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Processes
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Green Chemistry: From Wastes to Value-Added Products (2nd Edition)
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Green Chemistry: From Wastes to Value-Added Products (2nd Edition)

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

Deadline for manuscript submissions: 10 October 2025 | Viewed by 16200

Special Issue Editors

Dr. Roberto Palos

E-Mail Website
Guest Editor
Department of Chemical Engineering, University of the Basque Country UPV/EHU, PO Box 644, 48080 Bilbao, Spain
Interests: heterogeneous catalysis; development of environmentally friendly processes; sustainable production of fuels
Special Issues, Collections and Topics in MDPI journals
Dr. Alazne Gutiérrez

E-Mail Website
Guest Editor
Department of Chemical Engineering, University of the Basque Country UPV/EHU, PO Box 644, 48080 Bilbao, Spain
Interests: environmental awareness and sustainability; waste treatment; intensification of processes; valorization of secondary streams and recycling processes
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The predominant linear mentality that is maintained in modern society has only advanced the serious environmental crises, such as the rampant deposition of waste in our environment, the regulated accumulation in landfills, and the mismanagement of waste through incineration, resulting in harmful substances which are detrimental to both human health and ecosystems. An urgent paradigm shift towards circular thinking is imperative, in which the conventional concept of “waste” is dissipated, giving way to its reclassification as “raw material”. This transformative approach not only mitigates environmental degradation, but also promotes resource efficiency and sustainability. Adopting this ethic opens avenues for innovative recycling technologies and closed-loop systems, underpinning a sustainable future in which waste is no longer a burden, but rather a valuable asset in the resource ecosystem.

A previous edition of this Special Issue on “Green Chemistry: From Waste to Value-Added Products” has described different methods of waste recovery processes to produce value-added products. This second issue “Green Chemistry: From Wastes to Value-Added Products (2nd Edition)” aims to continue to cover advances in the development and application of processes in this field. Topics include, but are not limited to, the following:

  • Production of medium and small chain fatty acids from organic waste;
  • Production of bioplastics from waste;
  • Production of biofuels and biogas from organic waste materials;
  • Production of hydrogen from waste materials;
  • Production of fuels from waste plastics by cracking, hydrocracking and pyrolysis;
  • Recovery of monomers from plastic waste;
  •  Application and optimization of pyrolysis processes for waste recovery (biowaste, MSW...);
  • Biochar applications (in agriculture, biochar and carbon sequestration...).

Dr. Roberto Palos
Dr. Alazne Gutiérrez
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

  • sustainability
  • circular economy
  • recycling technologies
  • closed-loop systems
  • waste management

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Published Papers (8 papers)

