This is a repository copy of Particle design via spherical agglomeration: A critical review of controlling parameters, rate processes and modelling.

In this study, graphene-based titanium dioxide and zinc oxide composites (TiO 2 -G, ZnO-G) were synthesized using a hydrothermal process. Materials were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, UV−vis spectroscopy, scanning electron microscopy, and transmission electron microscopy. Photocatalytic activity of the composite materials under simulated solar light was studied using phenol as a model compound. A ca. 30% improvement on the degradation performance by the TiO 2 -G composite (and ZnO-G) was observed when reaction rate constants were compared with TiO 2 (and ZnO) only. This demonstrates the positive effect of graphene on suppressing charge recombination and extending the light absorption range. Further improvement on the photocatalytic degradation rate of phenol was obtained by coupling the two composites, ZnO-G and TiO 2 -G. This is attributed to more efficient charge separation and longer lifetime of the charge carriers, which eventually enhances the photocatalytic activity. The optimum stoichiometric amount of each component was obtained experimentally. Systematic parametric studies were also performed to study the effect of catalyst loading, initial phenol concentration, solution pH, and solar light intensity. Complete solar degradation of 40 ppm phenol was achieved within 60 min while using the coupled ZnO-G/TiO 2 -G photocatalysts at the optimum conditions.

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Oscillatory flow strategies through baffled tubular reactors provide an efficient approach in improving process kinetics through enhanced micromixing and heat transfer. Known to have high surface area to volume ratios, oscillatory flow baffled reactors (OFBR) generate turbulence by superimposing piston driven oscillatory flow onto the net flow generated by a pump. By tuning the oscillating parameters (amplitude and frequency), one can tailor the residence time distribution of the system for a variety of multiphase applications. Using a microscope camera, principal component image analysis, and pulse tracer injections, a novel noncontact approach has been developed to experimentally estimate dispersion coefficients in two geometrically different systems (DN6 and DN15, Alconbury Weston Ltd.). The paper also introduces for the first time a novel scaled-down version of the commercially available DN15 OFBR, the DN6 (about 10 times smaller scale), and provides a comprehensive experimental investigation of the effect of oscillation parameters on the residence time distributions (RTD) in both systems. The oscillation amplitude was found to have a significant positive correlation with the dispersion coefficient with 1 mm providing the least amount of dispersion in either system. Oscillation frequency had a less significant impact on the dispersion coefficient, but optimal operation was found to occur at 1.5 Hz for the DN6 and 1.0Hz for the DN15. Until now, OFBR literature has not distinguished between piston and pump driven flow. Pump driven flow was found to be ideal for both systems as it minimizes the measured dispersion coefficient. However, piston driven turbulence is essential for avoiding particle settling in two phase (solid-liquid) systems and should be considered in applications like crystallization.

L-ascorbic acid is synthetized in large industrial scale from glucose and marketed as an immune system strengthening agent and anti-oxidant ingredient. The overall yield of conversion of the precursor glucose to L-ascorbic acid is limited, therefore the crystallization is a critically important step of the L-ascorbic acid production from economic point of view. It is widely accepted that the crystal size distribution (CSD) influences numerous relevant macroscopic properties of the final crystalline product and it also significantly affects the downstream operations. The present paper discusses the chord length distribution (CLD, which is directly related to the CSD) control, during the crystallization of L-ascorbic acid from aqueous solution. Batch crystallization process is 2 employed, which is the classical, and still dominant, operation in fine chemical and pharmaceutical industries. A comparative experimental study of two state-of-the-art Quality-by-Control (QbC) based crystallization design approaches are presented: (1) a model-free QbC based on direct nucleation control (DNC) and (2) a model-based QbC using a novel nonlinear model predicative control (NMPC) framework. In the first investigation, the DNC, a process analytical technology based state-of-the-art model free control strategy, is applied. Although, DNC requires minimal preliminary system information and often provides robust process control, due to the unusual crystallization behavior of L-ascorbic acid, it leads to long batch times and oscillatory operation. In a second study the benefits of model-based QbC approach are demonstrated, based on using a NMPC approach. A population balance based crystallization process model is built and calibrated by estimating the nucleation and growth kinetics from concentration and CLD measurements. A projection based CSD to CLD forward transformation is used in the estimation of nucleation and growth kinetics. For robustness and adaptive behavior, the NMPC is coupled with a growing horizon state estimator, which is aimed to continuously improve the model by readjusting the kinetic constants. The study demonstrates that the model-based QbC framework can lead to rapid and robust crystallization process development with the NMPC system presenting good control behavior under significant plant model mismatch (PMM) conditions.