Nonconvex generalized disjunctive programs (GDPs) frequently arise in chemical engineering applications and are commonly reformulated as mixed-integer nonlinear programs (MINLPs). However, nonconvexities in these reformulations often lead to numerical difficulties, sensitivity to initialization, and degraded solution quality when solved with general-purpose MINLP solvers. This work proposes a two-phase strategy to mitigate these effects by generating improved initial points through the solution of a sequence of relaxed MINLPs, which are subsequently used to initialize the original formulation. The approach is evaluated on a family of purely disjunctive benchmark problems, referred to as the Crescent problems, with sizes ranging from 60 to 1000 binary variables. Numerical experiments using the DICOPT and SBB solvers assess performance in terms of objective value distributions, the percentage of feasible initial points, and average constraint violation. The results indicate that the proposed strategy improves solution quality, increases the likelihood of feasibility, and reduces the magnitude of constraint violations across all problem sizes.

Učbenik Python v kemiji in kemijskem inženirstvu je namenjen študentom prvega letnika, ki se prvič srečujejo z računalniškim programiranjem. Na preprost in sistematičen način uvaja bralca v osnovne pojme programskega okolja Python ter postopno prikazuje njegovo uporabo pri reševanju izbranih problemov iz kemije in kemijskega inženirstva. Poleg osnov programiranja prinaša uvodne primere uporabe sodobnih digitalnih pristopov, kot sta podatkovna analiza in umetna inteligenca, s čimer študentom odpira vpogled v sodobne trende kemijsko-inženirske stroke. Publikacija je zasnovana tako, da razvija praktične računalniške spretnosti ter spodbuja samostojno učenje in nadaljnje raziskovanje. Učbenik je objavljen kot odprto učno gradivo, kar študentom, učiteljem in strokovnjakom, ki jih zanima uporaba Pythona v kemiji in kemijskem inženirstvu, omogoča dolgoročno podporo pri študiju in delu.

Methanol is a versatile substance that can be used in combustion engines and fuel cells and as a feedstock for the production of various chemicals. However, the majority of methanol is currently produced from fossil fuels, which is not sustainable. The aim of this study was to analyze and evaluate the feasibility of methanol production from renewable sources as a bridge to a low-carbon economy and its potential as an alternative to fossil-derived chemicals. For this purpose, the process of methanol production from captured CO2 and water as an H2 source was simulated in Aspen Plus. For CO2 capture, the monoethanolamine (MEA) absorption process was assumed. The H2 required for methanol synthesis was obtained by alkaline water electrolysis using electricity from renewable sources. The captured CO2 and the produced H2 were then converted into methanol through the process of CO2 hydrogenation in two ways, direct and two-step synthesis. In the direct conversion, the hydrogenation of CO2 to methanol was carried out in a single step. In the two-step conversion, the CO2 was first partly converted to CO by the reverse water-gas shift (RWGS) reaction, and then the mixture of CO and CO2 was hydrogenated to methanol. The results show that direct synthesis has a higher methanol yield (0.331 kmol of methanol/kmol of H2) compared to two-step synthesis (0.326 kmol of methanol/kmol of H2). The direct synthesis produces 13.4 kmol of methanol/MW, while the two-step synthesis produces 11.2 kmol of methanol/MW. This difference amounts to 2.2 kmol of methanol/MW, which corresponds to a saving of 0.127 $/kmol of methanol. Besides the lesser energy requirements, the direct synthesis process also produces lower carbon emissions (22,728 kg/h) as compared to the two-step synthesis process (33,367 kg/h).

Given the urgency to combat climate change and ensure environmental sustainability, this review examines the transition to net-zero emissions in chemical and process industries. It addresses the core areas of carbon emissions reduction, efficient energy use, and sustainable practices. What is new, however, is that it focuses on cutting-edge technologies such as biomass utilization, biotechnology applications, and waste management strategies that are key drivers of this transition. In particular, the study addresses the unique challenges faced by industries such as cement manufacturing and highlights the need for innovative solutions to effectively reduce their carbon footprint. In particular, the role of hydrogen as a clean fuel is at the heart of revolutionizing the chemical and process sectors, pointing the way to cleaner and greener operations. In addition, the manuscript explores the immense importance of the European Green Deal and the Sustainable Development Goals (SDGs) for the chemical industry. These initiatives provide a clear roadmap and framework for advancing sustainability, driving innovation, and reducing the industry’s environmental impact, and are a notable contribution to the existing body of knowledge. Ultimately, alignment with the European Green Deal and the SDGs can bring numerous benefits to the chemical industry, increasing its competitiveness, promoting societal well-being, and supporting cross-sector collaboration to achieve shared sustainability goals. By highlighting the novelty of integrating cutting-edge technologies, addressing unique industrial challenges, and positioning global initiatives, this report offers valuable insights to guide the chemical and process industries on their transformative path to a sustainable future.

