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A special issue of Separations (ISSN 2297-8739). This special issue belongs to the section "Environmental Separations".

Deadline for manuscript submissions: closed (23 June 2023) | Viewed by 30461

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Prof. Dr. Yundong Wang

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The State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
Interests: solvent extraction; adsorption; absorption; fluid mixing and CFD simulations

Special Issue Information

Dear Colleagues,

This Special Issue focuses on a wide range of topics relevant to cutting-edge research, new technologies, and emerging growth areas in separation engineering. It strongly promotes international academic exchanges and collaborations. It is intended to bring together investigations from multiple disciplines to discuss recent advances in separation engineering. Topics of interest include but are not limited to:

Phase equilibria;
Transport phenomena;
Distillation and absorption;
Extraction;
Crystallization;
Membrane separation;
Bioseparation;
Novel separation materials, process and applications.

We seek contributions dealing with all aspects from fundamental to applied research in separation engineering and relevant fields.

Prof. Dr. Yundong Wang
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Separations is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

absorption
absorbent
adsorption
bioseparation
crystallization
distillation
extraction
extractant
membrane
modelling
separation agents

Published Papers (13 papers)

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Research

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14 pages, 3960 KiB

Open AccessArticle

Stripping Enhanced Distillation—A Novel Application in Renewable CO₂ to Dimethyl Ether Production and Purification

by Vladimir Dikić, Lawien Zubeir, Marija Sarić and Jurriaan Boon

Separations 2023, 10(7), 403; https://doi.org/10.3390/separations10070403 - 13 Jul 2023

Cited by 2 | Viewed by 1604

Abstract

The transition towards a CO₂ neutral industry is currently spurring many new developments regarding processes for the conversion of CO₂, or CO₂-rich streams, into platform molecules such as methanol and dimethyl ether (DME). New processes give rise to new separation challenges, as well as novel opportunities for joint optimization of reaction and separation. In this context, the separation of CO₂ and DME can be performed very efficiently using the newly developed concept of stripping enhanced distillation (SED). SED is a distillation process that utilizes an additional stripping component (clearing gas) to promote the separation in the column. SED benefits from the utilization of the feedstock components as a clearing gas that can afterwards be recycled back to the conversion unit with the vapor distillate. Strongly improving the separation performance in the column, this approach also removes the need for external stripping mediums and, in addition, this recycling approach may significantly reduce the demand on the conversion unit upstream of SED. The benefits of using SED are demonstrated for two different processes for DME synthesis: (i) CO₂–DME separation after the sorption enhanced DME synthesis (SEDMES) process, using hydrogen as clearing gas, and (ii) CO₂–DME separation after direct DME synthesis via dry reforming (DIDR), using methane as a clearing gas. For the different cases, it is shown that, with minimal adaptations, the energy consumption for distillation is reduced by 20–30%, while product losses are minimized at the same time. Full article

(This article belongs to the Special Issue Advances in Separation Engineering)

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22 pages, 32262 KiB

Open AccessArticle

CFD Simulation and Optimal Design of a New Parabolic–Shaped Guided Valve Tray

by Qiliang Ye, Chenyu Wang, Hao Sun, Yu’an Li and Peiqing Yuan

Separations 2023, 10(4), 267; https://doi.org/10.3390/separations10040267 - 20 Apr 2023

Cited by 1 | Viewed by 1379

Abstract

A new parabolic–shaped guided valve tray is proposed. The gas–liquid two–phase flow of parabolic and conventional rectangular guided valve trays is simulated using the computational fluid dynamics (CFD) method. The clear liquid height on the tray was predicted for different combinations of the superficial gas velocity, liquid flow intensity and weir height. The predicted values were in good agreement with the calculated ones. The parabolic–shaped guided valve tray has a more uniform flow form by comparing the gas–liquid two–phase flow behavior of parabolic and rectangular guided valve trays: the liquid level difference is slight, the guiding effect is strong, and the re–mixing phenomenon is improved. Further modeling and simulations were conducted for nine parabolic–shaped guided valve trays of different function expressions. The optimum valve structure is the parabolic–shaped guided valve of the a–value at 0.075 and the t–value at 26. Full article

(This article belongs to the Special Issue Advances in Separation Engineering)

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14 pages, 6237 KiB

Open AccessArticle

Fabrication of Organic Solvent Nanofiltration Membrane through Interfacial Polymerization Using N-Phenylthioure as Monomer for Dimethyl Sulfoxide Recovery

by Ayang Zhou, Guangle Hu, Keying Guo, Mengnan Zhang and Xiangnan Liu

Separations 2023, 10(3), 179; https://doi.org/10.3390/separations10030179 - 07 Mar 2023

