The interplay between nucleation and patterning during shear-induced crystallization from solution in a parallel plate geometry.

Cooling crystallization of small organic molecules from solution is an important operation for the separation and purification of drug products. In this research, shear-induced nucleation from a supersaturated solution is studied in a parallel plate geometry. Under conditions of shear and small gap sizes, narrow mesoscale circular bands of small crystals appeared spontaneously and reproducibly on the plate's surface. We have investigated the connection between nucleation and the emergence of these circular patterns. Our results show that nucleation occurs preferably in zones with high local shear rate (located at the outer edges of the plates), compared to zones with low local shear rate (at the center of the plates). The time before nucleation occurs decreases significantly for increasing mean shear rate and time. The circular crystalline patterns appear at the plate's surface, where heterogeneous nucleation first occurs. Multiple hypotheses are explored to understand the pattern formation in crystallization. Since no satisfactory explanation is found, a new mechanism is proposed. This hypothesis involves crystals initially forming on the surface of the plates and undergoing stick-slip motion, which influences the local nucleation kinetics. This results in an interplay between (secondary) nucleation and stick-slip motion at the start of the crystallization process. By modifying the surface of the plates, their ability to act as a heterogeneous nucleation site can be altered, allowing control over the formation of patterns.

An immersive virtual reality learning environment with CFD simulations: Unveiling the Virtual Garage concept.

Virtual reality has become a significant asset to diversify the existing toolkit supporting engineering education and training. The cognitive and behavioral advantages of virtual reality (VR) can help lecturers reduce entry barriers to concepts that students struggle with. Computational fluid dynamics (CFD) simulations are imperative tools intensively utilized in the design and analysis of chemical engineering problems. Although CFD simulation tools can be directly applied in engineering education, they bring several challenges in the implementation and operation for both students and lecturers. In this study, we develop the "Virtual Garage" as a task-centered educational VR application with CFD simulations to tackle these challenges. The Virtual Garage is composed of a holistic immersive virtual reality experience to educate students with a real-life engineering problem solved by CFD simulation data. The prototype is tested by graduate students (n = 24) assessing usability, user experience, task load and simulator sickness via standardized questionnaires together with self-reported metrics and a semi-structured interview. Results show that the Virtual Garage is well-received by participants. We identify features that can further leverage the quality of the VR experience with CFD simulations. Implications are incorporated throughout the study to provide practical guidance for developers and practitioners.

Droplet size distribution, atomization mechanism and dynamics of dental aerosols.

Since the outbreak of COVID-19 pandemic, maintaining safety in dental operations has challenged health care providers and policy makers. Studies on dental aerosols often focus on bacterial viability or particle size measurements inside dental offices during and after dental procedures, which limits their conclusions to specific cases. Fundamental understanding on atomization mechanism and dynamics of dental aerosols are needed while assessing the risks. Most dental instruments feature a build-in atomizer. Dental aerosols that are produced by ultrasonic or rotary atomization are considered to pose the highest risks. In this work, we aimed to characterize dental aerosols produced by both methods, namely by Mectron PIEZOSURGERY® and KaVo EXPERTtorque™. Droplet size distributions and velocities were measured with a high-speed camera and a rail system. By fitting the data to probability density distributions and using empirical equations to predict droplet sizes, we were able to postulate the main factors that determine droplet sizes. Both dental instruments had wide size distributions including small droplets. Droplet size distribution changed based on operational parameters such as liquid flow rate or air pressure. With a larger fraction of small droplets, rotary atomization poses a higher risk. With the measured velocities reaching up to 5 m s-1, droplets can easily reach the dentist in a few seconds. Small droplets can evaporate completely before reaching the ground and can be suspended in the air for a long time. We suggest that relative humidity in dental offices are adjusted to 50% to prevent fast evaporation while maintaining comfort in the office. This can reduce the risk of disease transmission among patients. We recommend that dentists wear a face shield and N95/FFP2/KN95 masks instead of surgical masks. We believe that this work gives health-care professionals, policy makers and engineers who design dental instruments insights into a safer dental practice.

Dawn of a new era in industrial photochemistry: the scale-up of micro- and mesostructured photoreactors.

