Urgent environmental challenges, along with recent advances in controlled materials synthesis and molecular characterization tools, are fundamentally transforming the landscape of chemical separations. Although traditional unit operations such as distillation and evaporation have historically accounted for the majority of energy consumption in chemical plants, mounting pressure to decarbonize is now driving demand for more energy-efficient and environmentally sustainable approaches.

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In recent years, innovations in both traditional and alternative separation methods have emerged from avenues such as electrification, precision fabrication, intensification and modular design. At the same time, progress in precise and effective separations has been further accelerated by methodological breakthroughs in numerical modeling, data-driven strategies, control systems and machine learning.

This convergence of societal imperatives and technological capabilities reinforces separation processes as a defining cornerstone of the future of chemical engineering. As such, this issue of Nature Chemical Engineering features a Focus on chemical separation science and technology.

Our choice to emphasize both technology and science is more than a semantic one. As an engineering research journal, we aim to make clear that our interest lies not only in process- and system-level work that advances the productivity, efficiency and viability of chemical separations, but also in the basic science that drives deeper understanding and broader application of these technologies.

As a reflection of this goal, this Focus showcases works that span this space, from insights into the multi-scale physics of bipolar membranes to the preparation of ultrathin membranes for selective and fast ion transport. And in this issue, a Perspective by Suljo Linic and co-workers explores strategies for integrating membrane and catalyst functionalities at molecular scales and discusses how such intensification can enhance challenging large-scale chemical transformations.

The Focus also highlights the accelerating push toward energy-efficient alternatives to traditional separation methods, including those powered by potentially renewable energy sources. A Feature in this issue compiles short essays from 17 attendees of a 2025 Telluride Science Workshop on electrochemical separations, which together form a broad vision for the future of the field and the technical hurdles that the community must surmount to sustain its momentum.

For a closer look at some of these hurdles, we refer the reader to a Review in this issue by Shihong Lin and co-workers, which discusses membrane and electrochemical separations for direct lithium extraction. And for a briefing on a new technological development, a News & Views article by Suzana Nunes highlights a fully aqueous electrochemical method for preparing sponge-like ultrathin membranes.

Advances in materials science continue to drive progress in traditional separation approaches. Porous materials, for example, offer exciting new possibilities and feature prominently in this issue, with coverage across scales. A Research Highlight presents recent work by Andrew Cooper and co-workers on a bottom-up computational screening workflow to identify promising organic linkers for CO2-selective metal–organic frameworks. Zooming out, an Article in this issue by Bo Wang and co-workers reports on a solid-phase hot-pressing method for rapidly producing highly crystalline covalent organic framework platelets in a solvent-free manner. Zooming further, a Comment by Matthew Dods and Jeffrey Long discusses key considerations for translating porous materials for CO2 capture from the laboratory to commercial scale.

Membranes and thin films, integral to traditional separation processes, are also featured prominently in this Focus. And while we covered membrane-based separations in an Editorial earlier this year (Nat. Chem. Eng. 2, 231–232; 2025), in this issue, an Article by Liwei Zhuang, Michael Tsapatsis and co-workers presents a method for depositing amorphous zeolitic imidazolate framework films with controllable thickness using dilute precursors, where the resulting films serve as versatile resist materials for advanced lithographic applications.

Continuing in the vein of renewed momentum in traditional areas of separations research, this issue features a Comment by Allan Myerson and co-workers that explores potential reasons why continuous crystallization remains underutilized in pharmaceutical manufacturing, despite its success in other industries. For a lighter-hearted look at crystallization in finer detail, we refer readers to this issue’s By the Numbers by Jerry Heng: ‘A chance for order at the interface’. And for look at crystallization in action as part of a more complex separation train, we refer the reader to an Article by Katrina Knauer and co-workers that reports on a catalytic methanolysis process for depolymerizing both fossil fuel-based and bio-based polyesters under mild conditions, with high monomer yields.

Taken together, the contributions in this issue reflect both the enduring relevance and evolving scope of chemical separation technologies. Advances in separation science were foundational to the rise of the petrochemical age, particularly through distillation columns capable of efficiently fractionating crude oil. Today, as we confront the environmental consequences partly stemming from that very success, the same underlying principles — thermodynamic driving forces, selective mass transfer, process intensification and process control — that once unlocked the petrochemical era now hold the potential to drive our transition away from fossil fuel dependence while also addressing the environmental legacy of our carbon-intensive past.