Sweep-gas Rates Research Articles

Tethered Liquid Perfluorocarbon Coating for 72 Hour Heparin-Free Extracorporeal Life Support.

Coagulopathic complications during extracorporeal life support (ECLS) result from two parallel processes: 1) foreign surface contact and shear stress during blood circulation and 2) administration of anticoagulant drugs to prevent circuit thrombosis. To address these problems, biocompatible surfaces are developed to prevent foreign surface-induced coagulopathy, reducing or eliminating the need for anticoagulants. Tethered liquid perfluorocarbon (TLP) is a nonadhesive coating that prevents adsorption of plasma proteins and thrombus deposition. We examined application of TLP to complete ECLS circuits (membranes, tubing, pumps, and catheters) during 72 hours of ECLS in healthy swine (n = 5/group). We compared TLP-coated circuits used without systemic anticoagulation to standard of care: heparin-coated circuits with continuous heparin infusion. Coagulopathic complications, device performance, and systemic effects were assessed. We hypothesized that TLP reduces circuit thrombosis and iatrogenic bleeding, without impeding gas exchange performance or causing untoward effects. No difference in bleeding or thrombotic complication rate was observed; however, circuit occlusion occurred in both groups (TLP = 2/5; CTRL = 1/5). TLP required elevated sweep gas rate to maintain normocapnia during ECLS versus CTRL (10-20 vs. 5 L/min; p = 0.047), suggesting impaired gas exchange. Thrombus deposition and protein adhesion on explanted membranes were comparable, and TLP did not preserve platelet or blood cell counts relative to controls. We conclude that neither TLP nor standard of care is an efficacious solution to prevent coagulation disturbances during ECLS. Further testing of promising biomaterials for ECLS utilizing the model outlined here is warranted.

Fast Pyrolysis of Spent Coffee Waste and Oak Wood Chips in a Micro-tubular Reactor

Fast pyrolysis of spent coffee waste, a major non-cellulosic material, and oak wood chips, a cellulosic material, was carried out in a micro tubular reactor over a temperature range of 550 to 750°C with sweep gas flow rates of 20 and 500 mL/min. When the temperature was raised from 550 to 750°C, the gas yields were significantly enhanced, but the liquid yields were reduced. The highest liquid yield, 63.4 wt%, was obtained after pyrolysis of spent coffee waste at 550°C at a sweep gas rate of 500 mL/min. The highest gas yield, 65.74 wt%, was obtained after pyrolysis of the oak wood chips at 750°C at a sweep gas flow rate of 20 mL/min. The gas products primarily included considerable amounts of CO, CO2, and hydrocarbon-rich gases but no hydrogen. Furthermore, regardless of the biomass source, the hydrocarbon-rich gases were qualitatively similar and largely consisted of methane, ethane, ethylene, propane, and propylene. The gas chromatography-mass spectrometry analysis of the pyrolyzed bio-oils demonstrated that the major compounds were phenol derivatives, aldehydes, ketones, acids, and alcohols.

The catalytic effects of La0.3Sr0.7Fe0.7Cu0.2Mo0.1O3 perovskite and its hollow fibre membrane for air separation and methane conversion reactions

Perovskite membranes have the potentials to be applied in a novel cost-effective technology for air separation or gas reactions. For this purpose, a cobalt free ceramic perovskite of La0.3Sr0.7Fe0.7Cu0.2Mo0.1O3 (LSFCM) with homogeneous composition was synthesized via the low temperature combustion process. LSFCM perovskite hollow fibre membranes were fabricated by the phase inversion/sintering technique using the prepared ceramic powder. The stability and the catalytic activity of the LSFCM ceramic powder and the prepared membrane reactor for the partial oxidation of methane into syngas were investigated. The oxygen permeation properties of the LSFCM membranes were also studied under the sweep gas mode. Under the oxygen concentration gradient created by air/sweep gas, the detected oxygen flux was 2.31mL/min/cm2 at 1000°C with sweep gas rate of 40mL/min. The experimental results indicate that the LSFCM ceramic powders and hollow fibre membrane exhibited good stability when exposed in inert gases like He and air, but they were not very stable for long run operation in reducing or acid gases like H2, CH4, and CO2. The LSFCM ceramic powder exhibited excellent catalytic activity in the partial oxidation of methane for syngas production with the maximum selectivities of CO and H2 both above 90%. In contrast, the prepared blank LSFCM ceramic hollow fibre membrane displayed good selectivity towards the C2 products of ethylene and ethane with best C2 yield up to 19% raising an interesting issue of the effects of catalyst geometry on its catalytic activity, which deserves further investigation.

Apnea Test for Brain Death Determination in a Patient on Extracorporeal Membrane Oxygenation

Apnea test is a key component to confirm brain death. For patients receiving extracorporeal membrane oxygenation (ECMO), apnea test remains challenging. Brain death (BD) diagnosis is often made without apnea test. We report the case of a 29-year-old man presenting clinical signs of BD while treated with ECMO therapy for refractory cardiogenic shock. Decreasing the ECMO sweep gas flow from 3 to 1 L/min and increasing oxygen delivery to 100% on ECMO during the apnea test have allowed increasing the PaCO2 of more than 20 mmHg without decreasing PaO2. In order to diagnose BD, neurological examination should be complete, including apnea testing, which can be not possible in patients receiving ECMO due to CO2 removal from the membrane. Decreasing sweep gas rate allows reduction in CO2 diffusion through the membrane. However, decreasing the ECMO gas flow to zero could be insufficient to maintain normoxemia. Decreasing (but not stopping) the sweep gas flow to 1 L/min and increasing the oxygen delivery through the ECMO have allowed performing the apnea test safely. To assess brain death in patients on ECMO, apnea test can be performed without compromising oxygenation by decreasing (but not stopping) the sweep gas flow and increasing oxygen delivery through the membrane.