The 6th International Conference on Technologies & Business Models for Circular Economy (TBMCE) was organized by the Faculty of Chemistry and Chemical Engineering, University of Maribor in collaboration with the Strategic Research and Innovation Partnership - Networks for the Transition into Circular Economy (SRIP- Circular Economy), managed by the Chamber of Commerce and Industry of Štajerska. The conference was held in Portorož, Slovenia, at the Grand Hotel Bernardin from September 6th to September 8th, 2023. The Netherlands joined us as a partner country of the conference. TBMCE 2023 was devoted to presentations of circular economy concepts, technologies and methodologies that contribute to the shift of business entities and society as a whole to a more responsible, circular management of resources. The conference program included 2 round tables, 6 panel discussions, plenary and keynote sessions, oral and poster presentations on the following topics: Sustainable energy, Biomass and alternative raw materials, Circular business models, Secondary raw materials and functional materials, ICT in Circular Economy, Processes and technologies. The event was under the patronage of Ministry of the Economy, Tourism and Sport and Ministry of Cohesion and Regional Development.

Transitioning towards net zero emissions is critical in the chemical and process industries to combat climate change and ensure environmental sustainability. Key focus areas of this review include the reduction of carbon emissions, the efficient utilization of energy resources, and the adoption of sustainable practices. Cutting-edge technologies such as biomass utilization, biotechnology applications, and waste management strategies are crucial in achieving this transition. Industries, including cement production, encounter unique challenges in their quest for sustainability and must actively seek innovative solutions to mitigate their carbon footprint effectively. The role of hydrogen as a clean fuel and its potential to revolutionize the chemical and process sectors is also discussed. The European Green Deal and Sustainable Development Goals (SDGs) are significant for the chemical industry. They provide a clear roadmap and framework for promoting sustainability, driving innovation, and reducing the industry's environmental impact. By aligning with these initiatives, the chemical industry can enhance its competitiveness, contribute to societal well-being, and foster collaboration across sectors to achieve shared sustainability objectives.

Process Integration (PI), which supports Process Design, Integration, and Optimisation, has been around since the early 1970s. PI evolved from Heat Integration, which remains the cornerstone of PI and its continuous advance. Heat Integration is closely related to the development of Chemical, Mechanical, and Power Engineering. It has been supported by the extensive implementation of mathematical modelling, simulation, and optimisation, as well as the application of information technology. Its development has accelerated over the years as its methodology has provided answers and support for important economic development issues—better utilisation and savings of energy, water, and other resources. This contribution provides a short overview of Heat Integration—its historical development, achievements, and future challenges.

Determining the optimal design of a Heat-Integrated Water Network (HIWN) is a complex task due to the existence of highly nonlinear relationships when considering concentrations, mass and heat balances. Due to that complexity, the solution is usually obtained by a sequential approach. In this approach, the minimum fresh water and utility consumption is firstly determined. Then, the exact design of the HIWN is synthesised with the fixed minimum fresh water and utility consumption. Another way to obtain the HIWN design is by using a simultaneous approach. However, such a model can be highly nonlinear requiring the application of a special solution strategy. In this work, a two-step approach was developed and applied. In the first step, a targeting Mixed-Integer Nonlinear Programming (MINLP) model with a high share of linearity was applied estimating also the HEN investment. In this way, the solutions are steered towards an optimal solution by establishing appropriate trade-offs between investment and operating costs during the targeting step. Based on the results of the first step, a reduced superstructure and MINLP model are used in the second design step to select promising matches for heat exchangers. By excluding the non-promising matches that previously led to an unnecessary increase in the complexity of the synthesis model, the second step MINLP model performs much better and enables synthesizing the entire HIWN simultaneously. The aim of this work was to verify whether the two-step approach is suitable for solving the HIWN problem. The obtained solution for case study considered in this work indicated the applicability of the proposed approach, which will be also applied in further research on large-scale HIWN problems.

The 5th International Conference on Technologies & Business Models for Circular Economy (TBMCE) was organized by the Faculty of Chemistry and Chemical Engineering, University of Maribor in collaboration with the Strategic Research and Innovation Partnership - Networks for the Transition into Circular Economy (SRIP- Circular Economy) and Chamber of Commerce and Industry of Štajerska. The conference was held in Portorož, Slovenia, at the Grand Hotel Portorož from September 12th to September 14th, 2022. TBMCE 2022 was devoted to presentations of circular economy concepts, technologies and methodologies that contribute to the shift of business entities and society as a whole to a more responsible, circular management of resources. The conference program included panel discussions, plenary and keynote sessions, oral and poster presentations on the following topics: Sustainable energy, Biomass and alternative raw materials, Circular business models, Secondary raw materials and functional materials, ICT in Circular Economy, Processes and technologies. The event was under the patronage of Ministry of Economic Development and Technology.

