Selective Separations: What Membrane Science Can Teach Chromatographers

🎤Dr. Steven Weinman (Associate Professor of Chemical and Biological Engineering at the University of Alabama)

Steven shares his journey from chemical engineering student to membrane researcher, and explains how membranes are used not only for water purification, but also for sample preparation, pre-treatment, and concentration in analytical workflows. The conversation dives deep into PFAS removal, nanofiltration vs. reverse osmosis, and how chromatography and mass spectrometry are essential for validating membrane performance.

Key topics discussed include:

• How membranes function as separation and concentration tools
• Nanofiltration vs. reverse osmosis for salts and PFAS
• The role of chromatography (LC-MS, GC-MS, ion chromatography) in verifying contaminant removal
• Challenges in scaling academic separation technologies to industry
• Sustainability in membrane manufacturing and PFAS-related regulations
• Training students to balance fundamental science with real-world applications

Whether you work in environmental analysis, chromatography, mass spectrometry, water quality, or separation science, this episode provides valuable insight into how different separation technologies complement each other—and where the field is heading next.

Video Transcription

Introduction

Membrane-based separations have become a central part of modern water treatment and resource recovery, offering energy-efficient routes for purification, concentration, and selective contaminant removal. In this discussion, Stephen reflects on his path into chemical engineering and membrane science, then explores how membrane technologies fit within broader separation science, how selectivity is designed into membrane systems, and why translation from academic research to industrial deployment remains challenging.

His perspective spans both fundamental membrane science and practical engineering, with particular emphasis on water treatment, contaminant removal, sustainable membrane manufacturing, and the realities of research funding and scale-up.

From Chemical Engineering to Membrane Research

Stephen’s route into membrane science began indirectly. Although his early interests were far removed from chemical engineering, he found himself drawn to chemistry and mathematics during high school, which led him to pursue chemical engineering at the University of Kentucky. His first direct exposure to research came through a cooperative placement with a university-affiliated research institute, where he worked on ceramic membrane systems for coal-fired power plant applications.

That experience introduced him to bench-scale research, scientific literature, and technical presentation, while also clarifying that research was more appealing to him than traditional industrial internships. He subsequently joined the laboratory of a membrane scientist at the University of Kentucky, where he began working on polymeric membranes for water treatment. This set the direction for graduate study, ultimately leading him to Clemson University, where he pursued PhD research on antifouling membranes using surface chemistry and patterning approaches.

Although his original career plan had been to join a membrane company after graduate school, that trajectory changed late in his doctoral training. Encouragement from colleagues and family led him to consider academia, where he could define his own research questions and continue mentoring students. He joined the University of Alabama immediately after graduation and has since built a research program focused on water treatment problems using membranes, solvents, and polymer-based sorbents.

Membrane Separation in the Broader Context of Analytical and Separation Science

Stephen frames membranes as one tool within a broader separation science landscape. Their role depends entirely on the feed composition, the desired product stream, and the ultimate process objective. In some cases, membranes are ideal for concentrating target species or dewatering mixtures. In others, they serve as pretreatment tools, removing particulates, unwanted macromolecules, or selected contaminants before downstream analytical or processing steps.

This logic parallels broader analytical workflows, including chromatographic and spectrometric methods, where sample preparation and matrix simplification are often critical. Even very routine laboratory operations, such as syringe filtration, rely on membrane principles. In that sense, membranes are already embedded in many analytical workflows, even when they are not the primary focus.

He also points out that certain membrane-based systems can begin to overlap conceptually with chromatographic approaches, particularly in applications such as protein and biologics purification, where membrane adsorbers and membrane chromatography can provide high-throughput alternatives to conventional packed columns.

Membrane Selectivity: Matching the Separation to the Problem

A recurring theme in the discussion is that membrane selection is application-specific. The right membrane depends on what must be retained, what must pass through, and whether the goal is purification, concentration, or fractionation.

Stephen distinguishes between several broad classes of membranes. Microfiltration and ultrafiltration operate largely through size exclusion, although charge effects may still contribute. These are useful when target species differ sufficiently in size. At the more selective end, nanofiltration and reverse osmosis are used for salts, small molecules, and persistent contaminants. Nanofiltration is often well suited for rejecting divalent ions while allowing more monovalent ions to pass, whereas reverse osmosis is required when more complete salt rejection is necessary.

For contaminants such as PFAS, nanofiltration can reject a substantial fraction of compounds, although shorter-chain and smaller species are more difficult. Reverse osmosis offers broader rejection, but also with higher pressure requirements. This highlights a central engineering tradeoff: tighter selectivity generally requires higher energy input.

He emphasizes that membrane systems always produce at least two streams: a permeate stream and a retentate or concentrate stream. Designing the separation therefore requires consideration not only of product quality but also of what happens to the reject stream. In many cases this becomes a waste stream; in others, it may represent a concentrated resource that requires additional processing or recovery.

Advances in Membrane Materials and System Performance

Over the course of more than a decade in membrane science, Stephen has seen important improvements in commercial membrane technology, particularly in the area of lower-pressure reverse osmosis. Traditionally, reverse osmosis has required higher operating pressures than nanofiltration. Recent developments have reduced that burden, allowing similar water productivity at lower pressure or smaller membrane area for a given throughput.

