Specific Membrane Area Research Articles

PULM5: Hyperbaric Blood Oxygenation – Basic Considerations and First Results

Hyperbaric oxygen therapy is beneficial in several applications, but hyperbaric chambers are scarce. We are developing a novel technology for extracorporeal hyperbaric blood oxygenation (HBOX). This extracorporeal procedure uses pressure to increase the oxygen (O2) concentration in blood. The technology can provide support when large amounts of oxygen are needed: In the treatment of CO poisoning the dissolved oxygen displaces the CO from the blood, removing it from the organism. This way, the oxygen deficiency can be ended rapidly, reducing or preventing secondary damage that frequently occurs. In acute respiratory failure (ARF) the HBOX technology can support lung function, by significantly increasing oxygen transport across a specific membrane area, while maintaining adequate CO2-removal. The prototype of the HBOX consists of 2 roller pumps with a hollow-fiber membrane oxygenator (HFMO) placed in between, a control unit for gas and blood flow and a double lumen catheter. By varying the flow rates of the roller pumps, excess pressure is generated in the HFMO without causing significant blood damage. Simultaneously, the oxygen pressure in the HFMO is increased, allowing for hyperbaric oxygenation. To avoid bubble formation, either O2 increase is limited, or excess O2 is removed in second HFMO before reinfusion. The prototype was tested in-vitro using porcine blood that was either CO poisoned or conditioned to mimic ARF. In acute in-vivo experiments for CO poisoning, we used CO-poisoned pigs (ca. 75 kg, COHb = 43 %, n = 3). For in-vivo experiments for ARF, 70 kg sheep were used with ventilator settings simulating respiratory failure, resulting in SaO2 = 69 %, paCO2 = 72 mmHg (n = 2). In-vitro test results show that the HBOX can fully oxygenate hypoxic blood (sO2 ca. 40 %) with a hilite 800 LT at a flow rate of 2 L/min, which is twice the amount of oxygen transferred, compared to conventional mode, Fig. 1. In in-vivo trials, the CO elimination rate from the animals’ blood doubled when using HBOX + oxygen mask compared to oxygen mask alone, see Fig. 2. In the ARF trials, the HBOX approach resulted in SaO2 of 89, 95, and 99 % and paCO2 was 49, 46, and 39 mmHg at blood flows of 0.5, 1.0, and 1.5 L/min, respectively, see Fig. 3. The HBOX is a promising approach to increase oxygen transport across a specific membrane area. The increased oxygen levels can be used for efficient extracorporeal CO removal. For respiratory support, the hyperbaric technology adds a new dimension to ECMO treatment, allowing the use of smaller oxygenators, potentially reducing the need for anticoagulation, as well as inflammatory responses and thus invasiveness. The hyperbaric technology can be used gradually, so that the membrane efficiency can be increased during intervention. This allows us to build an oxygenator with an ideal flow distribution over a wide range of blood flows, which avoids thrombus formation in the device at lower blood flows.Figure 1. Laboratory results oxygenation performanceFigure 2. Elimination rate COHb in in-vivo trialsFigure 3. Arterial blood gases during in-vivo trial for ARF

Mathematical modeling and process parametric study of CO2 removal from natural gas by hollow fiber membranes

Hollow fiber membranes show a great potential in natural gas sweetening by removing CO2 to meet gas grid specifications. A membrane model with high prediction accuracy is developed to model multicomponent gas transport through hollow fiber modules. The influences of hollow fiber diameter and length, and packing density on module efficiency related to pressure drops in both sides were systematically investigated based on the developed model. The total pressure drop along the length is less than 1% if the inner diameter of hollow fibers (0.6m length) is larger than 200μm. Moreover, the highest module packing density was found to be dependent on hollow fiber dimension, and too high packing density will cause extreme high pressure drops. Both feed CO2 concentration and pressure were found to significantly influence membrane module performance related to the required specific membrane area and hydrocarbon loss based on process parametric study of CO2 removal from natural gas. Larger pressure drops along fiber length was found for the more-permeable polyimide membranes compared to the less-permeable cellulose acetate and carbon membranes. The developed model can be used for guiding the design of efficient hollow fiber membrane modules and potentially process simulation of membrane gas separation.

