Advanced Separation Techniques Research Articles

Coupling Multidimensional Chromatography with Plasmonic Sensing: An Exploration of Electrochemical SERS as a Detection Modality for 2D-LC

Complex mixtures which may contain hundreds, if not thousands, of unique compounds pose an analytical challenge for complete and detailed analyses. For example, green tea is a well-known complex substance requiring advanced separation techniques and ultrasensitive detection methods for full characterization. Separation and identification of components in green tea help gauge tea quality, as green tea is one of the most consumed beverages in the world. In this work, the coupling of two-dimensional liquid chromatography (2D-LC) and electrochemical surface-enhanced Raman spectroscopy (EC-SERS) was explored for the first time to analyze compounds in green tea. 2D-LC offers enhanced separation compared to conventional HPLC systems due to the second dimension of separation. EC-SERS was used as an offline detection modality and qualitative tool to help identify the compounds in green tea fractions collected from the second dimension separation. 2D-LC and EC-SERS are coupled in this work for the first time and offer a pathway forward for sensitive and selective separation and identification of components in complex mixtures.

Greening the supply chain: Sustainable approaches for rare earth element recovery from neodymium iron boron magnet waste

The increasing demand for modern technologies has led to a growing reliance on rare earth elements (REEs). To address this issue, recycling used products such as permanent magnet waste containing REEs. However, this approach necessitates the development of advanced extraction and separation techniques to ensure high yields and purity of the REEs extracted. This review provides an overview of the latest extraction and separation technologies, with a particular focus on the hydrometallurgical approach for extracting REEs from secondary sources, notably permanent magnets. Hydrometallurgy, which involves leaching followed by solvent extraction for purification, has gained widespread use for obtaining REEs from secondary sources, as evidenced by its reported high recovery efficiencies. We found that the recovery of REEs using chemical leaching varied between 80% and 99%, influenced by factors such as type of source material, leaching solvent, leaching conditions, impurities, reaction kinetics and solid-liquid ratio. However, effectively employing this process on a larger scale still faces certain challenges due to the excessive use of corrosive solvents for leaching magnet waste and the generation of toxic chemicals as end products in the form of leachate. Additionally, the current process exhibits deficiencies in the targeted recovery of REEs from magnet waste, specifically in achieving purity and selectivity by eliminating iron impurities. This article concludes that the future prospects for the selective recovery of REEs from neodymium iron boron magnet waste lie in green and environment-friendly solvents. One such approach revolves around the utilization of biodegradable organic acids and salt aqua regia for leaching. These solvents are less corrosive and have high dissolution efficiency, which results in less chemical consumption and an overall environment-friendly and cost-effective recovery process.

Application of dodecyl amine/dodium petroleum sulfonate mixed collector in quartz-feldspar flotation separation

It’s highly challenging to separate feldspar from quartz by flotation owing to their similar crystal structure and physicochemical properties. Using mixed collectors has become a promising method to improve the quartz-feldspar separation. In this study, mixed dodecyl amine (DDA) and sodium petroleum sulfonate (SPS) surfactants were used in the flotation separation of feldspar and quartz, and the adsorption mechanism of mixed collectors and depression mechanisms of two depressants were investigated through zeta potential, contact angle and Fourier transform infrared (FT-IR) spectra. When the pH reached 4.5, the separation of feldspar from quartz was more obvious. In the presence of DDA/SPS collector, the contact angle of feldspar was increased more obviously leading to enhance hydrophobicity. The infrared spectra revealed the interaction of collectors on feldspar surface involved physical and chemical adsorption, whereas the adsorption of collector on quartz was only physical interactions. The use of sodium hexametaphosphate resulted in a significantly enhanced separation performance. The weaker physical adsorption of mixed collector on quartz can be destroyed by sodium hexametaphosphate. This study is beneficial for understanding the collect mechanisms of mixed cationic-anionic surfactants on quartz and feldspar minerals, and promotes the development of advanced feldspar separation techniques.

Reactivity of Monoethanolamine at the Air-Water Interface and Implications for CO2 Capture.

