Thermal-oxidative Degradation of PGA, PLLA, and Random Binary PLLA-PGA Copolymers

Dimerization process is essential for producing copolymers. The features of dimerization process like thermal-oxidative degradation should be well known to reach maximum efficiency and a superior reactor design. Also, the degradation mechanism of biodegradable polymers is important during sterilization processes. Thermal-oxidative degradation of PGA, PLLA, and their binary copolymers was investigated under isothermal heating as well as dynamic heating. All the samples were prepared by a polycondensation process and were characterized by TG, DTG, DSC, and HNMR analyses. Activation energy under dynamic heating was obtained by using Friedman plot. A new three stage mechanism, namely random, transition, and specific stages is proposed for dynamic heating degradation. Isothermal heating investigation is conducted under an inert atmosphere, and frequency factor and activation energy were achieved. It was found that the activation energy under isothermal heating is generally higher than that under dynamic heating. It was found that the rate of degradation increases significantly with an increase in temperature. The effects of pressure on the degradation rate were studied in different atmospheres with various oxygen partial pressures. Pressure effect was correlated by a second order polynomial in terms of total pressure. The obtained activation energies under isothermal heating were in good agreement with those reported by others. The complete kinetic scheme suitable for reactor design for the thermal-oxidative degradation of the samples was reported. Finally, the optimal operational conditions for the dimerization process were reported.</span

CFD Modeling of Particulates Erosive Effect on a Commercial Scale Pipeline Bend

The computational fluid dynamics modeling of solid particles hydrodynamic based on the Lagrangian framework for diluted solid-gas flow through 90° gas pipeline bend is carried out to discover the effect of particles size distribution on particles flow pattern and their erosive effect on the bend. Particles size distribution has been obtained experimentally by measuring the sizes of solid particles that are flowing through the gas pipelines of Aghajari gas booster station. Also the erosion rate at the outer wall of the bend is predicted. The pipeline bend under study has a pipe diameter of 56 inches and ratios of the bend radius of the curvature to the pipeline diameter of 1.5. For the validation of computational model, firstly, the computational modeling is performed for a published experimental solid-gas flow data. The computational results include radial gas velocity and radial particle velocity profiles on planes which are at different angles through the bend. The comparison between the predicted numerical results and similar experimental data proves that the predictions of the computational model are acceptable. Finally, the particles' size distributions on each plane through the bend and the erosion rate on the outer wall of the bend have been obtained. The maximum rate of erosion is found to be 3.2 nm/s, occurring between 40 and 65° of the bend. Document type: Articl

CFD analysis of hot spot formation through a fixed bed reactor of Fischer-Tropsch synthesis

One of the interesting methods for conversion of synthesis gas to heavy hydrocarbons is Fischer–Tropsch process. The process has some bottlenecks, such as hot spot formation and low degree of conversion. In this work, computational fluid dynamics technique was used to simulate conversion of synthetic gas and product distribution. Also, hot spot formation in the catalytic fixed-bed reactor was investigated in several runs. Simulation results indicated that hot spot formation occurred more likely in the early and middle part of reactor due to high reaction rates. Based on the simulation results, the temperature of hot spots increased with increase in the inlet temperature as well as pressure. Among the many CFD runs conducted, it is found that the optimal temperature and pressure for Fischer–Tropsch synthesis are 565 K and 20 bar, respectively. As it seems that the reactor shall work very well under optimal conditions, the reaction rates and catalyst duration would simultaneously be maximum

CFD analysis of hot spot formation through a fixed bed reactor of Fischer-Tropsch synthesis PUBLIC INTEREST STATEMENT

Abstract: One of the interesting methods for conversion of synthesis gas to heavy hydrocarbons is Fischer-Tropsch process. The process has some bottlenecks, such as hot spot formation and low degree of conversion. In this work, computational fluid dynamics technique was used to simulate conversion of synthetic gas and product distribution. Also, hot spot formation in the catalytic fixed-bed reactor was investigated in several runs. Simulation results indicated that hot spot formation occurred more likely in the early and middle part of reactor due to high reaction rates. Based on the simulation results, the temperature of hot spots increased with increase in the inlet temperature as well as pressure. Among the many CFD runs conducted, it is found that the optimal temperature and pressure for FischerTropsch synthesis are 565 K and 20 bar, respectively. As it seems that the reactor shall work very well under optimal conditions, the reaction rates and catalyst duration would simultaneously be maximum . PUBLIC INTEREST STATEMENT Nowadays, the energy crisis is a real challenge to human society, since oil sources in the world are declining. A promising alternative approach in this regard is to directly convert natural gas to liquid fuel by means of gas-to-liquid (GTL) technology. Fischer-Tropsch synthesis (FTS) with a complex network of reactions in parallel and/or in series converts synthesis gas into valuable liquid hydrocarbons, clean fuels, and chemical feedstock

Combining bioresorbable polyesters and bioactive glasses: Orthopedic applications of composite implants and bone tissue engineering scaffolds

International audienceThis overview showcases the current state of the art in the fabrication, properties and applications of bioactive glass-polyester composites for dentistry, craniomaxillofacial surgery, orthopedics and bone tissue engineering. The combination of these materials is a successful strategy to simultaneously modulate and optimize the degradation rate, mechanical properties, cell response and osteostimulation of bone substitutes. Two major approaches can be identified: bone regeneration or bone repair. The first is performed using porous scaffolding materials, the second one by dense molded implants. For both strategies, the synthesis, processing and characterization of materials are presented based on a comprehensive review of the available literature. Relevant recent in vitro and in vivo studies are also covered. Current and potential future applications of this interesting family of biocomposites are discussed. The literature search revealed a considerable body of work investigating the biological performance of these composites, evidencing the interest on the topic. In particular, the use of polyester/BG composites is well-studied in terms of material fabrication, as well as characterization of physicochemical and in vitro biological properties. On the other hand, there is much less evidence of translational research efforts. It is apparent that future research will have to focus on the collection of more in vivo and clinical data to broaden the knowledge of the time dependent performance of these materials in realistic condition