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[Display omitted] • A novel biphasic solvent with a high CO 2 loading in the solid phase was developed for CCUS. • The formation of H-bonding between EG and BDA was confirmed. • Particle self-aggregation induces the liquid – solid phase transition. • The interaction between the absorbed products was elucidated by ESP and IGMH analysis. • The phase-change mechanism of CO 2 absorption into BDA/EG system was elucidated. Liquid-solid phase change absorption has been considered a promising strategy for CO 2 capture. To achieve efficient and economic CO 2 capture in industrial-scale applications, it is essential to understand the phase-change behaviors and mechanisms of the biphasic system. In this study, a blend of 1, 4-Butanediamine (BDA) and ethylene glycol (EG) was developed as a biphasic solvent that can form a high CO 2 loading solid phase product (BESP) after absorption. The total solvent loading reached 0.9039 mol·mol−1, with 90.74% of the loading enriched in the solid phase, which only accounts for 51.01% of the total solvent mass. Based on the 13C NMR analysis and quantum chemical calculations, the reaction and phase change mechanism of CO 2 capture was proposed. The BDA/EG system absorbs CO 2 to generate carbamate species, protonated amines and alkyl-carbonates, which combine each other through hydrogen bonding or electrostatic attraction. The self-aggregation of zwitterions and the high polarity of the absorption products are considered to be the main reasons for the phase change. Alkyl-carbonate species are believed to co-precipitate through organic gelation via van der Waals force with the carbamate or protonated amine. Moreover, the viscosity, turbidity, solid-phase mass, and particle size distribution changes also demonstrate the growth and aggregation of particles during absorption. BESP, identified as a coupling product of carbamate and alkyl-carbonate ( [2BDAH + COO - ] · [EG‐OCO 2 - ]), decomposes at a peak temperature of 127.4 °C. The calorimetric method determined regeneration heat to be approximately 3.17 GJ·ton-1 CO 2 , indicating its potential for alternative uses rather than direct heat regeneration. Such a biphasic solvent may provide unique solutions for industries to reduce CO 2 emissions. [ABSTRACT FROM AUTHOR]

• Nitrogen rejection from methane was achieved with a kinetic DR PSA process. • A non-isothermal numerical model was shown capable of simulating kinetic DR PSA cycles. • A feed with 75% CH 4 + 25% N 2 was separated to achieve 90% CH 4 purity and 90% recovery. • Simulations provide insight into the separation mechanism of a kinetically N 2 selective adsorbent. Dual-reflux pressure swing adsorption (DR PSA) processes using a kinetically nitrogen selective molecular sieve carbon, MSC-3K 172, were investigated for the removal of nitrogen from a gas mixture consisting of 75 mol% CH 4 + 25 mol% N 2. The four DR PSA configurations (PL-A, PH-A, PL-B and PH-B) were experimentally demonstrated and compared in terms of their nitrogen rejection and methane recovery performance. The experimental results indicated the PH-B configuration in general performed the best in terms of the methane product purity and recovery using the kinetic MSC-3K 172 adsorbent. A non-isothermal numerical model was constructed for the kinetic DR PSA process to simulate and optimise the performance of the PH-B configuration. Model predicted gas loadings on the adsorbent indicated that selectively removing nitrogen from methane was feasible when a feed step time close to the characteristic adsorption time of nitrogen was selected. The effective usage of the adsorption bed in the PH-B configuration was also numerically studied via the capacity ratio C , with the feed step time and light reflux flow as key operational parameters, at fixed heavy product-to-feed ratio, bed pressure ratio and feed location. The numerical model for the PH-B configuration was also employed to study the effect of pressure in the purge step beyond those conditions accessible in the experiment. The simulation results revealed that the PH-B configuration could achieve a separation performance of 90 mol% CH 4 in the light product with 90% CH 4 recovery when the pressure in the light purge column was lower than 40 kPa while the adsorption pressure was maintained at 500 kPa. This result opens new opportunities for efficiently upgrading sub-quality natural gas reserves. [ABSTRACT FROM AUTHOR]

Reliable adsorption equilibrium data and theoretical models for their accurate representation are crucial to the design of any adsorption based separation. The adsorption equilibria of carbon dioxide, methane and nitrogen are particularly important to the development of industrial pressure swing adsorption processes intended to separate CO2 and N2 from a variety of conventional as well as unconventional natural gas sources. The adsorption equilibrium capacities of gas mixtures needed for process design and simulation are often predicted from pure component adsorption data using various models including the ideal adsorbed solution theory (IAST). In this work, we present the adsorption equilibrium capacity data for a ternary gas mixture of CO2, CH4 and N2 as well as pure and binary gas mixtures of the same components on a commercial zeolite 13X, measured at temperatures of (273, 303 and 333 K) and pressures from (25 to 900 kPa) using a dynamic column breakthrough (DCB) apparatus. Although previous adsorption studies have reported the adsorption equilibria of pure and to a lesser degree binary gas mixtures on zeolite 13X, no experimental data are available in the literature for a ternary gas mixture of CO2, CH4 and N2 on zeolite 13X APG-III, a promising adsorbent for carbon capture and natural gas separation. The measured pure component adsorption capacities were regressed to a Toth isotherm model and the obtained Toth parameters were used to implement an IAST model for binary and ternary adsorption predictions. The IAST predictions of mixture gas adsorption represented the binary and ternary adsorption equilibria well with their corresponding maximum deviations being 0.055 and 0.3 mmol/g, respectively. This indicates the IAST can be applied successfully to these adsorption systems even though they involve molecules with different adsorption affinity and adsorbents with heterogeneous surfaces. [ABSTRACT FROM AUTHOR]