The development of CO2-capture technologies is key to mitigating climate change due to anthropogenic greenhouse gas emissions. These cover a number of technologies designed to reduce the level of CO2 emitted into the atmosphere or to eliminate CO2 from ambient air. In this context, amine-based sorbents in aqueous solutions are broadly used in most advanced separation techniques currently implemented in industrial applications. It has been reported that the gas/liquid interface plays an important role in the early stages of the capture process, but how the interface influences the chemistry is still a matter of debate. With the help of first-principles molecular dynamics simulations, we show that monoethanolamine (MEA), a prototypical sorbent molecule, has a weak affinity for the air-water interface, where in addition it exhibits a lower nucleophilicity compared to bulk solution. The change in reactivity is due to the combination of structural and electronic factors, namely, the shift of the conformational equilibrium and the stabilization of the N-atom lone pair. Based on these results, strategies for improving the efficiency of alkanolamine sorbents are proposed.

Analysis of Softwood Lignans by Comprehensive Two-Dimensional Liquid Chromatography.

Lignans constitute a large group of phenolic plant secondary metabolites possessing high bioactivity. Their accurate determination in plant extracts with a complex chemical composition is challenging and requires advanced separation techniques. In the present study, a new approach to the determination of lignans in coniferous knotwood extracts as the promising industrial-scale source of such compounds based on comprehensive two-dimensional liquid chromatography separation and UV spectrophotometric detection is proposed. First and second-dimension column screening showed that the best results can be obtained using a combination of non-polar and polar hydroxy group embedded octadecyl stationary phases with moderate (~40%) "orthogonality". The optimization of LC × LC separation conditions allowed for the development of a new method for the quantification of the five lignans (secoisolariciresinol, matairesinol, pinoresinol, 7-hydroxymatairesinol, and nortrachelogenin) in knotwood extracts with limits of quantification in the range of 0.27-0.95 mg L-1 and a linear concentration range covering at least two orders of magnitude. Testing the developed method on coniferous (larch, fir, spruce, and pine) knotwood extracts demonstrated the high selectivity of the analysis and the advantages of LC × LC in the separation and accurate quantification of the compounds co-eluting in one-dimensional HPLC.

Integrating reaction pathways and downstream separation network for optimal sustainable process route selection

Reducing the environmental impact of chemical production has become a critical objective due to carbon emission regulations and the challenges the carbon market poses. Downstream separation network optimization, which can improve process sustainability by using complex heat exchanger networks, applying advanced separation techniques, optimizing the design/operating parameters, etc., has been researched for many years. However, most optimization work focuses solely on downstream separation sections without considering the selection of raw materials and different reaction pathways. This work aims to develop a mixed integer nonlinear programming (MINLP) optimization model, which integrates reaction pathway selection and downstream separation optimization, to select the optimal sustainable process route for utilizing raw materials or producing products. The objective is to maximize/minimize the process profit/cost. Decision variables such as binary variables, which represent the selection of separation task, key component, heating utility, and continuous variables, which influence the separation mass/energy balance, are considered. By giving parameters like reaction conversion rate, selectivity, and raw material/product price, this optimization model can identify the optimal process route for producing a target product or utilizing a raw material. The optimization model was applied to two case studies: one-step isobutylene and methanol utilization and two-step 1,4-butanediol (BDO) production. The process routes, using isobutylene for pivalic acid production and methanol for gasoline production, have the highest process profit per carbon emission. And the process route, which uses acetylene for BDO production, leads to minimum process cost.

20 Years of polyolefin HPLC: Accomplishments and challenges

The first publication on the interaction of polyolefins with stationary phases for high performance liquid chromatography at high temperatures (HT-HPLC) appeared in 2003. After the successful application of temperature rising elution fractionation and the introduction of crystallization fractionation for the analysis of polyolefins with regard to chemical composition this was a step towards methods for chemical composition analysis that are not based on crystallizability of the polyolefin. Polyolefins as semicrystalline polymers comprise crystallizable and amorphous components, and HT-HPLC opened the way to separate all sample components irrespective of their crystallizability. The first application of this new approach was the separation of ethylene–methyl methacrylate block copolymers, presented in 2005. The development of the first commercial HT-HPLC instrument and the discovery of graphitic materials as efficient stationary phases for HT-HPLC were further important milestones in the development of advanced separation techniques for complex polyolefins. The ultimate goal of comprehensively analyzing complex polyolefins by composition and molar mass was achieved by high temperature two-dimensional chromatography, which is based on the online coupling of HT-HPLC and HT-SEC. Further important developments include HT-HPLC using temperature gradients and the combination of solvent and temperature gradients. In this review, the most important developments in the field over the last 20 years are discussed, and different techniques, experimental protocols and some major applications are presented. In conclusion, challenges for future developments are outlined.