Photochemical activation routes are gaining the attention of the scientific community since they can offer an alternative to the traditional chemical industry that mainly utilizes thermochemical activation of molecules. Photoreactions are fast and selective, which would potentially reduce the downstream costs significantly if the process is optimized properly. With the transition towards green chemistry, the traditional batch photoreactor operation is becoming abundant in this field. Process intensification efforts led to micro- and mesostructured flow photoreactors. In this work, we are reviewing structured photoreactors by elaborating on the bottleneck of this field: the development of an efficient scale-up strategy. In line with this, micro- and mesostructured bench-scale photoreactors were evaluated based on a new benchmark called photochemical space time yield (mol·day-1·kW-1), which takes into account the energy efficiency of the photoreactors. It was manifested that along with the selection of the photoreactor dimensions and an appropriate light source, optimization of the process conditions, such as the residence time and the concentration of the photoactive molecule is also crucial for an efficient photoreactor operation. In this paper, we are aiming to give a comprehensive understanding for scale-up strategies by benchmarking selected photoreactors and by discussing transport phenomena in several other photoreactors.

Microbubbles as Heterogeneous Nucleation Sites for Crystallization in Continuous Microfluidic Devices.

Injecting a stream of microbubbles and thereby introducing a heterogeneous interface is proposed for enhancing nucleation and controlling particle formation in continuous microfluidic devices. Different gas and liquid flow rates were investigated to establish the two-phase flow regime map and to identify the optimum characteristics for microbubble flow. Subsequently, the effect of microbubbles was studied for the cooling crystallization of paracetamol. An enhanced nucleation rate compared to that in the operation without bubbles was observed and the presence of microbubbles results in the formation of more crystals, which indicates that nucleation is faster than that in operation without bubbles, i.e., the metastable zone width is reduced. Determining the crystal yield confirmed that a larger mass of crystals is obtained in a two-phase flow with microbubbles. Furthermore, results showed that the presence of microbubbles allows crystallizing continuously without clogging of the microreactor.

Ultrasound-assisted emerging technologies for chemical processes.

The chemical industry has witnessed many important developments during past decades largely enabled by process intensification techniques. Some of them are already proven at commercial scale (e.g. reactive distillation) while others (e.g. ultrasound-assisted extraction/crystallization/reaction) are on their way to becoming the next-generation technologies. This article focuses on the advances of ultrasound (US)-assisted technologies that could lead in the near future to significant improvements in commercial activities. The aim is to provide an authoritative discussion on US-assisted technologies that are currently emerging from the research environment into the chemical industry, as well as give an overview of the current state-of-the-art applications of US in chemical processing (e.g. enzymatic reactive distillation, crystallization of API). Sufficient information is included to allow the assessment of US-assisted technologies and the challenges for implementation, as well as their potential for commercial applications. © 2017 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Photochemical recovery of europium from non-aqueous solutions.

The photochemical recovery of europium from non-aqueous media, more specifically alcohols, is studied. The recovery was performed by photochemical reduction of europium(iii) to europium(ii) and subsequent removal as the insoluble EuCl2. Two charge transfer bands are present in the UV-C region, one originating from the alcohol (around 230 nm) and the other from the chloride anion (at 271 nm), which are responsible for the photochemical reduction when the solution is illuminated by a medium-pressure mercury lamp. When using different alcohol solvents, a trend is observed with regards to the removal rate and efficiency, following methanol (MeOH) < ethanol (EtOH) < isopropanol (IPA) <50/50 v/v ethanol/isopropanol (EtOH/IPA). This trend can be explained by the solubility of EuCl2 in the different solvents, and by the photon absorption at the wavelengths which provoke the reduction. In a 50/50 v/v EtOH/IPA solution, it is observed that addition of chloride ions (as LiCl) intensifies the chloride-to-europium(iii) CT band, effectively increasing the photon absorption in the 260-340 nm wavelength region. Moreover, addition of extra chloride ions decreases the solubility of EuCl2, which in turn accounts for a better recovery efficiency. However, this beneficial effect disappears when the water content rises above 1.5 wt%. For an EtOH/IPA solution with a high chloride concentration and low water content, it is feasible to recover europium from binary europium/yttrium mixtures with an efficiency of up to 94.7% and a purity of 96.7-99.8%, depending on the Eu/Y molar ratio. For higher yttrium excess, the removal rate of europium is higher, which is explained by the ability of yttrium to coordinate water molecules, decreasing the free water content in the solution. The fact that a large excess of yttrium does not compromise the removal rate of europium from the solution, proves that this technique has potential for europium recovery from red lamp phosphors (Y2O3:Eu3+), which consist entirely of europium and yttrium with a Eu/Y molar ratio of 1/20-1/30.