An advanced non-isothermal dynamic model for the simulation of Dual Reflux Pressure Swing Adsorption (DR-PSA) cycles was constructed using Aspen Adsorption ® . A new column pressure control method was developed to describe cycles that either continuously change pressure during the feed/purge steps or are held at constant pressure during these steps. This control method uses a dual convergence algorithm to adjust both the inlet volumetric flow of the compressor and the light product flow rate to achieve the desired pressure profile in the simulation. In addition, a choked flow valve after the compressor was employed to enable a high-fidelity simulation of the flows during the pressure reversal step in contrast to previous simulation approaches. To validate the model, predictions were benchmarked against the most detailed two sets experimental DR-PSA data available in the literature, which involved the separation of C 2 H 6 + N 2 mixtures where bed pressures changed continuously during the feed/purge steps and the separation of CH 4 + N 2 mixtures where bed pressures were constant during these steps. At cyclic steady state, the standard deviations of the model’s predictions from the experimental data involving C 2 H 6 + N 2 mixtures separations were 0.003 mol fraction in a rich product stream with an average ethane composition of 0.63 mol fraction; and for the separation of CH 4 + N 2 mixtures, the standard deviation of the predicted product mole fractions from the experimental values were 0.002 and 0.040 for the N 2 in the light (N 2 -rich) product and CH 4 in the heavy (CH 4 -rich) product streams, respectively. [ABSTRACT FROM AUTHOR]

Adsorption equilibria and kinetics of N and CH on four adsorbents, namely commercial activated carbon Norit RB3, zeolite 13X, zeolite 4A and molecular sieving carbon MSC-3K 172, were measured at temperatures of (273 and 303) K in the pressure range of (25-900) kPa using an improved dynamic breakthrough apparatus. Equilibrium adsorption measurements were performed with breakthrough experiments, and sorption kinetics were measured with a chromatographic pulse technique to eliminate undesirable systematics such as buoyancy and limitations imposed by heat transfer in conventional breakthrough techniques. The differential equations governing the spreading of a pulse passing through the column were solved in the Laplace domain to reduce numerical dispersion and artefacts associated with solving these equations for adsorption in the time domain on a finite grid. A method for identifying the reliable measurement range of sorption rates (mass transfer coefficients) from 10 to 1 s was proposed and demonstrated with the four adsorbents. The sorption rates for Norit RB3 and zeolite 13X had values above the upper resolvable limit of 1 s. The measured sorption rates for MSC-3K 172 and zeolite 4A were compared with values obtained independently using a static volumetric method on the same adsorbents at the same temperatures but over a lower pressure range (0-110 kPa) (Xiao et al., Adsorption 23 (2017) 131-147). The sorption rates obtained for the two adsorbents via these two independent techniques were consistent within the measurement uncertainty of each method, which significantly increases the confidence with which these values can be used in simulations of industrial PSA processes. [ABSTRACT FROM AUTHOR]

Adsorption equilibria and kinetics are two sets of properties crucial to the design and simulation of adsorption based gas separation processes. The adsorption equilibria and kinetics of N and CH on commercial activated carbon Norit RB3, zeolite 13X, zeolite 4A and molecular sieving carbon MSC-3K 172 were studied experimentally at temperatures of (273 and 303) K in the pressure range of (5-120) kPa. These measurements were in part motivated by the lack of consistent adsorption kinetic data available in the literature for these systems, which forces the use of empirical estimates with large uncertainties in process designs. The adsorption measurements were carried out on a commercial volumetric apparatus. To obtain reliable kinetic data, the apparatus was operated in its rate of adsorption mode with calibration experiments conducted using helium to correct for the impact of gas expansion on the observed uptake dynamics. Analysis of the corrected rate of adsorption data for N and CH using the non-isothermal Fickian diffusion (FD) model was also found to be essential; the FD model was able to describe the dynamic uptake observed to better that 1% in all cases, while the more commonly applied isothermal linear driving force model was found to have a relative root mean square deviation of around 10%. The measured sorption kinetics had no dependence on gas pressure but their temperature dependence was consistent with an Arrhenius-type relation. The effective sorption rates extracted using the FD model were able to resolve inconsistencies in the literature for similar measurements. [ABSTRACT FROM AUTHOR]