Techno-economical evaluation of membrane based biogas upgrading system: A comparison between polymeric membrane and carbon membrane technology

A shift to renewable energy sources will reduce emissions of greenhouse gases and secure future energy supplies. In this context, utilization of biogas will play a prominent role. Focus of this work is upgrading of biogas to fuel quality by membrane separation using a carbon hollow fibre (CHF) membrane and compare with a commercially available polymeric membrane (polyimide) through economical assessment. CHF membrane modules were prepared for pilot plant testing and performance measured using CO2, O2, N2. The CHF membrane was modified through oxidation, chemical vapour deposition (CVD) and reduction process thus tailoring pores for separation and increased performance. The post oxidized and reduced carbon hollow fibres (PORCHFs) significantly exceeded CHF performance showing higher CO2 permeance (0.021 m3(STP)/m2 h bar) and CO2/CH4 selectivity of 246 (5 bar feed vs 50 mbar permeate pressure). The highest performance recorded through experiments (CHF and PORCHF) was used as simulation basis. A membrane simulation model was used and interfaced to 8.6 V Aspen HYSYS. A 300 Nm3/h mixture of CO2/CH4 containing 30–50% CO2 at feed pressures 6, 8 and 10 bar, was simulated and process designed to recover 99.5% CH4 with 97.5% purity. Net present value (NPV) was calculated for base case and optimal pressure (50 bar for CHF and PORCHF). The results indicated that recycle ratio (recycle/feed) ranged from 0.2 to 10, specific energy from 0.15 to 0.8 (kW/Nm3feed) and specific membrane area from 45 to 4700 (m2/Nm3feed). The high recycle ratio can create problems during start-up, as it would take long to adjust volumetric flow ratio towards 10. The best membrane separation system employs a three-stage system with polyimide at 10 bar, and a two-stage membrane system with PORCHF membranes at 50 bar with recycle. Considering biomethane price of 0.78 $/Nm3 and a lifetime of 15 years, the techno-economic analysis showed that payback time for the best cascade is 1.6 months.

Assessment of membrane plants for biogas upgrading to biomethane at zero methane emission

In the future energy infrastructure there is a considerable potential for biogas and, in particular, for biomethane as a natural gas substitute. Among the alternatives of upgrading biogas to biomethane, this work focuses on membrane permeation. Taking cellulose acetate as membrane material and spiral-wound as membrane configuration, five layouts are assessed. All layouts have the same biogas plant rated at 500 m3/h (STP), yet they may adopt: (i) one- or two-stage permeation, (ii) permeate or residue recycle, and (iii) a water heater or a prime mover (internal combustion engine or a micro gas turbine) to exploit residues as fuel gas. Since residues are consumed, all layouts have zero emission of methane into the atmosphere. The membrane material is modeled considering the phenomenon of plasticization; the membrane modules are described by a crossflow permeation patterns without pressure drops. The results indicates that specific membrane areas range from 1.1 to 2.4 m2h/m3 (STP), specific energy from 0.33 to 0.47 kWh/m3 (STP), and exergy efficiencies from 57.6% to 88.9%. The splitting of permeation over two stages and the adoption of water heater instead of prime movers is a convenient option. The preferred layout employs a single compressor, a two-stage membrane permeation at 26 bar, a water heater fueled by the first-stage permeate, and a second-stage permeate recycle. Assuming a biomethane incentive of 80 €/MWhLHV and a project life of 15 years, the total investment of this plant is 2.9 M€, the payback time 5 years and the net present value 3.5 M€.

Disruption of OsEXO70A1 Causes Irregular Vascular Bundles and Perturbs Mineral Nutrient Assimilation in Rice.

