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Processes
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Advances in Sub-/Supercritical Water Processes
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Advances in Sub-/Supercritical Water Processes

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

Deadline for manuscript submissions: closed (30 September 2024) | Viewed by 17120

Special Issue Editors

Prof. Dr. Jaroslava Švarc-Gajić

E-Mail Website
Guest Editor
Faculty of Technology, Department of Applied and Engineering Chemistry, 21 000 Novi Sad, Serbia
Interests: Sub- and supercritical water processes; green technologies; bioactivity; chemical characterization; development of functional products; quality control; instrumental analysis
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Simone Morais

E-Mail Website
Guest Editor
REQUIMTE/LAQV, ISEP, Polytechnic of Porto, Rua Dr. António Bernardino de Almeida, 4249-015 Porto, Portugal
Interests: (bio)sensors; application of functional nanostructured materials; green technologies; new methodologies for (electro)analysis; environmental chemistry; monitoring/biomonitoring
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The modern industrial and scientific community strives to reiterate conventional approaches and to focus on advanced, more environmentally friendly, economical, safer and sustainable alternative technologies, implementing them into practice. Subcritical water extraction has emerged as a competitive technique for the isolation of phytochemicals, natural added-value and bioactive compounds, offering numerous advantages in comparison to other “green” techniques, such as superior efficiency, excellent selectivity with the possibility to finely tune solvating properties and target specific chemical classes, as well as safety, environmentally-friendly characteristics and a low price.

This Special Issue will be dedicated to different applications of hot compressed water in its sub- and supercritical state. Hot compressed water exhibits remarkably distinct properties in its sub- and supercritical state, thus, the use of this green solvent can be seen in both extraction and decomposition processes. The aim of this Special Issue is to cover both approaches. This Special Issue is therefore welcoming original research and review articles covering the following topics:

  • Subcritical water extraction of phytochemicals;
  • Extraction by subcritical water of non-plant matrices;
  • Decomposition in sub- and supercritical water;
  • Biowaste valorization by sub- and supercritical water;
  • Remediation of contaminated sites by sub- and supercritical water;
  • Biofuel production by supercritical water.

In the hope that this Special Issue will provide valuable insights into the possibilities of this powerful technology, we are pleased to announce the call for papers for this Special Issue.

Prof. Dr. Jaroslava Švarc-Gajić
Prof. Dr. Simone Morais
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

  • subcritical water extraction
  • supercritical water
  • decomposition in sub- and supercritical water
  • biowaste valorization
  • remediation

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Published Papers (4 papers)

