Colloidal Silica Research Articles

Preparation, characterization and mechanism of SiO2@SiO2 core-shell microspheres through polymerization-induced colloid aggregation for fast separation using ultra performance liquid chromatography

The polymerization-induced colloid aggregation (PICA) method is commonly used to create SiO2@SiO2 core–shell silica microspheres (CSSMs), but it often encounters challenges such as incomplete shell coating and poor reproducibility. In this paper, the formation mechanism of the silica shell layer during the preparation of SiO2@SiO2 CSSMs using the PICA method was investigated. It was found that ureido modification can reduce the Zeta potential of the silica core surface, facilitating the deposition of coacervates formed by urea-formaldehyde resin (UF) and silica nanoparticles on the silica core surface to form the SiO2 shell layer when the Zeta potential of the surface is in the range of −20.1 mV to −4.8 mV. By controlling the interfacial state and surface potential of the SiO2 core, the issue of inconsistent reproducibility in preparing SiO2@SiO2 CSSMs can be overcome. Furthermore, optimization of experimental parameters such as pH, reaction temperature, water content, and reaction time can enhance the formation process. The thickness of the shell and pore size of CSSMs can be successfully adjusted by varying the reaction time and the particle size of colloidal silica sol, respectively. With optimal conditions, the semi-scale production yield of SiO2@SiO2 CSSMs can be increased to 50 g. The SiO2@SiO2 CSSMs were modified with octadecyltrichlorosilane (ODS) to be used as stationary phases in reversed phase liquid chromatography (RPLC) for fast separation of small solutes, peptides, and proteins. The superior separation efficiency indicates that the improved PICA method has the potential to be utilized as an alternative to the layer-by-layer method for large-scale production of SiO2@SiO2 CSSMs.

Elaboration Mix Design Methodology for Obtaining Defined Properties of Cement Composite with Fly Ash, Silica Fume and Colloidal Silica

Elaboration Mix Design Methodology for Obtaining Defined Properties of Cement Composite with Fly Ash, Silica Fume and Colloidal Silica

Experimental Study on the Effect of Calcium Aluminate Cement Addition on the Drying and Physical Properties of Refractory Castables Containing Colloidal Silica.

Colloidal silica-bonded castables offer several advantages compared to traditional calcium aluminate cement (CAC)-bonded castables, including lower torque values during mixing, superior drying properties, and a lower CaO content. Nevertheless, information on the combination of CAC and colloidal silica is limited, and the effect of CAC additions on the drying properties of colloidal silica-bonded castables remains unknown. In this study, these drying properties were measured by rapidly heating 400 kg samples to 500 °C and assessing the resulting damage to each sample. Additionally, the physical and chemical properties of small-scale samples were analyzed to evaluate the impact of CAC addition. The analyzed properties included cold crushing strength (CCS), density, permanent linear change (PLC) and weight loss. The microstructure of the samples was investigated by FESEM and EDS. The results indicate that adding 1.5 wt.% increased the cold crushing strength at 20 °C, while lower CAC amounts had no noticeable effect. A mullite phase was observed in the sample without CAC, and correspondingly, anorthite was found in those with CAC additions. The samples exhibited significant differences in the drying tests, with the degrees of damage increasing with the CAC addition.

Preparation of Novel Hierarchical Catalysts by Simultaneous Generation of β-Zeolite and Mesoporous Silica for Catalytic Cracking.

The gel skeletal reinforcement (GSR) method was applied at the preparation stage of β-zeolite to prepare a novel hierarchical catalyst. A solution of hexamethyldisiloxane (HMDS) and acetic anhydride, a GSR reagent, was added to the mixture of colloidal silica, sodium aluminate, tetraethylammonium hydroxide, sodium hydroxide and water, and successive aging and hydrothermal treatment gave microporous β-zeolite surrounded by mesoporous silica like core-shell structure. Its properties were characterized by XRD, nitrogen adsorption and desorption, NH3-TPD, TEM, and TG-DTA measurements, and further characteristics of the catalysts produced were clarified by the catalytic cracking of n-dodecane. The hierarchical structure of microporous zeolite and mesoporous silica was shown from GSR-2.9HS-H-Beta to GSR-3.2HS-H-Beta, where the molar ratio of HMDS and silica source of β-zeolite was 2.9~3.2 : 100. It was found that in the catalytic cracking of n-dodecane, the relative activity (the conversion per the amount of zeolite crystals) increased with the increase in mesopore volume and surface area. The result indicated that the introduction of mesopores was effective even in catalytic cracking of small molecule of n-dodecane.

