Subwavelength Gratings for Polarization Control in Terahertz and Visible Frequency Ranges

Ph.DDOCTOR OF PHILOSOPH

Recent advances in multi-layer composite polymeric membranes for CO2 separation: A review

AbstractThe development of multilayer composite membranes for CO2 separation has gained increasing attention due to the desire for energy efficient technologies. Multilayer composite membranes have many advantages, including the possibility to optimize membrane materials independently by layers according to their different functions and to reduce the overall transport resistance by using ultrathin selective layers, and less limitations on the material mechanical properties and processability. A comprehensive review is required to capture details of the progresses that have already been achieved in developing multilayer composite membranes with improved CO2 separation performance in the past 15–20 years. In this review, various composite membrane preparation methods were compared, advances in composite membranes for CO2/CH4 separation, CO2/N2 and CO2/H2 separation were summarized with detailed data, and challenges facing for the CO2 separation using composite membranes, such as aging, plasticization and long-term stability, were discussed. Finally the perspectives and future research directions for composite membranes were presented

Solvent Regeneration by Thermopervaporation in Subsea Natural Gas Dehydration: An Experimental and Simulation Study

An in-house designed membrane process suitable for subsea natural gas dehydration was studied. The use of a membrane absorber together with a thermopervaporation (TPV) unit for solvent regeneration in a closed loop enables the effective and clean production of high-pressure natural gas close to the wellhead. This process avoids the continuous chemical injection for preventing hydrate formation in natural gas pipelines. The regeneration of the absorbent agent (triethylene glycol (TEG)) by TPV in the closed loop is highly energy-efficient, owing to the unlimited free cooling energy from the cold subsea water. In this work, the performance of membranes in TPV for TEG regeneration was evaluated experimentally for the first time. Morphological and permeation characterizations of an AF2400 thin-film composite membrane were carried out, and high separation factors outperforming the vapor–liquid equilibrium (VLE) were obtained for the solutions containing various water contents at feed temperatures ranging from 30 to 70 °C. The highest values of a separation factor (128,000) and a permeability (2380 (Barrer)) were obtained for the TEG solution containing 30 wt % water at 30 °C, while the highest water flux (468 (g/m2·h)) was reached at 70 °C. Moreover, the concentration polarization phenomenon induced by the temperature gradient was revealed in the membrane’s vicinity of the feed channel. A 3D computational fluid dynamics simulation was performed over the entire module to correct the driving force for a more precise assessment of the membrane permeance. The temperature and concentration profiles in the membrane module domains were explored, and a good agreement with experimental data was obtained.publishedVersio

CO2 capture using highly viscous amine blends in nonporous membrane contactors

New amine blends have shown a promising potential to reduce the energy penalty for CO2 capture in post combustion, making the deployment of carbon capture technologies one-step closer. However, their application at the industrial scale is threaten by their high volatility. Non-porous membrane contactors offer a viable solution to properly control amine emissions from these absorbents. In the present work, the CO2 capture performance of non-porous membrane contactors using new amine blends as liquid phase was investigated in a temperature range typical for the absorption step (25–60 °C). Different amine blends with promising features in terms of cycling capacity and regeneration energy requirement were selected as liquid absorbents. Thin composite membranes fabricated by coating a perfluoropolymer on the top of a porous polypropylene layer were used as the interface between the gas and the liquid. At room temperature, membrane contactors using new absorbents exhibit a lower CO2 mass transfer coefficient compared to the benchmark (30 wt% MEA), possibly due to the high viscosity of these liquids. The modelling analysis suggests that the liquid boundary layer dominates the mass transfer resistance in the temperature range up to 40 °C, but at higher temperatures, the decrease of the solvent viscosity makes the mass transfer dominated by the membrane phase. Interestingly, the new amine blends show better performance compared to the benchmark at higher CO2 concentrations in feed gas, highlighting a good potential to capture CO2 from concentrated flue gas from steel/cement industry or to upgrade biogas

