Large Separation Factors Research Articles

Systematic experiment on adsorption, separation and regeneration of X zeolites for LNG production with different regeneration strategies: vacuum, purging, heating and hybrid combinations

This work experimentally investigated the adsorption, separation and regeneration properties of two X zeolites for natural gas deep decarbonization in liquified natural gas (LNG) production. The regeneration properties of JLOX500 and 13X were compared with relation to regeneration efficiency, energy consumption, desorption and adsorption rate of CO2, and other factors in different pathways: vacuum, purging, heating, and hybrid combinations. The results demonstrated that fresh JLOX500 with more cations and less binders had significantly greater CO2 adsorption capacities and larger separation factor (CO2/CH4) than those of fresh 13X, because of its larger micro-porosity and higher CO2 isosteric heat. Due to higher partial pressure, the adversely significant effect of CH4 competing adsorption against CO2 on adsorbent regeneration is confirmed. The flow rate increases of purge gas had no effects on regeneration efficiency for 13X when the CO2 concentration of desorbed gas reached to zero. Because of a greater cumulative pore volume, JLOX500 after sufficient regeneration has a larger CO2 adsorption capacity and a higher desorption rate of CO2 than 13X, which also makes it more efficient with regards to purge gas and energy consumption utilization. With 150 mL/min of purge gas, the energy consumptions for 13X and JLOX500 regenerated at 150 °C were 4.20 and 2.89 MJ/kg-CO2, respectively. The CH4 recovery relied on the regeneration efficiency of adsorbents, duration of adsorption, and the amount of purge gas used. Both X zeolites regenerated by purging (150 mL/min) or vacuuming at 1 kPa at 150°C could purify the feed to the CO2 content less than 50 ppm, but JLOX500 is more efficient with regards to the overall performance.

Liquid solution centrifugation for safe, scalable, and efficient isotope separation

A general method of separating isotopes by centrifuging dissolved chemical compounds in a liquid is introduced. This technique can be applied to almost all elements and leads to large separation factors. The method has been demonstrated in several isotopic systems including Ca, Mo, O, and Li with single-stage selectivities of 1.046 to 1.067 per neutron mass difference (e.g., 1.43 in 40 Ca/ 48 Ca), which are beyond the capabilities of various conventional methods. Equations are derived to model the process, and the results agree with those of the experiments. The scalability of the technique has been demonstrated by a three-stage enrichment of 48 Ca with a total 40 Ca/ 48 Ca selectivity of 2.43, and the scalability is more broadly supported through analogies to gas centrifuge, whereby countercurrent centrifugation can further multiply the separation factor by 5 to 10 times per stage in a continuous process. Optimal centrifuge conditions and solutions can achieve both high-throughput and highly efficient isotope separation.

Aroma Compounds in Essential Oils: Analyzing Chemical Composition Using Two-Dimensional Gas Chromatography-High Resolution Time-of-Flight Mass Spectrometry Combined with Chemometrics.

Analyzing essential oils is a challenging task for chemists because their composition can vary depending on various factors. The separation potential of volatile compounds using enantioselective two-dimensional gas chromatography coupled with high-resolution time-of-flight mass spectrometry (GC×GC-HRTOF-MS) with three different stationary phases in the first dimension was evaluated to classify different types of rose essential oils. The results showed that selecting only ten specific compounds was enough for efficient sample classification instead of the initial 100 compounds. The study also investigated the separation efficiencies of three stationary phases in the first dimension: Chirasil-Dex, MEGA-DEX DET-β, and Rt-βDEXsp. Chirasil-Dex had the largest separation factor and separation space, ranging from 47.35% to 56.38%, while Rt-βDEXsp had the smallest, ranging from 23.36% to 26.21%. MEGA-DEX DET-β and Chirasil-Dex allowed group-type separation based on factors such as polarity, H-bonding ability, and polarizability, whereas group-type separation with Rt-βDEXsp was almost imperceptible. The modulation period was 6 s with Chirasil-Dex and 8 s with the other two set-ups. Overall, the study showed that analyzing essential oils using GC×GC-HRTOF-MS with a specific selection of compounds and stationary phase can be effective in classifying different oil types.

Enhanced selective separation of vanadium(V) and chromium(VI) using the CeO2 nanorod containing oxygen vacancies.