Comparative Assessment of Cellular Responses to Microscale Silica Morphologies in Human Gastrointestinal Cells: Insights for Occupational Health

Silicon dioxide (SiO2), commonly known as silica, is a naturally occurring mineral extracted from the Earth’s crust. It is widely used in commercial products such as food, medicine, and dental ceramics. There are few studies on the health effects of pyrogenic and colloidal silica after ingestion. No research has compared the impact of microscale morphologies on mitochondrial activity in colon cells after acute exposure. The results show that crystalline and amorphous silica had a concentration-independent effect on cells, with an initial increase in mitochondrial activity followed by a decrease. Vitreous silica did not affect cells. Diatomaceous earth and pyrogenic silica had a concentration-dependent response, causing a reduction in mitochondrial activity as concentration increased. Diatomaceous earth triggered the highest cellular response, with mitochondrial activity ranging from 78.84% ± 12.34 at the highest concentration (1000 ppm) to 62.54% ± 17.43 at the lowest concentration (0.01 ppm) and an average H2O2 concentration of 1.48 ± 0.15 RLUs. This research advances our understanding of silica’s impact on human gastrointestinal cells, highlighting the need for ongoing exploration. These findings can improve risk mitigation strategies in silica-exposed environments.

Quantifying the effects of size exclusion on colloidal particle transport in porous media at a pore scale and column scale

AbstractColloid‐facilitated transport has been widely acknowledged as a significant contributor to surface water and groundwater pollution. Compared to water‐dissolved solutes, colloids are subject to a size exclusion effect (SEE) due to their inherent size when transported through porous media. However, only a few studies have quantitatively assessed SEE on colloid transport in porous media. In this study, we conducted dynamic observation experiments (in a quartz sand micro‐model) using a high‐speed camera and directly observed the size exclusion phenomenon of colloid transport in pores. Moreover, we further performed column experiments to quantitatively characterize the breakthrough curves of silica colloids with diameters ranging from 0.1 to 5 µm through different‐size sands. Silica colloids displayed a distinct SEE, as demonstrated by their earlier breakthroughs compared to the NaNO3 tracer. This observation served as a quantitative indicator of the SEE. The breakthrough curves were fitted using the advection‐dispersion equation to quantify this phenomenon, allowing for calculating the water saturation that is inaccessible to mobile colloids (γ). It was determined that γ exhibited a significant negative linear correlation (p < 0.01) with the average grain size (d50) of porous media. Additionally, power–law correlations were identified between γ and the colloid diameter (dp) and dp/d50. When the grain size of porous media remained below 1031 µm, an increase in the colloid diameter (from 0.1 to 5 µm) resulted in a more noticeable SEE, leading to the proportion of inaccessible pore regions to all pores increasing from 0.017 to 0.098, with this change following a power–law trend. These findings provide valuable insights into quantifying the SEE on silica colloids during transport in porous media. Furthermore, they provide theoretical support for future quantitative research on the mechanisms underlying colloid‐facilitated transport.

Unveiling the Electrostatically Driven Collapsing and Relaxation of Polyelectrolyte-Colloid Complexes: A Tunable Pathway to Colloidal Assembly.

