Nicolas Abatzoglou

Phenomenological kinetics of complex systems: the development of a generalized severity parameter and its application to lignocellulosics fractionation

Abstract The modelling of complex reaction systems, either homogeneous or heterogeneous, is possible only when the sequence of all of the elementary steps is established. Few complex reactions have, however, a known and unambiguously determined set of elementary steps. Modelling of such complex systems is essentially phenomenological; thus, the estimated kinetic parameters lack mechanistic meaning and are functions of the ranges of experimental conditions used. Confronted with this situation, industrial applications of such complex reactions have adopted the use of severity factors which try to combine into a single parameter the effect of the different operational variables. In what follows we shall focus on the application of the reaction ordinate to the case of biomass fractionation leading to hemicellulose solubilization. We shall propose a new, generalized severity parameter which accounts for the acid catalyst effect on the extent of reaction. Despite the fact that the kinetics of complex systems are essentially phenomenological, we present here an approach derived from basic kinetic principles.

Connected Three-Phase Boundary Length Evaluation in Modeled Sintered Composite Solid Oxide Fuel Cell Electrodes

A numerical methodology for evaluating the three-phase boundary length (TPBL) in sintered composite solid oxide fuel cell electrodes is developed. Three-dimensional models of a representative volume element of sintered composite electrodes are generated for which the mean particle diameter, composition, and total porosity may be specified as input parameters. Tomographic methods are used to reconstruct the modeled electrode and the percolation for each phase is evaluated. The connected TPBL is calculated for a range of electrode designs and comparisons are made with calculated TPBL values available in the literature. The maximum connected TPBL occurred at a porosity of 0.21 and at equal solid volume fractions of ionic and electronic conducting phases for particles having the same mean diameter and particle size variance. A cubic envelope having a minimum length of 14 times the mean particle diameter was necessary to adequately represent the electrode structure.

Insights into the Role of Electrostatic Forces on the Behavior of Dry Pharmaceutical Particulate Systems

PurposeUnder different charging conditions, particles can be either attracted or repulsed by each other, causing powder agglomeration or segregation. Such behavior can be detrimental in many processes aimed at achieving particulate mixture homogeneity. Consequently, the effects of electrostatic charges on mixing kinetics must be well understood to insure a high level of process control, product quality, and reproducibility.MethodsIn Part 1, an electrostatic charger is used to evaluate the ability of the studied particles to develop and retain an induced charge at the surface for a fixed period of time. Part 2 assesses the natural electrostatic charge developed by powders sliding across a stainless steel, plastic, or Tyvek chute. In Part 3, 2 binary systems were formed according to an experimental design under different charging conditions, and their behavior was quantified by measuring the degree of agglomeration attained.ResultsThis work has shown that each raw material develops a different charge according to its physico-chemical properties and the type of contact surface. Electrostatic charges influence the creation of agglomerates under certain conditions.ConclusionsThe presence of electrostatic charges must be accounted for in any effort to maximize mixing efficiency.

Prediction of Segregation Tendency Occurrence in Dry Particulate Pharmaceutical Mixtures: Development of a Mathematical Tool Adapted for Granular Systems Application

Segregation phenomena are of importance in nearly all processes involving dry granular and powder mixtures. The extent of segregation directly influences the eventual rejection of a considerable percentage of the final product in the majority of pharmaceutical processes; among these are those mixtures destined for powder compression processing for the production of tablets. Although the parameters influencing segregation are relatively well-known qualitatively, there are, so far, no widely accepted quantitative prediction tools that permit process improvement and optimization of production as a function of the mixtures composition and the particulars of individual processes (e.g., geometry of the vessels). Thus, within present practice, only general design considerations and the technical expertise of engineers and operators are relied upon to optimize these processes on a case-by-case basis. It is in these circumstances that a study of the tendency towards segregation in free flowing granular materials was conducted, using a simple tool previously developed for the study of the behavior of continuous chemical reactors behavior with classical fluid flows. The measurement of average residence times and their variance is used to calculate the deviation of chemical reactors from the ideal behavior of a perfectly mixed vessel or a plug flow pattern. In this work, these measurements are adapted to evaluate the tendency of a granular mixture to segregate. The method consists of introducing a pulse perturbation (of another material) to the established regular flow of a single granular material or a granular mixture and to then calculate the response of the system in terms of the concentration of the pulsed material at the process outlet. The average granular particle residence time and its standard deviation are then related to the segregation tendency.

Powder and Other Divided Solids Mixing. Scale-Up and Parametric Study of a Ribbon Blender Used in Pharmaceutical Powders Mixing

This work is aimed at evaluating the effect of ribbon blender operational parameters on mixture quality. Mix quality parameters and blend uniformity limits are enforced by regulatory bodies. These limits have served in this present work as targets for blending end-points. In a laboratory-scale model ribbon blender, built by scaling down a real industrial unit, powder mixtures composed of white and blue microcrystalline cellulose (MCC) were blended. Blend uniformity was evaluated using a statistical analysis method under various operating conditions such as loading patterns, blender filling percentage, impeller rotational speeds, and mixing times. It was shown that the filling percentage is the most influential mixing parameter. At high impeller rotational speed, the blending end-point was never reached during experimentation.