Adsorption of vanadium from wastewater defends the environment from toxic ions and contributes to recover the valuable metal. However, it is still challenging for the separation of vanadium (V5+) and chromium (Cr6+) because of their similar properties. Herein, a kind of CeO2 nanorod containing oxygen vacancies is facilely synthesized which displays ultra-high selectivity of V5+ against various competitive ions (i.e., Fe, Mn, Cr, Ni, Cu, Zn, Ga, Cd, Ba, Pb, Mg, Be, and Co). Moreover, a large separation factor (SFV/Cr) of 114,169.14 for the selectivity of V5+ is achieved at the Cr6+/V5+ ratio of 80 with the trace amount of V5+ (~ 1mg/L). The results show that the process of V5+ uptake is the monolayer homogeneous adsorption and is controlled by external and intraparticle diffusions. In addition, it also shows that V5+ is reduced to V3+ and V4+ and then formation of V-O complexation. This work offers a novel CeO2 nanorod material for efficient separation of V5+ and Cr6+ and also clarifies the mechanism of the V5+ adsorption on the CeO2 surface.

Highly efficient and selective separation of dysprosium and neodymium from polyethylene glycol 200 solution by non-aqueous solvent extraction with P350

Recycling of Nd(III) and Dy(III) from waste NdFeB magnets is increasingly critical in the sustainable development of rare-earth elements (REEs) industry. The efficient separation of Nd(III) and Dy(III) from conventional aqueous solution by solvent extraction (SX) is facing huge challenge due to the high activity, high interfacial tension and the high dielectric constants of water that affect the coordination of REEs with the extractant. Herein, a novel non-aqueous solvent extraction (NASX) system based on neutral extractant P350 was developed to extract Nd(III) and Dy(III) with high extraction efficiency and separation factor. In this extraction system, the majority of water in the aqueous phase was replaced by different low-dielectric-constant polar molecular organic solvents (PMOSs) to reduce the influence of water during extraction. The effect of the type and content of PMOSs, P350 concentration, extract equilibration time and temperature on the separation performance were systematically investigated. It was encouraging to find that the favorable separation factor of Nd(III) and Dy(III) elements (βNd/Dy) was determined to be 201 when extracted from 70 vol% PEG 200 with 0.2 mol/L P350, which was higher than that in traditional extraction from aqueous phase. Slope analysis method was used to determine the extractant stoichiometry and the main species of extraction complex was identified as DyCl3·2L which was verified by Fourier infrared spectroscopy (FT-IR). Furthermore, in the simulation of recovery of NdFeB magnetic immersion solution experiment, the extraction efficiency (E%) of Dy(III) can reach 85 %, while co-extraction of Nd(III) was only 6 % and the βDy/Nd was as high as 83.4. According to the McCabe-Thiele diagram, 3-stages counter-current solvent extraction was needed to completely extract Dy(III). Moreover, 97.11 % of Nd(III) and 98.5 % of Dy(III) in the loaded organic phase can be sequentially stripped by 0.04 mol/L and 0.4 mol/L HCl, respectively. These results indicated that the developed processes in this work have superior extraction efficiency, large separation factors and excellent stripping stability. Eventually, a P350-PEG 200 extraction system-based separation process was proposed in the hope of providing a novel and low-cost alternative to the efficient recycle of Nd(III) and Dy(III) from end-of-life NdFeB.

Non‐Covalent Cross‐Linking Does the Job: Why PIM‐1/Silicalite‐1 Mixed Matrix Membranes Perform Well Notwithstanding Silicalite‐1

The macroscopic modeling of gas transport in mixed-matrix membranes (MMMs) made of a Polymer of Intrinsic Microporosity (PIM-1) and silicalite1 (MFI) is compared to the experimental results presented in a previous paper, which shows unexpectedly large gas separation factors, although the silicalite-1 filler is practically nonselective. The mismatch between the predictions of the Maxwell model and the experiments is zeroed by the recognition of nonideal effects, the extent of which is evaluated. The good performance of the PIM-1 MMM is explained by non-covalent cross-linking of the PIM-1 matrix. Cross-linking results from π-π stacking interactions between the 2-phenylethyl grafts on the outer surface of the MFI crystals and the aromatic ladder segments of PIM-1, in agreement with the current explanation of the good transport performance of PIM-1 MMMs containing porous aromatic fillers (e.g., PAF-1).

