1. Researchers at Fraunhofer ICT-IMM developed two types of microreactors - a falling-film microreactor (FFMR) and a capillary microreactor - to evaluate their performance for visible light photocatalysis reactions. 2. The study investigated the oxygenation of 1,5-dihydroxynaphtalene to Juglone using different photosensitizers, dyes, and microreactors under varying conditions. 3. Results showed that the capillary reactor achieved the highest productivity and energy efficiencies, while the FFMR design achieved higher space time yields and could be scaled up successfully. Optimal combinations of photosensitizers and light sources were also identified

1. RESEARCH POSTER PRESENTATION DESIGN © 2012
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φ
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Productivity
[mmol/h ]
Space time yield
[mol/(s m^3)]
Energy
efficiency
[10^-7 mol/J]
Energy efficency
/Illuminated
surface area
[10^-5 mol/(J
m^2)]
Absorbed
power density
[W/m^3]
Absorption
power
efficiency
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FFMR-L FFMR-S_600 Capillary
 Investigation of DHN photo-oxygenation in FFMR-S_1200 & FFMR-L:
• Higher light absorption by the dye results in higher product yield. It can be
improved by using appropriate LED, emitting at wavelengths matching the
absorption spectrum of the dye (e.g. violet with TcPP), or by increasing the
LED power.
• Yields are improved with pure oxygen as gas feed compared to air.
 Comparison of FFMR-S_600, FFMR-L and Capillary:
• The capillary reactor gave the highest productivity and energy efficiencies.
• The FFMR-S was successfully scaled-up with the FFMR-L (productivity x 9).
• Space time yields are 1 order of magnitude higher with FFMRs vs capillary.
 FFMR-S_1200, Influence of light source and LED power on conversion,
selectivity and yield:
 FFMR-L, Influence of residence time & gas feed:
Φ = Quantum yield =
Juglone produced
Photons absorbed
 Reactors’ performance comparison: RB-green, O2, X = 0.67
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100000
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410 455 520 nm
0.001 mM TcPP
s: 0.5 cm
ExtinctionCoefficient,(M-1
cm-1
)
Wavelength,  [nm]
UV-Vis Absorption Spectrum of TcPP in 2-propanol
FFMR: segregated continuous-phase flow
2 versions available:
• Standard FFMR (FFMR-S)
• Tenfold smart scale-up (FFMR-L)
FFMR-L: 50 channels of L = 212 mm, W = 1200 µm
FFMR-S_1200: 16 channels of L = 54 mm, W = 1200 µm
Fraunhofer ICT-IMM developed two types of photochemical microreactors
for gas-liquid reactions:
• Falling-film microreactor (FFMR) with film thickness below 100 µm.
• Taylor-flow capillary reactor (Capillary) with a diameter of 800 µm.
The aim of the thesis was to evaluate and compare their performance for
visible light photocatalysis.
1. Context and objective
2. Reaction of interest: the photo-sensitised oxygenation of
1,5-dihydroxynaphtalene (DHN) to Juglone in 2-propanol
6. Results: 0.5 mM dye, 10 mM DHN in 2-propanol, LED: 350 mA &
room temperature
7. Conclusions
• A metal-free sensitizer (dye) acts as catalyst by absorbing visible light to
produce in situ singlet oxygen (1O2), a highly reactive species.
Two dyes were compared: Rose Bengal (RB) & meso-tetra-carboxy-phenylporphyrin (TcPP)
1École polytechnique fédérale de Lausanne, 2Fraunhofer ICT - IMM in Mainz
Sylvain Gros1, 2, Thomas H. Rehm2, Patrick Löb2, Albert Renken1
Evaluation and performance comparison of micro-flow reactors for
visible light photo-catalysis
• 1O2 further reacts with DHN to form Juglone via mechanisms A & B.
