Natural gas (NG) reforming dominates global hydrogen production through three chemistry routes: autothermal (ATR), steam-methane reforming (SMR), and partial oxidation (POX). Hydrogen plants generate substantial amounts of CO2, and reducing the carbon intensity is vital for sustainable development. There is a lack of technoeconomic analyses exploring hydrogen production by natural gas partial oxidation (POX). This work examines two pathways to mitigate CO2 in POX plants by using recoverable heat from the process to (1) integrate the plant with an electrolyzer to enhance hydrogen production and (2) integrate with CCS (blue hydrogen). Design regimes are identified for the integrated POX-CCS process. Technoeconomic analyses show the trade-off between hydrogen costs and the reduction in CO2 emissions. Results show that electrolyzer integration is limited due to the electrolyzer's large power demand, while CCS integration achieves 95% emission reductions with only 9% cost increase. A life-cycle assessment compares the integrated POX system with conventional SMR and electrolysis.

Managing heat is a major challenge for oxidative coupling of methane (OCM) because of its high exothermicity. While recent innovations have mainly focused on reactor design, most studies assume isothermal operation, which is often impractical for scale-up. Adiabatic operation better reflects industrial conditions but remains underexplored. Additionally, little attention has been given to distributing O2 along the reactor or using inter-stage cooling to smooth temperature variations inside the OCM reactor and improve performance. In this work, we address those gaps by optimizing a multi-zone reactor design with distribution feeding of O2. Using Simulated Annealing, we model up to 30 reactor zones, each treated as a fixed-bed, one-dimensional and pseudo-homogeneous system. Our results show that distributing oxygen across multiple zones with interstage cooling increases the C2 yield by almost 8 times, from 5.7% in a single zone to 46.5 % across 30 zones, achieving smoother temperature profiles without changing the catalyst.

Organic Rankine cycle (ORC) systems are a class of distributed power-generation systems that are suitable for the efficient conversion of low-to-medium temperature thermal energy to useful power. These versatile systems have significant potential to contribute in diverse ways to future clean and sustainable energy systems through, e.g., deployment for waste-heat recovery in industrial facilities, but also the utilisation of renewable-heat sources, thereby improving energy access and living standards, while reducing primary energy consumption and the associated emissions. The energetic and economic performance, but also environmental sustainability of ORC systems, all depend strongly on the working fluid employed, and therefore a significant effort has been made in recent years to select, but also to design novel working fluids for ORC systems. In this context, computer-aided molecular design (CAMD) techniques have emerged as highly promising approaches with which to explore the key role of working fluids, and present an opportunity, by focusing on the design of new eco-friendly fluids with low environmental footprints, to identify alternatives to traditional refrigerants with improved characteristics. In this review article, an overview of working-fluid and system optimisation methodologies that can be used for the design and operation of next-generation ORC systems is provided. With reference to wide-ranging applications from waste-heat recovery in industrial and automotive applications, to biomass, geothermal and solar-energy conversion and/or storage, this review represents a comprehensive, forward-looking exposition of the application of CAMD to the design of ORC technology.

Greenhouse farming systems have the potential to sustainably relieve the stresses on food supply systems caused by a globally increasing population, together with the reduction of available agricultural land due to urbanization and soil degradation. However, literature regarding the sustainable design and operation optimization of greenhouse process systems remains scarce. This work focuses on the optimal planning and scheduling of a greenhouse farming system dependent on the utilized farming technologies, the available crops, and the selected geographic location. Ad extremum, the derived greenhouse optimization framework enables the generic trade-off analysis among completely isolated and transparent greenhouses, as well as energy and water saving greenhouses. Planning and scheduling decisions include the cover material transmissivity and isolation, cooling, heating, wetting and drying technologies, multi-crops farming strategies, irrigation, as well as artificial lighting and a dynamic shading system. To derive sustainable greenhouse system solutions, this work follows a food-energy-water nexus approach by analyzing not only an economic objective, but also resource-use objectives and a societal benefit objective, in the form of the nutritional value of the produced food basket, over one year of operation at an hourly timescale. Accordingly, this approach results in a multi-objective multi-scale mixed-integer linear programming optimization problem of large size. Various solution strategies to reduce the computational burden and solve this optimization problem to global optimality are discussed. The Pareto-front envelope for Doha, Qatar is characterized by a best-possible solution vector of $2.949M/year, 144 MW/year, 124 m3/year, and farming of carrot, lettuce, tomato, and spinach. In turn, the best trade-off solution for farming this nutrition optimal food basket consist of an annualized system cost of between $3.2M and $3.5M, energy-use between 186 and 189 MW, and water-use of 138 m3.

