Vapor Separation Research Articles

Experimental Investigation of a Regenerative Kalina Cycle for Electrical Power Generation Using Waste Heat

Kalina cycle is a thermodynamic power cycle uses any waste heat source (low temperature source) to generate electrical power or cooling. Many versions of Kalina cycle exist. In this paper a regenerative Kalina version is designed and constructed. The cycle consists of the following main components: heat recovery vapor generator (HRVG), separator, turbine, condenser, throttling valve, mixer (absorber), heat exchanger and pump. The heat exchanger is used to heat the working fluid coming from the pump before entering the HRVG by the hot saturated liquid (weak solution) coming from the separator. The cycle uses aqua ammonia mixture as the working fluid with different ammonia concentrations. The effect of many operating conditions on cycle performance is studied such as ammonia (NH3) mass fraction (range from 0.85-0.89), low pressure (range from 2-4 bar), and maximum pressure (range from 20-40 bar). The dryness fraction (DF) at separator entrance is kept at 0.3. The results show that the highest thermal efficiency obtained is 12.9% at Pmax=35 bar, Pmin=2 bar, and x=0.85. The highest value of the net power is 0.367 kW at x=0.89 at turbine inlet pressure of Pmax=20 bar. The highest value of exergy efficiency is 28.5% at Pmax=35 bar, Pmin=2 bar. It is noticed that the highest exergy destruction is in the heat recovery vapor generator (HRVG) which is about 48% due to high temperature heat exchange process and low mass flow rate. The exergy destruction is larger at Pmax=35 and x=0.89 than the exergy destruction at Pmax=20 bar and x=0.89.

Enabling simultaneous CO2 and water vapor removal by MOF-801/Pebax mixed matrix membranes: Molecular simulation and experimental study

Dehydration and CO2 removal are two important gas separation processes. An efficient membrane enabling simultaneous reduction of water vapor and CO2 levels from humid gas streams, such as natural gas and power plant flue gas, may advance these processes. In this study, a water-harvesting metal-organic framework, MOF-801, was synthesized with an average particle size of 120 nm, which was then dispersed in a Pebax matrix to fabricate mixed matrix membranes (MMMs). The potential of the MOF-801 as a filler in MMMs was evaluated for water and CO2 separation from CO2/N2 and CO2/CH4 mixed gas streams. Compared with the neat Pebax membrane, 70% enhancement in the water permeability was achieved for an MMM of 20 wt.% MOF loading at 10 bar with a humid feed composition of CO2/CH4. A considerable CO2/N2 separation factor (108) and CO2 permeability (270 Barrer) were also obtained, exceeding the Robeson upper bound at both dry and humid states. A molecular simulation study was performed to reveal the adsorption sites in the MOF lattice and favorable interactions with gases. Interestingly, competition between gas components close to the Zr atom was observed, which is the favorable site for both CO2 and water. Competitive adsorption was found to be the dominating transport mechanism for the selective transport of CO2 and H2O in MOF-801, revealing the role of MOF-801 in MMMs for CO2 and water vapor separation under both humid and dry conditions.

Synthesis of fluorinated ether free aromatic backbone copolymers containing trifluoromethyl and dimethylamino groups for CO2 separation: Investigation of pure and mixed gas performance under dry and humid conditions

