Energy-efficient Separation Research Articles

Enhancing dewatering and desalination of crude oil: A comprehensive study on energy-efficient separation technology driven by electric–magnetic coupling field

Enhancing dewatering and desalination of crude oil: A comprehensive study on energy-efficient separation technology driven by electric–magnetic coupling field

Synthesis of (222)-oriented defect-rich MOF-808 membranes towards high-efficiency uranium rejection

Energy-efficient separation of uranium from seawater elicits huge interest for sustainable development of nuclear energy industry. Aiming at high-efficiency uranium separation from seawater, in this study, we pioneered room-temperature preparation of (222)-oriented defect-rich MOF-808 membrane using Zr6-oxo cluster as metal source through oriented growth. Benefitting from higher missing-linker number in the framework and minimized diffusion path length in the membrane, accurate and facilitated ion-transporting channels with size larger than kinetic diameters of hydrated ions of common metal ions (Mn+, n = 1, 2, 3) except uranyl ions (UO22+) were established. Compared with other metal ions, our membrane exhibited rejection rate of almost 100 % for UO22+ ions with ideal K+/UO22+, Na+/UO22+, Ca2+/UO22+, Mg2+/UO22+ and Fe3+/UO22+ selectivity achieving 9210, 8330, 4990, 3040 and 140 on the basis of size-sieving; moreover, obtained membrane enabled rapid and efficient separation of trace amounts of uranium (∼3.0 ppb) from natural seawater with considerable selectivity towards K+/UO22+ (315.0), Na+/UO22+ (314.5), Ca2+/UO22+ (295.0), Mg2+/UO22+ (285.5) and Fe3+/UO22+ (7.1) ion pairs, respectively. Compared with results reported in literature, our membrane displayed the highest screening precision among state-of-the-art nanofiltration membranes, holding great promise for practical uranium separation from seawater.

Fluorinated Squareimines for Molecular Sieving of Aromatic over Aliphatic Compounds.

The development of more energy-efficient separation technologies is essential. Especially the separation of cyclic aliphatic hydrocarbons from their aromatic counterparts remains a significant challenge due to azeotrope formation and similar physical properties, often requiring energy-intensive processes. Herein, we introduce a novel class of electron-deficient macrocycles with a unique rectangular structure to optimise interactions within the pore, enabling the highly selective molecular sieving of aromatic compounds from mixtures. Utilising dynamic covalent imine chemistry, the squareimine NDI2F42-based crystalline functional material is directly obtained from the reaction mixture in a single self-assembly step in high yields of 83 %, alongside the larger NDI2F82 congener, which can be obtained in 69 % yield. In vapour sorption and diffusion experiments, NDI2F42 demonstrates rapid adsorption kinetics with selectivities of 97 : 3 for benzene over cyclohexane and 93 : 7 for toluene over methylcyclohexane, while single-crystal and powder X-ray diffraction studies indicate that the selectivity is primarily governed by directed interactions between the electron-deficient panels and aromatic guests.

Efficient separation of methyl ethyl ketone and water azeotrope using hydrophobic amino acid ester ionic liquids

BackgroundMethyl ethyl ketone (MEK), an essential organic solvent, is commonly produced via the n-butene method, where water emerges as the principal impurity. The conventional distillation processes, which are necessitated by the azeotropic behavior between MEK and water, result in a substantial expenditure of energy. As a result, liquid-liquid extraction represents a promising alternative for energy-efficient separation. MethodsIn this work, three hydrophobic amino acid ester ionic liquids L-phenylalanine ethyl ester bis(trifluoromethylsulfonyl) imide ([Phe][NTf2]), L-leucine ethyl ester bis(trifluoromethylsulfonyl) imide ([Leu][NTf2]) and L-valine ethyl ester bis(trifluoromethylsulfonyl) imide ([Val][NTf2]) were utilized as extractants for separation of the binary azeotrope methyl ethyl ketone and water. The effects of extraction time, extraction temperature, mass ratio of MEK-water mixture to ionic liquid and initial concentration of MEK on extraction efficiency were investigated. Significant findingsThe results demonstrate that the ionic liquid [Phe][NTf2] exhibits superior extraction ability for the separation of the azeotrope methyl ethyl ketone and water. The maximum extraction yield of 99.86 % was achieved with the optimum extraction conditions of extraction time, 10 min, extraction temperature, 293.15 K, mass ratio of mixture to ionic liquid, 1:1 and initial concentration of MEK, 20 %. In addition, the relationship between the structure of ionic liquids and their extraction performance was revealed by quantum chemical calculations of ionic liquids with MEK and water. These ionic liquids were positioned as promising environmentally friendly alternatives to traditional organic solvents for the recovery of MEK from aqueous solutions, providing valuable insights for industrial applications.