Normal uptake, transportation, and assimilation of primary nutrients are essential to plant growth. Tracheary elements (TEs) are tissues responsible for the transport of water and minerals and characterized by patterned secondary cell wall (SCW) thickening. Exocysts are involved in the regulation of SCW deposition by mediating the targeted transport of materials and enzymes to specific membrane areas. EXO70s are highly duplicated in plants and provide exocysts with functional specificity. In this study, we report the isolation of a rice mutant rapid leaf senescence2 (rls2) that exhibits dwarfism, ferruginous spotted necrotic leaves, decreased hydraulic transport, and disordered primary nutrient assimilation. Histological analysis of rls2-1 mutants has indicated impaired cell expansion, collapsed vascular tissues, and irregular SCW deposition. Map-based cloning has revealed that RLS2 encodes OsEXO70A1, which is one of the 47 members of EXO70s in rice. RLS2 was widely expressed and spatially restricted in vascular bundles. Subcellular localization analysis demonstrated that RLS2 was present on both membrane and nuclear regions. Expression analysis revealed that mutations in rls2 triggers transcriptional fluctuation of orthologous EXO70 genes and affects genes involved in primary nutrient absorption and transport. In brief, our study revealed that RLS2 is required for normal vascular bundle differentiation and primary nutrient assimilation.

Multistage vacuum membrane distillation (MSVMD) systems for high salinity applications

Multistage membrane distillation (MD) systems can have significantly higher efficiencies than their single stage counterparts. However, multistage MD system design has received limited attention. In this paper, the performance of a multistage vacuum membrane distillation (MSVMD) which is thermodynamically similar to a multi-stage flash distillation (MSF) is evaluated for desalination, brine concentration, and produced water reclamation applications. A wide range of solution concentrations were accurately modeled by implementing Pitzer's equations for NaCl-solution properties. The viability of MSVMD use for zero liquid discharge (ZLD) applications is investigated, by considering discharge salinities close to NaCl saturation conditions. Energy efficiency (gained output ratio or GOR), second law efficiency, and the specific membrane area were used to quantify the performance of the system. At high salinities, the increased boiling point elevation of the feed stream resulted in lower fluxes, larger heating requirements and lower GOR values. The second law efficiency, however, is higher under these conditions since the least heat for separation increases faster than the system's specific energy consumption with increase in salinity. Under high salinity conditions, the relative significance of irreversible losses is lower. Results indicate that MSVMD systems can be as efficient as a conventional MSF system, while using reasonable membrane areas and for a wide range of feed salinities. Given MD's advantages over MSF such as lower capital requirement and scalability, MSVMD can be an attractive alternative to conventional thermal desalination systems.

Effect of operating conditions on osmotic-driven membrane performances of cellulose triacetate forward osmosis hollow fiber membrane

Recent development in forward osmosis (FO) membranes is promising in providing a versatile potential application for further advance in the water treatment and energy production sectors. Using FO hollow fiber membranes to achieve wide application of FO at an industrial level is advantageous because of their large specific membrane area and easy module construction for large-scale applications. In this study, three types of cellulose triacetate (CTA) hollow fiber (HF) forward osmosis membranes with diameters of less than 200μm were evaluated under various operating conditions i.e., draw solution concentration, cross flow velocity, membrane orientation, and temperature. The osmotically driven performance evaluation revealed that the CTA HF membranes featured high water flux-to-reverse salt flux ratios, JwFO/JsFO, exceeding 800L/mol. These values are much higher than those of commercial and reported FO membranes. The performance of the obtained FO membranes was also analyzed theoretically and the theoretical results agreed well with the experimental data.

