Non-thermal plasma is gaining strong interest in chemical research because it allows chemical reactions to take place under mild conditions. Unlike thermal plasma, where the whole system is heated to very high temperatures, non-thermal plasma operates close to ambient temperature and pressure. The energy is mainly carried by electrons, not by heat.
This specific energy distribution leads to the formation of highly reactive species such as radicals, excited molecules, and ions. These species can trigger chemical reactions that are difficult, or even impossible, to achieve with conventional thermal or catalytic approaches. As a result, non-thermal plasma opens new pathways for chemical transformations while limiting overall energy consumption.
Over the past years, non-thermal plasma has been explored in many fields. It has shown strong potential for environmental applications such as wastewater treatment and pollutant removal, but also for gas conversion processes and chemical synthesis. More recently, researchers have started to combine plasma with microreactor technology to gain better control over reaction conditions, mass transfer, and reproducibility.
This shift toward non-thermal plasma microreactors marks an important step. By integrating plasma into continuous flow systems, researchers can move from exploratory batch experiments to more controlled and scalable processes. The publication, from Fabian Bruel and his team, discussed in this article is part of this evolution and demonstrates how non-thermal plasma can be used for organic chemistry in a continuous flow microreactor setup.
Schematic view of a continuous flow non-thermal plasma microreactor
A non-thermal plasma microreactor combines two ideas that are powerful on their own, plasma chemistry and microreactor technology. Put together, they offer a way to run highly energetic chemical reactions with a high level of control.
At the core of a plasma microreactor is a small channel, often at the sub-millimeter scale, where gas and liquid phases can flow together. Electrodes placed around or along this channel generate a plasma discharge in the gas phase. While the electrons reach high energies, the overall temperature of the system remains close to ambient. This is what makes the plasma “non-thermal”.
One key advantage of the microreactor format is mass transfer. In gas–liquid plasma reactions, reactive species are mainly generated in the gas phase and must interact with molecules in the liquid phase. The small dimensions of a microreactor shorten diffusion distances and increase the contact surface between phases. This improves reaction efficiency and reproducibility compared to larger, batch plasma systems.
Another important aspect is process control. In a non-thermal plasma microreactor, parameters such as residence time, flow rates, gas–liquid ratio, and energy input can be adjusted very precisely. This level of control is difficult to achieve in conventional plasma reactors and is essential for studying reaction mechanisms, selectivity, and energy efficiency.
Because of these features, non-thermal plasma microreactors are increasingly used as research tools to explore new plasma driven chemical reactions under continuous flow conditions, bridging the gap between fundamental plasma chemistry and more practical, scalable processes.
Non-thermal plasma is not limited to a single domain. Its ability to generate reactive species at low temperature makes it a versatile technology, already explored across a wide range of applications.
In environmental and water related processes, non-thermal plasma has been widely studied for wastewater treatment and pollutant removal. Reactive oxygen and nitrogen species generated by plasma can break down persistent organic compounds that are difficult to remove using conventional treatment methods. This includes emerging contaminants such as fluorinated molecules and other stable organic pollutants. Plasma treatment can operate without added chemicals, which makes it attractive for environmental remediation.
Energy and gas conversion represent another important area of research. Non-thermal plasma has been investigated for reactions such as methane conversion and partial oxidation processes, including the conversion of methane to methanol. These reactions normally require high temperatures or complex catalysts. Plasma provides an alternative pathway by activating molecules through energetic electrons rather than heat, opening new routes for more energy efficient chemical transformations.
Beyond environmental and energy applications, non-thermal plasma is increasingly explored for chemical synthesis. In this context, plasma can initiate radical driven reactions, enable catalyst free transformations, and activate otherwise inert chemical bonds. When combined with continuous flow microreactors, these reactions benefit from improved selectivity, better control of residence time, and enhanced safety compared to batch plasma systems.
Together, these applications highlight why non-thermal plasma is considered a promising tool across disciplines, from environmental engineering to advanced chemical synthesis, and why its integration into microreactor technology continues to attract growing interest.