Analytical and Preparative Separation of Softwood Lignans by Supercritical Fluid Chromatography

Lignans are widespread polyphenolic secondary plant metabolites possessing high biological activity. One of the most promising industrial-scale sources of such compounds is coniferous knotwood, containing a large number of polyphenolic compounds. Their use in pharmaceutical and other industries is limited by the difficulty in obtaining high-purity preparations from plant material and the requirement of advanced separation techniques. In this study, supercritical fluid chromatography on polar stationary phases was proposed for the efficient separation and identification of spruce, pine, fir, and larch knotwood extractives. Among the six tested sorbents, the best results were shown by silica with grafted diol and 2-ethylpyridine groups under conditions of gradient elution with a carbon dioxide–methanol mobile phase, which ensured the efficient retention and separation of analytes due to donor–acceptor interactions. Scaling up the method on a DIOL stationary phase provided a semi-preparative separation of extractives within 30 min to obtain 14 individual compounds with a purity of 90–99% and yields from 0.3 to 51% of the dry extract. These included eight lignans (nortrachelogenin, matairesinol, oxomatairesinol, α-conidendrin, 5-hydroxymatairesinol and its isomer, lariciresinol, and secoisolariciresinol), two oligolignans, three stilbenes (pinosylvin and its methyl ester, pterostilbene), and flavonoid taxifolin. The developed approach is distinguished with low operational costs, low consumption of organic solvents, environmental safety, and it is fully consistent with the principles of green chemistry.

Unraveling the comonomer distribution in ethylene – vinyl ester terpolymers through liquid chromatography with infrared detection

Polyolefins are the most commercially relevant polymers by volume. A readily available feedstock and their tailor-made microstructure allow to adapt polyolefins to many fields of application. Important molecular design features of olefin copolymers are the molar mass distribution (MMD) with the corresponding average values, comonomer type, chemical composition distribution (CCD) with the corresponding average and the tacticity distribution (TD). Advanced separation techniques i.e., high-temperature gel permeation chromatography (HT-GPC) as well as its hyphenation with high-temperature high performance liquid chromatography (HT-HPLC) in the form of high-temperature two-dimensional liquid chromatography (HT 2D-LC) have been successfully applied in this work. This allowed to deeply analyze the molecular heterogeneities of complex polyolefin terpolymers consisting of ethylene, vinyl acetate and branched vinyl ester monomers. By using filter-based infrared detection, the capabilities of HT-GPC are further extended so that the distribution of methyl- and carbonyl groups could be obtained along the molar mass axis. Using porous graphitic carbon (PGC) as a stationary phase for HT-HPLC separation provided information about the CCD of these complex polyolefins from experimental data as part of the hyphenated approach of HT 2D-LC. The latter revealed the full MMD x CCD distribution function, which is the key for a comprehensive analysis of the bivariate molecular structure of the polyolefin terpolymers.

