甘露醇喷雾干燥过程中液滴粒度分布变化的群体粒数衡算模拟和实验研究

利用群体粒数衡算（population balance，PB）计算机模拟和实验研究了甘露醇水溶液的喷雾干燥过程中液滴的粒度分布的变化规律。液滴干燥过程中的颗粒粒度的萎缩速率，在群体粒数衡算模型中描述为液滴的逆（或负）生长项，通过单个液滴反应动力学方法（reaction engineering approach，REA）获得。基于单个液滴干燥的反应工程方法模型REA和群体粒数衡算模型PB集成建立了PBREA模型。PBREA 模型的求解是通过高分辨率数值方法。本文模拟研究了不同工况下，不同粒径液滴的干燥时间、液滴平均含湿量以及液滴粒度分布随时间的变化。结果显示，液滴粒径越大，干燥时间越长，模型预测的颗粒平均粒径为实验值的1.0~1.5倍，粒度分布跨度是实验值的0.61~0.89倍。模拟误差主要来源于液滴及颗粒粒径分布统计精度、单个静止液滴与群体运动液滴干燥的差异、热导率及扩散系数是经验值3个方面。在使用Buchi 290 小型喷雾干燥仪进行的实验中，使用了图像采集和分析方法得到了液滴及颗粒的数密度分布，并和模拟结果做了对比。结果表明该模型可以有效地预测喷雾干燥过程中干燥颗粒的平均粒度及分布跨度。     

Effects of different nozzle materials on atomization results via CFD simulation

Spray drying, as a crucial operation in industrial production, converts solution to fine particle. The spray moiety directly affects the final particle morphology, size and distribution. Compared with the experimental method, computational fluid dynamics (CFD) modeling is a powerful and convenient tool for simulating the spray process. Based on the verified CFD model, different materials of atomizer were simulated to investigate the effect on droplet size and distribution in this work. The modeling result proved that the droplet size and distribution were influenced by the resistance coefficient of materials, wherein the Reynolds number could change the effect of roughness along with the change of mass flow rate on spray process. The results in this work have implication for controlling droplet size through developing new spray nozzle with different materials or surface coating.     

Comparison of freeze drying and spray drying to obtain porous nanostructured granules from nanosized suspensions

This work studies the spray drying and freeze drying of different nanosized ceramic materials and the physicochemical characteristics of the obtained granules. Colloidal suspensions of alumina, titania, and a 87/13 mixture were studied. The influence of temperature, pressure, nozzle diameter, and solids loading on the morphology and characteristics of dried granules were evaluated. It was demonstrated that these processing parameters have practically no influence, and the only parameter determining the granules characteristics is the solids content of the suspensions, in both processes. Spray drying leads to a monomodal distribution with higher granule size, while freeze drying produces more porous granules, with a bimodal intragranular distribution. The flowability of spray-dried powder is better than that of the freeze-dried powder and suit better the requirements of a feedstock targeted to obtain coatings by plasma thermal spraying whereas freeze drying can produce high porosity, softer granules.     

Controlling the morphology of ceramic and composite powders obtained via spray drying – A review

Spray drying is one of the most convenient methods for drying suspensions (slurries) and for granulation of materials. Spray dried powders have good flowability, narrow size distribution and controllable morphology. Morphology of powder particles (also called granules or microspheres) strongly affects the use and handling of powders. This review discusses the latest research on parameters that affect morphology and size of granules obtained by spray drying: atomization parameters, properties of sprayed slurry, mass transfer etc. The formation of hollow and dense granules is extensively reviewed. Granule size is affected by droplet size, slurry concentration and initial particle size. Morphology mostly depends on size distribution of initial ceramic particles, agglomeration tendency in the slurry and mechanical strength of the shell of a granule during the drying process compared to capillary force of the suspension liquid. Polymer additives (e.g. binders and lubricants) change the properties of granule shell and the evaporation of moisture; thus, polymer additives significantly affect morphology.     

Effect of Pore Size and Particle Size Distribution on Granular Bed Filtration and Microfiltration

Abstract

The paper reviews the effect of particle size distribution and pore size distribution on granular bed filter and crossflow microfiltration performance. The experimental results of the granular bed filter with pollen particles in suspension showed that the presence of large particles improved the filter efficiency of smaller particles in suspension. Microfiltration results with bi and tri‐modal latex suspensions showed that the permeate flux and the quality were significantly affected by the particle size and its distribution, especially when the particle size was smaller than the pore size of the membrane. The mathematical model simulation results of granular bed filtration show that media pore size distribution is an important parameter of filtration for the particle removal and pressure drop across the filter.     