• Challenges: Oxygen transfer from gas to liquid phase (2-propanol)
Oxygen saturation: 10 mM at a partial pressure of 101 kPa [3]
1O2 lifetime in 2-propanol: 22 ns [4]
3
𝑂 2
1
𝑂 2
Energy
transfer
hν
1
𝑆
1
𝑆
∗
3
𝑆
∗
ISCE
Parameters FFMR-S FFMR-L Capillary
Liquid flowrate, VL [mL min-1] 0.1 - 0.4 0.4 - 7 0.4 - 2.4
Residence time [s] 10 – 30 10 - 80 200 - 1300
Illuminated surface area [cm2] 16 182 475
Liquid volume [mL] 0.04 – 0.07 0.5 – 1.5 7 - 14
Pressure [kPa] 101.3 101.3 101.3 – 400
3. Reactors
0
100
200
300
400
0 200 400 600 800 1000
Intensity[Wm-2]
Path length [µm]
TcPP-violet
RB-green
4. Coupled with light-emitting diodes (LED)
Capillary: dispersed-phase flow
• Gas-liquid contacting via a T-mixer junction.
• FEP tubing wrapped 89 times
around a cylinder:
Capillary length: 28 m
Inner diameter: 0.8 mm
Volume: 14 mL
• Light source: mounted inside the cylinder, on a
heatsink (used for cooling).
VL = 0.6 mL min-1
Violet (410 nm), royal blue (455 nm), green (520 nm), cold white
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0.18 0.19
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Violet Royal Blue Green Cold White
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TcPP, variation of light sources
X,S,Y(-)
Light source (350 mA)
X, O2
S, O2
Y, O2
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Violet Royal Blue Green Cold White
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X,S,Y(-)
Light source (350 mA)
X, O2
S, O2
Y, O2
RB, variation of light sources
Highest yields for TcPP-violet and RB-cold white
Electrical-power: 2.2 W
0.5 mM dye
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Residence time (s)
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RB-green, O2
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X,S(-)
Residence time (s)
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TcPP-violet, O2
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1
350 450 550 650 750
RelativeRadiantPower[-]
Wavelength [nm]
Violet (410 nm)
Royal blue (455 nm)
Green (520 nm)
Cold White
Mathematical modelling of photon
emission & absorption for both reactor
designs [5]:
Photon flux & photon flow at the surface
Photon flow absorbed by the solution
200 300 400 500 600 700
0
20000
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60000
80000
100000
120000
0.25 mM RB
s: 0.1 cm
ExtinctionCoefficient,(M-1
cm-1
)
Wavelength,  [nm]
UV-Vis Absorption Spectrum of Rose Bengal in 2-propanol
410 455 520 nm
5. Light emission and absorption
Best emission-absorption couples: TcPP-violet, RB-green and RB-cold white
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1.1 W 2.2 W 3.6 W
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X,S,Y(-)
Electrical power (W)
X, O2
S, O2
Y, O2
RB-green, variation of power
Higher X and S with increasing power
O2: higher selectivity
RB: green LED more selective than cold white
TcPP-violet: highest reaction rate and selectivity
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Selectivity vs conversion, air vs O2
RB-green, O2
RB-cold white, O2
TcPP-violet, O2
RB-green, air
RB-cold white, air
TcPP-violet, air
S(-)
X (-)
Photos credit: ©Fraunhofer ICT-IMM
(32 channels of L = 54 mm, W = 600 µm)
Photo-induced production of 1O2 [1] Oxygenation of DHN to Juglone [2]
[1] K.-H. Pfoertner, T. Oppenländer, Photochemistry: Ullmann's Encyclopedia of Industrial Chemistry (2000).
[2] S. Croux, Kinetic Parameters of the Reactivity of Dihydroxynaphthalenes, New J.of Chem. (1990) 161–167.
[3] R. Battino et al., The Solubility of Oxygen in Liquids, J. Phys. Chem. Ref. (1983) 163–178.
[4] F. Wilkinson et al., Rate Constants for the Decay, J. Phys. Chem. Ref. (1995) 663.
[5] M. Roger, J. Villermaux, Modelling of light absorption in photoreactors Part I. The Chemical Engineering J. (1979) 219–226.
Gas & liquid slugs
Air flowrate: 0.48 mL min-1
0.5 mM RB, 10 mM DHN in 2-propanol
Reaction plates: FFMR-L & FFMR-S_1200
T-junction
FFMR-S FFMR-L Capillary
LEDs‘ power emission distribution
Power Intensity decrease along the path length
Geometrical models for FFMR and Capillary