Energy-Efficient Separation of Xylene Isomers through Stacked 1-Aminopyrene Polymer Composite.

Developing high-performance adsorbents for energy-efficient separation of xylene isomers has important research and application value. Identification and separation of xylene isomers (PX, MX, and OX) at room temperature based on the different relative positions of two methyl groups on the benzene ring is an unprecedented attempt. Herein, 1-aminopyrene polymer (PAP) is designed and electro-synthesized composited with a supporting electrolyte as an adsorbent for the separation of xylene isomers using a multi-stage dispersed liquid-solid adsorption process at room temperature. Each -NH-pyrene-NH- unit can form a force field to identify and discriminate xylene isomer through π-π interaction combined with -CH3···-NH- interactions of different strength, thereby achieving separation of PX, MX, and OX isomers by amplifying the slight differences in the adsorption capacity and diffusion rates. The density functional theory (DFT) simulations provide a more quantitative analysis of the adsorbate-adsorbent interactions to illustrate PX > MX > OX order of adsorption selectivity. This study may offer an alternative strategy for the precise designing of energy-efficient and adsorption-based separation materials.

Energy-efficient separation of a ternary azeotropic mixture via azeotropic reflux-induced sequences based on the intensified pressure-swing distillation

The recovery and separation of chloroform, acetonitrile and ethanol from waste water involving two azeotropes and a distillation boundary has emerged as a pivotal concern in the pursuit of environmental protection and resource conservation. Herein, the energy-efficient separation design of the ternary azeotropic mixture based on a triple-column pressure-swing distillation (TCPSD) process with five azeotropic reflux induced sequences is comprehensively investigated. The suitable operating pressure range of the distillation columns and the potential optimal distillation sequence is investigated based on the thermodynamic intrinsic probe. According to the optimal distillation sequence, further process intensification strategies are proposed to improve the thermodynamic efficiency encompassing the heat integration pressure-swing distillation (HI-PSD), heat pump assisted pressure-swing distillation (HP-PSD), and a combination of heat pump assisted and heat integration pressure-swing distillation (HPHI-PSD). It unveils the economic preeminence of the HI-PSD process, characterized by the lowest total annual cost (TAC) in a shorter payback period (3 to 7 years). Conversely, both the HP-PSD and HPHI-PSD processes exhibit superior environmental performance on CO2 emissions of 111.46 kg/h and 119.78 kg/h respectively, with the HP-PSD demonstrating prolonged economic viability and the HPHI-PSD showcasing heightened thermodynamic efficiency of a 65.12 % improvement. This study potentially provides a theoretical basis for devising industrial separation schemes for analogous pressure-sensitive ternary azeotropic systems.

Synergistic Tuning of Microstructure and Morphology in Carbon Molecular Sieve Hollow Fibers for Propylene/Propane Separation.

Asymmetric carbon molecular sieve (CMS) hollow fiber membranes with tunable micro- and macro-structural morphologies for energy efficient propylene-propane separation are reported here. A sub-glass transition temperature (sub-Tg) thermal oxidative crosslinking strategy enables simultaneous optimization of the intrinsic molecular sieving properties while also reducing the thickness of the CMS "skin" derived from the 6FDA : BPDA/DAM polyimide precursors. Such synergistic tuning of CMS microstructure and macroscopic morphology of CMS hollow fibers enables significantly increased propylene permeance (reaching 186.5 GPU) while maintaining an appealing propylene/propane selectivity of 13.3 for 50/50 propylene/propane mixed gas feeds. Our findings reveal a more refined and versatile tool than available with previous O2-doping pretreatments. The advanced approach here should be broadly useful to other polyimide precursors and diverse gas pairs.

Mind the Gap: The Role of Mass Transfer in Shaped Nanoporous Adsorbents for Carbon Dioxide Capture.

