Why is photochemistry more sustainable?
Chemical reactions are generally activated by heat or chemical reagents. Recent developments in laboratory equipment have allowed lesser methods to become more accessible: methods such as electrochemistry and photochemistry. Photoreactors (and indeed flow photoreactors) use light as a reagent allowing for a cleaner and therefore greener reagentless (also known as traceless) chemistry.
These improvements in technology have allowed for a significant increase in the use of photochemistry and the number of publications in this area. This increase has also been encouraged by the potential in developing of novel synthetic routes (reducing the number of reaction steps) and a growing range of novel photoredox catalysts. Reducing the number of steps saves resources, time, energy and waste. Further refinements in reactor design and improved light source technology will hopefully advance these sustainable aspects further in future and this is something our own R&D department is working on.
A diagram of a CSTR
Light sources for photochemistry:
Traditionally, mercury-vapour lamps have been used for photochemistry. There are some draw backs of using these as a light source: they emit a wider spectrum of light with multiple wavelengths, are energy inefficient and, of course, require increased safety precautions to protect the user from harmful irradiation. As a result, LEDs have become the go to for photochemistry, especially as technology has improved.
LEDs have much narrows peaks at discrete wavelengths allowing for better selectivity and optimisation of reactions. They are also safer (although safety precautions are still paramount when using very intense or ultraviolet light) and more efficient. All of our photoreactors feature LEDs either individually or arrayed, with a wide selection of wavelengths available.
Also, on the note of safety, flow systems tend to have a smaller volume of reactant active at any given time, reducing potential hazards from spills or exothermic reactions.
Our Illumin8 photoreactor with additional LED module
Flow Photochemistry reactors:
Irradiation is a crucial factor in photochemistry but rapidly reduces over any given distance. Batch photochemistry reactors solve this by mixing their reactants, placing the light source as close as possible to the reaction, or directly channelling the photons in the reactions in the case of our Lighthouse
This is where flow reactors provide a key advantage. The narrow diameter of capillaries and tubes allows for a much higher level of light penetration, ensuring rapid and even irradiation of your reactants. By coiling the tubing around the light source, such as in the case of our Borealis, you can also run for a longer residence time for your reaction while being irradiated.
Flow photochemistry also allows for more controlled and homogenous reactions, allowed for by precise stoichiometric mixing of reactants before they are pumped through the photo reactor.
Another method for combining flow and photochemistry is to irradiate continuous stirred tank reactors (CSTRs). CSTRs allow for a degree of multiphasic reaction conditions including solid components. In the case of our fReactor you can position up to 5 LED modules (of your preferred wavelength) on each CSTR. These shine through the CSTR’s windows into the reaction.
Cutaway image of our Borealis flow photoreactor showing the internal LED array
Conclusion:
Flow photoreactors represent an excellent opportunity to enhance photochemical processes, reducing waste, increasing throughput all with a safer and precise flow process. Continued advances in technology and synthetic routes open the future to exciting possibilities for new research.
If you’d like to know more about how Asynt’s lab tools can help you integrate flow and photochemistry in your lab don’t hesitate to get in touch! You can message us with the live chat in the bottom right corner, email [email protected] or call 01638 781709.