An experimental investigation on the onset from bubbling to turbulent fluidization regime in micro-structured fluidized beds

Membrane-assisted fluidized beds have been investigated for a number of industrially important applications. Recently, micro-structured membrane-assisted fluidized beds have been proposed and particular for efficient hydrogen production in particular for maximising the volumetric production rate by maximising the installed specific membrane areas. Another important advantage of micro-structuring became evident from computational studies. CFD calculations have shown that micro-structured fluidized beds can be operated in the turbulent fluidization regime at much lower superficial gas velocities compared with larger fluidized bed [1]. This work focuses on an experimental validation of the transition velocity in micro-structured fluidized beds. The influence of the reactor scale and the particle diameter on the transition gas velocity from the bubbling to the turbulent fluidization regime in micro-structure fluidized beds was measured in pseudo 2D column using different experimental techniques: in particular, the pressure drop fluctuation measured by pressure sensors and the local solid holdup fluctuation measured by digital image analysis on images recorded by high speed camera. It was found that smaller reactors filled with particles of smaller diameter can be operated in the turbulent fluidization at a relatively lower gas velocity compared with larger reactors. Interestingly, the different measurement techniques result in somewhat different transition velocities, i.e. the pressure drop fluctuation method generated higher critical velocities than the local solids' holdup fluctuation method. This difference is discussed in this paper. The experimental results confirmed that micro-structured fluidized beds can indeed be operated in the turbulent fluidization regime with lower fluidization velocities thus anticipating increased energy efficiencies and enhanced mass transfer rates.

Gas back-mixing study in a membrane-assisted micro-structured fluidized bed

Membrane-assisted micro-structured fluidized beds have been proposed as efficient membrane reactors and in particular for hydrogen production. However, very little information is available on the effects of gas permeation through the membrane on the gas back-mixing and mass transfer rates in this type of reactors. This study carefully investigates the gas back-mixing characteristics in a micro-fluidized bed and the influence of gas permeation (both addition and extraction) through flat membranes installed in the left and right walls confining the fluidized bed. The tracer gas injection (stimulus-response) method has been used combined with Particle Image Velocimetry and Digital Image Analysis techniques for additional insightful information on the solids flux profiles that strongly influence the gas back-mixing. The results of this study demonstrate that micro-structuring of the fluidized bed results in reduced gas back-mixing and thus in a more efficient membrane reactor configuration for hydrogen production because of the increased driving force for gas permeation. The results also provide some guidelines for the design of micro-structured fluidized bed membrane reactors in terms of preferred specific membrane area and particle size.

Asymptotic analysis of the Poisson–Boltzmann equation in biological membrane channels

The Poisson–Boltzmann equation has been increasingly used for the description of biomolecular systems in order to derive their electrostatic properties. We here consider a domain consisting of two living cells which communicate through a system of proteins which assemble at specific membrane areas building microchannels called gap junctions. We describe the asymptotic behavior of the solution of the Poisson–Boltzmann equation posed in this domain. Using Γ-convergence tools, we derive some electrostatic properties of the biological membrane with respect to a vanishing parameter which is simultaneously associated to the membrane thinness, to the diameter of the gap junction microchannels and to the Debye length parameter which characterizes the spatial scale electrostatic interactions between particles within the gap junctions.

Simulation of a membrane unit for oxyfuel power plants under consideration of realistic BSCF membrane properties

Oxyfuel processes represent a promising technique for carbon capture and storage since the related energy penalty is considered to be comparatively low. A possibility to separate the O 2 from air is the use of mixed ion electron conducting (MIEC) membranes. A favored membrane material is Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ since its permeation rate is high. In the work at hand this membrane material has been studied experimentally to determine the coefficients of the Wagner equation. The experiments have been performed with membrane tubes considering the use of tubular membrane systems for industrial application in future oxyfuel power plants. 3- and 4-end operating conditions have been applied to provide an additional degree of freedom for the integration of the membrane module into the power plant process. Wagner constants C = 1.004 × 1 0 − 8 mol/(cm s K) and K = 6201 K have been determined. A membrane model for Aspen Plus has been developed, which allows to calculate the heat and mass transfer in an oxygen membrane module. Calculations were performed based on data from oxyfuel membrane power plant simulations found in the literature. Compared to the 3-end concept the 4-end concept shows a higher net-efficiency together with a lower demand on membrane area. Depending on the operation mode and boundary conditions, the estimated specific membrane area is between 0.22 and 0.59 m 2 / kW th .

