Corrosion behavior of Eurofer 97 and ODS-Eurofer alloys compared to traditional stainless steels

In the present work, the corrosion resistance of ferritic-martensitic EUROFER 97 and ODS-EUROFER steels was tested in solutions containing NaCl or H₂SO₄ and KSCN, both at 25 °C. The results were compared to those of AISI 430 ferritic and AISI 410 martensitic conventional stainless steels. The as-received samples were tested by electrochemical techniques, specifically, electrochemical impedance spectroscopy, potentiodynamic polarization curves, and double-loop electrochemical potentiokinetic reactivation tests. The surfaces were observed by scanning electron microscopy after exposure to corrosive media. The results showed that EUROFER 97 and ODS-EUROFER alloys present similar corrosion resistance but lower than ferritic AISI 430 and martensitic 410 stainless steels.     

Modeling of multicomponent mass diffusion in porous spherical pellets: Application to steam methane reforming and methanol synthesis

The main purpose of this paper is the derivation and evaluation of various diffusion flux models. For this aim, a comprehensive catalyst pellet problem has been simulated for two test cases: the steam methane reforming (SMR) and the methanol synthesis, as these two important chemical processes cover various aspects of a chemical reaction. The pressure, temperature, total concentration, species composition, viscous flow, mass and heat fluxes within the porous spherical pellet are included in the transient pellet model. Mass diffusion fluxes are described according to the rigorous Maxell–Stefan and dusty gas models, and the respectively simpler Wilke and Wilke–Bosanquet models. Simulations are performed with these fluxes defined according to both the molar averaged and mass averaged definitions. For the mass based pellet equations, a consistent set of equations is obtained holding only the mass averaged velocity. On the other hand, the closed set of molar based pellet equations hold both the molar averaged and mass averaged velocities as the fundamental energy balance and the momentum balance (Darcy law) are derived according to the mass averaged velocity definition, whereas the diffusion fluxes are defined relative to the molar averaged velocity. Identical results of the molar and mass based pellet equations were not obtained; however, the deviations are small. It is anticipated that these discrepancies are due to some unspecified numerical inaccuracies. However, efficiency factors have been computed for both processes and the values obtained compare well with the available literature data. Furthermore, efficiency factor sensitivity on parameters like pore diameter, tortuosity, temperature and pressure have been accomplished, and the classical simplifications of the pellet equations have been elucidated: isothermal condition, constant pressure, and neglecting viscous flow. The following conclusions are established for the reactor operating conditions used in the present work. The methanol synthesis: The simulation results of the methanol synthesis indicate that the classical assumptions are very fair for this process. Moreover, both Wilke and Wilke–Bosanquet models are good replacements for the more rigorous Maxwell–Stefan and dusty gas models. However, the simulation results are affected by Knudsen diffusion, thus the diffusion flux is most appropriately described by the Wilke–Bosanquet model. The SMR process: Knudsen diffusion hardly influences the results of the highly intraparticle diffusion limited SMR process. As the Wilke model does not necessarily conserve mass, we recommend the Maxwell–Stefan model because the simpler Wilke closure deviates with several percents. However, it is not elucidated whether these deviations are numerical problems arising from the large gradients of this process, or related to the choice of diffusion model. Isothermal and isobaric conditions can be assumed within the particle, but significant external temperature gradients are observed. Convective fluxes are much less than the diffusive fluxes, hence viscous flow can be neglected.     

Ile-1781-Leu and Asp-2078-Gly Mutations in ACCase Gene,Endow Cross-resistance to APP,CHD, and PPZ in Phalaris minor from Mexico

Herbicides that inhibit acetyl coenzyme A carboxylase (ACCase) are commonly used in Mexico to control weedy grasses such as little seed canarygrass (Phalaris minor). These herbicides are classified into three major families (ariloxyphenoxypropionates (APP), cyclohexanodiones (CHD), and, recently, phenylpyrazolines (PPZ)). In this work, the resistance to ACCase (APP, CHD, and PPZ) inhibiting herbicides was studied in a biotype of Phalaris minor (P. minor) from Mexico, by carrying out bioassays at the whole-plant level and investigating the mechanism behind this resistance. Dose-response and ACCase in vitro activity assays showed cross-resistance to all ACCase herbicides used. There was no difference in the absorption, translocation, and metabolism of the ¹⁴C-diclofop-methyl between the R and S biotypes. The PCR generated CT domain fragments of ACCase from the R biotype and an S reference were sequenced and compared. The Ile-1781-Leu and Asp-2078-Gly point mutations were identified. These mutations could explain the loss of affinity for ACCase by the ACCase-inhibing herbicides. This is the first report showing that this substitution confers resistance to APP, CHD, and PPZ herbicides in P. minor from Mexico. The mutations have been described previously only in a few cases; however, this is the first study reporting on a pattern of cross-resistance with these mutations in P. minor. The findings could be useful for better management of resistant biotypes carrying similar mutations.     