The transition from indirect to direct methane conversion marks a significant advancement in chemical processing. One promising direct reaction is methane dehydroaromatization, which converts methane to aromatics in a single step with zero CO2 emissions. However, the commercialization of MDA faces major challenges including thermodynamic limitations, rapid catalyst deactivation, and high temperature requirements. Integrating MDA with another reaction offers a potential solution to these challenges combined. This work explores the potential opportunities and limitations for chemical synergy when coupling the oxidative coupling of methane (OCM) to MDA through mass integration. Experimental studies were conducted by passing the oxidative coupling of methane (OCM) reactor effluent to a downstream MDA reactor. Periodic feeding of OCM to the MDA catalyst showed limited improvement, indicating that OCM composition alone does not maintain stable MDA performance. Varying the temperature over time in MDA reactor demonstrated that C2 coming from OCM contribute to aromatic production even at low temperatures (450 degrees C). However, at such temperature, the conversion of CO2 to CO and CH4 to aromatics does not occur, highlighting the need for high operating temperatures in the OCM-MDA coupling process. The coupling of OCM and MDA was tested with different MDA space velocities as 3750, 1875, and 1250 mL/g/h, corresponding to 0.2 g, 0.4 g and 0.6 g catalyst loading, respectively. The case of 1250 mL/g/h maintained a stable 14 % conversion and 2.5 % yield of benzene over 10 h, converting all CO2 to CO. Characterization using TGA, Raman spectroscopy, and XPS on spent catalysts indicated limited carbon removal by OCM effluent, and confirmed that CO2 is causing the oxidation of Mo2C to MoOx. A reaction scheme for the OCM-MDA coupling using Mo/ZSM-5 is proposed to guide future exploration of this promising two-step process.

The food-energy-water nexus (FEWN) postulates that sustainable decision-making regarding the interconnected resources food, energy and water must consider all involved resources holistically. Due to its multi-scale complexity, modeling challenges and computational intractability regarding the interconnected FEWN optimization remain. To overcome these challenges, this work proposes employing surrogate models based on data-driven and model optimization techniques, while quantifying the introduced errors due to both the selected approximation and optimization methods. In turn, we derive a mixed-integer linear FEWN planning and scheduling optimization model based on a greenhouse farming, a renewable energy and a reverse osmosis desalination water supply system, which is initially computationally intractable. This computational complexity is first discussed and overcome for the energy-water nexus supply system, before solving the complete FEWN supply system by utilizing strategies such as relaxation, modularization and convex hull reformulation.

The implementation of electrified and compact reformers is a promising direction to intensify hydrogen production from natural gas and biomethane feedstocks and reduce carbon emission footprints. Piston reactor technology has the potential to reach this by utilizing the reactor unique high temperature and pressure operating window, mode of operation involving rapid adiabatic compression-expansion cycles and co-generation of electrical and mechanical power attractive for integration with other processing units to make efficient process design. This work aims to assess the piston reactor for hydrogen production process on its volumetric productivity, operating window, energy efficiency, CO2 emission, and initial economics. It will also theoretically evaluate whether gas-phase steam methane reforming (SMR) and autothermal reforming (ATR) are viable in this reactor technology. A piston reactor model is established using a zero-dimensional thermodynamic single-zone piston model coupled with an available gas-phase mechanistic model. The highly endothermic SMR reaction is not feasible under a wide range of conditions, leading to its elimination from further assessments and studies. ATR is an attractive route for hydrogen production. Compared to the simulated industrial catalytic ATR reformer at conventional conditions, the piston reactor reaches a similar methane conversion between 89 % and 97 % while operating in the gas phase without using any catalyst with an intake temperature lower by 300 K relative to the conventional case. An ATR process design is established showing attractive economics even at a small production capacity of 25 tons/day of hydrogen, and comparable CO2 emissions as that of a large-scale industrial ATR process.