This paper proposes a concept of a process design for the separation and recovery of n-butanol from a five-component mixture, consisting of n-butanol, isobutanol, formaldehyde, water and methanol. The mixture is a common waste stream in the production of butylated amino resins; therefore, recovery of n-butanol is crucial to the efficiency of the process. The results show that up to 94% of the n-butanol present in the waste stream can be recovered. Under the studied conditions, 99.76% pure n-butanol can be obtained, while formaldehyde, water and methanol are present only in traces. The energy intensity of the process is estimated at 2.42 MJ/kg of purified n-butanol. The economic analysis of the process shows that the process is economically viable over a wide range of production capacities, as evidenced by high net present values and high return on investment values.

In addition to the consumption of hot utilities, there is also a significant cost associated with the consumption of cold utilities when there is a high demand for cooling. A promising solution for cooling is an absorption chiller (AC), which uses heat instead of electricity for cooling. A thermodynamic approach for evaluating AC integrated with a process is presented in this work. A model for assessing the properties and duties of an AC cycle was developed. The integration of a combined process-AC system was evaluated using the Grand Composite Curve. Three different options of integration were analyzed: (i) above the Pinch, (ii) below the Pinch, and (iii) across the Pinch. AC represents the combined effect of a heat engine and a heat pump, as the generator together with the absorber and condenser has the function of a heat engine, while the evaporator combined with the absorber and condenser mimics the function of a heat pump. The comparison between the non-integrated and integrated process-AC systems has revealed that the proper placement of AC is across or below the Pinch and the improper is above the Pinch. If AC was entirely integrated below the Pinch, the integration would result in a complete (100%) reduction in the consumption of hot utility for the operation of AC. The most suitable placement of AC with double reduction of hot utility consumption and complete reduction of both hot and cold utility to operate AC is across the Pinch due to the pumping of heat through AC from below to above the Pinch.

Wastewater treatment in the cosmetic industry, which operates in batch mode, is a complex task due to the highly variable composition of the water to be treated. Among other parameters, n-heksan extractable material (HEM) and surfactants must comply with the specified limits. From theory, the advanced oxidation process (AOP) with a Fenton-like process is more suitable for surfactant degradation, while the coagulation/flocculation process (CFP) is more efficient for HEM removal. Determining the appropriate sequence of AOP treatment and CFP affects the quality of released water, the efficiency of each process step, and the consumption of required chemicals.The objective of this research was to optimize the treatment sequence, the time required for each treatment, and the amount of sludge from wastewater treatment. For this purpose, AOP treatment and CFP laboratory tests were performed for different groups of samples and samples with high HEM and/or surfactant content. Based on the efficiency of the laboratory tests and the assessed wastewater composition (from mass and concentration balances), an optimization model was developed. The optimization model enables optimization of the wastewater treatment plant (WWTP) by feeding each of the streams to either i) AOP treatment, ii) CFP treatment, iii) AOP treatment followed by CFP treatment, iv) CFP pretreatment followed by AOP and CFP, v) bypass (i.e. the wastewater stream is not treated but mixed with treated streams). The optimal solution can be determined by minimizing the total annual cost of treatment or/and maximizing removal of pollutants. An additional analysis was performed considering the dilution of wastewater with freshwater after the treatment process. The results show that this last proposal is more economical but leads to questionable environmental impacts.

In this paper, we present virtualization of the pressure control demonstration unit. The two main objectives were: to determine a dynamic mathematical model of the unit, and to use the mathematical model to virtualize the process that enables open and closed loop simulations. The dynamic model of the unit, which was developed based on experimental input-output data, shows Fit to Working Data greater than 95 %. Finally, the unit was virtualized in a form of a graphical user interface that hides all the modeling components from the user. The virtual unit is thus designed to enable students with limited or no prior knowledge of control theory and modeling of dynamic systems to study and analyze the dynamics of the system and to observe the effects of feedback control mechanisms.

This paper describes the state of the art and future opportunities for process design and sustainable development. In the Introduction, the main global megatrends and the European Union's response to two of them, the European Green Deal, are presented. The organization of professionals in the field, their conferences, and their publications support the two topics. A brief analysis of the published documents in the two most popular databases shows that the environmental dimension predominates, followed by the economic one, while the social pillar of sustainable development is undervalued. The main design tools for sustainability are described. As an important practical case, the European chemical and process industries are analyzed, and their achievements in sustainable development are highlighted; in particular, their strategies are presented in more detail. The conclusions cover the most urgent future development areas of (i) process industries and carbon capture with utilization or storage; (ii) process analysis, simulation, synthesis, and optimization tools, and (iii) zero waste, circular economy, and resource efficiency. While these developments are essential, more profound changes will be needed in the coming decades, such as shifting away from growth with changes in habits, lifestyles, and business models. Lifelong education for sustainable development will play a very important role in the growth of democracy and happiness instead of consumerism and neoliberalism.

