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Circular Economy in Process Engineering: Impact Assessment and Directions for Sustainability

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

Deadline for manuscript submissions: closed (15 July 2026) | Viewed by 10210

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Prof. Dr. Lucian-Ionel Cioca

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Industrial Engineering and Management Department, Faculty of Engineering, Lucian Blaga University of Sibiu, 10 Victoriei Blv., 550024 Sibiu, Romania
Interests: management; human resources management; occupational health and safety management; production systems engineering; ergonomics; circular economy
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Dr. Elena Simina Lakatos

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Guest Editor

Institute for Research in Circular Economy and Environment Ernest Lupan, 400561 Cluj-Napoca, Romania
Interests: social development and community sustainability; entrepreneurship and circular economy; sustainable development; renewable energy; environmental protection
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Special Issue Information

Dear Colleagues,

The circular economy represents a paradigm shift from the traditional linear economic model. It is based on maximizing the value of resources through reuse, recycling, and waste reduction, with long-term sustainability as its primary objective. The specific impact assessment of this paradigm shows that the benefits outweigh the challenges, but success depends on coherent implementation and the involvement of all social and economic actors.

Its major benefits are as follows:

(a) Economic sustainability:

Increasing resource productivity and reducing production costs.
Creating green jobs and developing skills in emerging areas.

(b) Ecological sustainability:

Reducing greenhouse gas emissions.
Reducing pollution and waste.

Conserving natural resources through efficient and responsible use.

In this Special Issue, "Circular Economy in Process Engineering: Impact Assessment and Directions for Sustainability", we invite researchers to contribute their recent scientific works on this topic.

Prof. Dr. Lucian-Ionel Cioca
Dr. Elena Simina Lakatos
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 250 words) can be sent to the Editorial Office for assessment.

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-anonymized 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 semimonthly 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

circular economy
sustainability
resources
recycling
innovation

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Published Papers (10 papers)

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Research

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17 pages, 5283 KB

Open AccessArticle

Kinetics of Hydroxychlorination of Styrene Using Hydrogen Peroxide and Hydrochloric Acid

by Rahul Shrikant Kamble, Sunil S. Bhagwat and Sujit Suresh Jogwar

Processes 2026, 14(15), 2398; https://doi.org/10.3390/pr14152398 - 24 Jul 2026

Viewed by 117

Abstract

Styrene chlorohydrin is an important intermediate used in the manufacturing of high-value specialty chemicals. This paper focuses on understanding the kinetic aspects of styrene chlorohydrin production using hydrogen peroxide and hydrochloric acid. For this two-phase non-catalytic system, lab-scale initial rate experiments are conducted to assess the impact of key design parameters, such as reaction temperature, speed of agitation, and phase volume fraction, on the observed reaction rate. Based on these studies, it has been shown that this reaction takes place in the aqueous phase and the apparent order of reaction with respect to styrene, hydrogen peroxide and hydrochloric acid is approximately one, one and two, respectively. The corresponding Hatta number values are much smaller than one and the enhancement factor is approximately one, confirming that the system operates in regime I. Subsequently, a detailed reaction mechanism is proposed to capture the composition profiles of styrene chlorohydrin as well as the other major side products. The proposed model is then validated against composition trends observed in full-batch experiments. The model captured concentration profiles accurately, yielding sum of squared error (SSE) values around three. This model can be utilized to design and optimize the commercial manufacturing process for styrene chlorohydrin. Full article

(This article belongs to the Special Issue Circular Economy in Process Engineering: Impact Assessment and Directions for Sustainability)