Radical driven chemistry, from Sungryeal Kim and al., Biomedicines, DOI: 10.3390/biomedicines9111700
The unique behavior of non-thermal plasma comes from the way energy is transferred into the chemical system. Instead of heating all molecules uniformly, energy is mainly injected through electrons, which leads to the formation of highly reactive species.
These reactive species play a central role in plasma driven chemistry:
Because reactions are driven by these short-lived species, plasma chemistry often follows different rules than thermal or catalytic processes. Reaction pathways are strongly influenced by factors such as residence time, gas composition, pressure, and energy density rather than temperature alone.
This radical-based chemistry explains both the strength and the challenges of non-thermal plasma. While it enables new reactions and high levels of activation, it also requires careful control to limit unwanted side reactions or excessive degradation. This is where reactor design and precise process control become critical, especially in continuous flow plasma microreactors.
Despite its strong potential, non-thermal plasma is not a universal solution. Several technical and scientific challenges still limit its broader adoption, especially when moving from laboratory studies to more advanced setups.
One of the main challenges in non-thermal plasma processes is energy efficiency. Only a fraction of the electrical energy supplied to the system is effectively used to drive the targeted chemical reactions. The rest can be dissipated through heat, side reactions, or the formation of unwanted by-products. Optimizing parameters such as voltage, power, and residence time is therefore essential to balance conversion and energy consumption.
Plasma generated reactive species are highly reactive but not selective by nature. This can lead to parallel reaction pathways, product degradation, or over-oxidation. Achieving good selectivity requires precise control of reaction conditions, including gas composition, flow rates, and exposure time to the plasma discharge. Without this control, valuable products can be rapidly transformed into undesired compounds.
The design of the plasma reactor plays a critical role in process stability and reproducibility. Electrode geometry, discharge mode, and gas–liquid contact strongly influence plasma behavior. Poorly designed systems can suffer from unstable discharges, fouling, or limited lifetime of components, which complicates long term experiments.
Scaling non-thermal plasma processes remains a major challenge. While microreactors offer excellent control and safety at small scale, translating these results to pilot or industrial scale is not straightforward. Issues such as uniform plasma generation, energy distribution, and material compatibility must be addressed before non-thermal plasma can be widely deployed in industrial chemical processes.
These limitations explain why many current studies focus not only on new reactions, but also on improving plasma microreactor design and process control, as demonstrated in recent research.
A recent publication in Green Chemistry reports an original use of a non-thermal plasma microreactor for organic synthesis under continuous flow conditions. The study focuses on the direct functionalization of saturated hydrocarbons using plasma activation, without the need for catalysts or additional reagents.
In this work, the authors demonstrate that dichloromethane, commonly used as an inert solvent, can be activated by non-thermal plasma to become a reactive species itself. When combined with a continuous gas–liquid flow microreactor, this approach enables chloromethylation reactions to occur at ambient temperature and pressure, conditions that are difficult to achieve with conventional chemistry.
The study uses cyclohexane as a model substrate to explore how plasma generated reactive species interact with organic molecules in the liquid phase. By carefully adjusting plasma power, residence time, gas–liquid ratio, and substrate concentration, the authors were able to analyze reaction pathways, product selectivity, and energy efficiency in detail.
Beyond the specific reaction studied, this publication highlights a broader message. It shows how non-thermal plasma microreactors can be used as controlled research tools to investigate plasma driven chemistry in the liquid phase. The continuous flow format allows reproducible experiments, fine control of reaction parameters, and systematic exploration of mechanisms, making it highly relevant for researchers working at the interface of plasma technology and chemical synthesis
The experimental setup described in the publication is built around a continuous flow non-thermal plasma microreactor designed to handle gas–liquid reactions under well controlled conditions. The goal is not only to generate plasma, but to do so in a way that allows reproducible chemistry and reliable data collection.
In this system, gas and liquid streams are introduced separately into the microreactor and meet inside a small channel, forming a segmented gas–liquid flow. The plasma discharge is generated in the gas phase using external electrodes positioned along the microreactor. This configuration enables the formation of reactive species in the gas phase, which then interact with the liquid phase as both phases flow through the channel.
