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A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Separation Processes".

Deadline for manuscript submissions: 20 December 2024 | Viewed by 13064

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Special Issue Editors

Prof. Dr. Inês Portugal

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CICECO–Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
Interests: chemical reaction engineering; biorefinery and sustainability; chemical engineering education

Prof. Dr. Carlos Manuel Silva

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CICECO–Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
Interests: transport properties (mainly diffusion coefficients in liquids and supercritical fluids; phenomenological modeling; molecular dynamics simulations); separation processes (adsorption/simulated moving bed; ion exchange; membranes; supercritical fluid extraction); synthesis and characterization of microporous materials for catalysis and separation processes
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Dr. José Aniceto

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CICECO - Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
Interests: separation processes: simulated moving bed chromatography; adsorption; supercritical fluid extraction; ion exchange

Special Issue Information

Dear Colleagues,

The road toward a sustainable chemical industry depends on the development and application of processes, solvents and materials with reduced environmental, health, and safety hazards. Hence, research is not only focused on the search for novel active compounds and products from renewable resources, but also on the optimization of their production processes, using non-conventional technologies and solvents, synthetic methodologies, solid-phase chemistry, and integrated reaction and purification of products.

This Special Issue on “Green Separation and Purification Processes” seeks to cover the latest developments in environmentally friendly separation processes and technologies. Topics include, but are not limited to:

Applications of green solvents;
Green extraction and purification techniques;
Combined and hybrid reaction/purification processes;
Green sampling and sample preparation in analytical chemistry.

Under the scope of these major topics are included, in more detail, bio-based molecular solvents and processes; supramolecular solvents, (immobilized) ionic liquids, deep eutectic solvents, switchable solvents, supercritical fluids, fluorinated solvents; membrane extraction; microwave, ultrasound and pulsed electric field assisted extraction; supercritical fluid extraction and processing; preparative chromatography processes; applications of nanostructures in separation; high-pressure processing and homogenization; separations with superheated water (or water as a solvent), etc.

Prof. Dr. Inês Portugal
Prof. Dr. Carlos Manuel Silva
Dr. José Aniceto
Guest Editors

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. Processes 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 2400 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

green processes
bioactive ingredients

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Published Papers (8 papers)

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Research

15 pages, 2009 KiB

Open AccessFeature PaperArticle

Hydrophobic Deep Eutectic Solvents for Ethanol, Propan-1-ol, and Propan-2-ol Recovery from Aqueous Solutions

by Dalal J. S. A. Audeh, Adriano Carniel, Cristiano Piacsek Borges, Maria Alice Zarur Coelho, Filipe Smith Buarque and Bernardo Dias Ribeiro

Processes 2024, 12(6), 1255; https://doi.org/10.3390/pr12061255 - 18 Jun 2024

Cited by 3 | Viewed by 1266

Abstract

Separating hydroalcoholic mixtures remains a significant challenge in engineering. Liquid–liquid extraction has emerged as an appealing alternative method, because it avoids the need for the large energy inputs, volatile organic compounds, and high pressures that are typically required by other separation processes. This study explores the use of hydrophobic deep eutectic solvents (HDESs) composed of terpenes and 10-undecenoic acid as extraction agents for the liquid–liquid separation of hydroalcoholic mixtures composed of alcohols (ethanol, propan-1-ol, and propan-2-ol) and water. The water content in the solvents studied was notably low, reflecting their hydrophobic nature. For the dried HDES samples, the water content ranged from 553 to 4901 ppm. In contrast, the water-saturated samples exhibited higher water contents, ranging from 7250 to 20,864 ppm. The HDES based on thymol, DL-menthol, and L-menthol displayed a eutectic point at an x_terpenes of approximately 0.67. These mixtures maintained a liquid state up to a mole fraction of terpenes around 0.75. In contrast, the HDES composed of carvacrol, fenchyl alcohol, and α-terpineol exhibited their eutectic point at an x_terpenes near 0.5. Notably, these mixtures remained in a liquid state across the entire composition range studied. The 2:1 molar ratio (HBA:HBD) presented the best values for extracting alcohols, reaching 34.04%, 36.59%, and 39.78% for ethanol, propan-2-ol, and propan-1-ol, respectively. These results show that HDES can be applied to overcome issues with existing extraction solvents, increasing the separation efficiency and making the process eco-friendly. Full article

(This article belongs to the Special Issue Green Separation and Purification Processes)