Polyelectrolyte-colloid (PEC) complexes, ubiquitous across diverse fields, exhibit remarkable phase transitions, mimicking intricate biological assemblies. While the role of electrostatic forces in the PEC complex assembly is undeniable, achieving a holistic comprehension remains an elusive goal. This study unveils a fascinating phenomenon: the formation of highly collapsed coacervate structures in PEC complexes at elevated polyelectrolyte concentrations, followed by the swelling of complexes at even higher concentrations. Employing anionic silica colloids and cationic chitosan as a model system, small-angle X-ray/neutron (SAXS/SANS) elucidates the transition from a bead-on-a-necklace-like phase to a dense packed coacervate state (with volume fraction ∼0.62) until 3 wt % concentration of the polyelectrolyte. However, beyond 3 wt %, swelling of the dense collapsed assembly is observed. This structural evolution of PEC complexes as a function of chitosan concentration is attributed to the interplay of electrostatically driven interactions and the Donnan effect. Notably, the critical concentration for coacervation, Cs*, demonstrates a linear dependence on the initial colloid concentration. Interestingly, a complete expansion of the coacervate is observed at a high polyelectrolyte concentration, particularly for dilute colloid solutions (2 wt %). Furthermore, the addition of an electrolyte sheds light on the delicate interplay of forces. While a low electrolyte concentration partially screens charges, leading to a shift in phase diagram, higher concentrations trigger complete coacervate dissolution beyond the critical electrolyte concentration of 0.2 M, due to the complete screening of electrostatic charges.

High-efficiency synthesis of colloidal silica via suppression of foam layer

As an important fundamental material, colloidal silica is widely used in many fields. Hydrolysis of elemental silicon is an important method for the preparation of colloidal silica. This method has been widely studied because of its simple process, low cost, easy control of colloidal particle size and good stability. However, this method has the problem of low reaction conversion rate (RCR). This paper proposed an efficient method to increase RCR of colloidal silica by inhibiting the formation of a foam layer. After the size of the silicon powder particle, reaction time, and the defoamer types were optimized, the defoamer of hydrophobic fumed silica could effectively inhibit the increase of foam layer and improve the yield of colloidal silica, the RCR was significantly increased from 54.8 % to 85 % within 4 h. This research provides an innovative strategy for the efficient chemical synthesis of colloidal silica.

Facile synthesis of SSZ-16 nanoaggregates with excellent performance in NH3-SCR reaction

d6r units were proved to be crucial for the synthesis of SSZ-16 zeolite with AFX topology, and FAU zeolite owning plenty of d6r units was chosen as the essential raw material for constructing AFX frameworks. In this work, SSZ-16 zeolite was directly synthesized using colloidal silica and sodium aluminate as the raw materials in short crystallization time of 5 h. The corresponding crystallization process were carefully investigated by various characterizations, demonstrating that the key to this success was the formation of d6r units built up by a large amount of s4r units which were formed with the assistance of the appropriate organic structure directing agent (OSDA) and seeds in the synthetic media. Interestingly, the products of C-SSZ-16 zeolites presented spherical shapes consisted of relatively small particles with size range from 30 to 50 nm. Moreover, after ion-exchanged with Cu ions, the Cu-C-SSZ-16 products showed excellent performance in the selective catalytic reduction of NOx with NH3 (NH3-SCR) and better hydrothermal stability than conventional Cu-SSZ-16-con samples due to slightly higher Si/Al ratio of the Cu-C-SSZ-16. Therefore, remarkable catalytic performance and the use of low-cost raw materials as well as short period of synthesis time make AFX zeolites as potential applicants in NH3-SCR field, from an industrial viewpoint.

Reusable metal-free mesoporous carbon-catalyzed reductive N-formylation of nitroarenes and quinolines

The high-value transformation of nitrogen-containing compounds through a facile, cost-effective, and eco-friendly one-pot strategy holds significant importance. However, this process typically involves the use of metal catalysts and is limited by low activity as well as the requirement of high temperature and pressure. Herein, we describe a general and efficient metal-free N-doped mesoporous carbon material using well-defined ligand 1,10-phenanthroline as the precursor and silica colloid as the hard template. Formic acid is both a reducing agent and a formylation reagent, and structurally distinct mono- or multi-substituted nitroarenes and quinolines can be selectively N-formylation in a one-pot method. The catalyst can be easily recovered without observable loss of efficiency for ten consecutive uses. The control experiments and density functional theory (DFT) calculations indicate that formic acid mainly obtains active hydrogen in the form of O–H bond cleavage, which benefits from the strong adsorption and enhanced activity generated by the interaction between graphitic nitrogen species in the catalyst and formic acid. The excellent catalytic performance of the meso-phen-X catalyst is attributed to the synergistic effect of graphitic N and large specific surface area, providing a promising method for the development of non-metallic catalyst-modified carbon materials.