Modelling of hydrogen perm-selective membrane reactors for catalytic methane steam reforming

Methane steam reforming is one of the most important pathways for producing high purity hydrogen. In this context, the use of fixed-bed catalytic reactors equipped with hydrogen perm-selective membranes is an interesting alternative for producing high purity hydrogen in one single step. In this work, this reactor is studied by means of numerical simulations using a 2D model, consisting of mass, energy and momentum balances. The fixed-bed is considered to be formed by Ru/SiO2 catalyst particles, especially tailored for steam reforming at low temperature and steam-to-carbon ratio, whereas a composite palladium membrane was considered for hydrogen permeation. The model was validated with experimental data, and the adequacy of a simplified 1D model to simulate the membrane reactor was evaluated and discussed in comparison to the 2D model. Then, the model was used to study the influence of the main operating variables (inlet temperature, pressure, space velocity, steam excess and sweep gas rate in the permeate side) on the reactor performance. Finally, the optimum operating conditions, corresponding to a maximum hydrogen permeation rate, were determined, and the behaviour of the optimized reactor is analysed in detail.

New morphological Ba0.5Sr0.5Co0.8Fe0.2O3−α hollow fibre membranes with high oxygen permeation fluxes

Perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−α (BSCF) hollow fibre membranes were fabricated by a combined phase inversion and sintering technique. The membranes were characterised by XRD, SEM and tested for air separation. The membrane possesses a novel morphology consisting of one dense layer and one porous layer. Oxygen permeation fluxes through the obtained hollow fibre membranes were measured in the temperature range 650–950°C using helium sweep gas rates from 50 to 200mLmin−1. Experimental results indicated the oxygen permeation flux through the BSCF hollow fibre membrane sintered at 1050°C was approximately 11.46mLmin−1cm−2 at 950°C when the helium sweep rate was kept at 200mLmin−1. The BSCF hollow fibre membrane showed a stable oxygen permeation flux of 8.60mLmin−1cm−2 over the investigated period of 120h at 900°C.

A simulation model for transient response of a gas separation module using a hollow fiber membrane

A simulation model has been developed for transient response of a gas separation module using a hollow fiber membrane for the removal of tritium from the atmosphere of the confinement space. The mass transfer process such as sorption and desorption of gases at the surface of the dense layer and the porous support layer, diffusive transfer in the both layers are treated in the model. Sorption isotherm, mass transfer rate and permeance are estimated through step-wise transient response experiments. The present model represents well not only separation factors and recovery ratio at the steady state but also responses to the multi-step wise change in the sweep gas rate.

Insensible Water Loss From the Medtronic Minimax Oxygenator: An In Vitro Study

The purposes of this study were to quantify the insensible water loss that occurs across the Medtronic Minimax oxygenator and to estimate the resultant rise in fluid sodium concentration.A Carmeda-coated extracorporeal membrane oxygenation circuit connected to a Medtronic Minimax Plus oxygenator was primed with normal saline and attached to a closed reservoir. The gas sweep was randomly assigned to one of three rates: 2, 5, or 10 LPM (liters per minute). Each sweep rate was run in triplicate. The sodium concentration of the circuit was assessed after 12 and 24 hours of each trial. At the end of each 24-hour run, the evaporative loss was calculated. The average insensible water losses were 6.9+/-0.4 ml/h, 16.6+/-1.5 ml/h, and 34.4+/-0.3 ml/h at gas sweep rates of 2, 5, and 10 LPM, respectively (p<0.0001). Daily evaporative water losses for the membrane can be estimated to be 82.7+/-2.2 ml for each 1 LPM of sweep gas flow for a normal saline pump flow of 300 ml/min. In a closed circuit, a faster sweep gas rate is associated with a more rapid rise in sodium concentration (p<0.0001).

Two-Dimensional Simulation of a Membrane Reactor for Dehydrogenation of Ethylbenzene, Considering Heat and Mass Transfer.

A membrane reactor is a reaction system that provides higher productivity and separation cost reduction in chemical reaction processes. In this research, we developed a numerical simulator, taking into account the mass transfer and heat transfer in the axial and radial directions, and analyzed characteristics for temperature distribution and hydrogen permeation in a membrane reactor with Pd-Ag membrane for dehydrogenation of ethylbenzene, with highly endothermic reaction heat.The simulation results exhibited that the temperature distribution in the reactor has considerably changed in the axial and radial directions, and the hydrogen permeability through the membrane has varied from position to position in the reactor. In membrane reactor analysis for the reaction with highly reaction heat, consideration of the temperature gradient in the reactor is believed to lead to the precise estimation of performance characteristics of the membrane reactor. Furthermore, on the basis of the analyzed results, some knowledge for the effects of the tube radius, sweep gas rate, operating pressure of reaction and thickness of membrane on the performance of the membrane reactor, was accumulated to design a membrane reactor system.