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26 pages, 4283 KB

Open AccessArticle

Process Intensification Through Square-Wave Modulated Forced Periodic Operation: Nonlinear Frequency Response Analysis of an Isothermal CSTR for Methanol Synthesis

by Dalibor Marinković and Daliborka Nikolić

Processes 2026, 14(14), 2288; https://doi.org/10.3390/pr14142288 - 14 Jul 2026

Viewed by 236

Abstract

Forced periodic operation (FPO) has emerged as a promising process intensification strategy for catalytic reactors. In this study, the nonlinear frequency response (NFR) methodology was applied to investigate square-wave FPO of an isothermal CSTR for methanol synthesis. The analysis focused on periodic modulation of the inlet CO and flow rate, considering both single-input and simultaneous-input forcing. The reactor response was evaluated using higher-order frequency response functions (FRFs) to quantify the non-periodic component responsible for time-averaged process improvement. The results showed that individual modulation of either inlet CO or flow rate does not provide significant improvement in reactor performance and may even reduce methanol productivity. In contrast, simultaneous modulation generates a strong positive nonlinear interaction that substantially improves reactor performance. Under optimal forcing conditions, methanol productivity increased from 336.9 mmol min⁻¹

{k g}_{c a t}^{- 1}

at steady-state to 553.6 mmol min⁻¹

{k g}_{c a t}^{- 1}

, corresponding to a 64.3% improvement. Compared with previously reported cosine forcing, square-wave modulation nearly doubled the attainable productivity improvement while also improving hydrogen utilisation efficiency. The results indicate that square-wave FPO represents an effective intensification strategy for methanol synthesis in a laboratory-scale isothermal CSTR and confirm the capability of the NFR methodology for the a priori evaluation and optimisation of periodically operated catalytic reactor systems. Full article

(This article belongs to the Special Issue Circular Economy in Process Engineering: Impact Assessment and Directions for Sustainability)

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26 pages, 3351 KB

Open AccessArticle

Retrofit Design of a De-Isobutanizer Column via Vapor Recompression: Techno-Economic and CO₂ Emission Analysis

by Maria Santos Coelho, Sophia Sardinha de Oliveira, Rafaella Machado de Assis Cabral Ribeiro, Fernanda Ribeiro Figueiredo and Diego Martinez Prata

Processes 2026, 14(5), 867; https://doi.org/10.3390/pr14050867 - 8 Mar 2026

Viewed by 785

Abstract

Isobutane is a key feedstock for alkylate production. For separating an equimolar isobutane/n-butane mixture with 2 mol% ethane, two conventional designs are reported in the literature: a single water-cooled condenser (SC) and a dual condenser system with refrigeration (DC). This study proposes two vapor recompression retrofit configurations, SC-VR and SC-PHVR (with preheating), to improve energy efficiency and enable electrification. Economic and environmental performance were evaluated using total annualized cost (TAC) and CO₂ emissions. Compared with SC and DC schemes, SC-VR reduces CO₂ emissions by 49 and 52%, while SC-PHVR delivers higher reductions of 64 and 66%. A sensitivity analysis of electricity prices across 3-, 5-, and 10-year payback periods indicates the most favorable performance at 10 years. At 16.67 USD/GJ, SC-PHVR lowers TAC by 22 and 25%; in contrast, SC-VR provides marginal savings. At 24.03 USD/GJ, SC-VR is not economically competitive, whereas SC-PHVR continues to outperform the conventional cases, with TAC reductions of 8% and 4%. Both retrofit options significantly reduce emissions, with SC-PHVR offering the best economic performance. Finally, the proposed configurations enable the complete electrification of the de-isobutanizer system, eliminating reliance on fossil-based thermal utilities, which allows the use of renewable sources in line with the decarbonization efforts. Full article

(This article belongs to the Special Issue Circular Economy in Process Engineering: Impact Assessment and Directions for Sustainability)

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16 pages, 2645 KB

Open AccessArticle

Bioethanol Production from Chemically Obtained Cassava Hydrolysates: Effect of Nature of the Acid

by Karina Pérez-Vargas, J. L. Aleman-Ramirez, Martín Barragán-Trinidad, Soleyda Torres Arellano and P. J. Sebastian