Water-Enhancing Gels Exhibiting Heat-Activated Formation of Silica Aerogels for Protection of Critical Infrastructure During Catastrophic Wildfire.

A promising strategy to address the pressing challenges with wildfire, particularly in the wildland-urban interface (WUI), involves developing new approaches for preventing and controlling wildfire within wildlands. Among sprayable fire-retardant materials, water-enhancing gels have emerged as exceptionally effective for protecting civil infrastructure. They possess favorable wetting and viscoelastic properties that reduce the likelihood of ignition, maintaining strong adherence to a wide array of surfaces after application. Although current water-enhancing hydrogels effectively maintain surface wetness by creating a barricade, they rapidly desiccate and lose efficacy under high heat and wind typical of wildfire conditions. To address this limitation, unique biomimetic hydrogel materials from sustainable cellulosic polymers crosslinked by colloidal silica particles are developed that exhibit ideal viscoelastic properties and facile manufacturing. Under heat activation, the hydrogel transitions into a highly porous and thermally insulative silica aerogel coating in situ, providing a robust protective layer against ignition of substrates, even when the hydrogel fire suppressant becomes completely desiccated. By confirming the mechanical properties, substrate adherence, and enhanced substrate protection against fire, these heat-activatable biomimetic hydrogels emerge as promising candidates for next-generation water-enhancing fire suppressants. These advancements have the potential to dramatically improve the ability to protect homes and critical infrastructure during wildfire.

Transferring red mud to efficient adsorbent for the adsorption and immobilization of Ni(Ⅱ) from aqueous solution

Red mud, a solid waste produced in large quantities, possesses a high specific surface area and is rich in metal oxides, making it a promising material for adsorbent preparation. However, its practical application is constrained by its relatively low adsorption capacity and the potential environmental risks it poses. This study focused on the preparation of modified red mud (MRM) with enhanced adsorption performance for Ni2+ using a hydrothermal method involving sodium hydroxide and colloidal silica. The maximum adsorption capacity of MRM for Ni2+ reached 8.22 mmol·g–1, a substantial improvement compared to raw red mud (0.28 mmol·g–1) and sulfuric acid-activated red mud (0.46 mmol·g–1). The pseudo-second-order kinetic and Langmuir isotherm models accurately described the monolayer chemical adsorption process of Ni2+ on MRM. Additionally, leaching tests with simulated rainwater demonstrated that Ni-loaded MRM exhibited high stability, suggesting its potential for safe stockpiling or repurposing, such as in construction materials. Sequential extraction, XRD, FT-IR, and XPS results revealed that cation exchange was the primary mechanism in the adsorption process, with Ni2+ being immobilized within the zeolite framework structure of MRM, contributing to its strong adsorption stability. Inner-sphere complex formation also played a role in Ni2+ adsorption. In conclusion, this method offers an effective approach to both red mud utilization and heavy metal removal from wastewater, presenting a practical solution for waste management through resource recovery and environmental remediation.

Enhanced particle removal ability of two representative nonionic surfactants: A reasonable interpretation based on DFT and coarse-grained molecular dynamics methods