Particles from fires—a screening of common materials found in buildings

Small combustion generated particles are known to have a negative impact on human health and on the environment. In spite of the huge amount of particles generated locally in a fire accident, few investigations have been made on the particles from such fires. In this article, 24 different materials or products, typically found in buildings have been exposed to burning conditions in order to examine their particle generating capacity. In addition, a carbon fibre based composite material was tested in order to investigate if asbestos‐resembling particles could be generated in a fire situation. The majority of the experiments were performed in the small‐scale cone calorimeter, and some further data were collected in intermediate scale (SBI) and full scale (room‐corner) tests. Additional testing of the composite material was made in a small‐scale tubular reactor. The amount of particles and particle size distributions were measured by the use of a low‐pressure impactor and particle aerodynamic diameter sizes from 30 nm to 10 μm were measured. The results from the project show that the yield of particles generated varied significantly between materials but that the shape of mass and number size distributions were very similar for all the materials tested. The maximum amount of particles was obtained from materials that did not burn well (e.g. flame retarded materials). Well‐burning materials, e.g. wood materials, tend to oxidize all available substances and thereby minimize the amount of particles in the smoke gas. It was found that asbestos‐resembling particles could be produced from under‐ventilated combustion of the composite material tested. Copyright © 2003 John Wiley & Sons, Ltd.     

Effect of process conditions on spray dried calcium carbonate powders for thermal spraying

Powder preparation is an important stage in the production of thermal spray coatings with the desired characteristics. An important powder feature is flowability, which can be adjusted through particle morphology, particle size and size distribution. Combined, these features dictate the quality of the coating produced. To increase a powder's flowability, spherical particles within a particular size range are ideal. One way to achieve this is through spray drying. The aim of the present study was to investigate the effect of spray drying process parameters on the physical properties of calcium carbonate powder, with the goal of producing large, spherical particles ranging between 50 and 100 μm in preparation for thermal spray experiments. A key aspect was the use of ethanol to aide in the production of large spheres. A 2³ factorial design of experiments (DoE) was utilised to study the following process parameters: gas flow rate, feed flow rate and solids loading. The resulting powders were characterised in terms of particle size, morphology and production yield. Porous, hollow, spherical particles were produced in a suitable size range for thermal spraying, which was attributed to the rapid evaporation of ethanol. Statistical analysis was utilised to interpret trends between the spray drying parameters and powder characteristics quantitatively.     

Spray Drying of Aqueous Salbutamol Sulfate Solutions Using the Nano Spray Dryer B-90—The Impact of Process Parameters on Particle Size

In order to prepare spherical salbutamol sulfate particles of adjustable size, a Nano Spray Dryer B-90 was employed. A 3³ full-factorial design was used to investigate the influence of process parameters (mesh size, feed concentration, and drying air temperature) on particle size (median size and width of the particle size distribution), amount of product produced per time, and product yield. The median particle size was significantly influenced by all three factors of the statistical design. Within the design space studied, particle sizes of 1.0 to 6.4 µm were obtained. The width of the particle size distribution (span) increased with increasing mesh sizes. All particles with a particle size greater than 2.4 µm showed a bimodal particle size distribution. Generally, larger mesh sizes as well as higher concentrations led to an increase in the amount of product prepared per time. The corresponding values observed were from 0.4 to 75.8 mg/min. The product yield was independent of the process parameters studied. All products were amorphous after spray drying and were stable up to a relative humidity of 60% at a temperature of 25°C.     

可再分散乳胶粉的制备与性能表征

研究间歇法、平衡溶胀法和半连续法不同工艺制备乳液，并对不同工艺制备的乳液测试其性能．详细分析了乳液胶粒粒径的分布，不同胶粒粒径对乳液性能差异的影响。对制得的产品的性能进行了表征，用喷雾干燥法可以制得性能良好的可再分散乳胶粉。     

Effects of different parameters on the characteristics of chitosan–poly(acrylic acid) nanoparticles obtained by the method of coacervation

Chitosan–poly(acrylic acid) polyelectrolyte complex nanoparticles were prepared by coacervation under mild experimental conditions without the use of any organic solvents or surfactants. The influence of some experimental parameters such as the pH of the polyelectrolyte solutions, their concentrations, and the purification procedure on the particle dimensions and their size distribution was studied in detail. The physicochemical properties of the obtained complex were characterized with Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, and dynamic light scattering. It was found that for solution concentrations below 0.1 wt %, it was possible to obtain suspensions of nanometer‐sized particles. Furthermore, it was established that the pH values of the reactant solutions had a great influence on both the particle size and the yield of the complex that was formed. The most convenient pH values for obtaining chitosan–poly(acrylic acid) particles with a nanometric size and optimum yield (near 90%) were found to be 4.5–5.5 for chitosan and 3.2 for poly(acrylic acid). Additionally, the effects of dialysis and ultrasonic treatment on the stability of complex suspensions, prepared under different experimental conditions, were clarified so that recommendations could be made to bring this system into practical use. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of Nanoparticles and Drop Size Distributions on the Rheology of w/o Pickering Emulsions