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Research

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17 pages, 4763 KiB  
Article
An Analysis of a Cement Hydration Process Using Glass Waste from Household Appliances as a Supplementary Material
by Karolina Bekerė, Jurgita Malaiškienė and Jelena Škamat
Processes 2025, 13(3), 840; https://doi.org/10.3390/pr13030840 - 13 Mar 2025
Viewed by 503
Abstract
Due to the significant increase in consumerism, the amount of household appliance waste has been growing, particularly in the form of glass. This study explores the possibility of using this glass (HAGw) as a replacement additive in cement-based products. The article examines the [...] Read more.
Due to the significant increase in consumerism, the amount of household appliance waste has been growing, particularly in the form of glass. This study explores the possibility of using this glass (HAGw) as a replacement additive in cement-based products. The article examines the properties of HAGw, including its chemical composition (XRF), mineral composition (XRD), particle morphology, and size distribution. Scanning electron microscopy (SEM) analysis revealed that HAGw particles could partially crystallise, forming needle-shaped minerals. When replacing 10%, 20%, and 30% of cement with dispersive HAGw, the rate of cement hydration remains unchanged; however, the amount of heat released decreases proportionally to the amount of waste used. Thermogravimetric analysis indicated that substituting a part of the cement with HAGw reduces the amount of portlandite over longer curing periods, indicating the pozzolanic activity of the glass, while the quantity of calcium silicate hydrates (C-S-H) remains similar to the control sample. In the microstructure of the samples, numerous agglomerates of glass particles are formed, increasing the porosity of the cement matrix and reducing its strength. However, over time, the surface of the glass particles begins to dissolve, leading to the formation of new cement hydrates that gradually fill the voids. This process enhances cement density, increases the ultrasonic pulse velocity, and improves compressive strength, particularly after 90 days, compared to the properties of the samples at 7 and 28 days of curing. Full article
(This article belongs to the Special Issue Green Chemistry: From Wastes to Value-Added Products (2nd Edition))
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13 pages, 2500 KiB  
Article
Ultrasound-Assisted Extraction of Phenolic Compounds from Tricosanthes cucumerina Leaves: Microencapsulation and Characterization
by Carlos Felipe Vendramini, Talita A. F. de Campos, Natallya M. da Silva, Marcos Antonio Matiucci, Eloize S. Alves, Patrícia D. S. dos Santos, Carlos Eduardo Barão, Oscar de Oliveira, Lucio Cardozo-Filho and Andresa Carla Feihrmann
Processes 2025, 13(2), 397; https://doi.org/10.3390/pr13020397 - 2 Feb 2025
Viewed by 1276
Abstract
This study utilized the ultrasound-assisted extraction method to obtain an extract rich in phenolic compounds from the leaves of Tricosanthes cucumerina. The optimization of the experimental design identified the optimal extraction conditions: a temperature of 40 °C, a duration of 6.25 min, [...] Read more.
This study utilized the ultrasound-assisted extraction method to obtain an extract rich in phenolic compounds from the leaves of Tricosanthes cucumerina. The optimization of the experimental design identified the optimal extraction conditions: a temperature of 40 °C, a duration of 6.25 min, and an amplitude of 40%. Under these conditions, the extraction yielded the highest levels of phenolic compounds, measuring 262.54 mg of GAE (gallic acid equivalent) per gram. Further analysis of these extracts using electrospray ionization mass spectrometry (ESI-MS) demonstrated that ultrasound extraction increased the availability of bioactive compounds, such as p-coumaric acid, ferulic acid, and caffeic acid. The resulting extract was microencapsulated with sodium alginate as the wall material and then lyophilized to enhance the shelf life and stability of the phenolic compounds. The thermogravimetric analysis confirmed that the microcapsules exhibited thermal stability, retaining their properties at temperatures up to 250 °C. Additionally, Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyses corroborated the effectiveness of the encapsulation process. Consequently, the ultrasound-assisted extraction of T. cucumerina leaves is a promising alternative for incorporating bioactive compounds into food products, nutraceuticals, and cosmetics, thus benefiting consumers. Full article
(This article belongs to the Special Issue Green Chemistry: From Wastes to Value-Added Products (2nd Edition))
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17 pages, 1511 KiB  
Article
Extraction of High Stearic High Oleic Sunflower Oil Using Eco-Friendly Solvents
