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In this study, DDR membranes with a layer thickness of approximately 700 nm were studied for separation feeds comprising mixtures of CO 2 and CH 4. The membranes displayed the highest CO 2 over CH 4 permselectivity and CO 2 permeability reported in literature. This was ascribed to a defect-free and ultra-thin zeolite film as well as an open and highly permeable support. For equimolar mixtures, the highest CO 2 over CH 4 permselectivity of 727 was observed when the pressure at the feed side was 5 bar(a) and the permeate pressure was 1 bar(a) at 25 °C. At these conditions, the CO 2 permeability was very high at 45 × 10−7 mol/(m2 s Pa). Separation experiments for 80/20 and 20/80 mixtures were also performed, and in these cases, CO 2 over CH 4 permselectivities of 1011 and 622 were observed, respectively. For all feeds, the membrane permselectivity decreased slightly at higher temperature and in all cases, higher permselectivity was observed when vacuum was applied at the permeate side. One-stage membrane processes for upgrading biogas to biomethane at three different operating pressures were designed based on the experimental data. In all cases, a quite low membrane area, methane slip and power need were observed. [Display omitted] • DDR membranes with ultrahigh CO 2 permeance for CO 2 /CH 4 separation. • One-stage DDR membrane processes for biogas upgrading. • Low membrane area, CH 4 slip, and power use for these processes. [ABSTRACT FROM AUTHOR]

The NET power cycle (NPC) offers an alternative way to inherently capture combustion derived CO2 with low efficiency penalty. This manuscript improves the NPC by recompressing a portion of the recycled CO2 stream to the exit of low temperate regenerator, forming a recompression NET power cycle (RNPC). The RNPC further enhances cycle recuperation and no longer needs to input extra heat to cover the heat gap between low pressure and high pressure CO2 streams in the regenerator. The model of internal convection cooling for the turbine in sCO2 cycle is also accomplished according to the semiempirical formula, aiming to investigate the effect of coolant flow. This manuscript respectively conducts the system multiparameter optimization for uncertain boundary parameters and the sensitivity analysis for definite boundary parameters. The simulation results show that RNPC can output 27.2 MWe more NEP than NPC without extra heat input, leading to 3.54% of the increase in net electric efficiency. RNPC's efficiency increases monotonically with not only turbine inlet temperature but inlet pressure, which indicates that RNPC has the potentiality to further improve its efficiency at higher turbine inlet temperature and inlet pressure. However, turbine outlet pressure has a nonmonotonic effect on the cycle performance, and the optimal turbine outlet pressure corresponding to the maximum cycle efficiency is about 38–42 bar. The multiparameter optimization indicates that the global optimal cycle efficiency is approximately 53.55% within the ranges of investigated parameters. The RNPC's efficiency is considerably influenced by the minimum cycle temperature (0.234%/°C), compressor efficiency (0.08%/%), turbine efficiency (0.355%/%), and regenerator temperature differences (0.083%/°C for HTR and 0.080%/°C for LTR). [ABSTRACT FROM AUTHOR]

We developed a series of molecule-scale hybrid amine-silica membranes synthesized from organoalkoxysilane precursors of 3-(triethoxysilyl)propan-1-amine (PA-Si) and 3-(triethoxysilyl)-N-methylpropan-1-amine (SA-Si), and made these functional using either unhindered amines or a 3-(triethoxysilyl)-N,N-dimethylpropan-1-amine (TA-Si) that is sterically hindered. CO 2 adsorption-desorption measurements of amine-silica powdered xerogels were conducted to observe the effect of amine type on CO 2 adsorption and desorption/diffusion properties. The results revealed that TA-Si xerogel powders demonstrated faster kinetics for both adsorption and desorption processes compared with those of the PA-Si and SA-Si samples due to the steric hindrance effect of the amine, which reduced the CO 2 binding energy and thereby boosted both the forward and reverse reaction rates of CO 2 -amine. In single-gas permeation performances, all the membranes exhibited excellent molecular sieving at higher temperatures and all the gases considered, except CO 2 , tended to permeate the membranes via activated diffusion. The effect of amine type on CO 2 separation performance was compared using CO 2 permeance, CO 2 /N 2 selectivity, activation energy for permeation ( E p ) of CO 2 [ E p (CO 2 ) ], and differences in E p between CO 2 and N 2 [ E p (CO 2 )-E p (N 2 ) ]. The TA-Si membrane demonstrated superior CO 2 separation performance, and achieved the highest values for both CO 2 permeance and selectivity. A relatively smaller difference in CO 2 separation performance was observed between PA-Si and SA-Si membranes despite some differences in basicity. This suggests that, rather than the basicity, it was the steric hindrance effect that played the greatest role in CO 2 transport performance across amine-silica membranes. [ABSTRACT FROM AUTHOR]