Cleaning of copper surfaces after chemical mechanical polishing is indispensable for removing particle residues, which is a critical step in integrated circuits manufacturing. This paper introduces two nonionic surfactants, coconut oil diethanolamine (CDEA) and fatty alcohol polyoxyethylene ether (AEO-9), into a basic alkaline cleaning solution comprising tetraethyl ammonium hydroxide and lysine to investigate their abilities to enhance particle removal performance. Cleaning performance was measured with scanning electron microscopy, which showed that the two surfactants achieved excellent particle removal efficiency (above 95 %), with CDEA performing slightly better in all tested concentrations. Concerning critical micelle concentration, surface tension tests showed that CDEA (at 1500 ppm) had superior wettability and dispersive capacity compared with AEO-9 (at 2000 ppm) and could prevent particle redeposition more effectively. Using density functional theory, CDEA was found to have more polar groups to form hydrogen bonds with the hydrophilic surface of colloidal silica particles or bond with the copper substrate, explaining CDEA’s ability to lower the surface tension of the cleaning solution and improve the zeta potential between particles and the copper substrate. Finally, based on the Martini forcefield, simulations of coarse-grained molecular dynamics provided valuable theoretical insights into the different dispersion abilities of the two nonionic surfactants that CDEA had a more significant diffusion coefficient (0.073 Å2/ps) and was able to form micelles more efficiently in solution compared with that of AEO-9 (0.066 Å2/ps).

Investigation of the Influence of Copovidone Properties and Hot-Melt Extrusion Process on Level of Impurities, In Vitro Release, and Stability of an Amorphous Solid Dispersion Product.

Hot-melt extrusion (HME) is a widely used method for creating amorphous solid dispersions (ASDs) of poorly soluble drug substances, where the drug is molecularly dispersed in a solid polymer matrix. This study examines the impact of three different copovidone excipients, their reactive impurity levels, HME barrel temperature, and the distribution of colloidal silicon dioxide (SiO2) on impurity levels, stability, and drug release of ASDs and their tablets. Initial peroxide levels were higher in Kollidon VA 64 (KVA64) and Plasdone S630 (PS630) compared to Plasdone S630 Ultra (PS630U), leading to greater oxidative degradation of the drug in fresh ASD tablets. However, stability testing (50 °C, closed container, 50 °C/30% RH, open conditions) showed lower oxidative degradation impurities in ASD tablets prepared at higher barrel temperatures, likely due to greater peroxide degradation. Plasdone S630 is suitable for ASDs with drugs prone to oxidative degradation, while standard purity grades may benefit drugs susceptible to free radical degradation, as they generate fewer free radicals post-HME. ASD tablets exhibited greater physical stability than milled extrudate samples, likely due to reduced exposure to stability conditions within the tablet matrix. Including SiO2 in the extrudate composition resulted in greater physical stability of the ASD system in the tablet; however, it negatively affected chemical stability, promoting greater oxidative degradation and hydroxylation of the drug substance. No impact of the distribution of SiO2 on drug release was observed. The study also confirmed the congruent release of copovidone, the drug substance, and Tween 80 using flow NMR coupled with in-line UV/vis. This research highlights the critical roles of peroxide levels and SiO2 in influencing the dissolution and physical and chemical stability of ASDs. The findings provide valuable insights for developing stable and effective pharmaceutical formulations, emphasizing the importance of controlling reactive impurities and excipient characteristics in ASD products prepared by using HME.

Cinnamaldehyde- and nonanal-incorporated polyvinyl alcohol/colloidal silicon dioxide films with synergistic antifungal activities

Biodegradable materials may help solve the problem of environmental pollution caused by conventional synthetic food packaging. Here, various amounts of colloidal silicon dioxide [CSD, 5, 10, and 15 wt% based on polyvinyl alcohol (PVA)] and 1 % SCAN, a 1:1 (v:v) combination of cinnamaldehyde and nonanal, were added to fabricate PVA-based films. Microstructure analyses using atomic force and scanning electron microscopes revealed that the films had uniform CSD dispersion, and the surface roughness rose along with the CSD concentration. The addition of SCAN prevented UV light transmission. In addition, the introduction of CSD enhanced the water-resistance abilities and tensile strengths of the composite films. The PVA/SCAN films exerted remarkable antifungal activities against Aspergillus flavus owing to a synergistic effect between cinnamaldehyde and nonanal. Furthermore, the PVA/SCAN/CSD film, contrasted with the PVA film containing SCAN alone, attenuated the SCAN loss during storage and also continually released SCAN from the film. In peanut preservation, the PVA/SCAN/CSD composite film was superior to the single-element films in antifungal activity, showing decreases of 76.66 % and 85.33 % in the production of conidia and aflatoxin B1, respectively. In conclusion, the PVA/SCAN/CSD composite film with high UV barrier, water-resistance ability, excellent mechanical properties and antifungal activity possesses a promising application potential in food packaging.