Impact of Tannery Effluent on the Self-purification Capacity and Biodiversity Level of a River.

The present study investigates the impact of tannery effluents on the self-purification capacity and the local macroinvertebrate community of one natural stream. As the concentration of chromium and sulfide increased from up- to downstream sites, the reduction of suspended solids, 5-days biological oxygen demand (BOD5), chemical oxygen demand and nitrification capacity decreased by 61 %, 21 %, 30 % and 74 %, respectively. Similarly, the share of Ephemeroptera, Plecoptera, and Trichoptera on the macroinvertebrate community decreased from 24 % to 0 %. Also the diversity (Simpson's) index and the correlation between the physicochemical parameters, BOD5 reduction, the macroinvertebrate abundance and the chromium concentration underpin the importance of the contamination by tannery effluents for the degradation of the stream habitat quality. In conclusion, although the physicochemical parameters indicate that the self-purification of the river can be maintained for a certain stream section, the biodiversity of the river is severely compromised.

Impacts of nickel nanoparticles on mineral carbonation.

This work presents experimental results regarding the use of pure nickel nanoparticles (NiNP) as a mineral carbonation additive. The aim was to confirm if the catalytic effect of NiNP, which has been reported to increase the dissolution of CO2 and the dissociation of carbonic acid in water, is capable of accelerating mineral carbonation processes. The impacts of NiNP on the CO2 mineralization by four alkaline materials (pure CaO and MgO, and AOD and CC steelmaking slags), on the product mineralogy, on the particle size distribution, and on the morphology of resulting materials were investigated. NiNP-containing solution was found to reach more acidic pH values upon CO2 bubbling, confirming a higher quantity of bicarbonate ions. This effect resulted in acceleration of mineral carbonation in the first fifteen minutes of reaction time when NiNP was present. After this initial stage, however, no benefit of NiNP addition was seen, resulting in very similar carbonation extents after one hour of reaction time. It was also found that increasing solids content decreased the benefit of NiNP, even in the early stages. These results suggest that NiNP has little contribution to mineral carbonation processes when the dissolution of alkaline earth metals is rate limiting.

The potential of biogas production from municipal solid waste in a tropical climate.

The objective of this study was to estimate the potential of organic municipal solid waste generated in an urban setting in a tropical climate to produce biogas. Five different categories of wastes were considered: fruit waste, food waste, yard waste, paper waste, and mixed waste. These fractions were assessed for their efficiency for biogas production in a laboratory-scale batch digester for a total period of 8 weeks at a temperature of 15-30 °C. During this period, fruit waste, food waste, yard waste, paper waste, and mixed waste were observed to produce 0.15, 0.17, 0.10, 0.08, and 0.15 m(3) of biogas per kilogram of volatile solids, respectively. The biogas produced and caloric value of each feedstock was in the range of 1.25 × 10(-3) m(3) (17 kWh)/cap/day (paper waste) to 15 × 10(-3) m(3) (170 kWh)/cap/day (mixed waste). Paper waste produced the least (<1×10(-3)(<17.8 kWh)/cap/day), and mixed waste produced the highest methane yield (10 × 10(-3) m(3) (178 kWh)/cap/day). Thus, mixed waste was found to be more efficient than other feedstocks for biogas and methane production; this was mainly related to the better C/N ratio in mixed waste. Taking the total waste production in Jimma into account, the total mixed organic solid waste could produce 865 × 10(3) m(3) (5.4 m(3)/capita) of biogas or 537 × 10(3) m(3) (3.4 m(3)/capita) of methane per year. The total caloric value of methane production potential from mixed organic municipal solid waste was many times higher than the total energy requirement of the area.

Copper-Catalyzed Continuous-Flow Transfer Hydrogenation of Nitroarenes to Anilines: A Scalable and Reliable Protocol.