Processes 2026, 14(5), 766; https://doi.org/10.3390/pr14050766 - 27 Feb 2026

Viewed by 1053

Abstract

Ethanol production from corn and sugarcane is well established; however, reliance on these feedstocks raises concerns related to food security, highlighting the need to explore alternative raw materials such as cassava. This study evaluates bioethanol production from different cassava root fractions—peeled cassava, starch, and peel—assessed individually within a unified experimental framework. Chemical hydrolysis using HCl or H₂SO₄ was employed as a cost-effective alternative to enzymatic saccharification. Hydrolysis efficiencies above 95% were achieved for both cassava and starch, regardless of the acid used, although HCl promoted higher glucose release in all samples. Chemical hydrolysis induced noticeable increases in surface roughness and porosity across all fractions. Fermentation efficiencies for cassava (93.1 ± 1.1% vs. 77.8 ± 4.9%) and peel (85.7 ± 2.8% vs. 69.8 ± 7.4%) were higher when HCl was used during hydrolysis, whereas starch showed no significant differences between acids. In contrast, the highest ethanol yields on a dry raw material basis were obtained from cassava hydrolyzed with H₂SO₄ (up to 0.37 ± 0.002 g/g), corresponding to a 73% ethanol recovery efficiency. The highest volumetric ethanol production rates were achieved with HCl hydrolysates, reaching up to 1.85 g/L/h for peel-derived hydrolysates. Full article

(This article belongs to the Special Issue Circular Economy in Process Engineering: Impact Assessment and Directions for Sustainability)

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20 pages, 3324 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Integrating Emerging Digital Technologies into Circular Economy Practices

by Elena Simina Lakatos, Andreea Loredana Rhazzali, Umberto Pernice, Oana Bianca Panait (Berce), Felix H. Arion and Lucian-Ionel Cioca

Processes 2026, 14(3), 556; https://doi.org/10.3390/pr14030556 - 5 Feb 2026

Cited by 2 | Viewed by 1456

Abstract

This study stems from the clear need to understand why and how organizations in Romania integrate emerging digital technologies into circular economy (CE) practices, given the critical role of this integration in improving resource efficiency and supporting sustainable business models. Data were collected through a structured questionnaire applied to 149 organizations of different sizes, ranging from SMEs (fewer than 50 employees) to large corporations (over 500 employees), operating across multiple sectors, including agriculture, construction, security, services and research. The questionnaire assessed organizations’ familiarity with CE principles, their stage of CE implementation, and their adoption of digital technologies, including artificial intelligence (AI), Internet of Things (IoT), blockchain, cloud computing and robotics. The results indicate that most organizations are aware of the potential benefits of digital technologies, particularly in terms of resource efficiency, enhanced product traceability and support for sustainability goals. However, effective implementation remains quite limited in many cases due to inadequate or outdated infrastructure, lack of technical skills, and organizational resistance to changes. At the same time, the findings further reveal a growing strategic interest in digitalization: approximately 41% of SMEs and 59% of large organizations plan to increase investments in digitalization, primarily to improve sustainability performance and foster innovation. Overall, the study provides a comprehensive overview of the current state of digitalization in support of CE in Romania and proposes practical recommendations for organizations and decision-makers, highlighting both emerging opportunities and persistent barriers. Full article

(This article belongs to the Special Issue Circular Economy in Process Engineering: Impact Assessment and Directions for Sustainability)

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28 pages, 2654 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Increasing Efficiency of Chemico-Technological Systems and Prevention of Accidents: Approaches, Models, Portfolios

