Advances and trends in two-zone fluidized-bed reactors

Two-zone fluidized bed reactors, devices to carry on two reactions in a single reactor, have been widely studied in our group. This work summarizes the developments achieved after a previous review published in 2005 and shows how this technology can be applied in a wide variety of reactions. The advantages for each kind of process are discussed, as well as several proposals for improvement of the reactor aimed to achieve new functions or to improve the process performance. Finally, the possibilities of this kind of reactors at industrial scale are discussed

Glycerol steam reforming with low steam/glycerol ratio in a two-zone fluidized bed reactor

The production of hydrogen from glycerol steam reforming has been studied in several reactors. In conventional reactors the catalyst is deactivated by coke: in fixed bed reactors plugging was observed if a low steam/glycerol ratio was employed, while in fluidized bed reactors it was possible to operate for a longer time-on-stream. The use of a two-zone fluidized bed reactor is studied in this work, as a method to counteract the problem of catalyst deactivation by coke. The glycerol reforming takes place in the upper part of this reactor while the catalyst is simultaneously regenerated in the lower part, where a stream of a regenerating gas is introduced. It has been found that CO2, O2 or H2O can act as regenerating gas in a two-zone-fluidized bed reactor, allowing steady state operation at a water:glycerol molar ratio as low as 1.25. The effect of the operating conditions has been studied and the yield to the main products was compared with the calculated values assuming thermodynamic equilibrium

Particle tracking in a Two-Section Two-Zone Fluidized Bed Reactor (TS-TZFBR). Experimental technique and CCBM model validation

The Two Zone Fluidized Bed Reactor (TZFBR) provides a high level of process integration, allowing reaction and, in situ, continuous catalyst regeneration, in a single fluidized bed. Reactive and regenerative atmospheres are induced simultaneously inside the single vessel due to a separated gas inlet and particles fluidization provides reactor continuous operation. Therefore, the fluid dynamic key factor in a TZFBR is the mixing rate between solids inside the two bed zones (a good mixture provides continuous catalyst regeneration, while bad contact between bed zones leads to deactivation and loss of catalytic surface). In the present study, phosphorescent particles have been used as optical tracers to measure solids axial mixing between reactor zones in a catalytic TZFBR. Additionally, a different cross-sectional area between zones has been studied to get a certain fluidization regime, allowing small flowrates in the regeneration zone. This geometry implied a transition angle α between zones to be implemented (Two-Section TZFBR). In line with it, a modified counter-current backmixing model (CCBM) without fitting parameters was developed to predict mixture rates inside the bed for different TS-TZFBR geometries. Modifications carried out in the CCBM basis model involved reactor geometry and the presence of two simultaneous gas feed points along the bed. Model parameters related to bubble/solid fraction and wake-emulsion mass transfer were fully correlated to operational conditions (gas velocity, feed point location and section change). The adapted CCBM model predictions were further validated with optical tracers experimental fluid dynamic data, resulting in a high agreement

Gas permeation effect on the Two-Section Two-Zone Fluidized Bed Membrane Reactor (TS-TZFBMR) fluid dynamics: A CFD simulation study

Two-Fluid Model simulations were conducted using the commercial software Ansys CFX and Fluent to study the effect of the gas extraction on the fluid dynamic behavior of a membrane-assisted Two-Section Two-Zone Fluidized Bed Membrane Reactor (TS-TZFBMR). Simulated bubble properties and bed dynamics were analyzed and compared among different membrane reactor configurations, including reactor-wall (RWM) and immersed tubular (ITM) membranes, for their future use in catalytic reactions, e.g., alkane dehydrogenation or methane steam reforming. According to the solids hold-up distribution at different fluidization regimes and permeation fluxes, the ITM configuration is the most suitable to enhance the gas-particle contact and to favor the solids axial mixing for in-situ catalyst regeneration purposes. However, the RWM configuration provides a greater permeation area for selective gas removal and is preferred to enhance purification. It was found that relative permeation fluxes above 20% of the total feed gas have a significant impact on the fluid dynamic regime within the TS-TZFBMR, concerning the appearance of local defluidized regions, gas channeling and solids axial mixing