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Research

15 pages, 501 KiB  
Article
Chemical and Biological Characterisation of Orange (Citrus sinensis) Peel Extracts Obtained by Subcritical Water
by Tanja Brezo-Borjan, Jaroslava Švarc-Gajić, Simone Morais, Cristina Delerue-Matos, Francisca Rodrigues, Ivana Lončarević and Biljana Pajin
Processes 2023, 11(6), 1766; https://doi.org/10.3390/pr11061766 - 10 Jun 2023
Cited by 9 | Viewed by 7999
Abstract
Orange peels, generally considered as waste, were treated with subcritical water (SWE)—a green technology and environmentally friendly extraction process—at different temperatures (120–200 °C) and extraction times (5–60 min). The extracts which were obtained were chemically and biologically characterised to evaluate this potential source [...] Read more.
Orange peels, generally considered as waste, were treated with subcritical water (SWE)—a green technology and environmentally friendly extraction process—at different temperatures (120–200 °C) and extraction times (5–60 min). The extracts which were obtained were chemically and biologically characterised to evaluate this potential source of bioactive compounds. The extracts total phenolics content (TPC) and total flavonoids contents (TFC), as well as total antioxidant capacity (TAC), DPPH radical scavenging activity, and total carbohydrate content, were determined by UV spectrophotometry. The pectin content was quantified by a gravimetric method. The dietary fibre content was investigated, and a phytochemical screening assay was performed. The extract obtained at 120 °C for 5 min displayed the highest TPC (45.45 mg GAE/g DW), TFC (9.29 mg RE/g DW), and TAC (130.47 mg AAE/g DW), indicating that relatively low temperatures and extremely short extraction times can be used in SWE to obtain orange peel extracts that are rich in bioactive compounds. The results of this study demonstrate the exceptional potential of orange peel extracts obtained with SWE. As shown, this biowaste represents a promising source of health-promoting compounds that could be used in pharmaceutical and dietary products. Full article
(This article belongs to the Special Issue Advances in Sub-/Supercritical Water Processes)
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17 pages, 2534 KiB  
Article
Subcritical Water Extraction of Mango Seed Kernels and Its Application for Cow Ghee Preservation
by Rambabu Krishnamoorthy, Abdul Hai and Fawzi Banat
Processes 2023, 11(5), 1379; https://doi.org/10.3390/pr11051379 - 3 May 2023
Cited by 7 | Viewed by 2130
Abstract
Mango seed kernel (MSK) extract contains phytochemicals, bioactives, and fatty acids that are of interest to food and nutritional scientists. The subcritical water extraction process (SCWE) can be effective in extracting valuable bioactives from MSK. In this study, SCWE was investigated and optimized [...] Read more.
Mango seed kernel (MSK) extract contains phytochemicals, bioactives, and fatty acids that are of interest to food and nutritional scientists. The subcritical water extraction process (SCWE) can be effective in extracting valuable bioactives from MSK. In this study, SCWE was investigated and optimized for the extraction of bioactives from MSK using Box–Behnken experimental design. The extract yield was examined as a function of various process variables, namely, solvent-to-feed (L/S) ratio, extraction temperature (T), and extraction time (t). Analysis of variance (ANOVA) for experimental results showed that extraction temperature was the most significant variable that impacted the extract yield. A maximum yield of 52.3% was obtained at optimized extraction conditions of L/S ratio = 20.7, T = 116.5 °C, and t = 45 min. Antioxidant assessment of the SCWE extract obtained at the optimized conditions showed higher total phenolic content (19.2 mg GAE/g), and DPPH and ABTS radical scavenging activity (>91%), than the extracts obtained by conventional hot water extraction and ultra-sound assisted extraction. Furthermore, an assessment of the MSK extract as a natural preservative showed that its inclusion (20% v/v) improved the oxidative stability of cow ghee with a par performance to synthetic butylated hydroxyanisole antioxidant (0.02% w/v). Thus, the study demonstrated SCWE as an effective green method for the production of MSK extract that could be applied for the preservation of oxidative food products. Full article
(This article belongs to the Special Issue Advances in Sub-/Supercritical Water Processes)
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18 pages, 4008 KiB  
Article
Process Effluent Recycling in the Supercritical Water Gasification of Dry Biomass
by Julian Dutzi, Nikolaos Boukis and Jörg Sauer
Processes 2023, 11(3), 797; https://doi.org/10.3390/pr11030797 - 7 Mar 2023
Cited by 8 | Viewed by 2313
Abstract
The influence of process water recycling during the Supercritical Water Gasification (SCWG) of dry biomasses was investigated. Dry biomass has to be diluted with water to a dry matter content of approximately 10 wt.% to gasify it in the process of supercritical water [...] Read more.
The influence of process water recycling during the Supercritical Water Gasification (SCWG) of dry biomasses was investigated. Dry biomass has to be diluted with water to a dry matter content of approximately 10 wt.% to gasify it in the process of supercritical water gasification. The treatment of wastewater in the SCWG process is cost intensive due to organic contaminants; therefore, the recycling of the process effluent is attractive. Salt separation is needed to avoid accumulation of salts in the effluents, since salts enhance corrosion rates and might cause blocking of the flow when the effluent is recycled. The grass Reed Canary Grass and grapevines were gasified. The recycling of the process effluent did not influence the composition of the product gas. In both cases the carbon efficiency decreased by 4% when wastewater was used to dilute the biomass. An increase in organic carbon and potassium in the reactor effluent was observed after gasification of the biomass with recycled process effluent. The addition of potassium hydroxide to the feed as a homogenous catalyst needs to be closely monitored and adjusted according to the potassium content of the reactor effluent. Insufficient salt separation proved to be an issue regarding formation of solid deposits in the reaction system. Full article
(This article belongs to the Special Issue Advances in Sub-/Supercritical Water Processes)
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8 pages, 881 KiB  
Communication
Subcritical Water Extraction as an Effective Technique for the Isolation of Phenolic Compounds of Achillea Species
by Katarina Radovanović, Neda Gavarić, Jaroslava Švarc-Gajić, Tanja Brezo-Borjan, Bojan Zlatković, Biljana Lončar and Milica Aćimović
Processes 2023, 11(1), 86; https://doi.org/10.3390/pr11010086 - 28 Dec 2022
Cited by 7 | Viewed by 3810
Abstract
The genus Achillea has significant medical potential due to the presence of highly bioactive compounds in its chemical composition. To take advantage of plants’ biomedical potential, it is of great importance to use a proper extraction process. This study aimed to determine and [...] Read more.
The genus Achillea has significant medical potential due to the presence of highly bioactive compounds in its chemical composition. To take advantage of plants’ biomedical potential, it is of great importance to use a proper extraction process. This study aimed to determine and compare the preliminary chemical composition of five different Achillea species extracted with two conventional (infusion and maceration) and two non-conventional (ultrasound-assisted extraction (UAE) and Subcritical water extraction (SWE)) techniques. The extracts were prepared using the previously described procedures for infusion, maceration, UAE and SWE extraction. For all extracts, the extraction yield (dry extract (DE)) was determined. The analyzed extracts were preliminarily chemically characterized spectrophotometrically in terms of total phenolic content (TPC) and total flavonoid content (TFC). The obtained results showed that non-conventional techniques delivered higher values of TPC and TFC than conventional. There is a statistically significant increase in DE and TPC content when applying SWE for all observed Achillea species. The highest DE value, 48.80 ± 1.76%, was observed for A. asplenifolia. The highest TPC values were observed after applying SWE: 93.63 ± 1.01 mg GAE/g DE for A. millefolium, and 90.12 ± 0.87 mg GAE/g DE for A. crithmifolia. The results for TFC revealed a statistically significant difference in values, with A. nobilis subsp. nelreichii as the sample with the highest content of TFC (11.11 ± 0.22 mg QE/g DE) when using UAE. Consequently, it could be concluded that SWE is a superior non-conventional extraction technique, and A. nobilis subsp. nerleichii presents as the most promising plant. Full article
(This article belongs to the Special Issue Advances in Sub-/Supercritical Water Processes)
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