Adsorptive separations by nanoporous materials are major industrial processes. The industrial importance of solid adsorbents is only expected to grow due to the increased focus on carbon dioxide capture technology and energy-efficient separations. To evaluate the performance of an adsorbent and design a separation process, the adsorption thermodynamics and kinetics must be known. However, although diffusion kinetics determine the maximum production rate in any adsorption-based separation, this aspect has received less attention due to the challenges associated with conducting diffusion measurements. These challenges are exacerbated in the study of shaped adsorbents due to the presence of porosity at different length scales. As a result, adsorbent selection typically relies mainly on adsorption properties at equilibrium, i.e., uptake capacity, selectivity and adsorption enthalpy. In this Perspective, based on an extensive literature review on mass transfer of CO2 in nanoporous adsorbents, we discuss the importance and limitations of measuring diffusion in nanoporous materials, from the powder form to the adsorption bed, considering the nature of the process, i.e., equilibrium-based or kinetic-based separations. By highlighting the lack of and discrepancies between published diffusivity data in the context of CO2 capture, we discuss future challenges and opportunities in studying mass transfer across scales in adsorption-based separations.

Virus-Based Separation of Rare Earth Elements.

The utilization of biomaterials for the separation of rare earth elements (REEs) has attracted considerable interest due to their inherent advantages, including diverse molecular structures for selective binding and the use of eco-friendly materials for sustainable systems. We present a pioneering methodology for developing a safe virus to selectively bind REEs and facilitate their release through pH modulation. We engineered the major coat protein of M13 bacteriophage (phage) to incorporate a lanthanide-binding peptide. The engineered lanthanide-binding phage (LBPh), presenting ∼3300 copies of the peptide, serves as an effective biological template for REE separation. Our findings demonstrate the LBPh's preferential binding for heavy REEs over light REEs. Moreover, the LBPh exhibits remarkable robustness with excellent recyclability and stability across multiple cycles of separations. This study underscores the potential of genetically integrating virus templates with selective binding motifs for REE separation, offering a promising avenue for environmentally friendly and energy-efficient separation processes.

Empowering Capacitive Devices: Harnessing Transfer Learning for Enhanced Data-Driven Optimization.

Developing data-driven models has found successful applications in engineering tasks, such as material design, process modeling, and process monitoring. In capacitive devices like deionization and supercapacitors, there exists potential for applying this data-driven machine learning (ML) model in optimizing its potential use in energy-efficient separations or energy generation. However, these models are faced with limited datasets, and even in large quantities, the datasets are incomplete, limiting their potential use for successful data-driven modeling. Here, the success of transfer learning in resolving the challenges with limited datasets was exploited. A two-step data-driven ML modeling framework named ImputeNet involving training with ML-imputed datasets and then with clean datasets was explored. Through data imputation and transfer learning, it is possible to develop a data-driven model with acceptable metrics mirroring experimental measurements. By using the model, optimization studies using the genetic algorithm were implemented to analyze the solution under the Pareto optimality. This early insight can be used in the initial stage of experimental measurements to rapidly identify experimental conditions worthy of further investigation. Moreover, we expect that the insights from these results will drive accurate predictive modeling in other fields including healthcare, genomic data analysis, and environmental monitoring with incomplete datasets.

A different strategy to reduce energy consumption for designing heterogeneous decanter-assisted advanced pressure-swing distillation process

In this work, we aim to explore the feasibility of integrating two strategies, i.e., (1) introducing a small quantity of solvent as a makeup stream and (2) employing a decanter, to develop an energy-efficient pressure swing distillation process for ternary azeotropic separation. The addition of a minor amount of solvent aims to facilitate the transition of the feed composition from outside the liquid–liquid equilibrium region to within it. This transition could enable the use of a decanter, thereby promoting a more energy-efficient separation process with reduced reliance on pressure-driven mechanisms. A systematic approach was proposed to explore this concept, involving the different thermodynamic features for conceptual design followed by process optimization and process evaluation. This approach was exemplified using a mixture containing chloroform, ethanol, and water. Two solvent and decanter-assisted triple-column pressure-swing azeotropic distillation (SD-TCPSAD) process were developed and evaluated against the conventional triple-column pressure swing distillation in terms of economic, energy, and environmental performance. Among the three configurations, SD-TCPSAD I exhibited the most favorable outcomes, achieving a 61 %, 69 %, and 69 % improvement in economic, energy, and environmental impact. These improvements were primarily attributed to the utilization of smaller column sizes, the utilization of different heating utilities, and a substantial decrease in overall energy consumption.

Speleothem-Inspired Copper/Nickel Interfaces for Enhanced Liquid-Vapor Transport by Marangoni and Soret Effects.