• Non-cryogenic helium recovery and purification by DR PSA cascade. • Self-contained system that is flexible for integration to existing facilities. • Helium upgrade from 0.1 mol% in natural gas to > 99 mol% purity product demonstrated. • Recovery up to 8% higher than other processes with dilute helium feeds. Low-cost helium recovery processes optimised for unconventional sources e.g. small-scale natural gas (NG) reservoirs, offer a new approach to meeting growing demand. We investigated a two-stage dual reflux pressure swing adsorption (DR PSA) cascade for the recovery and purification of dilute helium from various natural gas source analogues comprising of CH 4 + N 2 + He. First, adsorption isotherms of a binderless zeolite 13X with high methane and nitrogen uptake were measured at 283 to 323 K and pressures up to 10 bar. This material was then used in a laboratory-scale DR PSA apparatus to identify key parameters affecting the separation performance, namely feed step time and location, as well as heavy product and light reflux flow rate. The experiments agreed well with the results of a non-isothermal numerical DR PSA model with an average deviation of 1 mol% between simulated and experimental product purities. Then, the model was extended to consider a two-stage DR PSA cascade with waste recycle. Axial composition profiles within the beds of each stage were obtained numerically and analysed to explain the impact of key process parameters on the separation performance. Tuning these parameters accordingly led to a helium-rich product with over 99 mol% He purity, which could be produced from various natural gas feeds containing from 0.1 to 1 mol% He at 90 to 98% recovery, respectively. The separation performance was compared to other helium recovery processes based on cryogenic distillation, membranes, pressure swing adsorption, and combinations thereof. Compared to these other systems, the DR PSA cascade process delivered a 99 mol% purity product from a 0.1 mol% helium in natural gas feed with 8% higher helium recovery. [ABSTRACT FROM AUTHOR]

• Non-cryogenic helium recovery and purification by DR PSA. • Self-contained system flexible for integration to existing facilities. • Enriching helium from 1 mol% He + 99 mol% N 2 mixture to > 99.999 mol% He. • Helium recovery comparable to cryogenic process with room for further improvement. Global demand for helium has risen over the past few decades driven by a vast range of applications based on its unique properties. Helium is often produced industrially from the vent streams of nitrogen rejection units (NRU) in liquefied natural gas (LNG) plants, where it accumulates because of its low boiling point. Further deep cryogenic processing stages are then required to upgrade its concentration to saleable levels. We report here an experimental and simulation-based investigation of an alternative, non-cryogenic process based on dual reflux pressure swing adsorption (DR PSA) cycles to recover and purify helium from model binaries including a 1 mol% He + 99 mol% N 2 mixture representative of NRU vent streams. Binderfree zeolite 13X was used as the adsorbent in an experimental campaign employing a laboratory-scale DR PSA apparatus. The experimental runs validated a non-isothermal numerical model with an average deviation of 1 mol% between the simulated and experimental product compositions. The single-stage DR PSA experiments produced helium product streams with purities ranging from (30 to 99) mol% from feeds with concentrations ranging from (1 to 50) mol% He. Two DR PSA stages were required to upgrade mixtures containing 1 mol% He to a target product purity of > 99 mol%. A cascade arrangement of two DR PSA systems with a waste recycle enabled a 99.999 mol% He purity product at 95 % recovery, which is competitive with conventional cryogenic systems. This cascade DR PSA process used either two or three compressors depending on the feed gas pressure, with associated duty costs of 1.5 MJ∙(mol He produced)–1. This is lower than several membrane processes described in the literature and could be more cost-effective for smaller-scale applications than cryogenic processes with similar levels of separation performance. [ABSTRACT FROM AUTHOR]

• Sub-quality natural gas was upgraded to pipeline specification by DR PSA. • Minimal greenhouse gas emissions with 99 % CH 4 recovery for sub-quality natural gas. • General trends of the process performance for different adsorption cycles presented. The upgrading of a model sub-quality natural gas mixture containing 40 mol% CH 4 and 60 mol% N 2 by dual reflux-pressure swing adsorption (DR PSA) was studied numerically. A separation target of >93 mol% CH 4 in the heavy product and <1 mol% CH 4 in the light product was adopted for the purpose of evaluating the viability of the upgrading process. Two different CH 4 -selective adsorbents were considered: (i) a commercial activated carbon (AC1) and (ii) a novel ionic liquidic zeolite (ILZ), which has twice the selectivity of activated carbon. Key process parameters such as the heavy product to feed ratio, the feed step time, and the light reflux ratio were varied iteratively to maximize the separation performance and minimize the energy consumption in each of the four DR PSA cycle configurations (PL-A, PH-A, PL-B and PH-B). The simulation results showed that the separation performance of A cycles was superior to that of B cycles for both of the adsorbents studied. The ILZ adsorbent was able to achieve the separation target and in general performed substantially better under the conditions investigated than AC1, which did not meet the product specifications for any of the cycles tested. The best-performing DR PSA cycle (PL-A) with ILZ achieved 94 mol% CH 4 in the heavy product and 1 mol% CH 4 in the light product with a compressor duty of 19.1 kJ mol−1. The corresponding cycle with AC1 as the adsorbent only delivered 87 mol% CH 4 in the heavy product and 6.1 mol% CH 4 in the light product. This result shows that a DR PSA process using ILZ can effectively upgrade sub-quality natural gas while keeping associated methane emissions low. [ABSTRACT FROM AUTHOR]