Viewed by 1598

Abstract

To recover dimethyl sulfoxide, an organic solvent nanofiltration membrane is prepared via the interfacial polymerization method. N-Phenylthiourea (NP)is applied as a water-soluble monomer, reacted with trimesoyl chloride (TMC) on the polyetherimide substrate crosslinked by ethylenediamine. The results of attenuated total reflectance-fourier transform infrared spectroscopy and X-ray electron spectroscopy confirm that N-Phenylthiourea reacts with TMC. The membrane morphology is investigated through atomic force microscopy and scanning electronic microscopy, respectively. The resultant optimized TFC membranes NF-1NP exhibited stable permeance of about 4.3 L m⁻² h⁻¹ bar^-1 and rejection of 97% for crystal violet (407.98 g mol⁻¹) during a 36 h continuous separation operation. It was also found that the NF-1NP membrane has the highest rejection rate in dimethyl sulfoxide (DMSO), and the rejection rates in methanol, acetone, tetrahydrofuran, ethyl acetate and dimethylacetamide(DMAc) are 51%, 84%, 94%, 96% and 92% respectively. The maximum flux in the methanol system is 11 L m⁻² h⁻¹ bar⁻¹, while that in acetone, tetrahydrofuran, ethyl acetate and DMAc is 4.3 L m⁻² h⁻¹ bar⁻¹, 6.3 L m⁻² h⁻¹ bar⁻¹, 3.2 L m⁻² h⁻¹ bar⁻¹, 4.9 L m⁻² h⁻¹ bar⁻¹ and 2.1 L m⁻² h⁻¹ bar⁻¹, respectively. It was also found that the membrane prepared by N-Phenylthiourea containing aromatic groups has lower mobility and stronger solvent resistance than that of by thiosemicarbazide. Full article

(This article belongs to the Special Issue Advances in Separation Engineering)

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13 pages, 3220 KiB

Open AccessArticle

Preparation, Phase Diagrams and Characterization of Fatty Acids Binary Eutectic Mixtures for Latent Heat Thermal Energy Storage

by Dongyi Zhou, Shuaizhe Xiao, Xianghua Xiao and Yicai Liu

Separations 2023, 10(1), 49; https://doi.org/10.3390/separations10010049 - 12 Jan 2023

Cited by 2 | Viewed by 2060

Abstract

A series of fatty acid binary eutectic mixtures were prepared by using capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid (CA, LA, MA, PA, and SA) as raw materials. The phase diagrams of these fatty acid binary eutectic mixtures were drawn using the Schrader equation. The thermal properties and structure were determined using differential scanning calorimetry (DSC). The thermal stability was assessed using thermogravimetric analysis (TGA) and thermal cycling tests. DSC analysis results showed that the phase change temperature of these fatty acid binary eutectic mixtures is between 17.7 °C and 57.1 °C, and the phase change latent heat is between 145.2 J/g and 193.0 J/g. The results of TGA and thermal cycle tests showed that these fatty acid binary eutectic mixtures have good thermal stability and long-term cycle thermal reliability. These results indicated that these binary eutectic mixtures of fatty acids were suitable as thermal energy storage materials for low-temperature systems. Full article

(This article belongs to the Special Issue Advances in Separation Engineering)

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10 pages, 7360 KiB

Open AccessArticle

Application of Gas Chromatography Mass Spectrometry in Tar Analysis from Underground Gasification

by Lele Feng, Jie Liu, Haihui Xin and Jiabao Pang

Separations 2023, 10(1), 12; https://doi.org/10.3390/separations10010012 - 26 Dec 2022

Cited by 4 | Viewed by 1584

Abstract

The study of tar behaviors in underground coal gasification (UCG) is essential for pollution control, system safety and conversion efficiency; however, existing studies have only focused on tar in products without revealing tar evolution in the reaction zone, and the experimental conditions in reported work are far from those in the real situation. In this work, tar behaviors were studied with a self-developed apparatus to simulate the UCG process. During the experiments, the sampling method along the gasification channel was used to collect tar at different positions; the gasification object was a large raw coal block 460 mm × 230 mm × 230 mm in size, and the flow rate of the inlet gas was adjusted according to the composition of products. The tar samples were not only taken from the outlet, but also from the reaction zone, and then analyzed using gas chromatography mass spectrometry. For all the tar samples, C₁₅H₁₃N and its isomer were the most abundant compounds, with a total percentage greater than 14%. Most of the top five chemicals contained more than nine carbon atoms in their molecular formulae, indicating that more heavy tar than light tar is formed by low-temperature pyrolysis. Compared with the upstream tar, the downstream tar had fewer PAHs and a lower boiling point, due to the decomposition of the heavy tar. The downstream tar contained more of the element fluorine (F) than upstream and outlet tars, indicating that tar pollution remaining in the reaction zone cannot be evaluated by monitoring the outlet tar. Full article