Geological formations have superior wickability and support the absorption of water and oils into narrow spaces of Earth's crust without external assistance. In this study, we present speleothem inspired heterogeneous porous and wicked copper (Cu)/nickel (Ni) interfaces for enhanced nucleate boiling of water/ethanol mixtures for energy-efficient separation processes. The incorporation of Ni strands within the copper particle matrix significantly enhanced heat transfer. Compared to plain copper, the Cu/Ni speleothem surfaces exhibited a 61% increase in the heat transfer coefficient for water/ethanol mixtures and a 332% increase for water, with a 58% faster onset of nucleate boiling. This enhancement was attributed to Marangoni and Soret effects at the Cu/Ni interfaces, driven by surface tension and concentration gradients. Furthermore, the synergistic wicking action of the Ni strands facilitated rewetting of the surface, replenishing liquid to the porous nucleation sites and preventing surface dry-out, thereby improving the overall heat transfer performance.

Design of Mixed-Matrix MOF Membranes with Asymmetric Filler Density and Intrinsic MOF/Polymer Compatibility for Enhanced Molecular Sieving.

The separation of high-value-added chemicals from organic solvents is important for many industries. Membrane-based nanofiltration offers a more energy-efficient separation than the conventional thermal processes. Conceivably, mixed-matrix membranes (MMMs), encompassing metal-organic frameworks (MOFs) as fillers, are poised to promote selective separation via molecular sieving, synergistically combining polymers flexibility and fine-tuned porosity of MOFs. Nevertheless, conventional direct mixing of MOFs with polymer solutions results in underutilization of the MOF fillers owing to their uniform cross-sectional distribution. Therefore, in this work, a multizoning technique is proposed to produce MMMs with an asymmetric-filler density, in which the MOF fillers are distributed only on the surface of the membrane, and a seamless interface at the nanoscale. The design strategy demonstrates five times higher MOF surface coverage, which results in a solvent permeance five times higher than that of conventional MMMs while maintaining high selectivity. Practically, MOFs are paired with polymers of similar chemical nature to enhance their adhesion without the need for surface modification. The approach offers permanently accessible MOF porosity, which translates to effective molecular sieving, as exemplified by the polybenzimidazole and Zr-BI-fcu-MOF system. The findings pave the way for the development of composite materials with a seamless interface.

Fabrication of Two-Dimensional Material Membranes

Membrane separation is an energy-efficient separation process. Two-dimensional (2D) materials have shown potential as a new generation of membrane materials due to their unique structures and physicochemical properties. The separation performance of 2D material membranes crucially depends on how 2D nanosheets are assembled in membranes, such as interlayer spacing between stacked nanosheets, chemical properties of nanosheet surfaces, alignment of nanosheets and thickness of membranes, which are closely related to their fabrication methods. This short review concisely overviews commonly used membrane fabrication methods for different types of 2D materials, including graphene-based materials, 2D covalent organic frameworks, 2D metal-organic frameworks, MXenes and other 2D materials. The representative 2D material membranes resulting from their essential fabrication methods are discussed. The advantages and shortcomings of different fabrication methods are compared. The critical challenges to realising large-scale production of 2D material membranes for practical applications are highlighted.

Rigid-flexible coupled organosilica membranes toward high-efficiency molecules separation

Membrane-based technology has garnered significant interest in the separation and purification of molecules due to its inherent advantages, such as high efficiency, low energy consumption, and ease of operation. In this study, rigid-flexible coupled organosilica membranes were fabricated through co-polymerization using 1,2-bis(triethoxysilyl)acetylene (BTESA) containing rigid acetylene bridges and 1,2-bis(triethoxysilyl)propane (BTESP) containing flexible propane bridges. The incorporation of flexible propane bridges into BTESA networks allowed for precise adjustment of the network structures, resulting in composite BTESA-P membranes with improved molecular sieving properties. BTESA-P membrane demonstrated significant promise for applications in both CO2 capture and pervaporation (PV) dehydration due to its high potential. BTESA-P30 membrane, fabricated using the rigid-flexible coupled strategy, demonstrated a CO2 permeance of 3807 GPU and a CO2/N2 selectivity of approximately 40. These results surpassed those of numerous previously reported membranes, indicating significant potential for CO2 capture applications. BTESA-P30 membrane exhibited significant competitiveness in the decarbonization process of natural gas. More significantly, analogous occurrences are evident in gas permeation and PV separation process, where the permeation mechanism of gas and PV separation is primarily governed by molecular sieving. The utilization of diverse organosilica precursors in the rigid-flexible coupled strategy proposed in this study offers increased potential for membrane structure design and energy-efficient separation of molecules.

