Hydroconversion kinetics of Marlim vacuum residue

A kinetic model was obtained for the Marlim crude vacuum residue (VR) hydroconversion. Marlim VR mixed with FCC decant oil in an 80%/20% weight basis was put in contact with a commercial NiMo on γ-alumina catalyst in a stirred batch reactor. Several temperatures and oil/catalyst ratios were used over different times (0–240 min), at a 110 bar pressure and constant hydrogen flow. The analysis of the collected product showed residua conversions of up to 70%. Hydroconversion kinetics involving thermal and catalytic cracking contributions was proposed to represent the obtained data. The resulting system of differential equations of the kinetic model was solved within reaction time, taking into account the experimental temperature profile. The chi-square objective function was minimized to adjust model parameters. A proposed effective hybrid minimization method was used, by applying a Newton-type method between certain simulated annealing minimization steps. The proposed kinetic model allowed the representation of thermal and catalytic cracking effects, in order to take into account different catalyst concentrations. Therefore it is possible to consider distinct reactor hydrodynamics, such as expanded or bubble column reactors.     

Modelling the Spalling of Oxide Scales During Hot Rolling of Steel Strip

Production of hot rolled steel strip is carried out at temperatures at which oxidation is prone to occur. The oxide crust is subjected to stresses that are originated while growing or are due to the difference between the thermal expansion coefficients of steel and oxide. It is considered that the oxide crust will be in tension when the temperature at the surface of the steel increases and in compression when it decreases. These stresses may cause cracking, buckling and spalling of the oxide. Oxidation to hematite occurs very rapidly once the crust is detached from the surface of the steel, and, in some cases oxide dust clouds will be formed. A model was developed to predict the magnitude and nature of the stresses within the oxide layer considering the temperature changes that take place while the material is being rolled. The model predicts that the oxide crust will deform when compressed and may cause its spalling and, once this occurs it will be expected to form oxide dust clouds.     

Nafion-clay hybrids with a network structure

Nafion-clay hybrid membranes with a unique microstructure were synthesized using a fundamentally new approach. The new approach is based on depletion aggregation of suspended particles - a well-known phenomenon in colloids. For certain concentrations of clay and polymer, addition of Nafion solution to clay suspensions in water leads to a gel. Using Cryo-TEM we show that the clay particles in the hybrid gels form a network structure with an average cell size in the order of 500 nm. The hybrid gels are subsequently cast to produce hybrid Nafion-clay membranes. Compared to pure Nafion the swelling of the hybrid membranes in water and methanol is dramatically reduced while their selectivity (ratio of conductivity over permeability) increases. The small decrease of ionic conductivity for the hybrid membranes is more than compensated by the large decrease in methanol permeability. Lastly the hybrid membranes are much stiffer and can withstand higher temperatures compared to pure Nafion. Both of these characteristics are highly desirable for use in fuel cell applications, since a) they will allow the use of a thinner membrane circumventing problems associated with the membrane resistance and b) enable high temperature applications.     

Synthesis and characterization of a plant cutin mimetic polymer

A mimetic polymer of plant cutin have been synthesized from 9,10,16-trihydroxyhexadecanoic (aleuritic) acid through a low temperature polycondensation reaction. Reaction conditions (solvent, catalyst, temperature, etc…) were studied and modified to optimize yield and product characteristics. The resulting polyaleurate polymer was characterized by Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD) and solid state ¹³C-Cross Polarization/Magic Angle Spinning Nuclear Magnetic Resonance (¹³C-CP/MAS NMR). Mechanical and hydrodynamic properties were also investigated. In the average, the product obtained is physically and chemically very similar to plant cutin (a hydrophobic polyester). However, a more detailed analysis of results reveals that polyaleurate framework is more rigid than natural cutin and with additional larger short-range ordered domains. Also, the synthetic polymer displays slightly different mechanical properties with respect to natural cutin. Additional hydrogen bonding within the framework of polyaleurate is considered to be responsible for such experimental observations.     

Multiple hydrophilic polymer ultra-thin layers covalently anchored to polyethylene films

A novel procedure has been developed to covalently graft multiple hydrophilic polymer ultra-thin layers to functionalized polyethylene surface. Polyethylene films have been functionalized by two methods, chromic acid oxidation and maleic anhydride grafting, to produce surfaces containing reactive groups, carboxylic acid and anhydride, respectively. The reactive groups formed in the functionalization were used to anchor a poly(vinyl alcohol) (PVA) ultra-thin layer by thermal esterification. After anchoring PVA, a second ultra-thin layer, constituted of poly(acrylic acid) (PAA), was also anchored. The second layer was anchored by thermal esterification between PVA hydroxyl groups and PAA carboxylic acid groups. The procedure presented in this work allows the formation of an ultra-thin layer. The macromolecule anchoring reactions occur only at the interfaces, consequently, only the macromolecules in contact with the interface are anchored. The formation of the ultra-thin layer and the surface characteristics have been analyzed through XPS, ATR-FTIR, SEM, and AFM data.     