(This article belongs to the Special Issue Advances in Separation Engineering)

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21 pages, 6019 KiB

Open AccessArticle

A Novel Method for Simulating Micro-Scale Water Droplet Movements

by Zhijie Lin, Zhongtian Hu, Senyu Lou, Lingling Guo and Jingjing Chen

Separations 2022, 9(12), 451; https://doi.org/10.3390/separations9120451 - 19 Dec 2022

Viewed by 1357

Abstract

Micro-scale fluids are tiny droplets that adhere to the surface of an object as a result of rainfall, perspiration, etc. Micro-scale fluid simulation is widely used in fields such as film and games. The existing state-of-the-art simulation methods are not suitable for simulating water droplets moving on a surface due to the fact that the water droplets cannot leave the texture space and their movements always depend on the continuous UV region. In this study, a novel method for simulating water droplets moving on a surface is proposed. We divide the droplets into two types: (1) two-dimensional droplets and (2) three-dimensional droplets and we implement the transformation between two-dimensional droplets in the texture space and three-dimensional droplets in the physical space. In the preprocessing phase, jump textures, coordinate transform textures and force field textures are generated in the non-continuous UV regions on a 3D object’s surface. In the process of simulation, water droplets are treated as rigid particles. The Velocity-Verlet-based method is adopted to solve the motion trajectory equation, and the boundary droplet transport algorithm is implemented based on jump texture. In the process of rendering, the height map is generated according to the simulation in the texture space and then the liquid bridge phenomenon between the droplets is simulated based on the Gaussian blur and the color rank algorithm. Finally, they are converted into normal texture-rendering droplets. The experimental result shows that the proposed method works well when simulating the movements of water droplets on a surface in a real-time manner, and it makes the movement simulation of dimension-reducing water droplets no longer depend on the continuous surface and continuous UV region. Moreover, the simulation efficiency of the proposed method is two times higher than that of the Smoothed Particle Hydrodynamics (SPH) method. Full article

(This article belongs to the Special Issue Advances in Separation Engineering)

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14 pages, 2629 KiB

Open AccessArticle

Saline Diffusion Modeling for Sodium Chloride Aqueous Solutions: Freezing for Desalination Purposes

by Beatriz Castillo-Téllez, Rosenberg J. Romero, Karim Allaf and Isaac Pilatowsky-Figueroa

Separations 2022, 9(10), 272; https://doi.org/10.3390/separations9100272 - 30 Sep 2022

Cited by 3 | Viewed by 1640

Abstract

Given the high human demand for freshwater and its consequent scarcity, desalination processing seems to be a key solution, given the vast amount of seawater on the planet. Currently, desalination plants provide about 95 million m³/day freshwater in 177 countries worldwide. However, desalination is an energy-intensive, demanding technique that generally uses fossil fuels and contributes to global warming via greenhouse gas emissions. Freezing/melting desalination (F/M) uses about 70% less thermal energy than the boiling process. Unfortunately, this technique is rarely used, mainly because of salt separation problems at low temperatures close to 0 °C. Most models have determined their results assuming a saline concentration value of the retained liquid; however, there is a significant disagreement in this value. This study proposes a unidimensional model based on thermal and mass diffusion evolution. The model predicts the successful separation of salt-free ice to avoid salt diffusion before encapsulation; the process depends on temperature, saline gradients, and time. The calculations in this paper are based on the salt concentration in the liquid-solid interface, which has been extensively studied, achieving an accurate performance of the proposed model. Full article

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13 pages, 1793 KiB

Open AccessArticle

High-Purity Corundum as Support for Affinity Extractions from Complex Samples

by Jule L. Völzke, Parya Hodjat Shamami, Kornelia Gawlitza, Ines Feldmann, Annett Zimathies, Klas Meyer and Michael G. Weller