The rheological behavior of particle/oil suspensions and w/o Pickering emulsions consisting of water, 1‐dodecene and different fumed silica nanoparticles was investigated. The particles varied in hydrophobicity and specific surface area. The influence of particle concentration and water content on rheology was determined and the emulsion drop size distributions were examined. Emulsions with different drop sizes were created by either varying the particle concentration or the water content. It was found that the particles in the continuous oil phase and not the drop size distribution seem to be the major influencing factor on the Pickering emulsion rheology.     

Effects on the melt rheology of systems of Nd‐Fe‐B particles suspended in a poly(phenylene sulfide) and liquid crystalline polymer blend

The melt rheology of blends of a liquid crystalline polymer (LCP) and poly(phenylene sulfide) (PPS) and their composites with ferromagnetic Nd‐Fe‐B particles (MQP) was studied. We investigated the effects of LCP concentration, Nd‐Fe‐B particle volume fraction and size, distribution, and shear rate on the rheological properties of these composites. Enthalpy of fusion changes that were observed resulted from the addition of the LCP and Nd‐Fe‐B particles to the polymer blends/composites. The shear rate and frequency dependencies of the materials revealed a viscosity reduction at low (1–3 wt%) and moderate (10–15 wt%) LCP concentrations, and strong effects on the shear‐thinning characteristics of the melt. The suspensions of polydispersed Nd‐Fe‐B particle configurations in PPS that were of lower size ratios gave better processability, which is contradictory to previously reported behavior of suspensions containing spherical particles. Specifically, the compositions with unimodal and a bimodal distribution of Nd‐Fe‐B particles gave the lowest viscosities. The experimental data were correlated with semi‐empirical viscosity model equations of Maron‐Pierce, Krieger‐Dougherty, Eilers, and Thomas and were found to be consistent with the data. The maximum packing fraction, ϕ_m, of the MQP particles was estimated to be within the range of 0.78 ϕ ≤_m ≤ 1.0 through graphical and parametric evaluation methods.     

Preparation and Performance of Nano HMX/TNT Cocrystals

Cocrystals of 1,3,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane (HMX) and 2,4,6‐trinitrotoluene (TNT) with high energy and low sensitivity were obtained by a spray drying method. Scanning electron microscopy (SEM), X‐ray diffraction (XRD), and Fourier Transform Raman spectroscopy (FT‐Raman) were used to characterize the raw materials and cocrystals. Impact sensitivity and thermal decomposition properties of the cocrystals were tested and analyzed. The results show that microparticles prepared by the spray drying method are spherical in shape and 1–10 μm in size. The particles are aggregates of many tiny cocrystals, ranging from 50 nm to 200 nm. The formation of cocrystals originates from the N O ⋅⋅⋅ H hydrogen bonding between  NO₂ (HMX) and  CH₃ (TNT). Compared with raw HMX, the impact sensitivity of the cocrystals reduces obviously and it is much harder to decompose the cocrystal thermally.     

Characterization of the Residence Time Distribution in Spray Dryers

In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves.     

Spray drying of mannitol carrier particles with defined morphology and flow characteristics for dry powder inhalation

This study was dealing with the spray drying of tailored mannitol particles as carriers in dry powder inhalation formulations. A self-constructed spray tower equipped with a laminar rotary atomizer was used to generate very narrow particle-size distributions. A design of experiments with rotation speed and drying temperature as factors was applied for the preparation of a broad set of different mannitol particles. Drying parameters affected particle properties like particle size, particle shape, surface roughness, and flowability significantly. Here, rotation speed was mainly affecting droplet and therefore particle size. Further, it was found that the inner particle temperature, and so the pressure inside the early particle shell, plays an important role during particle formation as emerging water vapor at higher temperatures served for indented particles and rough surface structures. Lower drying temperatures resulted in spherical and smooth particles as the inner temperature remained below the boiling temperature. The occurrence of these particle properties could further be related to mannitol carrier particle flow dynamics as large indented carriers were found to be less flowable than small spherical ones. In general, it was possible to control particle properties by the parameters of the spray drying process.     

