Heating, ventilation, air conditioning, and refrigeration (HVACR) systems are essential across residential, commercial, and industrial sectors but are critical energy consumers, and their refrigerant emissions and energy use present a major challenge to global sustainability goals. This state-of-the-art review moves beyond tracing the evolution of refrigerants to evaluate key international agreements, including the Kigali Amendment, and national regulations as primary drivers of the transition to sustainable refrigerants. It critically assesses current sustainable alternatives, including natural refrigerants and low-global warming potential synthetic options, such as hydrofluoroolefins, highlighting the trade-offs in their technical application, economic viability, safety, and infrastructure implications. Emerging solutions, including not-in-kind cooling technologies, innovative thermodynamic cycles, advanced materials, artificial intelligence, digitalization, and refrigerant lifecycle management, are examined to provide critical perspectives and guide future research, development, and deployment. By integrating regulatory, market, and technological insights, this review offers a comprehensive road map toward a sustainable, low-emission, and energy-efficient HVACR sector.
I embody the quintessential Californian spirit: Raised in Los Angeles, I spent weekends either at the beach or skiing at Big Bear, rode motorcycles, hiked the Sierras, and cherished the sounds of the Beach Boys and Creedence Clearwater Revival. Restless, undisciplined, and irreverent, I applied to only one college-UC Santa Barbara-mainly because that is where my high school friends were going. Although we like to think our intellect transcends culture, my childhood and teenage years were shaped by the rhythms of the 1960s: space flight, NASA, and virtually every episode of Star Trek (often watched multiple times). Unmoored, I entered college intending to major in biochemistry but drifted into chemistry while also immersing myself in the physics curriculum. I earned a PhD in chemical physics at Caltech, yet chose to work with a chemical engineer. When my thesis advisor was suddenly killed, I completed my dissertation at Xerox Palo Alto Research Center, working on solar cell materials alongside Cambridge-educated physicists. While my chemistry peers pursued academic postdocs, I went instead to IBM Yorktown Heights, dividing my time between silane reactor engineering and amorphous semiconductor physics. Would I ever become anchored? Here is the rest of the story that led to 43 years on the Berkeley faculty. Including motorcycles.
Free-energy surfaces (FESs) offer a unifying framework for understanding molecular-level structures, transformations, and thermodynamic stability. They distill the complexity of atomistic simulations into interpretable landscapes of metastable states, bridging molecular-level detail with macroscopic observables. This review provides researchers in molecular simulations, computational physical chemistry, and chemical engineering with a conceptual and practical guide to computing and interpreting FESs, from their statistical-mechanical foundations to modern machine learning approaches that are transforming the sampling, representation, and analysis of molecular systems.
Suspensions of particles dispersed in liquids are ubiquitous materials in industry and geophysics; relevant examples include cement and mud. At high particle concentration, in what is called a dense suspension, crowding induces multiscale interactions ranging from local, particle-level contact forces to macroscopic, system-spanning contact networks that dynamically evolve under applied shear. As the number of constraints on relative particle movement increases, the suspension viscosity rises, and eventually the material reaches a jammed state. In this review, we discuss frameworks developed to predict the rheological behavior of dense suspensions in the vicinity of jamming and describe the resulting flow-state diagram. Going beyond mean-field models, we discuss recent advances in understanding the contact network of spatially correlated particles. We also review recent developments for tailoring flow constraints at the particle level, both by particle geometry and by interactions induced by chemical bonds, which can be used to engineer the location and extent of different regimes in the flow-state diagram. We end with a set of issues and perspectives for future research, including possible ways to extend the current theoretical framework, apply simulations to suspensions comprising particles with more complex nonspherical or highly anisotropic shapes, and develop approaches to predict how molecular-scale details influence macroscopic flows.