Several parameters are tightly controlled throughout the experiments. Flow rates define the residence time inside the plasma zone, while the gas–liquid ratio influences mass transfer and exposure of the liquid to reactive species. Electrical parameters such as voltage, frequency, and power determine the intensity of the plasma discharge and the nature of the generated species.
An important aspect of this setup is automation. The authors rely on an automated system to manage liquid injection, plasma operation, and sample collection. This reduces variability between experiments and allows systematic screening of reaction conditions. Such control is essential when studying plasma driven reactions, where small changes in operating conditions can have a strong impact on conversion, selectivity, and energy efficiency.
Overall, this experimental approach illustrates how careful reactor design and process control are key to unlocking the potential of non-thermal plasma chemistry in continuous flow systems.
While plasma generation often gets most of the attention, this study also shows that fluid handling and automation are essential to make non-thermal plasma microreactor experiments reliable and meaningful. In continuous flow plasma chemistry, poor control of liquids can quickly lead to inconsistent results.
In a plasma microreactor, reaction outcomes strongly depend on how long the liquid is exposed to reactive species. This makes residence time a key parameter.
Without accurate liquid handling, it becomes difficult to link plasma parameters to chemical results.
The study involves multiple experiments performed under different plasma and flow conditions. Automation plays a major role here.
This level of automation is especially important when screening many conditions or running experiments over extended periods.
Plasma chemistry can be sensitive to small changes in operating conditions. Automation helps reduce human variability and improves data consistency.
For researchers working with non-thermal plasma microreactors, fluid handling is not a secondary aspect. It directly impacts:
This study clearly illustrates that combining plasma technology with reliable fluid handling and automation is a prerequisite for advancing plasma driven chemistry in continuous flow systems.
In this study, AMF fluid handling components are used as enabling tools within the non-thermal plasma microreactor setup. Their role is not to drive the chemistry itself, but to ensure that the experimental conditions remain stable, reproducible, and automated throughout the study.
For liquid handling, an AMF syringe pump is used to deliver solutions into the microreactor with high precision. This allows the researchers to maintain a constant and well defined liquid flow rate, which is essential for controlling residence time inside the plasma zone. In plasma driven reactions, even small variations in flow can strongly influence conversion and selectivity, making accurate pumping a critical requirement.
In addition to injection, an AMF rotary distribution valve is used downstream of the microreactor to automatically collect reaction products. This enables clean and repeatable switching between collection vials during experimental sequences. By avoiding manual intervention, the setup reduces the risk of cross contamination and ensures that each experiment can be clearly associated with its operating conditions.
Together, these components allow the full experimental workflow to be automated, from liquid injection to sample collection. This level of integration is particularly valuable in plasma microreactor studies, where multiple parameters such as plasma power, gas–liquid ratio, and residence time are systematically varied.
Rather than being used as stand-alone instruments, the AMF products function here as building blocks within a larger experimental system. Their contribution lies in providing reliable fluid control and automation, which are essential for generating high quality data in continuous flow non-thermal plasma research.
In this work, the AMF LSPone, programmable syringe pump combined with a microfluidic rotary valve, used in the plasma microreactor are standard tools designed for demanding microfluidic and flow chemistry applications.
They are not specific to plasma systems, but their characteristics make them well suited for this type of experimental environment.
Key roles of the LSPone in this study:
Beyond this specific publication, these products are commonly used in flow chemistry, microreactor development, and automated screening setups. Their role is to support researchers by removing uncertainty from fluid handling, allowing them to focus on reaction design, plasma parameters, and data interpretation rather than on manual operations.
This article only highlights selected aspects of the study. The full publication provides a detailed discussion of reaction mechanisms, energy considerations, and the influence of multiple plasma and flow parameters on product selectivity and conversion.
If you are working on or considering:
we strongly recommend reading the complete paper published in Green Chemistry.
If you are developing a similar experimental setup or exploring plasma chemistry in continuous flow, feel free to reach out to discuss fluid handling, automation, or integration challenges.
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