These advances matter because they reduce either energy demand or plant footprint, both of which are significant in industrial and municipal treatment systems. While pressure recovery devices have also improved overall system efficiency, he distinguishes those engineering gains from the membrane materials themselves.

On the research side, he highlights the emergence of membrane adsorbers and related hybrid technologies that can support faster, higher-throughput separations than conventional column-based workflows. These have gained particular traction in the purification of proteins and biologics, although he suggests that similar concepts may become increasingly relevant in water treatment and selective ion or molecule recovery.

Chromatography and Mass Spectrometry as Tools for Membrane Research

Although many membrane processes target relatively simple separations such as desalination, more advanced membrane studies increasingly rely on analytical chemistry for validation and mechanistic insight. Stephen describes how chromatographic and mass spectrometric methods are essential when the separation targets are more complex than salts.

His group uses ion chromatography for specific ionic analytes, as well as GC-MS and electrospray-based methods for organic compounds and degradation products. One recent example involved a biocatalytic membrane designed to degrade phthalates, where GC-MS was used to detect both the parent phthalate and the resulting breakdown products. In such cases, analytical methods are not merely confirmatory; they are central to demonstrating that the membrane or membrane-coupled system is functioning as intended.

This reinforces the idea that membrane science and analytical chemistry are closely linked in emerging applications, especially where contaminant transformation, trace-level detection, or selective removal must be verified rigorously.

The Difficulty of Scale-Up

One of the most substantial barriers in membrane research is translation from academic bench-scale work to industrial or municipal scale. Stephen identifies two major constraints: time and cost.

Academic demonstrations often rely on reaction steps, modification procedures, or fabrication methods that work well on the laboratory scale but are far too slow for industrial practice. A protocol that takes hours or days in a research setting is rarely attractive to a manufacturer seeking cycle times measured in seconds or minutes. Likewise, materials that seem acceptable at gram scale may be prohibitively expensive at production scale, although the reverse may also be true if bulk pricing is favorable.

The more fundamental challenge is that academic research is not usually funded to perform pilot-scale development. The mission is often centered on fundamental science and student training, not industrial process engineering. Moving from proof-of-concept to deployable technology requires time, equipment, space, and funding that many university laboratories simply do not have.

For this reason, Stephen sees academia’s main role as laying the conceptual and technical groundwork. If a technology shows promise, the ideal outcome is that an industrial partner, start-up, or other translational pathway takes it further. In some cases, research can be designed from the start with scalability in mind. He cites current work on reverse osmosis membrane additives as an example, where the goal is not to reinvent membrane fabrication but to introduce a change that could plausibly fit existing manufacturing workflows.

Sustainability and Greener Membrane Science

Membrane processes themselves are often relatively energy efficient compared with thermal separations, but Stephen notes that membrane manufacturing still has significant room for improvement. Conventional membrane fabrication often relies on hazardous, petroleum-derived solvents, and one area of active research is the substitution of greener or bio-based alternatives.

Another direction is the use of waste plastics as feedstock for membrane fabrication. The rationale is pragmatic: if such plastics are already present in the environment, converting them into membranes may extend their useful lifetime and partially offset their environmental burden. More biodegradable or less petroleum-dependent polymers are also attractive, but they must still meet cost and performance requirements.

He also discusses an important regulatory issue involving polyvinylidene fluoride (PVDF), one of the most widely used membrane polymers. Debate over whether it should be treated as a PFAS-related material could have major implications for membrane manufacturing and use. From his perspective, classifying PVDF in that way would create significant disruption, especially given its central role in current membrane systems.

Funding, Student Training, and the Academic Mission

The final part of the discussion turns to the academic research environment itself. Stephen emphasizes that the most important responsibility of his laboratory is not simply generating new membrane concepts, but training students and ensuring that they can complete their degrees in a supportive research environment.

Funding uncertainty directly affects that mission. Reduced proposal success rates make it harder to maintain the number of graduate students needed for a healthy research group. This has implications beyond immediate staffing. Laboratories function best when experienced students train newer members, creating continuity in methods, culture, and technical knowledge. If groups shrink too far, that continuity is lost.

He views graduate research as both education and work experience. Students are not only learning theory; they are learning how to think as researchers, solve open-ended problems, and contribute to technologies that may eventually benefit industry. From that perspective, sustaining student support is one of the most important parts of maintaining a strong academic research ecosystem.

Conclusion

Stephen presents membrane science as a field that sits at the intersection of chemical engineering, separation science, and analytical chemistry. Membranes are already deeply integrated into both industrial treatment and laboratory workflows, but their future depends on continued progress in selectivity, sustainability, and manufacturability.

At the same time, the discussion makes clear that technical performance alone is not enough. For membrane technologies to move from the laboratory to practice, they must be scalable, economically realistic, and supported by strong analytical validation. Academic laboratories can provide the foundational science and early demonstrations, but broader adoption depends on partnerships, funding, and translational effort.

Perhaps most importantly, the conversation highlights that advances in membrane science are inseparable from the students and researchers who carry them forward. In that sense, the future of separations depends not only on materials and methods, but also on sustaining the people who develop them.

This text has been automatically transcribed from a video presentation using AI technology. It may contain inaccuracies and is not guaranteed to be 100% correct.

Concentrating on Chromatography Podcast

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