A robust supported catalyst that is made up of copper nanoparticles on Celite has been successfully prepared for the selective transfer hydrogenation of aromatic nitrobenzenes to anilines under continuous flow. The method is efficient and environmentally benign thanks to the absence of hydrogen gas and precious metals. Long-term stability studies show that the catalytic system is able to achieve very high nitrobenzene conversion (>99%) when working for up to 145 h. The versatility of the transfer hydrogenation system has been tested using representative examples of nitroarenes, with moderate-to-excellent yields being obtained. The packed bed reactor (PBR) permits the use of a setup that can provide products via simple isolation by SPE without the need for further purification. The recovery and reuse of either EG or the ion-exchange resin leads to consistent waste reduction; therefore, E-factor distribution analysis has highlighted the environmental efficiency of this synthetic protocol.

Tailoring Waterborne Coating Rheology with Hydrophobically Modified Ethoxylated Urethanes (HEURs): Molecular Architecture Insights Supported by CG-MD Simulations.

A novel investigation of the effects of the hydrophilic and hydrophobic segments of hydrophobically modified ethoxylated urethanes (HEURs) on the rheological properties of their aqueous solutions, latex-based emulsions, and waterborne paints is demonstrated. Different HEUR thickeners were produced by varying the poly(ethylene glycol) (PEG) molecular weight and terminal hydrophobic size. Results reveal that the strength of hydrophobic associations and, consequently, the rheological properties of HEUR formulations can be effectively controlled by modifying the structure of the hydrophobic segment, specifically, the combination of diisocyanate and monoalcohol. This allows for the on-demand attainment of diverse rheological behaviors ranging from predominantly Newtonian profiles exhibiting lower viscosities to markedly pseudoplastic behaviors with significantly higher viscosities. The length of the hydrophilic group appears to affect viscosity only marginally up to a molecular weight of 23,000 g/mol, with more notable effects at 33,000 g/mol. Additionally, it was indicated that the rheological responses observed in water solutions provide a reliable forecast of their behavior in latex-based emulsions and waterborne paints. Coarse-grained molecular dynamics (CG-MD) simulations were also applied to gain insight into HEUR micelle dynamics in aqueous solutions. Guided by the DBSCAN algorithm, the simulations successfully captured the concentration-dependent behavior and the impact of hydrophilic chain length, aligning with the experimental viscosity trends. Various metrics were employed to provide a comprehensive analysis of the micellization process, including the hydrophobic cluster volume, the total micellar volume, the aggregation number, and the number of chains interconnecting with other micelles.

Comparative study of ageing, heat treatment and accelerated carbonation for stabilization of municipal solid waste incineration bottom ash in view of reducing regulated heavy metal/metalloid leaching.

This study compared the performance of four different approaches for stabilization of regulated heavy metal and metalloid leaching from municipal solid waste incineration bottom ash (MSWI-BA): (i) short term (three months) heap ageing, (ii) heat treatment, (iii) accelerated moist carbonation, and (iv) accelerated pressurized slurry carbonation. Two distinct types of MSWI-BA were tested in this study: one originating from a moving-grate furnace incineration operation treating exclusively household refuse (sample B), and another originating from a fluid-bed furnace incineration operation that treats a mixture of household and light industrial wastes (sample F). The most abundant elements in the ashes were Si (20-27 wt.%) and Ca (16-19 wt.%), followed by significant quantities of Fe, Al, Na, S, K, Mg, Ti, and Cl. The main crystalline substances present in the fresh ashes were Quartz, Calcite, Apatite, Anhydrite and Gehlenite, while the amorphous fraction ranged from 56 to 73 wt.%. The leaching values of all samples were compared to the Flemish (NEN 7343) and the Walloon (DIN 38414) regulations from Belgium. Batch leaching of the fresh ashes at natural pH showed that seven elements exceeded at least one regulatory limit (Ba, Cr, Cu, Mo, Pb, Se and Zn), and that both ashes had excess basicity (pH > 12). Accelerated carbonation achieved significant reduction in ash basicity (9.3-9.9); lower than ageing (10.5-12.2) and heat treatment (11.1-12.1). For sample B, there was little distinction between the leaching results of ageing and accelerated carbonation with respect to regulatory limits; however carbonation achieved comparatively lower leaching levels. Heat treatment was especially detrimental to the leaching of Cr. For sample F, ageing was ineffective and heat treatment had marginally better results, while accelerated carbonation delivered the most effective performance, with slurry carbonation meeting all DIN limits. Slurry carbonation was deemed the most effective treatment process, achieving consistently significant leaching stabilization, while also effectively washing out Cl ions, a requirement for the utilization of the ashes in construction applications. The benefits of carbonation were linked to the formation of significant quantities of Ca-carbonates, including appreciable quantities of the Aragonite polymorph formed in the slurry carbonated samples.