A novel series of linear, high molecular weight aromatic copolymers containing trifluoromethyl and dimethylamino groups was synthesized via facile super-acid catalyzed polyhydroxyalkylation and investigated as CO2 gas separation membrane materials. The molar ratio of the two ketone comonomers used in copolymerization, trifluoroacetophenone (TFAp) and N,N-dimethylamino trifluoroacetophenone (dMATFAp), was systematically varied to produce five copolymers with different dMATFAp contents ranging from 12 to 73 %. The influence of dMATFAp content on physicochemical and mechanical properties as well as pure gas and water vapor separation performance was studied. All synthesized copolymers displayed excellent film forming ability, high thermal stability and high Tg values (Tgs > 380 °C). Pure gas permeability measurements revealed that the increase of dMATFAp molar content from 12 % to 34 % resulted in improved gas permeability, while, on the contrary, further increase of dMATFAp content from 34 to 73 % led to substantial gas permeability decrease ascribed to FFV decrease. In particular, among copolymers, the one with dMATFAp content of 34 % presented the highest CO2 permeability value of 290 Barrer due to its highest CO2 diffusion and CO2 solubility coefficients associated with its higher FFV value. The CO2/CH4 performance of synthesized copolymers fell very close to 2008 upper bound limit and exceeded most of the super-acid catalyzed copolymer membranes reported in the literature and commercial membranes. CO2/CH4 and CO2/N2 selectivity values for the different synthesized copolymers were in the range of 29.9–40 and 22.7–44, respectively. The study of the effect of dMΑTFA on water permeability unveiled that the membrane with the highest dMΑTFAp molar content (73 %) showed the highest water permeability value (23,100 Barrer) as well. This was attributed to the increased concentration of N-methyl substituent of dMΑTFAp which can interact with water molecules thereby increasing solubility. Under process gas stream conditions using a mixture of 3 % H2O-48.5 % CO2-48.5 % CH4, both CH4 and CO2 permeability were significantly reduced (by 35 % and 47 %, respectively) due to the preferential sorption of water vapor over other gases present in the mixture, highlighting the negative effect of water vapor on gas permeability. Accordingly, the CO2/CH4 separation factor was slightly increased from 23.8 to 29. Finally, stability test of the copolymer (BP-TFAp)66-(BP-dMATFAp)34 at 40 °C under humid mixed gas conditions showed that CO2 and CH4 permeability remained unchanged for one month after an initial condition stabilization that is required implying that these copolymer structures are promising materials for CO2 separation.

Vapor separation in minichannel heat sink flow boiling application using gradient porous copper ribs

The accumulation of a significant amount of vapor in minichannels severely limits their flow boiling heat transfer performance, posing a challenge for efficient thermal management in high-power electronic devices. To address this issue, we propose an innovative gradient porous copper rib minichannel with a vapor separation function. This design incorporates micro-pore porous copper and open-cell porous copper, where the unique structure of the micro-pore porous copper is crucial for achieving effective vapor separation. This innovative design not only expands the vapor discharge pathways within the minichannel but also significantly enhances the overall efficiency of vapor removal. Using water as the working fluid, flow boiling experiments were conducted across a range of mass fluxes (G = 26.1 kg/(m2s) ∼ 156.9 kg/(m2s)) and heat fluxes (qeff = 38.2 kW/m2 ∼ 267.5 kW/m2). The experimental results demonstrate that vapor separation significantly alleviates backflow and enhances heat transfer performance. Specifically, our findings indicate that the average temperature of the heat transfer surface decreases by 0 to 10 °C, while the maximum heat transfer coefficient increases by 2.3 times compared to conventional designs. This work presents a practical and innovative approach to mitigating vapor accumulation in minichannels, providing valuable insights for the design of high-performance minichannel heat sinks.

Electrospun nanofiber-supported thin-film composite membrane by introducing graphene oxide interlayer for water vapor/N2 separation

In response to the increasing challenge of global water scarcity, the need for alternative water resources has become increasingly critical. Membrane technologies for water vapor separation have emerged as promising approaches for water recovery and reuse. In this study, a polyethersulfone electrospun nanofiber-supported thin-film composite (eTFC) membrane structure with graphene oxide (GO) interlayer, specifically designed for water vapor/N2 separation was introduced. The interlayer was fabricated by controlling the deposition of GO on the electrospun nanofiber substrate. Subsequently, the thin-film was formed through interfacial polymerization using trimesoyl chloride and piperazine as monomers. All the prepared membranes were characterized using analytical techniques. Their water vapor separation performance was evaluated under different water activity conditions and compared to commercial membrane with similar average pore size. The optimized Gi-eTFC (with a GO interlayer of 0.4 mg) exhibited enhanced hydrophilicity, superior water vapor permeance of 3817 GPU, and a relatively high water vapor/N2 selectivity of 115, under conditions of 80 % relative humidity, 1 bar pressure, and a temperature of 30 °C. Gi-eTFC membranes with an optimized GO interlayer showed uniform and successful polyamide active-layer formation, confirming that the introduction of the GO interlayer and the use of nanofibers had a synergistic effect on improving water vapor separation performance.