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36 pages, 5363 KiB

Open AccessFeature PaperArticle

Thermodynamically Efficient, Low-Emission Gas-to-Wire for Carbon Dioxide-Rich Natural Gas: Exhaust Gas Recycle and Rankine Cycle Intensifications

by Israel Bernardo S. Poblete, José Luiz de Medeiros and Ofélia de Queiroz F. Araújo

Processes 2024, 12(4), 639; https://doi.org/10.3390/pr12040639 - 22 Mar 2024

Viewed by 1160

Abstract

Onshore gas-to-wire is considered for 6.5 MMSm³/d of natural gas, with 44% mol carbon dioxide coming from offshore deep-water oil and gas fields. Base-case GTW-CONV is a conventional natural gas combined cycle, with a single-pressure Rankine cycle and 100% carbon dioxide emissions. The second variant, GTW-CCS, results from GTW-CONV with the addition of post-combustion aqueous monoethanolamine carbon capture, coupled to carbon dioxide dispatch to enhance oil recovery. Despite investment and power penalties, GTW-CCS generates both environmental and economic benefits due to carbon dioxide’s monetization for enhanced oil production. The third variant, GTW-CCS-EGR, adds two intensification layers over GTW-CCS, as follows: exhaust gas recycle and a triple-pressure Rankine cycle. Exhaust gas recycle is a beneficial intensification for carbon capture, bringing a 60% flue gas reduction (reduces column’s diameters) and a more than 100% increase in flue gas carbon dioxide content (increases driving force, reducing column’s height). GTW-CONV, GTW-CCS, and GTW-CCS-EGR were analyzed on techno-economic and environment–thermodynamic grounds. GTW-CCS-EGR’s thermodynamic analysis unveils 807 MW lost work (79.8%) in the combined cycle, followed by the post-combustion capture unit with 113 MW lost work (11.2%). GTW-CCS-EGR achieved a 35.34% thermodynamic efficiency, while GTW-CONV attained a 50.5% thermodynamic efficiency and 56% greater electricity exportation. Although carbon capture and storage imposes a 35.9% energy penalty, GTW-CCS-EGR reached a superior net value of 1816 MMUSD thanks to intensification and carbon dioxide monetization, avoiding 505.8 t/h of carbon emissions (emission factor 0.084 t^CO2/MWh), while GTW-CONV entails 0.642 t^CO2/MWh. Full article

(This article belongs to the Special Issue Green Separation and Purification Processes)

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13 pages, 3690 KiB

Open AccessArticle

Recovery of Ionic Liquid from the Model Solution Mixture Mimicking the Catalytically Hydrolyzed Cellulose Product Utilizing Amberlyst Ion-Exchange Resin

by Chhabilal Regmi, Chidambaram Thamaraiselvan, Zhexi Zhu, Xianghong Qian and S. Ranil Wickramasinghe

Processes 2024, 12(1), 55; https://doi.org/10.3390/pr12010055 - 26 Dec 2023

Viewed by 1399

Abstract

The hydrolysis of cellulose using ionic liquid (IL) has been extensively studied but there is limited understanding of the removal of IL from the biomass hydrolysate. Finding a suitable method for the recovery and reuse of IL is one of the biggest challenges before its large-scale application. Selecting an appropriate combined recovery process is very important. This study proposed a facile ion-exchange combined method for the recovery of IL from the modeled cellulose hydrolysate mixture containing sugars as well as γ-valerolactone (GVL) via an adsorption–desorption mechanism using sulfonic acid cation-exchange (Amberlyst 15 (H)) resin. The results showed that the resin could adsorb more than 94% of 1-ethyl-3-methylimidazolium chloride [Emim]Cl IL at ambient conditions within a contact time of 20 min. The other coexisting constituents like glucose and GVL have no significant effect on the adsorption efficiency of IL. The adsorption of IL on Amberlyst 15 (H) resin was observed to be pseudo-second-order adsorption. The regeneration of the adsorbed IL was possible up to 70% using low-cost, easily available sodium chloride (NaCl) solution. Similarly, despite the interference of other unwanted byproducts in the real biomass hydrolysate sample, an IL adsorption efficiency up to 51% was reached under similar operating conditions. This study thus opens the facile possibility of extracting and recycling IL used in the biomass hydrolysis process. Full article

(This article belongs to the Special Issue Green Separation and Purification Processes)