Calcium aluminate cement in castable alumina: From hydrate bonding to the in situ formation of calcium hexaluminate

Calcium hexaluminate (CA₆) is an intrinsically densification-resistant material, therefore, its porous structures are key materials for applications as high-temperature thermal insulators. This article reports on the combination of calcined alumina and calcium aluminate cement (CAC) in castable aqueous suspensions for the in situ production of porous CA₆. The CAC content (10–34 vol%) and the curing conditions ensure structural integrity prior to sintering and maximize the development of hydrated phases. Changes in physical properties, crystalline phases, and microstructure were investigated after isothermal treatments (120–1500 °C), and three sequential porogenic events were observed. The hydration of CAC preserved the water-derived pores (up to 120 °C), and the dehydroxylation of CAC hydrates (250–700 °C) generated inter-particles pores. Moreover, the in situ expansive formation of CA₂ and CA₆ (900–1500 °C) hindered densification and generated intra-particle pores. Such events differed from those observed with other CaO sources, and resulted in significantly higher pores content and lower thermal conductivity.     

Analysis of sugars by liquid chromatography-mass spectrometry in Jerusalem artichoke tubers for bioethanol production optimization

Sustainability of biofuels is increasingly taken into account; therefore, sustainable production technologies are needed. There has been a long history of converting Jerusalem artichoke into ethanol. Jerusalem artichoke (Helianthus tuberosus L.) is a low-requirement crop, it has a high carbohydrates yield and, nowadays, it does not interfere with food chain. It is, then, a promising energy crop for sustainable bioethanol production. However, the main storage carbohydrate of Jerusalem artichoke, inulin, can not be directly fermented by classic fermentation yeasts, so, either a hydrolysis followed by fermentation with classical yeast or the use of yeasts with inulinase activity are required to obtain bioethanol. Therefore, it is needed to know not only total sugar content, but also their composition, for the bioethanol production optimization from Jerusalem artichoke tubers. Several methods have been used in literature for carbohydrates analysis present in Jerusalem artichoke tubers. However, for further development of carbohydrate analysis, faster and more reliable identification and peak confirmation, mass spectrometry (MS) detection is required. In this paper, liquid chromatography with electrospray ionization mass spectrometry (LC-ESI-MS) was used as an alternative technique to analyse sugars content and composition in tubers from Jerusalem artichoke. Two simple, rapid, sensitive and specific LC-ESI-MS methods were developed under the positive ionization mode. Glucose, fructose, sucrose, kestose and inulin were determined. Furthermore, inulin profile can be characterized. Analytical reversed phase LC columns were used using only water as eluent. These methods can be useful to optimize the whole bioethanol production chain from Jerusalem artichoke.     

Catalytic performance of Ni-Pr supported on delaminated clay in the dry reforming of methane

Mineral clay modified with Al, polyvinyl alcohol (PVA) and microwaves was used as a support to obtain a Ni-Pr catalyst. This catalytic system was evaluated in the reforming of methane with CO₂. The experiments were carried out under drastic conditions for 300 min, with a 50/50 CH₄/CO₂ mixture, total flux of 80 mL min⁻¹, without dilution gas (WHSV = 96 Lg⁻¹h⁻¹) and without previous reduction. The effect of the calcination temperature of the materials was studied at 500 °C and 800 °C as well as the effect of Pr (evaluating nominal quantities of 0, 1, 3 and 5%). The calcination temperature of the solid influenced the formation of the NiO species which had an effect on the activity and formation of coke on the material. The Pr had a promoter effect on the activity of the catalysts increasing the conversions of the CH ₄ as well as the CO₂. The formation of coke for the catalysts calcined at 500 °C presented a correlation with the praseodymium content while for those catalysts calcined at 800 °C there was no formation of coke.     

Prognostics and Health Management of PEMFC – State of the art and remaining challenges

Fuel Cell systems (FC) represent a promising alternative energy source. However, even if this technology is close to being competitive, it is not ready for large scale industrial deployment: FC still must be optimized, particularly by increasing their limited lifespan. This involves a better understanding of wearing processes and requires emulating the behavior of the whole system. Furthermore, a new area of science and technology emerges: Prognostics and Health Management (PHM) appears to be of great interest to face the problems of health assessment and life prediction of FCs. According to this, the aim of this paper is to present the current state of the art on PHM of FCs, more precisely of Proton-Exchange Membrane Fuel Cells (PEMFC) stack. PHM discipline is described in order to depict the processing layers that allow early deviations detection, avoiding faults, deciding mitigation actions, and thereby increasing the useful life of FCs. On this basis, a taxonomy of existing works on PHM of PEMFC is given, highlighting open problems to be addressed. The whole enables getting a better understanding of remaining challenging issues in this area.     

Concurrent Zero Knowledge, Revisited

We provide a more general and, in our eyes, simpler variant of Prabhakaran, Rosen and Sahai’s (FOCS ’02, pp. 366–375, 2002) analysis of the concurrent zero-knowledge simulation technique of Kilian and Petrank (STOC ’01, pp. 560–569, 2001).