In the present work, single channel tubular zeolite CHA membranes with a length of 50 cm and a membrane area of 100 cm2 were evaluated by SEM and permeation experiments with single components and industrially relevant humid mixtures. The membranes comprised well-intergrown and smooth CHA films with a thickness of <500 nm supported on the inside of a highly porous tube. For single component permeation, a very low SF 6 permeance of 4.5 × 10−10 mol/(m2‧s‧Pa) was observed, which indicated nearly defect free membranes. On the contrary, the membranes displayed a very high CO 2 permeance of 128 × 10−7 mol/(m2‧s‧Pa), which illustrated the very high permeability of the CHA pores. Finally, the membranes displayed excellent selectivity for separation of industrially relevant CO 2 /CH 4 /H 2 O mixtures, which was attributed to selective interaction between the CO 2 molecules and the polar water molecules in the pores. The highest observed CO 2 /CH 4 separation selectivity was as high as 198 in combination with a CO 2 permeance of 14 × 10−7 mol/(m2‧s‧Pa) at a feed pressure of 600 kPa (including 2.2 kPa water) and 293K. The corresponding CO 2 flux was 0.39 mol/(m2‧s) and the corresponding CO 2 /CH 4 separation factor was 162. The observed membrane performance was reduced by concentration polarisation due to the limited feed flow in the experimental setup. The corresponding selectivity and CO 2 permeance corrected for concentration polarisation were as high as 236 and 16 × 10−7 mol/(m2‧s‧Pa), and the corrected CO 2 flux was 0.44 mol/(m2‧s) and corrected separation factor was 198. An estimate showed that even at a low feed pressure of 500 kPa, it would be sufficient with as few as 64 membranes for processing of a feed of 100 Nm3/h raw biogas, i.e. the capacity of a typical biogas plant at a large farm, to biomethane with high purity. These results illustrated that the membranes are promising candidates for industrial separation of CO 2 from e.g. natural gas and biogas. [Display omitted] • The first report described industrially relevant CHA membranes. • The membrane was a single channel tube with a membrane area of 100 cm2. • CO 2 single gas permeances was as high as 128 × 10−7 mol/(m2‧s‧Pa). • The highest observed CO 2 /CH 4 separation factor was 169. • Effect of concentration polarisation on separation was discussed. [ABSTRACT FROM AUTHOR]

The abatement of defects in zeolite membranes is essential for achieving high selectivity. In the present work, a simple and effective method for blocking defects in ultra-thin (ca. 0.5 μm) MFI zeolite membranes has been developed. The method is based on deposition of an ultra-thin (~15 nm) layer of amorphous silica on the top surface of the membrane. Permporometry data indicated that the amount of defects, especially defects larger than 4 nm, in the membranes was significantly reduced after the modification. In mixture separation experiments, the CO 2 /H 2 separation factor increased dramatically after blocking the defects in a defective membrane that was selected for the experiments. For instance, at 263 K and 9 bar feed pressure, the CO 2 /H 2 separation factor increased from 8.5 to 36 after modification of the membrane, whereas the CO 2 flux only decreased by ca. 40%. [ABSTRACT FROM AUTHOR]

Postural orthostatic tachycardia syndrome (POTS) typically occurs in youths, and early accurate POTS diagnosis is challenging. A recent hypothesis suggests that upright cognitive impairment in POTS occurs because reduced cerebral blood flow velocity (CBFV) and cerebrovascular response to carbon dioxide (CO2) are nonlinear during transient changes in end-tidal CO2 (PETCO2). This novel study aimed to reveal the interaction between cerebral autoregulation and ventilatory control in POTS patients by using tilt table and hyperventilation to alter the CO2 tension between 10 and 30 mmHg. The cerebral blood flow velocity (CBFV), partial pressure of end-tidal carbon dioxide (PETCO2), and other cardiopulmonary signals were recorded for POTS patients and two healthy groups including those aged >45 years (Healthy-Elder) and aged <45 years (Healthy-Youth) throughout the experiment. Two nonlinear regression functions, Models I and II, were applied to evaluate their CBFV-PETCO2 relationship and cerebral vasomotor reactivity (CVMR). Among the estimated parameters, the curve-fitting Model I for CBFV and CVMR responses to CO2 for POTS patients demonstrated an observable dissimilarity in CBFVmax (p = 0.011), mid-PETCO2 (p = 0.013), and PETCO2 range (p = 0.023) compared with those of Healthy-Youth and in CBFVmax (p = 0.015) and CVMRmax compared with those of Healthy-Elder. With curve-fitting Model II for POTS patients, the fit parameters of curvilinear (p = 0.036) and PETCO2 level (p = 0.033) displayed significant difference in comparison with Healthy-Youth parameters; range of change (p = 0.042), PETCO2 level, and CBFVmax also displayed a significant difference in comparison with Healthy-Elder parameters. The results of this study contribute toward developing an early accurate diagnosis of impaired CBFV responses to CO2 for POTS patients. [ABSTRACT FROM AUTHOR]