Complementary Nanoparticle Characterization by Resistive-Pulse Sensing, Electron Microscopy, and Charge Detection Mass Spectrometry.

Nanotechnology has provided novel modalities for the delivery of therapeutic and diagnostic agents. In particular, nanoparticles (NPs) can be engineered at a low cost for drug loading and delivery. For example, silica NPs have proven useful as a controlled release platform for anti-inflammatory drugs. Despite the wide-ranging potential applications for NPs, robust characterization across all size ranges remains elusive. Electron microscopy (EM) is the conventional tool for measuring NP diameters. However, imitations in throughput and the inability to provide comprehensive information on physical properties, such as mass and density, without underlying assumptions, hinder a complete analysis. In addition, assessing sample heterogeneity, aggregation, or coalescence in solution by traditional EM analysis is not possible. Resistive-pulse sensing (RPS) provides a high throughput, solution-phase method for characterizing particle heterogeneity based on volume. Complementing these methods, charge detection mass spectrometry (CD-MS), a single particle technique, provides accurate mass information for heterogeneous samples including NPs. By combining EM, RPS and CD-MS, accurate volume, mass, and densities were obtained for silica NPs of various sizes. The results show that the density for 20 nm silica NPs is close to the density of fused silica (2.2 g/cm3). Larger silica NPs were found to have densities that were either smaller or larger, while also falling outside the range of densities usually found for silica colloids and NPs (1.9-2.3 g/cm3). Lower densities are attributed to pores (i.e., porous particles). For one sample, the mass distribution showed two components attributed to two populations of particles in the sample with different densities. The synergistic combination of EM, RPS, and CD-MS measurements outlined here for NP samples, allows much more extensive information to be obtained than from any of the techniques alone.

Investigate the influence of GO as an additive in the silica-based polyethylene glycol shear thickening fluid on the rheological properties

Abstract Shear thickening fluids (STF) represent stabilized and concentrated colloidal suspensions, wherein hard nanoparticles are dispersed within a liquid medium (polymer). Under the influence of impact forces, they exhibit non-Newtonian behavior, effectively dissipating energy through shear thickening. The optimization of the dispersion medium’s viscosity is critical, as it not only fosters shear thickening but also facilitates proper particle dispersion. This study investigates the impact of graphene oxide (GO) as an additive in STFs, analyzing both static and dynamic rheological properties. STFs were formulated using colloidal silica particles (600 nm) and polyethylene glycol (PEG-200), with varied concentrations of GO particles (0.12–0.5 % w/W). The systems underwent comprehensive analysis concerning steady-state and dynamic-state rheological behavior under diverse conditions. The findings reveal that the inclusion of GO augments both static and dynamic rheological properties, reaching an apex at an optimal concentration of 0.36 % w/W. GO functions as a network builder within the STF, interacting with the existing particle network to create a more robust and interconnected structure. These enhanced properties underscore the potential of the synthesized STF for applications requiring impact resistance.

Scale-up of the film coating process using the example of vitamin and mineral complexes: from idea to process validation