Deep removal of Sn, Pb, and Sb in refined indium by vacuum distillation

To deeply separate the azeotropic impurities from the refined indium, three novel processes of vacuum distillation by considering the variables of vacuum pressure, loading mass, distillation time, temperature, and the effective vacuum evaporation area are firstly presented. Thermodynamic calculations show that Pb, Sb and Sn can be separated from indium melt by vacuum distillation due to their great difference in saturated vapor pressure and separation coefficient. Experiments show that distillation at 800 ℃ for 7 h under a pressure of 10−3 Pa could achieve the Pb concentration of 0.004 ppm in indium melt by enlarging the evaporation area and small ratio of h1/h4. After 950 ℃ distillation, the concentrations of Sb and Sn in the condensing indium reduced respectively from 0.15 ppm to 0.009 ppm, and 8.1 ppm to 0.05 ppm. Multiple processes of vacuum distillation were used to achieve the 7 N purity of indium, with the removal ratio of over 99.5 %. Besides, it is found out that when the temperature dropped from 1075 ℃ to 780 ℃, the movement stroke of vapor atoms reduced from 509 mm to 209 mm.

Refrigerant charge influence on the performance of a transcritical CO2 system with flash-tank for low-temperature refrigeration

While the use of CO2 as a natural refrigerant become widespread, there is a scarcity of research on refrigerant charge effects in transcritical CO2 refrigeration applications, especially for systems with flash-tank and two-stage compressors. In this work, an experimental investigation of the effect of the Normalized Refrigerant Charge (NRC) on the parameters and performance of a Flash-Tank Vapor Injection (FTVI) CO2 refrigeration system is carried out. Within the explored NRC range of −0.02 to 0.247, an optimal NRC of 0.18 was identified that yields a maximum COP regardless of operating conditions. Results suggest that typical operating parameters such as temperature and pressure are not being affected by the NRC because of the charge buffering function of the flash-tank. However, the liquid–vapor separation capacity of the flash-tank causes a reduction in the refrigeration capacity when the system is not charged properly. This refrigeration capacity detriment related to undercharged conditions becomes more severe under high ambient temperatures, with a maximum COP penalty of 20 % when comparing the lowest charge versus the optimal charge performances at a gas cooler outlet temperature of 40 °C.

Vaporization in Liquid-Core Nuclear Thermal Rockets

This work provides an overview of vaporization phenomena in liquid-core nuclear thermal rockets to aid in unifying modeling assumptions by characterizing the impact of vaporization. Historical variations in vapor modeling have led to reported specific impulses ranging from 1000 to 2000s following model refinements in the 1960s and the omission of vaporization consideration post 1990. The only preexisting vapor transport study to not rely on the Reynold’s analogy was performed for the radiator design. This paper performs the first such analysis for the bubbler design, given its renewed interest. Consideration is given to potential centrifugal species separation, proposed fuel mixtures, interplay between chamber pressure and vaporization, impacts on propellant thermoproperties, evaporative cooling, power requirements for vapor separation, and the complexity of hydrocarbon interactions under the proposed chamber conditions. The bubbler design is shown to be well approximated as fully saturated, whereas the radiator and droplet designs may be configured to reduce vaporization to 20% saturation. Characterization of vaporization within liquid cores is essential to early design decisions, such as overall archetype, defining the operating point, and liquid media composition. For a threshold temperature corresponding to around 10% of the propellant being vapor by mass, further increases in temperature begin reducing the specific impulse. Below this threshold temperature, the impact of vaporization on thermal modeling with the chamber is likely negligible. Above this threshold temperature, higher-fidelity thermal modeling will be required, and the work required to separate the vapor begins exceeding 100 kW/(kgH/s). Nozzle kinetics are applied to liquid cores for the first time, showing that specific impulses increase with increasing chamber pressure contrary to historical findings. Historically, modeled uranium-zirconium-carbon mixtures are predicted to reach a specific impulse up to 1260 s. A uranium-tungsten-carbon fuel mixture yielded the best theoretical specific impulse of slightly under 1400 s; however, no nucleonic or thermal analysis has been conducted with this fuel composition.