Within the context of renewables and chemical energy storage, this work aims to explore chemical reaction conversion through the electro-mechanical route which is different from the commonly employed electro-thermal and electro-chemical conversion methods. Piston reactor is a novel equipment concept that can couple the rotational movement from an electric motor to a reciprocating piston within an enclosed reaction chamber resembling the operation of an internal combustion engine. Exploration of a reactor technology still in the laboratory stage requires an assessment of reaction intermediate mixtures to identify potential leads. This work uses a systematic methodology to assess these intermediate mixtures beyond typical reactor yield metrics to include economic values as part of the decision-making toward identifying lead candidates. Rather than focusing on a specific target reaction or product, this work is carried out as a model-driven study to cover a wider range of conditions and product scenarios. Propane as the main feedstock is selected because it is easier to trigger in the piston reactor, it is not a complex feed, a detailed kinetic mechanistic model is available to study it, and most importantly it can generate a wide range of industrially relevant products to serve the purpose of this study. The study revealed that the highly endothermic propane pyrolysis reaction requires intake temperatures larger than 950 K which is impractical. Diluting the feed with argon is one way to lower this intake temperature and achieve desirable conversion. This however is impractical because of additional separation steps and reduced production capacity. Thermal coupling of propane pyrolysis with exothermic side reactions by co-feeding oxygen, water, or carbon dioxide are investigated and showed promising results. A diverse range of products are produced such as hydrogen, carbon monoxide, ethylene, and propylene, achieving high conversions (>90%), while simultaneously generating useful work and process heat. Unconventional triggers such as using ozone to generate radicals and trigger ignition are investigated to further lower the intake temperature requirements. The explored solution space is then evaluated considering a new reactor metric as the value of products mixture stream. Regions of high-value products do not match those obtained using the traditional yield metrics. This shows the importance of what metrics to use for assessing reactors with wide range of reaction mixture intermediates as the piston reactor. Full economic analysis and optimization are the right direction in the future to properly assess the potential of piston reactor technology.

Greenhouse gas emissions produced from fossil-based power systems contribute significantly to the problem of global warming. Reducing these missions requires transitioning towards decarbonized systems where the emissions are either avoided, processed (utilized or stored), or offset. Different technological pathways, such as renewable energy production, CO2 capture and processing, or negative emissions technologies, aim to achieve these goals. Decisions on technology selection and system design are associated with high costs which can be reduced at the planning stage through optimization. The temporal variations in power demand and renewable energy supply can significantly impact the design of a low-emissions energy system. Hence, effective decision-making must consider such impact in a comprehensive framework that accounts for the potential synergies between different options. This work presents a mixed integer linear programming model that considers the impacts of energy supply and demand dynamics to optimize the design and operation of an integrated power system while also adhering to a set emissions limit. The model integrates renewable power production and storage with CO2 capture, utilization, and sequestration by considering H2 production and storage. This integrated approach allows for examining the effects of the dynamics on the cost of electricity, hydrogen, and CO2 capture, which impacts the profitability of the products. This is shown in a case study that demonstrates the effectiveness of the proposed method by analyzing the impact of emissions constraints on the design, operation, and total cost of the system. The case study showed that including negative emissions technologies and CO2 capture and processing beside renewable energy allows achieving net zero emissions power systems with a significant contribution of fossil-based power in the optimal energy mix.

Achieving worldwide sustainable development is a practical challenge that demands an efficient management of resources across their entire value chains. This practical task requires the optimal selection of pathways for extracting, processing, and transporting resources to meet the demands in different geographic regions at minimal economic cost and environmental impact. This work addresses the challenge by proposing a systematic framework for designing resource-processing networks that can be applied to resource management problems. The framework considers the integration and resource exchange within and across multiple processing clusters. It allows for the life cycle assessment of the environmental and economic impacts of the defined value chains, and design accordingly the different processing and transport systems from extraction to final use. The proposed representation and optimization model are demonstrated in a case study to assess the impact of energy transition under decarbonization constraints on long-distance energy supply chains. The objective is to identify optimal cluster designs and interconnecting transportation networks for decarbonized energy supply between energy exporters and importers.