Soaps are some of the oldest surfactants known to humans and remain indispensable in modern health, personal care, and sustainability agendas. Still, the simple chemistry of salts of fatty acids reveals a rich, multiscale landscape of self-assembly and flow behavior that controls soap processing and sensorial attributes. This review integrates phase behavior with rheological analysis to demonstrate how distinct microstructures, ranging from micellar to liquid-crystalline phases, possess unique rheological signatures. We further demonstrate how the coexistence and combination of these phases in a product such as a soap bar introduce additional levels of structural and rheological complexity. In addition, we highlight how linear viscoelastic analysis resolves relaxation hierarchies and how yield stress and thixotropic responses are inherent to the multiphase brick-and-mortar microstructures in products such as soap bars. The complex rheology of soap bars necessitates constitutive models that incorporate elasticity, plasticity, and time-dependent structure to predict extrusion or stamping performance. We also explore how the microstructure relates to cleaning efficacy, foam richness, lather dynamics, and rinse feel by coupling rheology measures with in-use dilution behavior. Finally, we discuss open questions, challenges, and future directions for developing more sustainable products.
The nonequilibrium self-consistent generalized Langevin equation theory of irreversible processes in liquids is a first-principles approach that allows for the derivation of general equations that describe the out-of-equilibrium and nonstationary relaxation of a liquid after a sudden quench or compression into an amorphous state. Proposed in 2010, the theory has since been systematically applied to describe a wide variety of model systems, with predictions rigorously and successfully validated against both experimental and simulated results. In this work, we briefly review the progress of this theoretical framework over the past 15 years, focusing on its applications to the description of the structural, dynamical, and rheological behavior of model glass- and gel-forming systems.
Genetic code expansion (GCE) is the ability to encode polypeptide building blocks beyond the standard 20 the ribosome uses for protein translation, known as nonstandard amino acids (nsAAs). The broadening of chemical functionalities in proteins produced by live cells has generated substantial value across fundamental and applied research settings. However, a common limitation of GCE approaches is their reliance on the supplementation of chemically synthesized nsAAs to cell culture media. To overcome this limitation of nsAA sourcing, efforts have engineered systems for nsAA biosynthesis, often in the same host that performs GCE. In recent years, these works have reported new chemical targets obtained through biosynthesis, as well as additional rationale for combining metabolic engineering and GCE, particularly for synthetic biology applications. Here, we review this rapidly advancing field and provide our perspectives on technical and conceptual innovations.
To overcome global water scarcity and pollution, nanomaterials have emerged as revolutionary tools for water remediation owing to their unique physicochemical properties, in particular, their ultrahigh specific surface area and programmable interface for molecular recognition. This review integrates multifaceted perspectives on contaminant treatment and compares the relative performance strength of nanomaterials for diverse contaminants, surpassing fragmented assessments focused on single contaminants. We taxonomize nanomaterial classes and highlight their recent advances across four domains: heavy metals removal, critical metals recovery, microbial contamination control, and emerging organic contaminants degradation. For each domain, we dissect scalability bottlenecks and define future research priorities, including database integration, graph neural networks, machine learning, and artificial intelligence. We provide design principles for high-performance water remediation by synthesizing cutting-edge materials using cross-disciplinary strategies. We describe eco-safe nanomaterials that guide industrial water management toward sustainable transformation, propelling global water remediation toward green, intelligent, and resource-recycling models.
Rich information in the chemical literature presents unprecedented opportunities for accelerating discovery and optimization in chemistry through data-driven approaches. Nevertheless, converting raw information in the literature into structured databases relies primarily on manual curation, which is time-consuming and costly. In this review, we comprehensively examine recent advances in automatic chemical information extraction from the literature, focusing on image and text modalities. We trace the evolution from early rule-based and machine learning approaches to state-of-the-art methods leveraging large language models (LLMs) and vision language models. We discuss core tasks such as optical chemical structure recognition, reaction diagram parsing, named entity recognition, and experimental procedure extraction, highlighting representative methods, benchmark data sets, and practical challenges such as multimodal integration and data annotation. By systematically comparing these approaches, we identify key trends and persistent limitations and outline promising future directions toward robust, scalable, and automated chemical information extraction frameworks. This review aims to provide a practical guide for researchers seeking to harness machine learning and LLM technologies to accelerate the digital transformation of chemical science.