Removal of microparticles from hydrogenated oil by a microchannel separation coupling hydrocyclone: Industrial application

Separation techniques utilized in industrial manufacturing account for approximately 10–15% of the total global energy consumption. Energy-efficient separation has been made possible through the use of deep filtration technology. Herein, a novel continuous and regenerative microchannel separator coupled with a hydrocyclone was proposed. The microchannel separator, which had a processing capacity of 30 t/h, was constructed in a petroleum resin plant. This device could separate trace microfine particles in hydrogenated oil. After treatment with the microchannel separator, the average particle removal efficiency was 50.7%, and the turbidity of the hydrogenated oil was reduced by a maximum value of 60.9%. The removal efficiencies of pollutant particles with diameters smaller than 5 μm, in the range of 5–10 μm, and larger than 10 μm in the hydrogenated oil were 44.0%, 54.9%, and 75.9%, respectively. The processing load on the downstream diatomite filter was effectively reduced by the microchannel separator. The lifespan of the diatomite filter increased by 2.3 times compared to its initial value. Hazardous waste emissions decreased from 104 tons/year to 58.5 tons/year. The microchannel separator could be used not only for separating trace fine particles from liquids but also for separating oil and water by modulating the hydrophilic and hydrophobic properties of the particle surfaces.

COF/MXene composite membranes compact assembled by electrostatic interactions: A strategy for H2/CO2 separation

H2 and CO2 separation in processes such as reforming hydrocarbons or gasifying fossil fuels using membranes has gained attention as an energy-efficient separation method. Covalent organic frameworks (COFs) are a promising class of organic porous crystalline materials, but their pore sizes (typically >0.5 nm) exceed the kinetic diameters of H2 (0.289 nm) and CO2 (0.33 nm). Herein, we aimed to improve the H2/CO2 selectivity of COF (TpPa-1) membranes by fabricating a two-dimensional composite membrane. This strategy involved the compact assembly of mesoporous COF (TpPa-1) nanosheets facilitated by non-porous MXene (Ti3C2Tx), driven by electrostatic interactions. The objective was to reduce the pore sizes of gas transport channels, enabling molecular sieving for H2/CO2 separation. Additionally, strong adsorptive interactions between CO2 and the COF/MXene composite membranes were leveraged to impede the transport of CO2 molecules. The results demonstrated that the 2D COF/MXene composite membranes with a Ti3C2Tx doping amount of 65 wt% achieved the highest H2/CO2 selectivity of 64.0 at 298 K, which was 5.67 times that of the pristine COF (TpPa-1) membrane. The H2 permeance reached 2.35 × 10−7 mol m−2 s−1 Pa−1, surpassing the latest Robeson upper bound. This innovative strategy not only presents a high-performance candidate for H2/CO2 separation but also provides inspiration for pore regulation of COF compactly assembled with non-porous MXene through electrostatic interactions.

Separation of Biobased Carboxylic Acids by Aqueous Phase Nanofiltration

AbstractNanofiltration is an energy efficient separation technology with yet not fully explored potential for in situ product recovery from fermentation solutions. In this work, a commercially available cellulose acetate nanofiltration membrane was investigated to separate different carboxylic acids from glucose in an aqueous solution. The membrane showed a high stability and good separation performance at low pH. Dead‐end and cross‐flow experiments revealed the transferability to real fermentation mixtures and demonstrate the possibility of coupling fermentation with in situ product separation.

Machine Learning-Assisted Discovery of Propane-Selective Metal-Organic Frameworks.

Machine learning is gaining momentum in the prediction and discovery of materials for specific applications. Given the abundance of metal-organic frameworks (MOFs), computational screening of the existing MOFs for propane/propylene (C3H8/C3H6) separation could be equally important for developing new MOFs. Herein, we report a machine learning-assisted strategy for screening C3H8-selective MOFs from the CoRE MOF database. Among the four algorithms applied in machine learning, the random forest (RF) algorithm displays the highest degree of accuracy. We experimentally verified the identified top-performing MOF (JNU-90) with its benchmark selectivity and separation performance of directly producing C3H6. Considering its excellent hydrolytic stability, JNU-90 shows great promise in the energy-efficient separation of C3H8/C3H6. This work may accelerate the development of MOFs for challenging separations.

Melt stability of carbonic anhydrase in polyethylene oxide for extrusion of protein–polymer composite materials

Enzymatic membranes manufactured via hot melt extrusion present an exciting, scalable route towards energy efficient separations.