by Gregory Yablonsky and Alexander Fedorov

Processes 2026, 14(3), 524; https://doi.org/10.3390/pr14030524 - 2 Feb 2026

Viewed by 904

Abstract

The aim of this work is to develop a beneficial methodology for improving the ecological and economic efficiency of chemico-technological systems (CTS). The problem is formulated as a control with a vector objective function that includes economic and environmental components. A practical approach to enhancing the environmental and economic efficiency of CTS is presented. Some approaches to accident prevention including the application of a problem-oriented dynamic model are introduced. Extended Ecological–Technological Portfolios have been developed. These Portfolios represent simplified visual models aiming to increase the environmental and economic efficiency of the CTS. Portfolios allow for the identification of dependencies between technological faults and ecological criteria and enable the investigation of the impact of the concrete chemico-technological process on the environment. Based on the Portfolios, decisions can be made for improving the economic–ecological efficiency of CTS and the prevention of accidents. Ecological–Technological Matrices, which provide a generalized characterization of technological breakdowns, have been developed. A strategy for adjusting technological constraints, using Matrices and vector criteria, has been proposed. Portfolios and Matrices can be applied in data preparation to solve certain artificial intelligence tasks for increasing the environmental and economic efficiency of potentially hazardous CTS. Some examples are given, presenting the industrial control of ammonia synthesis, methane conversion, and chemical absorption of CO₂. Full article

(This article belongs to the Special Issue Circular Economy in Process Engineering: Impact Assessment and Directions for Sustainability)

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14 pages, 4275 KB

Open AccessFeature PaperArticle

Modification of Commercial Pt/C via Deep Eutectic Solvent-Assisted Solvothermal Strategy for Efficient Selective Hydrogenation of Furfural Under Mild Conditions

by Tianran Kong, Annan Zhao, Yinghui Zhang, Zongxuan Bai, Hongying Lü and Kaixuan Yang

Processes 2026, 14(2), 223; https://doi.org/10.3390/pr14020223 - 8 Jan 2026

Viewed by 611

Abstract

Efficient conversion of biomass-based platform molecules into high-value derivatives is recognized as one formidable challenge in biomass upgrading. In this work, a one-pot deep eutectic solvents-assisted solvothermal method was developed for the modification of the commercial Pt/C catalysts by introducing a secondary metal (M = Sn, Bi, Ge, Sb, Pb). The structural and electronic properties of the catalysts were precisely tuned. Among the screened metals, the addition of Sn yielded the most significant improvement in catalytic activity. The optimized PtSn_0.5/C-140 catalyst achieved superior furfural (FAL) conversion and furfuryl alcohol (FOL) selectivity under mild conditions (20 °C, 2 MPa H₂). Comprehensive characterizations, including XRD, HRTEM, XPS, and H₂-TPD, confirmed the formation of Pt-Sn solid-solution phase. Furthermore, Characterization and reaction results revealed that the electronic and geometric effects induced by Sn modulated Pt active sites, significantly enhancing the adsorption of the active H species. Additionally, the SnO_x species adjacent to the Pt-Sn sites served as hydrogen spillover acceptors, further accelerating the hydrogenation process. The synergy between the Pt-Sn solid-solution phase and SnO_x species is identified as the origin of the superior performance at room temperature. These findings provide a new strategy for the design of high-performance biomass conversion catalysts by upgrading commercial noble metal catalysts. Full article

(This article belongs to the Special Issue Circular Economy in Process Engineering: Impact Assessment and Directions for Sustainability)

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28 pages, 1205 KB

Open AccessReview

Deep Eutectic Solvents as a Potential Alternative Extraction Technique for the Isolation of Phenolic Compounds from Economically Important European Tree Species

by Martin Štosel, Aleš Ház, Richard Nadányi and Veronika Jančíková

Processes 2026, 14(12), 1877; https://doi.org/10.3390/pr14121877 - 9 Jun 2026

Viewed by 562

Abstract

The by-products of the wood-processing industry are still predominantly used for energy generation, despite being a rich source of high-value phenolic compounds. This review focuses on the valorization of bark from economically crucial European tree species. Based on an extensive literature survey, three deciduous species (Fagus sylvatica, Quercus robur/petraea, Carpinus betulus) and three coniferous species (Pinus sylvestris, Picea abies, Abies alba) were selected on the basis of their distribution in the European Union, their industrial relevance, and the composition and bioactivity of their extractive phenolic fractions. Conventional and nonconventional extraction techniques are briefly compared, with particular emphasis on deep eutectic solvents (DESs) as emerging green media for the selective isolation of phenolics from bark and other lignocellulosic residues. DESs are typically renewable, nontoxic, biodegradable, and nonflammable, and their tunable composition allows them to be tailored to specific target compounds. The literature data demonstrate that DES-based extractions can provide phenolic-rich extracts with high antioxidant and antimicrobial activities and, in some cases, can outperform conventional solvents. Finally, the potential applications of bark-derived phenolic extracts in the pharmaceutical, agricultural, food, polymer processing, and cultural heritage sectors are outlined. The review also identifies knowledge gaps in DES selection, extract purification, and solvent recovery, highlighting future research needs for integrating DESs into sustainable wood-biomass biorefineries. Full article