The impacts of structural parameters on performance and energy loss of the supersonic separator: A sensitivity analysis

The supersonic separator uses pressure energy to achieve highly efficient carbon capture and water vapor separation from the natural gas mixture. Structural parameters are crucial in determining both separation performance and pressure energy loss of the supersonic separator. However, a comprehensive understanding of how them influence flow behaviors and performance is hindered by their coupling effects and the limitations of numerical methods. This study introduces Euler-Lagrange-Euler model to predict separation performance and pressure energy loss of supersonic dehydration process with varying structural parameters. The results show that the expansion ratio of the divergent section, length of the convergent section, inlet radius of the inner body, and throat radius of the inner body significantly impact separation performance and pressure energy loss. Especially the first parameter, the swirl strength and centrifugal acceleration decay to 0.044 and 2.41 × 104 m s−2 as it increases. At the same time, the droplet removal rate significantly improves, but the separation performance does not increase indefinitely due to the shock waves. The dehydration efficiency first increases to 95.09 % at Er= 1.5 and then decreases; the dew point depression also expands to 25.28 K and then drops, and the corresponding pressure loss rises to 0.47 and then falls.

Efficient separation and recovery of neodymium through volatilization in the recycling process of spent Nd-Fe-B magnets

Metal Pb can be used to selectively extract Nd from Nd-Fe-B magnet scraps. However, the separation of Nd from the recycled Pb–Nd alloys has become a new problem. In this work, the separation of Pb from the Pb–Nd alloys by vacuum distillation was investigated. The thermodynamic analysis based on the saturation vapor pressure and separation coefficient indicates that the component Pb is able to be separated from the Pb–Nd alloys by vacuum distillation. The effects of the distillation temperature and duration on the volatilization separation of Pb from the Pb–Nd alloy have been clarified, and the dynamic mechanism of the distillation separation was analyzed. The results show that the increase in the distillation temperature and duration can facilitate the separation between the components Pb and Nd in the Pb–Nd alloys. When the Pb-30 wt%Nd alloy was distilled at 1573 K and 0.1–5 Pa for 210 min, the removal rate of the Pb can reach more than 99.99 %, and the Nd content of the distillation residue was determined to be more than 99.41 wt%. This work provides a new and clean route for the separation and recycling of the rare earth metal Nd in the recycling process of spent Nd-Fe-B magnets.

Time-Resolved Ion Mobility Spectrometry with a Stop Flow Confined Volume Reaction Region.

An ion source concept is described where the sample flow is stopped in a confined volume of an ion mobility spectrometer creating time-dependent patterns of ion patterns of signal intensities for ions from mixtures of volatile organic compounds and improved signal-to-noise rate compared to conventional unidirectional drift gas flow. Hydrated protons from a corona discharge were introduced continuously into the confined volume with the sample in air at ambient pressure, and product ions were extracted continuously using an electric field for subsequent mobility analysis. Ion signal intensities for protonated monomers and proton bound dimers were measured and computationally extracted using mobilities from mobility spectra and exhibited distinct times of appearance over 30 s or more after sample injection. Models, and experimental findings with a ternary mixture, suggest that the separation of vapors as ions over time was consistent with differences in the reaction rate for reactions between primary ions from hydrated protons and constituents and from cross-reactions that follow the initial step of ionization. The findings suggest that the concept of stopped flow, introduced here for the first time, may provide a method for the temporal separation of atmospheric pressure ions. This separation relies on ion kinetics and does not require chromatographic technology.

