dimensionless forms to enable general conclusions and easy computer implementation. Model simulations were carried out by using a numerical solver for stiff differential equations and a reaction invariant was revealed by theoretical analysis. A series of transient laboratory-scale experiments for a strongly exothermic reaction, a reaction between sodium thiosulphate and hydrogen peroxide was conducted and the kinetic parameters, the pre-exponential factors and activation energies were estimated. The data fitting was further improved by incorporating the decomposition of hydrogen peroxide as a side reaction. The estimated kinetic parameters were investigated further by sensitivity analysis and Markov-Chain-Monte-Carlo-Method (MCMC) to confirm their reliability. The proposed method is applicable for relatively simple systems with a measurable heat effect. For complex multireaction systems the method should be completed with chemical analysis.

Hydrogen produced by the electrolysis of water using sustainable electricity will play an increasingly important role as an energy and a feedstock vector. Shifting from fossil to renewable resources means that new industrial platforms have to be set up to provide carbon-based fuels and bulk base chemicals to replace the current fossil resources based routes. The global demand cannot be met by indirect use of carbon dioxide via biomass necessitating the use from point sources or direct air capture, which changes the value of CO2 from waste to commodity chemicals. The production of chemicals by hydrogenation of CO2 is typically hampered by the thermodynamic conversion being far from 100% under currently viable reaction conditions. The equilibrium can, however, be shifted to increase conversion by removing one of the reaction products, namely water, from the reaction mixture with sorbents like zeolites. Prerequisite to conversion enhancement and process intensification is the close proximity of sorption and catalytic sites. This review presents the state of the art in synthesis and application of these, in fact, bifunctional materials.

BACKGROUND: Inulin is a valuable source of high purity fructose. The conversion of inulin to fructose utilizing an advanced sulfonic ion-exchange resin was previously investigated in detail in a batch reactor study, where a detailed mechanistic model for the reaction kinetics was demonstrated (J Chem Technol Biotechnol 2018;93:224–232). The same catalyst was employed in tailor-made continuous fixed-bed reactors in the current work in order to study the feasibility of continuous operation. RESULTS: Two types of reactors were utilized: a single-bed reactor and a multibed reactor with sample withdrawal between catalyst beds. The results from the single-bed reactor allowed optimal reaction conditions to be determined which were extrapolated and used for experiments in the multiple-bed reactor. High yields of fructose (75%) were obtained with the multiple-bed reactor without any degradation products. Detailed flow characterization was performed on the reactor system and residence time distribution results were merged with the detailed model for the chemical kinetics obtained from batch reactor studies taking into account mass transfer limitations, in order to obtain a rigorous model for the performance of the continuous reactor. The fit of the mathematical model to the experimental data was very good and this provides a useful tool for further development and scale-up purposes. CONCLUSIONS: The results of the two related studies highlight the potential of new reactor design strategies towards the realization of more efficient, sustainable and green processes, which can easily be scaled-up and implemented in bio-based industry.