Reducing emissions requires transitioning towards decarbonized systems through avoiding, processing, or offsetting. Decisions on system design are associated with high costs which can be reduced at the planning stage through optimization. The temporal variations in power demand and renewable energy supply significantly impact the design of a low-emissions energy system. Effective decision-making must consider such impact in a comprehensive framework that accounts for the potential synergies between different options. This work presents a mixed integer linear programming model that considers the impacts of energy supply and demand dynamics to optimize the design and operation of an integrated energy system while adhering to a set emissions limit. The model integrates renewable power with CO2 capture, utilization, and sequestration by considering H-2 production and storage. The case study showed including negative emissions technologies and CO2 capture and processing with renewable energy allows achieving net zero emissions power.

Work in Progress: Engineering for sustainable development. An undergraduate course inspiring new mentalities in engineering students of all majors. Abstract There is a realization that the world is becoming unsustainable because of the technology developed by engineers. National and international engineering bodies have recognized this problem, and have articulated the need for sustainable engineering. This is creating an increasing social demand both nationally and globally to graduate engineers who have been trained to respond to the modern economic and environmental challenges. In a previous work at a large university in the Southwest, the authors developed an instrument to measure sustainable development literacy in incoming freshman engineering students. This work demonstrated a lack of understanding about sustainable engineering among the incoming freshman and led to the development of a module on sustainable engineering. The student engagement and interest in this module was measured, and these results have led to the design of a full semester long course titled Engineering for Sustainable Development for undergraduate students of all majors. The course will take a modular approach in its development with each topical module having clearly defined and measurable outcomes with some independence. Some preliminary conversations have shown interest in this topic in industry, and the module approach of the course will be structured for workforce development with PDH and CEU credits for registered professional engineers. Responding to those demands for a more sustainable engineering practice, the course involves sustainable circular designs as core promoters of a circular economy. This innovative design thinking will create a new mentality in engineering students. In this paper, the authors present the process followed for the design, implementation and assessment of the course "Engineering for sustainable development" aimed to introduce and integrate sustainability engineering learning early in the engineering curriculum and leveraging the same content differentiated for adult learners in workforce development. The final paper will contain analysis of learning outcomes and learner feedback which will be cycled into the continuous development cycle of the course.

The pressing need to significantly reduce global CO2 emissions requires the decarbonization of the shipping industry. Currently, shipping relies on fossil fuels with a shift from heavy oil to liquefied natural gas. The main engine is the primary energy user onboard vessels, and its exhaust is the main CO2 emission source. A potential path to reduce emissions onboard vessels is the capture, compression, and storage of CO2 from the exhaust gases. This requires effective integration across the engine, the capture technology, the CO2 compression, cooling, and storage. The integration of four alternative capture technology options is conceptually explored and assessed: chemical absorption, membranes, temperature swing adsorption, and cryogenic distillation. Integration schemes are developed for each of the four technologies that achieve carbon capture, compression, and storage driven by the exhaust gas waste heat as the only energy source. Heat and power requirements are met through heat integration and heat-to-power conversions using organic Rankine cycles (ORCs). The study was performed on an LNG vessel using LNG fuel in its main engine. Thermal capture technologies (absorption and adsorption) are observed to significantly outperform their alternatives (membranes and cryogenic distillation) and capture, compress, and store more than twice the amount of CO2 emissions from the engine exhaust stream. Finally, the proposed integration schemes resulted in self-sustainable onboard capture systems without combusting additional fuel.