Modeling Isotope Separation in Electrochemical Lithium Deposition

Naturally occurring Li consists of two stable isotopes, 6Li with an abundance of about 7.5%, and 7Li making up the remainder with 92.5%. The development of a 6Li enrichment technique, in terms of technical reliability and environmental safety to reach 6Li future requirements, represents a key step in the roadmap for nuclear fusion energy supply worldwide. This paper uses finite element analysis-based models to simulate electrochemical Li isotope separation, which is an attractive method in terms of simplicity, safety, and scalability. In the model, we quantitatively analyze how different electrochemical factors including thermodynamics, charge-transfer kinetics, and diffusivities affect the separation process (separation factor), together with cell parameters, such as cell length and current density. The maximum separation factor of 1.128 could be obtained with the cell under the optimal thermodynamic, kinetic, and diffusive conditions, which is among the highest separation factors ever reported. These results will assist in designing the actual isotope separation setup with large separation factor and appropriate timing for sample collection.

Mo3 S13 2- Intercalated Layered Double Hydroxide: Highly Selective Removal of Heavy Metals and Simultaneous Reduction of Ag+ Ions to Metallic Ag0 Ribbons.

We demonstrate a new material by intercalating Mo3 S13 2- into Mg/Al layered double hydroxide (abbr. Mo3 S13 -LDH), exhibiting excellent capture capability for toxic Hg2+ and noble metal silver (Ag). The as-prepared Mo3 S13 -LDH displays ultra-high selectivity of Ag+ , Hg2+ and Cu2+ in the presence of various competitive ions, with the order of Ag+ >Hg2+ >Cu2+ >Pb2+ ≥Co2+ , Ni2+ , Zn2+ , Cd2+ . For Ag+ and Hg2+ , extremely fast adsorption rates (≈90 % within 10 min, >99 % in 1 h) are observed. Much high selectivity is present for Ag+ and Cu2+ , especially for trace amounts of Ag+ (≈1 ppm), achieving a large separation factor (SFAg/Cu ) of ≈8000 at the large Cu/Ag ratio of 520. The overwhelming adsorption capacities for Ag+ (qm Ag =1073 mg g-1 ) and Hg2+ (qm Hg =594 mg g-1 ) place the Mo3 S13 -LDH at the top of performing sorbent materials. Most importantly, Mo3 S13 -LDH captures Ag+ via two paths: a) formation of Ag2 S due to Ag-S complexation and precipitation, and b) reduction of Ag+ to metallic silver (Ag0 ). The Mo3 S13 -LDH is a promising material to extract low-grade silver from copper-rich minerals and trap highly toxic Hg2+ from polluted water.

Mo3S132− Intercalated Layered Double Hydroxide: Highly Selective Removal of Heavy Metals and Simultaneous Reduction of Ag+ Ions to Metallic Ag0 Ribbons

AbstractWe demonstrate a new material by intercalating Mo3S132− into Mg/Al layered double hydroxide (abbr. Mo3S13‐LDH), exhibiting excellent capture capability for toxic Hg2+ and noble metal silver (Ag). The as‐prepared Mo3S13‐LDH displays ultra‐high selectivity of Ag+, Hg2+ and Cu2+ in the presence of various competitive ions, with the order of Ag+>Hg2+>Cu2+>Pb2+≥Co2+, Ni2+, Zn2+, Cd2+. For Ag+ and Hg2+, extremely fast adsorption rates (≈90 % within 10 min, >99 % in 1 h) are observed. Much high selectivity is present for Ag+ and Cu2+, especially for trace amounts of Ag+ (≈1 ppm), achieving a large separation factor (SFAg/Cu) of ≈8000 at the large Cu/Ag ratio of 520. The overwhelming adsorption capacities for Ag+ (qmAg=1073 mg g−1) and Hg2+ (qmHg=594 mg g−1) place the Mo3S13‐LDH at the top of performing sorbent materials. Most importantly, Mo3S13‐LDH captures Ag+ via two paths: a) formation of Ag2S due to Ag‐S complexation and precipitation, and b) reduction of Ag+ to metallic silver (Ag0). The Mo3S13‐LDH is a promising material to extract low‐grade silver from copper‐rich minerals and trap highly toxic Hg2+ from polluted water.