Coherent elastic neutrino-nucleus scattering: EFT analysis and nuclear responses

The cross section for coherent elastic neutrino-nucleus scattering (CEνNS) depends on the response of the target nucleus to the external current, in the Standard Model (SM) mediated by the exchange of a Z boson. This is typically subsumed into an object called the weak form factor of the nucleus. Here, we provide results for this form factor calculated using the large-scale nuclear shell model for a wide range of nuclei of relevance for current CEνNS experiments, including cesium, iodine, argon, fluorine, sodium, germanium, and xenon. In addition, we provide the responses needed to capture the axial-vector part of the cross section, which does not scale coherently with the number of neutrons, but may become relevant for the SM prediction of CEνNS on target nuclei with nonzero spin. We then generalize the formalism allowing for contributions beyond the SM. In particular, we stress that in this case, even for vector and axial-vector operators, the standard weak form factor does not apply anymore, but needs to be replaced by the appropriate combination of the underlying nuclear structure factors. We provide the corresponding expressions for vector, axial-vector, but also (pseudo)scalar, tensor, and dipole effective operators, including two-body-current effects as predicted from chiral effective field theory (EFT). Finally, we update the spin-dependent structure factors for dark matter scattering off nuclei according to our improved treatment of the axial-vector responses

Diagnosticand pronostic utility of serum microrna-21 in colorectal cancer

Los microRNAs son estructuras moleculares de 20-22 nucleótidos con actividad post-transcripional que están implicados en la carcinogénesis mediante una regulación genética post-transcripcional. Presentamos un estudio prospectivo donde se determina la expresión sérica de microRNA-21 en pacientes con diagnóstico de adenocarcinoma de colon. MATERIAL Y MÉTODOS. Estudio de cohorte prospectivo de al menos 100 pacientes con diagnóstico de adenocarcinoma de colon, y de al menos 60 pacientes con apendicitis aguda como grupo control. Se realizó el análisis de microRNA-21 sérico mediante PCR de las muestras sanguíneas de los pacientes obtenidas de forma preoperatoria. RESULTADOS. La comparación de la expresión del microRNA-21 sérico fue mayor en los pacientes con cáncer colorrectal que en los pacientes del grupo control, siendo el área bajo la curva de 0,603. En el análisis univariante, la expresión del miR- 21 se relaciona de forma estadísticamente significativa con la recidiva local (p=0,025) y con la mortalidad (p=0,029). En el análisis multivariante también se puso de manifiesto que las expresiones mayores (sobreexpresiones) de miR-21 se relacionaban con una reducción del riesgo derecidiva del 51%, mientras que dicha sobreexpresión se relacionaba con una reducción de mortalidad del 50%. CONCLUSIONES. La expresión del microRNA-21 sérico podría ser considerado como un potencial marcador diagnóstico para el cáncer colorrectal. La expresión sérica del microRNA-21 se correlaciona con la recidiva y mortalidad en el cáncer colorrectal. Nuestros resultados sugieren que el miR-21 sérico es un prometedor marcador diagnóstico y pronóstico, y pone de manifiesto su potencial utilidad clínica en el cáncer colorrectalMicroRNAs (miRNAs) are small, noncoding RNAs that are involved in carcinogenesis through postranscriptional gene regulatory activity. Few studies have focused on the detection of miR-21 in serum rather than in tissue. The current study aimed to measure serum miR-21 expression levels and to evaluate their association with the outcome of colorectal cancer (CRC). METHODS. Blood samples were collected from almost 100 CRC patients undergoing surgery with curative intent, and almost 60 control patients. The expression levels of miR-21 were measured using a quantitative reverse transcription polymerase chain reaction (qRT-PCR). RESULTS. Serum microRNA-21 expression was higher in colorectal cancer patients than in control patients, with a ROC curve of 0.603. A univariate analysis revealed that lower expression levels of serum miR-21 were associated with higher local recurrence (p=0.025) and mortality (p=0.029). A logistic regression analysis demonstrated that the relative overexpression of miR-21 (expression >1) was associated with a 51% reduction in the risk of recurrence. A Cox regression analysis identified that a relative increase in miR-21 expression (>1) was associated with a 50% reduction in the risk of mortality CONCLUSIONS. Serum microRNA-21 expression could be considered as a potential diagnostic marker for colorectal cancer. The expression level of serum miR-21 correlates with the recurrence and mortality of CRC patients. Our results suggest that circulating serum miR-21 is a promising diagnostic and prognostic tumour marker, and they highlight the potential clinical utility of miR-21 in colorectal cancerEl presente estudio ha sido financiado con la ayuda otorgada por la Fundación para la Investigación Sanitaria en Castilla La Mancha (FISCAM) y por la Fundación Mutua Madrileña Investigación Médic

