A comparison between interparticle forces estimated with direct powder shear testing and with sound assisted fluidization

Understanding the role of the interparticle forces in fluidization of cohesive powders is crucial for a proper application of fluidization to these type of powders. However, a direct measure of the interparticle interactions (IPFs) is challenging, mainly because cohesive particles cannot be fluidized under ordinary conditions. That is the reason why IPFs are typically measured using a rheological approach. The aim of this study is, therefore, to evaluate the IPFs of cohesive powders under actual fluidization conditions, by using an experimental and theoretical approach. In particular, a sound assisted fluidized bed apparatus was used to achieve a fluidization regime of the particles. Then, the cluster/subcluster model was applied to calculate IPFs, starting from the experimental data. The obtained IPFs were then compared to those evaluated by using a shear testing approach

High-efficiency mixing of fine powders via sound assisted fluidized bed for metal foam production by an innovative cold gas dynamic spray deposition method

Metal foams are an interesting class of materials with very low specific weight and unusual physical, mechanical and acoustic properties due to the porous structure (1). These materials are currently manufactured by means of several conventional processes (2), limited by the impossibility to produce foams with complex geometry. This paper deals with the study of an innovative method to produce complex shaped precursors for aluminum foams through cold gas dynamic spray deposition process (CGDS), aluminum alloy (AlSi12) and titanium-hydride (TiH2) being the metal and the blowing agent, respectively. However, the success of this approach strongly depends on the achievement of a homogenous and deep mixing between AlSi12 and TiH2 fine powders, belonging to group C of Geldart’s classification. Classical mixing methods (such as tumbling mixers, convective mixers, high-shear mixers, etc.) are suitable for large non-cohesive particles (\u3e 30µm) but not for micronic particles (3), agglomerated due to strong interparticle forces. Alternatively, new wet and dry mixing techniques have been proposed for fine particles (4), suffering from different disadvantages: additional steps of filtration/drying are needed for wet methods, whereas, dry methods generally involves the reduction of the granulometry and the damaging or contamination of the original powders. The sound assisted fluidization technology (140dB-80Hz) has been adopted in this work to overcome the technical issues of mixing cohesive powders (5), thus obtaining a mixing to the scale of the primary particles in a simple, economic, not intrusive and not destructive way (the properties and morphology of the original particles were preserved). Therefore, the mixed powders were then sprayed by means of the proposed CGDS process on a stainless steel sheet to obtain the precursor. This was then heated up in a furnace at 600°C for 10 minutes to obtain the foam. In particular, two different types of mixtures with 1 wt% and 2.5 wt% of TiH2 were investigated; moreover, air compressed as well as helium were used as CGDS carrier gas in order to ensure a higher impact velocity and a better compacting of the powders. A very efficient mixing of powders has been achieved as confirmed by SEM/EDS analysis performed on samples taken from the sound assisted fluidized bed (Fig.1a) and by the time-dependence of the mixing degree (Fig.1b). Macrographs of created porous structures (Fig.2) showed that the coupling of sound assisted fluidization and CGDS process under optimal conditions is a promising and effective technique in manufacturing aluminum precursors for metal foams. Please click Additional Files below to see the full abstract

Mathematical modelling of clostridial acetone-butanol-ethanol fermentation

Clostridial acetone-butanol-ethanol (ABE) fermentation features a remarkable shift in the cellular metabolic activity from acid formation, acidogenesis, to the production of industrial-relevant solvents, solventogensis. In recent decades, mathematical models have been employed to elucidate the complex interlinked regulation and conditions that determine these two distinct metabolic states and govern the transition between them. In this review, we discuss these models with a focus on the mechanisms controlling intra- and extracellular changes between acidogenesis and solventogenesis. In particular, we critically evaluate underlying model assumptions and predictions in the light of current experimental knowledge. Towards this end, we briefly introduce key ideas and assumptions applied in the discussed modelling approaches, but waive a comprehensive mathematical presentation. We distinguish between structural and dynamical models, which will be discussed in their chronological order to illustrate how new biological information facilitates the ‘evolution’ of mathematical models. Mathematical models and their analysis have significantly contributed to our knowledge of ABE fermentation and the underlying regulatory network which spans all levels of biological organization. However, the ties between the different levels of cellular regulation are not well understood. Furthermore, contradictory experimental and theoretical results challenge our current notion of ABE metabolic network structure. Thus, clostridial ABE fermentation still poses theoretical as well as experimental challenges which are best approached in close collaboration between modellers and experimentalists

Immobilization of Actinobacillus succinigenes in Alginate Beads for Succinic Acid Production

Nowadays the succinic acid (SA) - a C-4 dicarboxylic acid - is considered as one of the most promising platform chemicals produced from renewable resources via fermentation. Enhancement of the SA fermentation efficiency and productivity may take advantages from immobilized cultures.. This work reports the immobilization of Actinobacillus succinogenes cells in calcium alginate beads. Glucose was used as carbon source for the fermentation. A parallel fermentation test with free cells was carried out to assess the advantages of the immobilization technology. The immobilization in alginate beads was proved to be an effective technique for SA production by A. succinogenes. The fermentation performances of the immobilized cells were higher than those of the free cells. In particular, at initial glucose concentrations of 40 g/L the maximum productivity in immobilized cells fermentation (0.77 g/Lh) is more than twice that measured for free cells (0.32 g/Lh

Continuous succinic acid production by immobilized cells of Actinobacillus succinogenes in a fluidized bed reactor: Entrapment in alginate beads

The production of succinic acid (SA) was investigated by using immobilized cultures of Actinobacillus succinogenes in alginate beads. Immobilized cell cultures operated in batch mode were tested by varying the initial glucose concentration between 20 and 80 g/L and the bead concentration (mass of beads per liter of fermentation broth) between 50 and 250 g/L. Free cells fermentation tests were also carried out to compare the performances of free cells vs. immobilized cells. The best results were obtained with immobilized cells at initial glucose concentration of 60 g/L and 250 g/L of beads: the final SA concentration was 69 ± 0.2 g/L and the SA yield was 1.15 ± 0.02 g/g. Repeated batch fermentation tests were performed to assess the mechanical stability of the alginate beads. The continuous fermentation process was investigated in a three-phase fluidized bed reactor (FBR) using cell entrapped in alginate beads (the solid phase). The process performances were studied and described as acid production (succinic acid included) and sugar conversion. The performances of the FBR were particularly attractive because it was possible to combine high SA productivity (35.6 g/Lh) with high SA concentration (31 g/L) and substrate conversion (76.4 %)