by Ana K. de Figueiredo, María B. Fernández and Susana M. Nolasco
Processes 2025, 13(2), 390; https://doi.org/10.3390/pr13020390 - 31 Jan 2025
Viewed by 704
Abstract
The present work aimed to evaluate the extractive performance of three green solvents—absolute ethanol, hydrated ethanol (96%), and absolute isopropanol (AIP)—in high stearic high oleic sunflower seeds, comparing them with the conventional solvent hexane. The oil yield from exhaustive Soxhlet extraction with hydrated [...] Read more.
The present work aimed to evaluate the extractive performance of three green solvents—absolute ethanol, hydrated ethanol (96%), and absolute isopropanol (AIP)—in high stearic high oleic sunflower seeds, comparing them with the conventional solvent hexane. The oil yield from exhaustive Soxhlet extraction with hydrated ethanol was significantly lower, with no significant differences being observed among the other solvents. Extraction with AIP produced the extract with the lowest non-lipid material content and the oil with the lowest concentration of crystallizable waxes, showing a 53% reduction compared to hexane. Since AIP showed a higher extraction efficiency than absolute ethanol after 4 h of processing, its oil extraction kinetics when used as a solvent were further studied. A modified Fick’s diffusion model revealed that, for hexane extraction at 50 °C, the effective diffusion coefficient and the washing fraction were higher than those for AIP extraction (26% and 5.4% higher, respectively). No clear dependence of the oil extraction kinetics on the temperature was observed between the studied temperatures (50 °C and 70 °C). The results showed the feasibility of using absolute ethanol and AIP as alternatives to hexane. Additionally, isopropanol presented operational advantages, producing oil that required less dewaxing during refining than that extracted with hexane or ethanol and showing higher oil selectivity than ethanol. Full article
(This article belongs to the Special Issue Green Chemistry: From Wastes to Value-Added Products (2nd Edition))
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13 pages, 927 KiB  
Article
The Functional Carbonated Beverage Properties of Guabiroba Juice Using the Ice Fraction from Gravitational Block Freeze Concentration
by Amanda Alves Prestes, Karine Marafon, Ana Caroline Ferreira Carvalho, Dayanne Regina Mendes Andrade, Cristiane Vieira Helm, Jefferson Santos de Gois, Bruna Rafaela da Silva Monteiro Wanderley, Renata Dias de Mello Castanho Amboni and Elane Schwinden Prudencio
Processes 2024, 12(10), 2235; https://doi.org/10.3390/pr12102235 - 14 Oct 2024
Cited by 1 | Viewed by 1019
Abstract
The freeze concentration of liquid foods generates a by-product that has few academic studies and no industrial application: the ice fraction of each concentration stage. Sugar-free carbonated beverages were produced from the addition of 20% residual ice fraction (stage 1—I120 and stage 2—I220) [...] Read more.
The freeze concentration of liquid foods generates a by-product that has few academic studies and no industrial application: the ice fraction of each concentration stage. Sugar-free carbonated beverages were produced from the addition of 20% residual ice fraction (stage 1—I120 and stage 2—I220) of the gravitational block freeze concentration process, and the result was compared with a control beverage produced with 20% guabiroba juice (J20). The physicochemical properties, carotenoid content, total phenolic content (TPC), vitamin C, and antioxidant activity were analyzed for all samples. There was no significant difference between J20 and I220 for the total solid content and total soluble solids. For the total phenolic compounds (TPC), the I220 content was 151.3% higher than that of the original juice J20 and, for antioxidant activity, 295.8% higher for ABTS and 130.2% higher for DPPH. The I220 beverage presented 159% more vitamin C content than the beverage containing juice (J20). The same behavior was observed for each carotenoid content, with 168% more for the I220 sample. The total color difference revealed no difference visible to the naked eye for the three formulated beverages (∆E < 3.0; p < 0.05). The promising results of the bioactive compounds from guabiroba juice retained in the ice fraction can add value to this process waste in the formulation of new products due to the remaining functional appeal of the original fruit matrix. Full article
(This article belongs to the Special Issue Green Chemistry: From Wastes to Value-Added Products (2nd Edition))
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20 pages, 1299 KiB  
Article
Integration of an Autothermal Outer Electrified Reformer Technology for Methanol Production from Biogas: Enhanced Syngas Quality Production and CO2 Capture and Utilization Assessment
by Loretta Salano, Marcello M. Bozzini, Simone Caspani, Giulia Bozzano and Flavio Manenti
