Estimation of particle size distributions from focused beam reflectance measurements based on an optical model

A popular in situ particle characterization technique, which can be applied without dilution, is the focused beam reflectance measurement (FBRM^®). The FBRM probe measures a chord length distribution (CLD) which is different from a particle size distribution (PSD). In order to compare results obtained by an FBRM probe with other measurement technologies such as laser diffraction, it is necessary to reconstruct the PSD from a measured CLD. For this reconstruction a measurement model and an inversion procedure are required. Most FBRM models presented in the literature assume that an FBRM records a geometric chord which can be deduced from a two-dimensional projection of the particle silhouette. In previous work [Kail, N., Briesen, H., Marquardt, W., 2008. Analysis of FBRM measurements by means of a 3D optical model. Powder Technology 185 (3), 211-222] it has been demonstrated that FBRM data show significant deviations from this geometric model. Consequently, an estimation of a PSD using such a geometric FBRM model will fail. A novel FBRM model is developed in this work. This model imitates the chord discrimination algorithm used in a Lasentec D600L FBRM system and takes the intensity profile of the laser beam and the optical aperture of the probe into account. The model is ideally suited for the estimation of a PSD from a measured CLD using a sequential, linear inversion routine, as proposed in this work. The novel FBRM model and the inversion procedure are evaluated using small, mono-disperse polystyrene beads, large ion-exchanger beads, and α-lactose-monohydrate particles. The applicability of the FBRM for PSD measurements is discussed on the basis of these results.     

Determination of non-spherical particle size distribution from chord length measurements. Part 2: Experimental validation

In this paper, the theory on the translation of a measured chord length distribution (CLD) into its particle size distribution (PSD), which was developed in the first part of this study [Li and Wilkinson, 2005. Determination of non-spherical particle size distribution from chord length measurements. Part 1: theoretical analysis. Chemical Engineering Science 60, 3251-3265], has been validated using experimental results. CLDs were measured using the Lasentec focused beam reflectance measurement (FBRM) with three different materials, spherical ceramic beads and non-spherical plasma aluminium and zinc dust particles. Meanwhile, the particle shape and PSD of each material were also investigated by image analysis (IA). Comparison of the retrieved PSDs with the measured PSDs by IA shows that the PSD can be retrieved from a measured CLD successfully using the proposed iterative nonnegative least squares (NNLS) method based on the PSD-CLD model.     

Measuring the particle size of a known distribution using the focused beam reflectance measurement technique

The accuracy of the focused beam reflectance measurement (FBRM) probe, which measures a chord length distribution, from Mettler-Toledo Lasentec^® has been explored. A particle video microscope (PVM) probe, which provides in situ digital images, was used as a direct visual method to test the reliability of the FBRM results. These probes can provide in situ particle characterization at high pressures. The FBRM has been used to study emulsions and ice and clathrate hydrate formation. The ability of the FBRM to accurately characterize unimodal and bimodal distributions of particles and droplets and to measure agglomeration events was investigated. It was found that while the FBRM can successfully identify system changes, certain inaccuracies exist in the chord length distributions. Particularly, the FBRM was found to oversize unimodal distributions of glass beads, but undersize droplets in an emulsion and was unable to measure full agglomerate sizes. The onset of ice and hydrate nucleation and growth were successfully detected by the FBRM, but quantitative analysis of the particle and agglomerate sizes required simultaneous PVM measurements to be performed.     

Modelling particle disruption of an organic fine chemical compound using Lasentec focussed beam reflectance monitoring (FBRM) in agitated suspensions

The focussed beam reflectance monitoring (FBRM) instrument developed by Lasentec is a ‘powerful’ tool used as an ‘in-situ’ particle monitoring technique for in-line real-time measurement of particle size. This technique was successfully used to monitor particulate attrition and breakage of an organic fine chemical in a turbulently agitated suspension. The great advantage of using the FBRM technique is that the change in the crystal size distribution (CSD) for different particle size classes (fine, intermediate and coarse) can be monitored as a function of time. The attrition rates can be calculated to produce a model for the disruption kernel for the organic compound. The shift in the CSD that was observed with an increase in the specific power input was found to be largely due to micro-attrition effects rather than particle breakage (splitting).     