High-pressure processing (HPP), also known as high hydrostatic pressure (HHP), is essential in contemporary food engineering. This review evaluates its significance through aspects like microbial safety, nutritional and sensory quality, sustainability, market acceptance, economic viability, and technological versatility. By critically examining the current state and potential of HPP, this article highlights that, despite emerging alternatives, food engineering remains strongly reliant on high pressure as an irreplaceable technology due to its unique benefits in ensuring sustainable, high-quality, and safe food products.
Chemical engineers have played a vital role in the pharmaceutical industry for more than a century, bridging the gap between scientific discovery and large-scale drug manufacturing. This review examines the evolution in the role of chemical engineers and their impact on the development of small molecules, biologics, and emerging modalities such as oligonucleotides and gene therapies. We provide historical context, from early breakthroughs in insulin and penicillin production to the integration of continuous processing and advanced modeling. Key areas of focus include reaction engineering, separations, crystallization, fluid dynamics, process control, and continuous manufacturing. Looking ahead, chemical engineers will be central to addressing challenges in sustainability, advanced delivery systems, and the application of artificial intelligence and data-driven technologies. As therapeutic complexity grows, the application of engineering fundamentals, integrated with life and natural sciences, remains essential for ensuring safe, efficient, and scalable manufacturing of medicines that advance global health.
Sodium-based batteries are gaining momentum as a cost-effective, sustainable alternative to lithium-based batteries, driven by the global demand for scalable energy storage. At the same time, polymer electrolytes are being widely pursued as safer, more electrochemically stable alternatives to liquid electrolytes. Sodium polymer electrolytes require advancement in various aspects, such as ion transport and electrode compatibility, before application in rechargeable sodium-ion or sodium metal batteries. This review examines the progress in characterization of the bulk properties of sodium polymer electrolytes, molecular interactions in the bulk, and their interfaces/interphases with electrodes, with attention paid to differences between characterization methodology and select properties of sodium versus lithium analogs. Highlighted topics include ionic conductivity, sodium transference, ion speciation, electrochemical stability, safety, and electrochemical and chemical characterization of interfaces, interphases, and with sodium sulfur cathodes.
Tissue engineering aims to restore, maintain, or improve damaged tissues through the use of polymer scaffolds that support cellular growth and regeneration. Copolymerization enables the fine-tuning of thermal, structural, and mechanical polymer properties, facilitating scaffold fabrication via techniques like electrospinning and 3D printing. Functionalization and bioconjugation approaches, including thiol-ene click chemistry, allow for targeted surface modification without altering bulk properties, improving interaction with biological environments and enhancing the specificity and functionality of polyester-based scaffolds. This review highlights the central role of polymer reaction engineering in advancing aliphatic polyesters for tissue engineering, focusing on recent innovations in synthetic strategies and functionalization techniques that expand their applicability in regenerative medicine.
The conversion of CO2 into fuels and chemicals requires significant energy input to break C-O bonds and create C-C and C-H bonds. This review explores the energy and capital barriers to CO2 utilization, using ethylene production as a case study by comparing CO2 electroreduction with other carbon mitigation options, including carbon capture and sequestration. The world's energy and capital resources are limited-scarce, in the parlance of economics-and choosing to use them to implement one path to decarbonization displaces other options for decarbonization or other priorities. These opportunity costs are significant and should not be ignored. Instead of breaking the C-O bonds in CO2 to produce chemicals and fuels, society should prioritize the higher CO2 mitigation efficiencies of alternative approaches, such as carbon capture and sequestration, new process and catalyst technologies for key molecules, and capital-efficient hydrogen production.