• Nitrogen rejection from natural gas by DR PSA was numerically studied. • The separation performance of two different adsorbents were compared and optimized. • An 85% CH 4 + 15% N 2 feed was upgraded to 93% CH 4 with 99% CH 4 recovery. • The energy requirements were estimated using a polytropic compression model. The separation of a natural gas mixture containing 85 mol% CH 4 and 15 mol% N 2 by dual reflux pressure swing adsorption (DR PSA) was investigated using dynamic non-isothermal numerical simulations previously benchmarked against experiments. Two different adsorbents were employed: a commercially available activated carbon (AC1) and the recently developed ionic liquidic zeolite (ILZ), which has about twice the selectivity for methane over nitrogen than the activated carbon. Four DR PSA cycle configurations (PL-A, PH-A, PL-B and PH-B) were studied and iteratively optimized in terms of separation performance and energy consumption. The dynamic non-isothermal simulations, implemented in the software platform Aspen Adsorption, included a polytropic compressor model with temperature dependent heat capacities for more realistic predictions of the compressor duty. The heavy product to feed ratio, the feed step time and the light reflux ratio were selected as key optimization parameters for all four cycles at fixed bed pressure ratio, feed location and feed flow rate. The simulations showed that A-cycles were superior to B-cycles in terms of their separation performance for both adsorbent materials. Overall, the separation performance achieved by AC1 was lower than that by ILZ. At optimized conditions for AC1, PL-A and PH-A cycles achieved approximately 92 mol% CH 4 in the heavy product and 4.5 mol% CH 4 in the light product with corresponding energy requirement at 9.9 kJ mol−1 (feed) and 8.7 kJ mol−1 (feed), while using the ILZ adsorbent, both PL-A and PH-A cycles were able to deliver 0.9 mol% CH 4 in the light product and 93.5 mol% CH 4 in the heavy product. The cycle work of the PL-A and PH-A configuration using ILZ was 8.8 and 7.7 kJ mol−1 (feed), respectively. These simulation results show that DR PSA processes using ionic liquidic zeolites can meet strict natural gas separation requirements and that such processes can efficiently upgrade sub-quality natural gas. [ABSTRACT FROM AUTHOR]

Pollution during rapid industrialization process is a serious environmental problem that seriously affects people's lives and livelihoods. Among them, the pollution of excessive heavy metals in wastewater has attracted wide attention. The current study proposes a novel effective and low-cost silica@polyacrylamide composites (SP-C) to capture cadmium ion (Cd2+) from wastewater contaminated by heavy metal. The chemical and physical properties of the surface and interior of silica@polyacrylamide composites were studied by different characterization methods. The adsorption capacity and kinetics of cadmium ions in aqueous solutions using silica@polyacrylamide composites were also studied, and some discussions about the mechanism of adsorption process were made. Silica@polyacrylamide composites showed enhanced cadmium ions adsorption with the maximum adsorption capacity of 211.86 mg/g (pH 6.5, T = 318.15 K), which was fitted by Langmuir model. The adsorption experimental kinetic data of silica@polyacrylamide composites could be excellently verified by pseudo-second-order model. Moreover, a comparison of the cost between the proposed silica@polyacrylamide composites and other reported adsorbents is provided. And the results indicate that the silica@polyacrylamide composites adsorption cost is 0.16 $/g cadmium ion, which means a promising cost-effective adsorbent for cadmium ion removing. [ABSTRACT FROM AUTHOR]

In this study, a non-invasive and environment-friendly acoustic emission (AE) technique, coupled with multiple analysis methods, was proposed to monitor the critical variation of separation efficiency of a cyclone separator by means of the gas-solid hydrodynamics. Acoustic energy analysis was used to reflect the characteristics of particle motion and particle-wall interaction. Shannon entropy analysis was adopted to reflect chaos and complexity of gas-solid two-phase motion. Multi-scale analysis (Hurst analysis and wavelet analysis) was used to obtain multi-scale characteristics inside the cyclone separator. To be specific, micro-scale collision behaviors of particle-particle and particle-wall, meso-scale interaction behavior between particle clusters and gas phase, and macro-scale interaction behavior (overall flow behavior). Furthermore, by comparison with the results of separation efficiency and pressure drop, the above-mentioned three methods based on AE technique can effectively reflect the critical variation of separation efficiency for cyclone separator. Unlabelled Image • Monitoring hydrodynamics of cyclone separator via acoustic emission technique. • Obtaining critical superficial gas velocity via three signal analysis methods. • Indicating critical separation efficiency via three signal analysis methods. • Critical values from AE technique coincide with from traditional techniques. [ABSTRACT FROM AUTHOR]