Monitoring of cell growth using the focused beam reflectance method

In this paper the use of a focused beam reflectance measurement (FBRM) particle characterisation probe was investigated as a tool for monitoring the growth of the filamentous bacteria Streptomyces natalensis. The optimum operating parameters of the probe were identified, and it was found that the sample agitation rate had the largest effect on the mean value of a number of statistics of the chord length distribution (CLD) measured by the FBRM probe. A series of fractions of the particle size distribution was generated by sieving. It was found that the mean chord length measured by the probe responded to changes in the size distribution examined, increasing from 57.2 µm to 69.9 µm with an increase in the upper particle size from 180 µm to 300 µm. It was also found that the average total counts measured by the probe also increased with increasing sample concentration. This relationship was further investigated and it was found that in the normal range of biomass levels experienced in a fermentation (up to 4.0 g dm^?3) there was an apparently linear relationship between counts and concentration. However, as concentration was increased further the relationship became increasingly non‐linear. Copyright © 2004 Society of Chemical Industry     

Effects of ionic impurities on crystallization of cobalamin

In this paper, the influence of two typical ionic impurities (Na⁺ and Mg²⁺) is investigated with the focused beam reflectance measurement (FBRM) technique. In this system, the on-line FBRM is used as a tool for monitoring the crystallization process of cobalamin by measuring the chord length distribution of particles and the particle counts. It is noted that impurity Mg²⁺ has a more significant effect than Na²⁺ in crystal growth of the whole crystallization process. From the microscopic observation of crystals, Mg²⁺ has an obvious effect on the crystal habit, while Na²⁺ has little effect. In addition, the crystal habit changes can be monitored by particle vision measurement (PVM). Understanding these effects is helpful to aid optimization and improve process control.     

Effect of solvent type on preparation of ethyl cellulose microparticles by solvent evaporation method with double emulsion system using focused beam reflectance measurement

The purpose of this study was to investigate the effect of solvent type on the solidification rate of ethyl cellulose (EC) microparticles and particle size/distribution of emulsion droplets/hardened microparticles during the solvent evaporation process using focused beam reflectance measurement (FBRM). EC microparticles were prepared with a water‐in‐oil‐in‐water solvent evaporation method using various solvents, including dichloromethane, dichloromethane–methanol (1:1), ethyl acetate and chloroform. The particle size/distribution of the emulsion droplets/hardened microparticles was monitored using FBRM. The morphology of EC microparticles was characterized using scanning electron microscopy (SEM). The transformation of the emulsion droplets into solid microparticles for all solvents occurred within the first 10–90 min. The square weighted mean chord length of EC microparticles prepared using chloroform was smallest, but the chord count was not the highest. The chord length distribution (CLD) measured by FBRM showed that a larger mean particle size gave longer CLD and a lower peak of particle number. SEM data revealed that the morphology of microparticles was influenced by the type of solvent. FBRM can be employed for online monitoring of the shift in the microparticle CLD and detect transformation of emulsion droplets into solid microparticles during the solvent evaporation process. The microparticle CLD and transformation process were strongly influenced by solvent type. © 2017 Society of Chemical Industry     

Effects of ionic impurities on crystallization of cobalamin

In this paper, the influence of two typical ionic impurities (Na⁺ and Mg²⁺) is investigated with the focused beam reflectance measurement (FBRM) technique. In this system, the on-line FBRM is used as a tool for monitoring the crystallization process of cobalamin by measuring the chord length distribution of particles and the particle counts. It is noted that impurity Mg²⁺ has a more significant effect than Na²⁺ in crystal growth of the whole crystallization process. From the microscopic observation of crystals, Mg²⁺ has an obvious effect on the crystal habit, while Na²⁺ has little effect. In addition, the crystal habit changes can be monitored by particle vision measurement (PVM). Understanding these effects is helpful to aid optimization and improve process control.     

On‐line monitoring of chord distributions in liquid–liquid dispersions and suspension polymerizations by using the focused beam reflectance measurement technique

The on‐line monitoring of the droplet/particle size distributions is very important to ensure the quality and applicability of various products in heterogeneous systems. For this reason, the main objective of the present work was to study the usage of the focused beam reflectance measurement (FBRM) technique for monitoring of liquid–liquid dispersions (styrene dispersion in aqueous solutions) and suspension polymerization of styrene. To do better understand the FBRM technique in these systems, the effects of surfactant concentrations, agitation speed and ambient light were evaluated during the in‐line monitoring of average chord lengths and chord‐length distributions (CLD) at different operation conditions in batch experiments. In addition, a preliminary investigation of the optimal probe position was conducted in the polymerization experiments. It is shown that the FBRM technique is sensitive to variations of particle sizes in the characteristic ranges of particle diameters of typical styrene suspension polymerizations, being useful for monitoring and also control applications that require the on‐line characterization of CLD in real time in liquid–liquid dispersions and polymerization systems. POLYM. ENG. SCI., 56:309–318, 2016. © 2015 Society of Plastics Engineers     