The emergence of the United States as the leading global producer of oil and gas has driven increased interest in the greenhouse gas emissions from US energy supply chains. Methane emissions are a major portion of these greenhouse gas emissions, and the spatial and temporal patterns of methane emissions from oil and gas sources are complex. A wide variety of measurement and modeling approaches for estimating methane emissions from US oil and gas supply chains have emerged over the last decade, and this review summarizes their current status and prospects for improvement. Although no single measurement method or modeling approach will be successful in accurately characterizing all emissions, the integration of multi-scale measurement and modeling approaches can provide accurate and comprehensive estimates of emissions.
The phase diagram of colloidal systems strongly depends on the nature of interparticle interactions, which reflect the physical mechanisms that stabilize the particles in the medium. In systems with dominant short-range attractions, where interactions act over distances much shorter than the particle diameter, the extended law of corresponding states asserts that an interaction potential can be described by three key parameters: effective diameter, interaction strength, and second virial coefficient. If these parameters are the same, then different systems exhibit identical phase behavior, structure, and dynamics. In this review, we outline the origin and formulation of this law and the evidence that supports it. We further examine its applicability to protein solutions near liquid-liquid phase separation and to colloidal systems with short-range attraction and long-range repulsion, exploring the possibility of a universal phase diagram and extending its relevance for understanding the nature of these complex fluids.
Reactive extraction is an attractive separation technology that can replace energy-intensive water evaporation steps in the industrial production of carboxylic acids. We systematically review the current literature on the extraction of low-value bioproducts and thereby identify the reduced availability of predictive models, limited selectivity, and challenging phase separation as possible bottlenecks in the industrial implementation of reactive extraction. Furthermore, we discuss requirements and strategies for closing the material cycles for batch and continuous processes. With these challenges in mind, we analyze the most widely used extractants (trioctylamine, trioctylphosphine oxide, and tributyl phosphate) in combination with common diluents (e.g., long-chain alcohols and alkanes) in terms of their ability to meet process needs. We illustrate the subordinate role of equilibrium constants in overall process design while emphasizing the potential for flexible reactive extraction systems tailored to process requirements.
This review focuses on how the cavitation mechanism in the snapping shrimp can be explored to intensify various chemical engineering applications. Effective bubble collapse can lead to hot spot formation, increased transport coefficients (momentum, heat, and mass), and enhanced interfacial area and also results in the formation of highly reactive radicals. Cavitation's ability to induce rapid micromixing, enhance mass transfer, and facilitate nucleophilic chemical reactions can find applications in various industries. An overview of cavitation applications, reactors used for cavitation, effects of operating parameters, and conclusions drawn from the studies so far is presented. Cavitation provides significant benefits for applications in synthesis reactions, wastewater treatment, food processing, emulsification, extraction, and crystallization. Learnings from snapping shrimp can be translated into process intensification of physicochemical and biological transformations in chemical engineering by harnessing these cavitational effects.
Biomass-derived energy sources represent a promising domestic route for fuel and chemical production, taking advantage of largely underutilized biological and waste resources. Heterogeneous catalysis plays a key role in these biomass conversion processes, as reflected by all American Society for Testing and Materials-approved pathways for producing sustainable aviation fuel proceeding through a catalytic step. This concise review seeks to establish the state of the art in thermal catalytic process development for various biomass-derived feedstocks and the current enabling capabilities that aid this development. Research needs are identified and described throughout the article, as further advancements in heterogeneous catalysis are required to improve the affordability and realize the full potential of biomass-derived products.
Respiratory conditions represent a significant global healthcare burden impacting hundreds of millions worldwide and necessitating new treatment paradigms. Pulmonary immune engineering using synthetic nanoparticle (NP) platforms can reprogram immune responses for therapeutically beneficial or protective responses directly within the lung tissue. However, effectively localizing these game-changing approaches to the lung remains a significant challenge due to the lung's natural defense. We highlight the target pulmonary immune cells and address advances to localize NPs to the lung via both aerosol and vascular delivery. For each administration route, we discuss physiochemical design rules and recent immune-modulatory successes of synthetic, extracellular vesicle, and cell-mediated NP delivery. We aim to provide readers with an updated summary of this emerging field and offer a roadmap for future research aimed at enhancing the efficacy of pulmonary immunotherapies.