Esterification of glycerol with conjugated linoleic acid and long-chain fatty acids from fish oil

Free fatty acids from fish oil were prepared by saponification of menhaden oil. The resulting mixture of fatty acids contained ca. 15% eicosapentaenoic acid (EPA) and 10% docosahexaenoic acid (DHA), together with other saturated and monounsaturated fatty acids. Four commercial lipases (PS from Pseudomonas cepacia, G from Penicillium camemberti, L2 from Candida antarctica fraction B, and L9 from Mucor miehei) were tested for their ability to catalyze the esterification of glycerol with a mixture of free fatty acids derived from saponified menhaden oil, to which 20% (w/w) conjugated linoleic acid had been added. The mixtures were incubated at 40°C for 48h. The ultimate extent of the esterification reaction (60%) was similar for three of the four lipases studied. Lipase PS produced triacylglycerols at the fastest rate. Lipase G differed from the other three lipases in terms of effecting a much slower reaction rate. In addition, the rate of incorporation of omega-3 fatty acids when mediated by lipase G was slower than the rates of incorporation of other fatty acids present in the reaction mixture. With respect to fatty acid specificities, lipases PS and L9 showed appreciable discrimination against esterification of EPA and DHA, respectively, while lipase L2 exhibited similar activity for all fatty acids present in the reaction mixture. The positional distribution of the various fatty acids between the sn-1,3 and sn-2 positions on the glycerol backbone was also determined.     

Investigation of the collapse of bubbles after the impact of a piston on a liquid free surface

A novel technique based on the impact of a piston on a liquid confined in a vessel is described. Pressure measurements reveal that strong pressure variations (up to 100 atmospheres) with a rich content of frequencies are efficiently transmitted to the liquid. High‐speed camera visualizations show that pre‐existing millimetric bubbles always collapse during the first instants of the impact whereas the behavior of submillimetric bubbles depends on the features of the pressure evolution in the system. In addition to the impact velocity, the amount of gas/vapor trapped between the piston and the liquid's surface plays an important role on how pressure evolves. Only when negative pressure occurs tiny bubbles grow significantly and collapse. The violent collapse of bubbles promote turbulence and mixing at very small length‐scales which renders this technique interesting to intensify processes limited by heat and mass diffusion. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2483–2495, 2017     

Effect of operating conditions in removal of arsenic from water by nanofiltration membrane

The removal of arsenic from synthetic waters and surface water by nanofiltration (NF) membrane was investigated. In synthetic solutions, arsenic rejection experiments included variation of arsenic retentate concentration, transmembrane pressure, crossflow velocity and temperature. Arsenic rejection increased with arsenic retentate concentration. Arsenic was removed 93-99% from synthetic feed waters containing between 100 and 382 μg/L as V, resulting in permeate arsenic concentrations of about 5 μg/L. Under studied conditions, arsenic rejection was independent of transmembrane pressure, crossflow velocity and temperature. In surface water, the mean rejection of As V was 95% while the rejection of sulfate was 97%. The co-occurrence of dissolved inorganics does not significantly influence arsenic rejection. The mean concentration of As in collected permeated was 8 μg/L. The mean rejection of TDS, total hardness and conductivity were 75, 88 and 75% respectively.     