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18 pages, 3364 KiB

Open AccessArticle

Reduced-Order Modeling and Control of Heat-Integrated Air Separation Column Based on Nonlinear Wave Theory

by Lin Cong and Xu Li

Processes 2023, 11(10), 2918; https://doi.org/10.3390/pr11102918 - 5 Oct 2023

Cited by 1 | Viewed by 1059

Abstract

The process of low-temperature air separation consumes a significant amount of energy. Internal heat-integrated distillation technology has considerable energy-saving potential. Therefore, the combination of low-temperature air separation and heat-integrated distillation technology has led to the development of a heat-integrated air separation column (HIASC). Due to the heat integration and the inherent complexity of air separation, the modeling and control of this process poses significant challenges. This paper first introduces the nonlinear wave theory into the HIASC, derives the expression for the velocity of the concentration distribution curve movement and the curve describing function, and then establishes a nonlinear wave model. Compared to the traditional mechanical models, this approach greatly reduces the number of differential equations and variables while ensuring an accurate description of the system characteristics. Subsequently, based on the wave model, a model predictive control scheme is designed for the HIASC. This scheme is compared with two conventional control schemes: PID and a general model control. The simulation results demonstrate that MPC outperforms the other control schemes from the response curves and performance metrics. Full article

(This article belongs to the Special Issue Green Separation and Purification Processes)

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13 pages, 5374 KiB

Open AccessArticle

Separation and Recovery of Rare Earths and Iron from NdFeB Magnet Scraps

by Houqing Wang, Jinliang Wang, Xiang Lei, Xiaochun Wen, Dewei Li, Fupeng Liu, Wenyue Zhou and Shengming Xu

Processes 2023, 11(10), 2895; https://doi.org/10.3390/pr11102895 - 30 Sep 2023

Viewed by 1629

Abstract

NdFeB magnet scraps contain large amounts of iron, which poses challenges in recycling and greatly hinders the recovery of rare earths through direct hydrometallurgical treatment. To address this issue, we conducted tests using a flash furnace to explore the low-temperature reduction behavior of NdFeB magnet scraps under an H₂ atmosphere based on thermodynamic calculations comparing the reduction properties of rare earth oxides (REOs) and iron oxide (FeO_x). The results demonstrated that the reduction rate of FeO_x surpassed 95% under optimal conditions including a reduction temperature of 723 K, a particle size (D₉₀) of 0.45 μm, and an H₂ flow rate of 2 L/min. X-ray diffraction and electron probe microanalysis of the reduction product revealed that the flash reduction at 723 K facilitated the selective reduction of FeO_x, owing to efficient mass and heat transfer. Consequently, a two-step magnetic separation process was employed to separate metallic Fe and REOs from the reduction product. Fe-rich phase, obtained with a remarkable Fe distribution ratio of 90.2%, can serve as an economical raw material for weathering steel. Additionally, the REOs are enriched in REO-rich phase, achieving a distribution ratio of 93.9% and significantly boosting the REO concentration from 30.2 to 82.8 wt%. Full article

(This article belongs to the Special Issue Green Separation and Purification Processes)

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23 pages, 6206 KiB

Open AccessArticle

Phosphorus Recovery from Wastewater Aiming Fertilizer Production: Struvite Precipitation Optimization Using a Sequential Plackett–Burman and Doehlert Design

by Paulo Victor Campos, Rômulo Simões Angélica, Lênio José Guerreiro de Faria and Simone Patrícia Aranha Da Paz

Processes 2023, 11(9), 2664; https://doi.org/10.3390/pr11092664 - 6 Sep 2023

Cited by 2 | Viewed by 1431

Abstract

The precipitation of struvite from wastewater is a potential alternative for the recovery of nutrients, especially phosphorus, which is an essential macronutrient for agriculture but can be harmful to the environment when improperly disposed of in water bodies. In addition, struvite has elements of great added value for agricultural activity (P, N, and Mg) and is, therefore, considered a sustainable alternative fertilizer. In its formation process, several intervening physicochemical factors may be responsible for the production yield levels. Optimization processes can help to define and direct the factors that truly matter for precipitation. In this context, a sequential design of experiments (DOE) methodology was applied to select and optimize the main struvite precipitation factors in wastewater. Initially, a screening was performed with eight factors with the aid of Plackett–Burman design, and the factors with a real influence on the process were identified. Then, a Doehlert design was used for optimization by applying the response surface methodology and the desirability function. The results were used to identify the optimal points of the pH (10.2), N/P ratio (≥4), and initial phosphorus concentration (183.5 mg/L); these values had a greater effect on phosphorus recovery and the production of struvite, which was confirmed through thermochemical analysis of the decomposition of its structure by differential scanning calorimeter—glass transition temperature (DSC-TG) and phase identification by X-ray diffraction (XRD). The determination of the best synthesis conditions is an enormous contribution to the control of the process because these conditions lead to better yields and higher levels of phosphorus recovery. Full article