Using multiple Process Analytical Technology probes to monitor multivitamin blends in a tableting feed frame

As Process Analytical Technology (PAT) implementation grows in the pharmaceutical industry, more studies are being performed to evaluate its suitability in new applications and processes within the manufacturing chain. As the last step in tablet production, the compression stage represents a critical phase that ensures product quality. In-line control put in place at this stage has the potential to detect powder blends that are out of specification limits and, thus, help to improve product quality. The objectives of the present project are to quantify the composition of a commercial 31-component multivitamin powder blend in real time on an industrial feed frame, using 3 different PAT tools: light-induced fluorescence spectroscopy, near infrared spectroscopy and red, green and blue color imaging. To do so, the concentrations of 5 components (Beta-Carotene, Riboflavin, Ferrous Fumarate, Ginseng and Ascorbic Acid) were alternately changed and monitored with one or many probes. Transition periods between batches served to quantify different powder flow dynamics with sequential composition step changes. The results showed that 4 out of 5 components, each present in commercially-relevant concentrations, could be monitored by one or more tools. Flow dynamics were measured and found to vary significantly in different powder blends.

From Nanoparticles to Process: An Aberration-Corrected TEM Study of Fischer-Tropsch Catalysts at Various Steps of the Process

χThe nanostructure of Fischer-Tropsch (FT) Fe carbides are investigated using aberration-corrected high-resolution transmission electron microscopy (TEM). The plasma-generated Fe carbides are analyzed just after synthesis, following reduction via a H2 treatment step and once used as FT catalyst and deactivated. The as-produced nanoparticles (NPs) are seen to be abundantly covered with graphitic and amorphous carbon. Using the extended information limit from the spherical aberration-corrected TEM, the NPs could be indexed as a mixture of NPs in the θ-Fe3C and χ–Fe5C2 phases. The reduction treatment exposed the NPs by removing most of the carbonaceous speSubscript textcies while retaining the χ–Fe5C2. Fe-carbides NPs submitted to conditions typical to FT synthesis develop a Fe3O4 shell which eventually consumes the NPs up to a point where 3-4 nm residual carbide is left at the center of the particle. Subscript textVarious mechanisms explaining the formation of such a microstructure are discussed.

Development of a multivariate light-induced fluorescence (LIF) PAT tool for in-line quantitative analysis of pharmaceutical granules in a V-blender

Process analytical technologies (PAT) enable process insight, process control and real-time testing. Light-induced fluorescence (LIF) spectroscopy is especially well suited for low-concentration ingredients as, in many cases, it is the most sensitive probe of the in-line PAT toolbox. This study is aimed at verifying the applicability of a multivariate LIF analyzer to monitor granulated powder blends in industrial settings. Its targets are to: (1) evaluate the critical parameters of powders to obtain robust, precise and accurate concentration predictions and (2) assess technology performance for in-line monitoring of blending operations. Varying dye properties, moisture levels and particle sizes have been shown to have the most significant impact on fluorescence emission. Reliable quantitative models can be obtained by controlling and/or mitigating these factors.

Application of Gasification to the Conversion of Wood, Urban and Industrial Wastes

Gasification is widely accepted as a technological option for the production of synthesis gas (SG) via partial oxidation of heterogeneous organic matter such as, residual biomass, classified urban wastes (RDF), autofluff, residual non-recyclable plastics, rubbers as well as other industrial organic wastes. The “producer gas”, after an appropriate conditioning step, whose nature depends upon its final intended utilisation, can be used either directly or mixed with natural gas (NG) for the generation of electricity and/or heat.

Monitoring the concentration of flowing pharmaceutical powders in a tableting feed frame

Abstract The use of process analytical technology (PAT) tools is increasing steadily in the pharmaceutical industry. Such tools are now located throughout the process. When producing tablets, the tableting step itself may be the ideal moment to assess final product composition. Being the last unit operation in tablet production where the elements are still free flowing, it is relatively straightforward to ascertain the composition of the blend in real time. However, a single probe cannot be expected to monitor the composition of every component of a multicomponent blend. In this study, three PAT tools (light-induced fluorescence spectroscopy, near-infrared spectroscopy and color (RGB) imaging) simultaneously checked the composition of powder blends flowing through the feeding unit (feed frame) of a tablet press. The results demonstrate the potential of these tools in monitoring changes in the concentration of a multicomponent mixture in real time, providing users with means to both scrutinize the process and better understand phenomena occurring inside the feed frame.