170,006 research outputs found
Biosyngas Fischer-Tropsch conversion by high Fe loaded supported catalysts prepared with ultrasound and microwave
No full textCatalysts with iron high loading of 30 wt%, promoted with K (2.0 wt%) and Cu (3.75 wt%), have been synthesized according to three different methods: 1) the traditional impregnation method (TR); 2) Ultrasound (US) assisted TR method; 3) Microwave (MW) assisted TR method. All the samples have been fully characterized by BET, ICP/OES, XRPD, TG-DTA, FT-IR, TPR, SEM and TEM and tested in a laboratory pilot plant for Fischer -Tropsch synthesis working at 220°C and 20 bar. The results of the catalysts characterization indicated that the morphology of the samples strongly depends on the method of preparation. The best FTS results in term of C2+ yield (41%) has been obtained using MW with a good value of the selectivity towards heavy hydrocarbons, while in term of CO conversion (58%), using US. The samples prepared with non-traditional methods show FTS better results, probably due to a more wide and uniform distribution of Fe in the medium during the synthesis phase
Effects of plasma amino acid and hormone levels on renal hemodynamics in humans
No full textThe effect of plasma amino acid and hormone (insulin, glucagon, and growth hormone) levels on renal hemodynamics was studied in 18 healthy subjects. The following four protocols were employed: study 1, a balanced amino acid solution was infused for 3 h to increase plasma amino acid concentrations two to three times base line; study 2, the same amino acid solution was infused with somatostatin (SRIF) and infusions of insulin, glucagon, and growth hormone were concomitantly administered to replace the time sequence of increase in peripheral concentrations of these hormones as observed during study 1; study 3, the same amino acid infusion was administered with SRIF plus infusions of insulin, glucagon, and growth hormone to maintain plasma hormone concentrations constant at the basal level; study 4, SRIF was infused with insulin, glucagon, and growth hormone to reproduce the time sequence of increase of these hormones as observed in study 1; amino acids were not infused in this study. During study 1, glomerular filtration rate (GFR) and renal plasma flow (RPF) rose by 19 and 21%, respectively. During study 2 both the time sequence of and magnitude of rise in GFR and in RPF were similar to the changes observed during study 1. In studies 3 and 4 neither RPF and GFR changed significantly from base line. These results indicate that 1) hyperaminoacidemia stimulates insulin/glucagon/growth hormone secretion and causes a modest rise in GFR and RPF; and 2) if hyperaminoacidemia is created while maintaining basal hormone levels constant or if plasma insulin/glucagon/growth hormone levels are increased while maintaining the plasma amino acid concentration at basal levels, neither RPF nor GFR rise. We conclude that the renal hemodynamic response following amino acid infusion is dependent on the release of some factor whose release is inhibited by somatostatin and restored by combined insulin/glucagon/growth hormone replacement
Ultrasonidos y microondas en la preparacion de catalizadores soportados a base de hierro para la sintesis de Fischer-Tropsch
No full textCatalizadores con un contenido de hierro del 30% en peso, promovidos con K (2,0% en peso) y Cu (3,75% en peso), fueron sintetizados utilizando tres métodos: 1) el método de impregnación tradicional (TR); 2) El método de impregnación tradicional asistido por ultrasonido (US) y 3) El método de impregnación tradicional asistido por microondas (MW). Todas las muestras fueron caracterizadas por BET, XRPD, TG-DTA, FT-IR, TPR, SEM y TEM y evaluadas en una planta de laboratorio para la síntesis de Fischer-Tropsch bajo condiciones de operación de 220oC y 20 bar. Los resultados de la caracterización de los catalizadores indicaron que la morfología de las muestras depende en gran medida del método de preparación. Los mejores resultados en términos de rendimiento (41%) y selectividad hacia los hidrocarburos pesados, fueron obtenidos utilizando las microondas; mientras que en términos de conversión de CO los mejores resultados fueron obtenidos utilizando ultrasonidos (58%). Las muestras preparadas con métodos no tradicionales arrojaron mejores resultados, probablemente debido a una distribución más amplia y uniforme del Fe en el medio durante la fase de síntesis
High Fe loaded supported catalysts for biosyngas Fischer-Tropsch conversion: experimental results and detailed simulation
No full textFischer-Tropsch synthesis (FT) is at the heart of the Biomass-to-Liquids process, one of the attractive options for the production of clean and carbon-neutral diesel from biomass. The H2/CO molar ratio of synthesis gas produced from biomass is between 1.0 and 1.5 and using this feeding iron based catalysts are more suitable in FT respect the cobalt-based ones.
Supported Fe- based catalysts have several advantages (greater surface area, better dispersion of the heat developed by the reaction and better mechanical resistance) compared to massive iron catalysts adopted in the current FT industrial plants. In particular, the optimized components loading was found, in our previous researches, to correspond to 30 wt% Fe supported on silica and promoted with K (2.0 wt%) and Cu (3.75 wt%).