Efficient elimination behavior and mechanism of heavy metal by eco-friendly potassium titanium trisilicate

Frame structural material holds great potential for adsorption but challenging for stable in harsh aqueous medium. Herein, a framework potassium titanium silicate K2TiSi3O9•H2O with wide acid durability is used for heavy metal purification and shows excellent performance. The adsorption capacity of K2TiSi3O9•H2O reaches maximum 221 and 123 mg/g towards Pb2+ and Cd2+ at room temperature. The residual Pb2+ concentration holds at 0.0006 mg/L that is far below the limits in drinking water, and the removal efficiency of Pb2+ (10–200 mg/L) still remains 60–73% even at strong acid solution. The readily exchanging K sites in K2TiSi3O9•H2O framework and abundant deprotonated hydroxyl groups afford the rapid adsorption rate and large uptake capacity. A large separation factor (102–103) between competitive Na/Ca and heavy metal ions demonstrates this good selectivity. The removal rate of K2TiSi3O9•H2O maintains 85% even after five cycles, indicating its good reproducibility. K2TiSi3O9•H2O is also extendable to cationic dye removal with a capacity of 45.6 mg/g. This work provides this kind of framework titanium silicates with great structural and crystal stability for the high-efficient and massive elimination of heavy metals.

Organoboron Ionic Liquids as Extractants for Distillation Process of Binary Ethanol + Water Mixtures

Aminoethers of boric acid, which are organoboron ionic liquids, were synthesized by using boric acid, triethanolamine, and triethylene glycol/diethylene glycol. Due to the formation of intermolecular complexes of borates, the structure of aminoethers of boric acid contains ion pairs separated in space, giving these compounds the properties inherent to ionic liquids. It is established that the thermal stability of aminoethers under normal atmospheric conditions increases with an increase in the size of the glycol. According to measurements of fast scanning calorimetry, density, dynamic viscosity, and electrical conductivity, water is involved in the structural organization of aminoethers of boric acid. The impact of the most thermostable organoboron ionic liquids on the phase equilibrium conditions of the vapor–liquid azeotropic ethanol–water mixture is studied. It is shown that the presence of these substances leads to increase in the relative volatility of ethanol. In general, the magnitude of this effect is at the level shown by imidazole ionic liquids, which provide high selectivity in the separation of aqueous alcohol solutions. A large separation factor, high resistance to thermal oxidative degradation processes, accompanied by low cost start reagents, make aminoethers of boric acid on the basis of triethylene glycol a potentially effective extractant for the extractive distillation of water–alcohol mixtures.

Optimal Multistream Cascades for Simultaneous Production of High-Enrichment Intermediate Components

A method was developed for optimizing a cascade with two additional product streams, in which two components of intermediate mass are concentrated simultaneously. The solution of the optimization problem is based on variation of the cuts of partial flows of the cascade steps with large separation factors. A minimum of the total feed stream of the steps with specified concentration of the isotopes is used as the optimization criterion. A computational experiment on separation of a tungsten hexafluoride mixture was performed. It is shown that high concentration of intermediate components can be obtained with additional product streams exceeding the primary product and waste streams of the cascade.

High-Selectivity Pervaporation Membranes for 1-Butanol Removal from Wastewater

Possibility of using polydecylmethylsiloxane in the pervaporation removal of organic compounds from aqueous media was examined. It was shown for the example of the system with 1 wt % n-butanol in water that this material is characterized by a large separation factor (69), which twice exceeds the separation factor of the commercial membrane polymer polydimethylsiloxane. A composite membrane was produced on the basis of polydecylmethylsiloxane. The selective layer was deposited from a solution of the polymer by the touching method onto an MFFK-1 domestic microfiltration substrate. Pervaporation experiments with the new composite membranes based on polydecylmethylsiloxane were used to determine the optimal separation mode of the water–butanol mixture: delivery rate of the mixture to be separated, 1.2 cm s–1; and separation temperature 40°C. It was shown that, at a selective layer thickness of about 4.5 μm, it is possible to reach a permeability of the PDecMS/ MFFK-1 membrane that is comparable with the permeability for 1-butanol of commercial composite membranes (5.2 mol m–2 h kPa–1). However, the butanol/water selectivity for the PDecMS/MFFK-1 membrane is 3–7 times that of the commercial membranes.