Restoration of particle size distributions from fiber-optical in-line measurements in fluidized bed processes

An in-line probe for the measurement of chord length distributions was employed in fluidized bed granulation processes to investigate the growth behavior and the influence of process parameters. The application of a transformation approach of chord lengths into particles sizes enabled the real-time detection of the evolving particle size distribution, which is a presupposition for the integration into process control systems. Due to the ill-conditioned nature of the transformation algorithm several concepts for noise reduction and stability preservation were investigated and revealed significant synergetic effects for the combination of filtering techniques with discretization parameters. In order to meet the fluctuating, process dependent SNR-levels of the chord length distribution measured by the probe the filtering approaches were required to be self-regulating. Featuring a dynamic noise reduction the power spectral density aided sliding discrete Fourier transform produced the most adequate filtering results.     

Determination of non-spherical particle size distribution from chord length measurements. Part 1: Theoretical analysis

In this paper, extensive theoretical studies are described on two important issues in translating a chord length distribution (CLD) measured by FBRM instrument into its particle size distribution (PSD) including PSD-CLD and CLD-PSD translation models for general non-spherical particles. Analytical solutions to calculate the PSD-CLD models for spherical and ellipsoidal particles are developed. For non-spherical particles, a numerical method is given to calculate the PSD-CLD model. The iterative non-negative least squares (NNLS) method is proposed in the CLD-PSD model, because of its many advantages converting measured CLD into its PSD, such as insensitivity to measurement noise and particle shape. The effectiveness of the proposed methods is validated by extensive simulations.     

Effect of sepiolite on the flocculation of suspensions of fibre-reinforced cement

Sepiolite is used to increase thixotropy of cement slurries for easier processing, to prevent sagging and to provide a better final quality in the manufacture of fibre-reinforced cement products. However, the effect of sepiolite on flocculation and its interactions with the components of fibre cement are yet unknown. The aim of this research is to study the effects of sepiolite on the flocculation of different fibre-reinforced cement slurries induced by anionic polyacrylamides (A-PAMs). Flocculation and floc properties were studied by monitoring the chord size distribution in real time employing a focused beam reflectance measurement (FBRM) probe. The results show that sepiolite increases floc size and floc stability in fibre-cement suspensions. Sepiolite competes with fibres and clay for A-PAMs adsorption and its interaction with A-PAM improves flocculation of mineral particles.     

自絮凝酵母颗粒的在线检测与定量表征

引　言固定化细胞可以提高生物反应器的设备生产强度指标, 并且使产物与细胞容易分离, 因此引起人们的极大兴趣[1,2]. 利用细胞的自絮凝功能, 将其作为一种有效的固定化细胞手段, 是近年来提出的新概念, 并在乙醇发酵领域得到了发展[3,4].然而, 细胞自絮凝形成的颗粒一般都具有     

Monitoring the Crystallization Process of Methylprednisolone Hemisuccinate (MPHS) from Ethanol Solution by Combined ATR-FTIR- FBRM- PVM

In-situ Attenuated total reflectance Fourier transform infrared (ATR-FTIR), focused beam reflectance measurement (FBRM) and particle video microscope (PVM) have been used simultaneously in this work to monitor the concentration, supersaturation, chord length distribution, and crystal habit, respectively, during a cooling crystallization process of Methyprednisolone Hemisuccinate (MPHS) from ethanol system. We developed a new calibration method based on peak ratios for the assessment of the concentration, solubility, and supersaturation in the 20–60°C temperature range. The crystallizations were conducted at two concentrations (7.5 and 9.5% w/w) with three different cooling rates (0.3, 0.5, and 0.7 K/min). The lower concentration was chosen within the constructed calibration range while the higher one was outside the calibration range and it was used to examine the extrapolating and predicting ability of the constructed calibration curves. The metastable zone widths (MSZW), supersaturation at nucleation, and the number of fine particle chord length of MPHS were all increased with the cooling rate, while the number of the larger chord length decreased with the increasing of the cooling rate.     