Advanced downstream processing of bioethanol from syngas fermentation

Syngas fermentation is used industrially to produce diluted bioethanol (about 1–6 wt%). This research study proposes a novel downstream process that recovers bioethanol in an energy-efficient and cost-effective manner, improves fermentation yield by recycling all fermentation broth components (microbes, acetate and water), and is designed for full-scale industrial-level application. Therefore, vacuum distillation at fermentation temperature was conceptually studied as an initial ethanol recovery step, leading to a bottom stream that may be recycled. Advanced separation and purification techniques were designed to recover 99.5% of initially present ethanol as high-purity product (99.8 wt%). Mechanical vapor recompression and heat integration methods were used to maximize sustainability and eco-efficiency of the proposed recovery process. Implementation of these techniques on a process using 6 wt% ethanol feed stream decreased the total annual costs by 54.2% (from 0.175 to 0.080 $/kgEtOH), reduced the primary energy requirement by 66.1% (from 2.82 to 0.96 kWthh/kgEtOH), lowered the CO2 emission by up to 82.6% (from 0.414 to 0.072 kgCO2/kgEtOH), and reduced the fresh water usage by 62.6% (from 0.242 to 0.091 m3W/kgEtOH). Sensitivity analysis for ethanol concentrations ranging from 6 to 1 wt% showed that the recovery costs and energy use increased to 0.336 $/kgEtOH and 1.78 kWthh/kgEtOH respectively. Since ethanol recovery performs better but fermentation will perform worse at higher ethanol concentration in fermentation broth, there is a trade-off concentration for the overall process. The current analysis is an important step toward determining this trade-off.

Application of an electro elution system for direct purification of linear covalently closed DNA fragments

Gene therapy is a powerful treatment modality. Non-viral gene therapy vectors power one arm of this important approach, due to their enhanced safety profile compared to their viral counterparts. New non-viral approaches continue to be developed, but purification can bottleneck the scaleup and cost-effectiveness and quality of some of these advanced vectors. We require more advanced purification and separation techniques compared to conventional methods to maximize resolution in a scalable manner. The Prep Cell system is a continuous electro elution system that contains a circular gel casting tube where DNA mixtures can be run through and subsequently migrate into an elution chamber, to be eluted by a peristaltic pump. This DNA separation and purification process confers advantages over other conventional methods, including i) the elimination of multiple downstream purification process requirements; ii) its ability to be applied in mid-scale settings, and iii), its high-resolution power. In this study, we assessed the ability of this Prep Cell Model 491 system to purify a novel type of non-viral linear covalently closed (LCC) DNA minivector (ministring DNA) from its precursor parent plasmid DNA and process by-product DNA species by analyzing for effective separation via agarose gel electrophoresis, recovery yield, single enzyme digestion, and quality control assessments. Overall, effective separation and resolution of mini-DNA vectors was obtained using the Prep Cell system, conferring its potential to be applied towards mid-scale purification of DNA vectors for a variety of research, and eventually, clinical applications.

Innovative Technologies for Sustainable Recycling and Re-manufacturing of Materials and Components

The increasing demand for sustainable manufacturing and recycling processes has driven the development of innovative technologies to address the challenges associated with the re-manufacturing and recycling of materials and components. This research paper presents a comprehensive review of the latest advancements in sustainable recycling and re-manufacturing technologies, with a focus on their potential to reduce environmental impact, enhance resource efficiency, and promote circular economy principles. We explore cutting-edge technologies such as additive manufacturing, smart disassembly, and advanced material separation techniques, which have shown promise in enabling efficient recycling and re-manufacturing of materials and components. Additionally, we investigate the integration of digital technologies, including the Internet of Things (IoT), machine learning, and blockchain, to optimize recycling and re-manufacturing processes. Our analysis reveals that these technologies can significantly improve the quality and efficiency of recycled and re-manufactured products, reduce waste generation, and minimize energy consumption. Furthermore, we discuss the potential economic and environmental benefits of adopting these technologies, as well as the challenges and barriers to their widespread implementation. The findings of this research provide valuable insights for policymakers, industry stakeholders, and researchers working towards the development and adoption of sustainable recycling and re-manufacturing technologies.

Emerging technologies for selenium separation and recovery from aqueous systems: A review for sustainable management strategy