Prediction on separation factor of chiral arylhydantoin compounds and recognition mechanism between chiral stationary phase and the enantiomers

Chiral hydantoins display potential antidepressant and anticancer activities. The quantitative structure property relationship (QSPR) study on chiral compounds plays a key role in predicting the retention factor and the separation factor even the elution order of the enantiomers. In this study, the structures of chiral arylhydantoin compounds have been built to compute molecular structural parameters using VolSurf program. The satisfying models were established between the parameters and the retention factor as well as the separation factor. Analysis on the variables shows that the large difference values of volume, hydrophilic regions and hydrogen bond acceptor and donor regions at some energy levels will result in the large separation factor. The differences of hydrophobic regions and the unbalance between the centre of mass and the barycentre of the hydrophobic region at high energy levels are also favorable to the separation. The differences of surface area, hydrophilic regions and hydrogen bond acceptor and donor regions at other energy levels as well as hydrophobic regions and the unbalance at low energy levels between the enantiomers are disadvantageous to the separation. The analysis on the chiral recognition mechanism demonstrates that the differences of the interaction energies between the enantiomers are mainly affected by the hydrogen bond, π-π interaction and CH3-π interaction. The retention factor and the separation factor, especially the elution order of the enantiomers can be easily predicted using the models. The study provides a helpful guidance for studying other chiral compounds.

Fabrication of Hydrogen-Selective Silica Membranes via Pyrolysis of Vapor Deposited Polymer Films

Efficient separation of hydrogen under steam reforming conditions is important for the development of clean energy sources. Although high-temperature and steam-stable membranes with high fluxes and large separation factors would be valuable for such an application, their fabrication remains a challenge. Silicon-based ceramic membranes are particularly promising due to their high temperature resistance and excellent chemical stability. In this study, we propose a new synthetic route for fabricating nanoporous, asymmetric membranes via the pyrolysis of silicon-containing polymer films deposited by initiated chemical vapor deposition (iCVD) on macroporous silicon carbide supports. Specifically, we systematically investigated the change in the chemical structure of poly(2,4,6,8-tetravinyl-2,4,6,8-tetramethyl cyclotetrasiloxane) films at different pyrolysis temperatures and found that the complete transition to a silica membrane occurred at ∼1100 °C. Three different supports composed of silicon carbide powders...

Preferential extraction of hafnium over zirconium with D2EHPA through selective complexation of organic acids

Nuclear grade zirconium and hafnium are important materials in nuclear power plants, which are usually produced with solvent extraction and separation technology. In this paper, the preferential extracting hafnium was successfully achieved by the selective complexation of the selected organic acids. Hydrochloric acid concentration, organic acid concentration, D2EHPA concentration were investigated to explore the optimum extraction conditions. Increasing acidity and extractant concentration was not conducive to the separation of zirconium and hafnium, while organic acid could effectively improve the separation factor, which was verified by ATR-FTIR spectroscopy. The largest separation factor, 9.936, for hafnium over zirconium was obtained.

Efficient adsorption separation of xylene isomers using a facilely fabricated cyclodextrin‐based metal–organic framework

AbstractBackgroundMetal−organic frameworks (MOFs) are energy‐efficient adsorbents for separating industrial chemical feedstocks. A type of MOF containing an extended porous network of γ‐cyclodextrin (γ‐CD) and alkali metal salts, CD‐MOF, has potential applications in adsorption separation processes in the petrochemical industry. This study aims to present the adsorption efficiency of CD‐MOF‐1 in separating xylene regioisomers.ResultsThe adsorption separation of xylene regioisomers on layered CD‐MOF‐1 microcrystals was studied using batch vapor‐phase adsorption and liquid‐phase breakthrough adsorption. CD‐MOF‐1 showed preferable adsorption of o‐xylene over the other two isomers, with adsorption strength in the order o‐xylene (oX) > m‐xylene (mX) > p‐xylene (pX). With increased temperature, high adsorption capacities of oX and mX over pX were detected. However, this also resulted in a decrease of the separation factors of oX/pX and mX/pX.ConclusionThe high resolution and large separation factors for oX/pX and mX/pX make CD‐MOF‐1 an efficient and reliable alternative adsorbent to the isolation protocols for xylene isomers currently used in the petrochemical industry. © 2018 Society of Chemical Industry