Processes 2024, 12(8), 1598; https://doi.org/10.3390/pr12081598 - 30 Jul 2024
Viewed by 1968
Abstract
Biogas has emerged as a valid feedstock for biomethanol production from steam reforming. This study investigates an alternative layout based on an auto-thermal electrified reforming assuming a 1 MW equivalent anaerobic digestion plant as a source for methanol synthesis. The process considers an [...] Read more.
Biogas has emerged as a valid feedstock for biomethanol production from steam reforming. This study investigates an alternative layout based on an auto-thermal electrified reforming assuming a 1 MW equivalent anaerobic digestion plant as a source for methanol synthesis. The process considers an oxy-steam combustion of biogas and direct carbon sequestration with the presence of a reverse water–gas shift reactor to convert CO2 and H2 produced by a solid oxide electrolyzer cell to syngas. Thermal auto-sufficiency is ensured for the reverse water–gas shift reaction through the biogas oxy-combustion, and steam production is met with the integration of heat network recovery, with an overall process total electrical demand. This work compares the proposed process of electrification with standard biogas reforming and data available from the literature. To compare the results, some key performance indicators have been introduced, showing a carbon impact of only 0.04 kgCO2/kgMeOH for the electrified process compared to 1.38 kgCO2/kgMeOH in the case of biogas reforming technology. The auto-thermal electrified design allows for the recovery of 66.32% of the carbon available in the biogas, while a similar electrified process for syngas production reported in literature reaches only 15.34%. The overall energy impact of the simulated scenarios shows 94% of the total energy demand for the auto-thermal scenario associated with the electrolyzer. Finally, the introduction of the new layout is taken into consideration based on the country’s carbon intensity, proving carbon neutrality for values lower than 75 gCO2/kWh and demonstrating the role of renewable energies in the industrial application of the process. Full article
(This article belongs to the Special Issue Green Chemistry: From Wastes to Value-Added Products (2nd Edition))
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13 pages, 291 KiB  
Article
Utilizing Used Cooking Oil and Organic Waste: A Sustainable Approach to Soap Production
by Leila Zayed, Natalia Gablo, Ludmila Kalcakova, Simona Dordevic, Ivan Kushkevych, Dani Dordevic and Bohuslava Tremlova
Processes 2024, 12(6), 1279; https://doi.org/10.3390/pr12061279 - 20 Jun 2024
Cited by 2 | Viewed by 5887
Abstract
This research examined the potential for utilizing waste materials generated during the production of dishes/meals and organic waste. Specifically, it evaluated the use of orange peel (OP), spent coffee grounds (SCG), and waste cooking oil in the production of soaps. For the purposes [...] Read more.
This research examined the potential for utilizing waste materials generated during the production of dishes/meals and organic waste. Specifically, it evaluated the use of orange peel (OP), spent coffee grounds (SCG), and waste cooking oil in the production of soaps. For the purposes of this study, homemade soaps were made from used food oils using the cold saponification method using sodium hydroxide. During the soap preparation, spent coffee grounds and orange peel were added to the samples in increasing concentrations of 1%, 2.5%, and 5%. The quality of the individual types of homemade soaps was evaluated on the basis of physicochemical properties such as pH, moisture, total alkalinity, total fatty matter, malondialdehyde content, fat content, foaminess, and hardness. All soaps produced using the cooking oil met the ISO quality criteria and reveal a high TFM content, low moisture content, and also very good foam stability and satisfactory foaming stability. However, no relationship was observed between the use of OP and SCG in soap production and these parameters. However, according to the ABTS test, OP and SCG significantly contributed to the antioxidant properties of the soaps, while SCG-impregnated soaps performed slightly better in this respect. Soaps with SCG also had the highest levels of flavonoids. On the other hand, the fillers used for the soap formulation reduced their hardness. All soaps showed 100% solubility in water, thus confirming the biodegradability of the product. This study demonstrated the novel potential of incorporating waste products like orange peel, spent coffee grounds, and waste cooking oil into homemade soaps, highlighting their contributions to its antioxidant properties and water solubility while ensuring high quality standards. Full article
(This article belongs to the Special Issue Green Chemistry: From Wastes to Value-Added Products (2nd Edition))