Kinetic modeling of catalytic conversion of methylcyclohexane over USY zeolites: Adsorption and reaction phenomena

Catalytic conversion of cycloparaffins is a complex process involving competing reaction steps. To understand this process, FCC experiments using methylcyclohexane (MCH) on USY zeolite catalysts were carried out in the mini‐fluidized CREC riser simulator. Runs were developed under relevant FCC process conditions in terms of partial pressures of MCH, temperatures (450–550°C), contact times (3–7 s), catalyst‐oil mass ratios (5), and using fluidized catalysts. MCH overall conversions ranged between 4 to 16 wt %, with slightly higher conversions obtained using the larger zeolite crystallites. Moreover, it was found that MCH undergoes ring opening, protolytic cracking, isomerization, hydrogen transfer and transalkylation. A heterogeneous kinetic model for MCH conversion including thermal effects, adsorption and intrinsic catalytic reaction phenomena was established. Adsorption and kinetic parameters were determined, including the heat of adsorption (?40 kJ/mol), as well as thermal and primary catalytic intrinsic activation energies, which were in the range of 43–69 kJ/mol, and 50–74 kJ/mol, respectively. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Analysis of flow in rotating packed beds via CFD simulations—Dry pressure drop and gas flow maldistribution

Three-dimensional unsteady-state turbulent rotating single-phase flows were simulated in rotating packed beds (RPB) and were validated using overall dry pressure drop measurements for three RPB designs [Liu, H.-S., Lin, C.-C., Wu, S.-C., Hsu, H.-W., 1996. Characteristics of a rotating packed bed. Industrial and Engineering Chemistry Research 35, 3590-3596; Sandilya, P., Rao, D.P., Sharma, A., Biswas, G., 2001b. Gas-phase mass transfer in a centrifugal contactor. Industrial and Engineering Chemistry Research 40, 384-392; Zheng, C., Guo, K., Feng, Y.D., Yung, C., 2000. Pressure drop of centripetal gas flow through rotating bed. Industrial and Engineering Chemistry Research 39, 829-834]. Analysis of the radial and tangential velocities highlighted the impact of gas feed entrance effects on the peripheral gas maldistribution in the rotating packing module. Recommendations were formulated for an optimum design with the aim to reduce gas flow maldistribution in RPBs. Breakdown of the overall pressure drop in its modular components for the housing, the rotating packing module, the free inner rotational zone, and the gas disengagement showed that the dissipation in the rotating packing could be a minor contributor to the overall pressure drop which may be undesirable in terms of RPB mass transfer and reaction efficiencies. Analysis of the simulated pressure drops allowed development of CFD-based Ergun-type semi-empirical relationships in which the gas-slip and radial acceleration effects, the laminar and inertial drag effects, and the centrifugal effect were aggregated additively to recompose the pressure drops in the rotating packing module.     

COMPOSITION AND QUALITY OF THE GASOLINE OBTAINED FROM SYNGAS ON Cr2O3-ZnO/ZSM5 CATALYSTS

The kinetic equations for the formation of the lumps of the gasoline produced (C₅⁺ fraction), paraffins (C₅-C₈), xylenes (o-xylene, m-xylene and p-xylene) and aromatics (benzene, toluene, C₉-C₁₁) in the transformation of syngas on Cr₂O₃-ZnO/ZSM5 bifunctional catalyst have been established as a function of the concentration of both reactants (CO and H₂) and CO₂ byproduct. The effect of the operating conditions on the RON and on the molecular weight of the gasoline has been studied by experimentation in an integral fixed bed reactor in the range between 10 and 50atm and between 300 and 425°C. The octane index increases with Cr/Zn atomic ratio of the Cr₂O₃-ZnO metallic function, with Si/Al ratio of the HZSM5 zeolite, with space time and with the CO/H₂ molar ratio in the feed, in that order, whereas it passes through a maximum with pressure (at 20 atm) and with temperature (at 375°C). On the other hand, the molecular weight of the gasoline increases with the Cr/Zn atomic ratio, pressure, CO/H₂ molar ratio and space time, and decreases with the Si/Al ratio and temperature.     

A self-tuning ANN model for simulation and forecasting of surface flows

Artificial neural networks (ANN) are applicable for and forecasting without the need to calculate complex nonlinear functions. This paper evaluates the effectiveness of temperature, evapotranspiration, precipitation and inflow factors, and the lag time of those factors, as variables for simulating and forecasting of runoff. The genetic algorithm (GA) is coupled with ANN to determine the optimal set of variables for streamflow forecasting. The minimization of the total mean square error (MSE) is considered as the objective function of the ANN-GA method in this paper. Our results show the effectiveness of the ANN-GA for simulating and forecasting runoff with consistent accuracy compared with using pure ANN for runoff simulation and forecasting.