Dutch chemical engineers and chemists have developed a stand-alone solar-powered mini flow reactor capable of producing fine chemicals in remote locations on earth — and, possibly, further afield.
“Our dream is to see our system used at a base on the Moon or on Mars, where self-sustaining systems are needed to provide energy, food and medicine. Our mini-plant could contribute to this in a fully autonomous, independent way,” says Timothy Noël, professor in the flow chemistry group of the Van't Hoff Institute for Molecular Sciences at the University of Amsterdam, the Netherlands.
The prototype reactor consists of a scaled-up luminescent solar concentrator photo-microreactor (LSC-PM) which converts direct and diffuse sunlight energy to a wavelength range that matches the absorption spectrum of a photocatalyst and, subsequently, guides this fluorescent light towards embedded reaction channels to drive photochemical transformations.
The reactor itself is based on a 15-mL LSC-PM module that started life as two 4-mm-thick polymethylmethacrylate (PMMA) plates each with an area of 470 mm2. Both plates were first doped with BASF’s commercial fluorescent dye Lumogen F Red 305 — chosen for its high fluorescent yields and excellent photostability. Then 16, 3.2-mm-diameter grooves were drilled along each plate. After gluing perfluoroalkoxy (PFA) tubing of the same external and internal diameter into each one of the grooves, the two halves were sandwiched together.
A pump introduces the reaction mixture into the reactor channels while an LSC guides light towards them. The incoming liquid flow is merged with a flow of oxygen governed by a mass flow controller.
A light sensor attached to the edge of the LSC-PM is monitored in real time, with a control system tweaking the flow rates of both oxygen and reagents to match the current light intensity. An experimentally established conversion correlation maintains production quality, no matter the weather.
For longer periods of poor light, or even darkness — a Lunar night lasts 14 days, for example — a solar-panel charged battery acts as a power buffer.
“Field tests confirmed that it is able to churn out chemicals at a constant rate even on days that are a mixture of sunny and cloudy,” notes Noël.
While these tests were carried out in the Netherlands, the team used solar data from the North Cape of Norway, Spain and Australia to check on global deployment possibilities.
“Even at the North Cape, with relatively little sun power, we estimate satisfactory production figures,” Noël states.
The researchers then compared the performance of their prototype system with production figures for the industrial photochemical synthesis of rose oxide.
A monoterperene, rose oxide is responsible for the typical floral fragrance found in roses and rose oil, plus the flavor in some fruits, and wines such as Gewürztraminer. It can be produced industrially by photooxygenation of citronellol to give the allyl hydroperoxide, followed by reduction and ring-closure.
The annual production of rose oxide is 60–100 tons. Using the solar data from Townsville, Australia, the team calculated that a mini-plant based there could produce almost 180 tons/yr. To match the current worldwide production, would call for approximately 150 m2 of solar coverage.
In contrast, found the team, actual industrial solar setups would require around 1,900 m2 of space deploying parabolic mirrors costing up to €196/m2 (U.S. $222.71/m2). LSC panels needed to build the reactor are sold for €99/m2 (U.S. $112.49/m2). Because two are needed per reactor, the price of the light concentrating material reaches €198/m2 (U.S. $224.98/m2).
Writing in a recent issue of ChemSusChem, Noël points out this shows the LSC-PM mini-plant actually is a more promising alternative, and with more flexible deployment options than industrial photochemical plants. Moreover, he adds, as the entire plant is run on solar energy, no energy cost is present in the operating expenditures, making it a sustainable strategy for future chemical production.
Commenting on the area of solar panels needed to meet current annual demand, Noël added, “That’s just one factory roof full of our mini-plants. So, this really could be a sustainable strategy for future production of chemicals such as rose oxide or pharmaceuticals.
You could even cover the facade of a building. Of course, the output would then be smaller than when the system is placed at an optimal angle to the sun, but it certainly is possible — and how cool would it be to have the walls make chemicals,” he concludes.