Two-stage membrane cascades for post-combustion CO2 capture using facilitated transport membranes: Importance on sequence of membrane types

The use of membrane module performance data obtained in industrially-relevant environment as the basis in process simulation can lead to a more realistic prediction of a CO2 capture system. In this work, we report the use of two classes of industrially validated membranes, i.e., hybrid facilitated transport membranes (HFTMs), which are characterized by higher permeances and lower selectivity, and the fixed site carrier (FSC) polyvinylamine (PVAm) membrane, which is characterized by lower permeance and higher selectivity relative to each other, to study the potential of these membranes in two-stage configurations for post-combustion CO2 capture applications. Two-stage cascades with and without recycle streams were simulated for a target CO2 recovery of >80% and purity of 80–99.5%. Recycle systems were found to contribute in reaching high purity targets of CO2 >90% at the fixed recovery of 90%. The positioning of membranes with different properties in different stages was found to influence the performance of the system significantly. Processes employing HFTMs in the first stage coupled with a PVAm membrane in the second stage performed best with the lowest total energy/membrane area requirement and recycle ratio for a target of 90% recovery and >90% purity of CO2. The process employing HFTMs in both stages outperformed all other cases in terms of membrane area required. The case employing PVAm membranes in both stages performs at its optimum only at a lower purity requirement (<90%). This study reveals the importance of using an optimized combination of membranes with different separation capabilities at different stages.publishedVersio

Enhanced CO2/H2 separation by GO and PVA-GO embedded PVAm nanocomposite membranes

Membrane technology for CO2/H2 separation, especially when using CO2-selective membranes to keep H2 on the high-pressure retentate side, has been considered promising and energy-efficient for further H2 transport and utilization. This work prepared and optimized a CO2-selective membrane based on polyvinylamine (PVAm) with embedded graphene oxide (GO) and grafted GO for CO2/H2 separation. The facilitated transport effect of PVAm enhances CO2 transport, while the GO-based 2D nanosheets bring in a barrier effect to compensate for the high H2 diffusivity. The GO-modified surface with higher CO2 affinity also provides additional CO2 sorption sites. The membranes’ chemical structure, thermal stability, and morphology were characterized. The effects of GO and PVA-GO in the PVAm matrix and optimal loadings of GO or PVA-GO were investigated. Introducing GO into PVAm significantly increased CO2 permeance with a slight increase in CO2/H2 selectivity. While by adding 0.5 wt% PVA-GO, CO2/H2 selectivity significantly increased from 10 to 22. The selective layer thickness also greatly affects CO2/H2 separation. By increasing the coating layer thickness to approx. 11 μm, the CO2/H2 selectivity substantially increased. The separation performances of the studied membrane are far above the current CO2/H2 upper bound.publishedVersio

Analysis of CO2 Facilitation Transport Effect through a Hybrid Poly(Allyl Amine) Membrane: Pathways for Further Improvement

Numerous studies have been reported on CO2 facilitated transport membrane synthesis, but few works have dealt with the interaction between material synthesis and transport modelling aspects for optimization purposes. In this work, a hybrid fixed-site carrier membrane was prepared using polyallylamine with 10 wt% polyvinyl alcohol and 0.2 wt% graphene oxide. The membrane was tested using the feed gases with different relative humidity and at different CO2 partial pressures. Selected facilitated transport models reported in the literature were used to fit the experimental data with good agreement. The key dimensionless facilitated transport parameters were obtained from the modelling and data fitting. Based on the values of these parameters, it was shown that the diffusion of the amine-CO2 reaction product was the rate-controlling step of the overall CO2 transport through the membrane. It was shown theoretically that by decreasing the membrane selective layer thickness below the actual value of 1 µm to a value of 0.1 µm, a CO2 permeance as high as 2500 GPU can be attained while maintaining the selectivity at a value of about 19. Furthermore, improving the carrier concentration by a factor of two might shift the performances above the Robeson upper bound. These potential paths for membrane performance improvement have to be confirmed by targeted experimental work