A critical requirement of a widely contemplated hydrogen economy is the development of a low carbon hydrogen supply chain that is cost competitive. This comprehensive techno-economic assessment demonstrates, for the first time, the viability of a complete hydrogen supply chain based on the transport of liquefied natural gas (LNG). This is demonstrated via the established LNG trade route from Australia to Japan against three key performance indicators (KPIs): delivered hydrogen cost, CO 2 emissions intensity (EI) across the entire supply chain, and technology readiness level (TRL). The hydrogen supply chain entails LNG export to Japan where it is used for blue hydrogen production; the by-product CO 2 is then liquefied and repatriated to Australia for sequestration or utilisation. Within this supply chain, various hydrogen production technologies are assessed, including steam methane reforming (SMR), autothermal reforming (ATR) and natural gas pyrolysis (NGP). SMR with carbon capture and storage (CCS) resulted in the lowest total hydrogen supply cost of 19 USD/GJ (2.3 USD/kgH2) which comfortably meets the 2030 Japanese hydrogen cost target of 25 USD/GJ (3 USD/kgH2) and is very close to the 17 USD/GJ 2050 Japanese hydrogen cost target. This technology also obtained the lowest CO 2 emission intensity (EI) of 38 kgCO2/GJ (4.5 kgCO2/kgH2); this was surprisingly lower than ATR with CCS primarily due to the emissions associated with ATR electricity provision for air separation. Future technologies and strategies are detailed so as to further reduce cost and supply chain emissions; these were shown to be able to reduce total CO2 EI to 14 kgCO2/GJ (1.6 kgCO2/kgH2). Hence this analysis indicates that this supply chain can act to significantly reduce CO2 emissions whilst uniquely meeting targeted hydrogen supply costs up to 2050. As such it is proposed here as an eminently viable hydrogen export option deploying both existing technology and capacity, at least until other hydrogen supply chain vectors (such as liquid hydrogen and ammonia) derived from green hydrogen production become competitive across all the KPIs. [Display omitted] • Comprehensive techno-economic assessment of LNG-based hydrogen supply chain. • An existing LNG trade route between Australia and Japan is considered. • A competitive total hydrogen supply cost of 2.3 USD/kg H2 was determined. • Total CO 2 emissions intensity of this supply chain is 40 kg CO2 /GJ. • Methods and impact of potential emissions reduction strategies are presented. [ABSTRACT FROM AUTHOR]

In practice, carbon capture processes in CCS (Carbon Capture and Storage) consist of two main units: the carbon dioxide (CO 2 ) capture plant and the CO 2 compression unit. This study considered a hybrid capture system that combined both the capture and the compression units. In doing so, the conventional multi-stage CO 2 compression unit was replaced with a low-temperature carbon capture separation and pressurising step. The advantages of replacing the compression unit are two-folds: firstly, the low-temperature separation unit can further purify the CO 2 stream and secondly, it produces liquid CO 2 that can be pumped to the supercritical state required for transportation and sequestration. In order to take advantage of the extra CO 2 purification of the low-temperature separation unit, a vacuum swing adsorption (VSA) was used as the initial CO 2 recovery stage. A hybrid process has a higher degree of freedom available and therefore a Multi-Objective Optimisation (MOO) technique in combination with heat integration was used to optimise the total shaft work and the overall CO 2 recovery rate of the capture process. The MOO provided a range of optimal solutions where the total shaft work increased with the total CO 2 being recovered by the hybrid process. However, a minimum optimum was determined for the total specific shaft work required at an overall recovery rate of 88.9%, which required 1.40 GJ/(t CO 2 captured). [ABSTRACT FROM AUTHOR]

Abstract: ZnO nanostructures with different morphologies and optical properties were prepared by a simple microemulsion process, and PEG400 was used as a directing agent. The samples were characterized by TEM, XRD, FTIR, and TG-DTA analysis. The XRD spectra indicate that the ZnO crystal has a hexagonal wurtzite structure. Needle-like, columnar, and spherical ZnO samples were synthesized respectively with the increase of PEG400 concentration in Zn(NO3)2 solution. TEM images and thermogravimetric analysis reveal that the microemulsion interface and the PEG400 agent have a synergistic effect on the morphology and crystalline size transition of ZnO nanostructures. The optical properties of the samples were investigated by measuring the UV–Vis absorbance spectra at room temperature. All the samples exhibit strong UV absorption at around 365 nm. ZnO products with band gap energies at 3.06, 3.02, 2.95, and 2.85 eV were obtained with 0, 12.5, 25.0, and 50.0% of PEG400 in Zn(NO3)2 solution, respectively. The formation mechanism of the ZnO nanostructures was proposed and discussed in detail. The synergistic control of the microemulsion interface and the agent on the growth of crystal nuclei reported here provides an alternative approach for preparation of other well-defined nanostructures. [Copyright &y& Elsevier]

[Display omitted] • In-situ Raman microscopy was used to reliably quantify gas adsorption in milli-gram samples. • The measurement is calibration-free and validated against standard techniques validated. • The structural transition of a flexible adsorbent ZIF-7 was characterized using in-situ Raman microscopy at a molecular level. • The pressure-regulated increase in adsorption capacity was associated with accessibility to multiple adsorption sites. Adsorbents are widely used in gas separation and storage processes. Performance improvements are largely achieved through the continual development of new materials with unique sorption properties. Adsorption characterization techniques, therefore, play a central role in material research and development. Here, in-situ Raman spectroscopy is presented as a multi-purpose laboratory tool for analyzing adsorption performance. In contrast to conventional laboratory techniques requiring macroscopic samples, adsorption analysis via Raman spectroscopy can be performed on samples of less than 1 mg. Furthermore, simultaneous Raman multi-phase measurements of the adsorbent structure as well as the free and bound adsorbate, are shown to provide molecular insights into the operation of functional adsorbents at conditions representative of industrial applications, which are often not attainable in conventional crystallography. Firstly, a Raman-based method is demonstrated for directly quantifying absolute adsorption capacity within individual particles. The technique is validated for Raman measurements of carbon dioxide on silica gel and compared to gravimetric and volumetric analyses. Secondly, Raman spectroscopy is applied to study a novel functional material, ZIF-7, and directly probe its pressure-regulated gate-opening mechanism, which was only observed through indirect means. These Raman measurements confirm that the sharp increase in capacity corresponds to a structural transition in the material and reveal that multiple adsorption sites contribute to the overall capacity. The Raman methods presented here can be applied to a wide range of adsorbent-adsorbate systems and present a basis for further studies into the kinetics of sorption processes. [ABSTRACT FROM AUTHOR]