Direct vs. indirect optical recombination in Ge films grown on Si substrates

The optical emission spectra from Ge films on Si are markedly different from their bulk Ge counterparts. Whereas bulk Ge emission is dominated by the material's indirect gap, the photoluminescence signal from Ge films is mainly associated with its direct band gap. Using a new class of Ge-on-Si films grown by a recently introduced CVD approach, we study the direct and indirect photoluminescence from intrinsic and doped samples and we conclude that the origin of the discrepancy is the lack of self-absorption in thin Ge films combined with a deviation from quasi-equilibrium conditions in the conduction band. The latter is confirmed by a simple model suggesting that the deviation from quasi-equilibrium is caused by the much shorter recombination lifetime in the films relative to bulk Ge

"Non-Target-Site" resistance mechanisms of "Papaver rhoeas" L. biotypes with multiple resistance

Hasta el momento en España no se han desarrollado estudios a fin de evaluar los mecanismos de resistencia “Non-Target-Site” en “Papaver rhoeas”. Tras constatar la resistencia múltiple de los biotipos empleados en este ensayo, los resultados de absorción y translocación obtenidos para 2,4-D y tribenuron-metil parecen arrojar conclusiones interesantes. Sobre todo, en el caso de la auxina sintética, donde una destacada menor translocación detectada en biotipos resistentes respecto a los sensibles está en sintonía con las más recientes teorías de mecanismos de resistencia a herbicidas hormonales.So far in Spain studies to evaluate the mechanisms of resistance “Non-Target-Site” on “Papaver rhoeas” have not been done. After finding multiple resistance in the biotypes used in this trial, absorption and translocation results obtained for 2,4-D and tribenuron-methyl seem to throw interesting findings. Mainly in the case of the synthetic auxin, where a lack of translocation was detected in resistant biotypes compared to the sensitive one. This could be related with the latest theories of mechanisms of resistance to synthetic auxin

Conventional and improved fluidized bed reactors for dry reforming of methane: Mathematical models

Dry reforming of methane is a potentially useful reaction, but has some drawbacks: catalyst deactivation by coke and yield limited by thermodynamic equilibrium. New improved fluidized bed reactors may compensate these disadvantages. Mathematical models for the dry reforming of methane in three types of fluidized bed reactors have been developed. These reactors include: a) conventional fluidized bed reactor, b) two zone fluidized bed reactor, which provides simultaneous reaction and catalyst regeneration in a single fluidized bed, and c) two-zone fluidized bed reactor with hydrogen selective membranes, which in addition to the previous one provides increased yield to hydrogen, because the selective removal of hydrogen through the membrane. The situations where these reactors counteract the two main drawbacks of dry reforming of methane are shown. Comparison with previous experimental results shows that the models predict well the effect of operating conditions

Kinetic Study of Dry Reforming of Methane Over Ni–Ce/Al 2 O 3 Catalyst with Deactivation

A kinetic study for dry reforming of methane over Ni–Ce/Al 2 O 3 catalyst was performed, taking into account both the main reactions and the catalyst deactivation. The catalyst was prepared by a sequential wet impregnation process, with loadings of 5 wt.% Ni and 10 wt.% Ce. Experimental tests were carried out in a fixed bed reactor between 475 and 550 °C and several spatial times, using nitrogen as diluent. Several kinetic equations were compared. The best fit of experimental data was achieved using a Langmuir–Hinshelwood mechanism which takes into account the presence of two active sites. Pre-exponential factor and activation energy were calculated. the kinetics of deactivation was also determined. The relationship between catalyst activity and coke concentration was also studied. Several deactivation equations were considered in order to choose the best fit with experimental data