EDTA-2Na对磷酸二氢铵连续稳态结晶过程的影响

针对目前工业上湿法磷酸生产高纯度磷酸二氢铵(MAP)过程中磷收率低、结晶母液利用困难以及晶体中金属离子含量高等问题,本研究提出螯合法生产高纯度MAP新工艺。在MAP结晶过程中加入螯合剂EDTA-2Na,螯合杂质金属离子,从而降低MAP晶体中杂质含量,提高MAP纯度。采用聚焦光束反射测量仪(FBRM)在线颗粒监测技术以及OptiMax全自动反应器的精确控温模块测定了溶解度和介稳区宽度等数据,分析了EDTA-2Na对MAP晶体的弦长分布、形貌和晶胞参数等的影响,系统研究了在生产过程中EDTA-2Na对MAP连续稳态结晶过程的影响。     

Chord length characterization using focused beam reflectance measurement probe - methodologies and pitfalls

The impact of the solid concentration and refractive index of dispersing medium on the FBRM measurement of chord length and particle counts were investigated using the PVC (polyvinylchloride) particle systems. It was found that the chord length increased with the solid concentration in the diluted region, but decreased as the concentration became greater than 1.1%. The total particle counts were found to increase initially with the solid concentration, tapering off at high concentrations. The measured counts of small chords (1 μm-50 μm) were found to increase linearly with the solid concentration, those of the large chords increased with the concentration initially and leveled off (50 μm-200 μm) or decreased (200 μm-500 μm) with further increase of concentration. The impact of the refractive index of the dispersing medium on the FBRM measurement was also investigated, the result of which was corroborated by microscopy studies. Comparison between the FBRM and other sizing techniques revealed that when appropriate weighting factors were applied, good agreement could be achieved between the median average values of the chord length and particle size distributions.     

Optimal seed recipe design for crystal size distribution control for batch cooling crystallisation processes

The paper presents a novel quality-by-design framework for the design of optimal seed recipes for batch cooling crystallisation systems with the aim to produce a desired target crystal size distribution (CSD) of the product. The approach is based on a population balance model-based optimal control framework, which optimises the compositions of seed blends, based on seed fractions that result from standard sieve analysis. The population balance model is solved using a combined quadrature method of moments and method of characteristics (QMOM-MOCH) approach for the generic case of apparent size-dependent growth. Seed mixtures are represented as a sum of Gaussian distributions, where each Gaussian corresponds to the seed distribution in a particular sieve size range. The proposed methods are exemplified for the model system of potassium dichromate in water, for which the apparent size-dependent growth kinetic parameters have been identified from laboratory experiments. The paper also illustrates the simultaneous application of in situ process analytical tools, such as focused beam reflectance measurement (FBRM) for nucleation detection, attenuated total reflection (ATR) UV/Vis spectroscopy for concentration monitoring, as well as the in-line use of laser diffraction particle sizing for real-time CSD measurement.     

FBRM and PVM investigations of the double feed semi-batch crystallization of 6-aminopenicillanic acid

6-Aminopenicillanic acid (6-APA) is a crucial pharmaceutical intermediate in the chemistry of semi-synthetic antibiotics. The focused beam reflectance measurement (FBRM) technology and particle vision measurement (PVM) technology were employed to the processes of online-monitoring of 6-APA crystallization behavior in a double-feeding semi-batch crystallizer. Experiments were carried out with four kinds of double-feeding policies and the results were compared with the traditional single-feeding. Records and analysis of FBRM indicated that the nucleation of double feeding policy was much higher than single policy, and chord length of 6-APA was almost determined and had little change after the nucleation peak. Ostwald ripening process had no significant effect on further growth of 6-APA crystal. PVM images showed that the crystal habit of 6-APA was continuously changed during the crystallization process. The development of (002) face in the final crystal for the five feeding policies were different.     

In‐Line Monitoring of Crystallization Processes Using a Laser Reflection Sensor and a Neural Network Model

Laboratory‐scale experiments were carried out for measuring the chord length distribution of different particle systems using a laser reflection sensor. Samples consisted of monodisperse, polydisperse and bimodal FCC catalyst and PVC particles of different sizes, ranging from about 20 to 500 μm. The particles were dispersed in water, forming suspensions with solid‐phase mass fractions ranging from ca. 0.2 % until ca. 30 %. The experimental results, consisting of the particle number counting per chord length class, were used in fitting a neural network model for estimating the mass concentration of particles in the suspension and the volume‐based size distribution, eliminating the effects of suspension concentration and particle shape. The results indicate the feasibility of using such a model as a software sensor in crystallization processes monitoring.