Modeling and optimization of a large-scale slurry bubble column reactor for producing 10,000 bbl/day of Fischer-Tropsch liquid hydrocarbons

A user-friendly simulator based on a comprehensive computer model for slurry bubble column reactors (SBCRs) for Fischer-Tropsch (F-T) synthesis, taking into account the hydrodynamics, kinetics, heat transfer, and mass transfer was developed. The hydrodynamic and mass transfer data obtained in our laboratories under typical F-T conditions along with those available in the literature were correlated using Back Propagation Neural Network and empirical correlations with high confidence levels. The data used covered wide ranges of reactor geometry, gas distributor, and operating conditions. All reactor partial differential equations, equation parameters and boundary conditions were simultaneously solved numerically.The simulator was systematically used to predict the effects of reactor geometry (inside diameter and height) as well as superficial gas velocity and catalyst concentration on the performance of a large-scale SBCR provided with cooling pipes and operating under F-T conditions with cobalt-supported catalyst and H₂/CO = 2. The performance of the SBCR was expressed in terms of CO conversion, liquid hydrocarbon yield, catalyst productivity, and space time yield. The simulator was also used to optimize the reactor geometry and operating conditions in order to produce 10,000 barrels/day (bbl/day) of liquid hydrocarbons.     

Effect of dimensions on the cooling rate of whole potatoes applying transfer functions

The evolution of temperature in the geometrical centre of potatoes during cooling was analysed using a transfer function approach. The response to a sudden change in the surrounding temperature was approximated assuming that the sample behaved as a delayed first-order system with unit gain. This model involves two parameters, the time constant and the dead time. These parameters depend on the product dimensions. Samples were assumed to have ellipsoidal shape. Expressions to estimate the time constant and the dead time from the three axes of the ellipsoid are presented. The temperature response in the geometrical centre subjected to changes in the surrounding temperature can be predicted using the model parameters. Good approximations between predicted and experimental values were obtained.     

Electric Field‐Induced Oxidation of Ferromagnetic/Ferroelectric Interfaces

Composite multiferroics are a new class of material where magneto‐electric coupling is achieved by creating an interface between a ferromagnetic and a ferroelectric compound. The challenge of understanding the chemical and magnetic properties of such interface is a key to achieve good magneto‐electric coupling. The unique possibilities offered by isotope sensitive techniques are used to selectively investigate the interface's chemistry and magnetism in Fe/BaTiO₃ and Fe/LiNbO₃ systems during the application of an electric field. With a large enough electric field, a strong oxidation of Fe is triggered, which creates a magnetically dead interface. This leads to an irreversible decrease of the magneto‐electric coupling properties. Material parameters are identified that determine under which electric field the interface may be modified. The results are confirmed on the two systems and are expected to be widespread in this new class of hybrid material.     

Stable Alignment of Tautomers at Room Temperature in Porphyrin 2D Layers

A major challenge in molecular electronics is to develop logic devices based on a truly intramolecular switching mechanism. Recently, a new type of molecular device has been proposed where the switching characteristic is mediated by the bistability in the position of the two hydrogen atoms which can occupy different, energetically equivalent positions (tautomerization) in the inner cavity of porphyrins and naphthalocyanines. Up to now, such a reaction has only been exploited at low temperatures and induced or detected through atomic scale manipulation. In addition, the unpredictability of the tautomer orientation currently excludes molecular interconnection to functional electronic circuits. Here, full evidence is provided that, following a newly proposed growth strategy, 2D layers of metal‐free tetraphenylporphyrins (H₂TPP) show frozen tautomerization even at room temperature on macroscopic domains, with the H atoms aligned along a direction settled a priori. This behavior is ascribed to the buckling of the molecule, anchored to the substrate, which removes the degeneracy between the two tautomer alignments. On this basis, a new way to exploit uniaxially oriented H₂TPP tautomers in a first elementary logic device is proposed.     

