Carbon dioxide recovery by means of tsa in a sound assisted fluidized bed of fine activated carbon

A large decrease in CO2 emissions through capturing and separation will be required to keep greenhouse gases at tolerable levels (1). Though several CO2 capture technologies have been proposed, temperature swing adsorption (TSA), consisting in adsorbing the CO2 on a solid material and, then, inducing the sorbent regeneration and CO2 recovery by a temperature increase and gas purge, has the potential to become one of the leading techniques by complementing or replacing the current absorption technology due to its low energy requirement (2). With reference to the sorbent, great attention is focused on fine powders (3). Indeed, sorbent in the form of fine powders can be the substrate to realize new highly specific materials whose properties can be tuned at a molecular level and, besides that, most of the commercial adsorbent materials are generally available in the form of fine powders (3). In this respect, sound assisted fluidization is considered to be one of the best technological alternatives to handle and process large amounts of fine powders (4). Moreover, it has already been proved to promote and remarkably enhance the CO2 capture on fine sorbents, due to large gas-solid contact efficiency, high rate of mass/heat transfer and low pressure drops (5,6). This work is focused on the CO2 desorption process by TSA in a sound-assisted fluidized bed (40mm ID) of fine activated carbon (Sauter mean diameter = 0.39m). In particular, desorption tests have been performed under ordinary and sound assisted fluidization conditions (140dB - 80Hz) in order to assess the capability of the sound in promoting and enhancing the desorption process efficiency in terms of CO2 recovery and purity and desorption time (td). The results obtained show that the application of the sound results in higher desorption rates, CO2 recovery and purity. Very regular and stable desorption profiles can be obtained under sound assisted fluidization conditions (Fig. 1). This stability makes it possible to successfully realize a cyclic adsorption/desorption process. Then, the effect of desorption temperature (Tdes) (25 - 150°C) and N2 purge flowrate (45.2 – 90.4Nl h-1) on the regeneration efficiency has also been assessed (Fig. 2a and b). An increase of both of them positively affect the desorption process in terms of enhanced desorption kinetics. Increasing temperatures also yield higher CO2 purities, whereas, no remarkable dilution effect has been observed when increasing the N2 flow rate. Finally, the activated carbon keeps its performances over 16 adsorption/desorption cycles, in terms of amount of CO2 adsorbed (nads), breakthrough time (tb) and fraction of bed used at tb (W), due to the stability of the regeneration process under sound-assisted fluidization conditions (Fig. 3c). Please click Additional Files below to see the full abstract

Butanol production by clostridium acetobutylicum in a series of packed biofilm bed reactors

The reactor design plays a key role in the fermentative production of biobutanol. The high cell concentration that may be reached in confined – biofilm, membrane, recycling - cell reactors offers high conversion rates. To the authors knowledge, the concentration of solvents in the broth from biofilm reactors reported in literature is not particularly high and it negatively affects the successive stages for butanol recovery. The low concentration of solvents in the produced stream is typically due to the inhibitory effect of solvents on the fermentation. Therefore, the butanol bioreactor productivity is as low as the bioreactor behaviour approaches the CSTR limit. The aim of this contribution is to report recent results on the design of a continuous biofilm reactor to optimize the process performances. Clostridium acetobutylicum DSM 792 was adopted for the fermentation process. The conversion was carried out in 4 packed bed reactors (PBRs) connected in series: the first reactor of the series was kept under acidogenesis and the successive reactors were kept under solventogenesis. Tests were carried out feeding the reactor system with solutions bearing glucose. Please click Additional Files below to see the full abstract

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

Biobutanol production from high sugar content wastewaters

Over the last decade, the depletion of oil resources and concerns regarding both economic and environmental issues associated with petroleum-based fuels have renewed interests in biofuel production from renewable resources . Industrial and academic researches have paid attention to the development of (bio)sustainable processes and to the produce biofuels by conversion of renewable feedstoks. The spectrum of biofuels includes the butanol, a simple four carbon alcohol characterized by interesting features. A biotechnological route to produce butanol is based on the fermentation of clostridia: saccharolytic butyric acid-producing bacteria able to produce acetone-butanol-ethanol (ABE) by fermentation adopting a wide spectrum of carbohydrates, typically present in renewable unexpensive feedstocks. This contribution reports about a study on the feasibility of bio-butanol production by fermentation of high-sugar content beverages (HSCBs). The anaerobic solventogenic bacterium Clostridium acetobutylicum DSM 792 was adopted for the fermentation process. Commercial pineapple juice, lemon syrup and tonic water were tested as substrate for the fermentation. Preliminary tests pointed out that: i) the microorganism did not grow on any of the HSBCs investigated without complex medium supplementation; ii) the conversion degree of sucrose was quite low. Therefore, tests were carried out with broth made of the complex medium and HSCB pre-idrolized (sucrose idrolized to glucose and fructose)

Procedimiento de captura de CO2 por CaO a alta temperatura asistido por vibración acústica

La presente invención tiene por objeto un procedimiento que incrementa la capacidad de captura rápido de CO2 por un reactor de lecho fluidizado de CaO a alta temperatura en el proceso "Ca-loopin"(CaL). El procedimiento propuesto de asistencia a la captura de CO2 se basa en la aplicación de vibraciones acústicas directamente sobre el material fluidizado en el reactor de carbonatación, para unos valores de la intensidad de la vibración acústica y de su frecuencia en torno a 150dB y 100Hz respectivamente. Con este procedimiento se consigue acelerar la carbonatación del material y reducir la pérdida de capacidad de captura tras ser sometido a sucesivos ciclos de calcinación/carbonatación. La presente invención tiene su aplicación en el área de la Energía y el Medioambiente, concretamente en sectores de actividad orientados a la mejora de eficacia de tecnologías energéticas.Españ

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