(This article belongs to the Special Issue Green Separation and Purification Processes)

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23 pages, 3865 KiB

Open AccessArticle

Pressurized Liquid Extraction (PLE) in an Intermittent Process as an Alternative for Obtaining Passion Fruit (Passiflora edulis) Leaf Hydroalcoholic Extract (Tincture)

by Larissa da Cunha Rodrigues, Renata Barbosa Bodini, Fernando de Lima Caneppele, Gustavo César Dacanal, Eduardo José Crevelin, Luiz Alberto Beraldo de Moraes and Alessandra Lopes de Oliveira

Processes 2023, 11(8), 2308; https://doi.org/10.3390/pr11082308 - 1 Aug 2023

Cited by 5 | Viewed by 1913

Abstract

Tinctures are medicinal plant extracts obtained by extraction with a hydroalcoholic solution (70%) by percolation (PER). This process takes about 26 h to prepare, in addition to using a large amount of solvent. In our research, passion fruit leaf tinctures were obtained using extract with the same pressurized hydroalcoholic solution as in an intermittent process. The objective was to demonstrate that this emerging technology can be economical and profitable. An optimization using Central Composite Rotatable Design (CCRD) was performed to evaluate the influence of process variables on the yields and compositions of the extracts. The temperature (T) was the factor that most influenced the responses. Extraction with pressurized liquid (PLE) provided total yields and total phenolic and flavonoid contents in greater amounts than PER. The optimized conditions of the process variables studied in the CCRD for the highest content of total phenolics (43.2 mg GAE/g) and flavonoids (58.8 mg QE/g) were at 100 °C with a rinse volume of 120% of the divided extractor volume in four cycles of the intermittent process. When adjusting the PLE in an intermittent process, and according to the one-dimensional mass transfer by the continuous diffusion of the Fick model, the effective diffusion coefficient (1.28 × 10⁻¹² m²/s) was not affected by T. The kinetic curve of PLE extraction indicates that the adjusted intermittent process occurred in the period of the constant extraction rate when compared to the kinetics of the semi-continuous process. The yielded extracts were rich in isovitexin, and the highest levels were identified in the extracts obtained via PLE, indicating that this intermittent process can bring a product to market with the same quality but with a much shorter production time and the use of fewer solvents. Antioxidant activity, determined by DPPH, FRAP and ORAC, was also higher in extracts obtained via PLE. Full article

(This article belongs to the Special Issue Green Separation and Purification Processes)

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11 pages, 4867 KiB

Open AccessArticle

Modeling and Operating Time Optimization of Layer Melt Crystallization and Sweating Processes

by Yunhe Bai, Luguang Qi, Ying Sun, Zhenxing Zhu and Chuang Xie

Processes 2023, 11(4), 1047; https://doi.org/10.3390/pr11041047 - 30 Mar 2023

Viewed by 2317

Abstract

Improving the separation efficiency of the layer melt crystallization process is a key but difficult task. Herein, a comprehensive model involving both crystallization and sweating was proposed and used to optimize the operating time of crystallization and sweating processes. The crystallization process was modeled based on the relationship between differential and integral distribution coefficients under a constant layer growth rate. For the sweating process, an empirical sweating equation was employed to govern the sweating model, the parameters of which were determined experimentally using P-xylene as the model substance. The separation efficiency was then optimized by minimizing the operating time at a given product purity and yield. A sensitivity analysis showed that the crystallization and sweating times nonlinearly increase with increasing yield. After the yield exceeds 0.65, an increasing crystallization time is the dominant factor in improving the separation efficiency, while the sweating time and ratio even slightly decrease. The total operating time at low yield is U-shaped with the layer growth rate. The optimal layer growth rate decreases with increasing yield. This model provides guidance for determining the optimal operating parameters of layer melt crystallization and sweating processes. Full article

(This article belongs to the Special Issue Green Separation and Purification Processes)

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