In 2018, the total international shipping industry emissions represented 1,056 million tonnes of CO2 and were responsible for 2.89% of global anthropogenic emissions. The industry is faced with a significant challenge to meet the strict and ambitious upcoming regulations planned by the International Maritime Organization (IMO) to reduce carbon intensity by at least 40% by 2030 and aim towards 70% by 2050, compared to 2008 levels. CO2 capturing technology options available from onshore applications require modifications to satisfy the ship requirements due to space limitations, scarce onboard energy availability, and mobile and dynamic ship operation. Existing studies related to onboard CO2 capture, utilization, and storage (CCUS) are very narrow in scope and limited to a few capture technologies and storage options. This work aims at reviewing studies concerning CCUS onboard ships and synthesizes gaps in existing knowledge to provide a focus for future studies. The work will provide relevant information to define the onboard CCUS problem and analyze potential technologies and solutions across known CO2 separation technologies, CO2 storage, and CO2 utilization in the context of ship characteristics and constraints. This includes an analysis of potential synergies between a wide range of existing onshore CO2 technologies and onboard applications. In addition, information is provided that allows quantifying the onboard CO2 storage volume requirements. This information combined with the identified research gaps and an outlook provides the industry with a starting point and direction for future research related to onboard CCUS which is one of the elements toward achieving the ambitious IMO regulation on carbon reduction.

The food-energy-water nexus (FEWN) has been receiving increasing interest in the open literature as a framework to address the widening gap between natural resource availability and demand, towards more sustainable and cost-competitive solutions. The FEWN aims at holistically integrating the three interconnected subsystems of food, energy and water, into a single representative network. However, such an integration poses formidable challenges due to the complexity and multi-scale nature of the three subsystems and their respective interconnections. Additionally, the significant input data uncertainty and variability, such as energy prices and demands, or the evaluation of emerging technologies, contribute to the system�s inherent complexity. In this work, we revisit the FEWN problem in an attempt to elucidate and address in a systematic way issues related to its multi-scale complexity, uncertainty and variability. In particular, we provide a classification of the sources of data and technology uncertainty from historic data, forecasting and process parameters, and propose ways to quantify their impact on the integrated system analysis. To effectively tame the FEWN�s multi-scale complexity, we distinguish between the introduced error of approximation and optimization of employed surrogate models. In turn, it is possible to characterize their impact on optimal FEWN decision-making based on the quantification of the introduced errors at all levels. Thus, we present strategies to systematically characterize FEWN process systems modeling and optimization. Ultimately, this facilitates translating obtained solutions into actionable knowledge by quantifying the level of confidence one can have in the derived process model and optimal results.

To meet the projected increase in global demand for energy while tackling sustainability concerns, the widespread adoption of renewable energy is inevitable. Once harnessed, exports of this renewable energy from regions with excess resources are anticipated to those that will require imports of energy. The shipping sector will thus play a pivotal role in enabling such trade through energy carriers such as hydrogen, ammonia, methanol, and liquid organic hydrogen carriers. Furthermore, in addition to these energy carriers, carbon dioxide is also expected to become an important maritime trade commodity to achieve climate targets. Through the deployment of carbon capture utilization and storage, and more recently, negative emission technologies, carbon dioxide will need to be transported to regions with the appropriate infrastructure and resources necessary for their anticipated implementation. Presently, in light of these circumstances, the lack of experience in shipping a number of these energy carriers and carbon dioxide must be addressed. As such, an understanding of the techno-economic and environmental feasibility of the large-scale shipping of these commodities must be established at all scales of operation. Accordingly, this work proposes the use of process systems engineering based approaches to enable the marine transportation of these future energy carriers and carbon dioxide from a multi-scale perspective. To lay the foundation in support of this initiative, a framework that considers the multiple scales involved is then presented for the design and operation of progressive ships and their supply chains as part of a decarbonized energy system.

The ongoing climate crisis requires the reduction and removal of carbon to avoid global catastrophic consequences to the environment. As such, efforts presently focus on understanding the impact of negative emissions technologies in actively removing carbon dioxide from the atmosphere. While these emerging technologies bring a distinctive set of feasibility challenges, their integration into existing systems is essential due to the inability of decarbonization strategies to solely mitigate greenhouse gas emissions. The objective of this work is to develop strategies for integrating negative emissions technologies with carbon capture utilization and storage options, spurred by the increasing relevance of circular economies. The multi-period resource integration approach will determine the optimal technology portfolios best suited to a specific industrial landscape to achieve net-zero emissions in the presence of environmental policy instruments across time. The analysis will provide decision makers with a preliminary understanding of the viability of these technologies and the progress needed in regulatory frameworks to enable their effective implementation. The applicability of the proposed approach is demonstrated through the deployment of negative emissions technologies, such as bioenergy carbon capture and storage, direct air carbon capture and storage, enhanced weathering of minerals, and utilization of biochar, in an oil and gas based industrial setting. The optimal strategies determined indicate that carbon caps and taxes are fundamental in reducing the creation of emissions, while carbon credits encourage the active removal of carbon dioxide from the atmosphere.