Introduction. The development of defect-free film coating modes is an urgent task when transferring film-coated tablets technology. Technology transfer is an integral stage of the life cycle of any drug approved for industrial production. During the development of the technological process, deviations may occur, to eliminate which it is necessary to introduce auxiliary operations or change the chain of technological equipment.Aim. Optimize the process of applying a film coating to tablets of the core of the vitamin and mineral complex.Materials and methods. The objects of the study were biconvex core tablets in the form of a boat of a vitamin and mineral complex consisting of vitamins C + E + B1 and minerals. To ensure the required technological properties, auxiliary substances were used: microcrystalline cellulose, sodium croscarmellose, potato starch, calcium stearate, colloidal silicon dioxide. Ready-made film-forming mixtures (Colorcon®) in beige Opadry® II 85F 270000 were used as film-forming compositions. The film coating was applied in the craters with a perforated drum BG-80 (Pro-face, China) and BGK-150 (Zhejiang Canaan Technology Limited, China).Results and discussion. The process of applying a film coating to the core tablets of a vitamin and mineral complex has been studied. The analysis of the current technological chain showed a number of disadvantages – a large amount of manual labor, the need for matting the drum, the duration of the process, low loading, braking of the production cycle due to lagging at the stage of applying the film shell. To solve the discovered problems, a project was developed to scale the technology at the stage of applying a film shell to tablets-the cores of a vitamin and mineral complex. During the implementation of the process, new equipment was purchased and installed for production. The development of the technological process made it possible to multiply the one-time loading into the boiler (by 2–3 times), automate the process due to the automatic operation function according to the parameters set before the start of the technological process, and exclude the matting of the drum from preparatory work. The quality of film-coated tablets has improved, and the risk of defects has significantly decreased.Conclusion. During the study, it was proved that transferring the film coating process to another piece of equipment can improve the quality of the resulting film-coated tablets and optimize the technological process. A multiple increase in the loading size is not carried out at the same time by changing the number of nozzles and the inner section of the hose for applying the film coating material.

Modeling the evaporation and drying of two-component slurry droplets

In this paper, we present a mathematical model and numerical simulation for the evaporation and drying of a liquid droplet containing suspended solids, relevant to processes such as spray drying and spray pyrolysis in the food and pharmaceutical industries. The model comprises three stages: first is the evaporation of the liquid droplet consisting of solid particles, followed by the second stage starting with the formation of a porous crust around a wet-core region and, finally, the third stage with sensible heating of the dry particle. Using a finite difference method with a moving grid, we account for the moving interface between the crust and wet core. Our model incorporates spatial temperature variations and is validated against experimental data on colloidal silica droplet drying, showing good agreement. We examine model assumptions and analyze the impact of drying conditions on drying rate and final particle morphology. Along with the temperature and velocity of the drying gas, we also find that the shape of suspended solid particles inside the droplet and assuming continuum flow of vapor through the crust influence drying quality. Finally, we develop a regime map to predict whether the final particle will be solid or hollow based on operating conditions.

Dynamics of water adsorption on SAPO-34: Comparison of three adsorbent bed configurations of adsorption chillers

Intensification of the adsorption dynamics is a strategic way to make adsorption chillers and heat pumps more competitive with conventional vapour compression systems. This can be achieved by consolidating the adsorbent bed with a heat exchanger to enhance heat transfer. This work investigates the dynamics of water adsorption on a commercial adsorbent SAPO-34 for three bed configurations, namely, a reference bed consisting of a monolayer of loose beads located on an aluminium plate, and two consolidated beds – a monolayer of beads glued to the plate, and a homogeneous coating of the plate prepared with binder. The morphology and texture of the prepared beds were studied by optical and scanning electron microscope techniques as well as by low temperature nitrogen adsorption. Six binders involved, both organic (hydroxyethyl cellulose, polyvinylpyrrolidone, polyaniline) and inorganic (heat-conductive compound CPTD, bentonite clay, colloidal silica sol), produced varying effects. It was found that the most preferred configuration involves SAPO beads glued to the plate with bentonite for which the heat transfer was enhanced by a factor of 1.2–1.7 while maintaining sufficient mass transfer. The effective heat transfer coefficient was measured for the most promising binders and selected configurations, and varied between 120 and 248 W/(m2 K). The heat transfer acceleration permitted the specific cooling power (at a conversion of 0.8) to increase from 2.7 kW/kg for loose beads of 0.8–0.9 mm size to 3.5 kW/kg for the same beads bound with bentonite. Thus, gluing pre-made commercial adsorbent beads with heat-exchanger with suitable binders presents a simple and promising method to enhance the adsorption dynamics, resulting in a more compact design of adsorption chillers.