"Breathing" and "gating" are striking phenomena exhibited by flexible metal-organic frameworks (MOFs) in which their pore structures transform upon external stimuli. These effects are often associated with eminent steps and hysteresis in sorption isotherms. Despite significant mechanistic studies, the accurate description of stepped isotherms and hysteresis remains a barrier to the promised applications of flexible MOFs in molecular sieving, storage and sensing. Here, we investigate the temperature dependence of structural transformations in three flexible MOFs and present a new isotherm model to consistently analyse the transition pressures and step widths. The transition pressure reduces exponentially with decreasing temperature as does the degree of hysteresis (c.f. capillary condensation). The MOF structural transition enthalpies range from +6 to +31 kJ·mol−1 revealing that the adsorption-triggered transition is entropically driven. Pressure swing adsorption process simulations based on flexible MOFs that utilise the model reveal how isotherm hysteresis can affect separation performance. Flexible metal–organic frameworks that undergo structural transformations upon gas sorption show great promise for applications in gas storage and separation, but accurately describing their stepped isotherms and hysteresis remains a challenge. Here, the authors introduce an empirical model to describe hysteretic MOF sorption isotherms and determine their temperature dependence, which is asymptotic at low temperatures. [ABSTRACT FROM AUTHOR]

Abstract Converting fly ash into zeolite is an alternative way to reduce the waste landfills while also producing high value-added products. However, hydrothermal synthesis of zeolite from fly ash in alkaline media could also induce mobilization of toxic heavy metals, possibly causing environmental contamination. Systematic research into this subject is rare in the open literature and the mobility of heavy metals from fly ash derived zeolites is yet to be understood. In the present contribution, we investigated the migration of heavy metals and quantified their distribution from fly ash to product zeolites and waste water during the synthesis of high-quality type A zeolites (471 m2/g surface area). High conversions of major elements (98.2% aluminium and 96.5% silicon) were achieved, with zero secondary solid waste. Metalloid elements including arsenic and selenium, and those with strong amphoteric properties e.g. molybdenum were found highly mobile and mostly presented in the wastewater. In comparison, less than 20% of the heavy metals with weak amphoteric nature including copper, chromium and lead from the fly ash went to the wastewater; the rest along with almost all cadmium, iron and nickel were fixed into the product zeolites. Despite the existence of heavy metal elements in zeolites, there was no noticeable leaching under various pH conditions, hence deemed safe for applications. Furthermore, the effective removal of trace strontium and caesium cations from contaminated water using such zeolites was demonstrated. [ABSTRACT FROM AUTHOR]

The four base configurations of Dual-Reflux Pressure Swing Adsorption (DR PSA) cycles, namely feed to the low (PL) or high (PH) pressure bed, with blowdown and pressurisation using either the heavy (A) or light adsorbate (B), were demonstrated and compared experimentally in terms of their respective performance separating N 2 and CH 4 using activated carbon. Non-isothermal numerical simulations of these four cycles were validated against the experiments and used to help develop a means of optimising DR PSA cycles. While previous theoretical treatments and experimental studies have largely focussed on situations where the heavy product-to-feed ratio, H / F , is near to the ideal value necessary to produce two pure products, we demonstrate how H / F can be used to bias the separation towards either improved stripping or enrichment; this can be of practical importance in physical cycles where perfect separation is not possible. Consequently, H / F can be considered together with bed’s capacity ratio, C , and the (heavy) reflux-to-feed ratio R / F as key operational parameters available for optimising cycle performance in terms of product purity, cycle work and productivity when adsorbent selectivity, bed pressure ratio and feed location are fixed. For N 2 -CH 4 separations biased towards stripping (larger H / F values), PL-A cycles achieved the best separation performance while PH-B cycles were best for separations biased towards enriching (smaller H / F values). In terms of cycle work per mole of feed treated, for a particular set of experiments with the same light reflux flow (2 SLPM) B configurations required about 15% less work than A configurations. For these experiments PH cycles required about 25% less work than the PL cycles because the feed was at a lower pressure than either of the products, which were both delivered at high pressure. [ABSTRACT FROM AUTHOR]