Understanding the ultrasound field of high viscosity mixtures: Experimental and numerical investigation of a lab scale batch reactor.

In this work, mixtures of increasing viscosity (from 0.9 to ≈720 mPas) are sonicated directly using an ultrasonic horn at 30 kHz to investigate the effect of viscosity on the ultrasound field both from an experimental and numerical point of view. The viscosity of the mixtures is modified by preparing water-polyethylene glycol solutions. The impact of the higher viscosity on the acoustic pressure distribution is studied qualitatively and semi-quantitatively using sonochemiluminescence. The velocity of light scattering particles added in the mixtures is also explored to quantify acoustic streaming effects using Particle Image Velocimetry (PIV). A numerical model is developed that is able to predict cavitationally active zones accounting for both thermoviscous and cavitation based attenuation. The results show that two cavitation zones exist: one directly under the horn tip and one around the part of the horn body that is immersed in the liquid. The erosion patterns on aluminum foil confirm the existence of both zones. The intensity of the cavitationally active zones decreases considerably with increasing viscosity of the solutions. A similar reduction trend is observed for the velocity of the particles contained in the jet directly under the tip of the horn. Less erratic flow patterns relate to the high viscosity mixtures tested. Finally, two numerical models were made combining different boundary conditions related to the ultrasonic horn. Only the model that includes the radial horn movements is able to qualitatively predict well the location of the cavitation zones and the decrease of the zones intensity, for the highest viscosities studied. The current findings should be taken into consideration in the design and modelling phase of horn based sonochemical reactors.

Continuous Counter-Current Ionic Liquid Metathesis in Mixer-Settlers: Efficiency Analysis and Comparison with Batch Operation.

Following the initial cation formation, the synthesis of ionic liquids (ILs) often involves an anion-exchange or metathesis reaction. For hydrophobic ILs, this is generally performed through several cross-current contacts of the IL with a fresh salt solution of the desired anion. However, if a large number of contacts is required to attain an adequate conversion, this procedure is not economical because of the large excess of the reagent that is consumed. In this study, the metathesis of an IL, Aliquat 336 or [A336][Cl], to ILs with other anions ([A336][X] with X = HSO4 -, Br-, NO3 -, I-, and SCN-) was studied in a continuous counter-current mixer-settler setup. McCabe-Thiele diagrams were constructed to estimate the required number of stages for quantitative conversion. Significantly higher IL conversions were achieved, combined with reduced reagent consumption and waste production. This improvement in efficiency was most pronounced for anions placed low in the Hofmeister series, for example, HSO4 -, Br-, and NO3 -, which are difficult to exchange. The performance of the counter-current experiments was compared with the conventional multistep cross-current batch process by calculating the reaction mass efficiency (RME) and the environmental factor (E-factor). The RMEs of the cross-current experiments were notably smaller, that is, 38-78% of the values observed for the counter-current experiments. The E-factors of the counter-current experiments were a factor of 2.0-6.8 smaller than those of the cross-current experiments. These sustainability metrics indicate a highly efficient reagent use and a considerable, simultaneous decrease in waste production for the counter-current IL metathesis reactions.

Insight Into Solventless Production of Hydrophobically Modified Ethoxylated Urethanes (HEURs): The Role of Moisture Concentration, Reaction Temperature, and Mixing Efficiency.

In this work, we report for the first time on the influence of the quality of reactants and reaction conditions on the production of hydrophobically modified ethoxylated urethanes (HEURs) and selected prepolymers without the use of solvents. We show that the polyol water concentration is detrimental to the progress of the main urethane forming reaction, confirming the necessity of carefully drying the reactants below 1000 ppm to suppress the consumption of diisocyanate toward urea during HEUR synthesis. Increasing the mixing speed (≈30 to 750 rpm), reaction temperature (80-110 °C), and catalyst concentration (0.035-2.1 wt % bismuth carboxylate) can significantly increase the rate of molecular weight buildup, but their effect decreases with time as the bulk viscosity increases and mixing limitations eventually take over, leading to the Weissenberg effect and chain growth termination. Consequently, for the selected formulation, the maximum product molecular weight attained lies in the range of ≈20 000-22 000 g/mol, irrespective of the specific process conditions applied.