Review

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26 pages, 2012 KiB  
Review
Biofuels from Microalgae: A Review on Microalgae Cultivation, Biodiesel Production Techniques and Storage Stability
by Amit Kumar Sharma, Shivangi Jaryal, Shubham Sharma, Archana Dhyani, Bhagya Sindhu Tewari and Neelima Mahato
Processes 2025, 13(2), 488; https://doi.org/10.3390/pr13020488 - 10 Feb 2025
Cited by 1 | Viewed by 2280
Abstract
Rising global energy demands, depleting fossil fuel reserves, and growing environmental concerns have led to an increasing demand for clean and renewable energy sources. Recently, microalgae biofuels have emerged as a promising and sustainable energy source due to their high biomass productivity, lipid [...] Read more.
Rising global energy demands, depleting fossil fuel reserves, and growing environmental concerns have led to an increasing demand for clean and renewable energy sources. Recently, microalgae biofuels have emerged as a promising and sustainable energy source due to their high biomass productivity, lipid content, and wastewater treatment capabilities. However, the viability of microalgae biofuels as a commercial-scale renewable fuel remains uncertain due to high production costs and storage stability issues. This review focuses on advanced technologies aimed at enhancing both the production of microalgae biodiesel and its storage stability. It explores the potential and challenges of recent developments in microalgae cultivation systems, particularly those factors that have contributed to increased lipid content in microalgae biomass. The study also examines the role of industrial wastewater in promoting microalgae growth and provides an overview of recent advances in biodiesel production. Additionally, it discusses various strategies to improve the storage stability of biodiesel, a critical consideration for the commercialization of microalgae biodiesel. Full article
(This article belongs to the Special Issue Green Chemistry: From Wastes to Value-Added Products (2nd Edition))
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38 pages, 1346 KiB  
Review
Two-Stage Anaerobic Digestion for Green Energy Production: A Review
by Ivan Simeonov, Elena Chorukova and Lyudmila Kabaivanova
Processes 2025, 13(2), 294; https://doi.org/10.3390/pr13020294 - 21 Jan 2025
Cited by 2 | Viewed by 1521
Abstract
Anaerobic digestion (AD) is a biotechnological process in which the microorganisms degrade complex organic matter to simpler components under anaerobic conditions to produce biogas and fertilizer. This process has many environmental benefits, such as green energy production, organic waste treatment, environmental protection, and [...] Read more.
Anaerobic digestion (AD) is a biotechnological process in which the microorganisms degrade complex organic matter to simpler components under anaerobic conditions to produce biogas and fertilizer. This process has many environmental benefits, such as green energy production, organic waste treatment, environmental protection, and greenhouse gas emissions reduction. It has long been known that the two main species (acidogenic bacteria and methanogenic archaea) in the community of microorganisms in AD differ in many aspects, and the optimal conditions for their growth and development are different. Therefore, if AD is performed in a single bioreactor (single-phase process), the optimal conditions are selected taking into account the slow-growing methanogens at the expense of fast-growing acidogens, affecting the efficiency of the whole process. This has led to the development of two-stage AD (TSAD) in recent years, where the processes are divided into a cascade of two separate bioreactors (BRs). It is known that such division of the processes into two consecutive BRs leads to significantly higher energy yields for the two-phase system (H2 + CH4) compared to the traditional single-stage CH4 production process. This review presents the state of the art, advantages and disadvantages, and some perspectives (based on more than 210 references from 2002 to 2024 and our own studies), including all aspects of TSAD—different parameters’ influences, types of bioreactors, microbiology, mathematical modeling, automatic control, and energetical considerations on TSAD processes. Full article
(This article belongs to the Special Issue Green Chemistry: From Wastes to Value-Added Products (2nd Edition))
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