AbstractSelenium (Se) is known both as an essential micronutrient for human health as well as a toxic element when consumed in excess. This work endeavours to critically review the existing selenium literature over the period 1980–2021, following a systematic sub‐classification into the domains of occurrence, speciation, and existing conventional and advanced technologies, while directing further research towards emerging integrated sustainable recovery strategies. The review reveals that the majority of the conventional and advanced separation techniques eventually lead to secondary pollution rather than offering a complete solution, whereas resource recovery studies from water are very scant. Some of the techniques, being miserably slow, cannot be applied in the situations of the occurrence of excess selenium in drinking water, posing a serious threat to human health. Research efforts have so far been directed mainly at the removal of selenium rather than recovery through processes that have the potential of turning selenium abatement technology into a sustainable one with value addition. Emerging integrated technologies involving resource recovery from waste streams or generated sludge such as physicochemical technologies, biochemical reduction, electro‐biological reduction, and membrane‐based hybrid technologies are presently at a very early development stage. Moreover, the application of studies where Se nanoparticles (SeNPs) ormetal selenides are obtained is very limited, which may be attributed to the particle size, purity, morphology, and challenges involved in their separation. This review evaluates the challenges in separation and resource recovery from contaminated streams and points future research in a new direction.

Reverse Engineering of Chemically Similar Bimodal High Density Polyethylenes: A Comprehensive Study Using Advanced Chromatographic Techniques

Back Cover: In article 2200149, Anthony Ndiripo, Albert Johannes van Reenen, and co-workers demonstrate the linking of mechanical properties of bimodal high-density polyethylene to molecular structure using tailored advanced separation techniques. Chemically similar resins with different end-use properties can be efficiently fractionated using tailored high-temperature twodimensional liquid chromatography.

Indirect Enantioseparations: Recent Advances in Chiral Metabolomics for Biomedical Research.

Chiral metabolomics is starting to become a well-defined research field, powered by the recent advances in separation techniques. This review aimed to cover the most relevant advances in indirect enantioseparations of endogenous metabolites that were published over the last 10 years, including improvements and development of new chiral derivatizing agents, along with advances in separation methodologies. Moreover, special emphasis is put on exciting advances in separation techniques combined with mass spectrometry, such as chiral discrimination by ion-mobility mass spectrometry together with untargeted strategies for profiling of chiral metabolites in complex matrices. These advances signify a leap in chiral metabolomics technologies that will surely offer a solid base to better understand the specific roles of enantiomeric metabolites in systems biology.

Microplastics in Aquatic Environments: Recent Advances in Separation Techniques

Separation and removal of microplastic pollution from aquatic environments as a global environmental issue is classified as one of the major concerns in both water and wastewater treatment plants. Microplastics as polymeric particles less than 5 mm in at least one dimension are found with different shapes, chemical compositions, and sizes in soil, water, and sediments. Conventional treatment methods for organic separation have shown high removal efficiency for microplastics, while the separation of small microplastic particles, mainly less than 100 µm, in wastewater treatment plants is particularly challenging. This review aims to review the principle and application of different physical and chemical methods for the separation and removal of microplastic particles from aquatic environments, especially in water treatments process, with emphasis on some alternative and emerging separation methods. Advantages and disadvantages of conventional separation techniques such as clarification, sedimentation, floatation, activated sludge, sieving, filtration, and density separation are discussed. The advanced separation methods can be integrated with conventional techniques or utilize as a separate step for separating small microplastic particles. These advanced microplastic separation methods include membrane bioreactor, magnetic separation, micromachines, and degradation-based methods such as electrocatalysis, photocatalysis, biodegradation, and thermal degradation.

Concentration of Antioxidant Compounds from Calendula officinalis through Sustainable Supercritical Technologies, and Computational Study of Their Permeability in Skin for Cosmetic Use.

The growing interest in the cosmetic industry in using compounds of natural and sustainable origin that are safe for humans is encouraging the development of processes that can satisfy these needs. Chlorogenic acid (CHA), caffeic acid (CAF) and ferulic acid (FA) are three compounds widely used within the cosmetic industry due to their functionalities as antioxidants, collagen modifiers or even as radiation protectors. In this work, two advanced separation techniques with supercritical CO2 are used to obtain these three compounds from Calendula officinalis, and these are then evaluated using a computational skin permeability model. This model is encompassed by the COSMO-RS model, the calculations of which make it possible to study the behaviour of the compounds in the epidermis. The results show that both CAF and FA are retained in the stratum corneum, while CHA manages to penetrate to the stratum spinosum. These compounds were concentrated by antisolvent fractionation with super-critical CO2 using a Response Surface Methodology to study the effect of pressure and CO2 flow rate. CHA, CAF and FA were completely retained in the precipitation vessel, with concentrations between 40% and 70% greater than in the original extract. The conditions predicted that the optimal overall yield and enrichment achieved would be 153 bar and 42 g/min.