Determination of Chlorides in Ionic Liquids by Wavelength Dispersive X-ray Fluorescence Spectrometry.

The synthesis of ionic liquids (ILs) usually involves two steps: (i) quaternization of a precursor followed by (ii) a salt metathesis reaction to introduce the desired anion. A consequence of the second step is that most ILs still contain some amount of the initial anion, often chloride. In this work, wavelength dispersive X-ray fluorescence (WDXRF) spectrometry is presented for the direct measurement of chlorides in ILs. The WDXRF settings were optimized, and the system was calibrated for the detection of chloride in several analogues of the commercially available IL Aliquat 336, [A336][X] (with X = I-, Br-, NO3 -, or SCN-). The Cl Kα intensity showed excellent linearity for samples with a conversion >0.80 (approximately Cl < 8000 ppm). Synthetic quality control samples showed that the instrumental error and deviations induced by the calibration procedure were small with maximum values of 1 and 5%, respectively. Detection and quantification limits depended strongly on the matrix (i.e., anion system and dilution) but were relatively low: 42-191 and 127-578 ppm Cl, respectively. Compared with other analytical techniques used for this purpose, the strengths of WDXRF include its ease of use, rapid measurements, the near absence of sample preparation steps, and versatility in terms of anion systems and chloride concentration range.

Effect of ultrasound on leaching of lead from landfilled metallurgical residues.

The potential of ultrasound as a process intensification technique in the extraction of lead from a landfilled metallurgical residues is explored. The silent or non-sonicated process makes use of acidic sodium chloride as the leachate with lead leaching in the range of 45% if a three-stage process is followed. The mixture was sonicated in a batch setup manufactured in-house. The yield obtained in silent conditions at the end of 240 min was already obtained within 30 min with ultrasound, which by itself was an improvement of 8 times. The yield of the process as a whole was improved by 19-26%. The reason for this improvement was investigated with respect to the reaction kinetics. The physical effect of ultrasound on the particle size was also studied by laser diffraction analysis. Finally, the improvement when using ultrasound in a multi-stage process was studied and it was shown that yields being obtained at the end of the 3rd stage in silent conditions is already obtained in the second stage when using ultrasound with 20% more selectivity.

Effects of ultrasonic irradiation on crystallization kinetics, morphological and structural properties of zeolite FAU.

In this work, NaX zeolite was synthesized and the effect of ultrasound irradiation on reaction kinetics, morphological and structural properties was investigated. Ultrasound was applied, by using a plate transducer (91.8 kHz), for the first time during the crystallization of zeolite NaX, at high temperature, varying the irradiation moment and its duration. Furthermore, ultrasound was applied after the crystallization by a horn-type transducer (20-24 kHz) at low temperature. The effects of irradiated volume (100-300 mL), sonication time (2-10 min) and ultrasound power (10-200 W) were studied with a power intensity up to 100 W/cm2. It was found that the application of ultrasound during the first hour of crystallization resulted in 20% reduction of reaction time compared to a standard crystallization. Ultrasound can also reduce the agglomeration degree of the final powder by combining high power and long sonication time. After 5 min sonication time at 0.3 W/mL, the tapped density of the powder was increased by 10%, from 0.37 to 0.41 g/mL. Finally, by scanning electron microscopy (SEM) it was demonstrated that ultrasound can disrupt the agglomerates without affecting the morphology of individual crystals.

SANS study of mixed cholesteric cellulose nanocrystal - gold nanorod suspensions.

Self-assembly of cellulose nanocrystals (CNCs) doped with anisotropic gold nanorods (AuNRs) was studied by small-angle neutron scattering. Correlation distances and structured domains were analysed to determine the influence of CNC and AuNR concentration on structuring. The transfer of the nematic structure of CNCs to AuNRs is explained in terms of an entropy-driven evolution from an isotropic to a cholesteric phase, with small nematic domains already present in the "isotropic" phase in equilibrium with the chiral nematic phase.