Investigation of a flexible triple-evaporator domestic refrigerator/freezer with R600a with integrated economization

Domestic refrigerator/freezers account for approximately 6 % of all energy consumption around the globe and mainly rely on vapor compression cycles to operate. Researchers have investigated alternative cycle architectures such as dual-loop cycles and parallel circuit cycles to improve their efficiencies. Despite the demonstrated energy saving potential of these advanced cycles, additional implementation costs are often not justifiable. However, to meet forthcoming stricter energy standards while ensuring flexible multi-temperature operation of domestic refrigerator/freezers, advanced cycle architectures are needed. In this paper, a state-of-the-art bypass circuit cycle triple-evaporator domestic refrigerator freezer with R-600a and a reciprocating compressor has been used as the baseline cycle investigate an alternative cycle configuration. Specifically, this work presents a two-stage vapor-injected cycle with a multi-evaporator system to enable energy savings and cost-effectiveness. The cycle establishes two separate evaporation temperatures to better match the cabinet temperature of fresh food and freezer compartment. The reduced difference between cabinet temperature and its evaporation temperature decreases the irreversibilities in the heat exchanger and improves overall system efficiency. Moreover, the addition of the economization line from the medium temperature evaporator reduces the compressor work. To capture the complex transient behavior of both the baseline system and proposed cycle architecture with their control strategies, a dynamic model has been developed and validated with experimental data. The validated dynamic model with the baseline cycle was modified to consider the two-stage vapor-injected cycle and its control logic, and simulation results yielded up to 13 % energy consumption reduction with respect to the baseline system.

An experimental study of dynamic flashing in a square tube using tap water

Flashing is a pressure driven phase change phenomenon. It is widely studied due to its richness in physics and applications such as in desalination, in nuclear industry to name a few. Dynamic flashing is a situation wherein the pressure drop for flashing is initiated through the flow of liquid. A recently developed novel desalination system [1] utilizes combined dynamic flashing and vapor separation through tangential injection for producing potable water. An understanding of dynamic flashing in a tube with reference to the novel desalination system could help with its optimization. In this work, dynamic flashing of tap water occurring in a clear quartz square tube was studied. The pressure and temperature measurements along the tube were made and analyzed for different inlet flowrates and initial liquid temperatures. The pressure and temperature values showed increasing gradients along the tube indicating increased vapor production or flashing for increasing flowrates and initial liquid temperatures. The vapor production from flashing and the resulting flow regimes along the tube were tracked and identified through high-speed imaging. Visual observations showed complex flow regimes with bubbles nucleating and growing throughout the tube due to flashing. Most of the bubble formation was observed in the bulk with little nucleation on the glass tube wall. Void fraction measurements along the tube based on capacitance impedance technique were performed to supplement the visual observations which showed increasing void fraction along the tube matching the observed flow regimes from vapor production.

Pore-filled composite membranes for water vapor separation: Bench-scale advancements and semi-empirical modeling

Efficient scale-up processes of gas separation membranes require a thorough assessment of performance across various parameters. Semi-empirical modeling based on theory and empirical data is an attractive approach to predict the required performance. Despite numerous studies on the performance of gas separation membranes depending on internal parameters such as morphology and geometry, relatively few studies on performance dependent on external parameters have been reported. In this study, we propose semi-empirical modeling for the performance of membranes as a function of external parameters using a bench-scale pore-filled composite membranes for water vapor separation. As external parameters, we selected temperature, pressure, relative humidity (RH), and feed flow rate. These parameters influence water vapor permeance, water flux, and RH reduction, which are theoretical indicators of the performance of water vapor separation membranes. A power regression analysis was used to find the power of individual parameters (Y = Coefficient (k) ∙ Xpower), and a multiple linear regression analysis (finite power law model, Y = k ∙ X1α ∙ X2β…) was used to develop a semi-empirical model with the correlations of these parameters. The modeling values closely coincided with measured values, suggesting the effectiveness of the proposed modeling. This method is expected to simplify the prediction of membrane performance, offering valuable insights for potential scale-up processes.