(This article belongs to the Special Issue Circular Economy in Process Engineering: Impact Assessment and Directions for Sustainability)

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41 pages, 7425 KB

Open AccessReview

Advancements in Plastic Waste Sorting: A Review of Techniques and Applications

by Felipe Anchieta e Silva, Amélia de Santana Cartaxo, Antônio Demouthié de Sales Rolim Esmeraldo, Elaine Meireles Senra and José Carlos Pinto

Processes 2026, 14(7), 1144; https://doi.org/10.3390/pr14071144 - 2 Apr 2026

Viewed by 1856

Abstract

The widespread utilization of plastic materials across various industrial sectors drives a continuous increase in global polymer demand. The exponential production growth generates severe environmental challenges regarding municipal solid waste management, as substantial fractions of post-consumer residuals enter landfills due to limited recycling infrastructure. Mitigating the global environmental burden requires the implementation of advanced recovery strategies to transition polymer waste into viable secondary feedstocks. Consequently, deploying efficient sorting techniques constitutes a fundamental requirement to integrate plastic materials into formal waste management protocols and optimize recycling yields. Technological innovations currently drive the transition from traditional manual segregation towards highly sophisticated automated sensor-based sorting architectures, maximizing separation efficiency. In this context, the present study comprehensively reviews pretreatment classification techniques engineered to fractionate heterogeneous waste streams into high-purity material flows. Rather than restricting the analysis to polyolefins, this review encompasses a broad spectrum of commodity polymers predominantly found in urban solid waste environments. Full article

(This article belongs to the Special Issue Circular Economy in Process Engineering: Impact Assessment and Directions for Sustainability)

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55 pages, 2718 KB

Open AccessReview

Eradication or Exploitation? Water Hyacinth Control Alternatives in Mexico: A Review

by María de Lourdes Cinco-Izquierdo, Ricardo Musule-Lagunes, Araceli Guadalupe Romero-Izquierdo, Rafael Maya-Yescas and Marco Antonio Martínez-Cinco

Processes 2026, 14(5), 745; https://doi.org/10.3390/pr14050745 - 25 Feb 2026

Cited by 2 | Viewed by 1936

Abstract

A systematic review of the scientific literature focused on the analysis of the main strategies related to the management of Eichhornia crassipes [water hyacinth] in Mexico is presented. The review was classified according to the levels of the biomass valorization pyramid, using specific inclusion and exclusion criteria: (i) eradication; (ii) physical control of the plant; and (iii) exploitation of its biomass. It focused on research conducted in Mexico from 1971 to 2023, which allowed for the analysis of a total of 147 studies. The results indicated that 73.4% of the research in Mexico is oriented towards the exploitation and valorization of water hyacinth biomass through the transformation of the plant into mid-value products, such as chemicals and materials (70.7%), energy (12.2%), food (7.3%) and health and lifestyle products (9.8%); however the sectors considered high-added-value, such as pharmaceuticals, fine chemicals and food, continue to be areas of opportunity. The remaining 26.6% focuses on control and eradication strategies, through the insertion of biological enemies, and physical control, by means of cutting and crushing the plant in situ. This situation underscores the importance of promoting integrated management approaches that incorporate biomass recovery, contributing to environmental sustainability and the responsible use of this invasive resource. Full article

(This article belongs to the Special Issue Circular Economy in Process Engineering: Impact Assessment and Directions for Sustainability)

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