Characterization of a biofilm membrane reactor and its prospects for fine chemical synthesis

Biofilms are known to be robust biocatalysts. Conventionally, they have been mainly applied for wastewater treatment, however recent reports about their employment for chemical synthesis are increasingly attracting attention. Engineered Pseudomonas sp. strain VLB120 Delta C biofilm growing in a tubular membrane reactor was utilized for the continuous production of (S)-styrene oxide. A biofilm specific morphotype appeared in the effluent during cultivation, accounting for 60-80% of the total biofilm irrespective of inoculation conditions but with similar specific activities as the original morphotype. Mass transfer of the substrate styrene and the product styrene oxide was found to be dependent on the flow rate but was not limiting the epoxidation rate. Oxygen was identified as one of the main parameters influencing the biotransformation rate. Productivity was linearly dependent on the specific membrane area and on the tube wall thickness. On average volumetric productivities of 24 g L(aq) (-1) day(-1) with a maximum of 70 g L(aq) (-1) day(-1) and biomass concentrations of 45 g (BDW) L(aq) (-1) have been achieved over long continuous process periods (>or=50 days) without reactor downtimes.

The potential of membrane distillation as a stand-alone desalination process

A mathematical model is developed to investigate the potential of the membrane distillation process to be a stand-alone process. The model includes internal heat recovery and relates the major cost parameters to the heat and mass transfer of the process. The cost parameters are the energy required for heating, the energy required for pumping, and the specific membrane area. It was found that the permeability of membrane distillation system (defined below) for the modules available in the literature is in the range of (1)10 −8 to (1.5)10 −6. Taking the upper limit, it was found that for membrane distillation system to become competitive for seawater desalination, the feed solution need to be discharged at temperature over 50°C and so a low-grade energy is needed. Moreover, it can be concluded that the process is closer to be economic when Reynolds number is in the range 3000–5000 (transition from laminar to turbulent flow).

Biodegradation of PCE in a Hybrid Membrane Aerated Biofilm Reactor

A continuous flow flat sheet hybrid membrane aerated biofilm reactor MABR was used to treat a synthetic wastewater containing perchloroethylene PCE; 1.25-2.5 g chemical oxygen demand COD/L of glucose was also added to the synthetic waste- water as a source of COD representative of a real wastewater. The reactor was able to biodegrade 70 mg L 1 of PCE in 9 h without the accumulation of any intermediate compounds, resulting in a removal rate of 247 mmol of PCE h 1 m 3 in a reactor with a specific membrane area of 4.048 m 2 m 3 . MABRs have never been used before for PCE degradation, and this rate is one of the highest volumetric PCE degradation rates reported in the literature. COD removal was also good and varied from 85 to 92%. Since very few volatile fatty acids accumulated in the system, most of the residual COD was attributed to soluble microbial products as reported by previous researchers. A mass balance on chloride during this study showed that only 72-81% of it could be accounted for. It is probable that some of the chlorinated ethenes were adsorbed onto the biofilm or that aerobic intermediates of low-chlorinated compounds such as trichloro- ethanol, dichloroacetyl, and chloroacetaldehyde were produced in the system. Nevertheless the chloride mass balance in this work compares well with the literature. Due to their high PCE and COD removal rates, hybrid MABRs have the potential to be used for a number of refractory organics which require combined anaerobic/aerobic biological treatment for degradation.