Experimental study of the effect of dedicated mechanical subcooling on the performance of a single multiparallel evaporator

In systems with a single machine and multiple parallel evaporators, issues such as uneven liquid–vapor phase refrigerant separation and low efficiency are prevalent. This study investigates the impact of distributor inlet conditions on liquid–vapor separation uniformity and proposes improving separation performance and system efficiency by adjusting the working fluid's dryness through subcooling. It introduces the use of a rectifying nozzle-type distributor (RD) instead of a centrifugal distributor (CD) and presents experimental studies on multiple parallel evaporators. A test setup featuring multiple parallel evaporators with mechanical subcooling unit was developed to investigate the subcooling degree's impact on various aspects: superheat unevenness across branches, refrigeration capacity disparity among cold storages, cooling rates, distributor pressure drop, and overall system energy efficiency. Findings indicate significant improvements with RD; at a 16 °C subcooling degree, superheat unevenness and refrigeration capacity unevenness decreased by 30.6 % and 23.0 % respectively, while cooling rates increased by 27.3 %. At a 26 °C subcooling degree, system energy efficiency improved by 15.4 %. Compared under identical conditions, the RD system outperformed the CD system. This research contributes to a better understanding of optimizing multiple parallel evaporator performance through subcooling degree adjustments and can be applied to multi-cold room cold storage systems.

Energetic Potential of Parallel Operation of Two Heat Sources in a Dual-Source Heat Pump

Dual-source heat pumps can mitigate disadvantages of single source heat pumps: They have fewer geological requirements compared to ground-source heat pumps while having higher efficiencies compared to air-source heat pumps. Parallel operation of two heat sources can also make electric heaters for peak loads obsolete, leading to economic benefits in the operational costs. Parallel operation has not been analysed thoroughly at different evaporation temperature gradients. To address this gap in research, four possible interconnections of two heat sources were analysed using a refrigerant cycle simulation, two with similar and two with separate evaporation pressures. The energetic potential of each interconnection is evaluated and compared to single source operation with an air-source and a ground-source heat pump. The results showed that only the interconnections with separate evaporation pressure allowed significant reduction in evaporation power from the ground source. As expected, the efficiency – compared to single air-source operation – increased for all parallel interconnections but decreased compared to ground-source operation. Efficient peak load coverage with small ground-source collectors therefore requires a more complex interconnection of completely split evaporator branches at different evaporation pressures. While the efficiency and heating power compared to single ground-source operation decreased slightly (by 4% and 6%, respectively), the power load on the GSHX and ASHX reduced to about 54% and 66% compared to the corresponding single-source operation, respectively. This allows high efficiency at reduced GSHX size and ASHX noise emission. Additionally, this interconnection also allows increased flexibility for improved heat source management.

Performance improvement analysis of the regenerative dual-pressure organic flash cycle assisted by ejectors

We proposed a dual-ejector-based regenerative dual–pressure organic flash cycle (DEj–RDPOFC) with higher performance than the RDPOFC. The effects of high and low pressures and the entrainment ratio of the ejector on the DEj–RDPOFC performance were analyzed from the viewpoints of thermodynamics and thermoeconomics. An exergy-flow distribution diagram revealed why the DEj–RDPOFC outperformed the RDPOFC. Next, the performances of the DEj–RDPOFC and dual–pressure organic Rankine cycle (DORC) were compared under the same boundary conditions. Finally, the performance of the DEj–RDPOFC was optimized using the nondominated sorting genetic algorithm (NSGA-II). According to the results, the power output of the high-pressure (HP) turbine of the DEj–RDPOFC can be increased by replacing the HP throttling valve (TV) with an ejector (which increases the working fluid dryness of the HP vapor separator and the mass flow rate of the HP turbine) and the low-pressure (LP) TV with an ejector (which increases the HP turbine expansion ratio). The DEj–RDPOFC achieves a higher maximum net power output (Wnet) and a lower corresponding levelized cost of electricity (LCOE) than the DORC. Under the optimum condition, the Wnet and LCOE of the DEj–RDPOFC are 9.71 % higher and 6.59 % lower, respectively, than those of the RDPOFC.