In order to optimize the activity, selectivity and the lifetime of this kind of FT catalyst in work conditions of biosyngas feeding, a series of experimental runs were performed with different reactor temperatures and different inlet H2/CO ratios. FT reaction activity tests were carried out in a fixed bed tubular reactor, using 1 g of fresh catalyst mixed with 1 g of diluting material (α-Al2O3, Fluka). All the catalysts were reduced in situ by a flow of H2/CO (2/1) at 350°C, 500 kPa for 4 h and tested with the standard conditions of 46.8 Nml min-1 flow of syngas (H2/CO ratio of 1/1; 1.5/1 and 2/1) plus 5.0 Nml min-1 of N2 as internal standard, at 2MPa and T= 230, 250 and 260°C for 90 h. FT results confirm the good activity of these samples (CO conversion and hydrocarbons selectivity) with low H2/CO feedings.
On the basis of the collected data, a rigorous simulation of the FT synthesis reactor has been developed for different purposes: (i) to support the experimentations when implemented for the experimental design of experiments; (ii) to predict the reactor yield and conversion; (iii) to optimize the performance of the reactor system with different operating conditions; and (iv) to calculate novel reliable kinetic parameters basing on the fitting of experimental data by means of model-based nonlinear regression techniques. To do so, the FT reactor is modeled as a catalytic plug-flow reactor using mass and energy balances and reaction kinetics for Fe-based catalyst defined by Zimmerman and Bukur leading to an ordinary differential equation system with structured Jacobian. Lumping techniques have been used to model heavy hydrocarbons. The system is solved by means of dedicated solvers to handle stiffness and nonlinearities of heterogeneous reactive systems
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Ultrasound and microwave assisted preparation of high Fe loaded supported catalysts for biosyngas Fischer-Tropsch conversion
No full textSupported Fe- based catalysts have several advantages (greater surface area, better dispersion of the heat developed by the reaction and better mechanical resistance) compared to massive iron catalysts adopted in the current Fischer Tropsch (FT) industrial plants. In particular, the optimized components loading was found to correspond to 30 wt% Fe supported on silica and promoted with K (2.0 wt%) and Cu (3.75 wt%) [1]. In order to study the influence of the preparation procedure, three different kind of catalysts were synthesized according to three different methods: 1) the traditional impregnation (TR) [1]; 2) Ultrasound (US) assisted TR method; 3) Microwave (MW) assisted TR method. All the samples were fully characterized by BET, ICP/OES, XRPD, TG-DTA, FT-IR, TPR, SEM and TEM and tested in a laboratory pilot plant. FT reaction activity tests were carried out in a fixed bed tubular reactor, using 1 g of fresh catalyst mixed with 1 g of diluting material (α-Al2O3, Fluka). All the catalysts were reduced in situ by a flow of H2/CO (molar ratio of 2/1) at 350°C, 500 kPa for 4 h and tested with the standard conditions of 46.8 Nml min-1 flow of syngas (molar ratio of 2/1) plus 5.0 Nml min-1 of N2 as internal standard, at 2MPa and T= 250°C for 90 h, as detailed in [1, 2].
The results of the characterization of the catalysts indicated that the morphology of the samples strongly depends on the method of preparation. Moreover, the samples treated with MW and US have higher surface areas than the traditional ones (Tab. 1).
FT catalytic results are displayed in Table 1. The best results in term of C2+ yield (41%), with a good value of selectivity towards heavy hydrocarbons, was obtained using MW, while in terms of CO conversion (58%), using US. The samples prepared with non-traditional methods show better FT results, probably due to a more wide and uniform distribution of Fe achieved during the synthesis. This result was verified by TEM and is in agreement with previous results [3]
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Co based bimetallic catalysts for Fischer-Tropsch synthesis prepared by high power ultrasound
No full textThe use of ultrasound in the preparation of cobalt based catalysts for Fischer-Tropsch synthesis was studied and discussed
Co-Zn-Al Based Hydrotalcites as Catalysts for Fischer-Tropsch Process
No full textCo-Zn-Al based hydrotalcites have been investigated as catalysts for the well-known Fischer-Tropsch synthesis. A series of ternary hydrotalcites in nitrate form was prepared with the urea method in order to obtain active catalysts for the above mentioned process. The thermal activation at 350°C gives raise to finely dispersed metallic Co on the mixed oxides, so resulting in retaining the metal distribution of the parent compounds. An optimization study concerning the amount of cobalt of the prepared catalysts (range 15-70% mol, metal based) and the reaction temperature (220-260°C) is reported. All the samples have been fully characterized (BET, ICP/OES, XRPD, TG-DTA, FT-IR, SEM and TEM) and tested in a laboratory pilot plant. Tests to evaluate the stability of these materials were carried out in stressed conditions concerning both the activation and the operating temperatures and pressures (up to 350°C and 2.0 MPa). The obtained results suggest the possibility of using synthetic hydrotalcites as suitable Co-based catalysts for the Fischer-Tropsch synthesis
Sonochemical synthesis of Co based bimetallic catalysts for Fischer Tropsch synthesis
No full textDiffertent Fischer-Tropsch catalyset, prepared with the ultrasound method were tested in a FT plant. The composition of these catalyst was Co10% on silica and 0.1-2% of Ruthenium as promoter
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