Metagenomic Microbial Diversity in Aguamiel from Two Agave Species During 4-Year Seasons

Aguamiel is the sap of “maguey pulquero” and can be consumed as a fresh beverage or after a cooking process. Further, it is also fermented for the production of “pulque,” a traditional Mexican alcoholic beverage. Use of aguamiel as a functional beverage has been suggested due to prebiotic activity of its fructooligosaccharides and probiotic activity of lactic acid bacteria that it contains. There are some reports about the culturable microbial diversity in aguamiel; however, the total microbial diversity has not been characterized. The objective of this study was to identify metagenomic populations in aguamiel using denaturing gradient gel electrophoresis and sequencing of the 16S rRNA gene and 26SrRNA gene regions. Microbial diversity in aguamiel from two maguey species was evaluated: Agave salmiana and Agave atrovirens, during the four seasons of the year. The highest diversity was found during summer season in aguamiel samples from both Agave species, detecting presence of Leuconostoc sp., Leuconostoc gelidum, Lactococcus lactis, Enterococcus casseliflavus, Pediococcus sp., uncultured Trichococcus sp., uncultured Leuconostoc, uncultured Lactococcus, Kazachstania zonata (not previously reported in aguamiel), Kluyveromyces marxianus, and Saccharomyces cerevisiae. Knowledge about the microbial populations of this beverage throughout the different seasons will provide advantages through understanding of aguamiel for application areas such as syrup elaboration and pulque making. In addition, this beverage could be industrialized as a functional beverage with a consistent quality.     

Synthesis,characterization and simulation of lithium titanate nanotubes for dye sensitized solar cells

In this work we present the comprehensive design of lithium titanate nanotubes (LiTNT) as semiconductors for DSSC photoanodes. The synthesis and characterization of Li_1.82Na_0.18Ti₃O₇.nH₂O nanotubes was performed and a prototype of cell using this material was assembled. The cell exhibited a 7.7% efficiency and a relatively high open circuit voltage, Voc?=?0.72?V. In comparison with previously obtained hydrogen titanate nanotubes (HTNT), improvements have been achieved, like better charge carriers’ lifetime and lower series resistance. In order to study this system, we carried out previous DFT simulations for this lithium titanate nanotubes through different model's complexity levels which were able to correctly predict its properties. Due to the improvements achieved this system would encourage further studies with the aim to explore its potential for solar cells applications.     

Effect of acetylation and oxidation on some properties of breadfruit (Artocarpus altilis) seed starch

Starch extracted from seeds of Artocarpus altilis (Breadfruit) was chemically modified by acetylation and oxidation, and its functional properties were evaluated and compared with these of native starch. Analysis of the chemical composition showed that moisture content was higher for modified starches. Ash, protein, crude fiber and amylose contents were reduced by the modifications, but did not alter the native starch granules' irregularity, oval shape and smooth surface. Acetylation produced changes in water absorption, swelling power and soluble solids, these values were higher for acetylated starch, while values for native and oxidized starches were similar. Both modifications reduced pasting temperature; oxidation reduced maximum peak viscosity but it was increased by acetylation. Hot paste viscosity was reduced by both modifications, whereas cold paste viscosity was lower in the oxidized starch and higher in the acetylated starch. Breakdown was increased by acetylation and reduced with oxidation. Setback value was reduced after acetylation, indicating it could minimize retrogradation of the starch.     

Neoliberal abandonment in disability housing provision: a look at England and Chile

Public or ‘social’ housing provision in many nations in the Global North is increasingly being driven by neoliberal strategies that include austerity cuts and market-led privatization. This context raises an important question of how likely the state’s reliance on the private sector can ensure that housing remains available and accessible to more disadvantaged low-income groups. To help answer this question, we draw on a comparative study of social housing provision for disabled people in England and Chile; two pioneers of neoliberal reform in this sector. Using interviews with key stakeholders, our findings reveal that the neoliberal reform strategies being employed have tended to dilute the statutory duties of providing accessible housing and to undermine disabled people’s choices in finding appropriate homes. Such lessons are timely and important in order to remain cognisant of the spaces of neoliberal abandonment that are leaving many people unable to gain access to appropriate housing.