Performance of individual fibers in a submerged hollow fiber bundle

Hollow fiber membranes are popular as they have a high specific membrane area. To take advantage of this, it is necessary to pack the fibers into closely packed bundles. The fibers in different positions in the bundle behave differently as they are exposed to different hydrodynamic conditions. In this paper, a 'model' bundle of 9 fibers was tested in a setup which provides flow measurement from individual fibers and the same suction pressure in each fiber. The parameters studied were packing density, cross flow velocity, feed concentration and bubbling. It was found that a low cross flow velocities, high pressures and high feed concentrations, the surrounded (center) fiber performed very poorly compared to the fibers at the corner and the sides. Under these conditions, the overall performance of the bundle was much worse that of a single fiber.

Distribution of regulatory subunits of protein kinase A and A kinase anchor proteins (AKAP 95, 150) in rat pinealocytes.

The rat pineal organ is an established model to study signal transduction cascades that are activated by norepinephrine (NE) and cause increases in cAMP levels and stimulation of protein kinase A (PKA). PKA type II catalyzes the phosphorylation of the transcription factor cAMP-response-element-binding protein (CREB) which is essential for the transcriptional induction of the arylalkylamine- N-acetyltransferase (AANAT), the rate limiting enzyme of melatonin biosynthesis. Moreover, PKA may control protein levels and enzyme activity via two PKA-dependent phosphorylation sites in the AANAT molecule. Despite the functional importance of PKA very little is known about the distribution of its isoenzymes and of A-kinase anchor proteins (AKAPs) that target the PKA to specific membrane areas and organelles by binding to the regulatory (R) subunits of PKA. We have addressed this problem by demonstrating the R subunits alpha and beta of PKA type I and II and two AKAPs (150 and 95) in NE-stimulated and untreated rat pinealocytes by immunoblot and immunocytochemistry. The immunoreactions (IR) of all four R subunits were confined to granules evenly distributed in the pinealocyte cytoplasm. Immunoreactions of RIIalpha and RIIbeta were stronger than those of RIalpha and RIbeta. AKAP 150-IR was concentrated at the cell periphery; AKAP 95-IR was restricted to the nucleus. Amount and subcellular distribution of the immunoreactions of all proteins investigated did not change upon NE stimulation. A substantial colocalization was observed between RII-subunits and AKAP 150-IR, suggesting that, in rat pinealocytes, AKAP 150 primarily anchors the R subunits of PKA II.

Regulation of fast inactivation of cloned mammalian IK(A) channels by cysteine oxidation

Modulation of neuronal excitability by regulation of K+ channels potentially plays a part in short-term memory but has not yet been studied at the molecular level. Regulation of K+ channels by protein phosphorylation and oxygen has been described for various tissues and cell types; regulation of fast-inactivating K+ channels mediating IK(A) currents has not yet been described. Functional expression of cloned mammalian K+ channels has provided a tool for studying their regulation at the molecular level. We report here that fast-inactivating K+ currents mediated by cloned K+ channel subunits derived from mammalian brain expressed in Xenopus oocytes are regulated by the reducing agent glutathione. This type of regulation may have a role in vivo to link metabolism to excitability and to regulate excitability in specific membrane areas of mammalian neurons.

The removal of sulphuric acid from natural and industrial waste waters

A process is described which enables the removal of sulphuric acid from effluents without the addition of chemicals to the effluent. The technique employs an anion selective membrane which separates the acidic effluent from a lime solution. In the case where no current is applied, facilitated transport occurs and the driving force for the demineralisation process is the difference in the chemical potential of the species on either side of the membrane. The equilibrium position may be shifted by the passage of a current through the membrane, in which instance the driving force becomes the applied electric potential. The sulphates are removed as calcium sulphate, which precipitates in the lime solution. The specific membrane area requirements are a function of the desired degree of acid reduction. The application of low current densities (500 A/m 2) reduces the specific membrane area requirements for a particular duty by two orders of magnitude compared to facilitated transport. Results of laboratory investigations are given and indicate that the sulphuric acid component can be removed from waste waters without an undesirable build-up of additional dissolved solids.