Bioactives in bovine milk: chemistry, technology, and applications.

The significance of dairy in human health and nutrition is gaining significant momentum as consumers continue to desire wholesome, nutritious foods to fulfill their health and wellness needs. Bovine milk not only consists of all the essential nutrients required for growth and development, it also provides a broad range of bioactive components that play an important role in managing human homeostasis and immune function. In recent years, milk bioactives, including α-lactalbumin, lactoferrin, glycomacropeptide, milk fat globule membrane, and milk oligosaccharides, have been intensively studied because of their unique bioactivity and functionality. Challenges for the application of these bioactive components in food and pharmaceutical formulations are associated with their isolation and purification on an industrial scale and also with their physical and chemical instability during processing, storage, and digestion. These challenges can be overcome by advanced separation techniques and sophisticated nano- or micro-encapsulation technologies. Current knowledge about the chemistry, separation, and encapsulation technology of major bioactives derived from bovine milk and their application in the food industry is reviewed here.

Multiple Heart-Cutting Two-Dimensional Liquid Chromatography: Recent Developments and Applications

Background: Over the last few decades, there has been a growing interest in Two- Dimensional Liquid Chromatography (2D-LC). This advanced technology has become a relevant solution for solving all the analytical challenges encountered in the pharmaceutical industry. The primary purpose of this review is to give a brief account of the developing techniques notable in 2D-LC. Methods: Review of recent literature on advanced separation techniques for complex mixtures revealed that 2D-LC is the most widely used technique in the pharmaceutical laboratory for the separation of complex samples. Among the various techniques used in 2D-LC, comprehensive 2D-LC and heart-cutting 2D-LC are highly used techniques. To enhance the resolution, further development has been made to heart-cutting 2D-LC called multiple heart-cutting 2D-LC, which has recently become a very popular technique in the pharmaceutical industry. Therefore research articles mentioning the use of multiple heart-cutting 2D-LC for separation of complex mixtures were reviewed. Results: The most crucial benefit of multiple heart-cutting 2D-LC is its reduced effort in method development and also the storage of multiple sample sections for further analysis. The multiple heartcutting 2D-LC is suited, preferably for method development and impurity analysis of pharmaceutical substances, fine chemicals and offers better peak separation, which is otherwise not possible by comprehensive 2D-LC. Conclusion: The advantage of two-dimensional liquid chromatography over one-dimensional liquid chromatography is its high resolving power. Further improvement in resolution was achieved by using the advanced multiple heart-cutting 2D-LC which appears to have an imperative role in pharmaceutical and food analysis.

Ultrarobust and Biomimetic Hierarchically Macroporous Ceramic Membrane for Oil-Water Separation Templated by Emulsion-Assisted Self-Assembly Method.

Reported herein is a novel ultrarobust and biomimetic hierarchically macroporous ceramic membrane that can achieve a high efficiency of up to 99.98% for oil-water separation, while the efficiency remains nearly unchanged even after 10 rounds of use and storage for up to 4 months. The macroporous ceramic membrane is prepared by combining surface hydrophobic coating with an emulsion-assisted template self-assembly of the modified Al2O3 ceramic powder. The as-prepared ceramic membrane is a lightweight material with high strength because the relative density is only ∼1.02 g/cm3; the compressive strength of the as-prepared ceramic membrane is expected to be 15-fold higher than that of the sample prepared using the traditional solid template approach even at a higher porosity due to the principle of self-assembly of Al2O3 particles. It is the mechanism of self-assembly that has broken the traditional principle in ceramic preparation that leads to a perfectly dense packing structure. Moreover, the ceramic membrane maintained excellent oil-water separation efficiency, because of which even after its top layer was damaged by sand impingement, superfine particles could be separated using our macroporous membrane due to the featured interconnected pore structure. We anticipate that this example of the combination of a superwettability theory and a traditional ceramic material can provide an important application direction of advanced oil-water separation techniques.