Remarkable Acid Stability of Polypyrrole‐MoS4: A Highly Selective and Efficient Scavenger of Heavy Metals Over a Wide pH Range

AbstractThe new material polypyrrole/MoS42−(MoS4‐Ppy), prepared by ion‐exchange of NO3‐ of NO3‐Ppy with MoS42−, displays high acid stability and excellent uptake for heavy metal ions such as Hg2+, Ag+, Cu2+, and Pb2+. The different maximum adsorption capacities (qm) for Cu2+, Pb2+, Hg2+, and Ag+ depend on the various binding modes arising from the different thiophilicity of these metal ions. The removals of Ag+ and Pb2+ reach >99.6% within 5 min, and for highly toxic Hg2+, >98% removal achieves at 1 min. At strong acid limit, the exceptional qm(Ag+) of 725 mg g−1 places the MoS4‐Ppy at the top of materials for such removal. Uptake kinetics of Ag+, Hg2+, and Pb2+ is extremely fast: >99.9% removal rates at wide pH range (0.5–6) within 1–5 min. Also, at strongly acidic conditions (pH ≈ 1), for highly toxic Hg2+, <2 ppb concentration can be achieved, accepted as safe limit. The MoS4‐Ppy demonstrates an outstanding ability to separate low‐concentrated Ag+ from high concentrated Cu2+ especially under strong acidic conditions (pH ≈ 1), showing a large separation factor SFAg/Cu (KdAg/KdCu) of 105 (>100). MoS4‐Ppy is a superior and novel sorbent material for water remediation applications as well as precious metals recovery.

Extraction and recovery of soft metal ion by porous silica coated by hydrophilic polymer gel with hexavalent nitrogen-donor ligand

ABSTRACTA hydrophilic N-isopropylacrylamide (NIPA) gel copolymerized with a hexavalent nitrogen donor ligand, N,N,N’,N’-tetrakis(4-propenyloxy-2-pyridylmethyl)ethylenediamine (TPPEN), adsorbs soft metals selectively from the acidic aqueous phase. We are developing porous silica particles coating the TPPEN-NIPA gel with high TPPEN content thinly on the pore surface of porous silica by a new gel-coating method using surface tension. Half of the pore volume of the silica particles remained by the coating of the TPPEN-NIPA gel with the high TPPEN content of 30 mol%. A large separation factor (SF) of Cd(II)/Eu(III) of 60 was observed at pH 2. The proposed chromatographic agent with the high TPPEN content is applicable for practical use.

An initial demonstration of hierarchically porous niobium alkylphosphonates coordination polymers as potent radioanalytical separation materials

Combining the merits of soft-templating and perchlorate oxidation methods, the first-case investigation of niobium alkylphosphonates has uncovered their unique morphology, backbone composition, thermal behavior and huge potentiality as radioanalytical separation materials. These hierarchically porous solids are random aggregates of densely stacked nanolayers perforated with worm-like holes or vesicular voids, manifesting the massif-, tower-like “polymer brush” elevated up to ∼150nm driven by the minimal surface free energy principle. These coordination polymers consist of distorted niobium (V) ions strongly linked with tetrahedral alkylphosphonate building units, exposing uncoordinated phosphonate moieties and defective metal sites. Despite the amorphous features, they demonstrate multimodal porosity covering continuous micropores, segregated mesopores and fractional macropores, beneficial for the sequestration by active Lewis acid-base center. Evidenced by the maximum distribution coefficients of thorium, lanthanides reaching 9.0×104, 9.5×104mLg−1 and large separation factor at pH≤1 20-element cocktail, this category of niobium alkylphosphonates are capable of harvesting thorium, lanthanides directly from the radionuclide surrogate, comparable to or even surpass the performance of the metal (IV) arylphosphonates counterparts. They also display appreciable SFEu/Sm ∼20 in 1molL−1 HNO3, shedding light on dual approaches to achieve the isolation of americium from curium. A combinatorial radioanalytical separation protocol has been proposed to enrich thorium and europium, revealing facile utilization of these highly stable, phosphonated hybrids in sustainable development of radioanalytical separation.