Highly CO2-permeable membranes derived from a midblock-sulfonated multiblock polymer after submersion in water

To mitigate the effect of atmospheric CO2 on global climate change, gas separation materials that simultaneously exhibit high CO2 permeability and selectivity in gas mixtures must be developed. In this study, CO2 transport through midblock-sulfonated block polymer membranes prepared from four different solvents is investigated. The results presented here establish that membrane morphology and accompanying gas transport properties are sensitive to casting solvent and relative humidity. We likewise report an intriguing observation: submersion of these thermoplastic elastomeric membranes in liquid water, followed by drying prior to analysis, promotes not only a substantial change in membrane morphology, but also a significant improvement in both CO2 permeability and CO2/N2 selectivity. Measured CO2 permeability and CO2/N2 selectivity values of 482 Barrer and 57, respectively, surpass the Robeson upper bound, indicating that these nanostructured membranes constitute promising candidates for gas separation technologies aimed at CO2 capturepublishedVersio

Comparative genomics reveals intraspecific divergence of Acidithiobacillus ferrooxidans: insights from evolutionary adaptation

Acidithiobacillus ferrooxidans serves as a model chemolithoautotrophic organism in extremely acidic environments, which has attracted much attention due to its unique metabolism and strong adaptability. However, little was known about the divergences along the evolutionary process based on whole genomes. Herein, we isolated six strains of A. ferrooxidans from mining areas in China and Zambia, and used comparative genomics to investigate the intra-species divergences. The results indicated that A. ferrooxidans diverged into three groups from a common ancestor, and the pan-genome is ‘open’. The ancestral reconstruction of A. ferrooxidans indicated that genome sizes experienced a trend of increase in the very earliest days before a decreasing tendency during the evolutionary process, suggesting that both gene gain and gene loss played crucial roles in A. ferrooxidans genome flexibility. Meanwhile, 23 single-copy orthologous groups (OGs) were under positive selection. The differences of rusticyanin (Rus) sequences (the key protein in the iron oxidation pathway) and type IV secretion system (T4SS) composition in the A. ferrooxidans were both related to their group divergences, which contributed to their intraspecific diversity. This study improved our understanding of the divergent evolution and environmental adaptation of A. ferrooxidans at the genome level in extreme conditions, which provided theoretical support for the survival mechanism of living creatures at the extreme

Association between Vitamin D supplementation and mortality in critically ill patients: A systematic review and meta-analysis of randomized clinical trials.

BACKGROUND: Observational studies suggest that low 25-hydroxyvitamin D status is common and has been associated with higher mortality in critically ill patients. This study aim to investigate whether vitamin D supplementation is associated with lower mortality in critically ill patients. METHOD: We searched Medline, Embase, and Cochrane databases from inception to January 12, 2020, without language restrictions, for randomized controlled trials comparing the effect of vitamin D supplementation with placebo in critically ill patients. Two authors independently performed data extraction and assessed study quality. The primary outcome was all-cause mortality at the longest follow-up. RESULT: We identified nine trials with a total of 2066 patients. Vitamin D supplementation was not associated with reduced all-cause mortality at the longest follow-up (RR 0.90, 95% CI 0.74 to 1.09, I2 = 20%), at 30 days (RR 0.81, 95% CI 0.56 to 1.15), at 90 days (RR 1.15, 95% CI 0.92 to 1.44), and at 180 days (RR 0.82, 95% CI 0.65 to 1.03). Results were similar in the sensitivity analysis. The sample size met the optimum size in trial sequential analysis. Similarly, supplemental vitamin D was not associated with length of ICU stay, hospital stay, or mechanical ventilation. CONCLUSION: Vitamin D supplement was not associated with reduced all-cause mortality in critically ill patients. SYSTEMATIC REVIEW REGISTRATION: Open Science Framework https://osf.io/bgsjq