In a continuous flow reactor, reaction parameters (such as temperature, pressure, and flow rate) determine the residence time—i.e., the amount of time the reactants remain in the reactor under controlled conditions.

Residence time = reactor volume / flow rate

In this way, Syrris systems (such as Asia) are able to operate with reaction times from a few seconds to a few hours and can be used to synthesize mg to kg quantities in 24 hours.

In Syrris microreactors, reagents do not mix by turbulence (as in a batch reactor); instead, the reagents mix by diffusion. Because the distance across the chip reactor channel is approximately 200 μm, the time taken for reagents to completely diffuse is from a few milliseconds to a few seconds. This precise control over flow conditions allows researchers to achieve consistent reaction results.

Syrris flow systems can be easily pressurised up to 20 bar. This allows reactions to be performed at temperatures well above atmospheric reflux in a flow stream, enabling faster and often cleaner, higher-yielding reactions. Typically, solvents can be heated 60 to 150°C above their boiling point in a continuous-flow system. Therefore reaction rate increases of the order of 1000-fold are possible.

Examples of the superheating effect that can be achieved include:

• DCM @ 158ºC (vs 40ºC at atmos. press.)
• THF @ 193ºC (vs 66ºC at atmos. press.)
• Dioxane @ 240ºC (vs 100ºC at atmos. press.)

Applying pressure to a flow reactor also suppresses the evolution of gas. (This is beneficial because if gas bubbles are formed they can propel the reaction mixture out of the reactor leading to uncertain residence times).

The surface area to volume ratio of the reaction mixture in a Syrris reactor is 1000s of times greater than a round bottom flask. Thus heat can be transferred to or from the reaction mixture much more rapidly than in a batch reactor. Greater temperature control can, therefore, be maintained for exo- or endothermic reactions, improving consistency and yield in flow synthesis.

Asia allows a number of reactions to be performed in a serial fashion. One reaction directly follows another and because of the “plug flow” environment the first reaction is simply pushed out and cleaned by the second.

 Flow chemistry and batch chemistry are two distinct approaches to performing chemical reactions, each with unique advantages. Batch chemistry, where all reactants are combined in a single vessel, is widely used for its simplicity and flexibility. However, it can lead to inefficiencies such as long reaction times, inconsistent heat distribution, and batch-to-batch variability.

In contrast, flow chemistry is a continuous process. It allows reactants to be pumped constantly at a steady rate through a reactor, offering precise control over temperature, pressure, and reaction conditions. This results in faster reaction times, improved efficiency, and enhanced scalability. Additionally, flow chemistry enhances safety of chemical processes by minimising the volume of reactants at any given time, reducing the risk of hazardous side reactions.

Flow chemistry encompasses several distinct methodologies, each tailored to different reaction requirements and applications. Microfluidic flow chemistry utilizes microreactors with channel widths in the micrometre range, enabling rapid heat and mass transfer, making it ideal for precise small-scale synthesis and screening applications. Continuous stirred-tank reactors (CSTRs) allow for constant reagent addition and mixing, making them useful for reactions requiring long residence times or homogeneous conditions.

Tubular flow reactors are designed for plug flow reactions (PFR), where reagents move through a heated or pressurized tube, ensuring efficient mixing and controlled reaction conditions. Photochemical and electrochemical flow reactors integrate light or electricity as reaction drivers, enabling unique transformations that are difficult to achieve in batch systems. Each type of flow chemistry reactor offers specific advantages, allowing researchers to optimise processes based on reaction kinetics, scalability, and desired product yield.

A continuous flow chemistry system maintains precise reaction control by continuously introducing reactants under controlled conditions. Essential components include pumps for accurate reagent flow, mixing units for uniform distribution, and temperature & pressure sensors for real-time monitoring. Back-pressure regulators ensure reactions occur at elevated temperatures without solvent evaporation, enabling efficient superheating in a continuous flow process. These elements contribute to enhanced heat transfer, reaction selectivity, and scalability.

Two common reactor types in continuous flow chemistry are PFRs and CSTRs. A PFR ensures a well-defined reaction trajectory, where reactants move sequentially through the reactor without back-mixing. In contrast, a CSTR maintains complete mixing and steady-state operation, making it ideal for reactions requiring extended residence times. The choice between these reactors depends on reaction kinetics, heat transfer requirements, and scalability.

Flow chemistry has revolutionized chemical synthesis by enabling faster reaction rates, improved safety, and enhanced efficiency compared to traditional batch processes. By allowing continuous reagent input and precise control over reaction conditions, flow chemistry minimizes waste, reduces energy consumption, and enhances product consistency.

Recent chemical reviews highlight groundbreaking innovations, including photochemical and electrochemical flow reactions, which enable unique transformations that are difficult to achieve in batch systems. The integration of automated flow systems has further streamlined reaction monitoring, optimisation, and scale-up, making flow chemistry a key driver in modern process development.

Additionally, advancements in reactor design, such as PFRs and CSTRs, have expanded the versatility of flow chemistry across multiple industries. Computational modelling and artificial intelligence-driven parameter optimisation are also playing a growing role in improving reaction efficiency and reproducibility. Furthermore, catalyst integration in flow systems has facilitated greener, more sustainable chemistry by reducing reagent waste and enhancing selectivity.

As research continues to push the boundaries of flow chemistry, its applications in pharmaceutical synthesis, materials science, fine chemicals, and green chemistry are rapidly expanding. With ongoing innovations, continuous flow chemistry systems are set to become an essential component of modern chemical manufacturing and laboratory research.