Piston reactor technology can enable process intensification for electrical and mechanical power conversion to chemical products. Previous work has investigated hydrogen production via partial oxidation of methane (POM) in piston reactors; however, other routes remain unexplored. This work aims to theoretically evaluate if catalytic steam methane reforming (SMR) and methane autothermal reforming (ATR) constitute promising routes for hydrogen production using piston reactor technology for typical parameters and conditions encountered in automotive internal combustion engines (ICE). Specifically, the aim is to use reactor modeling and consider process design aspects in the early stages of investigation to provide direction and justify the next research and development stages involving experimentation, while eliminating infeasible options from the further expensive analysis. The piston reactor is first modeled using a zero-dimensional thermodynamic single-zone piston model coupled with available steady-state kinetic models for these routes. This model-based analysis shows that the highly endothermic SMR reaction is not feasible at ICE conditions, leading to its elimination from further assessments and studies. Thermal coupling of an endothermic reaction with a side-exothermic reaction is a potential solution to drive thermodynamically limited endothermic reaction routes in the piston reactor. The reactor modeling revealed that operation become feasible by coupling SMR with POM in ATR-type scenarios and achieves process intensification compared to steady-state ATR reactors through a significantly higher hydrogen production per catalyst (287-fold increase) and similar methane conversion between 89% and 97% at significantly lowered intake feed temperature (reduced by 283 K). The implementation of ATR piston reactors into grey and blue hydrogen production process designs is explored to understand overall performance and economy of scale effects. The process design studies reveal that the piston reactor-based processes offer savings of approx. 20% in hydrogen production costs compared to conventional ATR processes considering identical plant sizes and natural gas prices. The hydrogen production study highlights the value of the implemented approach for quickly identifying promising directions for further detailed experimental and modeling studies during early-stage exploration.

The modeling and optimization of multi-scale process systems is based on several interconnected process sub-systems. Due to the complexity of each individual sub-model, the resulting integrated process framework optimization formulations are computationally challenging to solve. While the richness of the multi-scale model employed is desired to maintain in order to obtain a solution with some degree of accuracy, simpler surrogate models are typically more attractive as a means to tame the underlying complexity, albeit often leading to an increase of the problem size. Here, the food-energy-water nexus (FEWN) is selected as a representative multi-scale process system, with focus on the reverse osmosis (RO) water supply sub-system. Based on a RO desalination model, two models are developed and compared in terms of accuracy, model complexity and size as well as computational efficiency, (i) a mixed-integer non-linear programming (MINLP) surrogate model, and (ii) a mixed-integer linear programming (MILP) surrogate model of reduced complexity but larger size. The results indicate that improved computational times can be obtained for a valid (lower bound) solution based on the MILP modeling strategy within the same level of accuracy, further underlying the importance of the selection of an appropriate surrogate model.

To explore options for simple, safe, and compact chemical reactors that preserve wanted metastable initial products from sequential unwanted reactions, academic and industrial researchers have tried to repurpose reciprocating piston equipment or an "engine-like" design to be used as a chemical reactor. Piston reactors offer the benefit of achieving very high temperature and pressure conditions at very short and defined residence times. Such conditions offer promise for enhanced performance for several chemical conversions. This paper provides a review of the published literature and patents in the field of piston reactors to provide an overview of the current state-of-the-art. The review covers multiple aspects of piston reactors and their applications, reactor design options and their operation, catalyst and ignition placement, tested reactions, experimental setups as well as modeling and simulation. Several research gaps are highlighted as a motivation for future research in the field. To help interested readers into the topic, basic concepts and fundamentals of piston reactors are provided.