Separations 2022, 9(9), 252; https://doi.org/10.3390/separations9090252 - 07 Sep 2022

Cited by 1 | Viewed by 1953

Abstract

Nonporous corundum powder, known as an abrasive material in the industry, was functionalized covalently with protein binders to isolate and enrich specific proteins from complex matrices. The materials based on corundum were characterized by TEM, ESEM, BET, DLS, EDS, and zeta potential measurements. The strong Al-O-P bonds between the corundum surface and amino phosphonic acids were used to introduce functional groups for further conjugations. The common crosslinker glutaraldehyde was compared with a hyperbranched polyglycerol (PG) of around 10 kDa. The latter was oxidized with periodate to generate aldehyde groups that can covalently react with the amines of the surface and the amino groups from the protein via a reductive amination process. The amount of bound protein was quantified via aromatic amino acid analysis (AAAA). This work shows that oxidized polyglycerol can be used as an alternative to glutaraldehyde. With polyglycerol, more of the model protein bovine serum albumin (BSA) could be attached to the surface under the same conditions, and lower non-specific binding (NSB) was observed. As a proof of concept, IgG was extracted with protein A from crude human plasma. The purity of the product was examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). A binding capacity of 1.8 mg IgG per gram of corundum powder was achieved. The advantages of corundum include the very low price, extremely high physical and chemical stability, pressure resistance, favorable binding kinetics, convenient handling, and flexible application. Full article

(This article belongs to the Special Issue Advances in Separation Engineering)

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16 pages, 7008 KiB

Open AccessArticle

Numerical Simulation of Dense Solid-Liquid Mixing in Stirred Vessel with Improved Dual Axial Impeller

by Xia Xiong, Zuohua Liu, Changyuan Tao, Yundong Wang and Fangqin Cheng

Separations 2022, 9(5), 122; https://doi.org/10.3390/separations9050122 - 16 May 2022

Cited by 4 | Viewed by 2446

Abstract

Computational fluid dynamics (CFDs) were adopted in order to investigate the solid suspending process in a dense solid–liquid system (with a solid volume fraction of 30%), agitated by a traditional dual axial impeller and a modified dual axial impeller, otherwise known as a dual triple blade impeller (DTBI) and a dual rigid-flexible triple blade impeller (DRFTBI), respectively. The effects of rotational speed, connection strap length/width, and off-bottom clearance on the solid distribution were investigated. The results show that the proportion of solid concentration larger than 0.4 in the DTBI system was 26.56 times of that in the DRFTBI system. This indicates that the DRFTBI system can strengthen the solid suspension and decrease the solid accumulation in the bottom of the tank. Furthermore, the velocity and turbulent kinetic energy in the DRFTBI system were promoted. In addition, for an optimal selection, the optimum length of connection strap was 1.2 H₁, the optimum range of connection strap width was D/7–D/8, and the off-bottom clearance selected as T/4 was better. Full article

(This article belongs to the Special Issue Advances in Separation Engineering)

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Review

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30 pages, 3393 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Mass Transfer and Droplet Behaviors in Liquid-Liquid Extraction Process Based on Multi-Scale Perspective: A Review

by Sicen Yu, Jiyizhe Zhang, Shaowei Li, Zhuo Chen and Yundong Wang

Separations 2023, 10(4), 264; https://doi.org/10.3390/separations10040264 - 18 Apr 2023

Cited by 2 | Viewed by 4064

Abstract

Liquid-liquid extraction is an important separation technology in the chemical industry, and its separation efficiency depends on thermodynamics (two-phase equilibrium), hydrodynamics (two-phase mixing and contact), and mass transfer (molecular diffusion). For hydrodynamics, the dispersion size of droplets reflects the mixing of two phases and determines the mass transfer contact area of the two phases. Therefore, a deep understanding of the droplet dispersion mechanism can help guide process intensification. The mass transfer and droplet behaviors in the liquid-liquid extraction process are reviewed based on three scales: equipment, droplets, and the interface between two liquids. Studies on the interaction between mass transfer and other performance parameters in extraction equipment as well as liquid-liquid two-phase flow models are reviewed at the equipment scale. The behaviors of droplet breakage and coalescence and the kernel function of the population balance equation are reviewed at the droplet scale. Studies on dynamic interfacial tension and interaction between interfaces are reviewed at the interface scale. Finally, the connection among each scale is summarized, the existing problems are analyzed, and some future research directions are proposed in the last section. Full article

(This article belongs to the Special Issue Advances in Separation Engineering)