Development of an axisymmetric population balance model for spray drying and validation against experimental data and CFD simulations

An incremental model for spray drying, including a full droplet size distribution, has been implemented in a flowsheeting package incorporating tracking of distributed particle properties. Results were compared with expected trends based on standard theory and with results from a laboratory-scale spray dryer with a two-fluid nozzle for atomization. Predicted trends were as expected, with larger droplets giving substantially longer drying times and higher final moisture content. Predicted final moisture content was lower than measured values, as the very short residence times for fine particles were inadequately represented by first-order falling-rate drying kinetics. Dryer gas flow patterns were simulated by computational fluid dynamics. Calculated droplet residence times were much lower than for a plug-flow or fully mixed gas flow, because a high-velocity gas flow zone from the two-fluid atomizer persists down a substantial part of the dryer.     

Dispersion of TiO2 nanopowders to obtain homogeneous nanostructured granules by spray-drying

This work deals with the dispersion and stabilisation of nanosized TiO₂ particles in an aqueous medium as a first step in the preparation of spray-dried nanostructured powders.A colloidal route leading to the production of titania nanostructured feedstocks to obtain nanostructured powders was developed. The process was based on the production of homogeneous and concentrated TiO₂ nanosuspensions dispersed in deionised water with a suitable control of pH and the use of an appropriate anionic dispersant. Concentrated suspensions could be obtained by mixing with an ultrasounds probe at different times depending on the dispersing conditions.Homogeneous suspensions prepared were then reconstituted by spray drying into free-flowing powders with an adequate granule size distribution for diverse purposes, such as atmospheric plasma spraying coatings.     

Controlling lignin particle size for polymer blend applications

Softwood lignin produced by the LignoForce System^TM was physically processed using different milling approaches to ascertain effective and scalable means to yield micro to submicron particles of controllable and uniform size. Our work suggests that wet ball‐milling using a small milling medium is the most reliable method in terms of processing efficiency and particle‐size controllability. Controllable particle size reduction would permit lignin to be used as an effective filler in polymer blends. We show that wet‐milled lignin could, subsequently, be oven‐ or spray‐dried, and, subsequently, blended with, for instance, polypropylene (PP) through co‐extrusion. The spray‐drying method produced spherical lignin aggregates smaller and more uniform than oven‐dried ones. As a consequence, spray‐dried lignin demonstrated a more uniform distribution within the polymer melt, leading to noticeable improvement in the strain—or flexibility—of the lignin‐PP polymer blends. Furthermore, it is confirmed that the investigated drying methods had no effect on the thermal stability of the resulting lignin‐PP blends. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44669.     

Engineering Active Pharmaceutical Ingredients by Spray Drying: Effects on Physical Properties and In Vitro Dissolution

Active pharmaceutical ingredients have very strict quality requirements; minor changes in the physical and chemical properties of pharmaceuticals can adversely affect the dissolution rate and therefore the bioavailability of a given drug. Accordingly, the aim of the present study was to investigate the effect of spray drying on the physical and in vitro dissolution properties of four different active pharmaceutical ingredients, namely carbamazepine, indomethacin, piroxicam, and nifedipine. Each drug was dispersed in a solution of ethanol and water (70:30) and subjected to single-step spray drying using similar operational conditions. A complete characterization of the spray-dried drugs was performed via differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), particle size distribution analysis, solubility analysis, and an in vitro dissolution study. The results from the thermal analysis and X-ray diffraction showed that, except for carbamazepine, no chemical modifications occurred as a result of spray drying. Moreover, the particle size distribution of all the spray-dried drugs significantly decreased. In addition, SEM images showed that most of the particles had an irregular shape. There was no significant improvement in the solubility of the spray-dried drugs compared with the unprocessed compounds; however, in general, the dissolution rates of the spray-dried drugs showed a remarkable improvement over their non-spray-dried counterparts. Therefore, the results from this study demonstrate that a single spray-drying step may lead to changes in the physical properties and dissolution characteristics of drugs and thus improve their therapeutic action.     

悬浮剂粒径分布及研磨工艺研究

悬浮剂制备中普遍使用砂磨机作为研磨设备。通过改变研磨介质的直径、珠料比以及砂磨时间等工艺参数,使用激光粒度仪测量了不同工艺参数下制备的百菌清及甲氨基阿维菌素苯甲酸盐悬浮剂的粒径分布,研究了不同工艺参数对悬浮剂粒径分布的影响。试验结果表明,砂磨机中使用锆珠作为砂磨介质时,选用粒径较小的锆珠、适当的珠料比和足够的砂磨时间均可以得到粒径分布较窄的悬浮剂产品。