We introduce MIPSYN-Global - a unique computer-based process synthesizer. It is built on the foundations of its predecessor MIPSYN, using the knowledge and experience gained from decades of research in the field of PSE. One of its main features is the newly developed Graphical User Interface - MIPSYN- Global Modeler (MGM), which is specifically designed for fast modeling of process superstructures and representation of results. In addition, the modeler generates an Aspen Plus process simulator input file and runs the Aspen Plus simulation in which more rigorous thermodynamic and process unit models can be used. MGM is evidently the most notable new feature in the development of MIPSYN-Global. However, it is important to note that MIPSYN-Global inherits and builds upon the capabilities of its predecessor, making it a versatile and robust platform for solving process synthesis problems from engineering fields beyond chemical engineering. Nevertheless, since graphical modeling capability is a rather rare approach in equation-oriented synthesis, we present MGM's capabilities with an illustrative example of simple reactor network synthesis.

This work presents a preliminary design of a two-stage vacuum evaporation process converting a diluted liquid digestate into concentrated liquid fertilizers. Di-gestate is produced in a 1 MW biogas plant during the anaerobic digestion of poultry manure and corn silage. Laboratory experiments showed that in the first evaporation stage, about three-quarters of input digestate can be stripped to a diluted ammonia solution, while the concentrate can be used as phospho-rus-potassium PK-fertilizer. After neutralization with H2SO4, the ammonium sulphate solution is concentrated in the second evaporation stage. Feasible operating temperatures that allow heat integration between the two stages were determined in a laboratory environment at 40 ?C for the first stage and 60 ?C for the second. A preliminary process flow sheet was simulated in Aspen Plus to obtain data for heat integration and optimization of industrial-scale processes. The process was completely integrated by using the waste hot utility available at the site, while the external utilities demand was virtually zero. Optimizing the flow rate of the added sulphuric acid improved overall economic performance. The optimization and heat integration of the two-stage vacuum evaporation process within a biogas plant resulted in a circular and economically viable waste management technology.

In this paper, we present an approach to global optimization of bilinear programs based on a transformation of bilinear terms to elementary functions of single variables. The substitutions relocate bilinear terms to additional equality constraints. The complicating variables in these constraints are separated by logarithm operations. Finally, the log-linear constraints are relaxed by piecewise linear approximations and/or linearizations. The transformation produces a lower-bounding mixed-integer linear program, which is used in conjunction with the original bilinear program in a global optimization algorithm. The approach was tested by pooling problems from the literature. The global optimum was obtained in all the test problems; however, more elaborate algorithmic schemes would be needed to make the proposed approach computationally efficient.

This review paper describes some historical facts, the state of the art of process design and sustainable development. In the Introduction the most important global megatrends are presented and the European Union response to them, the European Green Deal. Process design and sustainable development are dealt with separately and holistically. Organization of professionals from the area, their conferences and publication are supporting the two topics. A short analysis of the published documents in two most popular databases shows that environmental dimension is prevailing, followed by economic one while social pillar of sustainable development is undervalued. The most important design tools for sustainability are described. An important practical case, the European chemical and process industries are analyzed and their achievements in sustainable development are shown; in particular their strategies are presented in more detail. The conclusions are embracing the most urgent future development areas of process industries, carbon capture with utilization or storage, the process analysis, simulation, synthesis and optimization tools; zero waste, circular economy and resource efficiency are already playing an important role. But deeper changes are needed in the future decades including de-growth with changes of habits, lifestyles, and business models. Lifelong education for sustainable development will play a very important role in the growth of democracy and happiness instead of the consumerism and neoliberalism.

In this work, we compare the performance of the Alternative Mixed-Integer (AMI) reformulation of GDPs against those of the Big-M and Hull Reformulation (HR) in a framework of nonconvex mixed-integer nonlinear models. The robustness and efficiency of the reformulations are tested on a synthetic example using commercially available solvers, namely SBB, DICOPT++, SCIP, and Alpha-ECP. The comparison is carried out on the following key criteria: efficiency (CPU usage, number of iterations), robustness (number of successfully solved problems), quality of the obtained solutions (comparison of the objective function values). Results obtained in this study indicate that the AMI reformulation represents a competitive alternative to Big-M and HR.