A non-isothermal model of dual reflux pressure swing adsorption (DR-PSA) was developed using a commercially available software package to numerically solve the dynamics of the unit operation. Importantly the model includes a full energy balance, which is a feature not reported previously in the literature for simulations of DR-PSA cycles even though bed temperature swings of 10–20 K have been observed in experimental studies. The simulation allowed solution of the pressure-flow network for cycles in the PL-A configuration, where feed gas enters the middle of the low pressure column and where pressure inversion is conducted by transferring gas rich in the more adsorbed component between beds. At cyclic steady state the simulations contained material balance errors comparable in magnitude to those reported previously for isothermal DR-PSA simulations; however, these were accounted for using a robust correction scheme. Predictions of the pressure, flow and temperature profiles within the beds for a range N 2 + CH 4 mixtures being separated using activated carbon were in good agreement with the corresponding results of 24 DR-PSA experiments recently reported by Saleman et al. (2015). The root mean square deviation of the predicted methane mole fractions from the experimental values were 0.003 and 0.024 for the light (N 2 -rich) and heavy (CH 4 -rich) product streams, respectively. Parametric studies conducted with the model show how the cycle design can be optimised with respect to reflux flow and the feed-purge step duration, and also illustrate the need for reliable values of the sorption mass transfer coefficient. [ABSTRACT FROM AUTHOR]

Highlights: [•] CO2 capture on activated carbon from wet flue gas streams. [•] Fundamental isotherms and kinetic data obtained. [•] Vacuum swing adsorption cycling conducted to determine effect on CO2 capture. [ABSTRACT FROM AUTHOR]

Abstract: Core–shell structures of zeolite X coated with silicalite as well as mesoporous (MCM-41) have been synthesized. Furthermore, the surfaces of the silicalite and mesoporous silica shells were silylated using organosilanes. The materials were characterized by X-ray diffraction, nitrogen adsorption/desorption, scanning and transmission electron microscopy. The results show that the properties of zeolite 13X@silicalite and zeolite 13X@mesoporous silica core–shells composite structures are well maintained even after the modification. As expected, the shell thickness increased with increase in synthesis time, however, the micropore volume decreased. Silylation with smaller organosilanes (trimethyl chlorosilane) resulted in decrease in surface area as they diffused through the pores; however, bulkier silane reacted with surface hydroxyl groups and maintained the pore structure. Contact angle measurements revealed that hydrophobicity of zeolite 13X was enhanced by the microporous and mesoporous shell coating and was further improved by silylation. [Copyright &y& Elsevier]

The water solubilization capacity (W0) of microemulsion system determines its physicochemical properties and interior structures. In this study, the effects of different kinds of additives such as inorganic salt, nonaqueous polar solvent, organic salt, amino acid, and polyethylene glycols (PEG series) on the water solubilization behavior of heptane/hexanol/TritonX-100/water microemulsion system have been studied in detail. The influence mechanism of every additive on W0 has also been proposed and discussed. Furthermore, the droplet size distribution and the interaction among the droplets have been investigated by dynamic light scattering technique with the presence of additives. The result shows that the hydrodynamic diameter of microemulsion droplet and the attractive interaction between the droplets increase with the increase of the water content and the additive concentration. This work presents a facile method to adjust the structure parameters and the interface strength of microemulsion system by adding additive to the system, and to direct the applications of microemulsion system in nanomaterials preparation and drug controlled release. [ABSTRACT FROM AUTHOR]

Abstract: The validity of percolation theories on TritonX-100/heptane/alkanol/water W/O (water-in-oil) microemulsion has been investigated based on conductivity analysis. The experiment results have proved that the microemulsion follows both Bernasconi–Weismann (BW) and effective medium theory with dipole–dipole interaction (EMTDD, clusters) theories in the water content range from W 0 =1 to W 0 =7. The results here are different from the reported microemulsions with CTAB, AOT or SDS as ionic surfactant and alkanols as cosurfactants, and those microemulsions always follow effective medium theory (EMT) perfectly. This suggests that nonspherical surfactant aggregates and droplet clusters exist in the microemulsion solution due to the dipolar interaction between the dispersed droplets. The size of water pool, the hydrodynamic diameter of droplet, and the number of surfactant and cosurfactant per droplet have been evaluated according to the two validated theories. The dynamic state and the calculated size distribution of droplets are agreed with the results detected by dynamic light scattering technique. The research has indicated that the percolation theories are also adaptable to nonionic surfactant microemulsions with low water content and the structure parameters of droplets can be calculated by the effective theories. [Copyright &y& Elsevier]

Abstract: Computational fluid dynamics (CFD) simulations were carried out for fluid flow in baffle-filled membrane tubes, in which an array of central baffles or wall baffles was inserted. The commercial CFD package FLUENT, which employs the finite-volume method, was used for numerical computations. Through CFD simulations, the qualitative and quantitative properties of fluid dynamics in a baffle-filled channel can be obtained, which benefits to fully understand the effects of two types of baffles on flow pattern, behavior and feature. The simulation results show that the presence of baffles causes remarkable increases of the average velocity and shear stress on the tube wall, which can significantly improve the filtration performance. The flux enhancement is also attributed to the intense fluctuations of wall velocity and wall shear stress, which can greatly disrupt the development of boundary layer, as well as the growth of cake layer. The experimental results of crossflow microfiltration of calcium carbonate suspensions are consistent with the CFD simulations. However, the pressure drop along the baffle-filled membrane tube is significantly increased owing to the frequent changes in flow direction and the energy dissipation of turbulent flow. [Copyright &y& Elsevier]