Novel method for recovering valuable metals from Sn ash: Vacuum carbothermal reduction-directional condensation

Sn ash recycling is an industry with positive development prospects, as it provides better-protected resources, promotes sustainable development, and lays a solid foundation for future development. In this study, an innovative vacuum carbothermal reduction-directional condensation process was developed. The thermodynamic analysis results indicated that the initial reaction pressure and temperature for the carbothermal reduction of the system was 1–10 Pa and 998–1063 K, respectively. The saturation vapor pressure, separation coefficient, and condensation temperature of Sn, Pb, and Zn in the reduced products differed significantly, and their separation could be achieved by controlling the volatilization and condensation temperatures. A single-factor experiment investigated the effects of carbon ratio, temperature, and time on the reduction efficiency, direct yield, and recovery rate. The optimal experimental conditions were the ratio of MeO to C of 4:1, temperature of 1373 K, and time of 120 min. Sn, Pb, and Zn products were obtained at different positions. This process shortens the traditional process, reduces the reduction cost of Sn, and enables the implementation of the process, making it environmentally friendly.

Dinuclear Copper Sulfate-Based Square Lattice Topology Network with High Alkyne Selectivity.

Porous coordination networks (PCNs) sustained by inorganic anions that serve as linker ligands can offer high selectivity toward specific gases or vapors in gas mixtures. Such inorganic anions are best exemplified by electron-rich fluorinated anions, e.g., SiF62-, TiF62-, and NbOF52-, although sulfate anions have recently been highlighted as inexpensive and earth-friendly alternatives. Herein, we report the use of a rare copper sulfate dimer molecular building block to generate two square lattice, sql, coordination networks which can be prepared via solvent layering or slurrying, CuSO4(1,4-bib)1.5, 1, (1,4-bib = 1,4-bisimidazole benzene) and CuSO4(1,4-bin)1.5, 2, (1,4-bin = 1,4-bisimidazole naphthalene). Variable-temperature SCXRD and PXRD experiments revealed that both sql networks underwent reversible structural transformations due to linker rotations or internetwork displacements. Gas sorption studies conducted upon the narrow-pore phase of CuSO4(1,4-bin)1.5, 2np, found a high calculated 1:99 selectivity for C2H2 over C2H4 (33.01) and CO2 (15.18), as well as strong breakthrough performance. Across-the-board, C3H4 selectivity vs C3H6, CO2, and C3H8 was also observed. Sulfate-based PCNs, although still understudied, appear increasingly likely to offer utility in gas and vapor separations.

Identifying the source and fate of boron in geothermal water: Evidence from B/Na and B isotopes

High level dissolved B, which poses risks to human health, has been widely observed in geothermal water. In the Guide Basin, NW China, a series of geothermal water samples along a fault show a wide range of B contents ranging from 3.14 to 8.33 mg/L, which are higher than the WHO Guideline value equaling 2.4 mg/L in drinking water. To identify the sources and fate of B, we conduct a comprehensive analysis of hydrochemistry and stable isotopes (D, 18O and 11B) of three thermal fields representing three stages of hydrogeochemical evolution (stages I, II and III). From stage I to III, there are trends of increasing mineral dissolution, which is supported by increasing mean reservoir temperature and concentrations of conservative elements (Cl, Na, K, Li and Si). Geothermal water in stage I with meteoric origin and the lowest reservoir temperature has the highest B/Na resulting from silicate dissolution and falls on the mixing line between granitoids and cold water on the plot of δ11B versus 1/B, showing the control of silicate dissolution. However, geothermal water in stage III has lower Ca, B Sr and B/Na than that in stage II. Because of the occurrence of other processes, geothermal water in stages II and III deviates from the LMWL. Compared with geothermal water in stage I, the increased Sr/Ca and decreased B/Ca show that B are removed by both coprecipitation and vapor separation. With the aid of B isotopes, we find vapor separation dominates in stage II, whereas carbonate precipitation dominates in stage III. Overall, a combined use of three isotopes (H, O and B) and three element ratios (B/Na, B/Ca and Sr/Ca) leads to a complete understanding of B cycle and hydrogeochemical evolution in hydrothermal systems.