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15 pages, 7415 KiB

Open AccessEditor’s ChoiceReview

Steric Exclusion Chromatography for Purification of Biomolecules—A Review

by Jennifer J. Labisch, G. Philip Wiese and Karl Pflanz

Separations 2023, 10(3), 183; https://doi.org/10.3390/separations10030183 - 08 Mar 2023

Cited by 2 | Viewed by 2541

Abstract

Steric exclusion chromatography (SXC) is a purification method that is based on steric exclusion effects from the surface of the target and a hydrophilic stationary phase after the addition of polyethylene glycol (PEG), which leads to an association of the target with the stationary phase without direct binding, such as covalent, electrostatic, and hydrophilic/hydrophobic interactions. The gentle nature of the method has led to an increased focus on sensitive targets such as enveloped viruses with potential for other sensitive entities, e.g., extracellular vesicles and virus-like particles. SXC is related to PEG-mediated protein precipitation, but investigation of further process parameters was crucial to gain a better understanding of the SXC method. After explaining mechanistic fundamentals and their discovery, this review summarizes the findings on SXC from its first reference 11 years ago until today. Different applications of SXC are presented, demonstrating that the method can be used for a wide variety of targets and achieves high recovery rates and impurity removal. Further, critical process parameters for successful process implementation are discussed, including technical requirements, buffer composition, and scalability. Full article

(This article belongs to the Special Issue Advances in Separation Engineering)

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20 pages, 3965 KiB

Open AccessReview

Preparation and Application of Graphene–Based Materials for Heavy Metal Removal in Tobacco Industry: A Review

by Xiaojiang Xu, Junling Zeng, Yue Wu, Qiaoying Wang, Shengchao Wu and Hongbo Gu

Separations 2022, 9(12), 401; https://doi.org/10.3390/separations9120401 - 01 Dec 2022

Cited by 8 | Viewed by 2721

Abstract

Heavy metals are nondegradable in the natural environment and harmful to the ecological system and human beings, causing an increased environmental pollution problem. It is required to remove heavy metals from wastewater urgently. Up until now, various methods have been involved in the heavy metal removals, such as chemical precipitation, chemical reduction, electrochemical, membrane separation, ion exchange, biological, and adsorption methods. Among them, adsorption by graphene–based materials has attracted much more attentions for the removal of heavy metals from wastewater systems in recent years, arising due to their large specific surface area, high adsorption capacity, high removal efficiency, and good recyclability. Therefore, it is quite important to review the heavy metal removal with the graphene–based material. In this review, we have summarized the physicochemical property and preparation methods of graphene and their adsorption property to heavy metals. The influencing parameters for the removal of heavy metals by graphene–based materials have been discussed. In addition, the modification of graphene–based materials to enhance their adsorption capability for heavy metal removal is also reviewed. The heavy metal removal by modified graphene–based materials in the tobacco industry has been especially described in detail. Finally, the future trend for graphene–based materials in the field of heavy metal wastewater treatment is proposed. This knowledge will have great impacts on the field and facilitate the researchers to seek the new functionalization method for graphene–based materials with high adsorption capacity to heavy metals in the tobacco industry in the future. Full article

(This article belongs to the Special Issue Advances in Separation Engineering)

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17 pages, 4397 KiB

Open AccessEditor’s ChoiceReview

Review of Hydrogen Sulfide Removal from Various Industrial Gases by Zeolites

by Tao Yu, Zhuo Chen, Zhendong Liu, Jianhong Xu and Yundong Wang

Separations 2022, 9(9), 229; https://doi.org/10.3390/separations9090229 - 25 Aug 2022

Cited by 10 | Viewed by 4437

Abstract

Hydrogen sulfide (H₂S) removal from various industrial gases is crucial because it can cause huge damage to humans, the environment, and industrial production. Zeolite possesses huge specific surface area and well-developed pore structure, making it a promising adsorbent for H₂S removal. This review attempts to comprehensively compile the current studies in the literature on H₂S removal in gas purification processes using zeolites, including experimental and simulation studies, mechanism theory, and practical applications. Si/Al ratio, cations of zeolite, industrial gas composition and operating conditions, and H₂S diffusion in zeolites affect desulfurization performance. However, further efforts are still needed to figure out the influence rules of the factors above and H₂S removal mechanisms. Based on an extensive compilation of literature, we attempt to shed light on new perspectives for further research in the future. Full article

(This article belongs to the Special Issue Advances in Separation Engineering)

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