Abstract: In order to further overcome the trade-off between high conductivity and good mechanical property of proton exchange membrane (PEM), direct covalent crosslinking of sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK) and poly(vinyl alcohol) (PVA) was prepared through post-heating process. Polymer PVA has attractive advantages to be a crosslinker with SPPESK, since the crosslinking of SPPESK with PVA requires relatively lower crosslinking temperature and has much higher stability in water, compared with small molecule crosslinker of glycol and glycerol. The crosslinking is confirmed by solubility change and analysis of ion exchange capacity (IEC) and sulfur content (C S) of uncrosslinked and crosslinked SPPESK with PVA (Un S-P and Cr S-P). Calculation of degree of crosslinking (DC) of sulfonic group shows that most –SO3Hs of SPPESK are not involved in the crosslinking, which can maintain the ion exchange and proton transport function. ATR-FTIR spectra analysis manifests the PVA in Cr S-P are oxidized and dehydrated during the crosslinking process with SPPESK. Cr S-P membrane still has higher thermal stability, despite T d (252–273°C) is less than that (306°C) of pristine SPPESK. SEM images and XRD patterns show that the Cr S-P is a homogenous and amorphous material. Water uptake of Cr S-P membrane decreases with increasing PVA content, and Cr S-P membrane with lower PVA content (e.g. 15% and 20%) has high water uptake (111.1% and 98.0%) at 80°C. All the swelling ratio values of Cr S-P (15–35% of PVA content) are at a lower level (≤36%) even at 80°C. Some Cr S-P membranes (with lower PVA content) have much higher conductivity than that of stable pristine SPPESK, e.g. conductivity of S-P 85/15 reaches 2.00×10−2 Scm−1 which is almost twice as that (1.03×10−2 Scm−1) of SPPESK DS 81% membrane. All above properties of Cr S-P membrane (especially PVA content: 15–20%) indicate the kind of crosslinked sulfonated polymer with PVA is another alternative or prospective approach to prepare PEM. [Copyright &y& Elsevier]

Abstract: Freeze/thaw treatment has been widely investigated for phase separation of oil-in-water (O/W) emulsions. However, it is a new application for destroying the inverted emulsions, water-in-oil (W/O) emulsions. In this study, freeze/thaw treatment was used to break the W/O emulsions with loosely packed droplets that were produced from the oils generally adopted as membrane phase in emulsion liquid membrane (ELM) process. The effects of emulsion system parameters and freezing conditions on demulsification performance were investigated. A near linear relationship was observed between demulsification performance and water content (30–65%). Demulsification performance greatly increased with the increase of droplet size (2.7–7.3μm), while it was slightly affected by oil type. Four freezing methods were employed including freezing in refrigerator, cryogenic bath, dry ice and liquid nitrogen. The best freezing method for water removal was freezing in cryogenic or dry ice, and its efficiency was over 70% for all experimental systems with 60% water content regardless of droplet size and oil phase type. Furthermore, microscopic process of demulsification was monitored using optical microscope and the coalescence of droplets was simulated. From the experiments, the gradual demulsification process induced by freeze/thaw was proven and a collision mechanism was proposed. Meanwhile, the volume expansion of water turning to ice and interfacial tension of oil–water interface were determined as main driving forces of demulsification. The proposed mechanism and driving forces can explain the influences of various parameters on demulsification performance well. [Copyright &y& Elsevier]

In this study, two viscous models, the Choi‐Schwalter and Phan‐Thien‐Pham models, are used to calculate the isotonic swelling ratio of emulsion liquid membrane. The purpose is to evaluate the usefulness of calculating isotonic swelling ratios of emulsion liquid membranes by viscous models through comparing theoretical isotonic swelling ratios with experimental swelling ratios of three kinds of emulsion liquid membranes. Comparison between theoretical swelling ratios and experimental swelling ratios indicates that experimental swelling ratios are close to those calculated by the Choi‐Schwalter model, but lower than those calculated by the Phan‐Thien‐Pham viscous model. But modified Phan‐Thien‐Pham viscous models predicts reasonable values. Therefore, the method of calculating the isotonic swelling ratio of emulsion liquid membrane by theoretical viscosity models is promising. [ABSTRACT FROM AUTHOR]

• First holistic review of N-functionalized solid adsorbents for CO 2 capture. • The criteria of developing high-efficiency and inexpensive N-functionalized solid adsorbents were summarized. • The opportunities and challenges of N-functionalized solid adsorbents were discussed. Over the past decade, amine-loaded solid adsorbents for capturing CO 2 from power plants have been widely studied. Various nitrogen (N) sources have been used for this purpose, and the current range of adsorbents, referred to here as N-functionalized solid adsorbent (NFSAs), are the subject of this review. The main synthesis methods of NFSAs are described and recent progress in the field discussed. Criteria for improving NFSA performance are highlighted with reference to a variety of solid supports, providing guidance on the selection of highly efficient, inexpensive adsorbents. A thorough assessment of adsorption mechanisms and factors influencing the adsorption process is given. The review concludes by exploring future research and development opportunities, as well as pathways for commercializing NFSAs. [ABSTRACT FROM AUTHOR]